Prelims-I044498.tex 11/9/2007 19: 2 Page ix

FOREWORD

The aim of this book is to present a reference for the research work done during the last two decades in laser processing assisted by neutral liquids (LALP). At present, the total number of scientific-technical papers dealing with LALP exceeds 700, and of patents 500, which justifies the need for a comprehensive reference. The book does not systematically cover the use of lasers in medicine, despite the fact that organs and tissues contain a significant amount of liquid. Nor does it cover laser etching in reactive liquids and laser deposition form solutions. References to these kinds of processing are given in the introduction (Chapter 1). The four main areas of LALP are: (i) laser peening, where water is used as a safe confining medium conforming with the workpiece; (ii) cutting and drilling, where water is also preferably used, in order to cool the workpiece and to prevent the redeposition of debris; (iii) the generation of colloidal particles in water or in organic solvents; (iv) the removal of microparticle contamination from solid surfaces through laser vaporization of a liquid film (water and alcohols) on the surface. Altogether, about 70 different liquids have been used until now,including liquid metals and liquefied gases. The principles of organising the data in the book are as follows: • Essential data of research reports about the main four kinds of processing (i) to (iv) are presented in chrono- logical tables, with an accent on the materials processed or achieved. Concise receipts of the processes are presented. As far as possible, the experimental conditions and results are described quantitatively. • General principles, experimental techniques, main phenomena, and mechanisms of every kind of processing are described by text and graphics. Related topics, such as residual stress measurement and alternative processing methods are dealt with to some extent in order to help the readers from other areas or students. • General topics on the physics and chemistry of laser–liquid–solid interactions are gathered in a special chapter (Chapter 7). • A comprehensive table of 61 properties of 100 liquids has been included. In addition to the liquids used in LALP,several common solvents and cryoliquids are added. • The book contains a glossary with about 330 terms. It is intended to help the less prepared readers, especially students, who do not have previous experience in this special field. The book contains material from literature sources originally acquired for the following research projects: Project 0140215s98 (Estonian Ministry of Education), Projects 4512 and 5864 (Estonian Science Foundation). The original figures were drawn by CorelDraw software licensed to the University of Oulu. I am grateful to many researchers, especially toYuji Sano, Stephan Roth,Walter Huber, Boris Luk’yanchuk, Vladimir P. Zharov,Tianqing Jia, and Dongsik Kim who provided me with original figures; to a number of publishers and authors who kindly permitted the use of their material in this book, and to the team Elsevier Science for their patience and good cooperation. Invaluable help in the manuscript preparation was provided by my son Aavo Kruusing and my daughter Airi Männamaa.

Arvi Kruusing, Oulu, April 2007

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CHAPTER ONE

Introduction

Contents 1.1 LALP Chronology 4 1.2 Laser Processing and Analysis of Liquid Systems That Are Not Covered in This Book 6 1.3 Inventions in Liquids-Assisted Laser Processing 8

There are occasions where the workpiece at laser processing is in contact with liquids (e.g. in natural bodies of water, nuclear reactors, boreholes, etc.); the workpiece may contain liquid in its normal state (e.g. moisture in building materials, wood, paper) or the liquid may be applied to workpiece in order to enhance the processing or to achieve some other useful effect. Very often the liquid present is water as most abundant and safe (see Fig. 1.1).

(a) (b) (c)

H2O

(d) (e) (f)

Figure 1.1 Examples of liquid presence at laser materials processing: (a) processing in water environment; (b) workpiece/material is immersed into/suspended in liquid; (c) liquid is applied onto surface of workpiece; (d) liquid acts as lightguide; (e) processing in vapour; and (f) material contains capillary or chemically bonded liquid.

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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2 Handbook of Liquids-Assisted Laser Processing

Table 1.1 Main physical principles of LALP (in ascending order pursuant to increasing laser–liquid interaction intensity). See also Fig. 2.24.

Light-matter interaction Desired changes in Method Why used needed the workpiece Liquid as waveguide Concentration of light Light reflection/ Various or lens without solid optical refraction/self- elements focusing in liquid Liquid as photomask; Liquid conforms Light absorption Various backside etching with the surface in liquid of transparent of workpiece materials Photochemical Liquid serves as the Photoactivation Photochemical processes source of chemical of liquid (oxidation, etc.) species Removal of particles Lower risk of Vaporization No changes from surfaces surface damage of liquid only Generation of Cleaner particles – no Vaporization of both Vaporization micro/nanoparticles extra chemicals used; workpiece and rapid and simple of liquid process Subtractive processing Practically no debris Vaporization of both Vaporization (cutting, drilling, redeposition in the workpiece and of liquid removal of oxide work zone; lower layers, etc.) thermal load on the workpiece Shock processing Shock pressures up to Vaporization and Plastic (peening, forming, 10 times larger than ionization of deformation densification) in gas or in vacuum; liquid only simpler and safer than in case of solid confinement media

Besides water, about 70 other liquids are used in laser materials processing, mostly organic solvents. In high-energy processing regarding the peening without exception water is used as the safest and cheapest liquid, in microprocessing (micromachining, particle generation) organic solvents are often the choice. Liquids metals (e.g., Hg, Ga) and molten salts (e.g., NaNO3, KNO3) have also been used. The book also refers to some cases where frozen liquid layers on the surfaces are laser ablated (water ice, solid N2, and CH4 a.o.). Table 1.1 lists the main types of liquids-assisted laser processing (LALP) andTable 1.2 provides a comparison of relevant advantages and disadvantages. Experiments of laser irradiation of liquid–solid interfaces started soon after the invention of lasers in 1960s, but systematic research on LALP began at the end of 1980s (see Figs 1.2–1.4). At the beginning of 1990s four main directions emerged: (i) laser peening, (ii) liquids-assisted laser micromachining, especially the backside etching of optical components, (iii) removal of microparticles from silicon wafers, and (iv) generation of nanoparticles in liquids. Ch01-I044498.tex 12/9/2007 18: 23 Page 3

Introduction 3

Table 1.2 Overall advantages and disadvantages of LALP (in comparison with laser processing in vacuum/gas and with alternative kinds of processing; only liquids neutral under normal conditions are considered). Advantages Disadvantages • Non-contact (low mechanical load on workpiece) • Expensive equipment (laser) • Flexible and rapid process control • Need for auxiliary liquid-handling system • Many process control parameters available in • Burn and eye damage hazard by laser light, extreme range: laser wavelength, pulse length, especially at IR-wavelength fluence, energy density,liquids properties, • Power loss due to cooling by liquid liquid’s temperature, flow rate, etc. • Explosion, toxicity,and electronic apparatus • Can be applied on inclined and curved surfaces damage hazard due to liquid vapours (light and liquid conform with sloped and • Explosion hazard due to thermal or uneven surfaces) photolytical liquid dissociation products • Can be applied inside of tubes, etc. (e.g. O2 + H2) • Can be applied under water (e.g. in nuclear • Reflection loss at water surface reactors, sea) without the need for local • Light scattering by mist, liquid surface dry zone unevenness, thermal gradients, suspended • High-energetic efficiency if short light particles and bubbles pulses are used • Splashes at liquid surface may contaminate • Low thermal load on workpiece: narrow the optical components HAZ, little damage of biomaterials • Light absorption and scattering in liquids is • Reduced risk of atmosphere contamination greater than in gases by gases and particles • Corrosion/oxidation (in case of oxygen- or • Liquid may serve as a lightguide halogen-containing liquids) • Liquid may serve as a source of starting • Contamination of workpiece with carbon, materials (carbon, nitrogen, oxygen), but also nitrogen, etc. from liquids of highly reactive species (OH, H2O2,F2,Cl2) • Hydrogen incorporation into workpiece • At elevated temperatures and pressures the from hydrogen-containing liquids (causes solubility of solids in liquids may increase brittleness) considerably (dissolution of debris, • Polymerization of organic liquids hydrothermal growth, etc.) • Laser-induced thermal and mechanical • Bubble dynamics and migration generates shocks are more intense than in gas or vacuum strong hydrodynamic forces that carry the (more dislocations, deformations, or cracking debris away of materials) • Shorter thermal relaxation time than in gas • Collapse of bubbles may cause surface damage or in vacuum • Process monitoring, modelling, and simulation • Laser wavelength is shorter than in vacuum and gases are more complicated than in gas or vacuum • Self-focusing in liquids may be used for • Lower optical breakdown threshold than in concentration of light. gas (water–air)

80 70 60 50 40 30 20 Number of publications 10 0

197419751976197719781979198019811982198319841985198619871988198919901991199219931994199519961997199819992000200120022003200420052006

Figure 1.2 Development of the number of scientific-technical publications (excl. patents) about LALP. The total number of research reports and reviews referred in this book is about 700. Ch01-I044498.tex 12/9/2007 18: 23 Page 4

4 Handbook of Liquids-Assisted Laser Processing

200 180 160 140 120 100 80 60 40

Number of publications 20 0

Shock aning Other Cle Particles Subtractive

Figure 1.3 Relative research activity in the four main areas of LALP.

35

30

25 subtractive shock 20 cleaning 15 particles 10 other

Number of publications 5

0 1985 1990 1995 2000 2005 2010

Figure 1.4 Development of research activities in the main areas of LALP.

1.1 LALP Chronology

1963 G.A. Askar’yan and E.M. Moroz (P. N. Lebedev Physics Institute, Moscow,Russia) propose mechanical momentum generation by laser vaporization on solid targets 1963 R.M. White (General Electric Company,Palo Alto, USA) reports about pressure pulse generated at ruby laser irradiation of aluminium target 1968 Studies of laser peening at Batelle Columbus Laboratories start (Columbus, USA) 1970 Confined ablation-mode laser shock processing reported (N.C. Anderholm – Sandia Laboratories, Albuquerque, USA) 1971 Generation of vacancies in laser-shocked materials reported (S.A. Metz and F.A. Smidt Jr. – Naval Research laboratory,Washington,USA) 1973 Permanent local deformation of laser-shocked metal targets reported (J.D.O’Keefe, C.H. Skeen, and C.M.York – TRW Systems Group and University of California, USA) 1974 Laser shock treatment in water confinement reported (J.A. Fox – US Army Mobility Equipment Research and Development Center, Fort Belvoir, USA) 1974 First laser peening patent issued (P.I. Mallozi and B.P. Fairand – US3850698) Ch01-I044498.tex 12/9/2007 18: 23 Page 5

Introduction 5

1975 Laser ablation of various metals in various liquids reported (V.A.Ageev –V.I. Lenin Tadzhik State University,Dushanbe, USSR) 1975 Surface damage of the backside of a glass plate in contact with water due to laser irradiation reported (R.K. Leonov,V.V. Efimov, S.I. Zakharov, N.F.Taurin, and P.A.Yampol’skii – All-Union Scientific-Research Institute of Optophysical Measurements, Moscow,USSR) 1981 Initiation of corrosion pits by laser ablation in electrolyte solution reported (R.K. Ulrich and R.C. Alkire – University of Illinois, Urbana, USA) 1983 Liquid jet–guided laser-enhanced electroplating reported (R.J. von Gutfeld, M.H. Gelchinski, L.T. Romankiw, and D.R.Vigliotti – IBM T. J. Watson Research Center,Yorktown Heights, USA) 1986 Laser cutting of 3-mm thick steel sheet under water reported (R. Schünemann – Universität Hannover, Germany) 1987 Metal ions desorption from silicon surface in water under laser irradiation was reported (E.Yu.Assendel’ft,V.I. Beklemyshev, I.I. Makhonin,Yu. N. Petrov,A.M. Prokhorov, and V.I. Pustovoi – Institute of General Physics, Moscow,Russia) 1988 Start of laser shock processing research in France at Laboratoire pour l’Application des Lasers de Puissance (LALP) 1988 Photo-resist particles removal from solid surfaces due to acoustic wave generated by absorption of the laser light on the free surface of water was reported (E.Yu.Assendel’ft,V.I. Beklemyshev, I.I. Makhonin, Yu. N. Petrov,A.M. Prokhorov, andV.I. Pustovoi – Institute of General Physics, Moscow,Russia)

1989 Backside drilling of holes and channels in fused silica in contact with water solution of NiSO4 (J. Ikeno,A. Kobayashi, and T. Kasai – Japan)

1990 Steam Laser Cleaning – removal of Al2O3 particles from Si wafer, covered with water film reported (K. Imen, S.J. Lee, and S.D. Allen – Center for Laser Science & Engineering, Iowa City,USA) 1991 Densification of porous materials by laser shock reported (D. Zagouri, J.- P. Romain, B. Dubrujeaud, and M. Jeandin – France) 1992 Formation of diamond particles at laser irradiation of graphite in benzene reported (S.B. Ogale, A.P. Malshe, S.M. Kanetkar, and S.T. Kshirsagar – Poona University,Pune, India) 1993 Water jet–guided laser technology was invented by B. Richerzhagen – Eidgenössische Technische Hochschule Lausanne (ETHL), Switzerland 1993 Generation of colloidal Au and Ni nanoparticles by laser ablation of metal targets in liquids reported (A. Fojtik and A. Henglein – Hahn-Meitner-Insitut, Berlin, Germany) 1995 Conversion of tensile surface residual stresses into compressive by laser peening in water without protective coating using multiple impacts demonstrated (N. Mukai, N. Aoki, M. Obata,A. Ito,Y. Sano, and C. Konagai – Toshiba Corporation,Yokohama, Japan) 1996 Improvement of laser cutting quality of marble by saturating it by water reported (K. Sugimoto,T. Aihara, H. Kamata, and S. Kanaoka – Taisei Corporation and Mitsubishi Electric Corporation, Japan) 1996 Cathodic potential controlled laser ablation of oxide layers in electrolytes reported (R. Oltra, O.Yava¸s, and O. Kerrec – Université de Bourgogne, France) 1996 Reduction of colloidal Ag particles size by laser irradiation reported (A. Takami, H.Yamada,K. Nakano, and S. Koda – University of Tokyo, Japan)

1998 Observation of PbZrTiO3 nanoplatelets growth at laser-irradiated solid–liquid interface (A. Kruusing – TallinnTechnical University,Estonia) 1998 Laser MicroJet® technology was commercialized by Synova S.A. in Lausanne, Switzerland 1998 Conversion of fluorocarbon resin surface from hydrophobic to hydrophilic by laser irradiation under water and aqueous solutions reported (K. Hatao, K. Toyoda, and M. Murahara – Japan) Ch01-I044498.tex 12/9/2007 18: 23 Page 6

6 Handbook of Liquids-Assisted Laser Processing

1999 Precise backside laser etching of fused silica in contact with pyrene solution in acetone reported (J. Wang. H. Niino, and A.Yabe – National Institute of Materials and Chemical Research,Tsukuba, Japan) 1999 Laser peening was applied to combat against stress corrosion cracking in Japanese nuclear power reactors 2000 Microscale laser shock processing reported (W. Zhang andY.L.Yao – Columbia University,NewYork,USA) 2000 Control of laser-ablation generated colloid size by surfactants reported (F. Mafuné, J. Kohno,Y.Takeda, T. Kondow, and H. Sawabe – Japan) 2000 Generation of conducting polymer particles by laser ablation in water reported (Y.Tamaki,T. Asahi, H. Masuhara, Osaka University – Japan) 2001 Photo-induced transformation of spherical Ag nanoparticles into nanoprisms reported (R. Jin,Y. Cao, C.A. Mirkin, K.L. Kelly, G.C. Schatz, and J.G. Zheng – Northwestern University,Evanston, USA) 2001 MAPLE and MDW/LIFT techniques reported (P.K.Wu, B.R. Ringeisen, J. Callahan, M. Brooks, D.M. Bubb, H.D.Wu,A. Piqué, B. Spargo, R.A. McGill, and D.B. Chrisey – Naval Research Laboratory,USA) 2002 Formation of polyynes by laser irradiation of graphite particles in liquids reported (M. Tsuji,T.Tsuji, S. Kuboyama, S.-H.Yoon,Y. Korai,T.Tsujimoto, K. Kubo,A. Mori, and I. Mochida – Kyushu University, Kasuga, Japan) 2004 Removal of particles from surfaces by laser-induced cavitation bubbles reported (W.D. Song, M.H. Hong, B. Lukyanchuk, and T.C. Chong – Data Storage Institute, Singapore) 2004 Laser backside etching of fused silica using an absorbed layer of toluene reported (K. Zimmer, R. Böhme, and B. Rauschenbach – Leibnitz-Institut für Oberflächenmodifizierung e.V.,Leipzig, Germany) 2004 Liquids-assisted laser shock cleaning for nanoscale particles removal reported (Deoksuk Jang and Dongsik Kim – POSTECH, Pohang, Korea) 2006 Observation of ZnSe nanorod growth at laser-irradiated solid–liquid interface (T. Jia, M. Baba, M. Huang, F. Zhao, J. Qiu, X. Wu, M. Ichihara, M. Suzuki, R. Li, Z. Xu, and H. Kuroda – Japan and China) 2006 Laser backside etching of fused silica in contact with gallium and mercury reported (K. Zimmer, R. Böhme, D. Ruthe, and B. Rauschenbach – Leibnitz-Institut für Oberflächenmodifizierung e.V.,Leipzig, Germany) 2006 Removal of oil film from metal surfaces by water decomposition products generated by laser cavitation reported (H. Hidai and H. Tokura – Tokyo Institute of Technology,Japan)

2006 Laser-assisted transformation of Hg into Au under laser exposure of Hg suspensions in D2O reported (G.A. Shafeev, F. Bozon-Verduraz, and M. Robert – A.M. Prokhorov General Physics Institute, Moscow, Russia; Université Paris 7, France)

1.2 Laser Processing and Analysis of Liquid Systems That Are Not Covered in This Book

Following publications are recommended for reference of LALP technologies and analytical techniques not covered in this book.

Stereolithography Ready JF, Farson DF, Feeley T,et al., eds. LIA Handbook of laser materials processing. Berlin: Springer-Verlag and Heidelberg GmbH & Co.; July 2001:545–554. Upcraft S, Fletcher R. The rapid prototyping technologies. Assemb Autom 2003; 23(4):318–330. Bertsch A, Jiguet S, Bernhard P,Renaud P. Microstereolithography: A review. Mater Res Soc Symp Proc 2003; 758:3–15. Ch01-I044498.tex 12/9/2007 18: 23 Page 7

Introduction 7

Liquid-phase photochemistry Donohue T. Applied laser photochemistry in the liquid phase. Opt Eng (Laser Appl Phys Chem) 1989; 20: 89–172. Eisenthal KB. Ultrafast chemical reactions in the liquid state. Topics Appl Phy (Ultrashort Laser Pulses) 1993; 60:319–356, 461–469.

Laser wet etching in reactive liquids Ogale SB. Laser-induced synthesis, deposition and etching of materials. Bull Mater Sci 1988; 11(2–3):137–157 Bäuerle D. Laser processing and chemistry, 3rd edn. Berlin: Springer; 2001:325–333.

Laser reactive quenching at liquid–solid interface Kanetkar SM, Ogale SB. Pulsed laser reactive quenching at liquid–solid interface. Bull Mater Sci 1988; 11(2–3):167–190.

Laser-assisted liquid-phase deposition and electroplating Ogale SB. Laser-induced synthesis, deposition and etching of materials. Bull Mater Sci 1988; 11(2–3):137–157. Bäuerle D. Laser processing and chemistry, 3rd edn. Berlin: Springer; 2001:449–458.

Laser machining and treatment of biological materials and objects Niemz MH. Laser-tissue interactions: Fundamentals and applications, 2nd edn. Berlin: Springer; 2002. Vogel A, Venugopalan V. Mechanisms of pulsed laser ablation of biological tissues. Chem Rev 2003; 103(2):577–644. Vogel A, Noack J, Hüttman G, Paltauf G. Mechanisms of femtosecond laser nanosurgery of cells and tissues. Appl Phy B: Laser Opt 2005; 81(8):1015–1047.

Laser desorption from solid surfaces .
. Lazneva, Lazerna fotodecopbci (od ped. . . Konopova) L.: Izd-vo LU, 1990, 199 c. (E. F. Lazneva, Laser photodesorption. Lenigrad, Leningrad State University Press, 1990).

Matrix-assisted laser desorption (MALDI) Stump MJ,Fleming RC,GongW-H,JaberAJ,Jones JJ,Surber CW,Wilkins CL. Matrix-assisted laser desorption mass spectrometry. Appl Spectros Rev 2002; 37(3):275–303. Creaser CS, Ratcliffe L. Atmospheric pressure matrix-assisted laser desorption/ionisation mass spectrometry: A review. Curr Anal Chem 2006; 2(1):9–15. MALDI Recipes. www.nist.gov/maldi; http://polymers.msel.nist.gov/maldirecipes/index.cfm

Laser-induced breakdown spectroscopy (LIBS) in liquids and at solid–liquid interfaces Rusak DA,Castle BC,Smith BW,Winefordner JD. Fundamentals and applications of laser-induced breakdown spectroscopy. Crit Rev Anal Chem 1997; 27(4):257–290. Song K, Lee YI, Sneddon J. Applications of laser-induced breakdown spectrometry. Appl Spectros Rev 1997; 32(3):183–235. Schechter I. Laser induced plasma spectroscopy. A review of recent advances. Rev Anal Chem 1997; 16(3):173–298. Ch01-I044498.tex 12/9/2007 18: 23 Page 8

8 Handbook of Liquids-Assisted Laser Processing

Cremers DA, Radziemski LJ. Handbook of laser-induced breakdown spectroscopy. Chichester: John Wiley; 2006. Miziolek AW, Palleschi V, Schechter I, eds. Laser-induced breakdown spectroscopy (LIBS): Fundamentals and applications. Cambridge: Cambridge University Press; 2006.

1.3 Inventions in Liquids-Assisted Laser Processing

Main classes of International Patent Classification (IPC, version 2007.01) regarding the main arts of LALP:

Subtractive processing B23K B23K 26/00 working by laser beam (e.g. welding, cutting, boring) B23K 26/12 in a special atmosphere (e.g. in an enclosure) B23K 26/14 using a flow (e.g. a jet of gas, in conjunction with the laser beam) B23K 26/16 removing of by-products (e.g. particles or vapours produced during treatment of a workpiece) B23K 26/36 removing material B23K 26/38 by boring or cutting B23K 26/40 taking account of the properties of the material involved

Shock processing B22F Working metallic powder; manufacture of articles from metallic powder; making metallic powder B22F 3/087 using high-energy impulses (e.g. magnetic field impulses)

B23K B23K 26/00 working by laser beam (e.g. welding, cutting, boring)

C21 Metallurgy of iron C21D 1/09 by direct application of electrical or wave energy; by particle radiation C21D 7/00 modifying the physical properties of iron or steel by deformation C21D 10/00 modifying the physical properties by methods other than heat treatment or deformation

C22 Metallurgy; ferrous or non-ferrous alloys; treatment of alloys or non-ferrous metals C22F 3/00 changing the physical structure of non-ferrous metals or alloys by special physical methods (e.g. treatment with neutrons) Ch01-I044498.tex 12/9/2007 18: 23 Page 9

Introduction 9

F01 Machines or engines in general F01D 5/14 form or construction

Cleaning B08 Cleaning B08B 3/00 cleaning by methods involving the use or presence of liquid or steam B08B 7/00 cleaning by methods not provided for in a single other subclass or a single group in this subclass B08B 3/10 with additional treatment of the liquid or of the object being cleaned (e.g. by heat, by electricity,by vibration)

Generation and modification of particles B22F Working metallic powder; manufacture of articles from metallic powder; making metallic powder B22F 9/00 making metallic powder or suspensions thereof B22F 9/02 using physical processes

B82 Nanotechnology B82B 3/00 manufacture or treatment of nanostructures The number of patents in LALP is around 500, about 50 per cent regarding subtractive processing, and 20 per cent regarding laser peening. Selected inventions are described under corresponding sections of this book. Ch02-I044498.tex 11/9/2007 18: 47 Page 11

CHAPTER TWO

Cleaning

Contents 2.1 Introduction 11 2.2 Principles of Liquids-Assisted Laser Cleaning 12 2.3 Particles on Solid Surfaces 17 2.4 Experimental Techniques in Laser Wet/Steam Cleaning Research 30 2.5 Physics and Phenomenology of Liquids-Assisted Laser Removal of Particles from Surfaces 37

2.1 Introduction

Liquids may facilitate the removal of particles or surface layers from solids in several ways: by reduction of adhesion forces, by providing expanding vapours, or by acting as a medium for acoustic or shock waves. At the presence of liquid, the threshold laser energies/fluences for cleaning and thus the surface damage hazard is lower, as a rule. The most important application of liquids-assisted (wet) laser cleaning has been the removal of particulate contamination from solid surfaces, especially from silicon wafers for semiconductor integrated circuits (IC). Particles on wafer mask light in photolithographic process and cause declinations from the desired geometry,in worst case shortcuts and breaks [1, 2]. According to different sources, the minimum permissible contaminating particle size is 1/10 to 1/4 of the minimum feature size of IC [3, 4].Today,there is a need to remove particles of diameters down to tens of nanometres. The particles may origin from the ambient atmosphere (SiO2,Al2O3), from previous processing steps (photoresist residuals, Cu,TEOS, Al-F), from equipment (wear particles), and from humans (textile wear). Regarding other areas, liquid-assisted laser techniques have proved to be effective for removal of small particles from rotating magnetic information storage disc surfaces [5] and from telescope mirrors [6]. Particles on surface are not always contaminants. Konov et al. [7] describe a process where dia- mond nanoparticles on surface were used as nuclei for diamond film growth. By selective laser removal of these seed particles in a water–alcohol solution, patterned diamond films were achieved in the subsequent diamond growth. Liquids may be beneficial also at laser removal of surface layers from solids, by lowering the thermal load on the materials and preventing the dissipation of debris into the ambient atmosphere. Local removal of oxide layers is needed, for example: • in microelectronics for fabricating openings in passivating the insulating layers for electrical contacts [8]; • in mechanical engineering to enable welding or gluing [9]; • in corrosion research for initiation of corrosion pits.

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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12 Handbook of Liquids-Assisted Laser Processing

Table 2.1 Liquids used at laser cleaning. Liquids Additives Water, ethanol, methanol, IPA, acetone NaCl, methanol, ethanol, IPA

Laser techniques have been considered appropriate also for removal of radioactive contaminants (water- containing or under water) in nuclear facilities, and for cleaning of optical surfaces in space systems from frozen water and gases. Table 2.1 lists the liquids and their additives used in wet laser cleaning. Alcohols and alcohol additives to water were used for better wetting (for achieving of continuous liquid film on surface). NaCl additive to water was found to enhance the ‘long-term memory effect’ of acoustic cavitation [10] (see Section 7.2.4). Advantages of liquids-assisted laser cleaning of surfaces (in comparison with dry laser cleaning (DLC) and other cleaning methods): • Liquid may considerably lower the adhesion forces (van der Waals and double-layer forces). In liquid the capillary force is absent. • The cleaning threshold (minimum laser fluence) is lower in liquids. • Smaller particles can be removed. • Particles may be removed individually. • Lower hazard to damage the surface to be cleaned: the focusing of light at transparent particles can be avoided by using absorbing in the liquid light or by choosing a liquid with index of refraction equal to that of the particles [11]. • Consumption of ultra-pure liquids is drastically reduced (in comparison with conventional wet cleaning). • Electrical (electrochemical) layer removal control is possible. Disadvantages and hazards of liquids-assisted laser cleaning: • Laser sources are expensive. • Liquid droplets on surface may act as lenses and concentrate the light. • Generated vapours may be harmful to optical and electronical systems.

2.2 Principles of Liquids-Assisted Laser Cleaning

2.2.1 Particles removal by frontside laser irradiation (steam laser cleaning) Steam laser cleaning (SLC) is the most important kind of laser removal of particulates from surfaces. Here, a thin liquid film, of thickness up to some micrometres, is condensed from vapour onto the contaminated surface. At laser irradiation, the liquid vaporizes and the pressure and movement of the expanding vapours propels the particles off the surface (Fig. 2.1). Also the displacement of surface due to thermal expansion and acoustic transients may contribute to the removal of particles (see Section 2.5.3). The film may be discontinuous, but it is important that there is liquid in contact with the particles. The liquid may origin also from the humidity in the ambient atmosphere – if the substrate and particle surfaces are hydrophilic, a capillary condensation of the humidity occurs.

2.2.2 Particles removal by backside laser irradiation Particles on transparent to laser light substrates may be effectively removed by heating the liquid through the substrate by absorbing in the liquid light. In case of water, the Er:YAG lasers emitting at water absorption maxima near 2.94 µm is often the choice. In comparison with SLC, the thermal load on particles is greatly reduced; for example, living cells have been safely removed from glass slides (Fig. 2.2). Ch02-I044498.tex 11/9/2007 18: 47 Page 13

Cleaning 13

(a) (b)

(c) (d)

Figure 2.1 Situations in Steam Laser Cleaning; (a) transparent liquid – transparent substrate – opaque particle; (b) transparent liquid – opaque substrate – transparent particle; (c) transparent liquid – opaque sub- strate – opaque particle; (d) opaque liquid (after the articles by Tam et al. [3], Oltra and Boquillon [12], andVeiko and Shakhno [13]).

Cover slide Micro-objective H2O Sample cavity Lens CCD Particles or cells Absorbing layer X, Y, Z stage Er:YAG Fast thermal µ µ Laser 2.94 m, 400 s expansion 2 beam 0,1–100 J/cm

Figure 2.2 Principle of removal of particles and living cells by backside laser irradiation [14]. © SPIE (2002), reproduced with permission from Ref. [14].

2.2.3 Removal of particles by laser-generated acoustic waves in liquid In the pioneering work about laser particles removal from an immersed into liquid substrate, Assendel’ft et al. [15, 16] used a 100 ns, 0.3 J pulsed CO2-laser beam focused onto free surface of water. Photo-resist particles of size 1–0.1 µm were effectively removed from Si substrates by laser-induced acoustic transients. Acoustic pressure at particles in the cleaning regime was estimated to be in range from 0.02 to 38 MPa.

2.2.4 Liquid-assisted laser shock cleaning Liquid-assisted laser shock cleaning (LLSC) is a combination of SLC with laser shock cleaning (LSC), where a shock wave is generated by laser breakdown in the gas above the specimen. In LLSC, the surface to be cleaned is first covered by a liquid film and then subjected to laser heating and shock wave simultaneously (Fig. 2.3). The technique has been proved to be effective to remove nanoparticles as small as 20 nm with over 90% efficiency from silicon wafers, thus being superior to any other cleaning method [17].

2.2.5 Removal of particles by bubble collapse induced flow

Song et al. describe an experiment [18] where SiO2 and polystyrene particles were removed from Si wafers by laser-generated bubbles collapse induced flow (Fig. 2.4). The bubbles collapse flow near solid surfaces in the cleaning regime was later studied by Ohl et al. [19] using particle image velocimetry (PIV). The tangential to surface flow velocities were highest during the time interval of jet impact (see Section 7.2.4) and exceeded 10 m/s (at bubble max size 2 mm); the high tangential velocities were deemed to be the main reason for particles detachment. Ch02-I044498.tex 11/9/2007 18: 47 Page 14

14 Handbook of Liquids-Assisted Laser Processing

Timinig Compressed gas control unit

Flow controller Translation stage

Laser for optical Sample brakedown

Liquid reservoir

Lens Heater

Temperature Thermometer Laser for liquid- control unit film evaporation Mirror

Figure 2.3 Scheme of liquid-assisted laser shock cleaning. The substrate to be cleaned is covered with a thin liquid film (condensed vapour). An Nd:YAG laser pulse then induces breakdown of air and a spherical shock wave propagates from the centre of the plasma. An excimer laser pulse is fired at the moment when the shock wave touches the centre of the cleaning zone with the sample moving periodically on a translation stage under multiple number of laser pulse irradiation. Courtesy by D. Kim, POSTECH, Pohang, Korea, © Dongsik Kim, reproduced with permission.

Optical Laser system

Stage

Bubbles Substrate Liquid

Figure 2.4 Schematics of particles removal by bubble collapse induced flow. © American Institute of Physics, reprinted with permission (2004) from Ref. [18].

2.2.6 Removal of surface layers by laser ablation/spallation in liquid In situ local removal of passive oxide layers from metal surfaces by a focused laser beam was found to be useful in corrosion studies (initiation of corrosion pits). In comparison with mechanical methods like scraping, straining, abrading, shearing, guillotining, and fracturing, laser ablation method provides several advantages: (i) there is no contamination form film removing tools, (ii) uniform and reproducible depassivation is achieved in a few microseconds, (iii) depassivated area is well defined and can be controlled easily by changing the size of the laser beam on the working electrode surface [20, 21]. Interestingly, removal of iron oxide layers by this scheme was found to be enhanced when the specimen was held in an electrolyte solution under proper cathodic potential (e.g. 1.45V/SCE for 40 min) (Fig. 2.5) Ch02-I044498.tex 11/9/2007 18: 47 Page 15

Cleaning 15

Laser pulse Electrolyte

Potentiostat Oscilloscope

Transducer

Figure 2.5 Experimental configuration for the laser-induced oxide film removal in a liquid confinement at con- trolled electrochemical potential [22]. The workpiece is immersed into the liquid and laser irradiation causes melting, vaporization, or spallation of the oxide layer. Here, the laser light is fed to the sample through an optical fibre and the ablated area corresponds to the core diameter of the fibre. © Elsevier.

0.8 0.7 0.6 0.5 4 Before polarization O 3 0.4 Fe k 0.3 0.2 After 40 min of polarization 0.1 0.0 500 600 700 800 1000 Wavelength (nm)

Figure 2.6 Computed spectra of the imaginary part of the refractive index k ofaFe3O4 layer before and after cathodic polarization. © SPIE (2000), reproduced with permission from Ref. [25].

[23, 24]. Further studies revealed that at cathodic polarization the transparency of the oxide layer was increased considerably (Fig. 2.6), so that the laser light could penetrate deeper and cause the oxide layer spallation due to thermal stresses. In addition, mechanical effects resulting from H2 incorporation (enbrittling of the material and increase of stresses due to volume increase) might have been contributed to the oxide layer removal as well. In the article by Cortona et al. [26], the removal of porous oxide layer, containing 18 per cent of water, from AlMgSi1 alloy surface by laser ablation is reported. Some investigations directed to laser removal of radioactively contaminated layers from concrete are described in the articles by Savina et al. [27–29] (see Table 4.11, Savina (1998) [27], Savina (2000) [28], and Robinson (2001) [29].

2.2.7 Removal of frozen gas and liquid layers from optical surfaces

Orbiting earth spacecrafts optics suffers form contamination by dust, H2O, CO 2,O2, and various organic molecules, originating from micrometeorite impacts, from high-energy particles (electrons, oxygen a.o.) irradiation of construction materials (outgassing and offgassing), and from manoeuvring motors. Organic contaminants tend to polymerize under sunlight UV radiation.The condensates form islands at surface defects and degrade the performance of optical components [30]. Different techniques have been proposed for removal of contamination from optical surfaces of orbiting spacecrafts, like electron and ion bombardment. Laser irradiation was found to be a favourable alternative here. Ch02-I044498.tex 11/9/2007 18: 47 Page 16

16 Handbook of Liquids-Assisted Laser Processing

Laser pulse

Micro phone

Shock HCI Wave front solution Sample

Figure 2.7 Experimental setup for the removal of oxide scale on low carbon steel enhanced by shock wave generated by laser breakdown on the surface of a aqueous HCl solution [33]. Microphone was used for shock intensity estimation by audible sound level. ‘Fig. 1 of Laser-assisted chemical cleaning for oxide scale removal from carbon steel surfaces’ reproduced with permission from Journal of Laser Applications, February 2004,Volume 16, Issue 1, pp. 25–30, Laser Institute of America, Orlando, Florida. The Laser Institute of America disclaims any responsibility or liability resulting from the placement and use in the described manner. © Laser Institute of America (2004). www.laserinstitute.org. All rights reserved.

Piper et al. [30],Pierce et al. [31] have investigated laser cleaning of cryogenic mirrors (Ni-coatedAl,Au/Ni- coated Al, Be) by CO2 and Nd:YAG lasers. The mirrors were contaminated by dust and frozen at 100–140 K components of laboratory air, mainly H2O and CO2. It was found that CO2 laser was proper for contaminants removal, because its light was effectively absorbed in the contaminant layer, but 1.06 µm Nd:YAG laser not.

2.2.8 Laser-generated shock wave enhanced scale removal In the articles by Lim et al. [32, 33], an oxide scale on low carbon steel was removed by laser-generated mechanical impact in liquid; but only in case when the workpiece was held at least 10 s in at least 10% HCl solution before laser irradiation. Without laser, the minimum HCl concentration needed for scale removal was 18 per cent (Fig. 2.7).

2.2.9 Removal of organic contaminants by water decomposition products In the article by Hidai et al. [34], a tapping oil contamination was removed from various metal surfaces (Ni, Cu, Zn, SUS304), thereby from the inside of holes, by water decomposition products, generated by a 150 mJ ArF laser beam focused onto water surface. Except Zn, no damage of the metal was observed (Fig. 2.8).

2.2.10 Cleaning of surfaces through contaminants dissolution in laser-generated supercritical solution

Dolgaev et al. [35] report about non-diamond carbon layer removal from suspended in HNO3 aqueous solution diamond particles (4 nm) in result of irradiation of the suspension by YSGG:Cr3+:Yb3+:Ho3+ laser beam (2.92 µm, ≈130 ns, 1 kHz, 10 J/cm2). Contamination removal was ascribed to the solvation of non-diamond carbon in supercritical solution.

2.2.11 Dehydroxylation of a silica glass surface Halfpenny [36] and Fernandes [37] report about dehydroxylation of silica glass surface by laser irradia- tion (Fig. 2.9). Irradiation of the surface by UV light (255.3 nm = 4.86 eV) led to breaking of OH bonds (ED = 4.436 eV) and removal of the hydroxyl groups. The process was proposed for controlling the particles adherence to silica surfaces. Ch02-I044498.tex 11/9/2007 18: 47 Page 17

Cleaning 17

Laser beam

Lens F180

Sample

Water surface

L

Figure 2.8 Experimental setup used for cleaning of metal samples from tapping oil by laser-generated water decomposition products [34]. Oil layers were totally removed by 18 000–36 000 laser pulses of energy 150 mJ at 193 nm wavelength. © Elsevier.

UV photon HH HH O O H H HHHetc. OOOO O O O Si Si Si Si Si Si Si Si Si OOO Heat O O O Bulk silica Bulk silica

Figure 2.9 Modification of the chemical structure of a silica surface by laser irradiation: an hydrophilic to hydrophobic transition occurs [36]. Reproduced with kind permission of Springer Science and Business Media.

2.2.12 Ice-assisted laser particles removal In patent US2004140298 [38], a water ice layer deposition onto surface to be cleaned before laser irradiation was proposed.

2.3 Particles on Solid Surfaces

2.3.1 Adhesion phenomena and adhesion forces In order to remove a particle from a surface, the adhesion forces need to be overcome. In laser removal of micrometre and nanometre-sized particles from solid surfaces, the adhesion forces to be considered are: van der Waals force, double-layer force, capillary force, and chemical bond force (Fig. 2.10). On ferromagnetic substrates, also magnetic forces may be significant. In comparison with macroscopic systems, the gravitational force is unimportant.The adhesion is greatly affected by the surface roughness and the environment (Fig. 2.11). Much of experimental and theoretical research is done by spherical particles; highly spherical latex, glass, silica, and alumina particles of various sizes are commercially available,also of calibrated size. In real cleaning situations, however, the particles are mostly of irregular shape.

Cohesion energy approach Interaction energy of electrically neutral bodies in vacuum can be expressed by Dupré equation:

γ = γ1 + γ2 − γ12, (2.1) Ch02-I044498.tex 11/9/2007 18: 47 Page 18

18 Handbook of Liquids-Assisted Laser Processing

105

6 10 Capillary force van der Waals force due to 1% deformation

107 van der Waals force Force (N) Force

Electrostatic image force 108

Electrical double- layer force Gravitational force

109 0.1 1.0 10 100 Partical diameter (m)

Figure 2.10 The adhesion forces as a function of the diameter for an Al2O3 particle on a flat Si substrate [39–41]. In dry ambient, the capillary force may be absent. Compilation of data by Kohli [42]. © Koninklijke Brill NV. Republished with permission.

Capillary condensed water

(a) (b)

(c) (d)

Figure 2.11 Situations in a particle–substrate system: (a) irregular particle on a rough surface (the real case); (b) model spherical particle on a flat surface; deformation of the substrate by adhesion forces and capillary liquid are shown; (c) immersed into liquid system; and (d) particle–substrate system after long storage (hundreds to thousands of hours).

where, γ is the energy per unit area of the interface (Dupré energy or thermodynamic work of adhesion), γ1 and γ2 are the respective surface energies (surface tensions) of both materials, and γ12 is the interfacial energy. Dupré energy of adhesion corresponds to the work per unit area required to separate the surfaces from contact to infinity. For completely apolar materials. √ γ12 = 2 γ1γ2. (2.2)

Hamaker constants Aii (see below) are related to γ1 and γ2 as [43]:

= Aii → = A11 = A22 γi 2 γ1 2 , γ2 2 , (2.3–2.5) 24πl0 24πl0 24πl0

where l0 is the ‘practical’ minimum equilibrium distance, l0 = 157 ± 9 pm. Ch02-I044498.tex 11/9/2007 18: 47 Page 19

Cleaning 19

Electrostatic forces In general, the force on a charged particle resting on a conducting substrate in the presence of an applied electric field is given as [39, 42]:

2 3 6 2 = − q + qEd − 3 πε0d E Fe qE 2 3 4 , (2.6) 16πε0h 16h 128 h where d is the particle diameter, E the electric field strength, h is the distance of the particle from the surface, and q is the total electrical charge of the particle. The physical meanings of the terms in this formula are: 1st term: Coulomb force, 2nd term: image force exerted by an image charge of −q at position −h from the surface, 3rd term: dielectrophoretic force on the induced dipole caused by the gradient of the field from the image charge, 4th term: polarization force due to interacting of the induced dipole and its image. Image and polarization forces between a particle and a surface are always attractive, the other forces may be whether attractive or repulsive. Formulae for electrostatic forces acting on rough particles are given in the article by Soltani andAhmadi [39]. When the particle and the substrate are materials with different contact potentials, electrons from the material with lower work function are transferred to the material with higher one until the Fermi levels in both materials reach the same level. The potential difference U arising from this levelling can reach values of up to 0.5V. For a sphere on a flat surface, the corresponding force is [44]:

R (U)2 F = πε , (2.7) el 0 h where h is the distance of the particle from the surface.

Chemical bond forces In adhesion of oxide particles to oxide or oxidized surfaces, the hydrogen bond forces may be considerable or even dominant (Fig 2.12) [45]. Wu et al. [45] estimate the hydrogen bond force as:

DSEbond FHbond = , (2.8) dbond

where D is the OH group density, S and Ebond are the total interaction area and the hydrogen bonding interac- tion energy between particle and substrate, respectively,and dbond is on the dissociation length of the hydrogen

O H H

O O H H H R H O O O

Si Si Si Si Si

OOO OOO OOO OOO OOO

Figure 2.12 Hydrogen bonding between a SiO2 or oxidized Si surface and a hydrogen-bonded liquid. The dashed lines are hydrogen bonds. ‘R’ may be a hydrogen atom (for water) or a radical (for alcohols). After Wu et al. [45] and Fernandes et al. [37]. Ch02-I044498.tex 11/9/2007 18: 47 Page 20

20 Handbook of Liquids-Assisted Laser Processing

bond. Ebonddepends on the nature of the surfaces, in particular on their degrees of hydroxylation and on the electronic structure of the materials. The average bonding energy of the O—H—O hydrogen bond is about 5 kcal/mole (∼0.22 eV/bond) [46, 47]. The dissociation length of the hydrogen bond in the order of 1 Å [45]. According to Wu et al. [45], the hydrogen bond force for SiO2 and Al2O3 particles on silicon is an order of magnitude greater than the van der Waals force, both in air and in alcohols.

van der Waals force van der Waals force is an electrical force caused by polarization induced mutually in the particle and in the substrate. For spherical particles, the corresponding interaction energy and force are expressed as:

A R A R W =− 123 , F = 123 , (2.9) vdW 6h vdW 6h2

where A123 is the effective Hamaker constant, R is the particle radius in sphere–plane interactions, or the reduced particle radius in sphere–sphere interactions,

R R R = 1 2 , (2.10) R1 + R2 and h is the distance between the particle and the substrate. Equation (2.9) is valid if the distance h is less than few per cent of the particle’s radius. At larger separations, the potential retardation can be taken into account by formula [48]:
 A R 1 W =− 123 (2.11) vdW 6h 1 + 11.12h/λ where λ is the characteristic wavelength for interaction (distance between atoms in solids ∼90 nm). This expression is a good approximation in case of separation distances smaller than 20 per cent of the particle radius and in particle size range at least 0.1–1 µm. The effective Hamaker constant A123 depends on the materials that are interacting and may be calculated from the individual Hamaker constants Ajj [49, 50], √ √  √ √  A123 = A11 − A33 · A22 − A33 , (2.12)

where A11 and A22 are the Hamaker constants for the particle and the surface, respectively, and A33 is the Hamaker constant for the third medium (gas or liquid). The Hamaker constants Aii for some materials of interest to this book are given in Table 2.2. For interactions across vacuum, A123 reduces to A12, √ A12 = A11A22. (2.13)

When inserted into liquid, the van der Waals interaction (adhesion force) may be reduced considerably: for example about 2 times for Au or Ag surfaces, 4 times for polystyrene (PS), and 6 times for MgO surfaces [50]. Equation (2.12) suggests also that effective Hamaker constant may also obtain negative values, thus the force between particles may become repulsive if immersed into a liquid. The condition for repulsion is [50]:

A11 < A33 < A22 or A11 > A33 > A22. (2.14)

Photoenhanced van der Waals force According to Kimura [53], the illumination of metal colloids at Mie resonance frequencies (see Section 5.2) can accelerate their coagulation by 100 to 5000 times due to decrease of interparticle potential energy and the corresponding increase of van der Waals force. Ch02-I044498.tex 11/9/2007 18: 47 Page 21

Cleaning 21

Table 2.2 Non-retarded (static) Hamaker constants Aii for two identical materials interacting over vacuum (at room temperature if not given else).

Material Aii [J] Reference Au 54.5 × 10−20 Visser [51] Ag 44.6 × 10−20 Visser [51] Cu 30.6 × 10−20 Visser [51] Diamond 32.6 × 10−20 Visser [51] Si 25.6 × 10−20 Visser [51] 6H−SiC 24.8 × 10−20 Bergström [52] β-SiC 24.6 × 10−20 Bergström [52]

−20 β-Si3N4 18 × 10 Bergström [52] −20 Si3N4 (amorphous) 16.7 × 10 Bergström [52] −20 α-Al2O3 15.2 × 10 Bergström [52] −20 TiO2 (tetragonal) 15.3 × 10 Bergström [52] MgO (cubic) 12.1 × 10−20 Bergström [52] ZnO (hexagonal) 9.21 × 10−20 Bergström [52]

−20 SiO2 (quartz) 8.68 × 10 Bergström [52] −20 SiO2 (amorphous) 6.50 × 10 Bergström [52] PS (polystyrene) 7.3 × 10−20 Visser [51] Glycerol 6.7 × 10−20 van Oss [43] Benzene 4.66 × 10−20 van Oss [43] Water 4.62 × 10−20 van Oss [43] Ethanol 4.39 × 10−20 van Oss [43] Argon (−188◦C) 2.33 × 10−20 van Oss [43] Nitrogen (−183◦C) 1.42 × 10−20 van Oss [43] Helium (−271.5◦C) 0.0535 × 10−20 van Oss [43]

The ratio of interparticle potential energy when illuminated Uirr, to the potential energy in dark Udark is expressed by:
 U 16α E2k2 R 2 irr =− 0 0 , (2.15) Udark 27
ωM DM

where α0 is static polarizability, E0 is the amplitude of the external field, k is a numerical factor, ωM is Mie resonance frequency,and R is the (reduced) radius of the particles. DM = ReD(ωM),where D(ω) is the centroid of the surface screening charge. DM roughly coincides with the position of maximum induced electron density. For silver, DM ≈−0.85 Å and the photoenhanced interaction energy has maximum at particle radius of R ≈ 20 nm. Ch02-I044498.tex 11/9/2007 18: 47 Page 22

22 Handbook of Liquids-Assisted Laser Processing

Capillary force Capillary force is due to capillary condensed liquid (Fig. 2.13) [54, 55]. It may be the dominant particle adhesion force in humid ambient [54]. Due to increased vapour pressure at a concave interface, Eq. (7.57), capillary condensed water can be very stable – according to Bhattacharya and Mittal [40] even a 24 h baking at 180◦C did not decrease the adhesion strength of particles to silicon. Capillary force has two components, the capillary pressure force Fcp and the surface tension force Fst [55]. Capillary pressure force:

Fcp = 2γπR (cos 1 + cos 2) . (2.16) Surface tension force:

Fst = lγ cos α, (2.17)

where γ is the surface tension, and 1 and 2 are the wetting angles of the particle and of the substrate. The total capillary force becomes:

Fc = Fcp + Fst = 2γπR( cos 1 + cos 2) + lγ cos α. (2.18)

The analysis by Pakarinen et al. [55] showed that the surface tension force is negligible for a 1 µm radius spherical particle, but for a 15 nm radius particle of it can be the largest component of the total capillary force. For a Si—SiO2 system, the capillary force should be taken into account beginning from RH > 20 per cent [55]. The volume of the capillary condensed liquid for complete wetting may is expressed by [56, 57]:

≈ 2 Vl 4πRKR, (2.19)

where RK is the Kelvin radius. For water: µσ R ≈  , K −1 ρlRGT ln RH or in nanometers 0.52 RK ≈  , (2.20) ln RH −1

where RG is the universal gas constant, ρ is the density of the liquid, µ its molar weight, σ the surface tension coefficient, and RH is the relative humidity.

1

R

2

Figure 2.13 Capillary liquid at a particle (hydrophilic particle on a hydrophilic substrate). The liquid may originate from capillary condensed vapour of a rest of the bulk liquid. After Pakarinen et al. [55]. Ch02-I044498.tex 11/9/2007 18: 47 Page 23

Cleaning 23

Double-layer force Double-layer force is an electrostatic force determined by ions distribution at charged surfaces in electrolytes. Solid surfaces may acquire charge in several ways, for example, at SiO2 surface the process goes on the way:

− + −SiOH ↔−SiO + H (2.21)

Cations from solution absorb on the negatively charged surface and attract in turn negative anions from the solution, thus building up a double ion layer structure [58]. Different double-layer theories use different simplifications of the physical situation; a solution proposed for cleaning situations (spherical particle on a flat surface, low constant potential approximation) is given by [59, 44, 60]:    2 2 εR 2 0 part 1 + exp(−κh) W = 2 + 2 · · ln + ln [1 − exp(−2κh)] (2.22) dl 0 part 2 + 2 − − 4 0 part 1 exp( κh)

where ε is the permittivity of the medium, 0 is the surface potential of the surface, part is the surface potential of the particle, and κ is the Debye–Hückel inverse double-layer thickness (reciprocal length parameter):

2000e2N I κ = A , (2.23) εkBT

where e is the electronic charge, kB is the Boltzmann’s constant, T is the temperature, NA is the Avogadro constant, and I is the ionic strength of the (bulk of) solution,

1 n I = C Z2 2 i i i=1

where Ci is the molarity concentration (mol/l) of ion i, Zi is the charge of that ion, and the sum is taken over all ions in the solution (Table 2.3). Equation (2.22) is a good description of the interaction energy for part and 0 values smaller than 50–60 mV and if the product κR > 5. This means that for an average particle radius of 0.12 µm, the equation holds if the ionic strength is larger than 10−4 M. At lower ionic strengths, as in case of deionized water, the calculated electrostatic interaction energy should, therefore, be considered as indicative [60]. For practical calculations the surface potentials may be approximated by their zeta-potentials (ζ-potential). ζ-potentials are dependent on the nature and concentration of the ions, and on the pH of the solution (Fig. 2.14). However, the isoelectric points of oxide materials (Table 2.4), which are of main interest in laser cleaning, are rather independent on kinds of ions and their concentration, but depend on the structure of the material [61].

Table 2.3 Debye–Hückel inverse double-layer thickness for some electrolytes. [43] Solution 1/κ(nm)

H2O 1000 10−5 mol NaCl 100 10−3 mol NaCl 10 10−1 mol NaCl 1 Ch02-I044498.tex 11/9/2007 18: 47 Page 24

24 Handbook of Liquids-Assisted Laser Processing

10 Al2O3 20 30 ZnO 40 0 TiO2 40

ζ -potential (mV) 30 SiO2 20 10 Neutral 024681012 pH

Figure 2.14 Dependence of ζ-potentials of some materials on pH of the solution (schematically after Hunter [61] Hann [62] Vos et al. [60] Kamada et al. [63] and Kalin et al. [64]). Other oxides behave similarly.

Table 2.4 Point of zero charge (isoelectric point) of some materials of interest to wet laser cleaning and to laser particles generation [60, 63, 64]. Material Isoelectric point (pH)

Quartz, SiO2 2–3.7 Silicon carbide 3.2

Cassiterite, SnO2 4.5

Rutile,TiO2 4.7–6 Zirconia 6

Hydroxyapatite, Ca5(PO4)3(OH) 7

Si3N4 4.6–8.8

Corundum, Al2O3 8–9 ZnO ∼9.7 Magnesia, MgO 12

Electrostatic double-layer force can be calculated by Hogg–Healy–Fuerstenau (HFF) equations [50]: (1) constant potential approximation:

  −κh εR κe 2 − F(h) = 2 + 2 01 02 − e κh , (2.24) 01 02 − −2κh 2 + 2 2 1 e 01 02 (2) constant charge approximation:

  −κh εR κe 2 − F(h) = 2 + 2 01 02 + e κh , (2.25) 01 02 − −2κh 2 + 2 2 1 e 01 02

where 01 and 02 are the potentials of the interacting surfaces and κ is the inverse double-layer thickness (Eq. (2.23)). Ch02-I044498.tex 11/9/2007 18: 47 Page 25

Cleaning 25

Double-layer force may be considerably reduced by proper choice of the liquid and the solutes. Principally, at high pH values the potential or the charge of the adherents increases, the adhesion lowers and the attraction may change into propulsion [50].

Magnetic force Force F on a magnetized particle in a magnetic field B can be calculated by [65]:  F = (M · B)dS, (2.26) S

where M is the magnetization and dS is a vector in the surface normal direction, whose modulus equals to the area dS.

2.3.2 Adhesion force theories considering the deformation of the particle and the substrate Adhesion forces cause deformation of both substrate and of particle leading to an increase of the contact area and this way to an increase of the adhesion force as well. According to Kohli [42], due to the deformations, the adhesion force between polymer particles rises about 100 times and the force between metal or oxide particles about 20 times. In the following, some significant to laser cleaning results of adhesion theories are presented [66–69]. In the formulae below, K and E* are the combined elastic moduli of two spheres (or of a sphere and a plane), given by:
 − 2 − 2 1 = 3 1 ν1 − 1 ν2 = 3 · 1 ∗ , (2.27) K 4 E1 E2 4 E Parameters µ and λ, used as criteria for applicability of different models, are:

32 2RW 2 µ = 3 a and λ = 1.16 µ. (2.28) ∗2 3 3π πE z0

Hertz model In Hertz model no adhesion is considered, the deformation is elastic and is caused by the external force F only (Fig. 2.15). The radial distribution of the contact pressure is given by:       3Ka r 2 3F r 2 p (r) = 1 − = 1 − , (2.29) 2πR a 2πa2 a

where a is the contact radius, a3 = RF/K. Due to deformation, the sphere approaches to the surface (Fig. 2.39) by: F δ = . (2.30) Ka Without external force no deformation occurs. Hertz theory is not applicable directly to the particle adhesion problems; however, it is incorporated into other theories which consider the adhesion forces as well. Hertz pressure distribution is shown in (Fig. 2.16). Ch02-I044498.tex 11/9/2007 18: 47 Page 26

26 Handbook of Liquids-Assisted Laser Processing

Bradley’s model This model considers two rigid spheres interacting via Lennard–Jones potentials. Force between two spheres:  
−
− 8πwR 1 h 8 h 2 F (h) = − . (2.31) 3 4 h0 h0

The maximum adhesion force (pull-off force) occurs at h = h0:

FBradley = 2πRW a. (2.32)

DMT model (Derjaguin, Muller, Toporov) The bodies are considered to deform according to Hertz theory,but forces acting outside of the contact region are taken into account. Contact radius:  R a = 3 (F + 2πW R) . (2.33) A K Contact radius at zero external force:  2 3 πW R a = A . (2.34) 0 K Pull-off force:

FDMT = 2πRW a, (2.35) This model is applicable to small compressible solids where µ<1.

JKR model (Johnson, Kendall, Roberts) This model neglects long range forces outside the contact area and considers only short range forces inside the contact region. Deformation is assumed to be Hertzian. Contact radius:

 R a = 3 F + 3πRW + 6πRW F + (3πRW )2 , (2.36) K a a a

F R (1) y Hertz

aHertz JKR

δ aJKR

Figure 2.15 Surface deformations according to Hertz and JKR models [69]. © Elsevier. Ch02-I044498.tex 11/9/2007 18: 47 Page 27

Cleaning 27

Contact radius at zero external force:  2 3 6πW R a = a . (2.37) 0 K Pull-off force: 3 F = πRW (2.38) JKR 2 a The model is applicable to highly adhesive bodies where µ>1.

MD model (Maugis, Dugdale)

Adhesion is considered as a constant additional stress σ0 over an annular region around the contact area up to a maximum separation h0 beyond which it falls to zero, as shown in (Fig 2.16). Adhesion energy is Wa = σ0h0. This model applies to all materials, from large rigid spheres with high surface energies to small compliant bodies with low surface energies (Fig 2.17) [69, 70]. The adhesion force in MD theory can be calculated from a set of parametric equations [69, 70]:  4 δ = A2 − Aλ m2 − 1, (2.39) 3

2        λA   4λ2A m2 − 1 + m2 − 2 arctan m2 − 1 + −m + 1 + m2 − 1 arctan m2 − 1 = 1 (2.40) 2 3 and    F = A3 − λA2 m2 − 1 + m2 arctan m2 − 1 , (2.41) where, a A =  , (2.42) 3 2 πWaR /K F F = , (2.43) πWaR

p1 R p P1 a a

d s h0 pa 0 Pa cc

(a)

da

ρ h0 u

(b)

Figure 2.16 (a) The MD traction distribution is made up of two terms: Hertz pressure p1 on area r < a, and adhesive tension pa on area r < c. In the annulus a < r < c the traction is constant (=σ0) and the surfaces separate up to a distance h0. The net load P = P1 − Pa. (b) A liquid meniscus at the edge of a contact gives rise to a Dugdale adhesive tension σ0 = γ/ρ, where γ is the surface tension of the liquid [67]. © Elsevier. Ch02-I044498.tex 11/9/2007 18: 47 Page 28

28 Handbook of Liquids-Assisted Laser Processing

104

103 Hertz 0.05 /p p 0 JKR 2

/ p wR 10 d MD 1 /h 0 DMT

101 0.05

20

0.05

Load P

0

h

0

/

h 0

0 Bradley / d

10 0

(rigid) d

101 103 102 101 100 101 102 Elasticity parameter, l 1.16 µ

Figure 2.17 Adhesion map for elastic spheres based on the MD model [67]. In the Hertz zone adhesion forces are negligible. The Bradley, DMT, and JKR asymptotic theories may be used in the zones so marked. © Elsevier.

and δ δ =  . (2.44) 3 2 2 2 π Wa R/K The material properties are taken into account by a dimensionless parameter λ (cf. Eq. (2.28)):  2 2.06 3 RW λ = a 2 , (2.45) h0 πK

where h0 is a typical atomic dimension. DMT and JKR models are special cases of MD model (λ → 0 and λ →∞, correspondingly). According to Johnson and Greenwood [67], MD model exactly reproduces also the adhesion due the capillary forces exerted by the meniscus (Fig. 2.13). In this case the Dugdale stress σ0 is given by the capillary pressure γ/ρ, and the thickness h0 by 2ρ cos θ, where γ is the surface tension of the liquid. The effective work = of adhesion is then given by Wa 2γ cos θ.

MP model (Maugis, Pollock) MP model assumes the contact profile of pressure Hertzian, but with the radius of curvature changed due to the plastic deformation [71, 72]. Adhesion force: √ 9 π W K √ F = a F + 2πW R. (2.46) a 8 H 3/2 a Contact radius:  2W R a = A , (2.47) 3Y where, H is contact hardness, H ≈ 3Y and Y is yield strength of the material in compression. Ch02-I044498.tex 11/9/2007 18: 47 Page 29

Cleaning 29

Deformation of the surface can be accounted in the van derWaals force Eq. (2.9) by adding a term derived from the formula for van der Waals force per unit area between two plates [50]:

= A Fdeform 3 , (2.48) 6πh0

yielding
 AR a2 = − + = + Fa Fsphere plane Fdeform 2 1 , (2.49) 6h0 Rh0

where A is the Hamaker constant, R the particle radius, h0 the distance between particle and substrate (often assumed as 4 Å),and a the contact radius that may result from adhesion-induced deformation, Eqs (2.34), (2.36), (2.37), (2.42), and (2.47).

Numerical solutions Elasticity-adhesion problem for two spheres was solved numerically (iteratively) by Greenwood [73]. Gilabert et al. [74] simulated the adhesion and pull-off force of polystyrene spheres of radia 1–8 nm by molecular dynamics method using Lennard–Jones potential. These calculations demonstrated a pretty good adequacy of analytical models (from Bradley to MP) to particle adhesion problems.

Influence of the surface roughness For particles on dry surfaces the adhesion force decreases considerably if the surface roughness increases (Fig. 2.18).

1.4 1.3 1.2 c 1.1

/ N p 0.1 c 0.9 P c 0.8 0.7 0.6 0.5 JKR 0.4 0.3 Total pull-off force, P pull-off force, Total DMT 0.2 0.1 0 0 0.5 1.01.5 2.02.53.0 3.5 4.0 s d Roughness, / c

Figure 2.18 Effect of random roughness on adhesion between nominally flat surfaces having N asperities each of radius R and standard deviation of height σ. Pc = JKR pull-off force (=1.5πωP) and δc = JKR pull-off = 2 2 2 1/3 displacement (3/4)(π Wa R/E* ) for each aspherity [67]. © Elsevier. Ch02-I044498.tex 11/9/2007 18: 47 Page 30

30 Handbook of Liquids-Assisted Laser Processing

(a) (b)

Figure 2.19 Scanning Electron Microscope (SEM) images of 1.5 µm SiO2 particles: (a) after 17 h storage and (b) after 1350 h storage [76]. Reproduced with kind permission of Springer Science and Business Media.

Long-time stability of particle-surface contact Adhesion forces cause a deformation of both the particle and of the substrate, balanced by elastic forces arising from deformations of both of the particle and the substrate. The elastic deformation tends to relax in time (hundreds and thousands of hours) via creep and migration of the matter (Fig. 2.19), causing the increase of the adhesion force [75, 76].

2.4 Experimental Techniques in Laser Wet/Steam Cleaning Research

2.4.1 Preparation of particles covered surfaces In the research of laser cleaning, there is a need for controlled covering of substrates with particles.The particles density should be high enough to achieve statistically reliable counts over the laser spot and coarse enough to avoid particles aggregation.

‘Dip and tap’ method (Fig. 2.20a) The substrate to be covered is dipped into a large volume of particles or the particles are spooned onto the substrate. The loose particles are then removed by sharp tapping or fast flow of dry gas. The method leads to a medium density of particles, 10–40 per cent coverage by area, on solvent cleaned glass slides, and to lower densities on ultrasonically cleaned slides, 0.1–7 per cent, average 1.8 per cent [77, 78].

Drying of a suspension (Fig. 2.20b) Suspension of particles in an organic solvent (e.g. isopropylalcohol, IPA) is prepared by ultrasonic agitation. A drop of the suspension is applied onto the substrate.The solvent vaporizes but particles remain on the surface. Particles density may be controlled by spinning of the suspension-coated substrate. Higher rotating velocities result in thinner fluid films and lower surface density of particles [79, 80]. A variant of this method is described in the article by Neves et al. [81] (Fig. 2.20c). The substrate to be coated by particles was placed in a 10-cm-diameter Petri dish with ethanol, the whole being placed on a heated vibrating table (≈50◦C) and a specific amount of metallic particles was placed in the centre of the wafer. After a certain time, the ethanol evaporated leaving the metallic particles uniformly distributed over the surface of the wafer. Ch02-I044498.tex 11/9/2007 18: 47 Page 31

Cleaning 31

(a) (b)

(c) (d)

Figure 2.20 Some important methods of preparation of particle-covered surfaces. (a) ‘dip and tap’ method, (b) drying of particles suspension, (c) in situ suspension preparation, and (d) laser ablation of a compacted powder target.

fluence xy stages 10–200 J/m2, 10 ns 0.1–3.5 s Valve opening control Substrate Flow meter z stages 50°C Heater Focusing lens

Pulsed laser: Computer water + 8% excimer, alc. Mirror Nd:YAG, etc. 40°C Thermometer Laser triggering Nitrogen

Figure 2.21 Schematics of steam laser cleaning system developed at École Polytechnique de Montréal. The wafer is kept face down to avoid resettlement of the removed particles. © SPIE (1999), reproduced with permission from Ref. [85].

Laser ablation deposition (Fig. 2.20d)

Particles with high tendency to form aggregates like Al2O3 may be effectively dispersed by laser ablation [78]. A compacted Al2O3 powder target was irradiated by a focused XeCl laser beam (308 nm) at fluence 4.4–12.3 J/cm2. Prepared by this method samples had 1 µm alumina particle densities of 0.01–1.5 per cent, in average 0.6 per cent. Particles may be deposited also electrophoretically [82], be dusted or sprayed onto surfaces. Fernandes and Kane [83] list the particle deposition methods and give further references. There are industrial devices for controlled deposition of particles onto silicon wafers available as well, for cleaning standards and for research purposes [84]. Figs. 2.21–2.23 present some complete steam laser cleaning systems.

2.4.2 Application of liquid and monitoring the liquid film thickness and condition In steam laser cleaning process, the liquid film is formed by condensation of vapours on the contaminated surface (Figs 2.21–2.23).Vapour is generated by heating the liquid (water–alcohol mixture) in a special vessel and fed to the cleaned surface by pulsed nitrogen flow. The thickness of the liquid film may be controlled by vapour pulse duration. Usually the vapour pulse lasts some seconds yielding a liquid film of thickness Ch02-I044498.tex 11/9/2007 18: 47 Page 32

32 Handbook of Liquids-Assisted Laser Processing

Low pressure N2

Liquid film

Flow Sample stage controller controller Port Filter Nozzle Level sensor Liquid supply controller Stage Servo controller Heater- Puffer Liquid supply thermocouple (8% IPA) Filter Beam assembly splitter Heater Mirror Rotating Heater power Thermo- mirror Energy Lenses supply & couple meter temperature Reservoir Beam controller (40% IPA, 60% water) homo- genizer Lens Beam Controls expander KrF excimer laser each Mirror subcontroller Computer and laser

Figure 2.22 Schematics of a high-throughput laser cleaning tool developed at IBM [86]. The beam from an industrial KrF excimer laser (248 nm radiation, 200 Hz repetition rate, 200 W output) is scanned galvanometrically and the wafer by a translation stage; the liquid film is deposited continuously. © Elsevier.

Focusing Process monitoring lenses and Humidified N2 Dry N2 microscope mirror OPO

Pulsed laser

Laser beam Humidifier Photodiode Dark field Particle Reflected light illumination laser Suction Water layer Narrow gap suction Valve MFC consensed Translation Rotation axis axis

Figure 2.23 Particle removal system for high-volume manufacturing system by Sumitomo Mitsubishi Silicon Group [87]. An image analyzing system detects individual particles which are thereafter removed by local steam deposition, laser irradiation, and suction. Capability of the system to clean 4000 silicon wafers in 2 weeks was demonstrated. © Trans Tech Publications Inc., reproduced with permission. Ch02-I044498.tex 11/9/2007 18: 47 Page 33

Cleaning 33

° Ip( C) 104

Abiation 3 10 10 4 Hotter

Melting 2 10 3 10 Deeper ) 2 10 2 Cleaning 10 10 Photothermal sensing I (MW/cm 1

10 1 10 3 10 2 10 1 1 10 102 103 104 105 106 t(ns)

Figure 2.24 Parametric space indicating various possible effects when a solid surface (e.g. stainless steel) is irradiated by a laser beam with various intensities, I and pulse widths, τ [86]. © Elsevier.

0.2–10 µm. Liquid film last on the surface some seconds, therefore, the laser pulse is fired about 0.1 s after the vapour pulse. The vapour may be supplied also continuously (Fig. 2.22). The thickness of the liquid film can be monitored interferometrically and its lasting by optical reflectometry (Figs 2.27–2.28).

2.4.3 Choice of laser beam parameters In steam laser cleaning, it is energetically advantageous to use lasers whose wavelength does not absorb in liquid, but in the substrate. Thus, excimer and frequency multiplied Nd-ion lasers are the best choice. For 1.06 µm wavelength form Nd:YAG and similar Nd-ion lasers, the reflectivity of solid surfaces is usually higher that in the UV-VIS region. The use of CO2 laser, whose 10.6 µm light cannot penetrate a common liquids film, but vaporizes the liquid surface only, is rationalized by independence of the cleaning process of the substrate material and by absence of the substrate damage hazard. A discussion about the choice of laser wavelength for steam laser cleaning is presented in the article by Oltra and Boquillon [12]. Figure 2.24 presents a comparison of laser beam parameters in cleaning with these in other kinds of laser processing.

2.4.4 Measuring and monitoring techniques in steam laser cleaning Detection of acoustic emission (sound) Thermal expansion of the laser heated target and rapid vaporization of the liquid induce hearable sound transients, whose intensity can be used for monitoring the laser–matter interaction intensity (Fig. 2.7).

Detection of displacements of interfaces Laser heating caused displacement of the rear side of the substrate can be measured by interferometric or piezoelectric probes (Fig. 2.25) (cf. Figs 3.13 and 3.15). Probing of the backside displacements is needed also for precise determination of vapour film thickness by an interferometric probe at the front side (Fig. 2.26). Ch02-I044498.tex 11/9/2007 18: 47 Page 34

34 Handbook of Liquids-Assisted Laser Processing

Laser pulse Laser pulse

Oxidized metallic sample Oxidized metallic sample

Interferometric Piezoelectric probe transducer

(a) (b)

Figure 2.25 Experimental setups for on-line monitoring of laser-induced oxide film removal process using: (a) interferometric probe and (b) piezoelectric probe [22]. © Elsevier.

Light source

Beam splitter

I 1

I 2 Mirror

Effective bubble layer

Solid sample

Probe beam Bubbles (diameter ~1 mm) Water

Cr

Quartz substrate

Figure 2.26 Principle of interferometrical measurement of vapour film thickness [88]. © Elsevier.

Detection of reflected and scattered light Level of surface contamination and the vaporization onset can be monitored by reflected or scattered light (Fig. 2.27). The dynamics of vaporization and ejected particles flow can be probed by deflection/scattering of a probe beam parallel to the surface (Fig. 2.28).

Surface plasmon probe A versatile high-resolution probe,sensitive to refractive index change of a liquid at a solid interface,is the surface plasmon probe (SPP) (Figs 2.29 and 2.30). Because the refractive index of a liquid or a gas depends on the density,pressure, and temperature, these parameters may be measured and mapped by SPP.The time resolution Ch02-I044498.tex 11/9/2007 18: 47 Page 35

Cleaning 35

FM BS 40/60 Nd:YAG Dump Attenuator BS 50/50

PD3 p–pol. IF IF PD2 PBS s–pol. NDF M AFR L4 Cell PD1

L3 IF L1 L2

Sample F Cover Heater

Ar laser M

Figure 2.27 Reflecting/scattering light probe for monitoring of vapour layer state [80]. The response time of the system to bubble nucleation was <1 ns. © World Scientific Publishing Co Pte Ltd., republished with permission.

Mirror He–Ne laser Beam expander

He–Ne laser Lens

Lens UV mirror

Beam homogenizer Lens

Photodiode Interference filter Sample Beam Energy splitter Knife edge Lens meter Interference filter

Excimer laser beam

Photodiode

Figure 2.28 Schematic diagram of the experimental setup with optical reflectance probe and the photoacoustic deflection probe. The diameter of the deflection probe beam is exaggerated, it was ∼10 µm in the cited work. Probe beam deflection signal ϕ(t) is proportional to the time derivative of the pressure pulse at the probe beam position, ϕ(t)∝ ∂P/∂t. Pressure transients with peak values of order 1 bars were recorded by this technique. © American Institute of Physics (1996), reprinted with permission from Ref. [89]. Ch02-I044498.tex 11/9/2007 18: 47 Page 36

36 Handbook of Liquids-Assisted Laser Processing

PIN diode HeNe (optical KrF l 348 nm reflectance probe) FWHM 25 ns

Quartz window

Cuvette filled with water

Ag u HeNe (surface plasmon probe)

PIN diode

Figure 2.29 Combined optical reflectance and surface plasmon resonance probe for monitoring temperature, pressure, and vaporization transients [80]. The thickness of the Ag film was ≈50 nm. © World Scientific Publishing Co Pte Ltd., reproduced with permission.

100 1 nm vapour film 80 without vapour film

60

40 Reflectivity (%)

20

0 52.5 53.0 53.5 54.0 54.5 Angle of incidence u (deg)

Figure 2.30 Response of the surface plasmon wave sensor to vapour film generated by laser heating [80]. ©World Scientific Publishing Co Pte Ltd., reproduced with permission.

in micrometres and spatial resolution in nanoseconds may easily be achieved. Pressures are measured at least in range of 0.2–20 MPa [80]. The drawback is that a specially prepared target is needed for implementation of this method.

Using temperature dependence of optical properties of materials Leung et al., Zapka et al. [91, 92] used the temperature dependence of the transmittance and reflectance of amorphous silicon for determination of dynamic temperatures in steam laser cleaning process. Temperature dependence of refractive index, extinction coefficient, and optical gap energy for both amor- phous and crystalline silicon in region 20–360◦C and at 0.752 and 1.15 µm light wavelength are presented in the article by Do et al. [93]. Ch02-I044498.tex 11/9/2007 18: 47 Page 37

Cleaning 37

2.5 Physics and Phenomenology of Liquids-Assisted Laser Removal of Particles from Surfaces

2.5.1 Detailed description of the standard steam cleaning process Common steam laser removal of particles form silicon wafers proceeds the following way [94]: • Condensation of a liquid film of micrometre thickness onto the sample surface to be cleaned just prior to laser irradiation. • Short pulse laser irradiation, for example 20 ns from an excimer laser. • The laser radiation is strongly absorbed within a surface layer of the sample. • Heat is transferred from the substrate to the liquid film. • Superheating of the liquid sheet at the interface between the liquid and solid surface. • Heterogeneous bubble nucleation process at interface sites of the solid sample; particles can act as nucleation sites. • Creation of a dense population of bubbles. • Fast growth of the bubbles in the liquid sheet interface layer. • Explosive blast wave generation by rapidly expanding vapour layer; the pressure pulse lasts ∼40 ns. • At a time delay of 200–400 ns after the laser pulse the bulk of the liquid film is ejected as a liquid disc and accelerated to a lift-off velocity of the order of 40 m/s; during lift-off the liquid disc experiences an acceleration of order 109–1010 m/s2. • The expanding vapour generates a lifting force on the particles; if the adhesion forces are overcome, the particles are removed from the surface. • The liquid film and the ejected particles are propelled to macroscopic distances of more than 10 mm away from the surface before the atmosphere decelerates them. • The redeposition of particles is avoided by placing the substrate face down or using a gas flow.

2.5.2 Optical effects The principal optical effects that may affect the liquid-assisted laser cleaning process are: • Reflection of the light at interfaces – air/liquid and liquid/substrate. The light intensity losses may be tens of percents (Section 7.1.2). • In case of insufficient wetting, steam condensates into droplets. The curved surfaces of the droplets act as convex lenses, focusing the light. • Light refraction on the curved surface of the meniscus near the particles (in case of capillary condensed liquid or at deposition of a very thin liquid layer) [95]. • Focusing of light in transparent particles (SiO2, PSL) (Fig. 2.31). Light focusing in liquid droplets and in particles may cause a damage of the substrate. Figure 2.31 presents light rays in a transparent particle in geometrical optics approximation. Field concentration occurs also when particle’s diameter is comparable with the wavelength of the light; some examples of light field distribution may be found in the articles by Luk’yanchuk et al. [96] and by Arnold et al. [56]. According to Mosbacher et al. [97], Mie resonances of light field may enhance the light intensity at particles up to ∼30 times.

2.5.3 Acceleration and inertial effects Acceleration Acceleration of both laser-heated substrate and of particles, caused by their rapid thermal expansion, is one of the major factors in DLC, but it may affect the laser wet cleaning process as well [98]. In air, the detachment of particles from solid surfaces occurs at accelerations in order of ∼106 g [99]. Figure 2.32 shows measured surface displacements of a water-covered quartz plate at nanosecond pulsed laser irradiation. The surface accelerations range up to 5 × 105 m/s2 (50 000 g). Ch02-I044498.tex 11/9/2007 18: 47 Page 38

38 Handbook of Liquids-Assisted Laser Processing

n 1.5 1

0.75

0.5

0.25

0.00 y / a 0.25

0.5

0.75

1 0.5 0 0.5 1 1.5 z/a

Figure 2.31 Ray tracing for a big particle of diameter a >> λ with refractive index n = 1.5 [96]. Reproduced with kind permission of Springer Science and Business Media.

30 (a) 55 61 64 20 67 68 (mJ/cm2) 10

Surface displacement (nm) 0 0 200 400 600 800 1000 Time (ns)

Figure 2.32 Displacement of a cleaning target induced by an excimer laser pulse with liquid-film deposition (pure water) on the laser spot (248 nm, 24 ns). Recorded by an interferometric probe at backside of the substrate © American Institute of Physics (2003), reprinted with permission from Ref. [100].

Laser beam man

Particle Fad

Substrate SAW pulse

Figure 2.33 Interaction of particles with short-pulsed laser-generated surface waves. © American Institute of Physics (1998), reprinted with permission from Ref. [103].

Surface waves Rapid thermal expansion of laser-heated substrate may excite surface waves, which can accelerate the particles also outside of the irradiated area (Fig. 2.33). Detachment of 1–2 µmAl2O3 particles by laser-generated surface waves have been investigated by Kolomenskii, Mikhalevich et al. [101, 102]. Particle detachment from Ch02-I044498.tex 11/9/2007 18: 47 Page 39

Cleaning 39

silicon surfaces occurred at some mJ/cm2, thus at ≈100 times lower fluences in comparison with direct laser irradiation [103].

Inertial force Grigoropoulos and Kim [98] present a formula for scaling of the inertial force acting on a particle on a rapidly heated surface 4 πR3ρβd T F ∝ th , (2.50) i 3 τ2 where R is the particle’s radius, ρ is the particle’s density, β is the volume expansion coefficient of the substrate, T is the temperature increase, τ is laser pulse length, and dth is thermal penetration depth,

√ λτ d = ατ = , th ρC

where α is the thermal diffusivity, λ is thermal conductivity, ρ is density,and C is the material specific heat.

2.5.4 Heating and phase change (absorbing substrate, non-absorbing liquid) Because the laser spot diameter is usually much larger than the thermal penetration depth of the substrate, heat transfer may be considered 1D.Temperature transients and temperature distributions in laser cleaning situations were calculated byYavas et al. [104], Park et al. [95] Kim et al. [88] (Figs 2.34 and 2.35). The temperatures in (Figs 2.34 and 2.35) were calculated without taking heat resistance of interfaces into account. For silicon and water/IPA interfaces the heat transfer coefficients were measured by Leiderer et al. = × 7 2 = × 7 2 [80]: hH2O 3 10 W/m K, hIPA 1 10 W/m K. Rapid heating, ∼1010 K/s, drives the liquid into superheated state (see Section 7.2.3). Below critical temperature, the vaporization (bubble nucleation) is a statistical process that depends also on surface properties.Theoretical and experimental determination of the superheating temperature and of vapour dynamics in real situations has been the topic of many investigations (see Table 2.5).

250 at the surface at 0.5 m from the surface 200 at 2.0 m from the surface

150

100 Temperature ( C) Temperature

50

0 0 100 200 300 400 Time (ns)

Figure 2.34 Computed temperature transients at different locations inside a crystalline silicon irradiated with a KrF excimer laser (λ = 248 nm, τ = 16 ns) [95]. Heat transfer to the ambient was neglected. © IEEE (1994), reproduced with permission. Ch02-I044498.tex 11/9/2007 18: 47 Page 40

40 Handbook of Liquids-Assisted Laser Processing

550 (a) 40 70 500 50 80 60 (mJ/cm2) 450

400

350

Surface temperature (K) 300 Laser pulse

250 0 200 400 600 800 Time (ns)

Figure 2.35 Calculated temperature increase at the Cr–water interface heated by an excimer-laser pulse of differ- ent fluences [88]. The dotted line shows the temporal shape of the laser-pulse intensity in arbitrary units (triangular pulse with peak intensity at t = 17 ns and width of 48 ns). © Elsevier.

14 60 PZT I 12 OPT I 50 PZT II OPT II 10 PZT III 40 OPT III 8.0 PZT IV 30 OPT IV 6.0 PZT V 20 OPT V 4.0 10 Reflectance drop (%) 2.0 0 Bubble nucleation threshold Maximum pressure (bar) (absolute) 0.0 10 0 20 40 60 80 100 120 Fluence (mJ/cm2)

Figure 2.36 The pressure pulse amplitudes (water on chrome) plotted as a function of excimer laser fluence (248 nm, 24 ns). The data produced by piezoelectric transducer are represented by the symbols labelled with ‘PZT’ and the data by the deflection probe are represented by the symbols labelled with ‘OPT’. The experiments were repeated 5 times as indicated by the Roman numerics. The amplitude of the optical specular reflectance drop is also plotted with the dashed line. The bubble nucleation threshold is marked by the arrow. The experimental setup is shown in (Fig. 2.28). © American Institute of Physics (1996), reprinted with permission from Ref. [89].

For nanosecond laser pulses, the following observations have been made (transparent liquid, opaque surface, water of water–alcohol mixtures): • Superheated liquid layer thickness is some hundreds of nanometres.[104] • Embryonic nucleation starts immediately after the temperature exceeds boiling temperature. [105, 106] • Superheating temperatures range up to 250◦C on atomically smooth silicon surfaces; on rough surfaces the superheating temperatures may be 2 times lower. [97, 80]; • Bubble-growth induced pressures reach several MPa [89, 107] (Fig. 2.36). • A vapour layer is formed near the heated surface that lifts a liquid disc from the surface (Fig. 2.37). Both high-speed photography (Fig. 2.37) and molecular dynamics simulations (Figs 2.38 and 7.8) have revealed that in a typical steam laser cleaning process a liquid disc is ejected from the surface. Ch02-I044498.tex 11/9/2007 18: 47 Page 41

Cleaning 41

OTISCE T8000.IAX1

Figure 2.37 Image of liquid disc ejected from laser-heated surface. Snapshot was taken 8 µs after laser pulse [108]. © Koninklijke Brill NV, republished with permission.

Figure 2.38 Snapshots of molecular dynamics simulations of a 3.4 nm water film with 6.46 nm diameter particles on a rigid gold substrate, suddenly heated from 48.4 K to 193.6 K [109]. From left to right, the elapsed time is 0.22, 0.44, 0.66, 0.88 ps, respectively. Simulations with identical initial conditions did not result in particles removal in any case: the upper row shows a simulation where there was particle removal, while the lower row shows a simulation, at the same temperature, where particle removal did not occur, cf. Fig. 7.8. Reproduced with kind permission from Springer Science and Business Media.

Lang and Leiderer [107] measured the dynamics of the ejected liquid film by optical reflectivity with high precision (2 nm spatial and 0.2 ns time resolution) (Figs 2.39 and 2.40). Under assumption that the vapour follows the equation of state PV n = constant, where n is the polytropic exponent, and neglecting the compression of the liquid, the following equation of motion of the liquid layer was proposed [107]:

 d2 P d n P d(t) = 0 · 0 − atm , (2.51) dt2 ρ · h d(t) ρ · h

where P0 is the initial pressure under the film,Patm is the atmospheric pressure,d0 is the initial distance of the film from the surface after the vapour formation, ρ is the density of liquid, and h is the thickness of the liquid film. For a case of an isopropanol film, the fitting of the experimental data using initial conditions d(t = 7.1 ns) = 8.7 nm and v(t = 7.1 ns) = 0 m/s, yielded P0 = (4.9 ± 0.2) MPa and n = 1.00, indicating an isothermal process. Ch02-I044498.tex 11/9/2007 18: 47 Page 42

42 Handbook of Liquids-Assisted Laser Processing

2500

2000

1500

d (nm) 1000

500

0 0 20 40 60 80 110 120 140 160 t (ns)

Figure 2.39 Trajectory of an isopropanol film after laser heating of the substrate [107]. The solid line represents a parabol fit to the data points and corresponds to a constant acceleration of the film. © Institute of Physics, reproduced with permission.

120

100

80

60 d (nm) 40

20

0 678910 t (ns)

Figure 2.40 Magnification of the first few nanoseconds of the ejection process in Fig. 2.39 [107]. The solid line corresponds to the same fit as in Figure 2.39. After the formation of a vapour layer in the first 700 ps (6.4–7.1 ns), the overlying liquid is accelerated away from the substrate for about 8.6 ns until the expansion causes the pressure under the film to drop below the pressure above. © Institute of Physics, reproduced with permission.

Ejection force Lu et al. [5, 110] estimated the force excerted by expanding vapours on a particle by  2 Fc = πR 2ρc(Pv − P∞)vf , (2.52)

where R is the particle radius, ρ is liquid density, c is transmit speed of the stress wave, Pv is vapour pressure inside the bubble, P∞ is ambient pressure, v is expansion velocity of the vapour, and f is volume fraction of vapour. The assumptions of the model were: (i) bubble generation is an inertia-controlled process; (ii) in the region near the liquid/substrate interface, the vapour layer created by the evaporation of the liquid acts as a plane piston, compressing the adjacent liquid and generating stress waves; (iii) the value of the volume fraction of Ch02-I044498.tex 11/9/2007 18: 47 Page 43

Cleaning 43

vapour inside the superheated liquid layer is less than 1; (iv) the expansion velocity of the vapour layer is equal to the growth velocity of the bubbles; and (v) the pressure inside the vapour layer is equal to the saturation vapour pressure of the superheated vapour layer due to the non-uniform temperature distribution in the liquid film (citation from the article by Wu et al. [111]). Wu et al. [111] presented a modified version of Eq. (2.52):  2 4 8 F = πR ρc2f 2 (P − P∞)3. (2.53) c 3 v

The same authors presented also a different laser wet cleaning theory, based on a model where the laser- generated bubble growth in the fluid medium generates an explosive blast wave, and the particle is lifted by the pressure of this wave after reflection from the substrate surface. They found for upper limit of the particle removal force due to bubble generation:

2 Fc = πR Prefl, (2.54) where Pshock (8Pshock − P∞) Prefl = ; (2.55) Pshock + 4P∞

with notations: Prefl is reflected from the substrate surface overpressure and Pshock is shock-generated pressure. The other assumptions of the model were: (1) the shock-generated pressure is approximately equal to the vapour pressure in the vapour layer at the water/substrate interface, i.e. Pshock ≈ Pv(T); T is the tempera- ture in the vapour layer; (2) the temperature in the vapour layer is approximately equal to the temperature at the substrate surface; (3) the pressure inside the vapour layer is equal to the saturation vapour pressure of the superheated vapour layer due to the non-uniform temperature distribution in the liquid film and (4) the vapour layer thickness, limited by the thickness of the superheated liquid layer, may exceed the particle radius since the thermal penetration depth in water is of the order of 1 µm (citation from the article by Wu et al. [111]). A discussion of these ejection force models is given in the article by Leiderer et al. [80] It is pointed to, that the high superheating temperatures at smooth silicon surface, the finite temperature jump between the substrate and the liquid, and the thickness of the liquid film should be taken into account in the future models.

2.5.5 Hydrodynamic effects In the pioneering reports about water-assisted laser cleaning by Assendel’ft et al. [15, 16], laser-generated acoustic waves were used for removal of the particles form solid surfaces. Later, in studies of laser-generated bubbles collapse assisted particle removal from surfaces, the high-speed near-surface flow was found to be responsible for the cleaning process [18, 19]. Near-surface flow is also the main factor in megasonic cleaning. Zhang et al. [112] give following criterion for particles detachment from surfaces by a boundary flow (see notations in Fig. 2.41): F R RM = 1.339 · D > 1, (2.56) Faa

where RM is adhesion resisting moment, FD is the drag force, R is the radius of the particle, Fa is the adhesion force, and a is contact radius. Drag force on a spherical particle in a slow linear shear flow is expressed by:

FD = 10.2πµR · U(R) (2.57) and for near wall sub-layer flow by: 32µ ∗ F = (Re )2, (2.58) D ρ Ch02-I044498.tex 11/9/2007 18: 47 Page 44

44 Handbook of Liquids-Assisted Laser Processing

F U el

Mr

Fd 1.4R R a

Ma Fa

Figure 2.41 Conditions at a particle in a surface flow. U is the liquid velocity, Fa is the adhesion force, Fel is the elastic force, Fd is the drift force, Ma is the adhesion moment, and Mr is the flow caused rotation moment.

where µ is the fluid viscosity, U(R) is the fluid velocity at a distance of R from the wall, ρ is the fluid density, and Re∗ is the shear Reynolds number and is given by: ∗ ∗ RU Re = , (2.59) v where v is the kinematic viscosity of the fluid and U ∗ is the friction velocity:

∗ 2τ U = , (2.60) ρ

where τ is the shear stress, τ = F/A. A review of particle-wall hydrodynamics is given by Kim and Lawrence [113].

2.5.6 Particles removal threshold and efficiency in steam laser cleaning Threshold fluence Veiko and Shakhno [13] provided the following first-order criteria for particles removal thresholds for different situations in light transmission/absorption.

(a) Absorbing particle at a transparent substrate

ρpcphp εth = (Tb − Tin) , (2.61) Ap

where εth is the cleaning threshold, ρc is density of the particle, cp is specific heat of the particle, hp is the height of the particle, Ap is the average absorption coefficient of the particle, which includes the influence of the angle of incidence, Tb is boiling temperature of the liquid, and Tin is the initial temperature.

(b) Transparent particle at an absorbing substrate Particles detachment occurs when the substrate surface temperature Tm exceeds a critical value Tth,givenby relation: √ asτ Tm − Tb · + R = hmin, (2.62) γ Tm − Tin where as is substrate, τ is laser pulse duration, γ is laser radiation absorbance, R is the height of unevenness of rough surface, and hmin is the bubble critical size. Ch02-I044498.tex 11/9/2007 18: 47 Page 45

Cleaning 45

100 Before cleaning After cleaning Particle density Cleaning threshold Cleaning efficiency (%) Surface damage threshold 0 0.1 0.3 1 3 10 0 0.1 0.2 0.3 0.4 Particle diameter (m) Laser fluence (J/cm2) (a) (b)

Figure 2.42 Schematical dependences of steam laser cleaning efficiency on particle size (a) and on laser fluence (b). (Schematically after Héroux et al.,[82] Meunier et al.,[85] Leiderer et al. [80]). For silicon the surface damage (melting) threshold is ∼275 mJ/cm2 (λ = 532 nm, τ = 8 ns) [115].

(c) Absorbing particle at an absorbing substrate The nature of the particle detachment process is judged by a criterion, ϕ: √ Ap ap ϕ = √ , (2.63) As as

where as is thermal diffusivity of the particle and As is absorption coefficient of the substrate. If ϕ>1, the situation reduces to case (a), if ϕ<1, to case b). Leiderer, Mosbacher et al. [114, 79, 115] have proved experimentally that the threshold fluence of steam laser cleaning of silicon wafers (110 mJ/cm2) is independent of particles material, size, and shape. Such universal threshold indicates that the particle removal forces are far larger than the adhesion forces. The universal threshold for SLC differs from bubble nucleation threshold for bulk water–silicon system, 80 mJ/cm2 (single 1064 nm pulse) [80].

Cleaning efficiency The typical steam laser cleaning efficiency dependences on particle size and on laser fluence for nanosecond laser pulses are given in (Fig. 2.42). The cleaning efficiency starts to decrease for particle size <100 nm. However, SLC is capable to remove particles as small as 60 nm with 90 per cent efficiency [80]. Laser cleaning efficiencies under concrete conditions can be found inTable 2.5. As a rule, cleaning efficien- cies of 90–100 per cent have been achieved by a few cleaning cycles at laser fluences well under the substrate damage level (Fig. 2.43).

2.5.7 Effect of capillary condensed water in ‘dry’ laser cleaning Even if no liquid/steam has been applied, some amount of capillary condensed water between the particles and the substrate is present in most cases (Fig. 2.11). While heated by laser, the liquid vaporizes and provides an extra impulse to the particles (Fig. 2.44). Leiderer et al. [115] compared the laser cleaning thresholds and efficiencies in high vacuum and in ambient atmosphere.The cleaning threshold was lowered from ∼280 in vacuum to ∼120 mJ/cm2 in moist air. (500 nm SiO2 particles on silicon, laser 248 nm, 30 ns.) Figure 2.45 shows photographs of silicon surface, laser irradiated with a dust particles in vacuum and in ambient atmosphere. Table 2.5 presents a chronological reference of research about liquids-assisted laser removal of particles from solid surfaces, and Table 2.6 about liquids-assisted laser removal of surface layers from solids. Ch02-I044498.tex 11/9/2007 18: 47 Page 46

46 Handbook of Liquids-Assisted Laser Processing

600 CML

) 500 Dry cleaning Steam cleaning 2

400

300 SiO2 Al2O3 Al O 200 2 3 SiO PSL 2

Partice densities (cm 100

0 Before cleaning After cleaning

Figure 2.43 Particle densities before (grey bars) and after (white bars) laser cleaning. During DLC, the laser 2 fluences for PSL, SiO2,Al2O3, and CML were 326, 314, 326, and 353 mJ/cm , and 2, 4, 4, and 2 cleaning scanning cycles were used, respectively. During steam cleaning, the laser fluences for SiO2 and Al2O3 were 180 and 154 mJ/cm2, respectively, and 4 cleaning scanning cycles were used. PSL stands for polystyrene latex and CML for carboxylate-modified latex. Substrate– 100 silicon. The diameters of the particles ranged from 0.1 to 2 µm. Laser used: KrF, 248 nm, 22 ns. © SPIE (1999), reproduced with permission from Ref. [85].

VAC SiO2/Si ) 2 RH

1.5Tbs (mJ/cm

cl 102 Tcl

Tms Threshold, f

102 103 Radius, r (nm)

Figure 2.44 Comparison between the cleaning thresholds at 248 nm in vacuum ( filled symbols), and in RH = 94 per cent–97 per cent (open circles) [56]. Solid curve: threshold based on the evaporation of the substrate; dashed curve: threshold based on the critical temperature for water; Dash dotted curve: melting of the substrate. Reproduced with kind permission of Springer Science and Business Media. Analogous diagram for polystyrene particles on silicon is presented in the article by Mosbacher et al. [97]. Ch02-I044498.tex 11/9/2007 18: 47 Page 47

Cleaning 47

(a)

1cm

(b)

Figure 2.45 Photographs of a silicon surface with dust particles after exposure to 50 laser pulses: (a) in ambient air and (b) in vacuum. The difference in ablation craters may be attributed to the presence/absence of capillary water. © American Institute of Physics (1998), reprinted with permission from Ref. [103]. Ch02-I044498.tex 11/9/2007 18: 47 Page 48 [118], (1991) [122] [121], (1993) [15, 16] References 2 al: [120], (1992) ption (1987) [116] capillary ≈ 1.5 J/cm particle [123], (1992) ; µ s pulses, 1 ms (1993) [91, 92] cycles; also the concentration of Assendel’ft µ m ere removed after 5 water Imen (1990) layer ejected the particles Lee (1991) d from surface due to Assendel’ft from silicon surface under Beklemyshev µ m) ≈ 3 times (initial concentration (1988) [117] µ m light absorbing in water [3], Zapka µ m wavelength and from laboratory air gave the [119] observed ); conductivity type of the substrate − 2 generated by absorption of the (1988) at 9.6 2 cm 4 µ m ions desorption 10 µ m in water is 20 nm light (does not absorb in liquid but in Tam (1991) × phenomena, comments 1.5 than pure ethanol; cleaning efficiencypulses of was 10 much ns better thanpulses of did 1 not remove thesame particles fluence at all at the (1992) [125], surface; 10% ethanol solution was more effective (1991) [124], ≈ 2.2 J/cm did not affect considerably Metal acoustic wave mechanism obviously involves photoexcitation of Si and subsequentelectrons recombination with of metal excited ions condensed moisture same effect; without water filmnot the removed; absorption particles length were of10.6 laser light at at 10.6 particles decreased calculation of acoustic pressure neededdesorption for of particles: 0.02–38 MPa (particle size 1–0.1 ≈ 0.5 s was blown onto the from surface; thresholds for particles remov 2 (evaporates) into water, water layer laser light on the free surface of water contaminated insalt solutions laser irradiation was observed; the desor vapour condensation 3 s pause 1–10 mm 2 , micrometer thick formed the substrate) provided more efficient , into water 2 2 2 µ m, from pulsed vapour jet; removal than 2.94 2 µ m, Fogged and liquid droplet Most of the particles w ≈ 1 µ s tail, surface; 6 s vapour pulse, , 100 ns, Substrate immersed Particles were remove , 10.6 , 9.6 and Water vapour carried by Vaporization of water µ m, 100 ns N 2 2 2 , 514 nm, Si wafers were , 488 nm, Substrates immersed Due to laser irradiation + + µ s total pulse film formed by water adsorption–laser irradiation 1 length, 30 J/cm some mW/cm 0.3 J, focused vertically or horizontally 10.6 some minutes 100 mW/cm spike, Lasers and beam Other features of Novel features, 2.63–13.15 J/cm 10% KrF, 248 nm, 16 ns, Liquid film of few 248 + l of particles from surfaces and related experiments. Liquids parameters the experiment ethanol 2.94 Er:YAG, or IPA 10 ns–1 ms film lasts µ m µ m methanol, 30–300 mJ/cm , Si, Water 3 O , different Water CO , 5 and Water CO µ m µ m 2 3 3 , Cu and ions; also Water Ar µ m; PS 1 O O + 2 2 + sizes in micrometer range Na 0.1–1 (photo-resist), 9.5 Fe ions 0.1–1 Liquids-assisted la ser remova -Si and Phenol resin Water Ar -Si [100] K -Si (photo-resist), PI, photo- latex; 0.1–10 resist p Si Phenol resinn WaterSi CO (111) Al Si (100) Al Si (SC), Au,Al Substrates Particles n Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 49 ) ( Continued [126], (1994) [104] (1993) [90, 92] [128] Leung (1992) Yavas (1994) ing [90], Zapka (633 nm) Do (1993) (ethanol) ) and and 2 2 2 measurements Yavas (1993) -reflectances ing of probe laser Lee (1993) Maxwell–Garnett theory ; p (particles removal 2 ), the shock wave to substrate surface, [122, 127] 2 - and estimation of substrate s (water); the thresholds correlate 2 temperature profile calculated 2 from temperature dependence of front side optical reflectance photodeflection of a probe beam C at fluences up to 30 mJ/cm ◦ -Si optical parameters at 752 nm; spontaneous 1.2–5 mm above) by shock wave and ejected (various fractional volume of bubbles)solid–liquid at interface using determined experimentally phase explosion thresholds range from 14.9 mJ/cm a bubble nucleation times were 150–300after ns laser pulse (water–IPA), independentfluence on in laser the usedinterface fluence range; temperatures solid–liquid were estimated to400 be up to evolution and temperature well with boiling temperatures of liquids Studies of Studies of computed for a case of 100 nm foamy layer [104] threshold was 2.2 J/cm energy was estimated to beirradiation 1.8 30 mJ mJ (surface corresp. 7.9 J/cm KrF laser irradiation, parallel to the target’s surface≈ 0.4 mm; at longitudinal distance acoustic wave echosfound were to be reliable indicators of liquid explosion reported above (Yavas (1993) [126]), temperature vapour/particles; threshold for shock wave generation was 4.3 J/cm to 27.4 mJ/cm velocity up to 620 m/sto at 1.5 fluences J/cm up Transient reflectance and scattering ≈ 5 mm liquid layer above specimen using a probe beam; ≈ 5 mm liquid layer Transient optical reflectance/scattering and liquid film on substrate transmission of liquid covered sample dur liquid above specimen acoustic measurements; in addition to results 2 2 2 2 µ m, Condensed from vapour Studies of deflection/scatter ≈ 62 mJ/cm , 9.6 2 µ s tail, 2.63–13.15 J/cm ≈ 1 100 ns spike, water film on substrate beam (488 nm, parallel + IPA IPA + + IPA ethanol, up to 40 mJ/cm ethanol, water methanol, methanol, methanol methanol, water IPA, water ethanol, up to ethanol, 8–78 mJ/cm Water, KrF, 248 nm, 16 ns, Condensed from vapour Water, IPA, KrF, 248 nm, 16 ns Water, IPA, KrF, 248 nm, 16 ns, Target immersed into Water, IPA, KrF, 248 nm, 16 ns, Water CO 3 O 2 µ m) µ m),Al (1, 5 and 9.5 PS (1 µ m) µ m) µ m) µ m) -Si film No (0.2 a Cr layer (0.2 Si PI, Cr layer on sapphire 1 on sapphire (250 on quartz a-C, a-Si (0.1 and Ch02-I044498.tex 11/9/2007 18: 47 Page 50 [95, 129], References Yavas (1994) ) the (2002) [98] 2 < 5 Hz, Mann (1996) memory the pressure 2 ); heated Si layer 2 (nuclei) remain ≈ 3.6 m/s (water) was observed; in dry air for removal of particulate Park (1994) does not affect the effect bserved /min; visual substrate damage [86] C (110 mJ/cm 2 2 ◦ µ m; induced in Si thermal stresses ≈ 0.37 MPa; at 100 J/cm , 100 Hz; calculated Si surface peak ; after 3–5 laser pulses 80% of mirrors [6] 2 2 ≈ 1.9 m/s (IPA) and ≈ 1 ≈ 1 MPa (Fig. 2.36) ’ of acoustic cavitation observed: after collapse [10] liquid-assisted laser tool of laser heating generatedmetastable bubble obviously ultramicroscopic bubbles at solid–liquid interface andcavitation decrease threshold; the temporal acoustic decay ofeffect the reminds memory a diffusion process;enhanced the in effect cases is ofmethanol, NaCl but additive N to water and (1D-model); transient acoustic signals presented (oscillations at substrate resonance frequency), superheated liquid layer thickness estimatedsome to hundreds be of nanometer andvelocities bubble growth reaches target’s surface was used forat pressure bubble measurements; nucleation threshold (49.8 J/cm Grigoropoulos the particles were not removed;surface ethanol enhanced film the on cleaning efficiency Long-term (hundreds of microseconds) ‘ Photoacoustic deflection of a probe beam parallel to Park (1996) [89], effect temperature 220 galvanometrically scanned beam provides cleaningrate over 200 cm Tam (1998) was not observed even for150 mJ/cm 4 h irradiation at pressure was thickness ≈ 70 MPa was reflectivity was recovered; at high laser fluences ; 160 mJ/cm 2 substrate contaminants from surfaces is described; 4mm × experiment phenomena, comments water, inclined window water reflection Homogenized laser Optimal cleaning regime: 248 nm, 30 ns, beam, 4 2 2 2 ) 2 ≈ 110 J/cm to 400 mJ/cm up to 110 mJ/cm (typically Lasers and beam Other features of Novel features, o 1–100 Hz, determined from optical fragmentation of particles 0.05–1 J/cm 8% KrF, 248 nm, 16 ns, Condensed from vapour A 0.5% + + NaCl contact with atmosphere) (liquids in methanol, water Water, KrF, 248 nm, 1 ns Sample immersed into Water KrF, 248 nm, 24 ns, Target immersed into Water ) 3 µ m), ethanol and 50–200 ns, cleaning efficiency O 2 (as example) IPA up to 300 Hz, up liquid film on water-marks Al Continued ( µ m) µ m) Substrates Particles Liquids parameters the on fused quartz; bulk Ni on poly-Si Cr Si Cr layer (0.15 BK7 andZerodur 100 finger-prints, (0.1 (80–100 nm) (some few moisture, and 355 nm, 30 ns Al-coated Quartz sand Atmospheric 193, 248, 308, 351 Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 51 ) ( Continued (1996) [130] 2 2 while ≈ 40 ns C 3 on Schilling ◦ O and (1998) [114] 2 2 ≈ 0.05–0.1; ≈ 100 ; MgO > 1.5 J/cm ),Au and 2 ved to start at [132] -potential of 2 ζ ); at 3 C); fractional volume ◦ O 2 transient pressures -potential -potential of Al ζ ζ (Al > 6.2 J/cm before and after cleaning Héroux before and after cleaning Boughaba 2 µ m particles were removed, (1996) [82] ,Al 2 2 cleaning regimes: 0.5–1.5 J/cm (threshold 0.65 J/cm ); vaporized mass in of order 1% (superheating 11 2 2 2 particles were harder to remove from ≈ 1–5 MPa with a pressure pulse length , PSL), 0.8–1 J/cm – 3.2–6.7 J/cm surface has negative 3 2 2 2 -Si reflectance (from both front and rear side, O p 2 fluence optically visible surface damage observed; Optical front-and rear-side transient reflection (SPP) Yavas (1997) SiO (42.2 mJ/cm obviously due to positive (SiO solid surface in water, usingof temperature dependence [105, 106], 10.5 mJ/cm enabling more precise measurements inwith comparison Leung (1992) [90]); embryonicimmediately nucleation after starts temperature exceeds boiling temperature; max. superheat temperatures (bubble growth threshold) was measured to be nanosecond time scale using surfacedescribed; plasmons laser irradiation of solid–liquidgenerated interface pressures 1.8 MPa at 43 mJ/cm Leiderer (1996) [131], particles were hard to removeobviously from due silicon to surface strongly positive MgO in water; water dropslenses on and surface cause may high act local as light intensities SiO 2.8 MPa at 62 mJ/cm of bubbles in the superheated(using layer Maxwell–Garnett’s theory) was estimated to be bubble-growth induced pressures were measuredrange to Al Arrangement for measuring Transient temperature studies at laser irradiation of Park (1996) substrate condensed from but not all; optimal cleaning regimes: Si – substrate 100 at% by window vapour film on 2.9–3.2 J/cm , water, vessel covered studies; bubble nucleation was obser 2 2 2 2 2 2 µ m, Surface to be cleaned Particle size distributions µ m, Condensed from Particle size distributions , 10.6 , 10.6 µ s, 0.9 J, mounted downwards, presented, down to 0.1 2 2 µ s, 0.95 J, vapour film on presented; optimal up to 62 mJ/cm 0.5–25 J/cm up to 60 mJ/cm 0.5–3 J/cm spot 1 × 1cm 0.25 0.2 methanol 15–82 mJ/cm Water CO Water KrF, 248 nm, 25 ns, Water KrF, 248 nm, 25 ns, Target immersed into Water, KrF, 248 nm, 16 ns, Static pressure up to µ m) , 2 µ m) µ m), , MgO, Water CO 3 3 µ m), O O 2 2 PSL (0.1 (0.1–0.2 fumed silica µ m on Si (0.1 µ m) ,Al (sizes 0.1–10 2 2 -Si; quartz (80 nm) on layers of BC, diamond 100 nm SiC, CeO SiO (53 nm) (0.15 Si (100), Al Hydrophilic Al Cr layer and Au on 0.35 SiO p substrate quartz Ag layer Ag layer Ch02-I044498.tex 11/9/2007 18: 47 Page 52 (1997) s ˛ (1998) [139] (2000) [137, 138], (2001) [110] Kolomenskii References Leiderer Lu (1998) 2 surface 2 ; at 2 yer, no (1998) [140] independent of Leiderer 2 µ m particles were Beaudoin ≈ 30 mJ/cm measurement proved to [4] ≈ 88% of particles were DeJule ≥ 0.3 imental investigation of l required 5–9 cleaning cycles; Allen (1997) C); bubbles growth velocities: (1998) [114] ◦ observed , 90% of ( ≈ 100 times less fluence needed 2 (SAW) in Si wafers, generated by laser (1998) [103] 2 , 90% of particles were removed with the ≈ 90% of particles were removed; [5, 134, 135], 2 2 2 200 mJ/cm irradiation; accelerations needed for particles removal can be achieved atsome laser mJ/cm fluences of acoustic waves removed contra 12% in dry air than at direct irradiation); SAW-assisted cleaningvacuum and in in ambient airthe compared; cleaning in process vacuum was more efficient 4 m/s (water), 2.2 m/s (alcohols) Particles removal threshold Bubble nucleation studies by optical reflection, Yava (superheating 11 theoretical estimation of bubble expansionforce generated on particles and of cleaning threshold (1999) [136], first laser shot; surface damage threshold 320 mJ/cm particles material and size (down to 60 nm); at (1998) [114] scattering, piezoelectric transducer and SPP;embryonic in bubbles water, nucleate at 9.5 mJ/cm [133], be suitable for monitoringon water surface film and droplets 170 mJ/cm considerable cleaning occurred up350 to mJ/cm laser fluences 50 mJ/cm µ m experiment phenomena, comments moisture film on substrate removed from surface; without water la onto surface Air saturated with In moisture saturated air 2 2 2 µ m, Condensed from vapour 100% particle remova 0.8 mm 2 , 10.6 × 2 µ s, up to film on substrate surface optical reflectivity , 337 nm, 10 ns, SAW Rayleigh pulse of Theoretical and exper -Nd:YAG, Condensed from vapour Cleaning threshold 110 mJ/cm 2 0.2 2 J/cm 2 ω Lasers and beam Other features of Novel features, 180 mJ/cm + + µ m up to 200 mJ/cm wateror opaque 0.15 illuminated area was formed liquid layer (0.1 mm) water IPA IPA, up to 45 mJ/cm methanol, Capillary N ethanol, layer Water, KrF, 248 nm, 16 ns, Water, KrF, 248 nm, 22 ns, Condensed from vapour At µ m) Water µ m) IPA KrF, 248 nm, 23 ns A IPA drop was applied (1 µ m) 2 µ m) condensed up to 50 Hz, 9 mJ, wavelength of 100 (0.3 3 ) 3 3 2 O O O 2 2 2 1–9 nm Water CO (0.5–2 spheres, 800 nm alcohol 532 nm, 7 ns, up to film on substrate Continued ( µ m) µ m; 380 Fused silica thickness (1–10 Si Si wafer Silica and PSNiP Water Al Si waferSi wafer SiO Fe Si (100), Al for SPP) (0.2 SubstratesCr Particles layer Liquids parameters the layer (53 nm, and Ag Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 53 ) 143] ( Continued She (1999) Grigoropoulos [45], (2000) µ m Halfpenny ), ejection 2 for particles (1999) [85], < 5 )was 2 for wet surface; (2002) [98, force presented, Lu (1999) (1064 nm) and [144], provided 2 2 ◦ ; adhesion forces [111] and SiO 4 N 3 for removal of ) 2 100%) did not affect the (1999) removal of particles removal of spherical particles is more > 1000 times lower than (1999) [141] µ m particles the threshold is particles, the RH of air during Vereecke 2 for dry and 115 mJ/cm (355 nm); damage threshold was 2 ), for 1 2 2 µ m particles (both Si µ m SiO µ m the efficiency is lower than for greater Wu (1999) µ m particles the threshold is lower in ethanol r 1 cleaning efficiency considerably,but the removal [142, Steam-assisted cleaning in more effective and has Meunier of multiple jets from liquid-coveredobserved surface was highest efficiency of particles removal optical reflectance, photoacoustic deflection andhigh-speed photographical studies; pressure wavefront velocity was 350 m/s (355 nm, 51.9 mJ/cm 145] 100 mJ/cm lower in acetone (80 J/cm many times more efficient forlaser 100% beam RH angle case; of incidence of 10 did not depend considerably oncondensed particle water may size; capillary be acleaning cause threshold of lowering the of 0.3 lying on bubble growth inducedinto pressure account and van taking der Waals andforces; laser capillary fluence adhesion dependence ofanalysed, lift-off cleaning [146], (2001) force threshold fluences calculated:0.3 for (110 [110] J/cm < 0.3 particles (aggregates); effective than of irregularly shaped ones account van der Waals forces andadhesion hydrogen and bonds; removal forces (notdependence in on Wu (2000) particles [111]) size presented and bubble removal forces calculated, taking into particles particles were up to 3 O 2 agglomerated predicted by 1D thermal expansion theories and , liquid film (10 cleaning cycles) were 86 mJ/cm ◦ µ m liquid film First-order theory of particles lift-off condensed from vapour 63 mJ/cm film on substrate lower threshold fluence than dry cleaning; 0.1 < 0.1 mm;Al 2 2 2 2 2 -Cu-vapour, Focused laser beam, spot Threshold fluences needed up to 200 J/cm ≈ 30 ns, up to in 100% RH air for samples storage (40% or Nd:YAG, 355 and Incident angle of laser Thresholds of complete to 86 mJ/cm 100 Hz. up to some days 300 mJ/cm + water 1064 nm, 6 ns, up beam 40 present obviously to 0.5 J/cm Water KrF, 248 nm, Some samples were held Fo µ m) IPA (8%) µ m), Water KrF, 248 nm, 22 ns, Condensed from vapour µ m) 2 (0,1, Capillary 2 ω (0.3 (0.3 Ethanol, 248 nm, µ m), µ m) µ m) acetone 80–120 J/cm 3 3 3 3 3 4 µ m), 2 O O O O O N µ m) water in kHz range, up were partly 2 2 2 2 2 3 SiO agglomerated (0.2–2 and 1 0.3, 1, 3 and condensed 255.3 nm, 35 ns, (0.1–0.2 and SiO (0.2 Fe 10 (0.3–1 Al Al -Si (100) Si Glass Al p NiP Al Si Si (100) PSL (0.1 Ch02-I044498.tex 11/9/2007 18: 47 Page 54 (2000) [147] References [25] Leiderer (2000) [79], Wu (1999) ; 2 hydrogen ≈ 3 times surface forces: 7 ns) was = > 90% were reached µ m of size were efficiently Wu (1999) independent of the particles size arrangement for observation of 532 nm, FWHM bserved of the steam cleaning process at Mosbacher particles harder to remove than PSL pusles, the cleaning fluence threshold Mosbacher = 3 , independent of the pulse durations (1999) [148], 2 ; both cleaning thresholds were O ( λ 2 2 ; an efficiency above 90% after 20 cleaning (2000) [115] 2 is dominant in inorganic particles adhesion [45] threshold particles 0.1–0.2 and Al 2 2 as 50 mJ/cm plasmon microscopy pressure distribution over the substrate’s area bond force to hydrophilic silicon surface; hydrogenSiO bonds make experiments with irregularly shapedexhibited alumina the particles same threshold as for spherical particles In addition to results presented in Mosbacher (1999) Oltra [148], this work contains a description of a steps was reached at a laser fluence of 170 mJ/cm and material observed, which was for both pulse durations lower than the melting thresholdsparameters; for cleaning these efficiencies laser (2.5 ns and 8 ns)used; and for the 30 wavelengths ps (532 pulses andto (583 nm) 583 20 nm) mJ/cm this threshold lowered Oltra (2000) [25] measurements using a piezoelectricof sensor the on substrate backside were performed;the in acoustic case wave of amplitude water waswithout film, twice film, greater and than contained acomponent; comparison higher frequency of adhesion forcesand for steam dry cleaning cases performed particles; hydrogen bonds formed withmolecules alcohol have stronger interaction energieswith than water Theoretical evaluation of particles adhesion the experiment phenomena, comments film on substrate removed, in contrast to DLC; photoacoustic 2 ≈ 1 mm film on substrate 110 mJ/cm up to 187 J/cm Nd:YAG, 532 nm, Condensed from vapour A sharp Nd:YAG, 532 nm, Condensed from vapour For nanosecond Lasers and beam Other features of Novel features, o Dye, 583 nm, 30 ps and 2.5 ns + + alcohols 10% IPA 2.5 and 8 ns film on substrate w Water KrF, 248 nm, 22 ns, Condensed from vapour SiO Water , Water, 3 O µ m, 2 ) µ m), (500 3 ,Al 2 2 2 O 2 (300 nm 25% IPA, 7 ns, spot (0.1–3 PSL and 800 nm) SiO and 800 nm), (60, 480, 500 film mean), PS 200–400 nm (0.1–0.2 agglomerated) SiO Continued ( Substrates ParticlesSi Liquids PSL parameters Si SiO Si wafer PS, 800 nm Water Si wafer Al Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 55 ) [11] ( Continued Kim (2001) [151] (2000) [149] 2 vapour ≈ 15 and ; threshold Zapka nm Grigoropoulos ≈ 100% of [153], (2002) fractional metal masks a comparison (2000) [115] (KrF laser) 2 presented in Mosbacher (1999) Leiderer : maximum thickness, achieved at [88], particles were 280–350 mJ/cm ); order of magnitude of acoustic (2002) [98] 3 2 calculated optical fields at particles particles from PMMA, but in case of (2001) [152] had no considerable effect for removal Fourrier O 2 of steam starts at particles resulting all Neves (2001) 2 2 of wet laser removal of particles from surfaces Veiko (2000) ; the criterion being that the temperature of the [150], (2001) ometric determination of laser-generated µ m SiO ≈ 1MPa ≈ 10 J/cm to Studies of surface damageconcentration at at DLC particles, due damage to may light occur intensity even at Mosbacher (2001) cleaning threshold; liquid-assisted laser cleaningof is many free of DLC problems:field lower concentration threshold avoidable fluence, by selectionwavelength of or laser refractive index of the liquid (XeCl laser) and 260–320 mJ/cm metal particles were removed bywater 5 layer laser 100 pulses pulses (without wereresulted needed); both laser in cleaning dry and [81] steam case in a layer effective thickness Raised humidity augmentation by vaporization was estimatedbe to of cleaning efficiencies atand various ambient fluences air, in vacuum field concentration caused surface damage micrographs PI substrate the cleaning threshold lowered from calculated particle or of thetemperature substrate of reaches the the liquid; boiling variousabsorbing/transparent combinations particles of and absorbing/ transparent substrate are considered of 0.4 (at 53–68 mJ/cm Thresholds apour Particles were effectively removed from ) 2 roughness 20 nm 100–400 ns after laser pulse, ranges 100–270 liquid, target’s surface water film on surface particles to be immersed in water drops; ≈ 90% (N film on substrate [148], (2000) [79], this work contains film on substrate fluences for Al 2 2 2 up to 106 mJ/cm ≈ 30 ns, 0.3 J/cm XeCl, 308 nm ≈ 31 ns, 1 Hz, up Various sources Condensed from vapour In addition to results + Water, KrF, 248 nm,Water RH 24–27% (air) and KrF, 248 nm, 24 ns, Target immersed intoWater Interfer KrF, 248 nm, Condensed from vapour Condensation µ m), condensed µ m) µ m), µ m), µ m) moisture µ m) , PS, Water (see 10% IPA (250, Water KrF, 248 nm Condensed from v (0.4 from to 220 mJ/cm 3 3 2 2 2 O O 2 2 (0.6–1.8 and 0.8 SiO (0,2–2 Cu (0.5–5.5 Mosbacher (2000) [79]) Al W (0.4–4 µ m SiO µ m) µ m (0.11–1.7 (0.3 C-coated) 1200 nm); on quartz Si wafer Al Si (3 PI, PMMA(50 PS Cr film Si (100) Au foils) SiO thick mask, 500 and Ch02-I044498.tex 11/9/2007 18: 47 Page 56 [77] Zapka (2002) References Fernandes ; 2 for velocity 2 10 m/s independent × 2 ≈ 4 of thickness ); cleaning thresholds was observed, starting cleaning was enhanced 2 ≈ 90 mJ/cm liquid disc ), a d 2 ≈ 0.5 J/cm of microparticles by laser ablation Kane (2002) (effects of agglomerated particles (2002) [154] for CVL and 330–400 mJ/cm 2 ; the surface roughness was reduced acoustic wavefront and hydrocarbons from laboratory air; (at distance from substrate’s surface / s fluence was measured with 73 refs. about experimental research on Kane (2002) of steam laser cleaning of surfaces from µ m); liquid film acceleration was ≈ 100 mJ/cm µ m was formed, departing the substrate with technique for deposition review cleaning efficiencies 95–100% were achievedsingle using laser a pulse (CVL, of packed particles target inagglomeration air of was particles developed; due the was to avoided capillary forces of 37–20 m 0–800 Cleaning results did not depend considerably on the Kane (2002) properties of two very differentdry glasses cleaning in theory,obviously contrast the withby capillary water [77] monolayer on surface in cleaning process, obviously dueof to adsorbed removal contaminants excimer lasers, obviously due todifference coherence length 0,87 both dry and wet laserexperiment cleaning conditions of and particles main from results surfaces; tabulated [77] History particulates, with accent on workResearch performed Laboratories; contain at also IBM newliquid data film about dynamics, achieved of byphotography; high-speed at irradiation of Si/water-alcoholby interface KrF laser (180 mJ/cm [94] were above the disc, an with 400 ns delay beforewith laser velocity pulse of and 370 propagating m/s on particle surface density A A Threshold > by laser experiment phenomena, comments performed in RH ablation (Kane(2002) [78]) were reduced) 2 XeCl, 308 nm, 8 ns ns 12 ns ns Lasers and beam Other features of Novel features, observe KrF, 248 nm, ≈ 10 J/cm moisture coherent beam moisture µ m, Water, XeCl, 308 nm, Particles were (0.1, Water, Cu-vapour Experiments were (1 ) 3 3 3 O O O µ m) 2 2 2 µ m) from 35 ns, high- 50% laboratory air (1 Al Continued ( microscopic 0.3, 1 and condensed (CVL), 255 nm, slides,fused silica 3 Substrates Particles Liquids parameters the Glass Al Glass Al microscopicslides reduced agglomeration) condensed from 8 ns, up to deposited Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 57 ) [80] [156] ( Continued onov (2002) (2002) [98] [7] bubble × reflectivity inertial particles 3 3 = determined O 2 H2O ξ µ mAl K; a critical 2 heat transfer coefficients case calculated; superheating C); W/m ◦ 7 earlier results (She (1999) Grigoropoulos 10 C; Si with nano-holes/water: ◦ × 1 , Mosbacher, Schilling above); ˛ = non-adiabatic smooth and structured surfaced of the use of laser cleaning for removal of Song (2002) IPA for ξ K, 2 (56 pp., 27 figs., 79 refs.) of steam laser cleaning Leiderer review is highlighted: inertial forces on micrometre-sized C, smooth Si/IPA: 116 -polarized probe light is much more sensitive than of ◦ W/m p 7 review -polarized light for nucleated bubbles detection; and Ni substrate is presented and significance of particles should be taken intocleaning account also in laser wet 10 160 comparison of wet laser cleaning theories presented with accent on the(see research done Leiderer,Yavas at University Konstanzof s (2002) growth velocity temperatures for (smooth Si/water: 250 moulding flash on ICand packages of heat particles sinks (dry from MRassisted); process), steam head cleaning sliders efficiency (dry wasdry and higher cleaning steam than of [155] stable bubble shape obtained, takingtemperature into gradient account in theand liquid; wet superheating cleaning temperature threshold are calculatedcondition from that critical bubbleheated diameter up equals to to boiling the (transparent temperature particles liquid layer on thickness absorptive (2002) surface,ethanol); water surface and roughness is takenroughness-dependent into surface account tension by of liquids between Si and water/IPA determined: Cleaning in liquid was moresurface efficient damage and did not cause K forces A A short An analytical expression for an attached to heated surface Veiko , condensed [144], Park (1996) [89], Kim (2001) [88]), a diagram ◦ substrate from vapour film on of adhesion forces between 0.1–100 Nd:YAG, 355 and Incident angle of laser In addition to presented 24 ns KrF, 248 nm, KrF, 248 nm, 2 × + + 0.1 mm, 0.8 J/cm 50 pulses IPA 1064 nm, 6 ns beam 40 vol), film thickness a few micrometer (30–50% Water 3 O 2 5–7 nm) spot 0.1 (5–20 nm and alcohol 20 ns, 50 Hz, Si wafers Diamond Water NiP Al Ch02-I044498.tex 11/9/2007 18: 47 Page 58 [13] [159] Mosbacher References (2002) [157] r s Bregar (2002) C), on d by Zharov ◦ ≈ 30%; at resonances may enhance the 1–2; the actual dependence (2002) [97] = ; backside irradiation was (2002) [14] d k ≈ 30 times (computed) causing , depends on particles radius probe beam (HeNe laser); [160] k th F 1/ r C ◦ ≈ (8 pp., 3 figs., 34 refs.) of laser removal Allen ) r ( at particles th µ m); in case of 532 nm light, jumping of F review threshold (30 pp., 8 figs.) of physical mechanisms of dry Veiko (13 pp., 3 figs., 59 refs.) of laser removal of(19 pp., 9 figs., 44 Lu refs.) (2002) of laser removal of(13 pp., 9 figs., 17 refs.) of laser removal of Mosbacher Zapka (2002) as ≈ 0.8 ) included an oscillating component due to Mie r ( review review review review th some PS particles was observed,thermal obviously expansion due generated to forces overheating (absorption depth of 2.94water nm light in and wet laser cleaning ofsurfaces, seeVeiko particles [150, and 151, 156] solid films from (2002) F holy Si and rough Agwere the 160 superheating and temperatures 130 of particles from surfaces, both dry and wet on experimental work particles from surfaces, mostly ofon dry adhesion process; and with removal accent forcesenhancement theory near and particles light [158] particles from Si wafers, both dry and wet, with accentparticles from Si wafers (2002) and Si membrane stencil masks [108] chosen in order to avoid cell damage due to evolution of signal’s amplitude andfunction delay of time number as of a cleaning cycles presented backside 2.94 nm irradiation light intensity local surface damage; in airlower for the particles cleaning threshold smaller was thanatomically 800 smooth nm Si up surface to temperature the was water close superheating to theoretical value (250 A A general A A A experiment phenomena, comments vacuum and air Condensed from Optoacoustic transient 4–88 mm above the target’ Laser irradiation from Cells and PS particles were successfully remove (RH 30–40%) resonances of light field; these on surface backside (see Fig. 2.2) 2 2 µ J µ s, -Nd:YAG 1–100 ≈ 300 mJ/cm 2 ω 532 nm, 10 ns, Lasers and beam Other features of Novel features, observe 0.1–100 J/cm 20 ns, 130–200 mJ vapour water film surface recorded using condensed) Water (bulk Nd:YAG, 532 nm, Experiments Cleaning µ m) and capillary 8 ns, up to performed in water, roughly ) µ m) (10 cells, PSspheres solution 400 Continued ( (50 nm) Substrates Particles Liquids parameters the Si wafer, PS Steel, glass, KaolinQuartz Water Red blood XeCl, 308 nm, Water Er:YAG, 2,94 nm, on glass Ag film (0.11–4.1 Al, marble Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 59 ) [76] ( Continued (2003) [161], Kim (2003) [109] Lang (2003) (2003) [163] (2003) [164] (2003) [100] :in , due initial 2 particles Schrems 2 film thickness vapour plume surface damage ); 2 of liquid-assisted laser Smith focusing by liquid droplets ranges 10–20 m/s; the (at fluence 68 mJ/cm at Si wafer – SiO substrate performed a normal > 70 nm; in 90–130 nm was 25 m/s (4:1 solution) and reaching the wafer surface; light field (2 pp.) of research on dry and steam Leiderer < 2 nm at 93 mJ/cm substantial particles removal was achieved [162] reflectivity and vapour plume transmission Kudryashov interference in liquid film , the review ements (0.5–3 mm above the surface); iments with precise control of liquid layer Molecular dynamics calculation Interferometrical and optical reflectance studies of Lee match with experimental results; evenmonolayer a had liquid a clear effect on cleaning processes at explosive vaporization of liquid; the contact during ‘storage time’ 100–1350(see h Fig. observed 2.19); dry cleaningon efficiency fluence dependence and ‘storage time’ presented (2003) displacement up to 27 nm only at film thickness thickness range particles redepositionto occurred, due light affects the energy concentration at particles caused water for particles size overIPA 840 at nm cleaning in threshold any damageremoval case; free was in observed; particles light may also contribute to surface damage velocity of plume expansion initial velocity decreased with laserto fluence the increase phenomenon, that atliquid higher in fluences contact the withtemp. substrate faster reaches and the vapour critical layerheat hinders transfer the from further surface to liquid Meniscus growth observed laser cleaning recently done atKonstanz, Inst. University de of Optica (Madrid)(see and Leiderer Univ. and Linz Mosbacher above) propagation velocity 36 m/s (10:1 solution) dry surface covered by liquid film A short Liquid layer thickness 1.02–23.8 nm removal of particles on surface; good qualitative 2 2 2 KrF, 248 nm, 24 ns Several sources, from 150 fs to several ns to 0.67 J/cm + IPA (10:1 Nd:YAG, 355 and from steam) steam) 250 mJ/cm on surface(condensed 20 ns, up 0.76 J/cm to by cylindrical lens measur and 4:1) 1064 nm, 6 ns, up Water Water or IPA, Nd:YAG, 532 nm, Liquid layer thickness Exper Water droplets KrF, 248 nm, Laser beam focused Optical µ m) (condensed 8 ns, up to was varied 0–255 nm thickness: µ m) (0.5 , PS and 2 2 6.46 nm (0.14–1.3 SiO and 1.5 PMMA, 60–1000 nm µ m) Si wafer SiO Cr film Rigid Ausubstrate Spherical particlesSi Lennard–Jones wafer liquid PS Si wafer Monodisp. Si wafer (0.3 on quartz, NiP Ch02-I044498.tex 11/9/2007 18: 47 Page 60 (2004) [56] Kudryashov (2004) [164] References : Fernandes ; laser (2004) [18] 1 ns (2004) [166] of laser ablative taking into Arnold ), corresponding 2 at particles µ m; µ m, and has no m/s was varied 2–8 mm; − 8 2 10 for beam width 3–0.25 mm; (2006) [83] at laser-heated surface was Arnold 2 × y of dry cleaning does not observed yields realistic threshold fluence photoacoustic investigations thresholds were calculated laser-induced cavitation bubbles impact was achieved without scanning; highest light field concentration 2 300–50 mJ/cm ≈ th phenomena, comments account F Cleaning Removal of particles from surface was achieved Song nearly 100% cleaning efficiency of areas up to explain the observed results presented and discussed; explosive vaporization threshold was 0.17 J/cm to a pressure difference ofthe 740 liquid hPa; at film falling obviously disintegrated down into droplets resolution; the acceleration of theto film be was constant found (10.5 Cleaning threshold was lower for narrower laser beam 64 mm Dynamics of liquid film cleaning efficiency was achieved whenbeam the was laser focused in depthsurfactant 0–4 were mm added and to alcohol water(2006) or (see [19]) also Ohl cleaning model dependence on particle size; highimproves cleaning humidity for small particles,that hinders of particles ofeffect size of 0.6–3 larger ones C for particles radii 10 nm–100 ◦ into free through < 1 mbar); 23.5–27.5 humid environment liquid film on surface irradiation generated IPA plume propagation IPA film on surface recorded by optical reflectivity with 2 nm, the experiment 2 2 , up to surface liquid (Fig. 2.4) beam distance from surface 2 2 1064 nm, 6 ns 20 ns, up to 0.7 J/cm Lasers and beam Other features of Novel features, KrF, 248 nm, Condensed from vapour Results of width 0.25–3 mm, 20–1000 mJ/cm cylindrical lens, line before experiments acceleration theor from condensed Nd:YAG, 532 and 31–37 mbar (other gases to 50%) andnon-ionic 100 pulses IPA film(90 nm) KrF, 248 nm, 29 ns, 150 mJ/cm Condensed from vapour IPA (up to 12%) surfactant moisture) Water (capillary KrF, 248 nm, 28 ns RH 94–97%; pressure Water; aqueous KrF, 248 nm, 23 ns, Substrate immersed Water (capillary KrF, 248 nm, beam Samples were held in ) 3 2 2 O µ m), PS solutions of 10 Hz, up to vertically 2 (1 (51–110 nm) ethanol (up 10.7 J/cm Continued ( fused (0.1 nm, condensed) focused by Si wafer SiO Si wafer No Si wafer SiO Glass, Al Substrates Particles Liquids parameters Si wafer silica agglomerated) Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 61 ) ( Continued Ohl (2006) [19] Wachs tested; (2005) [87] nm, 1 ns [169] y (PIV); was ≈ 10 m/s with 2 nm, 0.2 ns [107] for high-volume on laser-heated surface was Lang (2004) at laser-heated surface was Lang (2006) ∼ 50 m/s (97 nm film) to bubble growth and collapse ∼ 5 MPa; ejection velocity of liquid near a solid surface during of research of dry and steam laser cleaning Graf (2005) > 4000 wafers were cleaned in 2 weeks particle removal system review Dynamics of liquid film resolution; the liquid film moved10–140 in ns interval after laser pulseacceleration with constant an image analyzing systemindividual was used particles for which detecting were thereafterby removed local steam deposition, lasersuction; irradiation and Dynamics of liquid film Liquid flow of particles from Si wafersin done part at of Univ. SLC Konstanz;(2003) (see [162],(2004) Mosbacher [169]) (2000) [79], Lang [168] ∼ 40 m/s (227 nm film) resolution; estimated with aid ofcalculations temperature initial vapour pressure (atlift-off liquid ) film was film varied from tangential to surface flow velocityduring is the highest time interval(bubble of max jet size impact: 2 mm);velocity the is high obviously tangential responsible forparticles removal from of surface incleaning cavitation-induced (see, e.g. Song (2004) [18]) A µ m laser-induced water film on surface manufacturing system was developed and liquid film on surface(90 nm) recorded by optical reflectometryCondensed with from 2 vapour A PIV visualization of flow fields using 8 fluorescent particles investigated by particle image velocimetr , IPA film on surface recorded by optical reflectivity 2 spot several mm Isopropanol KrF, 248 nm, 29 ns, Condensed from vapour IPA film Nd:YAG, 532 nm, Condensed from vapour (97–227 nm) 7 ns, 138 mJ/cm (obviously) Water Si wafer No Si wafer Not specified Water OPO, 2.94 nm Si wafer No Ch02-I044498.tex 11/9/2007 18: 47 Page 62 Fernandes References of particles Jang (2006) 3 O 2 ved (20 cleaning [17] shadowgraph images over 90% for Al and liquid film vaporization of Kane (2002) [77] with med at room temperature if not mentioned else. observed vapour laser. review crystalline silicon wafer, as a rule; water was distilled and deionized with 60 refs. about the principles and Bäuerle polystyrene latex; SPP: surface plasmon probe; RH: relative humidity; review phenomena, comments theory of dry andsurfaces wet/steam laser from particles; cleaning surface of nanopatteringparticles by arrays determined lightpolishing fields, surface by laser irradiation, andsurface about modification PTFE for enhanced biocompatibility (2006) [57] 120 refs. about experimentaldry research on and both wet laser cleaningsurfaces; experiment of conditions particles and from maintabulated results (2006) [83] A updated A cleaning was enhanced cycles; scanned substrate); the experiment (for liquid film on surface; as small as 20 nm was achie pulsed laser beams are for one pulse; the experiments were perfor 2 ; PIV: particle image velocimetry; MR: magnetoresistive; CVL: copper polymethylmethacrylate; IPA: isopropylalcohol (isopropanol); PSL: eed here; the entries are mostly in the original style;‘Si’ means single heating) Nd:YAG, 1064 nm, by shock wave generated shock propagation Lasers and beam Other features of Novel features, 60 ns, 520 mJ (forshock generation) in air above the substrate are presented KrF, 248 nm, 25 ns Condensed from vapour Cleaning efficiency + IPA (10:1) 170 mJ/cm 3 O 2 ) (50 and 100 nm av) aver.),Al Continued ( -lasers are usually CW; the energies and energy densities for + Substrates Particles Liquids parameters Si wafer CuO (50 nm Water SAW: surface acoustic wave; OPO: optical parametric oscillator Reports where only reactive liquids were used, are not refer as rule;Ar Notations SC: single crystalline; PS: polystyrene; PI: polyimide; PMMA: Table 2.5 Ch02-I044498.tex 11/9/2007 18: 47 Page 63 ) ( Continued (1983) [170] Osiecki (1990) [172] Oltra (1993) [173] References by Oltra (1986) [171] µ m, depth oblems µ m (cryogenic Piper (1990) [30] µ m thick laser was able 2 areas on mirrors Pierce (1990) [31] space optics was removed by laser Ulrich (1981) [20], 2 10 cm µ m × and cleaning options is Oxide layer were cleaned successfully in 15 min by a scanned laser beam to remove over 5 frozen layer from surfaces, but Nd:YAG laser only 0.1 laser ablation in coursepit to initiation study process the ablation crater was 5–10 for transient electrochemistry studies successfully removed from initiation process; diameter of the 14 different surfaces Torr presented; CO − 6 –10 − 5 Other features of Novel features, observed cell, 860 mV SCE 1–2 Process was In air (Au also 12 different contaminants were solution Flowing electrolyte, Local depassivation of a Fe electrolysis 1 cm/s, 300 mV SSE electrode by laser ablation in vacuum situ in an 2 µ m, carried out in ablation in course to study the pit 6G dye, Specimen immersed Oxide layer was removed in situ 2 for at 35 K) , , 2 2 2 µ s, up to Experiments A review of particles) ,2 , pulsed At 34 and 90 K 10 W/cm 2 2 2 µ J, spot 5 10 beam parameters the experiment phenomena, comments 0.2 J/cm 15 J, some pulses were performed optics) contamination pr Nd:YAG, 10 ns, in vacuum Laser and 150 J/cm (0.9 J/cm up to 25 Hz, 1.5 J 308 nm, irradiation time up to 240 s CO 10 Hz, up to 1 J, 10 10 SiO ayers and related experiments (examples). , pH 1 1–40 MW/cm + 4 7 O 4 B 2 Liquids 0.01 M NaCl solution of 30 0.1 M No of HClO of NaCl(30 g/l) 570–625 nm, 15 Hz into free-surface Na O 2 ,NoCO 2 , 2 µ m , vacuum , up 3 2 ∼ 10 assisted laser removal of surface l Native oxide Aqueous Dye, 15 ns, 20 Hz, to SiO Native oxide Water solution Nd:YAG, 6 ns, Carbon particles, frozen water Layer and CO ( ∼ 100–140 K) Liquids- -over- Carbon particles, 2 (mirrors) of air, mainly H Fe Substrate removed coated Ni on NH Stainless steel(CrNiMo Fe) Native oxideNi-coated Al, Dust Water from solution Rhodamine No Be Fe on quartz MgF coated Al solvent residues Al, Be frozen constituents Al (mirror) pump oil, dust Au-over- Water, CO Au/Ni-coated laboratory air; Au Table 2.6 Ch02-I044498.tex 11/9/2007 18: 47 Page 64 ¸s(1996) [8], Cooper (1995) Halfpenny (1997) [175] [22, 176] [177], (2000) [36] Oltra (1996) References µ m, µ m, (10.6 2 (10.6 2 surface removed by laser Jette (1994) [174] ); scattered in < − 1.5V; etching starts 2 particles to the µ m diameter cryofilms 3 O dehydroxylated 2 oxidation achieved in basic µ s)– close to measured values Cleaning efficiency was higher when water without any incubation time Solid reduced up to 56%); the adherence Laser irradiation resulted removed material plume probe light intensity and acoustic signal were proportional, thus acoustic signal may beto used control the cleaning process 200 ns) and 120 J/cm treated hydrophobic surface was reduced up to 80%; of 0.3 was applied – dryneeded cleaning 30 laser pulses, wet cleaning only 10 pulses (0.4 J/cm solution at cathodic 2 distributions presented, taking into account temp. dependences of materials properties; bulk Au surface damage threshold was estimated to be 37 J/cm for 1D transient temperature (SiOH concentration was Al ≈ 25 K irradiation; analytical expressions Other features of Novel features, observed distance to sample≈ 1 mm potential Substrates for 100 ms per and liberation of water; Laser light feed Efficient oxide removal without Yava the experiment phenomena, comments Water was The samples , workpiece 2 , optical fibre, 2 2 µ m, temperature 0.1 mm, µ m, 6 ns, brushed onto ∼ 0.4 and 0.8 J/cm and 10.6 Nd:YAG, 44–110 J/cm Laser and spot 5 mm to microsecond pulse length nanosecond 308 nm, 1.06 255.3 nm, 35 ns,4.25 kHz, 100–250 mW,spot were irradiated each spot in Cu-vapour, hydroxidesolutions 20 pulses borate buffer 1064 nm, 14 ns, trough 1.5 mm re and sodium 0.55–0.66 J/cm 2 O No 2 µ m), ) µ m) and CO µ m 2 Layer ( ≈ 1 0.1 Continued ( mirrors O sculpture 0.05 mm 0.1 mm layer 1.06 (2 mm) groups Limestone Black crust, Water, Fe, steel Native oxides,Silica glass Boric acid, Hydroxyl Nd:YAG, No Substrate removed Liquids beam parameters Au-coated (1–10 Au and Solid H Table 2.6 Ch02-I044498.tex 11/9/2007 18: 47 Page 65 ) ( Continued Lee (1998) [179] (1998) [180] Sakairi (1998) [21] [178] Ellegaard (1998) Alloncle , 2 obviously ved µ m) ; calculated (IPA film); ∼ 0.3 molecules ); 2 2 ∼ 0.5 mm µ m, depth 0.8 bubble dynamics were cleaned by 120 laserat pulses 80 mJ/cm generation of multiple damage from shock induced collapse of micro-bubbles (residue of disintegration of previous bubbles); in water, the oxides were removed fromlarger 60% area than in gas 0.6 repassivation process; the diameter of the ablated area was ablation in order to study removed locally by laser highly light-absorbing acetone did not enhance thedry cleaning; cleaning needed 200 mJ/cm 120 pulses; bubbles obviously play important role in wet cleaning of holes temperature profiles during laser heating, and ablation rate dependence on film thickness and incident laser intensity are presented for solid nitrogen and water films Torr (8 MW/cm re Surfaces and holes (diam. − 8 liquid liquid, liquid dipped into Experiment was Ablation rate Samples were High-speed photographs chemical cell Process was carriedan electro- Anodic oxide films were vacuum, 10 2 , 2 up to 30 Hz 13 ns, up to 1.2 J, spot 0.5–3 mm layer at least 5 mm pits observed, resulting 532 and 1064 nm, immersed into of N Nd:YAG, Nd:YAG, 532 nm, 8 ns,0,1–6W out in situ in 1.5–8 MW/cm 10 Hz, 337.1 nm, 3 ns, performed in per photon was obser − 3 − 3 µ m 23 ns, 7 O 4 3 B 2 BO 3 layer) H + Na 0.05 kmol/m Water , IPA, acetone KrF, 248 nm, Samples we z µ m O y F x Ti,Al, Cu (some 100 M = Native anodic oxide 0.5 kmol/m (100–600 nm) Inconel 600 0.1– 10 316L XC35, oxides, Quartz Solid nitrogen No Si wafers MC Steel, Native Al Ch02-I044498.tex 11/9/2007 18: 47 Page 66 (1999) [24], Cortona (2001) [26] Fernandes (2002) Oltra (2000) [25] Pasquet (1999) [24] Meja (1999) [23], References 2 10 ≈ ≈ 3 J/cm µ m; concentration [181] film efficiency of silica 4 ≈ 40 O 3 − 1.45V/SCE) enhances dehydroxylation of the oxide was reduced revealed defects in heat times what explains thelaser enhanced ablation efficiency (see also Meja (1999) [23]) up to 10 times; dependencies of (decided by SIMS analysis) on laser fluence, pulse repetition (e.g. of surface silanol groups after 40 min polarization at − 1.55V the extinction coefficient k under proper cathodic potential the shock affected zoneestimated was to be no defects were found in transparent coatings; laser irradiation removed opaque coating slice by slice, but delaminated the transparent one oxide film, obviously due to diffusion and entrapment of hydrogen in the oxide film during the cathodic reduction process in opaque coating; at L aser irradiation in solution − 1.55V changes in Fe Other features of Novel features, observed vertically into optical fibre, in air feed trough 1.5 mm distance to sample≈ 2 mm the removal efficiency of polarization before laser treatment under cathodic polarization; liquid, focusedlaser beam and shock affected zones 40 min cathodic Studies of optical properties Pasquet Laser light 2 , 2 nm, Workpiece immersed Open circuit potential 2 2 7 mm, × beam parameters the experiment phenomena, comments 17 ns, 1 Hz, Laser and 450 and 900 pulses 2–200 Hz, spot was performed surface reduced the KrF, 248 nm, The experiment Laser irradiation 14.5 ns, 1–21 J/cm 3 0.1–1.2 J/cm 0.5 J/cm 3 BO 3 7 7 4 3 O O 4 4 B B SO 2 2 2 BO 3 of 0.075 M+ 0.05 M 1064 nm, of 0.075 MNa 7 ns, 0.38–0.7 J/cm H + 0.05 M H 4 3 3 O 3 O O 2 2 µ mNa ) 4 µ mFe µ mNa O 3 oxide, 20and 50 of 0.1 M Fe water content ≈ 18% Layer and opaque), (transparant Native oxides: Aqueous solution Nd:YAG, 1064 nm, + 1 + 1 Native oxides: Aqueous solution Nd:YAG, 20 nm Fe 20 nm Fe Continued ( 2 O 2 Substrate removed Liquids silica,H groups Fe Fused Hydroxyl No cleaned Fe AlMgSi1 Anodic Aqueous solution XeCl, 308 Table 2.6 Ch02-I044498.tex 11/9/2007 18: 47 Page 67 ) ( Continued [33] Kautek (2003) Brennan (2003) [183] Marczak (2003) [182] [184] Lim (2003) [32], was in liquid, -cleaned 2 removed O 2 removal of the scale was held at least 10 s in the during laser ablation recorded and modelled by a capacitance and a resistance found to affect the ablation of graphite rate and total pulseis number presented; H Includes a short review with over 10 references about laser irradiation effects of electrodes in electrolytes, incl. heating, desorption and ablation samples were contaminated in laboratory air by hydrocarbons in a day irradiation; use of laser enabled to remove the scale atconcentration HCl of only 10%, instead of 18% inpurely case chemical of treatment Water film was not horizontally into free- enhanced by laser-generated (2004) surface of the solution (Fig. 2.7) HCl solution before laser to window 5 mm,focused laser beam repassivation current transients (lasting some milliseconds) beam focused onto but only when the workpiece Workpiece immersed The 2 2 Hz, into liquid, distance the oxide slice by slice; µ m, surface solution, laser mechanical impact 2 µ m, ≈ 10 5–50 ns, up to 200 J/cm 0.562 and XeCl, 308 nm, Workpiece immersed Laser irradiation 0.9–24 J/cm 1.06 C; spot ◦ HCl Nd:YAG, 4 + SO 2 a , 1 mm layer over up to 0.5 J/cm 3 O 2 , and the workpiece µ m, µ m), (5, 10 and 18%); 1064 nm, 6 ns, 4 O µ mN 3 machining oil (transparantand opaque) 0.1 M Fe Graphite, 3and 8 0–60% pores Water layer 0.266, 0.355, 70 C FeO, Fe ◦ > 800 6061 oxide, 30 and solution of 17 ns, 0.5 steel, hot ( ≈ 10 Low carbon Oxide scale Water rolled at composed of 25 and 80 Al AlMgSi1- Anodic Aqueous Ch02-I044498.tex 11/9/2007 18: 47 Page 68 Hidai (2006) [34] (2006) [37] Dolgaev (2004) [35] References ratio laser : + 3 + water /Si and hole) + from experiments is presented; ; the range of laser removed the 3 + (26 pp., 13 figs., 27 refs.) of Fernandes :Ho 3 + review region cleaned was 5 mmfocal around point the of thedecomposition lens; the products water etched Zn, but not other metals laser pulses causing the decomposition Removal of oil film dehydroxylation laser dehydroxylation was found to be mainly a thermaldependence process; of SiOH laser led to increase ofnon-diamond the carbon amount; the cleaning occurred obviously mainly as result of non-diamond carbon solvation in supercritical solution of dehydroxylated samples at SIMS analysis on laserpulse fluence, repetition rate and total pulse number is presented (see also Halfpenny (1997) [177] and Fernandes (2002) [181] in this table) particles, irradiation by Cu-vapour Other features of Novel features, observed surface (Fig. 2.8) was achieved using 18 000–36 000 focused laser beam non-diamond carbon layer from the experiment phenomena, comments 2 , in air 2 : Particles suspension Irradiation byYSGG:Cr , irradiated by Yb 3 + 3 + 2 :Ho 3 + 30 Hz, 150 mJ focused on water metal surfaces (plates KrF, 248 nm, The experiment A 300–10 000 pulses Cu-vapour, 510 nm, 20 ns, 10 kHz, 2–3 J/cm Laser and 12 ns, 20–200 Hz,0.1–1.2 J/cm was performed silica surface structure and ≈ 130 ns, 1 kHz, 10 J/cm ArF, 193 nm, Laser beam YSGG:Cr 3 eed here. HNO + 10 ml solution) 2.92 µ m, ) Layer groups Continued ( 2 O 2 Zn, SUS304 Sumitap super particles carbon layer ( ≈ 1 ml for Yb Ni, Cu, Tapping oil Water Fused silica, Hydroxyl No H (4 nm) SubstrateDiamond removed Non-diamond Water Liquids beam parameters cleaned Reports where only reactive liquids were used, are not refer Notations SCE – saturated calomel electrode; SSE – silver–silver chloride referenceSUS304 electrode; – a kind ofSIMS stainless – steel; secondary ion mass spectrometry. Table 2.6 Ch03-I044498.tex 12/9/2007 17: 40 Page 69

CHAPTER THREE

Shock Processing

Contents 3.1 Introduction 69 3.2 Residual Stresses and Their Measurement 70 3.3 Laser Shock Peening 77 3.4 Laser Shock Forming and Cladding 140 3.5 Densification of Porous Materials 141

3.1 Introduction

In laser shock processing (LSP), the mechanical recoil impulse of rapidly expanding vapour and plasma is utilized for introduction permanent changes in the workpiece (Fig. 3.1). The light power density on the workpiece surface is chosen to be so high (1–100 GW/cm2) that optical breakdown occurs and plasma is created. The rapid expansion of high-pressure plasma (velocity ∼1500 m/s and pressures over 2 GPa in water) creates a shock wave that, propagating through the material, creates dislo- cations and induces plastic deformations. A higher dislocation density results in higher surface hardness and strength, while plastic deformations reduce porosity and can create compressive surface stresses, the latter being responsible for increased fatigue and cavitation strength and stress corrosion resistance of the material. Also an increase of theYoung’s modulus and Poisson’s ratio, and grain refinement due to the shock has been reported. If the surface is covered by a transparent coating, solid or liquid (Table 3.1), the expansion of the vapour and plasma is suppressed and the pressure and impulse on the surface are considerably higher. As confinement

Laser pulse Lens

High-pressure Water plasma

Material

Figure 3.1 Principle of LSP. Sudden expansion of laser-generated plasma creates a pressure pulse that drives a shock wave into the workpiece. © ASME, reproduced with permission from Ref. [185].

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

69 Ch03-I044498.tex 12/9/2007 17: 40 Page 70

70 Handbook of Liquids-Assisted Laser Processing

Table 3.1 Comparison of different confinement media for LSP.

Confining medium Advantages Disadvantages

Inorganic solid Highest pressure and Not applicable to curved surfaces, (glass, quartz) impulse (due to highest glass pieces remain inside the acoustic impedance) machinery,multiple shocking troublesome Polymer (acrylic, Can be applied to curved Multiple shocking is time- and rubber) surfaces material consuming Liquid (water) May be applied to curved Wet method, lower pulse pressure surfaces, suits well for multiple shocking

41 (a) (b)

A 44 38 46

40 42

(c) (d) (e)

Figure 3.2 Principles of: (a) shot peening; (b) deep rolling; (c) water cavitation peening; (d) ultrasonic shot peening (after Xing and Lu [187]) and (e) ultrasonic peening by strikers (after patent US2002037219 [188]).

medium (tamper layer) glass, water, and some polymeric materials have been used (see also Table 2.2 in the book by Ding andYe. [186]). In LSP, only a mechanical impact on the workpiece is desired. Heating of the material by laser light is kept minimal by using short laser pulses and protective coatings (ablators). In technology,LSP has been applied for peening, densification, and forming of materials, the peening being of greatest importance. In many aspects similar to laser peening results may be achieved also by shot peening, water cavitation peening, and deep rolling (Fig. 3.2 and Table 3.2). In fundamental research of matter behaviour under shock loads, flyers and explosives are used as well.

3.2 Residual Stresses and Their Measurement

Residual stresses play a critical role in fatigue, creep, wear, stress, corrosion, cracking, fracture, buckling, etc. [195]. Conversion of tensile residual stresses into compressive is the main goal of LSP and residual stresses are the most important process parameters of LSP. Research and process control of LSP rely to a great extent on the determination of surface and bulk residual stresses in the material. Harmful tensile surface residual stresses are created by majority of subtractive machining methods,including mechanical and chemical milling, turning, broaching, grinding, electro-discharge machining, and laser cutting. Ch03-I044498.tex 12/9/2007 17: 40 Page 71

Shock processing 71

Table 3.2 Comparison of some peening methods. There are several examples of SP and DR performance in Table 3.8 along with laser peening results.

Method Important characteristics References

Shot peening (SP) Simple, inexpensive; risk of introducing foreign material [189] into the workpiece or its surroundings, roughens the surface Laser peening Laser beam can access places non-accessible by Peyre (1996) [190] (LSP) accelerated shots; the impacts may be localized (down to Hammersley (2000) [191] micrometers), but also have large area (up to 100 mm2); well controllable, rapid, does not cause significant macroscopic deformation of the treated zone; strain rate up to 106/s achievable, plastically affected zone 5–10 times deeper than in case of SP; does not increase surface roughness considerably; high cost of the equipment Deep rolling (DR) Better finish in comparison to LSP at equal plastically Nalla et al. (2003) [192] affected depth; workpiece geometry restricted, high load on workpiece Water (jet) Up to 1000 MPa residual compressive stresses were Qin et al. (2006) [193] cavitation achieved in spring steel SAE 1070 peening (WCP) Ultrasonic peening Plastically affected depth from 0.3 mm (using shots) to Xing and Lu (2004) [187] 1.5 mm (using strikers) Kudrjavtsev (2004) [194]

Macrostresses

Peening

Cold hole expansion

Bending

Welding

Figure 3.3 Some common cases of residual stress formation. © The Institute of Materials, Minerals and Mining, reproduced with permission from Ref. [200]. Ch03-I044498.tex 12/9/2007 17: 40 Page 72

72 Handbook of Liquids-Assisted Laser Processing

Table 3.3 Residual stress measurement techniques [196,201,200,198].

Restrictions Technique to materials Penetration Spatial resolution Accuracy Comments X-ray diffraction Crystalline 5 µm (Ti), 20 µm ±20 Mpa Combined often 50 µm (Al) depth, 1 mm with layer removal Lateral for greater depth Synchrotron Crystalline >500 µm, 20 µm ±10 × 10−6 Triaxial stress, diffraction (hard 100 mm for Al lateral to incident strain access difficulties X-rays) beam, 1 mm parallel to beam Neutron Crystalline 4 mm (Ti), 500 µm ±50 × 10−6 Triaxial, low data diffraction 25 mm (Fe), strain acquisition rate, 200 mm (Al) access difficulties Curvature/Layer 0.1–0.5 of 0.05 of thickness Stress field not removal thickness uniquely determined Hole-drilling ∼1.2 hole 50 µm ±50 Mpa Flat surface needed diameter Depth (for strain gauges), semi-destructive Slitting (crack Flat surface needed, compliance) destructive Surface contour Simple and cheap, suits well for welds, destructive Ultrasonic Metals, >10 cm 5 mm 10% 0.5–10 MHz ceramics Magnetic Magnetic 10 mm 1 mm 10% Microstructure sensitive Raman/ Ceramics, <1 µm <1 µm 50 Mpa Not applicable fluorescence/ polymers approximately directly for metals birefringence (feasible by using proper coatings)

Tensilestresses build up also at rod and wire drawing and in weld joints. On the other hand, compressive surface stresses develop for example at peening, nitriding, and sometimes in quenching [196–199] (Fig. 3.3). Table 3.3 and Fig. 3.4 present an overview of common residual stress measurement methods. Low pen- etration methods are often combined with layer removal in order to get information on stress profiles [198]. Layers may be removed for example by grinding or electro-polishing. Some chemical machining receipts can be found in the article by Flavenot [202].

X-ray diffraction Strain in crystalline materials causes shifts in X-ray diffraction angles. The sin2 ψ technique If the stress tensor is biaxial, strain in direction N (normal to a {hkl}-plane in a crystalline grain) εϕ,ψ becomes (Fig. 3.5) [196, 203]: + 1 v 2 v εϕ ψ = σϕ sin ψ − (σ − σ ). (3.1) , E E 11 22 Ch03-I044498.tex 12/9/2007 17: 40 Page 73

Shock processing 73

Depth (mm) 0.001 0.01 0.1 1 10 100 X-rays Neutrons Non- Magnetic destructive Ultrasonic

Hole-drilling Semi- Ring core destructive Crack compliance

Layer removal Destructive Measurement techniques Sectioning

Thin films Stresses Machining, peening produced by Welding, case hardening common Cladding, heat treating, quenching processes Forming, casting, extruding

Crack initiation Depth Wear ranges Fatigue that Fracture contribute to failure Distortion Buckling, creep

0.00004 0.0004 0.004 0.04 0.4 4 Depth (inches)

Figure 3.4 Depth ranges of residual stress measurement techniques compared with typically observed profiles and failure mechanisms. © ASME, reproduced with permission from Ref. [195].

If the strain in the probe volume is 1D or 2D and homogeneous, there is a linear dependence on εϕ,ψ on sin2 ψ, and the experimental data can conveniently be fitted by least square method. The sin2 ψ technique may fail in case of steep stress gradient near the surface [204]. X-ray diffraction method is non-destructive, but in case of LSP it suffers from small penetration depth. Modifications of the procedure like the layer removal technique by grinding or electro-polishing are no longer non-destructive and require long preparation times and complicated analysis to relate the measured strains to the original stresses of the component [196, 205].

Synchrotron diffraction (hard X-rays) Hard high-intensity X-rays from synchrotron sources allow fast measurements at greater depths comparable with those reached by neutron diffraction. However, due to the low scattering angles in synchrotron radiation X-ray diffraction experiments, the gauge volume is strongly elongated making the spatial resolution low in at least one of the three perpendicular sample directions. Therefore, the application of this technique is limited to cases where the stress state is essentially biaxial within the surface plane [206–207].

Neutron diffraction The significant advantages of neutron diffraction over other methods are the high penetration depth in engi- neering materials and a scattering angle near to 90◦. This latter property allows strain data to be collected Ch03-I044498.tex 12/9/2007 17: 40 Page 74

74 Handbook of Liquids-Assisted Laser Processing

s x3 33 {hk1} Nw,c 33 w,c

c

x2 s 22 22 w

sw x1 s 11 11

Figure 3.5 Definition of angles and stress/strain components in sin2ψ technique.

essentially from the same sampling volume in three perpendicular specimen directions. The limitations of neutron diffraction method are low particle flux compared for example to the synchrotron X-ray method and the fact that beam divergence does not generally allow a very precise definition of the gauge volume (citation from the article by Bruno et al. [205]). If high resolution is needed or if the specimen are thick, the data accumulation takes a long time. ‘There are technical issues to be addressed when performing near-surface measurements. If the sampling (gauge) volume is not fully buried within the sample spurious readings of strain can be recorded. The use of a radial collimator in the incident beam can reduce this problem [208]. An alternative solution has been found by Edwards and Wang [209], who used a z-scan. This technique uses a very long gauge volume in at least one direction and consequently assumes the in-plane stress being is isotropic, which in most problems is not the case’ (citation from the article by Bruno et al. [205]).

Curvature/layer removal method Here, layers are removed from parallelepiped-shaped specimen and deflections or curvature changes induced by stress relaxation are measured [202]. Layers may be removed by mechanical or chemical machining. The technique is destructive, but of low cost.

Hole drilling (hole-drilling incremental method) and ring core methods In hole-drilling method, stress relaxation is achieved by drilling a small hole into the specimen. Changes in surface strain during drilling, measured commonly by a strain rosette, give information about residual stress distribution [210, 211] (Figs 3.6a and 3.7). In ring core method, stress relaxation is achieved by a ring core (Fig. 3.6b). From hole/ring core depth vs. strain data, the initial in-plane stress components depth profiles in the specimen can be computed. The hole is drilled by a conical shape mill and has diameter and depth ∼1–4 mm. To avoid production of additional residual stresses during the drilling process, high-speed drilling machines are recommended [212].

Slitting (crack compliance) method In slitting (crack compliance) method, stress relaxation is achieved by fabricating a slit into the specimen (Fig. 3.8). The slits are cut incrementally in-depth using wire electrical discharge machining (EDM). The strain vs. depth data is then used to compute the variation of the pre-slit residual stress component normal to the slit face with depth from the surface (i.e. the stress profile). Ch03-I044498.tex 12/9/2007 17: 40 Page 75

Shock processing 75

Strain gauge Strain gauge rosette rosette

Hole Ring core

(a) (b)

Figure 3.6 Principles of (a) hole-drilling and (b) ring-core residual stress measurement techniques. © The Fairmont Press, Inc., reproduced with permission from Ref. [213].

(a) (b) Strain gauge Strain gauge

A

B B

Figure 3.7 Stress relaxation induced by drilling a hole into specimen: (a) before drilling and (b) after drilling. Changes in surface stress are usually measured by strain gauges (need a flat surface) alternatively, optical methods may be applied. © Michal Švantner (University of West Bohemia) reproduced with permission from Ref. [212].

Strain s gauge

Lg a w

Figure 3.8 Principle of the slitting method. A straight slit is incrementally cut into workpiece by EDM and surface stress is measured by strain gauges [214]. © Elsevier.

Surface contour method The principle of the contour method is that when a part containing residual stresses is cut in half along a straight line, the newly created free surface will deform as the stresses normal to the surface are released by cutting (Fig. 3.9). The deformations of the cut surface can be used to uniquely determine the initial residual stress acting normal to the cut plane using Bueckner’s superposition principle [215, 216]. Surface contour technique does not need strain gauges and suits well for mapping residual stress over a plane in weldings. Ch03-I044498.tex 12/9/2007 17: 40 Page 76

76 Handbook of Liquids-Assisted Laser Processing

() Tension Compression

() Original part Y s contains xx(y)

X () (a)

Cut in half (deformations exaggerated)

(b)

Force deformed surface flat to recover initial residual stress s ( xx(y))

(c)

Figure 3.9 Principle of surface contour method. Residual stresses are computed from relaxed surface contour. No strain gauges are needed and stresses can be determined in the full extent of the specimen © ASME, reproduced with permission from Ref. [216].

One of the biggest limitations of the standard contour method is that it can only map a single residual stress component. In long prismatic specimen like weldings, the mentioned limitation may be overcome by cutting the specimen multiple at different angles towards the longitudinal axis – the multi-axis contour method [217].

Ultrasonic methods Stress-related changes in elastic wave velocity can be used for stress determination in solids [218]. Application to LSP needs wavelength of order 0.1 mm, which corresponds to frequencies over 10 MHz.

Magnetic methods For macroscopic stress measurements, the dependence of Barkhausen noise and magnetic permeability on mechanical stress have been used [219].

Raman spectroscopy Raman-active materials undergo a frequency shift of Raman spectra when the crystal lattice is strained. The resolution on the method is order of a few micrometers and it is capable to probe local non-uniform stress distribution [220, 221]. The method cannot be applied to metals and to materials that radiate fluorescence strongly. However, a Raman-inactive specimen can be coated by a Raman-active material like PbO. In the work by Miyagawa et al. [222] surface strains in epoxy, Al-alloy and stainless steel were determined this way in range ε = 0–0.4 with ±20 MPa scatter.

Fluorescence spectroscopy The method relies on piezospectroscopic properties of fluorescent materials – the shifts and broadening of optical fluorescence lines due to mechanical stresses. It can be applied to non-metallic single- and polycrystalline materials like Al2O3 and MgO up to stresses at least 400 MPa [223]. Ch03-I044498.tex 12/9/2007 17: 40 Page 77

Shock processing 77

Photoelastic coatings Changes in surface stresses may be visualized using photoelastic coatings which become birefringent under strain. The coating is applied onto a mirrored surface and illuminated by polarized light. The polarization state of the reflected light is dependent on the strain in the coating. High-sensitivity photoelastic materials are among other polycarbonate, glass, and epoxy resins [224, 225]. Moiré interferometry Moiré interferometry is an optical method, providing wholefield contour maps of in-plane displacements with subwavelength sensitivity. In this method, a high-frequency crossed-line diffraction grating is replicated on the surface of the specimen and it deforms together with the underlying specimen. Two coherent beams create a virtual reference grating in their zone of intersection. The deformed specimen grating and reference grating interact to produce the Moiré fringe pattern which represents contours of constant u and v displacements [226, 227]. The described optical methods can be used in laser peening research in conjunction with relaxation methods (instead of strain gauges).

3.3 Laser Shock Peening

3.3.1 Introduction Industrial applications targeted laser peening research started in 1968 at Batelle Columbus Laboratories (Colum- bus, USA), and the first published report dates from 1974 (J.A. Fox, US Army Mobility Equipment Research and Development Center, Fort Belvoir, USA) [228]. Other centres that have essentially contributed to laser peening research and development are Laboratoire pour l’Application des Lasers de Puissance (LALP) in France and Toshiba Corporation in Japan. The main purpose of LSP is the formation of a compressively stressed surface layer in the workpiece. Such compressive field is beneficial in many ways, first of all for improving fatigue and corrosion strength. In LSP, a high-intensity laser pulse irradiates the surface of the workpiece (optionally covered with a protective coating and/or a transparent overlay). The protective coating (ablator) or a thin surface layer of a bare workpiece is vaporized and the vapour partly ionized.The recoil pressure of free expanding or confined by the transparent overlay plasma generates a shock wave that propagates into the target.The depth of penetration of shock wave is about 2–3 mm, after that it converts into an acoustic wave [229]. The volume affected by the shock wave is plastically strained during its propagation (Fig. 3.10a). The surrounding material is opposed to this straining and therefore biaxial compressive residual stresses on a plane parallel to the surface develop (Fig. 3.10b) [190, 230].

3.3.2 Experimental techniques Majority of water confined laser peening research has been done using the scheme Fig. 3.11, which suits for treating of machine parts in a workshop. At laser peening of stationary constructions under water, or those filled with water-like nuclear reactors, the application of protective coating on surfaces may be troublesome. In 1995, a technology of laser peening

P

(a) (b)

Figure 3.10 Principle of the generation of compressive residual stresses with laser shock treatment: (a) during the interaction and (b) after the interaction (after Peyre et al. [190] © Elsevier). Ch03-I044498.tex 12/9/2007 17: 40 Page 78

78 Handbook of Liquids-Assisted Laser Processing

Water Coating Workpiece 0.5–5 mm 20–120 m

Laser

Plasma

During laser irradiation

Figure 3.11 Schematics of water confined laser shock peening with a protective layer (metallic foil or paint) on the surface. The function of the protective coating (ablator) is to avoid the heating of the workpiece by laser beam. Proper ablator (a material with low heat of vaporization and low shock impedance) can also increase the stress wave amplitude by 30–50% (Fig. 3.19).

Nd:YAG laser Mirror (Frequency doubled)

XY table Test sample

Lens

Water jacket Window

Figure 3.12 Experimental arrangement for laboratory studies of laser shock peening without coating (LPwC). © Trans Tech Publications Inc., republished with permission from Ref. [231].

without protective coating (LPwC) was invented at Toshiba Corporation, Japan. In essence, the workpiece is shocked by high-density laser impacts of relatively low fluence. Despite the surface initially remains tensile stressed,at repetitive shocking it becomes compressive-stressed as well (Fig. 3.26). An experimental arrangement used in laboratory studies of LPwC is presented in Fig. 3.12, and a system used for treatment of nuclear reactor components in Fig. 3.39. When thin sections are treated, the reflected from the rear side shock wave may reduce the residual stresses formed at the front side due to Bauschinger-effect. The solutions are the shocking of both sides of the workpiece simultaneously or to use a‘momentum trap’– a solid plate in contact with the backside of laser-shocked sample, avoiding the wave reflecting from the back. The momentum trap should have the same shock impedance that of the workpiece [232].

Lasers For shock peening in water confinement, the laser light should pass the water layer without significant absorp- tion. If centimetre-sized areas need to be treated, the laser should be able to generate tens of Joules in Ch03-I044498.tex 12/9/2007 17: 40 Page 79

Shock processing 79

nanoseconds. These requirements are met economically at 1.06 µm Nd:YAG, Nd:glass, and other neodymium ion lasers whose overall energetic efficiency reaches tens of percents. In case of laser peening without protective coating (LPwC),bare metal surfaces reflect most of the 1.06 µm light, and shorter wavelength lasers are needed: frequency doubled Nd:YAG (532 nm) and copper vapour laser (∼510 nm). The absorption of light in water is also lower at these wavelengths. Because relatively low energy impacts are used (40–250 mJ), commercial low cost laser systems are applicable. In Table 3.8, the main laser beam parameters are given for every research report. A comparison of laser systems used for peening is given also in the book by Ding andYe. [186].

Shock measurement techniques Shock pressure is commonly measured by piezoelectric quartz transducers (Fig. 3.13). X-cut quartz pressure transducers provide a linear response up to 4–6 GPa. The piezoelectric current i is related to pressure p as (p − p )dS i = 0 , (3.2) t0 where p0 is pressure at the electrode opposing that of p, d is piezoelectric coefficient, d = 2.05 pC/N, S is the area of collecting electrodes, and t0 is the transit time of the pressure pulse through the quartz crystal, g t = , (3.3) 0 v where g is the thickness of the quartz crystal and v is the speed of the acoustic wave through the crystal, v = 5730 m/s [234–236]. Alternatively, piezoelectric polymers like PVDF (polyvinylidene fluoride) can be used as shock pressure transducers. The piezoelectric coefficient of poled thin films of the material is up to 6–7 pC/N. PVDF sensors were found to be able to measure accurately laser shock wave profiles in 0–200 GW/cm2 range [237].

Displacements measurement by EMV gauges Besides the pressure, the displacement of the target’s rear surface can give useful information about the shock, for example, the mechanical impulse can be directly calculated from the target’s velocity (Eq. (3.21)).

Laser Glass overlay

Aluminium foil Water

Quartz crystal

Screw

Positive electrode

Ground 50 Ohm structure

(a) (b)

Figure 3.13 Principle of shock pressure measurement by quartz transducers: (a) glass confinement and (b) water confinement. © American Institute of Physics (1990), reprinted with permission from Ref. [233]. Ch03-I044498.tex 12/9/2007 17: 40 Page 80

80 Handbook of Liquids-Assisted Laser Processing

Thin Laser Water foil

Uf (m/s) Parallel pins B E (V)

Figure 3.14 Use of a EMV gauge for measurement of displacements of a laser-shocked target. The displacement of the target causes a change of the magnetic flux through a conductor loop and a electromagnetic force is generated. © Institute of Physics, reproduced with permission from Ref. [237].

Displacements may be conveniently measured by EMV gauges (Fig. 3.14). The technique was reported to be applicable at laser energy densities up to 20 GW/cm2 [237]. The electromagnetic force is related to the particle velocity u as [238]

ε(t) = l · [u(t) × B] (3.4)

where l is the length vector of the gauge, u is the particle velocity,and B is the magnetic field strength.

Displacements measurement by VISAR In VISAR interferometers (velocity interferometer system for any reflector), the Doppler shift of a laser beam reflected from the moving target is utilized (Fig. 3.15). The free-surface motion creates a Doppler shift of the light wavelength λ (formula 3.5) and the com- bination of two signals (a delayed and a non-delayed one) creates a fringe count F(t) which allows to access to the specimen free surface velocity vs. time Vs(t) (formula 3.6). The advantage of VISAR in laser shock research is that there are no pressure limits for this method (as for quartz gauges above 4–5 GPa) and that,

Ar laser

Optical fiber

Photomultiplier tube M1

Target Beam splitter Oscilloscope

M2 Computer Nd: YAG pulse laser

Figure 3.15 Schematics of target’s rear side displacement measurement byVISAR. The technique provides a time resolution of 1–2 ns. © American Institute of Physics (1998), reprinted with permission from Ref. [241]. Ch03-I044498.tex 12/9/2007 17: 40 Page 81

Shock processing 81

contrary to electromagnetic systems, measurements can be performed on any kind of reflective surface, even on the ferromagnetic ones (citation from the article by Peyre et al. [239])

V (t) λ(t) − λ λ −2 s = 0 = , (3.5) C λ0 λ0

λ V (t) = 0 F(t), (3.6) s 2τ where C is constant and τ is the time difference of light paths in the interferometer [240, 239]. In case of shock transit time through the target being much greater than the laser pulse duration, the maximum pressure Pmax at the target can be calculated from free surface velocity profile Vs(t)as V V 2 P = ρ · C + S · s1 · s1 + y + δP, (3.7) max 0 0 2 2 3 0

where ρ0 is the density, C0 is the bulk sound velocity, S is linear Hugoniot slope coefficient, Vs1 is first rear surface velocity peak, y0 is the initial yield strength, δP is empirical correction term, taking into account the pressure decay of the shock wave during the sample crossing (Fig. 3.21). For 250-µm thick Cu and Al samples δP = 2 kbar [241], for shock attenuation in steel, see the article by Peyre et al. [239]. Figure 3.19 presents an application example ofVISAR technique. All the measuring methods described above are applicable to the rear side of the target only. For to get adequate information about the situation at the shocked side, the specimen should be thin enough (see Table 3.8). The phenomena inside the specimen can been investigated using mathematical models only.

3.3.3 Shock pressure Figure 3.16 presents calculated and Fig. 3.17 a measured by a quartz transducer pressure transient in a typical laser peening process. Note that the pressure lasts longer than the laser pulse and that water confinement increases the pressure amplitude many times. In Fig. 3.18 the dependences of the peak pressure on laser energy density and pulse duration are presented. Figure 3.19 illustrates the effect of a protective coating (ablator) on peak pressure. The theory of pressure formation is given in Section 3.3.6.1.

3

In water 2

1 Laser power Plasma pressure (GPa) In air 01020304050 Time (ns)

Figure 3.16 Calculated plasma pressures at laser shocks in air and in water near a solid boundary. Focal spot diameter 0.75 mm, laser fluence 22.6 J/cm2, peak power density 4.5 GW/cm2. The plasma pressure amplitude in water is 4–10 times greater than that in air and its duration is two- to three-fold compared to the laser pulse duration. (Adapted from the article by Sano et al. [242] © 1997 Elsevier.) Ch03-I044498.tex 12/9/2007 17: 40 Page 82

82 Handbook of Liquids-Assisted Laser Processing

Pressure pulse

Laser pulse

100 0 100 200 300 400 Time (ns)

Figure 3.17 Experimental pressure pulse submitted to the target, compared with the laser pulse [190]. Experi- mental conditions: Nd:glass laser, 1.06 µm, 25 ns (Gaussian), spot 5–12 mm, 1–8 GW/cm2; water layer 2–5 mm; target: Al-alloy. © Elsevier.

10 Pmax(0.6 ns) 9.5 GPa

Pmax(10 ns) 6GPa Pmax(25 ns) 5GPa

25 ns

Peak pressure (GPa) Peak 0.6 ns Analytical model 10 ns (a 0.3) 1 1 10 100 Incident laser intensity (GW/cm2)

Figure 3.18 Influence of laser intensity and pulse duration on the plasma pressure generated in water confinement regime (laser wavelength λ = 1.06 µm)[243]. Analytical model corresponds to Eqs (3.13)–(3.17), α is thermal to internal energy ratio of the plasma, Eq. (3.12). The pressures saturate at high-laser intensities due to optical breakdown at water/air interface. At shorter laser wavelengths, the peak pressure saturates at lower laser intensities, for example ∼4.5 GPa for 0.532 µm and ∼3.5 GPa for 0.355 µm (both for 25 ns pulse length). © SPIE 1998, reproduced with permission from Ref. [243].

3.3.4 Shock propagation and wave phenomena A schematic presentation of wave propagation in a laser-shocked elasto-plastic body is given in Fig. 3.20, and corresponding dynamic stresses in Fig. 3.21. Sudden rise of plasma pressure creates a plane longitudinal wave at the surface, which propagates into material inducing plastic deformation εp of the form ε11 = ε22 = εp, ε33 =−2εp, εij = 0(εp > 0). At the border of the impact, two types of release waves are created: a longitudinal or P wave, and a transverse or S wave created by the shear εrz occurring at the side of the impact. The interaction of P release wave with the surface creates a ‘head wave’ H, but the amplitude of both is too low to produce any permanent (i.e. plastic) deformation. On the other hand, the S wave strongly interacts with the surface to form a Rayleigh wave. As the Rayleigh wave approaches the centre of the impact, its amplitude rises as a result of the conservation of kinetic energy (see also model Eqs (3.45)–(3.51)). According to calculations by Dubrujeaud et al. [244] the P component creates deformations εp < 0 and thus reduces the plastic deformations left by the plane Ch03-I044498.tex 12/9/2007 17: 40 Page 83

Shock processing 83

8

316L steel 300 7 100 30 m Al

6

5 200

Bare 316L

Stress (GPa) 4 steel Free velocity V (m/s) velocity Free 3 100 Analytical model 2 2 4 6 8 10 12 Peak power density f (GW/cm2)

Figure 3.19 Influence of an aluminium overlay on peak plasma pressure at water-confined laser peening (VISAR measurements) [239]. Target: 316L foil, water layer thickness 3–4 mm, laser wavelength 1.06 µm, pulse temporal shape Gaussian. © American Institute of Physics (1998), reprinted with permission from Ref. [239]. Pressure increase occurs if Zoverlay = ρoverlay · Us,overlay < Ztarget, where Z is shock impedance, ρ is density, and Us is shock velocity.

S Emission of plane wave P P H and release waves P an S. Interaction of P release P wave with surface head wave H

Interaction of the S release wave with the surface S creation of Rayleigh wave RAY (RAY). Propagation of Rayleigh wave

RAY - Focusing of Rayleigh wave S P plastic flow of affected layer. Creation of residual stresses at centre

Figure 3.20 Schematics of wave phenomena√ in a laser-shocked elasto-plastic√ body. The released P and S waves move at a longitudinal velocity α = λ + 2µ/ρ and transverse velocity β = µ/ρ respectively, where λ and µ are Lamé constants, and ρ is the density [244]. © The Institute of Materials, Minerals and Mining, reproduced with permission from Ref. [244].

wave. The S component produces a shearing plastic deformation εRay–S of the form ε13 = ε31 = εp,rz, all other components of the tensor being zero. Here, εp,rz is approximately a linear function of r for r < cRt0/2. This induces aV-shaped plastic deformation of the surface near the centre of the impact zone. After the passage of the Rayleigh wave, the bulk of the substrate tends to react against the deformation created in the surface layer, flattening the V,then opening its vortex to create tensile stresses σrr and σθθ for r < cRt0/2. Consequently the stress drop at the centre of the impact is a result of the effect of both the P and S components of the Rayleigh waves which are emitted at r = R and which reach the centre at the same time (citation from the article by Dubrujeaud et al. [244]). The residual stress drop in the centre caused by surface wave focusing (Fig. 3.22a) may be avoided by elliptical/square impacts or by overlapping impacts [245, 246, 190]. Ch03-I044498.tex 12/9/2007 17: 40 Page 84

84 Handbook of Liquids-Assisted Laser Processing

(a) 0

300

600

900

1200 800 ns Dynamic stresses (MPa) 400 ns Radial stress, 1500 rr Axial stress, 200 ns yy 1800 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Depth y (mm)

(b) 0

yy 300

600

900 rr

800 ns 400 ns 200 ns Dynamic stresses (MPa) 1200

1500 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Surface r (mm)

Figure 3.21 Calculated numerically by Ding and Ye [186] dynamic stresses (a) in depth along centre line (r = 0), (b) on the surface of a 35CD4 30HRC steel target, laser shocked in water confinement by a triangular pressure pulse of 2.8 GPa amplitude and of 50 ns duration (FWHM) (see also op. cit., Figs 4.6 and 4.7 for dynamics of the energy components – internal, kinetic, elastically stored, viscously and plastically dissipated). © Woodhead Publishing Limited, reproduced with permission from Ref. [186].

3.3.5 Shock-induced changes in materials Residual stresses A typical residual stress distribution induced by a single macroscopic circular laser shot is given in Fig. 3.22.The residual stress drop in the centre is due to S release wave focusing as described in Section 3.3.4. In Fig. 3.23, the laser peening induced residual stresses are compared with shot peening ones. However, deep rolling may well drive the compressive stresses as deep as LSP [192]. Figures 3.24 and 3.25 present examples of the dependencies of plastically affected depth and maximum achievable surface stress on shock impulse and material static yield strength, respectively. In all of these experiments the targets had protective coatings. Ch03-I044498.tex 12/9/2007 17: 40 Page 85

Shock processing 85

600 rr suu 100 500 s 0 z 400 rr 0.5 1.0 1.5 2.0 r 0 mm Depth, mm 100 300 200 200 r 3 mm

Residual stress, MPa Residual stress, 300 100 Impact

Radial residual stress, MPa Radial residual stress, 400 0 r 5 05 Radius, mm 500 (a) (b)

Figure 3.22 Residual stresses on Astroloy after a circular confined plasma laser shock [245] (τ0 = 40 ns, I = 5.9 GW/cm2, P = 37 GPa); (a) Superficial residual stresses; (b) In depth profile of residual stresses. Copy- right 1990 from “Laser shock surface treatment of Ni-based superalloys’’ by Forget P, Strudel JL, Jeandin M. Reproduced by permission of Taylor & Francis Group, LLC., http://www.taylorandfrancis.com

0 20 Shot peened 60 Laser-shot peened 100

140 Inconel 718 Residual stress (MPa) 180 0 0.2 0.4 0.6 0.8 1.0 1.2 Depth from surface (mm)

Figure 3.23 Comparison of depth profiles of residual stresses achieved by a typical shot peening and by a typical laser shock. Shot peening: FOD 0.010A; laser: 100 J/cm2; one pulse. Exact pulse length was not given (in range 10–100 ns). Adapted from the article by Hammersley et al. [191] © Elsevier Science Ltd (2001).

1.2

1.0

0.8

0.6

0.4 25 ns 0.2 2.5 ns Plastically affected depth (mm) Plastically affected 0.0 0612 Impluse (Mbar ns)

Figure 3.24 Relation between impulse and plastically affected depth. Target: 35CD4 50HRC, water confinement (2 mm) [247]. © EDP Sciences, reproduced with permission from Ref [247]. Ch03-I044498.tex 12/9/2007 17: 40 Page 86

86 Handbook of Liquids-Assisted Laser Processing

0 A356 7075-T7351 200 s . . res 0 5 Y 400 316L Astroloy

600 55C1 X12CrNiMo12-2-2 800 X35Cr4-50HRC 1000 First impact 1200 Residual surface stresses (MPa) Residual surface Maximum level X100CrMo17 1400 0 500 1000 1500 2000 Static yield strength (MPa)

Figure 3.25 Influence of the mechanical properties of the targets on the residual stress levels achievable by LSP (Compilation by Peyre et al. [243]). © SPIE (1998), reproduced with permission from Ref. [243].

600 600 Coverage: 0 % (ref.) Coverage: 0 % (ref.) 400 100 % 400 100 % 200 % 200 % (MPa) (MPa) x 200 800 % y 200 800 % 0 0 200 200 400 400

600 600 Residual stresses, s Residual stresses, s Residual stresses, 800 800 0 0.1 0.2 0.3 0 0.1 0.2 0.3 Depth from surface (mm) Depth from surface (mm)

Figure 3.26 Depth profiles of residual stress in SUS304 stainless steel laser shocked without protective coating in water (LPwC process). Laser: Nd:YAG, 532 nm, 8 ns, 10 Hz, spot ∼1 mm. The insets at bottom show the laser scanning pattern (lines) and the direction of the stresses (pile) [231]. © Trans Tech Publications Inc., reproduced with permission from Ref. [231].

An example of residual stress evolution at laser peening without protective coating is presented in Fig. 3.26. Although after first impacts the surface remains under tension, the deformations from subsequent shocks add to the previous ones until also the surface becomes compressively stressed. Because the laser peening induced residual stress/strain depends besides the shock-induced plastic defor- mations also on the specimen shape and dimensions, for unique characterization of the laser peening results, it is convenient to determine the eigenstrain (plastic strain) (Fig. 3.27) [248, 249].

Fatigue strength Laser peening induced compressive residual stresses can considerably inhibit the initiation and propagation of cracks (Fig. 3.28) and this way prolong the fatigue life of machine parts (Fig. 3.29). Ch03-I044498.tex 12/9/2007 17: 40 Page 87

Shock processing 87

0.004

0.003 Eigenstrain

Strain 0.002

0.001

0 01 23Depth, mm 0.001

0.002 Residual elastic strain

0.003

Figure 3.27 Elastic and eigenstrain distribution in a laser peened titanium alloy. Schematically after Korsunsky [249].

Edge of notch Edge of notch

Laser shocked zone Shear lip (a) (b)

Figure 3.28 Schematics of the crack propagation in a notched test sample (2024-T3, 6.4-mm thick), (a) unshocked, (b) – laser shocked simultaneously from both sides (Nd:glass, 30 ns, ∼12 × 109 GW/cm2) [232]. Dashed lines – river line patterns, solid lines – crack front contours. Reprinted with permission of ASM International®. All rights reserved. www.asminternational.org (see also the article by Fabbro et al. [250] for crack propagation speed measurements).

320 S–N curves at R0.1 300 5 280 22 260 90

(MPa) Laser shock 240 max 236 MPa

s 1 220 Untreated Shot - peening 2 215 MPa 200 195 MPa 180 104 105 106 107 108 Number of cycles (N)

Figure 3.29 Comparison of fatigue life σmax–N curves for unshocked, shot-peened, and laser shocked 7075-T7351 aluminium alloy. Notched samples of thickness 11 mm (see the inset) were tested using a three-point bending machine, stress ratio R = 0.1, frequency 40–50 Hz (adapted from the article by Peyre et al. [190]). © Elsevier. Ch03-I044498.tex 12/9/2007 17: 40 Page 88

88 Handbook of Liquids-Assisted Laser Processing

Table 3.4 Influence on laser peening on surface roughness.

Confining Materials medium/Coating Changes in surface roughness Reference

2024-T62 Glass (4.5 mm)/ Surface roughness lowered from Ra Zhang (1999) [252] black paint 6.3 µmtoRa 0.1 µm A5083 Water/without Surface roughness of laser-treated Kusaka (2005) [253] coating material increased with increase of laser power density and with decrease of scanning speed (scanning speed range was 0.1–15 mm/s), exceeding tens of µm Rz

SUS304, Water/without Surface roughness Ra was less than 2 µm Sano (2006) [254] SUS316L coating (1.2–1.3 µm for 304 stainless steel)

Hardness Laser peening has been found to increase the surface hardness in many materials, see Table 3.8 and the book by Ding andYe [186] pp. 40–43. The following mechanisms responsible to hardness increase were reviewed by Peyre and Fabbro [230]: (1) Increase in dislocation density. (2) Phase transformations like γ–α in iron-based materials. (3) Structural modifications such as twinning in stainless steels.

Surface roughness Laser shocking tends to create a certain surface roughness/waveness (Table 3.4) independent on the initial state of the surface due to inhomogeneity and interference in high-intensity laser beams, see for example the articles by Colvin et al. [251] and Forget et al. [245]. Among competitive to laser peening methods, the shot peening introduces considerably higher surface roughness (is used for creating decorative surfaces) and deep rolling results in considerably lower surface roughness than laser peening [192].

3.3.6 Mathematical models of laser shock peening 3.3.6.1 Plasma processes and pressure generation Fairand and Clauer Fairand and Clauer [255] report about 1D-computer code called LILA for calculation of confined plasma pressure at laser peening. Absorption of light in plasma was accounted by Kramer’s formula for inverse Bremsstrahlung (7.82). No further details of plasma process modelling were given. The simulation agreed fairly good with the experiment in laser intensity range 1–4 GW/cm2.

Griffin, Justus, Campillo, Goldberg Griffin et al. [256] presented a 1D-model for ablation shock pressure in 1986, using the same assumptions as Fabbro et al. (see below), except that the laser pulse was Gaussian, 2 I(t) = I0exp −4ln2(t/τ) (3.8) Ch03-I044498.tex 12/9/2007 17: 40 Page 89

Shock processing 89

f10 J/cm2 I

3 2 P L 2

1 Pressure (kbar) 1 Plasma depth ( m)

0 300 600 Time (ns)

Figure 3.30 Calculated by the 1D-model by Griffin et al. [256] plasma pressure P and plasma depth L for a 2 2 Gaussian laser pulse I. The model parameters were β = 3, f = 0.1, φ = 10 J/cm , τ = 150 ns, I0 = 63 MW/cm , and Z = 63 kbar s/km. Plasma geometry was assumed the same that in Fig. 3.31. © American Institute of Physics (1986), reprinted from Ref. [256].

Differential equations for energy balance and for plasma opening width were solved numerically by Runge– Kutta method; an example is given in Fig. 3.30. According to the Griffin’s model, the peak shock pressure approximately equals γfZφ P =∼ 0.95 (3.9) peak (1 + β)τ

Z Z with Z = 1 2 , (3.10) Z1 + Z2 where φ is laser fluence and f is the fraction of the driver laser energy absorbed in an ideal gas, 4 γ = ln 2, (3.11) π β = 3/2, 5/2, or 3 for mono-, di-, and polyatomic gases, respectively.

Fabbro, Fournier, Ballard, Devaux, Virmon The widely used Fabbro’s model is based on Griffin’s model, but the assumption of constant energy density during the laser pulse enabled to get analytical solutions for plasma parameters (Fig. 3.31) [233, 230, 257]. Nomenclature: I(t) – laser power density I0 – laser power density of a rectangular pulse τ – laser pulse duration Elaser – laser energy Eint – internal energy of the plasma, Eint = Eth + Eioni Eth – thermal energy Eioni – ionization energy α – fraction of incident laser energy absorbed by the plasma and transformed into shock energy: E α = th ; (3.12) Eint Ch03-I044498.tex 12/9/2007 17: 40 Page 90

90 Handbook of Liquids-Assisted Laser Processing

Laser beam

2 Glass or water overlay u2 Shock wave D2

Opening of the L Plasma interface Absorptive overlay u1 Shock wave

D1 Metallic target 1

Figure 3.31 Geometry of the plasma in the models by Griffin et al. and Fabbro et al. [230]. Sudden increase of laser ablation plasma pressure creates two shock waves and drives the target and the confining medium into motion. The structure is assumed to be of infinite width and depth; u1 and u2 are the particle velocities and D1 and D2 are the shock velocities. Compare with laser cleaning process (Fig. 2.36). Reproduced with kind permission of Springer Science and Business Media.

the fraction (1 − α) is used for the generation and ionization of the plasma (α = 1 for a perfect gas) Z1 – shock impedance of the target, Z1 = ρ1D1 Z2 – shock impedance of the confining medium, Z2 = ρ2D2 ρ1, ρ2 – densities of the target and confining medium, respectively m1, m2 – masses of the target and of the confining medium D1, D1 – shock velocities in the target and confining medium, respectively. (also U1 and U2) u1, u2 – particle velocities (velocities of the opening boundaries) L – width of the plasma opening A – relative part of absorbed in the plasma laser energy Evap = mHvap – energy of vapourization of the target m – (experimental) ablated mass Hvap – enthalpy of vapourization of the target Assumptions (1) The model is 1D. (2) Laser pulse is rectangular of intensity I0 and duration τ. (3) Laser energy Elaser is totally converted into internal energy of the plasma Eint and the work of pressure forces to open the interface between the solid target and the confining medium; thermal losses on walls and radiative emission are negligible. (4) Plasma is an ideal gas in thermodynamical equilibrium so that the pressure (P) is related to the thermal energy by P = 2/3 Eth = 2/3 αEint. (5) Target and the confining medium have constant shock impedances Z1 and Z2. (6) Boundaries of the opening move with shock wave particle velocities u1, u2. The model is based on two differential Eqs (3.13) and (3.13): (1) Energy conservation relation: dL d Eint(t)L I(t) = P(t) + ; (3.13) dt dt (2) Expansion of the plasma opening: dL(t) 1 1 V (t) = = + P(t). (3.14) dt Z1 Z2 Ch03-I044498.tex 12/9/2007 17: 40 Page 91

Shock processing 91

Table 3.5 Approximate plasma absorption coefficient at 1.06 µm, measured in a quartz confinement. [233].

Laser intensity (GW/cm2) Plasma absorption (A) 0.1 65% 1 80% 10 97%

For a constant laser power density I0 and pulse duration τ,the integration of these equations gives the maximum pressure generated by the plasma: α P = A ZI (3.15) 0 2α + 3 Here A is a constant, Z is the combined shock impedance of the target material and the confinement medium, defined by 2 1 1 = + , (3.16) Z Z1 Z2

and I0 is the absorbed laser intensity. In practical units, the formula (3.15) becomes α P(GPA) = 0.01 Z(g/cm2 s) I (GW/cm2). (3.17) 2α + 3 0

The parameter α should be determined from experiment or using a detailed plasma model. In laser peening regimes, values of α = 0.1–0.5 have been reported Berthe et al. [258, 257] and by Wu and Shin [259]. As pointed out by Wu and Shin [259], the low values of α account for neglected light reflection at water–plasma interface and plasma energy losses through conduction and radiation in simple models. For water confinement, the formula (3.17) is further simplified: 2 P(GPA) = 1.02 I0 (GW/cm ). (3.18)

The plasma thickness at the end of laser pulse is given as

L(τ)(µm) = 2 × 103 · P(GPa)τ(ns) (3.19)

According to Sollier et al. [260] the plasma thickness at the end of the laser pulse is 2–3 mm. The formula (3.17) may easily be modified to account to the absorption A of the plasma and the energy expended to ablate the target Evap: α P(GPa) = 0.01 Z(g/cm2 s) AI(GW/cm2) − E (J/cm2)/τ(ns) (3.20) 2α + 3 vap

Measured by Fabbro et al. [233] plasma absorption coefficients A for 3 and 30 ns laser pulses of wavelength of 1.06 µm are presented in Table 3.5. Impulse momentum, delivered to a unit mass/area target is given by √ m1 J = m1V1 = 2Ek , (3.21) 1 + m1 m2 Ch03-I044498.tex 12/9/2007 17: 40 Page 92

92 Handbook of Liquids-Assisted Laser Processing

where Ek is the kinetic energy of the system,

m V 2 m V 2 E = 1 1 + 2 2 (3.22) k 2 2 As noted by Lee et al. [261] once the peak pressure exceeds the Hugoniot elastic limit, the impulse momentum is a better parameter than the pressure for estimating the result of laser peening (Fig. 3.24). According to the measurements by Fabbro et al. [233] in confined ablation regime the impulse is of order 1 Mbar ns at 1–10 J/cm2 and rises up to ∼10 Mbar ns at 100 J/cm2. Thus Eq. (3.21) overestimates the impulse. For constant laser intensity I0, the pressure at the end of the laser pulse τ is m I α P(τ) = 1 0 (3.23) 2τ(α + 1)

and the velocity of the target τ V1(τ) = 2P(τ) . (3.24) m1 The last formula enables to calculate the plasma pressure from VISAR measurements of target velocity (e.g. Fig. 3.19). The model of Fabbro et al. includes two free variables to be determined from experiment or from advanced models: the ratio of plasma thermal energy to internal energy α and plasma absorption coefficient A.

Limitations of the Griffin’s and Fabbro’s models (after Griffin et al. [256]) (1) The details of the formation of the plasma have been ignored, that is the ideal gas was assumed to have existed prior to the laser pulse. In reality,a threshold fluence exists before the plasma is formed. (2) It was assumed that the mass of the plasma is constant and that it behaves as an ideal gas. However, the rates of vaporization, ionization, and recombination vary during the process. The experiments by Sakka et al. (see Table 7.6) have shown that water plasma at laser fluences around 10 J/cm2 starts to behave as a strongly coupled plasma. (3) The variation of shock impedance Z with pressure has been ignored. (4) The target was assumed to be very thick. (5) The only energy–loss mechanism included in these models is the work of expansion. Losses due to radiation, thermal conduction, and target deformation were ignored. Thermal conduction losses are expected to become significant at times much greater than 2τ. (6) The model is not valid in case of picosecond or shorter laser pulses, where the plasma does not have an opportunity to expand during laser excitation. Assuming ideal gas behaviour also in the picosecond case, the peak pressure is expected to vary linearly as also observed [256].

Sollier, Berthe, Fabbro, Peyre, Bartnicki In the article by Sollier et al. [262] the transmission of light by water plasma in the laser peening regimes was calculated numerically using the model in Sollier et al. [260] which takes into account the cascade and multiphoton ionization, and diffusion and recombination losses of electrons (see also Section 7.3). The plasma parameters (density, temperature, ionization) were calculated according to the mass balance equation dn(t) 1 2 = nV (t) − P(t)n(t) , (3.25) dt L(t) abl Z

where n is the density of the neutrals and Vabl is the ablation velocity from Hertz–Knudsen theory. The plasma was considered as a gas of neutrals from the target only,and thermal losses with cold materials (water and target) Ch03-I044498.tex 12/9/2007 17: 40 Page 93

Shock processing 93

7.1021 3.5 4 8 21 6.10 3 3.5 7 1 ne Pmax experimental 5.1021 2.5 3 6

) P 2.5 5

3 21 4.10 2 1 Z

(eV) 2 4

21 e (cm 3.10 1.5 e T e T

n 1.5 3

21 Z u 2.10 1 Pression (GPa) 1 2 21 1.10 0.5 0.5 1 0 0 0 0 0 20 40 60 80 100 0 20 40 60 80 100 Time (ns) Time (ns)

Figure 3.32 Example of simulation of confined laser peening plasma parameters [262]. Gaussian pulse τ = 15 ns, 2 λ = 1064 nm, 5 GW/cm . Notations: ne is the electron density, Te is the electron temperature, Z is the reduced temperature, P is the plasma pressure, 1 is the coupling coefficient, θ is the degeneracy parameter. © SPIE (2003), reproduced with permission from Ref. [262].

were taken into account. Using experimentally determined absorption of laser light, the plasma parameters were calculated in 1D by the ACCIC code (Auto Consistent Confined Interaction Code) (Fig. 3.32). The calculations showed that the plasma was partly degenerated (θ close to 1) and correlated (>1). At 1064 nm, the breakdown process was found to be dominated by avalanche ionization whereas at 532 and 355 nm the multiphoton ionization played the dominant role [260].

Zhang, Yao, Noyan Zhang et al. [263] present a laser plasma model for the case of microscale laser impacts (spot size ∼10 µm) under the following conditions: (1) Plasma expands only in the axial direction in the early stage; density, internal energy, and pressure of the plasma are uniform within the plasma volume but can vary in time. (2) Plasma obeys ideal gas laws. (3) Only the coating layer is vaporized, the metal target experiences neglible thermal effects. (4) The coating layer is thin and well coupled with the metal target, thus the shock pressure and the particle velocities of the coating layer and the metal target are equal. The water–plasma target system was divided into six regions: unshocked water, shocked water, plasma, coating layer, shocked solid, and unshocked solid.The shocked and unshocked properties of water were related by mass, energy,momentum-conservation, and shock speed constitutive relations: ρ U − U w0 = 1 − w w0 , (3.26) ρw Dw − Dw0

Pw − Pw0 = ρw0(Dw − Dw0)(Uw − Uw0), (3.27) 2 2 Uw Uw0 1 1 1 Ew + − Ew0 + = (Pw + Pw0) − , (3.28) 2 2 2 ρw0 ρw

Dw = Dw0 − SwUw, (3.29) where U denotes the particle velocity, D the shock velocity, with subscripts w0 for unshocked and w for shocked water. Mass and energy conservation equations for plasma were used in form:

t t

ρP(t) (UpL + UpR)dt = (MFw + MFc)dt, (3.30) 0 0 Ch03-I044498.tex 12/9/2007 17: 40 Page 94

94 Handbook of Liquids-Assisted Laser Processing

where UL is the particle velocity near water, UR is the particle velocity near target, MFw is the mass flow from water into plasma, and MFc is the mass flow from the coating into plasma; and t

Ept + Wp − EMF = AP × I(t)dt, (3.31) 0

where Ept is the total energy stored in the plasma, Wp is the work done by the plasma, EMF is energy exchanged through mass flow,and AP is fraction of the energy absorbed by the plasma (determined from experiments). The set of equations was solved numerically,using mass and energy conservation relations at interfaces.

Colvin, Ault, King, Zimmerman Colvin et al. [251] developed a computational model for pressure generation in case of solid dielectric con- finement, accounting for the initial absorption of light onto a metal surface, low-intensity photoionization absorption in neutral vapour, collisional ionization, recombination, dielectric breakdown and band gap col- lapse of the dielectric, electron conductivity, thermal transport, and constitutive properties of the materials. Analytical Quotidian EOS (Eq. 3.64) was used for all of the materials. The model was incorporated into a 2D-radiation–hydrodynamics code LASNEX. No free variables were needed. Simulations showed that most of the laser energy is absorbed in the dielectric tamper (fused silica or sapphire), and a little part in the ablator (Al or Zn).

Wu and Shin Wu and Shin [259] presented a self-closed thermal model for LSP under water confinement. The model considered laser ablation of the coating layer, water evaporation, plasma ionization and expansion, energy loss of plasma through radiation and electron conduction,laser absorption by plasma through inverse Bremsstrahlung effect and photoionisation, and reflection of laser beam at the air–water interface and plasma-water interface. No free variables were needed. Assumptions taken in the model are the following: (1) The physical processes were considered 1D. (2) Plasma state variables as temperature, density,etc. are uniform in space, but vary with time. (3) The main mechanisms of laser absorption by plasma are electron-ion and electron-atom inverse Bremsstrahlung absorption and photoionization. (4) All the free electrons in the plasma were assumed to have the same temperature Te, and all the particles (atoms and ions) in it were also assumed to have the same temperature Ti (two temperature model). (5) Water molecules were assumed to be completely dissociated into H and O atoms immediately after evaporation. The receding velocities of coating and water surface due to evaporation were calculated from Hertz–Knudsen equation (Eq. 7.58). The plasma pressure caused moving velocities of the water and the coating surface were calculated separately through the momentum–conservation equation and shock speed constitutive relations, the same way as in (Eqs 3.26–3.27): P P uw,pre = = , (3.32) ρwDw ρw(Dw0 + Swuw,pre)

P P uc,pre = = , (3.33) ρcDc ρc(Dc0 + Scuc,pre)

where ρw and ρc are densities, and Dw and Dc are shock velocities of water and coating, respectively. Dw0, Sw, and Dc0, Sc are material property constants (cf. Eq. 7.119) for shock velocity calculations. The total receding velocities of the water and the coating surface were taken as a sum of the evaporation and plasma pressure caused boundary velocities. The calculation by this model peak plasma pressure was in good agreement with experiments (less than ±10 per cent difference) in range of laser power densities 1–10 GW/cm2 and for different combinations of Ch03-I044498.tex 12/9/2007 17: 40 Page 95

Shock processing 95

pulse shape, wavelength and duration: (Gaussian, 25 ns, 1064 nm), (Gaussian, 25 ns, 532 nm), (Gaussian, 0.6 ns, 1064 nm), (short-rise-time pulse, 30 ns, 1064 nm). At power densities more than 25 GW/cm2 the measured pressure was lower than the calculated one. The calculations demonstrated that the reflection of laser light at water–plasma interface ranges up to ∼35 per cent for 1064 nm light and up to 8 per cent at 532 nm, and that the stable value of α is ∼0.5.

3.3.6.2 Models for residual stresses Nomenclature a – edge of square-shaped impacts r0 – radius of circle-shaped impacts τ – pressure pulse duration P – shock pressure ρ – density of the target λ, µ – Lamé constants v – Poisson’s ratio ε – strain ε – strain tensor, also strain vector εp – plastic strain εp – plastic strain tensor σ – stress σ – stress tensor, also stress vector σ0 – initial residual stress σY,YS – uniaxial compressive static yield strength (elastic static limit) σsurf – surface (superficial) residual stress PH, Ph, HEL = Hugoniot elastic limit = yield strength under a uniaxial shock condition Lp – plastically affected depth Ce – speed of elastic longitudinal waves Cp – speed of plastic longitudinal waves

Ballard’s model Ballard’s model describes analytically the plastic deformation and the magnitude and depth of induced residual stresses in a laser-shocked body [264, 265, 190, 230]. Assumptions (1) The shocked body is a elastic-perfectly plastic half-plane. (2) Shock waves are longitudinal and plane. (3) Plastic strain follows a von Mises yielding criterion,|σr − σx| = σ0 + σY. (4) The applied strain is uniform over the impacted area. (5) Duration of the impact is sufficiently small, satisfying the relationship: ρ (λ + 2µ) τ  r (3.34) 0 4µ(λ + µ)

In such case, the induced waves can be considered longitudinal and plane. (6) Applied pressure pulse is rectangular (P is constant); the pressure is uniform on the impacted surface. (7) Viscous effects in the material are negligible. This assumption is applicable for steels and aluminium alloys at laser pulse durations greater than 1 ns [265]. (8) Work hardening of the material is ignored. Under these assumptions, the shock may be described by propagating into the depth independent elastic and plastic waves (Fig. 3.33). Ch03-I044498.tex 12/9/2007 17: 40 Page 96

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Elastic recoil waves (2HEL amplitude)

Plastic waves Peak pressure Z Stress profiles Elastic waves (HEL amplitude)

Figure 3.33 Schematics of waves propagation in the Ballard model, after Peyre et al. [190] © Elsevier.

In cylindrical coordinates r, θ, z, the tensors of applied strain and stress and of induced plastic strain become 000 ε = 000, (3.35) 00ε σr 00 σ = 0 σr 0 , (3.36) 00σz ⎡ ⎤ −εp 20 0 p ⎣ ⎦ ε = 0 −εp 20 . (3.37) 00εp From generalized Hooke’s formula,

σ = λ tr(ε) + 2µ(ε − εp), (3.38) the radial stresses are expressed as

σz = (λ + 2µ)εσr = λε (elastic) (3.39)

σz = (λ + 2µ)ε − 2µεp σr = λε + µεp (elastic–plastic). (3.40) p Elastic PH 2PH deformation P 0

Bounding Hugoniot limit condition straining condition Reverse straining with surface release waves

2PH Plastic strain induced by LSP, ε LSP, induced by Plastic strain 3l2m Plastic bounded plastic strain deformation bounding

Figure 3.34 Surface plastic strain dependence on peak pressure induced by a laser impact. Below PH, no plasti- fication occurs; between PH and 2PH, plastic strain occurs with a purely elastic reverse strain; above 2PH, elastic reverse strain is bounded to 2PH and plastic strain is also bounded to 2PH/(3λ + 2µ). Above 2.5 PH, in reality, surface release waves focus and amplify from the edges of the impacts thus modifying the residual stress field (see Fig. 3.20). Schematically after Ballard [264] and Peyre et al. [190,230]. Ch03-I044498.tex 12/9/2007 17: 40 Page 97

Shock processing 97

From von Mises yielding criterion in a biaxial condition,|σr −σx| = σY − σ0,the Hugoniot limit PH becomes λ 1 − v P = 1 + · (σ − σ ) = (σ − σ ) (3.41) H 2µ Y 0 1 − 2v Y 0 Without initial stresses, the introduction of plastic strain in the Ballard’s model can be schematically represented as shown in Figs 3.34 and 3.35. Table 3.6 presents a summary of Ballard’s theory results, and Fig. 3.36 compares the experimental values of HEL with theoretical ones. s x 2 P

2PH

Plastic loading ing Magnitude of elastic release waves 1 PH Elastic unload

Impact pressure YS Elastic loading 3 4 Plastic unloading s YS 0 YS r

r x von Mises criterion P 2PH

Figure 3.35 Surface stress excursion during pressure transient at laser peening according to the model by Ballard [230]. Reproduced with kind permission of Springer Science and Business Media.

3 Previous studies X12CrNi12-2 (martensitic) 2.5 This study

55C1 steel 2 (ferritic)

1.5 7075 316L stainless HEL (GPa) steel 1 (austenitic) (1v) HEL s (12v) Y 0.5 AI-12%Si

0 AI-7%Si 0 0.2 0.4 0.6 0.8 1 s Static yield strength Y (GPa)

Figure 3.36 Dependence of the Hugoniot elastic limit (HEL) of various materials under laser shock loading on the corresponding static values [239]. American Institute of Physics (1998), reprinted with permission from Ref. [239]. Ch03-I044498.tex 12/9/2007 17: 40 Page 98

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Table 3.6 Analytical expressions for mechanical effects induced by a fast laser shockimpact on an elastic-perfectly plastic material. After Ballard [264], Dubouchet [266], and Peyre et al. [190, 230, 267].

Equation Calculated value Analytical formula number Comments Plastic strain conditionλ (3.42) For a pure uniaxial P = 1 + (σ − σ ) (Hugoniot elasticH 2µ Y 0 deformation; limit – HEL) PH increases with σ0 < 0 Peak pressure conditionλ (3.43) P = 2P = 2 1 + (σ − σ ) (saturated plastic strain) sat H 2µ Y 0 Plastic deformation2P P (3.44) Starts at PH, saturates ε =− H − 1 p at 2PH and depends 3λ + 2µ PH linearly on P

Optimal pressure P = 2–2.5 PH (3.45) Drives εp to saturation Plastified depthCelCplτ P − (σY − σ0) 1 + λ 2µ (3.46) Depends linearly (triangular pressureL = on the pressure C − C 2σ 1 + λ 2µ pulse) el pl Y duration τ √ Superficial residual (3.47) 1 + ν 4 2 Lp stresses (square impact) σ = σ − µε + σ − + ν Increases with εp surf 0 p − 0 1 (1 ) 1 ν π a Decreases with Lp √ Increases with σ0 <σ Superficial residual1 + ν 4 2 L (3.48) Increases with the stresses (circular σ = σ − µε + σ − + ν √p surf 0 p − 0 1 (1 ) size of the impact impact) 1 ν π r0 2

Nomenclature a – square-shaped impact edge r0 – circle-shaped impact radius τ – pressure pulse duration (FWHM) P – shock pressure λ, µ – Lamé constants ν – Poisson’s ratio σ0 – initial residual stress (for unshocked material) σY – static yield strength (actually,the dynamic yield strength should be used [229], see Fig. 3.37) σsurf – surface residual stress εp – plastic deformation induced by LSP Lp – plastically affected depth Ce and Cp, the speeds of elastic and plastic longitudinal waves in the target [268]. λ + 2µ (1 − ν)E 1 λ + 2µ/3 E 1 C = = · , C = = · (3.49) and (3.50) el ρ (1 + ν)(1 − 2ν) ρ pl ρ 3(1 − 2ν) ρ

Chen, Hua, Cai Chen et al. [269] assume the residual axial stress profile exponential and the same over the shocked area, −bz/E σz(z) = EkPmaxe , (3.51)

where Pmax is peak shock pressure at the surface, and k and b are empirical constants. It follows for in-plane stress Eν − σ (z) = σ (z) = kP e bz/E (3.52) x y ν − 1 max Ch03-I044498.tex 12/9/2007 17: 40 Page 99

Shock processing 99

For 35CD4 steel, k = 2.3 × 10−6 MPa−1 and b = 2.16 × 108 MPa/m. The plastically affected depth becomes: −9 −6 −1 Pmax zpl = 4.63 × 10 · E · ln 2.3 × 10 · (ν − 1) · E · ν · (3.53) σY

Forget, Strudel, Jeandin Forget et al. [245] presented an analytical model of surface residual stress distribution for circular impacts. The main assumptions taken in this model were: (1) 2D-model, planar uniform circular loading. (2) Neither yield strength nor Hugoniot elastic limit were considered. (3) Energy dissipation (friction and plastic deformation losses) was not taken into account. (4) When subjected to a stress loading σ, the material instantaneously reacts according to Hooke’s law:

σ = εe, (3.54)

where  is the stress tensor. (5) Plastic flow appears progressively with time, εp being proportional of the time and the deviatoric part of the stress tensor: εp = C s dt, (3.55)

where C is a proportionality coefficient depending on the material and s is the deviatoric part of the stress tensor. The matter in the shock area deforms according to

ε = εe + εp, (3.56)

where the only non-zero value is εzz (planar shock). (6) At the impact boundary,two cylindrical waves are created, one of whose propagates towards the centre of the impact at speed c. The amplitude of the waves was estimated by

w u = (r − r + ct)f (r) for r − ct < r < r , (3.57) r c 0 0 0 w u = (r − r + ct)f (r) for r < r < r + ct, (3.58) r c 0 0 0 ν where w = (3.59) 2ρc(1 − ν)

and r f (r) = 0 (3.60) r

with notations: r0 is radius of the impact,  is plasma pressure, ν is Poisson’s ratio, ρ is density of the target. (7) Kinetic energy during the wave movement was assumed constant (no energy dissipation occurs), therefore the displacement increases as the wave approaches the centre resulting in a wave focusing and residual stress drop formation. Ch03-I044498.tex 12/9/2007 17: 40 Page 100

100 Handbook of Liquids-Assisted Laser Processing

1600

800 Mayer, Tension Mayer, Compression

Yield stress (MPa) Follansbee, Compression Maiden & Green , Compression LSP analysis model 0 1.E03 1.E00 1.E03 1.E06 Strain rate (per second)

Figure 3.37 Titanium-6Al-4V yield strength strain-rate dependence [270]. © Elsevier.

Despite its simplicity, the model realistically predicted the magnitude and distribution of surface residual stresses in an Astroloy sample.

Numerical models Numerical models enable to take into account dynamic and non-linear phenomena,additional material param- eters, real shape of the workpiece, and coupling between mechanical and thermal phenomena, including damping, viscosity, work hardening, thermal stresses, and strain rate effects (Fig. 3.37). Using numerical models, it is possible to study the phenomena inside the workpiece, not accessible to measurements.

Equations of state Mie–Grüneisen equation of state (EOS) is frequently used for solids and liquids. It establishes an hydrostatic relationship between pressure P and internal energy E with reference to the material Hugoniot curve: ρ C2η η p = p (1 − η) + 0 0 · 1 − + ρ (e − e ), (3.61) 0 (1 − sη)2 2 0 0 where ρ η = 1 − 0 , (3.62) ρ V ∂T β  =− · = · · , (3.63) T ∂V S κ ρ cV

with notations: ρ0 is the density, C0 is the speed of the sound,  = 0 is the dimensionless Grüneisen coefficient in normal state, e − e0 is specific internal energy (per unit mass), s is the linear Hugoniot slope coefficient s = dUs/dup, β is the volumetric thermal expansion coefficient, κ is isothermal compressibility, cV is the heat capacity at constant volume. Mie–Grüneisen EOS is used for example in SHYLAC code and in laser peening simulations by Peyre et al. [229].

Quotidian equation of state (QEOS) Quotidian equation of state is a general-purpose analytical equation of state model for use in hydrodynamic simulation of high-pressure phenomena. Electronic properties are obtained from a modified Thomas–Fermi statistical model, while ion thermal motion is described by a multiphase equation of state combining Debye, Ch03-I044498.tex 12/9/2007 17: 40 Page 101

Shock processing 101

Grüneisen, Lindemann, and fluid-scaling laws. The theory gives smooth and usable predictions for ionisation state, pressure, energy, entropy, and Helmholtz free energy. When necessary, the results may be modified by a temperature-dependant pressure multiplier which greatly extends the class of materials that can be treated with reasonable accuracy. (citation from the article by More et al. [271]). The QEOS is applicable for both solid and gaseous states. Quotidian equation of state is presented through Helmholtz free energy per mass unit

F(ρ, Te, Ti) = Fi(ρ, Ti) + Fe(ρ, Te) + Fb(ρ, Te), (3.64)

where ρ is density, Te is electron temperature, Ti is ion temperature, Fi is ion free energy, Fe is electron free energy,and Fb is a correction for chemical bonding effects that can also represent exchange or other quantum effects. The expressions for the terms of Eq. (3.64) and application examples are given in the op. cit. [271]. Quotidian EOS was used for simulation of laser peening by Colvin et al. [251].

Linear equation of state is given by

P = KV , (3.65)

where K is the bulk modulus, K = E/3(1 − 2ν) This EOS was used by Braisted and Brockman [270] in a 2D-axisymmetric numeric simulation of laser shock propagation and residual stresses in Ti-6Al-4V and 35CD.

Stress–strain constitutive relations Johnson–Cook law To reproduce the stress–strain dependence at high strain rate, the Johnson–Cook plasticity law with isotropic work hardening was used in FEM-simulations by Peyre et al. [272 , 229] and Fan et al. [273]The Johnson–Cook law −2 enabled to take into account the strain rate dependence of the stress between ε0 = 10 /s (quasi-static load) and ε = 106/s occurring at the laser shock. The stress σ is expressed as ε˙ − m = + n + × − T T0 σ (A Bεeq) 1 C ln 1 , (3.66) ε˙0 Tm − T0

where A, B, C, and n are material constants (e.g. for pure aluminium A = 120 MPa, B = 300 MPa, n = 0.35, and C = 0.1), εeq is equivalent plastic strain, and ε˙ is strain rate, ε˙0 is strain rate under quasi-static loading, T0 ◦ is the reference temperature (e.g. 20 C), and Tm is the melting temperature.

Steinberg–Cochran—Guinan model The constitutive relations for G and Y as functions of ε, P, and T for high ε˙ in this model are [274] G  p P GT G = G0 1 + √ + (T − 300) , (3.67) G0 3 η G0

Y   n p P GT Y = Y0[1 + β(ε + εi)] × 1 + √ + (T − 300) , (3.68) Y0 3 η G0

subject to limitation that n Y = Y0[1 + β(ε + εi)] ≤ Ymax. (3.69) Ch03-I044498.tex 12/9/2007 17: 40 Page 102

102 Handbook of Liquids-Assisted Laser Processing

Notations: G is the shear modulus, Y is the yield strength (in the von Mises sense), P is the pressure, Y0 and G0 are the values of reference state (e.g. T = 300 K, P = 0Pa,ε = 0), η is the volume compression coefficient, defined as the initial specific volume v0 divided by the specific volume, v, β, and n are the work-hardening parameters, εi is the initial plastic strain, normally equal to zero. Primed parameters are defined as:

   = dG  = dG  = dY YP ≈ GP GP , GT , YP , . (3.70) dP dT dP Y0 G0

Tabulated values of this model’s parameters for 14 materials are given in the op. cit. [274]. Steinberg–Cochran–Guinan model does not take into account strain rate effects. It was used by Zhang and Yao [275] at modelling of laser shocking by micrometer-sized impacts at pressures above 10 GPa, where rate-dependent effects played a minor role, but the pressure effects were of importance.

Selected numerical LSP modelling codes and cases SHYLAC SHYLAC code (Simulation Hydrodynamique Lagrangienne des Chocs) was developed at Laboratoire de Combustion et de Détonique (LCD), ENSMA, Poitiers, France [241, 276]. It enables 1D-simulation of elasto-plastic and hydrodynamic response of materials under a laser-driven loading. The code includes a Mie– Grüneisen equation of state referenced to the linearized Hugoniot curve, and elasto-plastic behaviour for solid materials. The SHYLAC code can also simulate the spallation process. The data required for the simu- lations are the laser–matter interaction pressure profile and the mechanical properties of the material: density, yield strength, shear modulus, Mie–Grüneisen coefficient, bulk sound velocity, and linear Hugoniot slope coefficient.

Braisted and Brockman Braisted and Brockman [270] performed a 2D-axisymmetric numeric simulation of laser shock propagation and residual stresses using ABAQUS software. The materials (Ti-6Al-4V and 35CD4) were modelled as elastic-perfectly plastic with a yield strength defined by Y = HEL(1 − 2ν)/(1 − ν). Thus, it was assumed that all the plastic deformation occurs at roughly the same high strain rate. From consideration, that the pressure levels induced during LSP are generally less than 3 times the HEL, a linear equation of state was used (see above). The materials were specified by four constants, ν, E, HEL, and ρ, only.

Sano, Yoda, Mukai, Obata, Kanno, Shima Sano et al. [277,278] conducted 3D-axisymmetric and spherical FEM simulations of shock propagation and residual stresses at laser peening of SUS304 stainless steel, taking into account adiabatic cooling of the plasma, realistic stress–strain relation (without idealizations), and strain hardening.

Ding and Ye Ding andYe [186] considered the target elastic-perfectly plastic, but took damping and materials viscosity into account. The damping was accounted by a ‘damping stress:’

el σd = βRD ε˙, (3.71)

el where βR is constant, D is elastic stiffness, and ε˙ is the strain rate. Viscosity was introduced with purpose to improve the modelling of high strain rate phenomena (to limit numerical oscillations). The ABAQUS/Explicit algorithm contains: (a) Linear bulk viscosity stress e σ1 = b1ρCdL ε˙, (3.72) Ch03-I044498.tex 12/9/2007 17: 40 Page 103

Shock processing 103

e where b1 is a damping coefficient, ρ is density, Cd is dilatational wave speed, L is element characteristic length and (b) Quadratic bulk viscosity

e 2 σ2 = ρ(b2L ) |εvol| min(0, ε˙vol), (3.73)

where b1 is a damping coefficient and ε˙vol is the volumetric strain rate (was applied only when the volumetric strain rate was compressive). The simulations were performed by ABAQUS in up to 3D.

Zhang, Yao, Noyan Zhang et al. [263] performedABAQUS simulations of laser micro-shocking of copper/silicon bilayer structures with copper layer thickness of 1, 1.5, and 3 µm, and silicon thickness of 20 µm. Laser spot diameter was 12 µm. At simulation of tangential sliding at interface, the Coulomb’s friction law was used

τ = µσn, (3.74)

where τ is the frictional shear stress, µ is the friction coefficient, and σn is the normal (compressive) stress. The plasma pressure model developed in this work was described above.

Fan, Wang, Vukelic, Yao Fan et al. [273] report about an explicit/implicit finite element simulation (using ABAQUS) of microscale materials processing by laser-generated shock waves. Explicit dynamic analysis was implemented for shock wave propagation in strain-rate dependent and elastic–plastic solids, and implicit analysis was applied for relaxation of pressured materials. The Mie–Grüneisen equation of state was implemented; the materials were 5-mm thick Al samples (simulation of peening) and 100-µm thick copper sheets (simulation of forming).

Peyre, Chaieb, Braham In the recent work by Peyre, et al. [229] 2D-axisymmetric shock propagation and residual stresses in 12Cr and 316L stainless steels were simulated by ABAQUS/Explicit software (12 000 elements). The materials were assumed to follow the Grüneisen EOS and Johnson–Cook’s plasticity model. The simulation agreed with experiment rather well except a 50–100 µm thick surface region, probably due to the ignorance of initial stresses and surface waves phenomena, or due to inadequacy of X-ray stress measurements.

3.3.7 Applications of laser peening There are two important applications of laser peening: the treatment of aeroplane components, and of nuclear reactor components. In both cases water confinement is used.

Aeroplane components Turbine blades, rotor components, fastener holes, etc. have been treated with laser shocks with purpose to enhance/restore their fatigue strength. A running water curtain on the workpiece has been commonly used (Fig. 3.38) and the productivity reaches 1 m2/h [191] (see also the book by Ding andYe [186], pp. 43–44 for a short overview).

Nuclear reactor components Laser peening technology for in situ treatment of nuclear reactor components against stress corrosion cracking (SCC) was developed in 1990s by Toshiba Corporation in Japan and has since been applied to reactor core shrouds and nozzle welds of 10 nuclear power reactors in Japan [280] (Fig. 3.39). LPwC process is applied (Tables 3.7 and 3.8). Ch03-I044498.tex 12/9/2007 17: 40 Page 104

104 Handbook of Liquids-Assisted Laser Processing

134 Workpiece

119 Water Water 20 16 AX1 103 AX2 102 05 121

A1 Laser A2 Laser 145 beam 153 beam 152 LD

Figure 3.38 Schematics of simultaneous dual-sided laser shock peening process (after EP1088903 [279]).

Optical fiber Laser system

Controller

Shroud

Remote handling system

CRD stub tube

Figure 3.39 Fibre-delivered laser peening system for control rod drive (CRD) stub tube of boiling water reactor (BWR) [281]. © ASME, reproduced with permission from Ref. [282]. Table 3.7 Comparison of laser peening process parameters in aerospace industries and in nuclear reactor maintenance (after Sano et al. [282]). Parameter Aerospace industry Nuclear reactor maintenance Protective coating (ablator) Yes No Laser wavelength 1064 nm 532 nm Pulse duration <100 ns <10 ns Pulse energy ≤100 J 40–250 mJ Pulse repetition rate ≤10 Hz ≤300 Hz Spot size ≤10 mm ≤1.2 mm Impact overlap (coverage) ≤300% ≤8000% Delivery system Mirror Fiber of mirror Ch03-I044498.tex 12/9/2007 17: 40 Page 105 (1964) (Continued) [288] References Skeen (1968) , [286] 2 by quartz Anderholm (PETN, Yang (1971) ≈ 4 decades [285] ≈ 1 GW/cm in targets, up to Metz (1971) , maximum pulse 2 ed by a pendulum; Gregg (1966) pressure transients measured by piezoelectric Anderholm were recorded ; pressure pulse duration was 100 ns (1968) [287] kbar depending on target material [288] pressures crystal lattice vacancies detonation of various explosives on solid targets by recoil pressure Askar’yan (1963) tens of kbar µ s; pulse repetition rate, Hz; pulse energy, corresponding to laser pulse and not explainable by White (1963) ing layers or environment; (thickness in mm); moments up to 0.36 dyn s shock pressure 7–36 is the number of laser spots in unit area. d features, observed phenomena, comments N ; maximum pulse energy density, J/cm momentum has maximum at laser energy density 2 Measurements of laser pulse induced gauge, epoxy bonded to the Al film; maximum pressure of 34 kbar (1970) light pressure was observed; black coating Enhanced the pressure [284] 1 at%, probably due tosurface shock waves; damage no and ablation slight crater, but depression some of the foils were observed [290] RDX, tetryl) in contact withthese the explosives Al was layer; 7–15 the kbar shock strength of [291] was recorded; pressure pulse wasexperiments longer than were performed the in laser vacuum pulse; chamber transducer reached Generation of momentum of laser evaporated materials isbeing proposed, the possible acceleration applications of bodies and generation of ultrasound [283] Momentum achieved by target was measured by piezoelectric Neuman depending on target more that the momentum of light transducer; Novel A pressure pulse , the 2 2 µ m, Momentum achieved by target was measured by a pendulum; µ s 20 ns, 5 J Damage of targets observed; beam W/cm 10 ≈ 500 10 × Ruby,12 ns, 7 J, spot 6 mm Ruby,up to 4 J Laser irradiation caused spot 3 mm Nd:glass, 1.06 Ruby,694.3 nm, Laser irradiation generated Ruby 50 ns, 0.32 J Ruby,7.5 ns, up to≈ 4 Momentum achieved by target was measur spot 3.4–29 cm 60 ns, 60 J, 1 GW estimated µ m or mm, or spot area, mm µ m; pulse length, usually FWHM, in fs, ps, ns, or als/targets: (thickness in mm): Confining/absorb ; plasma pressure in MPa or GPa. 2 , where D is the diameter of the laser spot and d N × , or TW/cm /4) 2 2 D π (optionally) ? (not specified) avoiding layers or environment properties Vacuum (for , GW/cm 2 Laser shock peening µ m µ m) µ m layer Glass (5.1 mm) µ m film Quartz (6 mm) on back side of a foils) on glass) quartz plate) Processed materials/ Confining/absorbing Lasers and DuraluminiumCu,Al, Pb,Ta, Black coating Be, C (graphite), Vacuum Vacuum Ni,V (50 Pb,V,Hf, Zn, 0.1–152 porcelain steel, brass, 6061-T6,AISI 304 breakdown) targets Al and Cu (films Transparent materialAl (0.5 Q-switched Al (100 Al, Zn,Ag,W Ta,Ag, Sn, Si, µ J, mJ, or J; laser spot size on the surface of workpiece, Lasers and beam properties: wavelength in nm or Numerical values indicate: Processed materi power density, W/cm Table 3.8 The coverage is defined as ( Ch03-I044498.tex 12/9/2007 17: 40 Page 106 [297] [294] (1972) [293] (1974) [296] Fox (1974) [228] Fairand (1972) [292] 2 and ) were 2 2 in conjunction with 55.2 MN/m 3000 dyns/cm effects of confining/absorbing > was observed in the targets; O’Keefe (1973) [295] fatigue life improvement water confinement over unshocked values; microstructural compressive stress yield strengths of materials were µ m) recorded; pressure absorption in samples features, observed phenomena, comments References on induced by laser pressure investigated; greatest layers coated targets was over 10 times largerpressure than dependence on bare on targets; laser fluenceexperiments presented; were the performed in vacuum were treated by laser pulse;workpiece fatigue was life enhanced; of the treated (Fe, 14 Recorded by piezoelectric gauge pressures reached O’Keefe Surroundings of a small hole (3.175 mm diameter)corresponded to Permanent local Hsu deformation (1973) estimated specific impulse Peak pressures at backside of samples up to 56.6 kbar Fairand increased up to 30% analyses showed that laser shockingdislocation induced substructure a similar tangled toshocked explosively aluminium 7.9 kbar (Duco cement layer on surface); pressure on pressure up to 30 kbar;µ s deformation (determined occurs by in a some deformation probe beam); mechanism discussion on of theplastic basis wave of propagation elastic/ in thethe targets experiments presented; were performed in vacuum compared with calculations observed in case of black paint absorber (5.2 and 1.9 mm); pressuresthe up pressure to depend 20 kbar nearly were linearly recorded, on laser fluence Novel The 0.2% offset Target films were confined between two glass plates Yang (1974) µ m, Target’s surface damage and 2 2 2 beam 2 ≈ 50 ns, 2 2 ≈ 30 ns, spot 2.8 mm, up to pressure (3.8 kbar peak – 1 mm Al, 10 J/cm 1.5 and 500 J/cm up to 91 J/cm 1 ms, 4 J, spot 9.53 mm 20–30 ns, up to Nd:glass, 1.06 Nd:glass, 32 ns, Nd:glass, Ruby,694 nm, Nd:glass, 25–55 ns, up to Nd:glass, 31.2 J/cm Ruby,5 J, up to 14 kJ/cm + µ m) µ m) contact layer up to 72 J/cm 3 SiO µ m) or Duco 2 paint adhesive or Mylar film 1.7 GW/cm (25 Glass (1 mm) with Plexiglass or fused cement (63 layers or environment properties Water droplet ) µ m); (3 mm) Continued ( µ m – for 1100-series Al (3.2–12.7 mm), and/or black (0.17 mm), (0.76 mm) (rolled, 92.7–300 Processed materials/ Confining/absorbing Lasers and 1100-0 Al alloy Silicone adhesive 2024 T3 Al alloy Air? Stainless steel Fe-3 wt% Si alloy Fused silica Plexiglass B, C, Mg,AI, Si,Ti, Cr, Borosilicate 7075 T73 and (0.63 and 0.76 mm), silica/Al (1 Fe (14 7075 T6 Al alloys Na Mn, Fe, Co, Ni, Cu, Zn, glass (5.2 mm) pressure measurement) 6061-T6 Al (1 mm) Ge, Zr, Mo,Ag, In, Sn, targets Al (0.41 mm) Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 107 (Continued) (1976) [300] (1976) [299] Clauer (1977) [302] on µ m; ; grease 2 2 ≈ 10 kbar and > 2GPawere central (micrographs W/cm dislocations W/cm 9 9 was observed; enhances the plasma < 10 in 5086 H32 and 6061 ≈ 30 ns laser pulses the Pb sublayer for ; ≈ 7 times longer than the laser weld zones slip but also twinning µ m Fe film), but attenuated to (19 refs., 5 figs) on LSP techniques Fairand (1976) [301] quartz overlay provides up to 40% higher peak of blow-off vapour-generated shock fracture of Steverding (1976) review theory sealant had little effect on peak power (20 ns laser pulse) pressure than water overlay; pressure pulse was up to pulse; yield strength of and results; bulk value (weld zone micrographs presented) with a vacuum grease sealant; peak pressures power density; paint coating had significantpressure effect on peak only at power densities brittle and ductile materialsconsiders is the presented; degree the of theory ionization ofattenuation; the plasma and shock [298] recorded; peak pressure rises nearly linearly with laser in 1.5-mm thick samples; shock-induced surface melting occurred in case offor 200 ns specimen laser of pulses only; thickness over 0.2 mm the presented); mainly zone remained less deformed pressure and deformations atreduces low energy them densities, at but energy densities over 10 was raised to the bulk level and the yield strength of hardness were smaller than thestrength; the increases microstroctures in after shocking the showed yield heavy presented); melted surface layer thickness was 5–50 shrinkage cracks in melted layer were observed A short After laser shocking the tensile yield strength of 5086-H32 Clauer A T6 Al-alloys was increased after laser treatment to the The foils were pressed onto pressure gauge (quartz) surface Fairand ; 6061-T6 was raised midway between the welded and bulk , cross-sections of samples studied (many micrographs 2 2 2 ,up to to 56.6 kbar (14 2 W/cm W/cm , up to 9 9 W/cm 25–200 ns, Shock pressures measured at backside of samples reached 2 , up to 9 2 10 10 10 × × × 101 J/cm Nd:glass, 20 and 30 ns, up to Nd:glass 30 J/cm Nd:glass, 25 and 1.2 4.04 irradiation also from levels; the increases in ultimate tensile strength spot 1.3–2.7 mm up to 101 J/cm 185 ns, up to 2.16 both sides of the sample (also simultaneously andof overlapped dislocation tangles typical of cold working areas) µ m Fused quartz, targets) on some Al the target or (2 mm on one side of 3 mm on both sides) µ m) foil, optionally) µ m foils µ m foil Water (2 mm)/ µ m layer black paint µ m foil) Fe (film 14 films alloys, foils, and water and 3 on quartz), Zn (optionally ( ≈ 0.15–3 mm), and/or Pb (10 or films on glass) Sb, Pt,Au, Pb, Bi (25–1100 5086 H32 and Fused quartz Fe-3 wt% Si alloy Fused quartz (3 mm) Nd:glass, (12.8 zones) 6061-T6 Al alloys (welded Al (25.4 Aluminium Ch03-I044498.tex 12/9/2007 17: 40 Page 108 (1979) [303] (1979) [304] (1983) [232] (1981) [305] ; peak Fairand (1979) [255] 2 W/cm 9 10 multiple shock were greater in 2 × W/cm 9 features, observed phenomena, comments References (surface hardness increased for 40%); results of calculation surroundings processed by annular beamresults as were achieved well; best by simultaneousshocking, two- but sided the use ofnearly momentum the trap same provided results; fatiguehole life was of increased plates up with toprocessing; fractographs 40 and times fracture due propagation toschemes shock presented (Fig. 3.28) LSP resulted in increased surfaceand hardness, fatigue yield strength ofzones homogeneous samples, and weld fastened joint specimens; Fairand treatment (five shocks) was advantageous for AISI 304 of transient temperatures and pressurespresented by – LILA Zn code coating onboth Al temperature target and should pressure; microstructure enhance of photos unshocked/shocked aluminium alloys andpresented steels Pb, or by acoustic impedancesuperposition mismatch techniques and (examples stress-waves provided) 2024-T351, tensile strength of 7075-T73,and 2024-T351, fatigue life offrom 7075-T6; irradiation both of sides samples simultaneously gives better results Peak pressures reached 6 GPa at 4 Laser shocking increased considerably hardness of Clauer One and two-sided (simultaneous and subsequent, Clauer of the table) shock processing compared; hole case of pressures below 10 results achieved on at Batellesee Columbus Fairand Laboratories, and Clauer above Zn target in comparisonthat with pressure Al; on calculations target showed may beconductivity raised by low use heat of of low thermal vapourization coatings like Novel A review (28 pp., 31 ref.) of physics of LSP and of Clauer , also with ‘momentum trap’ (see notations at the end 2 W/cm 2 9 beam 10 22 × W/cm 9 ≈ 40 ns, 10 × also annular beam and Nd:glass, Nd:glass, 30 ns, up to 12 spot 1.1–1.6 mm, 4 20–40 ns, up to black + paint primer acrylic (both 6.4 mm)/metal layers or environment properties ) µ m, Quartz, water Continued ( µ m) 2024 T8, 5086 H32, 6061 T6, Si,Ti- and 7075 T73, 7075 Water, quartz, plastic Nd:glass, transducer), black Krylon paint (8–10 7075-T6, 7075-T73,7075-T651 (0.9–3 mm) water/black paint Processed materials/ Confining/absorbing Lasers and Zn,Al (both 3 2024-T351, 2024-T851, Quartz or 2024-T3 (6,4 mm) Water, quartz, onto quartz pressure vacuum deposited (both 3 mm) targets AISI 304, Fe-3 wt% TiV-alloys T6, 2024 T3, Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 109 (Continued) (1987) (1987) (1984) [306] (1987) [309] (1986) [256] s (1987) [308] µ m ≈ 40% greater Fabbro (1986) [307] µ m; melted layer µ m; no improvement ≈ 1 ≈ 3 kbar; a first-order theory of dependence, consistent with a ≈ 20 kbar;the pressure dependence ≈ 20% greater momentum µ m light provided − ½ t µ m in diameter was formed on the [311] µ m µ m; for confined ablation, the momentum was sealed with mineral oil; movement of the target was all materials shock pressure reached on fluence wasprofile observed of to the be wave hadwhich linear a followed rapid and at rise the ( ≈ 2 ns) temporal and a tail Plasma temperature was 100 000–300 000 K (by Walter Momentum generated by confined andplasma free determined expanding as function of laser fluence for 0.53 Fournier [310] Estimated shock pressures were 0.6–60 Mbar; a spherical Hallouin shock pressure than with 1.06 crater of 140–450 surface of specimen; twin dislocations,and martensitic melted phase, material were found in the process zone; the and sealed with mineralrecorded oil; movement inteferometrically of from the backside; peak targetwere pressures was estimated to reach plasma pressure presented thickness on surface was radiometer measurement); damage was observed in and 1.06 ≈ 100 times larger thanwavelength in provided case of free ablation;than 0.53 1.06 microhardness was enhanced by laser shock of materials properties was observed recorded inteferometrically from backside; estimated Irradiation with 0.53 simple model Targets were confined between two fused silica plates Griffin Targets were confined between two-fused silica plates and Schoen TEM micrographs of dislocations presented Target was shocked by 50 kbar pulses; shock caused Ayrault , dislocations and plastic deformations up to 1%; 2 2 2 2 µ m, W/cm µ m, 14 2 , 2 2 2 10 ≈ 150 ns, µ m, 60 J/cm × µ m, ≈ µ m, 20 ns, µ m, 0.5, 2.5, Wcm YAG, µ m, 31–111 J, 10 1–10 J/cm 1.054 up to spot 0.5 mm Nd: 0.05–1 GW/cm 2.5 kJ/cm Nd:glass, 10 ps, 1.06 and 0,53 10 1.06 Nd:glass, 1,06 Nd:glass, 0.53 and 1.06 Nd-ion, 1.06 and 0.6–3 ns, up to 0.26 and 25 ns, spot 90 0.6–32 25 GW/cm 2.8 and 3 ns, spot 1 cm Air? Transparent µ m Fused silica µ m Fused silica oxidized foils, also with and graphite/epoxycomposites (1.5 mm) and/or black Krylon paint martensitic) surface) foils) fibreglass/epoxy, overlay Cu (40–250 Carbon steel Kevlar/epoxy, CMSX-2 (single Cu (0.2 and 4 mm) glass Fe (single and perlitic or (0.18–0.9% C, polycrystalline) crystalline [001]) Al, PE (20–250 Ch03-I044498.tex 12/9/2007 17: 40 Page 110 es [312] Ballard Forget (1990) [245] the streak Cottet (1988) [313] 2 2 ) and 5TPa 2 ≈ 1 GW/cm ; surface roughness optical breakdown and impulse Fabbro (1990) [233] > ≈ 1 GW/cm during both has been W/cm 15 10 ≈ 3 times lower in the plasma in laser-shocked half-plane (1988) [314], × calculation the thickness of ; confined ablation provides Cu overlapping shocks ; at intensities over model which permits approximate Phipps 2 ) ≈ 100% 2 upon single-pulse laser intensity,wavelength, W/cm 15 features, observed phenomena, comments Referenc 10 × laser-target scaling solid presented (see section 3.3.6.2);and residual plastically stress affected profile zoneshocked thickness 35CD4 presented alloy; the for simulation laser- (1991) yieldedPAZ twice [265] than deeper observed in the experiment plastically affected zone (PAZ) prediction of the dependence ofmechanical ablation coupling pressure, coefficient, and relatedin parameters vacuum and pulse width over broadof ranges corresponding is Los presented; Alamos the experiments results (1988) are reported residual surface stresses were middle of the shocked areadrop (Fig was avoided 3.22); central by stress momentum were measured for different conditions at was practically unaffected by lasermodel shocks; for a residual 2D stresses explaining analytical drop also is the presented central stress target (vacuum, air, confined) at0.03–100 light GW/cm intensities camera; comparison with numerical simulationsSHYLAC2 code by showed that thepressures laser were ablation 2.5TPa peak (0.3 absorbance reaches 4–10 times larger plasmaablation; pressure the than pressures free-surface are limitedof by confining media; a 1D- analyticalof model plasma for layer calculation thickness anddeveloped (see pressure Section 3.3.6.1), heatingadiabatic and cooling subsequent are dealt separately;with the exp. theory results accords at light intensities (1 Combustion turbine blade materialsprocessed; (Ni-based) spot diameter mostly 8patterns mm; diffraction observed on shocked surface; shock-induced Novel A A 1D-analytical model for Absorption of laser light by 15 µ m Movement of the rear side of foils was recorded by 10 2 2 × µ m, µ m, ≈ 0 . 3 W/cm beam 15 10 ≈ 800 GW/cm × µ m, 25 ns ≈ 6 mm 260 nm, 0.5 ns, spot 50 (half-energy), 3 and 30 ns 1.06 and 0.53 Nd:glass, 1.06 spot (90% of energy), and 1 up to 0.6–40 ns Nd:YAG, 1.06 µ m) with vacuum grease 0.6, 3, and 30 ns, sealant ( ≈ 10 layers or environment properties Vacuum ) µ m) µ m), µ m), Continued ( µ m to 10 mm), BK7 glass (6 mm) µ m foil) steel Cu (foil 26 Processed materials/ Confining/absorbing Lasers and 35CD4 stainless Cu (20 CMSX-2,AM1 Water/black (both single crystalline), paint (polycrystalline) targets Al (foil 26.5 Al (5 Au (foil 25.5 Astroloy Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 111 (Continued) (1991) (1990) (1990) [316] ´s(1990) [215] [265] Hallouin (1991) – (20 min 0.1 for ≈ ) was ∼ 40 GPa [318] 2 α 0.01 for 3 ns pulses ( α ≈ ∼ 400 kg/mm α presented; repeated shocks [247] 2 compared with shot peening α -phase embryos were found cycles) 380 and 587 MPa, respectively 6 10 ∼ 20 GPa (25 ns) respectively presented in Ballard (1988) [314] is laid out Ballard (1991) × µ m, containing reverted austenite phase theory ≈ 50 fraction of incident laserand energy transformed absorbed by into the shock plasma and energy); calculated velocity pressure transients presented forby Al glass foils confined and increased dislocation density (according to was residual stresses) were 0.05 andSP, respectively,the 0.25 mm residual for stresses LSP inand and weldments 893 – MPa, and 416 thesamples fatigue (2 strength of welded increase the plastically affected depththe but surface decrease stress (1–6increased laser fatigue pulses); laser strength peening 40% and did not 15–40 ns laser pulses and on laser pulse length; twinincreasing density shock increased pressure with (histograms forsystems 1–4 presented); twin in material shocked by 25 GPa pulses strength (17%) of weldments; plastically affected depth with chopped steel fibres of 0.5 mm diameter and of Bana Maximum microhardness ( the modified depth (raised hardness and compressive Reports about an 1D-codeplasma and pressure results and of velocity calculation offoils; of the confined simulation laser-shocked code isequation based and on elastic–plastic Romain Mie-Grüneisen behaviour offit materials; [317] with best experiment was achieved using affect the surface roughness in more detail; measured residual stresses and (0.6 and 2.5 ns); the maximum hardness depended little achieved at LSP results have been 1.5 mm length in a 0.54 MPa air, 100% coverage) results; Shock processing increased the hardness and fatigue Bana´s Residual stress distribution vs. depthdensities for 1–70 irradiance GW/cm power Fournier plastically affected zone depthwith agreed the fairly calculations TEM studies) The 2 2 2 µ m, µ m, , µ m, 2 2 W/cm 10 W/cm ≈ 0.1 mm, ≈ 0.1 mm, 12 –10 8 scanning with shot overlapping spot scanned beam (Gaussian or asymmetrical), spot 8 mm, up to 70 GW/cm up to 55 Gpa 10 spot ∼ 10 150 ps, 8 Hz, 100 ps, 20 mJ, 8 Hz, Nd:glass, 1.06 30 ns, 8–10 GW/cm Nd:glass, 0.6, 2.5 and 25 ns, spot 1 and 4 mm, 0.1–5TW/cm 2.5, 3, 25 and 30 ns ( ≈ 0.1 mm) black paint Glass black paint No/black paint black paint water (2 mm)/ Water ( ≈ 3.5 mm)/ 1.06 Nd:YAG, Water ( ≈ 3.5 mm)/ 1.06 Nd:YAG, Water µ m) HRC steel (4.15 mm), alsoweld zones ( ≈ 0.1 mm) maraging steel 18 Ni(250) 18 Ni(250) 35CD4, XC38 Glass or 35CD4 50 304 steel maraging steel 10–300 Al (foils Ch03-I044498.tex 12/9/2007 17: 40 Page 112 es (1994) [327] (1993) [326] Clauer (1991), (1992) [321, 322], [324] (1992) [320] Vaccari (1992) [323] ), the 2 (1–2 GPa, Gerland (1992) [325] ), − 1 stacking faults [319], Puig s ∼ 4 GPa; shearing Décamps (1991) − 3 residual stresses in both cases 10 laser energy density the µ m) was observed 2 × ≈ 150 close to the back face of Grevey (1992) ), then remained rather constant 2 appears to be the main limiting (period nearly sinusoidal depth distribution ∼ 300 HV in both cases, the surface hardness compared with explosive shock treatment features, observed phenomena, comments Referenc µ s); the formed microstructures and hardness profiles Data about residual stress distribution, fatigue life and surface hardness of laser-shocked the sample observed, obviously induced by the samples presented Measurements of the pressure inducedperformed; by for the 1–10 GW/cm plasma Devaux Martensitic transformation expansion wave generated at wave reflection from were stable during(constant plastic a strain rate whole 2 cycling of a plastic fatigue test were quite similar; surface mirohardness180 was HV raised to from of LP processed samples wasbut somewhat the higher hardness (345 decrease HV) wasexplosively treated more material; faster the than in measured pressure agrees particularly wellanalytical with model; at an high-power densities (10W/cm propagation was simulated by EFHYDphysical code model – used the in EFHYDin code detail is explained the back face; of residual stresses contrary to SP processed material dielectric breakdown process of the confining method;the for breakdown threshold shorter was laser higher; short-rise-time pulses pulse laser provided greater peak pressure than Gaussian pulse LP was 1 Surface hardness increased with peak shock pressure up Gerland were observed in the shocked zone; the shock to 25 GPa (0.5TW/cm Measured peak shock pressure was Novel 2 µ m, µ m, and , beam 2 2 11 ≈ 20 ns, µ m, µ m, 1 ns, W/cm 13 spot 5–10 mm 4 kJ, spot 4.3 and 25 mm, 10 Nd:glass, 1.06 3 and 30 ns 1.06 0.53 10 18 GPa (Gaussian and short-rise pulses), 20–30 ns, 60 J, spot 4, configurations involving superlattice spot 5–6 mm 0.6 ns, 80 J, spot 7.2 mm, Nd:glass, 1.06 Nd:glass, 0.6 ns, 5 and 8 mm, 0.3TW/cm spot 3–6 mm, 0.5–9.5 GW/cm paint No/black Glass (5 mm)/ No/black Sellotape paint layers or environment properties ) µ m Water (2–3 mm), < 001 > Continued ( -precipitates, Al foil or  µ m layer quartz (6 mm) γ and 5456 Al alloys; blackalloy,30% paint Ni), 1026 and 4340 steels 2-mm thick sample and 1 Processed materials/ Confining/absorbing Lasers and 7075-T6, 2024-T3, Mostly water/ Fe–Ni alloy (TRIP Vacuum 304 austenitic on quartz) 4 mm) with steel (foil) targets AISI 316L Al (foil 25–150 Waspaloy (SC Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 113 [328] (Continued) Chu (1995) [331] Forget (1995) [329] [330] Virmoux (1996) combined ε -hcp C); ◦ ≈ 1 mm (3 passes) F20-23A/F23-27A, hexagonal ε (35 vol%) and caused ), then decreased at higher 2 formation of martensite embryos were only present in the were present at any shock pressure, the treatment was found to be beneficial; the α -phase twins (17 pp., 22 ref.) of techniques, theory and Peyre (1995) [230] LSP cycles) in cryogenic conditions ( − 195 7 + review experimental results are compared withnumerical analytical (SHYLAC and 1D) models predictions Residual stress and hardness profiles, and fatigue resistance Peyre (1995) were determined for both laser shocked and shot peened pressures; number of twin sets increased withthen pressure decreased, up but to the 25 GPa, decreased; mean twin spacing continuously pressure range 15–25 GPa; histogramsof of twin the density dependence onpresented twin spacing for 1–4 twin systems are applications of laser shock treatment of materials up to a 130%strengthening increase effect of was attributed surface to the hardness; combined theof effects LSP the partial dislocation/stackinggrain fault refinement arrays due and to the the presence of the SP close-packed (hcp) martensite; a comparison with shotpresented; SEM/TEM peening micrographs is of materials structure (11 photos) are presented and discussed coverage rate 125%) samples;greater LSP improvement of was fatigue found limit to than provide SP; Superficial micro-roughness of laser-shocked samples studied; variation of deformations withfrom distance centre of the spotpropagation is and explained formation by of release residual wave stresses LSP caused extensive (see also Fabbro (1998) [250]) nearly 50% increase in thecontact maximum force sustainable (from 8 toof 11.5 oxidation GPa) was and achieved; surface hugesamples hardness reduction was of enhanced shocked up to a depth of LSP processed samples were fatigue-contact(10 tested A , up to 55 GPa (1.5TW/cm 2 2 2 µ m, , overlap 2 − 2 W/cm ∼ 25 ns, 12 1–7 GW/cm (square and circular), (0.6 mm steel beads,Almen intensity to 16.9 GW/cm Nd:glass, ≈ 8 GW/cm Nd:glass, 1.054 0.6 ns, 100 J, spot 3–3.5 mm, 2.4 × 10 spot 0.5–1 mm 15–60 GPa 66%, 1–3 passes 0.25–1.62TW/cm µ m) foil (0.1 mm) (40–50 self-adhesive Water/black adhesive tape 17–40 ns, spot 8 mm, up Water/Al Vacuum/black paint [111] and [110]), Inconel 718 7075-T7351 Z100CD17 (martensitic) Hadfield manganese steel (1%C-14%Mn, 3.3 mm) AM1 (SC, [001], Ch03-I044498.tex 12/9/2007 17: 40 Page 114 es Mukai (1995) [332] Peyre (1996) [333] Peyre (1996) [190] Masse (1995) [246] µ m; ∼ 7700 m/s 1–2 mm ∼ 10 ns; plasma expansion + 10% of the initial value, ∼ 1500 m/s, in air µ m; high-speed photographs cycle tests) of lasershocked 7 range could provide at least as beneficial features, observed phenomena, comments Referenc µ m; the peened sample’s surface was oxidized It was demonstrated that LSPspot-size with surface effects as larger0.8 ones mm but in limited depth to whereasmore about large than impacts 1.2 mm affected atsimulation the by same SHYLAC power demonstrated densities; thatshock the wave from small impactsbecause decayed of earlier spherical attenuation specimen exceeded these ofreview shot of peened; a LSP theory withtheses reference of to Ballard the (1991) [264](1993) and [266] Dubouchet is included Laser shock-induced residual compressive stressextended field to depth more thanhardening was 1 mm, limited surface to half of the increase achievableSP by ( + 22%); conventional in contrast tonot SP, affect laser the shocking surface did fatigue roughness of life the (10 materials; beam, coverage 500–8000%; surface compressive residual stresses of 200–400 MPathe were depth built of up; compressive residual200 stresses was over down to a depth of 3 of plasma radiation inin air water and the in plasma water lasted presentedvelocity – in water was Residual compressive stresses down to1.1 depth mm of exceeding up toformed; –350 shocked MPa surface on depression surface was were up to 7 the surface hardness was notstress modified; drop the was central present inbut case was of absent circular in laser case spot, of square spot Novel The specimen were laser peened using scanned , 2 µ m, µ m, µ m, 25 ns, , ;upto 2 2 2 beam Nd:glass, 1.06 20–25 ns, spot 1–2 mm, 1 shot every 1.5 min four impacts (square, ellipse or circle, up to 67% overlapping) 15–75TW/m 25% overlap Nd:glass, 1.06 Nd:glass, 1.06 Cu-vapour (511 nm) and Nd:YAG (532 nm), 5–50 ns, spot 0.2–1.1 mm, 75–375 J/cm 25 ns (Gaussian), spot 5–12 mm, 1–8 GW/cm spot 5 mm (circle and square), 1.7–10 GW/cm µ m) (specimen were immersed into water) paint (100 layers or environment properties Air and water Water (2–5 mm) Water or glass Water (3–5 mm)/ ) Continued ( 7075-T7351 (Al alloys) 0.55% C steel Processed materials/ Confining/absorbing Lasers and SUS304 (austenitic, 20 mm) 55C1 steel targets A356-T6,Al12Si-T6, Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 115 (Continued) Peyre (1996) [267] Berthe (1996) [334], (1997) [335] Sano (1996) [337] Sano (1997), (1998) [242, 339] Romain (1997) [338] Konagai (1996) [336] 2 reviewed ; residual 2 ≈ 7500 m/s in air; ≈ 10 GW/cm µ m laser in Ar atmosphere sample was µ m was observed; the physical ; a 50% increase of surface stresses 2 µ m in depth; in case of ∼ 500 ≈ 1500 m/s in water and ) of the target with theory; as confirmed 2 − 420 MPa) and a suppression of the tensile ≈ 2.5 GPa by high-speed photography of plasmapressure radiation, saturates the at light intensities Relatively large pulse frequencies werein used large resulting shot coverage factorspower densities of ranged 500–8000%; peak 15–75TW/cm shocked by Nd:glass laser ( − 280 to peak at depth of processes and analytical modelling of LSP are 20% of the plasmainto energy thermal was energy; estimated and to plasma pressure bethe to converted measured exceed values 2 GPa; were compared with calculated ones Shock pressure dependence on laserdetermined fluence by comparison the measured by 2 GW/cm due to optical breakdown atdue the to water the surface; breakdown, thetarget laser shortens; pulse numerical length simulations at ofvelocity target by SHYLAC are comparedmeasurements withVISAR Compressive residual stresses over 100by MPa laser were shocking created Experimental, numerical, and analytical studythe results acceleration of and decelerationfoils process presented; of peak thin velocities reached metallic 650 m/spressures and shock Compressive residual stresses over 200 MPaby were laser created shocking; plasma radiationand photographs 25 ns at in 5, 15, airvelocity and was in water presented; plasma expansion compressive stresses exceeding 400 MPadeveloped were over 100 60 ns, 4 kHz laser irradiation,surface a layer 10 exhibited tensile stresses Quenched by 5 kW CO VISAR rear side velocity (exceeds 250 m/s at 2 2 2 ≈ 20 ns, µ m, 20 ns, µ m, W/m 2 14 2 , 50TW/m 2 N:A,532-Nd:YAG, nm, spot-Nd:YAG, 0.75 mm, 532 nm,-Nd:YAG, 5 ns, Nd:glass, 1.064 Nd:glass, 1.06 ≈ 4 GW/cm Nd:glass, 10 2 ω 5 ns, 10 Hz, spot 0.75 mm Cu-vapour, 511 nm, 60 ns, 4 kHz, spot 0.5 mm 2 ω 230 kJ/m 2 ω spot 0.75 mm, 45TW/m 6GPa ≈ 40 J, spot 3 mm, up28 to GW/cm the foils) Glass/PMn treated surface Water (3–4 mm) Water (on both sides of Water Water µ m µ m foil, optionally supported by BK7 glass plate) foils) 55C1 steel (10 mm) SUS304 SUS304, Inconel 600 Water SUS304 Al (457 Al, Cu (20–120 Ch03-I044498.tex 12/9/2007 17: 40 Page 116 es Clauer (1997) [340] Dubrujeaud (1997) [244] Peyre (1997) (1998) [342, 343] Scherpereel (1997) [341] Peyre (1997) [344] 2 ≈ 20 times occurs while µ m) than for 316L ≈ 50%; HEL µ m Y ≈ 6 GPa) agreed σ in lasershocked work- ∼ 120 GW/cm (1 mm, 25% overlap) 0.1 = max for 7075; 2.3 / σ Y ≈ 2 times greater (1,3 min σ of principles of LSP and its applications waves propagation small impacts σ = was (1.2 surface depression about 6 R review (13 pp., 11 figs.) of LSP with accent to (10 pp., 8 figs., 10 refs.) of LSP physics and features, observed phenomena, comments Referenc ≈ 30% at review laser shocked greater than that of(55C1 untreated material steel); fatigue life offor 55C1 was improved in case of 6 mm impacts (50% overlap) and Plane and surface piece and their interactionalso is a discussed short in detail; contains Evolution of plastically affected depth, surface hardness, residual stresses withlaser the shots number (up of topresented; 12 laser shots, impacts 316L overlapping steel) ofprovided 66% even distribution of residual(Z12 stresses steel); corrosion properties ofwere Z12 advantageously steel modified in courseLSP: free of potentials were shiftedvalues to and anodic passive current densitieswhen reduces; the pressure pulse lengthbreakdown in was 0.6 water ns, occurred the at behind foil targets (upwell to with 500 m/s SHYLAC-simulations; paint/adhesive at layers enhanced the shock pressure for of materials was determinedinflection from point BFV at elastic-plastic applications (shock pressure, residual stresses, andlife); comparison fatigue of maximum residualdifferent stress materials achieved presented in (Fig. 3.25) residual stress distribution and fatiguealloys a properties; in slight soft the achieved residual stresses weresurface higher, but waviness and 55C1); using Novel A A review VISAR-measurements of back free velocities (BFV) , spot 2 µ m, ,upto beam 2 Up to 8.5 GW/cm 12 shots sizes 1 and 6 mm Nd:glass, 1.06 2.3 and 20 ns, spot 6 mm, up to 40 GW/cm µ m) metallic paint or foil adhesive (90–140 layers or environment properties Water or glass/ Water/Al-based paint or ) Continued ( µ m foil), µ m and µ m), 55C1 (austenitic), Z12 CNDV 12.02 (martensitic) 500 (360 notched samples), 7075-T7351 (1.6 mm) Processed materials/ Confining/absorbing Lasers and targets AISI 316L Al (200 AISI 316L (200 and Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 117 (Continued) Peyre (1998) [239] Peyre (1998) [349] Dane (1998) [347, 348] Berthe (1997) (1998) [345, 346] Tollier (1998) [241] / + , 2 min σ ; the = 2 of LSP ; the 2 review ≈ 6 GW/cm , kept the pitting 2 A/cm µ , the power density transmitted /s; simulation of attenuation of shock 2 at the water surface was investigated /s; some 50–100% increases could be ): LSP reduced the passive current − 3 6 4 SO 2 0.1) than 7 mm impacts; for 12% Cr steel, = max 10 mM Na corrosion tests were performed (10 mM NaCl waves in depth matched wellsteel with but experiments not for for 316 X12CrNiMo12-2-2;316 L it L was that shown shock on decaysexhibiting could a be large reduced work-hardening on levelshot-peened materials such surfaces as found between dynamic yield strengthsflow and limits static at plastic 10 by the plasma is limited to 10 GW/cm potential almost constant, and preventedinitiations anticipated of pits orthe inclusions article at lower also potentials; includes a concise mechanisms, experimental techniques and applications Optical breakdown by transient transmission of atransmission probe cut-off beam occurred (514 at nm): Laser shock-induced residual stress profilesand for dual single impacts are presented;operation construction principles and of theNd:glass LLNL laser new are 100 J, laid 6 Hz out in detail For 55C1 steel, small impacts30% (1 greater mm) fatigue provided limit (490 MPa at R Precise data concerning theinduced pressure loading by pulsed laser irradiationface at of the a front solidlaser material intensity were range obtained of in 10– the 500 GW/cm laser pulse transmitted by theapproximately to plasma the corresponds part ofpulse the preceding incident the laser transmission cut-off σ pressure amplitudes determined inincident function laser of intensity,reached 60 kbar above 10 GW/cm Stress loadings close to 7surface GPa, 20 of ns the were targets;VISAR-measurements createdfor were at used determination the of shockestimation, wave through decay the and determination for ofprecursors, elastic the dynamic yield strengthsapproaching at 10 strain rates density from 1.2 to 0.5 2 2 µ m, µ m, 2 µ m, W/cm , coverage 2 2 11 –5 × 10 10 Nd:glass, 1.06 25 ns, spot 1–3 mm, 10 Nd:glass, 1.064 30 ns, 200 J/cm 0.6, 2.3, and 10–25 ns; spot 1 and 7 mm;40 up GW/cm to Nd:glass, 1.064 8–10 ns, spot 3–4 mm, 10 GW/cm rate up to 300% 25–30 ns, spot 3–4 mm, up to 25 GW/cm µ m) µ m) µ m) µ m) Not specified or Al adhesive (100 or Al adhesive (70 Air? Al paint (70 Water Water/Al paint (140 Water (3–4 mm)/ µ m µ m), foils) (50 and 250 (Inconnel) Metal plate 316L (200 55C1, 12%Cr (martensitic) X12CrNiMo12-2-2 (martensitic, 0.2–1.29 mm); 316L (austenitic, 0.2–1.25 mm) Al,Ta, Cu, Mo Ti-6Al-4V Ch03-I044498.tex 12/9/2007 17: 40 Page 118 Zhang (1999) [252] Peyre (1998) [243] Berthe (1999) [351] Fabbro (1998) [250] Berthe (1998) [350] Sano (1998) [339] ≈ 6 times µ m per of ; (15 pp., 33 figs., ≈ 50%; µ m; dislocation comparison review µ m deep dip was provides greater peak and its absorption near 80%; 2 µ mto0.1 6.3 provides somewhat greater a R features, observed phenomena, comments References 0.1, 13 Hz); surface roughness = lowered from density increased and 110 formed onto surface surface hardness of laser shockremained peened lower surfaces than ofLSP shot increased peened the surfaces corrosion resistance of X12CrNiMo12-2-2 steel; results with other steels andNi-alloys Al is and provided graphically Shorter laser pulse duration plasma pressures (up to 9.5shorter GPa wavelength at 0.6 ns); pressure, but water breakdown occurslower at laser intensities;Al-based protective coating enhances plasma pressure the thickness of ablated matter was about 2 52 refs.) of LSP Experimental investigations of LSP physics:of on laser part pulse lengthpeak and plasma wavelength dependence pressure, see of Ref.breakdown, see [243]; on Ref.[345] part and of Ref. water [346]. In addition to thethis results presented article in presents Sano the (1992)(2D results [242], of cylindrical FEM-simulation coordinates) ofpropagation shock and wave residual stresses 2 mm diameter hole areasides was separately; shock as treated a from resultthe both of fatigue laser life shock of treatment ( R the sample was enhanced for Laser beam interaction withhas water in been typical investigated experimentally LSP by regime reflected recording laser light and waterradiation; the breakdown plasma threshold of generationplasma of was confined 5 GW/cm Novel A comprehensive up to date 2 2 µ m, µ m, µ m, beam 2 ≈ 50 GW/cm µ m, 3 ns, Nd:glass, 1.06 0.6–20 ns 1.06 Nd:YAG, 6–7 ns, 10 Hz XeCl, 308 nm, 40 ns, 5 Hz 1.064 up to dYG 532Nd:YAG, nm, 5 ns, 100 mJ, spot 0.75 mm, 230 kJ/m Nd:glass, 1.06 30 ns, spot 7 mm, 0.7–1.75 GW/cm µ m, optionally) (70–130 into water) Glass (4.5 mm)/ black paint (0.1 mm) layers or environment properties Water Water/Al-based coating Water (sample immersed ) Continued ( Processed materials/ Confining/absorbingX12CrNiMo12-2-2 Lasers and SUS 304 2024-T62 (2.5 mm) targets Al Al, 316L, 55C1, Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 119 (Continued) Chu (1999) [354] Brar (2000) [355] Berthe (1999) [258] Ruschau (1999) [353] Braisted (1999) [270] Peyre (1999) [352] µ m ≈ 1.5 corrosion , and the 3 of laser shock /cm shorter wavelengths + 100 mV were 22 10 ≈ 30% larger peak × µ m; surface hardness ≈ 100 ≈ 6 corresponding to ; the estimated (by comparison with 2 numeric simulation was obtained in NaCl 0.05 M; anodic ≈ 80%; comparison with shot peening 1 GPa; the laser shock amplitude decays to ± increased is presented about 2.7 GPa while propagatingdisk through of 3-mm titanium thick 6-4. and resulted in extensive formationmodified of depth dislocations; was Laser shock stress amplitudes ontargets the were monitored back withVISAR of the the using window LiF material; as the peakin shock LiF stress (titanium produced thickness16 zero) was measured to be simulations by ACCIC) temperature of≈ 1 plasma eV, electronic was density 2 pressures, but water surface breakdownwere thresholds lower; it was concludedare that advantageous for LSP pulse at 23 GW/m Comparison of laser wavelength dependenceplasma of peak pressure and pressureshorter pulse wavelengths duration; provided LSP caused the surface to be recessed for laser shock processed from bothresults sides of simultaneously; fatigue crackinvestigations growth are rate presented and fractographic 2D-axisymmetric propagation and residual stresses usingsoftware; pressure ABAQUS pulse was assumedtriangular to (for be Ti-6Al-4V) whether or Gaussianthe (for model 35CD4); realistically predicted thedistribution, thereby residual the stress central stress drop Despite no chemical changessurface at the were detected lasershocked (SIMS, EPMA),improvement a shifts on pitting potentialsobserved nearly after treatment, together withrepassivating increases potentials of during cathodic polarizations coupling parameter strongly coupled plasma The narrower edge of the sample (0.75-mm thick) was 2 µ m, 2 , 3 and 2 W/cm µ m, 25–30 ns, 12 10 × Nd:glass, 1,064, 0.532 and 0.355 spot 1–3 mm, 1–20 GW/cm 3 and 10 ns, spot 12–13 mm, 6 and 20 GW/cm overlap 30% Nd:glass, 1.054 20 ns, 50 J 0.6 ns, 120 J, spot 3 mm, 2.4 50 ns, spot 8 mm. 2.8–5 GPa 7 impacts µ m) µ m) (40 or 80 black paint paint (40–50 Water Water/Al adhesive Water curtain/paint Spot 5.6 mm, Water (flowing)/ Vacuum/black µ m foils, with open backside of on 5 mm BK7 glass) geometry sample) (0.1–3.05 mm, glued to 6.35 mm LiF) SAE1010 (ferritic, 1.3 mm) Al (150–200 AISI 316L Ti-6Al-4V (airfoil Ti-6Al-4V,35CD4 Ti-6-4 Ch03-I044498.tex 12/9/2007 17: 40 Page 120 es Berthe (2000) [257] Fabbro (2000) [356] Sano (2000) [277; 278] Obata (2000) [357] Sano (2000) [277] ∼ 40% µ m ); at fixed spot size 2 µ m (3 ns squared pulse, ≈ 1 mm; corrosion tests performed (water, 8 ppm, 500 h,), LSP totally inhibited the ∼ 1 mm; numerical simulation 2 (10 pp., 14 figs., 24 refs.) of achievements ∼ 200 mJ laser pulse; cold working rate had features, observed phenomena, comments Referenc review in LSP during 1995–1999: influenceintensity,wavelength of and laser pulse length oneffect LSP, of different protective coatings,breakdown optical in water, effect ofresidual LSP stresses, on fatigue, and materials corrosion properties stress corrosion cracking; FEM-simulation results (2D cylindrical coordinates) ofpropagation shock and wave residual stresses presented;for a in system situ processing ofshrouds in nuclear reactor water core is described greater in the laserthe beam transverse scanning direction; direction surface than residual in maximum stress value had at a spot sizeenergy 0.8 200 mm mJ, 3600 (constant pulses/cm pulse Surface tensile stresses converted toto compressive depth up of 561 K, O Residual surface compressive stresses were Laser beam interaction withregime water in has typical been LSP- investigated experimentallyrecording reflected by laser light andplasma water radiation; depending breakdown on laserthe pulse absorption duration, of thethe confined ablated plasma thickness was was 80–90%; 1.1 0.8 mm the surface residualvalue stresses at had a minimum little influence on thesurface residual stresses; was the oxidized material’s up to a depth of 1.2 Laser peening was applied inneutron irradiation order to hardening; shocking simulate with multiple laser pulses extends thedepth stress-improved to (3D axisymmetric and spherical)propagation results and of residual shock stresses areagreement presented; with the the experiments was reasonable Novel A 2 2 µ m, 3 and 2 beam Nd:glass, 1.064 dYG 532Nd:YAG, nm, 8 ns, 200 mJ, spot 0.8 mm, 36 impacts/mm 532Nd:YAG, nm, 8 ns, 10 Hz, 100–300 mJ, spot 0.4–1.2 mm, 1800–5400 impacts/cm 532Nd:YAG, nm, 8 ns, 10 Hz, 200 mJ, spot 0.8 mm, coverage 1800% 15 ns, spot 5–6 mm, 1–50 GW/cm into water) layers or environment properties Water Water (sample immersed Water/no Water/no ) Continued ( Processed materials/ Confining/absorbing Lasers and SUS 304 (20% cold worked, 10 mm) SUS 304 (0–30% cold worked) SUS 304 (20% cold worked, 10 mm) targets Al (polished) Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 121 (Continued) Peyre (2000) [237] Peyre (2000) [359] Berthe (2000) [358] Peyre (2000) [360] ; 2 , was 2 α , corrosion 2 0.25) ≈ µ m, providing α > 1–2 GW/cm C solution ◦ (0.6–10 ns) µ m, 2 , degree of ionization 0.39– 3 surface layer was contaminated -0.3 M solution; only in as shock wave sensors were 4 /cm µ m in depth; corrosion tests µ m (15 ns Gaussian pulse, 44%, 153 21 2 and this of PVDF gauge 10 ∼ 9.5 GPa maximum pressure, 2 × ∼− 500 MPa (6 GW/cm ; both 0.6 and 3.2 ns laser pulses 2 ∼ 60–100 J/cm ) and 0.75 2 ); plasma parameters were estimated with aid 2 µ m independent on laser pulse length ∼ 10 25% more intense plastification ofmaximum the remanent surface target; deformationwas of Al12Si the case of G41400of martensitic the steel corrosion was a current reduction degree observed, depending of on work the hardening andcompressive stresses; the laser amplitude shocking of of AISIsuppressed extensively 316L stress corrosion cracking during 24 h in MgCl of an updated theoryparticles as follows: 3.4–4.6 density range of heavy 1 GW/cm provided the same limited by water breakdown; waterthreshold breakdown was 0–160 GW/cm 1.3, temperature 1.7–4.0 eV; couplingfined parameter plasmas of 0.2–1 con- depending sublinearly on laser pulseoptimum Al duration; overlay thickness was 12 20 GW/cm Peak pressures up to 2.5by GPa optical were breakdown generated, limited in water at Structural changes in materialthose are induced compared by with shot peeningpresented); surface (microphographs residual stress ofmaterial laser reaches shocked EMV and PVDF gauges compared; the operation range ofwas EMV 0–20 GW/cm gauge the plasma thermal toestimated internal to energy equal ratio 0.4 (at 1.06 Laser-shocked G10380 and G41400 were tested in an acid HKSO 12 impacts) and hardness 250 HV (8 GW/cm 6 impacts); laser-shocked by C, O, and H forin 0.4 NaCl (30 g/l) showedcorrosion an behaviour improvement of of both shotshock peened processed samples and laser 2 4 mm, 2 2 µ m, × µ m, 50 and 2 µ m, µ m,10 ns Gaussian,up to µ m, 3 ns, 0.2 ns rise time, 1.06 0.6 ns (Gaussian) or 3.2 ns (rise time 0.2 ns), spot 6–10 mm, 0–200 GW/cm XeCl, 0,308 150 ns, spot 1 0.1–6 GW/cm 1.06 Nd:YAG, 10–20 ns, up to 30 J, spot 6–7 mm, 1 shot/min 1.06 GW/cm 1.06 up to 20 GW/cm µ m) µ m) (12–60 (0.1 mm) flowing)/Al adhesive (100 Water (2–5 mm)/Al paint Water Water/Al based coating Water (2–5 mm, µ m), µ m),Al12Si µ m foils) 1000 8 mm), G10380 (ferritic, 8 mm), G41400 (martensitic, 8 mm) 13 mm 316L (75 Al (200, 457 and AISI 316L (austenitic, AISI 316L (austenitic, Al (50 and 100 Ch03-I044498.tex 12/9/2007 17: 40 Page 122 es [364] Zhang (2000) [275] Montross (2000) Hammersley (2000) [191] Schmidt–Uhlig (2000), (2001) [361, 362] Tang (2000) [363] 3mm , 2 + 4% µ m below (core diameter ∼ 30 both shot µ m diameter /4.2 GW/cm ∼− 30 MPa; fracture sur- 2 ∼ 30%, and surface ; procedure of ∼ 100–200 ; ) − 700 MPa, peak 2 0.1), hardness + 10% and in hardness from = R (11 pp., 7 figs., 7 refs.) of features, observed phenomena, comments Referenc light was fed through silica fibre − 5% to + 76%; measured hardness and elastic modulus review face micrographs are presented residual compressive stress was the surface, irradiation 21 J/cm Laser shocking increased the hardness down to 10 000 pulses/cm peening and laser shockcalibration peening of shot peening machines using techniques and performances areachievements compared; in high-power pulsed lasers development at LLNL are overviewed caused plastic deformation ofvariables the as sample; process shock pressure andbeen plastic calculated strain in have cylindrical(3D-simulation) coordinates by ABAQUS software, using Steinberg constitutive model taking into (account pressure effects but not strain rate effects) tensile test, increased in thezone; overaged the metal changes in in elasticfrom the modulus were HAZ andto weld profiles are presented Microscale LSP studies Laser 1.5 mm, length 5 m); tensile(up near-surface to stresses 400 MPa) werestresses converted (down to to compressive Novel A ‘Almen strips’ is described; laser and shot peening , in depth; the elastic modulus of material was 2 2 2 µ m, dents on laser-shocked surface proved that shocking µ m, 30 ns, As result of LSP, the fatigue life of the specimen beam ∼ 12 2 ∼ 40 ns, 1.8 and 2.75 mm, decreased in the bulk peak-aged material, but ∼ N:A,355-Nd:YAG, nm, N:A,532-Nd:YAG, nm, 2.5 and 5 GW/cm 4 GW/cm spot 8.1–20.2 J, spot 7 mm,0.7–1.75 GW/cm increased by 2.2–8.7 times (different specimen, 6–8 J, 100 and 200 J/cm 2 ω 5 ns, 10 Hz, 100 mJ, spot 0.6–0.7 mm µ m) µ m) and vacuum 50 ns, spot grease ( ∼ 10 (16 K9 glass/black paint Nd:glass, 1,06 layers or environment properties Water (3 mm)/Al foil 3 ω Water (flowing) ) Continued ( µ m foil) and 5356) (70 cold-worked, 10 mm) (2.5 mm) Processed materials/ Confining/absorbing Lasers and 2024-T62 6061-T6 (6 mm, Water (1–3 mm)/black 1064 nm, welded by 5083 paint targets Al 1100 AISI304 (20% Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 123 (Continued) Peyre (2001) [368] Montross (2001) [367] Clauer (2001) [365] Sollier (2001) [260] Fukumoto (2001) [366] 100 mV + method; (3.5 GPa) increased 2 was investigated; − pitting )on corrosion 2 Cl was investigated theoretically + 220 mV in case of laser surface + molecular dynamics (6 GPa) increased the surface 2 (22 pp., 23 figs., 36 refs.) of LSP, transmission of breakdown plasma in water review melting; it was assumed thatcompressive LP-induced stresses promote the growthof kinetics the passive film (dualcomposition) oxide thus and reducing hydroxide the sensitivityLP to without pitting; protective coating resultedshift in in cathodic pitting potential hardness to a value greaterwith than one that or achieved five repetitionswaves and with five 3.5 GPa repetitions shock atincreased 6 the GPa significantly surface hardness andproperty shock modification wave depth over oneat repetition 6 GPa the hardness at the surfacea depth from 1.19 of to 1.75 mm, 1.34significantly and GPa change 5 to the repetitions surface didshock hardness not wave or property depth modification; of aof single 5 impact GW/cm includes a description ofat processing LSP equipment Technologies, Inc. during LSP experiments for laser wavelengths from 355pulse to length 1064 of nm 25 and ns;process at was 1064 found nm to the be breakdown ionization, but dominated at by 355 avalanche andmultiphoton 532 ionization nm by Impact of an intensewas laser simulated pulse by on Al target ablation, shock wave formation anddislocations stress generation and has beenon simulated ps-timescale Influence of LP and954 laser nm, surface 1 kW,25 melting kW/cm (CW, anodic shifts of pittingin potentials case were of LP and resistance in 50 mM Na A A single impact of 2.5 GW/cm The 2 , spot 1.8 2 ,3or 2 , 16 impacts ∼ 40 ns, 100 2 2 µ m, N:A,266-Nd:YAG, nm, 2.5 ns, 80 J, spot 13 mm, 25 GW/cm 4 ω 1.5 and ps, spotand 27.8 nm, 200 GW/cm 100 1.064 and 200 J/cm 5 impacts 7 ns, 0.2 J, spot 0.8 mm, 4 GW/cm and 2.75 mm, 2.5 and 5 GW/cm µ m, in case of 2.5 nsbare pulses) surface or (7 ns pulses) 1–3 mm)/black paint Water/Al adhesive (50 400 atomic layers 6061-T6 (6 mm) Water (curtain Al single crystal (111), AISI 316L Ch03-I044498.tex 12/9/2007 17: 40 Page 124 Zhang (2001) [373, 374] Kaspar (2001) [369] Zhang (2001), [371, 372] Yang (2001) [370] ∼ 2–6 times, were used for 100 MPa; crack length vs. λ , and Poisson’s ratio , = 11 C max σ ∼ 10 times 2 features, observed phenomena, comments References 0.1, 10 Hz, = number of cycles diagramsthe are presented; crack due initiation to life LSP, and was increased fatigue life distribution in shocked samples; allconstants these had elastic raised values (12–24%)of at the the laser centre impact; yieldand strength, surface tensile hardness strength increased (13–117%)of as LSP, saturating result at power∼ 1.5 laser GW/cm density determination of Distinct and long-range hardening wasonly observed at LSP withablation nanosecond conditions pulses using under a confined thermoprotective coating; in material modification regime,deformation slip twinning and was observedmetals in investigated; all in the Mo bcc andinduced Fe, the hardening laser-shock was ascribed todensity raised and dislocation not totwins; the the formation defect of density deformation inabout Mo 6 and and Fe 24 saturatedmicrographs impacts, after respectively; of SEM treated and TEM surfaces are presented Specimen with a fasteneror (5 mm) 6 hole crack and stop-holes withfrom (1.5 mm) 2 both were sides; laser fatigue shocked testsR were performed at Microstucture studies by orientation imagingmicroscopy revealed that LSP improveduniformity grain and size increased texture; fatigue(0.8 mm test Cu, axial loadshowed 110–220 a MPa, 80 2 Hz) times fatiguelaser-shocked lifetime samples; results improvement of of numerical simulation of plasma pressure andphenomena stress/strain in the target are presented Both sides of theultrasound sample velocity were shocked measurements successively; Novel , 2 and 2 2 µ m, 2 ∼ 2mm 2 µ m, 2 beam 2 , 260TW/cm 30 ns, 40 J, spot 2 N:A,355-Nd:YAG, nm, Nd:glass, 1.054 3 ω 50 ns, 1 kHz, spot 12 2.83–4.24 GW/cm 7 mm, 0.5–2.3 GW/cm 6 ns, 50 mJ, spot 0.09 mm 9 GW/cm Excimer lasers, 45 and 50 ns, 1–1.5 J, spot 18 ns ( ∼ Gaussian), spot 10 mm, 5 GW/cm ∼ 1 GW/cm Ti-sapphire, 210 fs and µ m) µ m) and vacuum (25 grease ( ∼ 10 layers or environment properties Water (3 mm)/Al foil ) µ m) Continued ( µ m and Processed materials/ Confining/absorbing Lasers and 2024-T3 (2 mm) Water/black paint Cu (90 2024-T62 (2.5 mm) Glass/black coating Nd:glass, 0.8 mm), Ni (120 targets Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 125 (Continued) Montross (2001) [375] Sano (2002) [378] Zhang (2002) [378] [204] Zhang (2002) [380] (2004) [376, 377] Yoshioka (2002) Yakimets (2002), µ J) method ψ µ mwas 2 µ m and of ∼ 1 − 800MPainupto residual stress in laser beam scanning treatment of pipes inner surface ∼− 400 MPa) and of surface hardness µ m were formed into sample’s with negative sign form surface to fluence; as result of LSP, the hardness is described, laser beam being fed ∼ 50 2 µ m in depth Investigation of the effect ofLSP; self-adhesive various Al-foil coatings was on superiorcoatings to in other sense of100 adherence, withstanding J/cm of samples surface increasedelastic by 7.5–15%, module the was reduced for 5–12%; underwater through a gas-filled tube; LSPsimilar experiments conditions on with Alloy 600showed plates the and feasibility pipes of generationcompressive stresses of up surface to 1 mm depth at each location; dents of depth surface; shock propagation and deformationscalculated were by ABAQUS (stress andgraphs strain presented), distribution calculated surface compressive residual stresses were up to 165 MPa (single pulse 240 diameter only; compressive residual stresses were formed500 till direction were lower thanstress in gradient transverse direction; a steep inner part of thegradient specimen was cannot discovered; be this detected by using sin Extended version of the reportdue by to Zhang laser (2001) impact, a [373]; formed crater in of the depth surface 275 calculation of of the laser sample; formulae shockwaves generated for are displacement presented; ultrasonic velocity distributionsand surface micrographs are presented LSP caused an enhancementstresses of (up surface to compressive (from 270 to 350 HV),waviness, an a increase decrease of of the frictionwear surface coefficient rate and (rolling–sliding of contact, 75 MPa) A system for LSP The samples were shocked by up to six laser impacts The LSP-induced , 2 2 2 µ J, , 4 GPa, 2 (3.5 and 2 , 2.5 and 2 µ m, 40 ns, spot N:A,532-Nd:YAG, nm, N:A,355-Nd:YAG, nm, µ m, 160–240 2.83–4.24 GW/cm 5 GW/cm 2 ω 130 mJ, 20–50TW/m 1.064 1.8 mm, 100 and 200 J/cm 532Nd:YAG, nm, 60 and 200 mJ, spot 0.4–1 mm, coverage 1696–10603% 10 ns, 22 J, spot 7 mm, 5.5 GW/cm 3 ω 1 kHz, 50 ns, spot 12 Nd:glass, 30 ns, 30 J, spot 7mm 6GPa) overlap 25% spot 0.7 mm, 18–27 impacts/mm µ m) µ m) µ m) and vacuum automotive primers and black paint (0.1 mm) orfoil Al (0.11 mm) coating (100 (16 grease ( ∼ 10 Water Water/no coating Water (3 mm)/Al foil µ m) 1D 15 mm) 2011-T3 (10 mm) Water (flowing, 1–3 mm)/ SUS304,HT1000,S15C (12 mm) 100Cr6 steel (38 mm) Water Cu (90 2024-T62 (2.5 mm) Glass (4.5 mm)/black Alloy 600 (pipes of Ch03-I044498.tex 12/9/2007 17: 40 Page 126 es Montross (2002) [381] Rankin (2002), (2003) [214, 383] Peyre (2002) [382] Oros (2002) [236] Sollier (2003) [262] ∼ 4GPa ∼ 30–50% by direct by ABAQUS of plasma pressure and temperature and of residual stresses results (16 pp., 15 figs., 87 refs.), covering LSP (13 pp., 12 figs., 24 refs.) of research in features, observed phenomena, comments Referenc ∼ 50–120% by confined ablation, the changes were ∼ 0.3 GPa for direct ablation and review review techniques, residual stress distribution, LSPon effect fatigue and hardness, and applications of LSP Residual stress distribution was measuredmethod by using slitting 0.79 mm long14 strain different gauges; combinations effects of of 2spot laser size, fluence, shots pulse of width different compared and with location each were other andthe with results are shot presented peening; inextensively 10 graphs and discussed LSP during 1996–2000, containing alsofrom information doctoral theses, research projectconference reports, proceedings; and the review coverspressure the dependence shock on laser pulsewavelength, confined length LSP and with andprotective without coating, influence of LSPresistance, on fatigue corrosion life and wearaluminium of alloys steel and Pressure transients for direct andfor confined various ablation targets are presented;was the peak pressure for confined ablation forhardness all of the the targets targets wasand used; enhanced the surface largest in Al Simulation by ACCIC are presented and compared withresults; graphs experimental presenting plasma pressure, temperature, electron density,impedance, coupling, and degeneracy parameters areplasma given (Fig. peak 3.32); temperature at LSP4000–7000 K ranges Novel A A 2 µ m, 80 ns beam 2 , overlap 10% 2 dYG 1.06 Nd:YAG, (Gaussian), 6 J, spot 2 mm, 2.39 GW/cm 10 GW/cm and 50% Nd:glass, 12–18 ns, spot 3.2–5 mm, 45 and 60 J/cm µ m) 1064 nm, 3 ns, vacuum grease + Glass (3 mm)/black paint layers or environment properties Water? Water/Al paint (60 ) Continued ( steel (1.5 mm) Processed materials/ Confining/absorbing Lasers and 7049-T73 (9.5 and 25 mm) Stainless steel targets Al, Cu,Ti, 40C130 Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 127 (Continued) Nalla (2003) [192] Peyre (2003) [272] Rodopoulos (2003) [385] [384] Arif (2003) [386] Thorslund (2003) was in solids, for ;DR by combined SP and LSP compared with LSP , coverage 200%) and LSP (2 and ◦ in cylindrical coordinates elasto-plastic wave propagation (roll diameter 6.6 mm, 150 bar, feed the plasma temperature, pressure, and thermal stresses computer, program LSP-1D, for solving provided up to 40% longerobviously fatigue due life to than a LSP, highercompressive stresses, magnitude a of higher induced degreehardening, of and work significant decrease inroughness the surface induced residual stresses; Johnson–Cook plasticity law with isotropic hardening, takingstrain into rate account dependence ofpressure the pulse stress and was applied; HEL wereexperiments; taken shock from propagation and residualdistributions stresses are presented for singlelaser and impacts; simulation multiple describes thestress central drop Residual stress and hardness profilesvs. and maximum fatigue surface life stress forincident SP angle (intensity 45 4A, Deep rolling 0.1125 mm/revol.) is 3 passes) processed specimens presented;provided LSP hardness increase and compressivestresses residual to a larger depth; proved to be advantageous forfractographic fatigue analysis life results, extension; and fracturemicrophotographs surface are presented FD-method is described; a hypo-elastic rate-dependentdeformation plastic is assumed forbehaviour; modelling examples the of material calculated shock propagation and stress fields are presented LSP for ramp-up, ramp-down, and rectangular laser pulses, including confined ablation with coating (see Fig. 7.13temperatures) for calculated Axisymmetric 3D-FEM-simulation of laser peening A Analytical models 2 , spot 2 µ m, ∼ 1.3 J, spot 2.6 mm, to both × sides simultaneously coverage 200% 6–7 ns, 2 mm, 10 GW/cm 18 ns, 7 GW/cm Pressure pulse 2.5, 10, or 25 ns ( ∼ 5 GPa), 50% overlap 2.6 µ m) 0.532 Nd:YAG, Water? Water/Al coating (70 diameter 7 mm) 12% Cr steel,Al, 7075-T7351 Fe, SS304 2024-T351 Ti-6AL-4V (rod of Ch03-I044498.tex 12/9/2007 17: 40 Page 128 [387] [388] Ding (2003) [390] Altenberger (2003) Altenberger (2003) Yilbas (2003) [389] µ m; C ∼ 20% ◦ C (deep ◦ near-surface (roll diameter 6.6 mm, in ABAQUS, C; in the whole temperature ◦ 3D-model of the experiment by Ballard − 400 MPa (LSP) vs. over ); calculated dynamic stresses and C (laser shocked) ◦ )/(1– ν ∼ 800 ν C (micrographs presented), the features, observed phenomena, comments References ◦ work-hardened zones were stable up to 650 region, the lifetime of rolledthan specimen that was of higher untreated one;and microstucture LSP of processed both AISI DR 304to was 900 investigated up the compressive residual stresses relaxed− 200 to MPa about in both cases,properties the however, remained fatigue improved, obviously duemore to stable nanocrystalline surfaceformed structure at DR and LSP residual stress profiles are presentedshock for pressures, shock different duration, andof the impacts number − 900 MPa (DR); DR provided somewhatfatigue longer life than LSP; at fatigue tests at 450 assuming pressure pulse square inover laser time spot, and and uniform theMises plastic yielding strain criterion following von withHEL(1–2 dynamic yield strength Comparison of LSL and150 deep bar, rolling feed 0.1125 mm/revol.); maximumstresses residual were over Numerical simulation (1991) [264], using a rolled) and Fatigue lifetime of deepinvestigated rolled up specimens to was 600 (mild steel), respectively 70% (SS)of higher untreated than materials; that the modified depth was 450 shock pressure and elastic–plastic wavewere propagation calculated numerically assuming Maxwelldistribution velocity of vapour moleculespower-law and work-hardening linearly plastic elastic, stress–strain relationship of the target material Novel The hardness of lasershocked materials was 3 mm, 5 mm, µ m, × × beam , coverage , 3 GPa 2 2 18 ns, spot 2 7 GW/cm 30 ns, spot 5 8 GW/cm 200% See the entry for(2003) Nalla [192] 1.06 Nd:YAG, 9 ns, 10 Hz, 0.5 J, spot ∼ 1.5–2 mm Glass (0.1 mm) layers or environment properties Water? ) Continued ( Processed materials/ Confining/absorbing Lasers and 304 stainless steel and mild steel (both 4 mm) 35 CD4 50 HRC Water/black paint targets AISI 304, Ti-6Al-4V (20 mm) ? Ti-6AL-4V (20 mm) Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 129 (Continued) Hill (2003) [393] Colvin (2003) [251] Rankin (2003) [395] Evans (2003) [394] Hill (2003) [392] Wang (2003) [391] ◦ − 800 MPa were was observed; in range 0–60 – the methodology is laid out in − 300 MPa and the depth of compressive laser beam incident angle down to the depth ofof 0.7 treated mm;TEM material micrographs areinduced presented: laser martensitic shocking transformation instainless 1Cr18Ni9Ti steel and denseGH30 dislocations superalloy and twins in LASNEX code, is presented; thefor model the accounts initial absorptionlow-intensity onto photoionization a absorption metal in surface, vapour, neutral collisional ionization, recombination, dielectric breakdown, band gap collapsetamper, electron of conductivity,thermal the transport, and constitutive properties of the materials;laser most energy of is the absorbedthe in ablator; the the dielectric simulations tamper, agreed not experimental well results with the LSP technology at LLNL-MIC isdemonstrating described, the cases usefulness ofof LSP aircraft for parts processing are presented[392]); the (see magnitude also of Hill residual (2003) in Ti-6Al-4V compressive stresses was found toof be largely independent Residual stress distribution was determinedslitting method by detail, the number and positionswere of optimized; the strain near-edge gauges compressivestress residual reached 98% of thebut material’s extended yield over 38% strength, of the laser peened area Compressive residual stresses up to induced at the specimenresidual surface, balancing stresses tensile were located 2the mm material’s deep surface; beneath residual stresswas distribution determined by neutron diffraction Plastically affected depth up tonear-surface 12 residual mm compressive stresses werethan larger stresses was up to 7.7 mm As result of LSP, materials hardness was enhanced A 2D-computational model, incorporated into 2 , 2 ,upto 2 µ m, µ m, 2.5 mm, , 3 layers, both ∼ 4 GW/cm 2 × 2 126 J/cm sides simultaneously Nd:glass, 1.06 20–50 ns, spot 9 mm (super Gaussian) up to 60 J/cm Nd:glass, 1.06 20–50 ns, 10–50 J, spot 3–7 mm, 25 ns, 10 GW/cm ns-pulses, 180 J/cm Nd:glass, 18 ns, spot 2.5 200% coverage 20 peening layers µ m) µ m) µ m) or sapphire/Zn (0.5 Quartz (4 mm)/black paint (120 Fused silica/Al (50 Water (1 mm)/Al tape 1Cr18Ni9Ti (1.2 mm), GH30 (1.6 mm) UNS N06022 (20 and 33 mm, weldments) Cu Ti-6Al-4V (8,7 mm) ? Ti-6Al-44V (1,6 mm) Water? Ch03-I044498.tex 12/9/2007 17: 40 Page 130 es (2004) [263] Zhang (2004) [401] Shaniavski (2004) [396] DeWald (2004) [216], Hill (2005) [398] Yilbas (2004) [400] Yilbas (2004) [399] ; calculated 2 /cm 11 the depth of 10 improved analytical × field of lasershocked X-ray microdiffraction ; hardness of shocked regions determination methodology for µ m Cu); a ∼ 50%; calculated peak surface temperature both axial and radial effects features, observed phenomena, comments Referenc for plasma pressure is presented, taking fractal dimension ∼ 300 MPa for 3 and nanoindentation Laser shocking enhanced theworkpiece surface for hardness of the was over 5000 K; calculatedat stress different profiles times in are the presented;described material the (see numerical the model entry is forYilbas, 2003 [389]) Laser shocking induced stress in Cu layer has been Zhang ( recoil pressure vs. laser intensity,andare presented; stress the transients numerical modelthe is entry described forYilbas, (see 2003 [389]) analysis of fracture surfacesfatigued of laser specimen peened is and described; formechanics fractal see fracture the review by Cherepanov et al. [397] Residual stress distribution was determinedslitting and by contour methods; compressive residual stresses varied from 4.3–7.7 mm model in to account (important for small potanalysis size); the was stress/strain performed by ABAQUS(stress software and strain distributions are presented) was increased by 11%; compressivestresses residual were found in shocked(by material; the simulated model describedstrain in energy Zhang distribution (2004) [263]) is presented Laser shocking enhanced thethe surface workpiece hardness for of 80%; thetreated dislocation areas density exceeded of 2–8 Novel A , 2 2 2 µ m, evaluated from structure curvature measurements µ J, ,up 2 beam , 67% overlap, ∼ 10 2 µ J; 3.08, µ m, 174, 209, areas was investigated by 3.67, and 4.31 GW/cm 25 ns, 6 Hz, 20 J, 7–13 GW/cm 10 ns, 22 J, spot 0.75 cm 355Nd:YAG, nm, 8 ns, 10 kHz, 450 mJ, spot 2.515 mm, impacts 355Nd:YAG, nm, 3.67 and 4.31 GW/cm ( ∼ 209 and 244 50 ns, spot spot 12 and 244 3GPa to 20 layers dYG 355Nd:YAG, nm, 8 ns, 10 kHz, 450 mJ, spot 2.5 mm, 15 impacts 3 GW/cm µ m) Nd:YAG, 355 nm, 50 ns, Hardness and stress/strain + µ m) µ m) vacuum grease vacuum grease Flowing watertape (1 (120 mm)/Al Overlay (0.1 mm) foil (16 + layers or environment properties ) µ m Water?/Al foil (16 µ m) Water curtain/Al Continued ( 20 mm; welds in 33 mm plate) BS L65 l, 2024-T351 ? Processed materials/ Confining/absorbing Lasers and 316 stainless steel (2 mm) Cu (1 and 3 Cu (1, 1.5, and 3 on Si (111) films on 0.5 mm Si <004>) targets Alloy 22 (13.5 and Ti-6Al-4V (2 mm) Overlay (0.1 mm) Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 131 (Continued) Rubio–González Nikitin (2004), (2005) [406, 407] Chen (2004) [403] Chen (2004) [402] Akita (2005) [231] Yang (2004) [405] − 165 to ;at was (spherical rolling C, but near-surface ◦  K 1 / 2 µ m in depth in Cu sample; the ◦ lattice rotation ∼ 1.3 without protective coating ∼ 2 ; surface hardness was increased (2004) [404] 2 measurements (X-ray beam − 100 MPa were found; asymmetry in Al and C; residual compressive stress relaxation µ m) of residual stress in lasershocked ◦ ◦ ; the depth of hardened layer was 0.31–1.4 mm C parameters of LP were optimized by an ANN ∼ 3 ◦ 2500 pulses/cm work hardening started to anneal400 out only at over was reduced by 20 MPa(m) up to 10%, residual compressive− 280 stresses MPa up were to formed (belowand the fatigue surface), crack growth rate (EBSD) method; maximum in-plane rotation was measured rotation distributions are comparednumerical with simulation data; the Alwas sample deformed surface up to Microdiffraction size 5–7 successive impacts (at rising coverageresidual rate), tensile the surface stresses wereconverted gradually into compressive (see Fig. 3.26) LSP was performed method (1–4 impacts);the hardness was increased bycompressive 45–82%;peak residual surface stresses ranged from − 410 MPa (12–20 J); laser shockdense treatment-induced dislocations and refined grains LSP was compared with deepelement rolling of diameter 6.6 mm,treatments 150 kbar); produced both almost identical fatigue lifetime enhancements in temperature range 25–600 was fastest between RT and 100 samples are described; compressive residualstresses surface up to of diffraction peaks indicatedcell dislocation structure formation The , 200% 2 2.5 mm µ m, measured by electron backscatter diffraction µ m, The specimen were laser shocked by 900, 1350, and µ m, × nm, 50 ns, Laser shock-induced 2 18 ns, spot 2.5 (sq.), 10 GW/cm dYG 1.064 Nd:YAG, Nd:glass, 1.064 25 ns ( ∼ Gaussian), 10–30 J, spot 7 mm 532Nd:YAG, nm, 8 ns, 10 Hz, spot 0.8, and 1 mm, coverage up to 800% 8 ns, 10 Hz, 1.2 J, ∼ 4 GW/cm coverage spot 1.5 mm Chen (2004) [402] µ m) See the entry for vacuum 10 kHz, spot 12 + µ m) vacuum grease film grease + Water? Water 10), Cu (001), Water (5 mm)/Al foil 355 Nd:YAG, 7mmin diameter) 6061-T6 (6.3 mm) Water QT700-2 (10 mm) ?/LTV silicone rubber SUS304 both 5 mm thick both 5 mm thick (16 Al (1 Al (001), Cu (110), (3 mm)/Al foil (16 AISI 304 (rod, Ch03-I044498.tex 12/9/2007 17: 40 Page 132 Kusaka (2005) [253] Fan (2005) [273] Shepard (2005) [408] Wu (2005) [259] ; 2 at water and 0.1 mm/s; 2 ; at fixed power − 80 MPa and 2 ); surface 2 ∼− 600 MPa surface µ m were created in the same maximum 2 µ m at 61 MW/mm ∼ 100 µ m (10–310 MW/mm z R features, observed phenomena, comments References µ m mathematical model of pressure generation confined LSP is described; thethe model processes considers to be 1D,and the two-temperature plasma laser homogeneous beam absorptionel.-ion due and to el.-atom IBand and Hertz–Knudsen photoionization only, surface evaporation; thewas model in good agreement with532 experimental and 1064 data nm, at 0.6–25 ns, and 1–10 GW/cm the calculations give insight intoas plasma the parameters density ofthermal species, light to transmission, internal energyinterface ratio, water–plasma reflectivity,and energy balance compressive stress was achieved atdepth 1 mm/s; was ablated compressive stress ( ∼− 250 MPa) waslaser achieved at power density of 31 MW/mm Residual compressive stresses up to dents of depth down tothe 1.8 surface of specimen; shockdeformation propagation simulation and results are presented Laser shocks were applied simultaneouslysides to of both the samples; shotas peening well was (6–8A investigated usingglass cast beads); steel LSP shots resulted and in 6–9 N using residual stresses; a linear elasticanalysis fracture of mechanics crack growth thresholdproved to is be presented; LSP superior over SP density of 61 MW/mm roughness of laser treated materialof increased laser with power increase density and with(scanning decrease of speed scanning range speed was 0.1–15of mm/s), exceeding tens at 2 mm/s the averageexceed ablated 6 depth did not Novel A At a fixed scanning speed 2 mm/s the maximum 2 µ J, µ m, beam 2 2 µ m, 226 N:A,532-Nd:YAG, nm, 4 GW/cm dYG 355Nd:YAG, nm, 50 ns, spot 12 6–7 ns, 10 Hz, 10–250 mJ, spot 0.4 mm, 12–310 MW/mm Nd:glass, 1.054 20 ns, spot 5.3 mm, 8 GW/cm vacuum + C)/no coating 2 ω ◦ µ m) grease foil (16 vinyl tape layers or environment properties Water (3 mm)/Al Water (22 ) Continued ( Processed materials/ Confining/absorbing Lasers and targets Al (5 mm) A5083 Ti-6Al-4V (12.7 mm) Flowing water/black Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 133 (Continued) Cheng (2005) [414] [411] Mukai (2005) [409] Schneider (2005) [413] Chen (2005) [415] [410] King (2005) [412] Altenberger (2005) Aldajah (2005) C) ◦ : was studied by numerical was determined quantitatively µ m); data about structure and dynamics in SC Si during LSP (6 pp) of the work at University of Kassel, see temperatures 850–1073 K review simulation; it was concluded, thatgenerate LSP plastic process flow can in brittle materials boiling water nuclear reactor (BWR)described; cores the is laser beam wasby transported mirrors whether or by lightsystem are guide; presented;focusing optical system schemes is of described the in detail shot peening (SP) andstrength deep rolling can (DR); highest be fatigue treatment obtained (SP or by DR) thermomechanical at elevated surface temperatures (300 Slip-twinning transition and predicted as aand stacking function fault of energy; the orientation,determined experimentally temperature, threshold twinning stressthe for [0 pure 0 copper 1]for orientation in the was [1 25 GPa, 3 whereas 4] the orientation one wasDislocations between 40 and 60 GPa. at LSP-induced dislocations wereXRD studied (beam size by 5–7 measured synchrotron distribution of average mosaicand size, dislocations strain density are givenwith and FEM-simulations; are compared materialand with material (001) with higher orientation (Al) stack showed fault higher energy dislocation density under LSP Four kinds of laserlaser surface modifications shock were peened compared only,laserglazed glazed then only,laser shock peened, andthen laser glazed; the shock latter peened providedreduction maximum 43% friction in a dry pin-on-disc test against alumina Residual stress vs. depth profileswere of measured laser-shocked by samples neutron diffraction;from compressive LSP stress reached 1.25tensile mm stresses (160 in MPa) depth; located at the a maximum depth of of 2.6 mm A laser peening system for in situ treatment of A Altenberger, Nalla, Nikitin above; LSP is compared with , 2 2 2 2 µ m, 2 N:A,355-Nd:YAG, nm, 3 ω 1 kHz, spot 10 4 GW/cm KrF, 248 nm, 10–50 ns, 1.33–6 GW/cm dYG 532Nd:YAG, nm, 6–10 ns, 120 and 300 Hz, 60–250 mJ, spot 0.4–1.2 mm, 36 and 70 pulse/mm ? ? 2.5 ns, 40–300 J, spot 3 mm, 15–70 MJ/m 12–40 GPa/cm vacuum grease + -glass/Cu 2 µ m) (0.05–0.3 mm) (16 ? SiO ? Water (3 mm)/Al foil Water 134], 134], (001), Cu (110) and 15 mm) SUS304 1080 carbon steel ? Cu ([011] and [ Si (SC) 3–5 mm) 3–5 mm), CuAl ([011] and [ Al (110) and Ti-6Al-4V (10 Ch03-I044498.tex 12/9/2007 17: 40 Page 134 es Gomez-Rosas (2005) [416] Bugayev (2005) [418], Bugayev (2006) [419] Morales (2005) [417] Lee (2006) [261] Korsunsky (2006) [420] ,eigenstrains such code,, HYADES nanoparticles − 1400 MPa in 2024 ∼ 60 nm was − 1600 MPa were produced (2024); compressive 2 with diameter of features, observed phenomena, comments Referenc 5000 impacts/cm residual stresses up to in 6061-T6 alloy and up to alloy; It was found that thesurface laser during spot processing scanning resulted ofcolumn-like in the microstructure , a which system was of tilteddirection in of the scanning; spherical formation observed during LSP was developed; examples of simulationresidual the stress distribution of givenregime materials are presented at given problem about elastic deformationdue of to a a flexible plate prescribed distribution of was adopted for simulation ofof plasma propagation pressure of and laser shockas in an Al;Al elastic-perfectly was plastic considered propagation material; the of the shockto wave inside be the mainly influenced metal by wasintensity; calculated the found plasma laser peak fluence , not pressure,and impulse by shock laser velocity dependence ontime laser (1–17 ns) pulse and rise- intensity/fluence are presented as may be generated duringthe spatial shot variation peening of treatment; through residual the stresses plate and thickness, strains andshape, can the be deformed predicted plate usingapproach this may technique; be the applied alsodemonstrated for by case Korsunsky of (2006) LSP [421] as Novel A 3D-LSP simulation computer program, SHOCKLAS, A solution has been presented of a axisymmetric A 1D-Lagrangian hydrodynamic The specimen were laser shocked by 2500 (6061-T6) and , 2 µ m, 8 ns, 2 beam 2 , scanned 2 µ m, dYG 1.064 Nd:YAG, 10 Hz, spot 0.8 and 1.5 mm beam 2–10 GW/cm 1.064 trapezoidal pulse, 8–50 J/cm dYG 10Nd:YAG, ns, spot 0.75 mm, 0.3–1 J, 900 impacts/cm 12Nd:YAG, ns, 4 Hz, 0.8 J, spot 1 mm, 100 J/cm layers or environment properties Water Water (3–10 mm) ) Continued ( 6061-T6, 2024 Water Processed materials/ Confining/absorbing Lasers and Inconel 600, 316L (5 mm) targets Al Al2024 Ti-6Al-4V, Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 135 (Continued) Sano (2006) [254] Sano (2006) [422] Sánchez-Santana (2006) [425] El-Dasher (2006) [423] Chen (2006) [269] Wu (2006) [426] steels # − 1000 MPa at by solving an electron ; with LSP the 2 through water breakdown was simulated µ m; the depth of LPPC-induced ∼ 1 mm in depth were formed were tested for wear and friction µ m depth and surface roughness 2 ; the shocked surface of SUS304 was 8 ppm, conductivity 0.1 mS/m, 500 h) ∼ 1 2 2 axis nearly parallel to the specimen surface empirical formulae for estimation of residual stress c was less than 2 a compressive residual stress exceeded 1 mm from the demonstrated complete suppression of stress corrosion cracking by LSP by roll-on-flat tribometer; wear rateabout was 68% reduced using 5000 pulse/cm time to reach the sameby as wear depth much was as increased 100%,and depending pulse on density; the wear mechanisms appliedwear, abrasive included load wear, and adhesive wear due to plastic deformation normal; grains with slip stepsfactors; all had the the localized lowest Taylor latticeconcentrated rotations about were the steps, withorientation almost variations no in between slip steps rate equation coupled withthe Maxwell’s wave calculated equation; with aidlaser of peak this power model density,transmitted transmitted laserlength, peak pulse pressure, and pressure duration as function of incident power densityexperimental agreed well data with from the literature Compressive residual stresses up to New Slip steps were observed withintheir grains oriented with Laser beam transmission plasma in LSP regime impacts/mm surface and up to in the LSP-treated materials; corrosiondissolved tests O (561 K, distribution in laser-shocked materials(see is section presented 3.3.6.2); the calculationswith matched experimental well data for 40Cr and 45 5000 pulses/cm oxidized for R The specimen were laser shocked by 36–135 The specimen laser shocked by 900, 2500, and 2 µ m, 2 2 N:A,532-Nd:YAG, nm, -Nd:YAG, 2 ω 100 mJ, spot 0.6–1 mm, 36–70 impacts/mm 18 ns, spot 3 mm, 12 GW/cm 1.064 Nd:YAG, 8 ns, 10 Hz, spot 1.5 mm 532 nm, 60–200 mJ, spot 0.4–1 mm, 9.5–100TW/m Flowing water/Al tape Water 15 mm) Inconel 132, Inconel 182, also weldments with SUS304 and Inconel 600 6061-T6 (6.3 mm) Water SUS304, SUS316L Water/no protective layer 2 ω Ti-6Al-4V (BSTOA, Ch03-I044498.tex 12/9/2007 17: 40 Page 136 es Hu (2006) [426] King (2006) [427] Ding (2006) [428] ); )/(1– ν fretting fatigue extending to a HEL(1–2 ν 8 ppm, 500 h); ) introduced by peening 2 = cycles dyn Y 8 σ stress relaxation of single and multiple LSP by features, observed phenomena, comments Referenc calculated residual stress distribution (alsodeformed 3D) surface and profiles areexperimental presented for conditions the of Ballard (1991) [264] surface for boththe materials; initiation LPPC of completely SCC prohibited pre-cracks and on the SUS304 propagation in of an small SCC environment that (water accelerates 561 K, dissolved O loading of Dovetail Biaxial Rigtreated samples with combined LSP andsurface SP causes on their significant contact depth of 0.5 mm;profile FEM of has plastic been misfit ( eigenstrain usedresponsible for to the determine observed the distributions of elastic strain In-plane residual stresses of orderwere introduced 700–800 MPa by laser shockthe peening compressive near region surface, extending to∼ 1.5 mm; a a depth tensile of peakwas residual stress located of at 250 MPa a depth of around 2.5 mm; rotating bending fatigue tests showedLPPC that enhanced the fatigueby strength a of factor SUS316L of 1.4–1.7 at 10 3D-FEM analysis LS-DYNA and ANSYS commercial softwaredescribed; is the target material wasperfectly assumed elastic–plastic to and be thefollow plastic the strain von to Mises yielding criteriondynamic yield and strength the be Laser shock propagation in thestresses specimen were calculated and by residual ABAQUSaxisymmetric using a model; calculated 2D residual stress distributions are compared with analyticalexperimental and results of Peyre (1998)(1991) [264] [239] (diagrams and presented);the Ballard size offield residual stress and the depthclearly of when the the plastic diameter deformationfrom2to8mm of increases the spot is increased Novel 5 mm, × beam , 2 2 30 ns, spot 5 8 GW/cm coverage 200% 9 GW/cm 50 ns (Gaussian), spot 8 mm, 2.8 GPa layers or environment properties Water? Water ) Continued ( engine fan blade contact surfaces) Processed materials/ Confining/absorbing Lasers and 35CD4 50 HRC Water/black paint 35CD4 30 HRC (15 mm) targets Ti-6Al-4V (aero- Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 137 (Continued) Korsunsky (2006)[421] Rubio–González (2006) [429] Korsunsky (2006) [430] Ding (2006) [186] DeWald (2006) [217] using a variational − 4000 were [430] residual elastic for determination (162 pp., 85 figs., 123 refs.); α -phase (00.2) and (11.0) eigenstrain profile was deduced book about LSP multi-axial contour method strain distributions were modelled usinglaser a shock-induced distribution eigenstrain of nearmost the likely surface; and the matching procedure; the mathematical frameworkapproach of is this presented and discussed compressive residual stress in samplesreached was at a depth aboutcorresponding 0.7 value mm; for the coated samples was between 0.1 and 0.2given); mm superficial (stress grooves along profiles the scan direction were observed LSP-induced residual elastic strain profilesmeasured were by synchrotron radiation ( ∼ 60diffraction; keV) microstrain values up to measured; plastically affected depth wasdifference over between 3 mm; hcp peak strains displayed the greatestplastic sensitivity deformation; to strain measurement methodologythe by presented method is laid out in detail main topics covered: physical and mechanical mechanisms of LSP, simulation methodology,2D/3D-simulation of single and multiple LSP30HRC), (examples 2D-simulation presented of for two-sided LSP 35CD4 sections on (examples thin presented forof Ti-6Al-4V); LSP simulation on cylindrical7050-T7451); surface history (examples of presented mechanical for energiesdistribution and of dynamic andworkpiece residual stresses in are presented for various LSP conditions; of residual stresses in continuouslymaterials processed is described andlaser-shocked applied specimen to ABAQUS software was used in all simulations A Without absorptive coating, the maximum The first , 2 ∼ 7 GW/cm µ m, 2 3 mm, × coverage 200% dYG 1.064 Nd:YAG, 8 ns, 10 Hz, spot 1.52500 mm, pulse/cm Nd;YAG, 355 nm, 20 ns, spot ∼ 2 see Korsunsky (2006) [430] The measured in Korsunsky (2006) µ m) (13 Water jet/black paint 6061-T6 (5 and 6.3 mm) 35CD4 30HRC, Ti-6Al-4V (8.5 mm) ? Ti-6Al-4V (8.5 mm) ? Ti-6Al-4V,316L Ti-6Al-4V,7050-T7451 Ch03-I044498.tex 12/9/2007 17: 40 Page 138 es Sano (2006) [282] Sano (2006) [280] Peyre (2007) [229] Yoda (2006) [185] features, observed phenomena, comments Referenc µ m (6 ns pressure pulse) technology: residual stress profiles inSKD61 laser and peened SUS304 are presented;stress the profile achieved in SUS304 wasthermal quite loading stable up even to at push–pull 673 K; fatigue rotating-bending life and ofand SUS316L,Ti-6Al-4V AC4CH was improved significantlyincrease despite of of surface roughness; SSCin (accelerated SUS304 tests) was completely eliminatedlaser in peening result of technology: in addition to theSano material (2006) presented [282], LPwC by treatmentdiameter of SK3 9.5 steel mm tubes, inner andpropagation investigation in of AC4CH crack by X-rayis micro tomography described; fibresystem delivery are of also laser described beam and autofocus Residual stress profiles in lasersamples peened are Alloy presented; 600 laser peeningwelds operations in of PWR nuclear reactorsin are detail described FEM calculation (2D axisymmetric, byof ABAQUS) shock propagation and residualwere given stresses; materials by hydrodynamic GrüneisenJohnson–Cook’s EOS plasticity and model; effects ofpressure impact and diameter, pressure pulse duration,impacts number and of of sacrificialnumerically; overlay without were studied sacrificial layer, theof heating workpiece by plasma wasmicroseconds found and to thermally last affected several ∼ 30 depth was Novel A overview of recent advances in LPwC- A overview of recent advances in LPwC- 2 2 2 beam dYG 532Nd:YAG, nm, 80 mJ, spot 0.4 mm, 70 pulse/mm dYG 532Nd:YAG, nm, 8 ns, 70–200 mJ, spot 0.6–0.8 mm, up to 100 pulse/mm dYG 532Nd:YAG, nm, 8 ns, 60–200 mJ, spot 0.6–0.8 mm, up to 200 pulse/mm Pressure duration 6–50 ns, peak pressure 3–5 GPa, impact size 1.6 and 5mm µ m, optional) layers or environment properties Water/no coating Water/no coating Water/no coating Water/Al (70–80 ) Continued ( SKD61, SUS304, SUS316L,Ti-6Al-4V, Processed materials/ Confining/absorbing Lasers and SKD61, SK3, SUS304,AC4CH 12Cr steel, 316L (4 mm) targets Alloy 600 AC4CH Table 3.8 Ch03-I044498.tex 12/9/2007 17: 40 Page 139 and shock wave propagation, developed at LCD-ENSMA at CLEA-LALP,Arcueil, France back side of the sample (see Clauer et al. [232]) uctures under externally applied loading rying loop area s – a computer code for hydrodynamic simulation of fluid motion ic polymer program gram, designed primarily to model the behaviour of solids and str of laser-shocked sample, in purpose to avoid wave reflecting from relies on change of magnetic flux due to change of current car a code for simulation of laser – confined target interaction, developed C) ◦ Notations FWHM – full-width half maximum CW – continuous wave (laser) SP – shot peening LSP – laser shock processing, laserLP shock – peening laser peening LPPC, LPwC – laser peening withoutSC protective – coating single crystalline, single crystal HAZ – heat affected zone PAZ – plastically affected zone SHYLAC – Simulation Hydrodynamique Lagrangienne des Choc IB – inverse Bremsstrahlung XRD – X-ray diffraction BSTOA – beta solution treated andSCC overaged – stress corrosion cracking PWR – pressurized water reactor EOS – equation of state Poitiers, France SEM – scanning electron microscope SIMS – secondary ion massEPMA spectrometry – electron probe microanalysis PE – polyethylene LLNL – Lawrence Livermore National Laboratory MIC – Metal Improvement Company BFV – back-free velocity,the velocity of target’s free back side EMV – electromagnetic displacement gauge, the operation FEM – finite element method, finiteFD element – modelling finite difference ID – inner diameter 1D, 2D, 3D – one-dimensional, two-dimensional, three-dimensional HV –Vickers hardness DR – deep rolling SS – stainless steel HEL – Hugoniot elastic limitRT (see – Glossary) room temperature ( ∼ 20–25 PVDF – polyvinylidene fluoride, a high performance piezoelectr ACCIC (Auto Consistent Confined Interaction Code) – ANSYS – a commercial multiphysics finite element simulation ANN – artificial neural network ABAQUS – a commercial general-purpose finite element pro ‘momentum trap’ – a solid plate in contact with the backside TEM – transmission electron microscope Ch03-I044498.tex 12/9/2007 17: 40 Page 140

140 Handbook of Liquids-Assisted Laser Processing

3.4 Laser Shock Forming and Cladding

3.4.1 Forming Deformation of thin metal foils due to laser plasma pressure was observed already by O’Keefe and Skeen [295] and Ageev [431] in the 1970s. Later the process was developed by Dubrujeaud and Jeardin, Zhang et al. Zhou et al. [432–439] who all used solid confinement layers. Water confinement has been applied only recently, by Fan et al. [273] for micro forming. Laser shock forming (also called laser peen forming) has considered as an alternative to other dynamic forming methods like explosive and magnetic forming. It is a convenient tool for introducing microscale deformations into materials (Fig. 3.40) [273].

3.4.2 Cladding Laser cladding is an alternative to explosive cladding, capable to join dissimilar materials with uneven surfaces. Laser process has been implemented using a glass confinement layer only so far. In the work by Dubrujeaud and Jeandin [432], a grooved 2024 aluminium alloy specimen was clad by an 20-µm thick aluminium foil; 6 ns laser pulses of fluence 350 J/cm2 were used, the estimated pressure being 6 GPa (Fig. 3.41). The process was carried out in vacuum. Melted material was found at the bottom of the grooves, obviously due to shock wave focusing.

Pulsed laser Transparent overlay Vapourized opaque material (explosive pressure) Opaque material Shock compressive wave Metal sheet

Deformation f dl Pulsed laser Top press plate Transparent layer Black paint f Metal sheet db Bottom base Figure 3.40 Schematics of confined laser shock forming [434]. © Elsevier.

Laser

Glass

Black paint Metal foil

Workpiece Figure 3.41 Principle of laser shock cladding [432]. The process may principally carried out also in water confinement, but the space between foil and the workpiece should be evacuated. Ch03-I044498.tex 12/9/2007 17: 40 Page 141

Shock processing 141

3.5 Densification of Porous Materials

Fabrication of machine parts by powder compacting (powder metallurgy) is attractive because‘near-net’shaped parts are ready achieved, and because complicated-shaped parts of hard materials like carbides may be easily fabricated. However, the porosity of compacted from powder parts causes a reduction of their strength and an increase of friction and wear. In some cases, however, the porosity is a benefit. Porosity may be reduced by compacting the material by flyers or explosives [440–442]. The laser shock process (Fig. 3.42), is a less dangerous and easier to control alternative here. Some laser process examples are given in Table 3.9. The process has been carried out mostly using glass confinement [230, 244, 443–447], and to a less extent in water confinement [448, 449, 445]. The compacted depths achieved were about 0.5 mm and the surface residual porosities some per cents (Table 3.9). Numerical simulation of shock phenomena and residual porosity profiles are reported in the article by de Rességuier and Romain [450]. A computational model of shock compression of loose (also metal) powders can be found in the work by Benson et al. [451].

Improved wear properties Laser impact Shock waves attenuation

Confining medium Porosities Densified (glass) depth Figure 3.42 Principle of surface densification of porous materials by confined laser shocks [230]. Reproduced with kind permission of Springer Science and Business Media. Ch03-I044498.tex 12/9/2007 17: 40 Page 142 de Rességuier (2001) [450] Podlesak (2000) [449] Schnick (1999) [448] References µ m; calculated porosity phenomena, comments shocked side was reduced upthe to depth 3 of times; porosity reductionto was hundreds up of profiles agreed reasonablemental with results; cross-section experi- micrographs of the material before andpresented; after Hugoniot shock curves are of therials mate- and rear-side pressurepresented transients are Laser shock treated samples exhibited lower porosity and better contacts between Al and SiC reinforcement; plastic deformation of Al matrixdislocations generation and was observed; sliding wear resistance of shockedwas surface somewhat greater that ofone unshocked LSP rendered the surfaces slightlyhomogeneous and more smooth, and less porous; but the wear ofwas treated greater surfaces than of untreated After laser shocking, the porosity near the 2 , 2 m Novel features, observed µ m, µ m, 2 ∼ 20 J, Nd:glass, 8–10 ns, 0.011 Hz, spot 6 mm, 5 and 8 GW/cm overlapped impacts 5–20 ns, spot 6 mm, 10 GW/cm ∼ 20 ns, spot 5 mm, 5 GW/cm µ m Nd:glass, 1.06 environment properties µ m) layers or Confining/absorbing Lasers and bea (100 A drop of water Nd:glass, 1.06 Water/Al adhesive of porous materials. no 1 wt% Pb, 1 wt% Mg, 1 wt% Mn, 0.5 wt%10-mm Fe, thick) Al (10-mm thick) Water/Al foil 100 Al-alloy (5 wt% Cu, µ m, µ m Laser shock densification HVOF-sprayed, ∼ 400- µ m thick) Distaloy AE (sintered porous steel, 190–570- µ m thick, void volume 15% and 28%) thermal sprayed, 15 and 50 wt% SiC, 3.5–45 thick) Porous material Substrate Al-SiC (50–50%, Al-SiC (100–410 Notation HVOF – high velocity oxy-fuel Table 3.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 143

CHAPTER FOUR

Subtractive Processing

Contents 4.1 Frontside Machining 143 4.2 Liquid-Jet-Guided Laser Beam Machining 171 4.3 Water at Backside of an Opaque Material 177 4.4 Backside Machining of Transparent Materials 177 4.5 Machining of Liquid-Containing Materials 202 4.6 Laser Cleaving of Crystals in Water and of Water-Containing Crystals 203

4.1 Frontside Machining

4.1.1 Introduction Laser machining (drilling, cutting, carving, etc.) has been recognized to be useful and competitive in case of hard materials,curved surfaces,hard to access places (inside of tubes,etc.),rapid prototyping,carving of complex patterns onto surfaces, micromachining, etc. The process is non-contact, can be carried out at atmospheric pressure, and is easy to control. However, laser machining is a thermal process where the material removal occurs via melting and vapori- sation. Looking, for example, at a laser cut in a metal, all typical to thermal processes imperfections like taper, structural changes, recast, debris, and burr can be found (Figs 4.1 and 4.2).

Debris Recast

fs/ps- Taper ns-pulses pulses or in liquid

Burr HAZ (a) (b)

Figure 4.1 Imperfections of a laser cut in a metal (schematically). The cut quality may significantly be improved by presence of a liquid without a need for ultrashort laser pulses or vacuum.

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

143 Ch04-I044498.tex 12/9/2007 16: 11 Page 144

144 Handbook of Liquids-Assisted Laser Processing

Konventionelle Strukturiering: Strukturiering unter Flussigkeit: 2 200 m 2 200 m HE = 9 J/cm . ff = 20 Hz HE = 9 J/cm . ff = 20 H z (a) (b)

Figure 4.2 Effect of water film on laser carving results in Si3N4 ceramics. (a) Process performed in air and (b) a water film was sprayed onto surface. Laser: KrF,248 nm, energy density 9 J/cm2, pulse frequency 20 Hz, 500 pulses. The pattern was created by mask projection technique. Courtesy by Stephan Roth, Bayerisches Laser Zentrum GmbH (BLZ), Germany. © Stephan Roth, published with permission. See also the article by Roth and Geiger [452] for a similar experiment with SiC.

Techniques of avoiding redeposition of laser ablation debris and its removal • Ablation in vacuum. • Purging the ablation zone by a high-speed gas jet. • Aftercleaning of the workpiece by solvents, detergent solutions, reactive oxygen plasma or in ultrasonic bath. • Using water-soluble protective coatings like polyvinyl alcohol (PVA) [453]. • Machining in liquids or having a liquid film on the surface of the workpiece.

Reasons why liquids are applied in laser machining • Little or no debris and/or recast, less melt, reduced HAZ depth, less taper, and burr. • Contamination of the ambient atmosphere by aerosols and gases is extensively avoided. • Lower thermal load on heat-sensitive materials, for example, decomposition of heat-sensitive materials like HgCdTe can be avoided [454]. • Cracking of brittle materials (e.g. SiN) is reduced or avoided [455]. • Graphitization of diamond can be avoided;graphitic layer is electrically conducting and decreases the catalytic activity of diamond in metal deposition [456–458]. • Silicon layer formation on an SiC surface can be avoided; silicon layer leads to a reduction of catalytic activity of SiC in metal deposition [459–461]. • In water, it was possible to capture and fix latex microparticles to be machined by optical tweezers [462].

Possible disadvantages and hazards of liquids-assisted laser machining • Contamination of the workpiece surfaces by liquid dissociation products (oxygen and hydrogen from water, carbon from organic solvents, nitrogen from liquid nitrogen, etc.). • Vapours of the liquids and their decomposition products may be harmful for personal and electronic equipment. For frontside laser machining, non-toxic transparent to laser light liquids have been commonly used. Molten NaCl and NH4Cl were tested as self-focusing media for laser drilling by Ramanathan and Molian [463], molten NaNO3 and KNO3 jets were proposed for guiding the laser light in DE10238339 [464] (Table 4.1). Addition of salts and bases to water was found to improve the finish [465] and to enhance the etch rate [466] in some cases. Organic additives are used for improving the wetting of thin water film on the surfaces [467]. Soapy additives were tested by Roth and Geiger [452], but no effect on the machining results was observed. Water with a saccharose additive was applied as a micromachining mask [468] (see section 4.1.2.7). The main parameters of lasers used for subtractive processing are given inTables 4.2, 4.3, 4.6 and 4.9–4.11. For frontside micromachining, nanosecond-pulsed UV–VIS–NIR lasers of wavelengths in liquids transparency Ch04-I044498.tex 12/9/2007 16: 11 Page 145

Subtractive processing 145

Table 4.1 Liquids and their additives used at frontside laser machining (for backside machining, see Table 4.9).

Liquids Additives

Water,heptane,perfluorocarbons,benzene,o-xylol,p-xylol, H2O2, NaCl, CaCl2, NaNO3, KNO3,Na2SO4,K2SO4, ethanol, glycerin, ether, DMSO, DMFA, N2H4, liquid CuSO4, KOH, methanol, ethanol, isopropanol, soapy nitrogen. molten NaCl, NH4Cl, NaNO3 and KNO3 additives, saccharose

Notations DMFA – dimethylformamide DMSO – dimethylsulfoxide (CH3)2SO

window are commonly used. In high-power applications, cheap and energetically effective CO2 lasers are the choice. 4.1.2 Frontside micromachining 4.1.2.1 Experimental arrangements Figure 4.3 schematically depicts the main methods of providing the working zone with liquids. In Figs 4.4 and 4.5 two more sophisticated systems including means for process monitoring and control are shown. 4.1.2.2 Phenomenology and mechanisms: nanosecond-laser pulses Ablation mechanisms Similar to the ablation in gases, in liquids the major ablation mechanisms are melting and vaporization of the material. In addition, some phenomena that are of second order in gas and vacuum become more pronounced in liquids, because the cooling rate and the density of chemically active species is larger in liquids (see also Section 4.1.2.3). Pressure effects Many times higher vapour and plasma pressures in confined ablation in comparison with ablation in vacuum and in gas are believed to be responsible for high ablation rate in liquids, but the detailed mechanism has not been clarified yet. Fatigue damage At low laser fluences (surface temperature below the melting point of the material), fatigue damage was observed in single-crystal silicon [471, 474, 475]. Xia et al. [476] calculated thermal stresses in laser-heated single-crystalline Si and Ge (below ablation threshold) to be ∼1 GPa (laser: 1.06 µm, 10 ns, 6.4 GW/cm2), that is, larger than the stress thresholds for fracture in these materials. Cavitation impact Isselin et al. [477] have studied the surface damage of metals due to bubble collapse (cavitation erosion) in relation to the bubble diameter (0.9–3.8 mm) and the distance of bubbles from the surface. They estimated the peak shock wave pressure to be 120–160 MPa, the microjet impact pressure to be 1–7 MPa, and the pressure influence time to be about 300 ns. Geiger et al. [469] also found evidence of

Water Steam

(a) (b) (c) (d) (e)

Figure 4.3 Methods for providing liquid into the working zone during laser micro machining. These method were used, for example in: (a) Geiger et al. [469], (b) Sakka et al. [470], (c) Shafeev and Simakin [471], (d) Dupont et al. [472], (e) Geiger et al. [469]. In the cases (d) and (e), laser light not well transmitted by the liquid can be used. The thickness of the liquid layer over the target in the case (a) has typically been 1 mm. Besides focused laser beam, mask projection pattering has been widely used as well. Ch04-I044498.tex 12/9/2007 16: 11 Page 146

146 Handbook of Liquids-Assisted Laser Processing

Compressed air

Timing Air filter control unit

Flow controller Translation stage

Sample Nozzle

Aperture Beamsplitter

Energy Heater meter

Temperature Thermo- Nd:YAG laser controller λ couple ( = 1064 nm FWHM = 6 ns)

Figure 4.4 Schematics of a steam-assisted laser ablation system. A liquid film is formed on the workpiece surface through vapour condensation [473]. © Elsevier.

Photodetector

Interference filter Lens HeNe laser Target

Nd:YAG laser pulse

Microphone Lens Liquid film Lens

Photodetector

HeNe laser

Figure 4.5 Techniques of monitoring of liquid-assisted laser machining process by surface reflectivity,photoacous- tic deflection and acoustic emission techniques. Onset and intensity of vaporization, and the velocity of acoustic and shock waves can be determined this way [473]. © Elsevier. Ch04-I044498.tex 12/9/2007 16: 11 Page 147

Subtractive processing 147

mechanical damage in A12O3 ceramics laser etched in water. Shafeev et al. [458] assumed that the microjets (Fig. 7.10) damage the graphite layer at diamond etching in water, resulting in high catalytic activity of the etched diamond for electroless metal deposition. Dissolution Dissolution of workpiece in laser-generated supercritical water was deemed to contribute to machining of Si3N4 in the work by Hidai andTokura [478] and of Al2O3 in the work by Dolgaev et al. [479].

Physical conditions at laser micromachining in liquids Pressure The pressure dynamics at laser etching of solids in water was investigated by Ageev et al. [480] and Zweig [481]. Ageev et al. [480] recorded, using a piezoelectrical sensor, the oscillations of pressure in the etching vessel (laser: pulse length ∼500 µs, pulse energy some J). They estimated by calculations the peak pressure to be 10 GPa and measured the bubble diameters to be 0.55–0.58 mm (irradiation power density 1.2 × 107W/cm2). Zweig [481] measured, optically, the velocity of the shock wave near the surface of a polyimide sheet target at distances up to 1 mm from the target and calculated the corresponding pressures. He got a pressure value >10 kbar (1 GPa) at the target’s surface at laser fluence of 90 J/cm2. Shock pressure varied as a square root of the incident laser fluence of up to 90 J/cm2. Bubble generation started at 8 mJ/cm2, and pressure waves were detected beginning at 50 mJ/cm2. The dependence of pressure on fluence was in good agreement with the ideal gas model. Zhu et al. [482] using the theory of Fabbro et al. [233] estimated that the pressures at ablation in water are 5.8 times greater than at ablation in air (4.5 J/cm2, 23 ns). As reported by Daminelli et al. [483] at machining by nanosecond-laser pulses, 50–70 per cent of the incoming energy may be coupled into photoacoustic phenomena, such as shock wave pressure and cavitation bubbles; for 30-ps pulses the conversion of laser energy into mechanical effects is about 18 per cent and for 100-fs pulses 7 per cent. Vapour and plasma dynamics Many researchers have photographed the liquid, vapour, and plasma dynamics at laser etching in water, thereby using high-speed cameras [452, 469, 472, 480, 484]. Roth et al. [452] report that in case of a sprayed water film on surface the vapour phase lasts for about 500 µs (laser fluence 25 J/cm2), but in case of dry ablation the plasma relaxes in 2.5 µs; Geiger et al. [469] measured for the duration of the vapour phase under water ∼800 µs (20 J/cm2, water level 10 mm); Dupont et al. [472] photographed the plasma luminescence both in air and in water. The duration of the luminescence was about 80 µs in air, and about 25 µs in case of a vertically flowing water film (laser: 17 J/cm2,24× 109W/cm2). Acoustic emission Roth and Geiger et al. [452, 485] reported that both the brightness of plasma and the emitted sound were significantly lower at laser ablation under water compared to these in air (laser fluence up to 30 J/cm2, sprayed water film on the workpiece surface). In contrast, Zhu et al. [482] found that sound was 25 per cent stronger at ablation in water compared to the ablation in air (2–5 J/cm2, 1-mm water film).

Mechanisms responsible for debris removal Laser heating generated thermal gradients and bubbles cause a convection of the liquid, whereas drag forces on particles are much larger than in gases. On the other hand, the settling velocity for particles is considerably lower in liquids.Thus,the debris is effectively removed from the working zone,and fabrication of deep trenches and long channels by ablation in a neutral liquid becomes possible (Figs 4.6 to 4.8). Drag force on small spheres in an incompressible viscous fluid is given by Stokes formula [486]:

FD = 3πµ dv, (4.1) and gravitational settling velocity by: 1 g v = (ρ − ρ) d2, (4.2) 18 µ 1 where µ is (dynamic) viscosity of the fluid,d is diameter of the sphere,v is velocity, g is gravitational acceleration, ρ1 is density of the sphere, and ρ is density of the fluid. For example, the viscosity of air is 18.3 µPa s and of water is 0.89 mPa s (25◦C), thus the drag force is 48 times larger and settling velocity is 48 times lower in water than in air. Despite the settling time of debris is much longer in liquids, a circulation of the liquid is recommended, because the suspending debris scatters and absorbs the laser light. Ch04-I044498.tex 12/9/2007 16: 11 Page 148

148 Handbook of Liquids-Assisted Laser Processing

Laser Laser

Window

Workpiece

(a)Heated zone (b)

Figure 4.6 Thermal (a) and bubble-driven (b) convection of liquid in laser irradiated zones. (Schematically after Shafeev et al. [471] and Ohara et al. [484].) When the liquid has a free surface, the Marangoni convection may contribute essentially.

In air

a b c

100 m

Figure 4.7 Effect of liquid ambient becomes especially pronounced at machining of deep grooves and blind holes. Here, grooves machined in a NdFeB magnet in air and in water are compared [487]. Laser: 1.064 µm, 180 ns, 1.8 mJ, 1 kHz (feed rate in mm/s)/(number of passes): (a) 0.8/6; (b) 0.8/8; (c) 0.08/8; (d) 0.08/2; (e) 0.08/4; (f) 0.08/8. © Elsevier. Ohara et al. [484] estimate the rate of bubble generation by the formula:

E = ρ[(tv − tR)C + Hv], (4.3) 3 where ρ is specific gravity (g/cm ), tv is vaporization temperature, tR is initial liquid temperature, C is specific heat, and Hv is latent heat of vaporization; and the discharge rate of produced bubbles by the formula dv 6η = g − v, (4.4) dt a2ρ where g is the constant of gravity, η is the coefficient of viscosity,and a is the radius of the bubble. For Cu and Al etching in water, EtOH and PFC, the observed etching rates correlated with calculated by Eqs. (4.3) and (4.4) bubble generation and discharge rates (0–10 mJ laser pulses, 10 µm spot size): it was concluded, that the more the bubbles were generated and the faster they were discharged, the faster was the removal of debris and the higher the etching rate. Shafeev et al. [471] presented photographs of the convective flow of a 300-µm-thick horizontal liquid layer between the target and the window, and estimated flow velocity to be about 1 cm/s (water, DMFA, or DMSO, irradiation power densities up to some kW/cm2).

Chemical processes at laser ablation in liquids At laser-induced plasma temperatures, thousands of kelvins, and due to plasma UV radiation, liquids molecules may be excited, ionized, and dissociated and thus become chemically active. In many investigations, the formation of oxides in laser plasma [470] and on the workpiece surface [459–461, 471, 472, 475] were observed at laser ablation in water. Shafeev et al. [458] suppose that released from the liquid hydrogen contributes to laser etching of diamond in water and in (CH3)2SO. Ch04-I044498.tex 12/9/2007 16: 11 Page 149

Subtractive processing 149

10mm 0459 6KV ×400 16mm

Figure 4.8 A trench in oxidized (111) silicon laser cut under still water layer [488]. Laser: Nd:YAG, 1.06 µm, 180 ns, 1 kHz, ∼1,7W average, spot 50 µm, scanning speed 0.1–2 mm/s. No debris is left, but the quality of the cut is poor for this pulse length. © SPIE (1999), republished with permission.

2 1 Al2O3 1,6 2 In water 1,2 3

0,8

0,4 Ablation rate ( m/pulse) rate Ablation In air 0 1 1020253035 Laser fluence (J/cm2)

Figure 4.9 Dependence of the ablation rate on the laser fluence at laser etching of Al2O3 in water and in air [469]. Laser wavelength: 308 nm (XeCl laser); pulse duration: 50 ns; pulse frequency 2 Hz. Curves: 1: sprayed water; 2: 2-mm-thick water layer; 3: 10-mm-thick water layer. Al2O3 exhibits an exceptionally high etching rate in water. Elsevier Science Ltd (1996).

+ + Hidai and Tokura [478] identified hydrothermal reaction products, NH4 ,NH4 –N, and silica ion/boric ion after laser ablation of Si3N4/cBN in water (Table 4.9, Hidai 2001). Also Dolgaev et al. [479] found evidence that laser ablation of sapphire in water and electrolyte solutions (see Table 4.9, Dolgaev 2001) was assisted by dissolution of the material in supercritical liquid. Ablation rate was dependent on type and concentration of cations, but independent of anions. Miyazawa and Murakawa [489] report about formation of CO, CO2,CH4, and misty particles of K2CO3 at laser cutting of diamond in aqueous KOH solution. Chemical reactions at laser ablation of carbon in organic solvents and water are reported in Section 7.5.

4.1.2.3 Ablation efficiency In most cases the ablation rate by nanosecond-laser pulses has been larger in liquids than in gases (see Fig. 4.9 and Table 4.2). This is explained by the following: • Increased energy-coupling efficiency by optical matching: since the refractive index of water is greater than that of air, the overall optical absorptivity of air–water–aluminium system was found to be larger than that at the air–aluminium interface [467]. Ch04-I044498.tex 12/9/2007 16: 11 Page 150

150 Handbook of Liquids-Assisted Laser Processing

70 000 Dry surface

3 60 000 H2O-coated surface m 50 000

40 000

30 000

20 000

Ablation rate (volume), (volume), rate Ablation 10 000

0 0.5 0.6 0.7 0.8 0.9 1 2

Normalized laser fluence (F/Fd)

Figure 4.10 Ablation rates of dry and liquid-coated aluminium (100-µm-thick foil) as a function of laser fluence normalized by the ablation threshold of a dry surface Fd. © American Institute of Physics (2001), reprinted with permission from Ref. [467].

• The bubbles carry the debris effectively away, thus avoiding the absorption of laser light on debris. • High temperature of confined plasma [459, 482]. Liquid prevents the expansion of plasma and thus enhances the action of laser radiation. • Mechanical impact of microjets generated at collapse of vapour bubbles [467]. • Shock waves, originating from plasma expansion, collapse of gas bubbles and from microjet impacts can destroy passive layers on the target surface: for example, graphite layer on the diamond [456–458]; Si and SiO2 layers from an SiC surface [460, 461]. Shafeev et al. [471] observed that when bubbles were generated, there was always some surface damage of single-crystal silicon. Geiger et al. [469] suppose that shock creates cracks in ceramic workpieces. • Dissolution of workpiece and debris in supercritical water [478, 479]. • Laser-enhanced electrochemical dissolution in neutral salt solutions: metal dissolution may set in due to localized breakdown/dissolution of the passive film induced by the laser beam [465].

Occasionally,the etch rate may be lower in liquids than in gases/in vacuum, due to:

• reduction of the transparency of the liquid due to accumulation of debris in suspension [459]; • scattering of light by bubbles, lowering this way the energy density at workpiece; • hardening of the material due to laser shocks (observed e.g. in steel 304 AISI) [472].

Ablation threshold and incubation effect A higher etching threshold in liquids compared to this in air has been commonly observed and explained by larger heat losses in the liquid (Figs 4.9–4.11). In single-crystalline materials, the etching rate (both in gases and liquids) has been observed to increase with the number of laser pulses (Fig. 4.12) [474, 475, 483]. This phenomenon, called incubation, is explained by enhancement of laser–material interaction due to defect accumulation (see also Section 4.4.2.1). According to Jee et al. [490] the threshold fluence Fth decreases with pulse number N as:

ξ−1 Fth(N) = Fth(1) × N , (4.5)

where ξ is the incubation coefficient. For example in silicon ablation with 800 nm, 130-fs pulses, ξ = 0.83 ± 0.04 and ξ = 0.82 ± 0.02, for water and air, respectively [483]. Ch04-I044498.tex 12/9/2007 16: 11 Page 151

Subtractive processing 151

14 000

12 000

10 000

8000

6000

4000 Ablation depth (nm) Ablation 2000

0 0 0.5 1 1.5 2 2.5 (a) Fluence (J/cm2)

14 000

12 000

10 000

8000

6000

4000 Ablation depth (nm) Ablation 2000

0 0 0.5 1 1.5 2 2.5 (b) Fluence (J/cm2)

Figure 4.11 Variation of silicon ablation depth with laser fluence for different number of pulses in air (a) and under water (b) [491]. () 5000 pulses (×), 4000 pulses, (
) 3000 pulses, (×) 2000 pulses, (+) 1000 pulses, and () 500 pulses. Laser: 248 nm, 25 ns. © Elsevier.

Influence of liquid layer thickness Influence of water and water/IPA film thickness in micrometre range on 6 ns Nd:YAG laser ablation of aluminium was studied by Kim and Lee [467] The ablation rate was found to be strongly dependent on the liquid film thickness and to increase with the film thickness for both liquids. However, once the thickness exceeded a certain critical value, typically few microns, the ablation rate saturated and then decreased slightly as bulk liquid layers of thickness ≈1 mm were applied [467].

4.1.2.4 Surface quality As a rule, the higher ablation rate in liquids is accompanied by increased surface roughness and in some cases also increased porosity (Figs 4.13 and 4.14). Geiger et al. [485] measured the change in the flexure strength of ceramics after etching in water and in air. After processing in water, Si3N4 was stronger but Al2O3 was weaker in comparison with specimens processed in air. They also report that the surface roughness of all materials was greater when etched in water compared to etching in air. Shafeev et al. [471] and Kruusing et al. [488] observed pores formation on a single-crystal Si surface laser irradiated in water. Laser-assisted etching of various materials in salt, base, or acid solutions is known to yield smoother surfaces than etching in pure water [465, 489, 493, 494]. Also etching of SiC in N2H4 resulted in a smoother surface than etching in water [461]. Ch04-I044498.tex 12/9/2007 16: 11 Page 152

152 Handbook of Liquids-Assisted Laser Processing

14 000

12 000

10 000

8000

6000

4000 Ablation depth (nm) Ablation 2000

0 0 1000 2000 3000 4000 5000 (a) Number of pulses

14 000

12 000

10 000

8000

6000

4000 Ablation depth (nm) Ablation 2000

0 0 1000 2000 3000 4000 5000 (b) Number of pulses

Figure 4.12 Variation of silicon ablation depth with the number of pulses at various laser fluences in air (a) and under water (b) [491]. () 1.7 J/cm2,(×) 1.8 J/cm2,(
) 1.9 J/cm2,(×) 2.0 J/cm2,(+) 2.1 J/cm2, and () 2.2 J/cm2. Laser: 248 nm, 25 ns. © Elsevier.

100 m

Figure 4.13 Rutile target surface etched by laser under water. Laser: 266 nm, spot 40 µm, 100 J/cm2. © American Chemical Society (2004), reprinted with permission from Ref. [492]. Ch04-I044498.tex 12/9/2007 16: 11 Page 153

Subtractive processing 153

nm x Profilenm x Profile 50 600 30 320 10 40 −10 −240 −30 −520 −50 −800 0 79 159 238 318 397 0 79 159 238 318 397 micrometer micrometer 20 pulses (a) (b)

Figure 4.14 Cross-sectional profiles of silicon surface etched by laser in air (a) and under water (b) [491]. Laser: 248 nm, 25 ns. © Elsevier.

4.1.2.5 Machining by ps/fs-laser pulses In comparison with nanosecond pulses, ablation with fs/ps-pulses has differences in etch rate and in machined surface morphology.

Ablation rate and crater shape Compared with nanosecond pulses, in case of fs/ps pulses the ablation rate at the same laser fluence is lower, probably due to weaker conversion of incoming energy into mechanical effects [483]. Ablated surfaces are at least at moderate fluences better defined and smoother in case of nanosecond pulses, even in high thermal conductivity materials like gold and silver (Figs 4.15 and 4.16).

Formation of ripples and rings on ablated surface Irradiation of single-crystalline silicon by femtosecond laser pulses in known to produce short-period surface ripples [497]. In water, the period of the ripples is smaller, 100 nm vs. 700 nm in air (Fig. 4.17). Katayama et al. [498] observed formation of concentric ring patterns at laser irradiation of silicon surface by 200 fs 15 mJ/cm2 pulses under water (Fig. 4.18). Their formation was explained by bubbles oscillation induced acoustic waves impact on liquid silicon.

4.1.2.6 Laser beam autofocusing in liquid At high laser intensities, some liquids may act as focusing lens, a phenomenon called autofocusing [499]. Ramanathan and Molian [463] used laser beam autofocusing for drilling of micrometre-sized holes in 316 stainless steel. A two-fold decrease in the hole size and reduced taper was achieved in comparison with traditional solid focusing optics. Polarization effects were also substantially reduced (Fig. 4.19). Best results were achieved using carbon disulfide (CS2), a well-known optically nonlinear liquid. Self- focusing of a light beam is due to increase of the refractive index (decrease of the speed of light) with laser field intensity: |E|2 n = n + n = n + γI = n + n , (4.6) 0 0 0 2 2 where n0 is linear refractive index of the medium, n is refractive index change, n2 is nonlinear refractive index, I is the intensity of the light, and E is the amplitude of the electric field. For carbon disulfide at 1064 nm, 6 −12 2 n = 9.0 × 10 + 9.6 × 10 ×|E| (in esu units; n2 [esu units] = (c ×n0/40π)γ [SI units], where c is the speed of light in vacuum). Self-focusing length (distance at which the beam shrinkage occurs) is [500]:

n D D n l = 0 · = 0 , (4.7) δn 2E 2 2n2I0 Ch04-I044498.tex 12/9/2007 16: 11 Page 154

154 Handbook of Liquids-Assisted Laser Processing

In water (900 shots) 100 m 120 fs 8ns m/div) m/div) Depth (20 Depth (20

(a)Diameter (100 m/div) (b) Diameter (100 m/div)

In air (450 shots) 120 fs 8ns m/div) Depth (20 m/div) Depth (20

(c)Diameter (100 m/div) (d) Diameter (100 m/div)

Figure 4.15 SEM (Scanning electron microscope) images and depth profiles of craters in silver targets generated in various ablation conditions [495]. Focusing condition was adjusted for each ablation condition; 900 and 450 pulses were applied to targets in water and those in air, respectively. © Elsevier. Ch04-I044498.tex 12/9/2007 16: 11 Page 155

Subtractive processing 155

(a) (b)

Figure 4.16 Typical craters in a gold target in water after 5000 laser pulses at F = 60 J/cm2 (a) and F = 1000 J/cm2 (b). Laser: 800 nm, 110 fs. Dimensions of the craters/scale of the images were not given. © American Institute of Physics (2003), reprinted with permission from Ref. [496].

Water Air

2.5 m 2.5 m (a) (b) Water Air

2.5 m 2.5 m (c) (d)

Figure 4.17 Femtosecond laser irradiated silicon surface: comparison of ripple periodicities observed in water and −2 air experiments (SEM view) [483]. (a) F = 1.6Jcm (7 × Fth), N = 100, specimen vertically; (b) F = (0.20 ± 0.02) −2 −2 −2 Jcm (1 × Fth), N = 100; (c) F = 1.5Jcm (8 × Fth), N = 1000, specimen vertically; (d) F = (0.45 ± 0.06) J cm (4 × Fth), N = 1000. Laser: 800 nm, 130 fs. © Elsevier.

where D is the initial diameter of the beam and I0 is the maximum intensity. In the work by Ramanathan and Molian [463], l = 40 mm. Critical power needed to self-focus the beam is [501]:

2 π(1.22λ) ε0c Pcr = , (4.8) 32n2

where λ is wavelength of the laser beam,ε0 is dielectric permittivity of vacuum,and c is speed of light in vacuum. For carbon disulfide the calculated critical power for self-focusing is 11.32 kW (at 1064 nm wavelength). Ch04-I044498.tex 12/9/2007 16: 11 Page 156

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10 m

Figure 4.18 A typical AFM image of a silicon surface after irradiation by a single-laser pulse in water. Laser: 800 nm, 200 fs, 15 mJ/cm2. © American Institute of Physics (2003), reprinted with permission from Ref. [498].

Laser Prism and Solid Lens

Liquid optics

Stainless steel X–Y Stage

Figure 4.19 Experimental setup for nonlinear liquid-assisted laser drilling. Laser: 1064 nm, 15 ns, 1 Hz, 400 mJ. © American Institute of Physics (2001), reprinted with permission from Ref. [463].

6 Besides CS2, another candidate nonlinear liquid for laser machining is benzene with n = 8.5 × 10 + 5.4 × 10−12 ×|E|2, and critical power of 20.12 kW (at 1064 nm). The holes drilled by 316 stainless steel with the solid optics [463] were distorted in shape due to the linear polarization of the Nd:YAG beam. Using liquid optics, the polarization effects were considerably reduced. In addition, the number of pulses required to drill through the sample with liquid optics was much less than that required with solid optics (Fig. 4.20). 4.1.2.7 Liquid as micromachining mask In the work by Lapczyna and Stuke [468], a droplet of saturated saccharose solution in water was used as an ablation mask in laser etching of circular structures on the surface of PMMA (Fig. 4.21). Ablation was performed with an F2 laser (157 nm) in vacuum. The mask surface remained smooth even after more than 1 h of pumping at 10−2 mbar. The diameters of the mesas (Fig. 4.22a) were about 10 µm and their height about 6 µm. The surface roughness of the ablated areas was below 100 nm. By injecting an air bubble into the masking fluid (Fig. 4.22b), rings with an outer diameter of 650 µm and an inner diameter of 350 µm were achieved. The high surface tension of solution provided a regular shape of the droplets and thus of ablated areas as well. Ch04-I044498.tex 12/9/2007 16: 11 Page 157

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180 Entrance 4–8 pulses 160 140 120 Solid optics 100 Entrance 1 pulse 80 60

Hole diameter (microns) 40 Liquid optics Exit 20 180 210 240 270 300 330 360 Energy (mJ)

Figure 4.20 Variation of hole diameter in 316 stainless steel with pulse energy for solid and liquid optics (CS2). Laser: 1064 nm, 15 ns, 10 Hz. © American Institute of Physics (2001), reprinted with permission from Ref. [463].

Air Liquid mask bubble

Substrate

Result (a) (b)

Figure 4.21 Formation of surface relief on PMMA using a liquid droplet as an ablation mask [468]. Reproduced with kind permission of Springer Science and Business Media.

Acc.V Spot Magn WD 5m Acc.V Spot Magn WD 200m 5.00 kV 4.0 5000x 8.9 PMMA. 157nm 5.00 kV 5.0 150x 8.5 PMMA. 157nm (a) (b)

Figure 4.22 Circular (a) and annular (b) mesas ablated in PMMA using liquid droplet as ablation mask. The micro trench (vertical line in (b)) was etched through a silicon contact mask prior to the ring. The horizontal line crossing the ring in the lower part of the picture indicates a step ablated subsequent to the ring, again by means of a silicon mask [468]. Reproduced with kind permission of Springer Science and Business Media. Ch04-I044498.tex 12/9/2007 16: 11 Page 158 Misawa (1990) [462] [431] (1987) [502] Hussey (1991) [503] Morita (1988) [455] Datta (1987) [465] Ageev (1975) Arzuov omments References ); 3 ere used, are not refereed here). in water depending on pulse intensive boiling and nitride film 2 µ m/s (0.5 M NaNO bubble growth y reactive liquids w Dependence of through-hole drillingpower time and on water laser layer thicknessliquids presented; drilling is slower in than inethanol; bubble air generation and and faster contamination insurfaces of water by than oxygen in andand carbon ethanol; and in observed LN in water role of water was to enable optical tweezering correlation between thermal parametersformed of crater targets dimensions and tabulatedand for in ablation water in air Etch rate up to 4 formation observed Studies of width and frequency; in KOHwere solution smaller the and bubbles did notaddition adhere of to salt did sample’s surface; notCu-vapour enhance laser the etch rate in case of water; in water with 100-nsrecast pulses layer below and 10 cracks kHz were no observed crystallization of salt observed; etch cratersand are having irregular melted surface ingood water, morphology but in of salt relatively solutions About 100- µ m diameter holes drilled in air and in Through-holes of sub-micrometre diameter drilled;the The etching rate in water was about half of that in air; 2 µ m 2 W/cm 5 10 W/cm × 7 Focused beam 1–30 mm water layer over the specimen Specimen immersed into circulating water, focused beam 0.3 mm, up to 7.1 × 10 Optically tweezered particles of diameters 4–7 Focused beam, no scanning, specimen immersed into water specimen immersed vertically into water Specimen under a liquid layer (2 mm) Focused beam, 3.3 the experiment Novel features, observed phenomena, c eam Other features of 2 µ s, 10 J, W/cm 10 , CW , 514 nm, 1W peak, –10 N:A,355-Nd:YAG, nm, 6 + + 1-ms pulsed laser, 120 Hz dYG 100WNd:YAG, Focused beam, Nd: glass, 140 10 Nd:YAG, 100 ns, up to 50 kHz 3 ω 7ns CW,pulse modulated Cu-vapour, 510.6 nm, 25 ns, 6 kHz parameters Ar Ar 2 ser micromachining and related experiments. (reports where onl , NaCl 4 -xylol, o ) 2 SO 2 ,K -xylol, 3 p spirit, ether, glycerin nitrogen (LN NaNO solutions Air, water, heptane, benzol, Air, water, ethanol, liquid Air, water Water, water solutions of Water Water, KOH and CaCl assisted frontside la µ m; Zr Liquids- 0 . 4 4 Zn O 0 . 6 2 . 3 Sn, Pb, Zn, Bi, Mg, plate 0.5 mm Materials Liquids/gases in contact Laser type and b Precision tool steel, 304 stainless steel Silicon nitride ceramics Pyrene-doped PMMA latex Mn Fe ferrite machined with specimen Al, Cu, Mn, Mo, Ta, W Ti sheet 60 Table 4.2 Ch04-I044498.tex 12/9/2007 16: 11 Page 159 ) ( Continued Brook (1992) [454] Shafeev (1994) [474] Shafeev (1992) [471] Dupont (1995) [472] Miyazawa (1994) [493] Zweig (1992) [481] Leung (1992) [504] ;in ); in 2 phenomena , deformation of 2 incubation bubbles cause always ; formation of oxides on , the ablation rate was in 2 µ m observed > 20 J/cm phenomenon observed; water plasma µ m/pulse (alumina, 1064 nm, < 0.5 avoids decomposition of HgCdTe < 20 J/cm incubation ; pores formation and oxidation observed; ) – many times greater than in air; high-speed 2 µ m particles formed; etch caused by dislocation accumulation observed Cooling by liquids comparison with laser etching innon-irradiated reactive areas solutions are the notparticles etched; generation of of diameter In DMSO and DMFAhigher the than etching in rate water; was attemperature 2–3 low below times laser the fluences melting (surface fatigue point damage of was the observed; material) surface damage photographs of the convective flow presented photography studies of the steel surface observed;no deposits around the crater water the same that in air; 15 J/cm Irradiation below the meltingmaterial point of removal; reflected Si light causes transients0.5 recorded; No carbon contamination of theatmosphere);bubbles and surface particles (as generation observed; in oxygen grooves fabricated in water wereuniform irregular in and contrast not to KOH Etching rates up to 12 the foil was observed;shock velocity measured bybeams, probe an analytical model of shock pressure presented Etching rate up to 80 nm/pulse (PI, 140 mJ/cm case of Si etch film was used for enhancementfrom ablation of zone: acoustical acoustical signals signalsfluences at and different different laser angles presentedalso (mostly Si) PI, but At laser fluences 2 µ m, 2 2 W/cm 4 10 × Specimen under a steady or flowing liquid layer, scanning by focused beam Specimen immersed vertically into liquid, or having glass covered liquid layer above it, focused laser beam Specimen immersed vertically into water Some micrometre-thick liquid film formed by vapour condensation 1-mm liquid layer over thescanned specimen, laser beam and mask-defined irradiation; up to 0.85 J/cm Falling free-surface water film on vertical surface of the specimen; 0.1–30 J/cm Free-surface liquid layer over the specimen, scanned focused beam of diameter 80 2.5 , 2 , 2 2 -Nd:YAG, 1064 and 10 kHz, 1–50 mW average XeCl, 308 nm, 20 ns, 0.15–90 J/cm 4.5 GW/cm focused beam Cu-vapour, 10 ns, 10 kHz, 1–50 mW average KrF,up to 1.3 J/cm Cu-vapour KrF,248 nm, 30 ns; XeCl, 308 nm, 30 ns; 2 ω 532 nm, 7 ns dYG 1064Nd:YAG, nm, 5 kHz 3 (1:1) Br-containing etchants HNO solution Air, water Water, DMSO, DMFA Cu-vapour, 20 ns, Water–ethanol mixture Te Water, DMSO, DMFA, 1-x µ m) Water -based 3 Cd x O 2 ceramics, stainless steel stainless steel 304 Hg Si (SC) PI, Si, C,TiC, SiC, glass ceramics, PI (25 Si [100] and [111] Water, DMSO, DMFA, HF, Diamond Air, water, 10 wt% KOH Alumina, silica, AISI Al Ch04-I044498.tex 12/9/2007 16: 11 Page 160 Lu (1996) [494] Geiger (1996) [469] Shafeev (1997) [456], Shafeev (1997) [457] (1998) [458] Dolgaev (1997) [461] Simakin (1995) [475] (1996) [459] Dolgaev (1996) [460] [480] Ageev (1997) Voronov ≈ 30 nm presented omments References shock pressure intense evolution of etched surface was bubbles 4 ) 2 H 2 on thermal parameters of µ m/s; in comparison with ); hydrodynamic impact probably 2 ablated mass and generation of particles observed; etching in KOH solution,the etches surfaceetch quality rate and were significantly lower in pure water ≈ 10- µ m wide and 25- µ mbeam deep scanning trenches etched speed at 3 removes the graphitized layer surface – about 10particles times generated; higher photographs than of in air; 10- µ m smoother than in water;surface 33 etched nm in Si water clusters was oxidized on surface; gas microbubbles etched surfaces were catalytically active dueelemental to Si particles on them materials in analytical formmeasured presented; 5–60 MPa 100- µ m deep grooves etched; etchthan rate in was air; greater X-ray diffraction studies; No debris on etched surfaces;N Dependence of Etching incubation time aspresented a (in function region of 70–90 the J/cm fluence Etched surfaces were almost withoutthreshold graphitic fluences and layer; incubation timeshigher several than times in air; etching(DMSO, 18 rate J/cm up to 100 nm/pulse Ablation rate was highest when water was sprayed onto 2 2 W/cm µ m spot ; water 7 2 2 10 × ≈ 2-mm liquid layer above the specimen, focused laser beam Specimen immersed into water, focused beam, no scanning, 1.2 sprayed onto specimen or 1–20-mm water layer over the sample 1-mm liquid layer over the specimen, scanned laser beam and mask-defined irradiation 1–2 mm liquid layer over the specimen, scanned laser beam, up to 16 J/cm 1–2-mm steady free-surface liquid layer over the specimen, focused laser beam, static and scanned; up to 16 J/cm Mask-defined irradiation, up to 35 J/cm 1 mm liquid layer over the specimen, scanned laser beam, 20 the experiment Novel features, observed phenomena, c µ m µ s, , nm, beam Other features of 00 µ s, 1–5 J , CW,TEM + Cu-vapour, 511 nm, 15 ns, 10 kHz Cu-vapour, 510 nm, 10 ns, 8 kHz 514.5 nm, 100–960 mW, spot size down to 4 15 ns, 8 kHz XeCl, 308 nm, 50 ns, 20 Hz, 2 J 10 ns, 8 kHz Nd:glass, 140–900 0.5–1.5 J Ruby,500 parameters Ar 4 H 2 KOH + 3 ) (0.1–20 M) HNO Air, water Air, water, DMSO Cu-vapour, 510 nm, Air, water Water, water Water, DMSO, DMFA, HF, Continued ( TiC, 3 O 2 polycrystal Materials Liquids/gases in contact Laser type and Poly-SiC Air, water, DMSO96% alumina Cu-vapour,ceramics 510 SiC ceramics Air, water, DMSO, N Diamond (synthetic SC and CVD films on Si) Sn, Pb, Zn, Bi, Mg, machinedSi (SC) [100] and [111] with specimen Al Al, Cu, Mn, Mo, Ta, W, Ni Table 4.2 Ch04-I044498.tex 12/9/2007 16: 11 Page 161 ) ( Continued Geiger (1998) [485] Lapczyna (1998) [468] Berthe (1999) [351] Ohara (1997) [484] Kruusing (1999) [488] von Gutfeld (1998) [505] Roth (2000) [452] , 4 –up studies N 3 3 O 2 cracks and ) are higher µ m/pulse 2 strength µ m per pulse ); plasma 2 for laser light (see µ m/pulse in air by ACCIC code emission; µ m) if machined under µ m fabricated; ,308 nm:4 J/cm ); ablation rates were about 2 3 (more than in air); fog and 3 calculated ); threshold fluences (Si 3 O 2 O 2 2 O 2 , 308 nm, 25 J/cm 3 , – lower than in air); up to ,Al 4 2 O is greater ( ≈ 1 2 O plasma and sound 3 ; less than 2 µ s (Al of laser etching in both neutral and reactive water/saccharose droplet as mask , SiC, Si µ m/pulse in water contra 0.1 2 at etched surfaces observed µ m) µ m/pulse for Al review (XeCl laser, 12.5 J/cm (ZrO at 23 GW/m Figs 4.21 and 4.22) Circular and annular mesasusing were a ablated into PMMA than in air;less (3.6 No debris; etching rate inetching in water PFC greater is than faster and inin in air; water; ethyl etching alcohol slower rate than isvaporization greater for energy, liquids low withgravity viscosity low and high specific pores 248 nm:1· 6 J/cm material; melting of the irradiatedsurface roughness material is reduced; liquids water film (except Al times lower than in air, with exception of Al to 1.4 ablated material plume photographedafter – 500 plume decays 0.9 emission was faint in water;little additives effect in water had Ablation rate in water at 248 nm up to 0.1 Almost total avoidance of redeposition of the ablated A The thickness of ablated matter was 2.2 Trenches of width of 20–30 2 µ m ; alcohol 2 µ m, 0.1–2 mm/s onto surface, mask-defined ablation, up to 30 J/cm added to water in course to enhance wetting immersed into free-surface water onto surface, focused laser beam, up to 12.5 J/cm Experiment was performed in vacuum, < 0.01 mbar Sample immersed into liquid, scanning by focused beam, spot size 10 5–6-mm water layer (covered by window) over the sample, scanning by focused beam, spot 50 Water film sprayed Workpiece Water film sprayed , µ m, 2 2 µ m, 3 ns, up to µ m/s , 157 nm, 20 ns, 2 KrF,248 nm, up to 800 mJ and 150 Hz XeCl, 308 nm, up to 2and J 20 Hz 2 Hz, 0.4 J/cm KrF,248 nm XeCl, 308 nm scanned focused beam 80 1.064 ≈ 50 GW/cm Nd:YLF,1047 nm, 10 ns, 10 mW average F 1.06 Nd:YAG, 180 ns, 1 kHz , 1–2W average 5% 5% + + ethanol, water with soapy additives methanol, water perfluorocarbon (PFC) Concentrated solution of saccharose in water Air, water Air, water Air, water, water Water Water, ethyl alcohol, , 4 , 3 3 N , 3 4 O O 2 2 N 3 , 2 , AlN, Si 2 SiC; glass, stainless steel, polyamid Cu Ceramics Al PMMA Si (SC), (111), oxide and nitride coated Ceramics:Al (99.7%), Si SiC; ZrO ZrO high-speed steel 1.3343 Al Ch04-I044498.tex 12/9/2007 16: 11 Page 162 Zhang (2000) [275] Li (2001) [506] Berthe (2000) [257] Miyazawa (2000) [489] Hidai (2001) [478] Zhu (2001) [482] µ m —N and omments References + 4 ); chip breaker a ,NH ion were found in + 4 2 of etched in solutions µ m(R µ m/pulse (3 ns squared µ m/pulse (15 ns Gaussian hydrothermal reactions N and SiO + 4 µ m in depth fabricated (30 scans); ) and 0.75 µ m in width fabricated; etching in ablation, and NH 2 ) 2 surface roughness 4 µ m in diameter was drilled into 70 ,NH N recorded + 4 3 ∼ 30 ablation threshold was lower in water and steam 4 N 3 the taper was small andhole the was reduced redeposition around the Grooves about 30 water was slower than in air, butachieved much (no better debris, finish better was surface quality) water after Si grooves fabricated into sintered diamondcutting and inserts, providing c-BN 55% longer life and boric ion after BN ablation acoustic signals pulse, 1 GW/cm Grooves up to 120 liquid flow (by jet) is essentialfor for sintered good etch; materials best results were achievedKOH in solutions; 10% and 30% sintered materials was up to 4.5 compared to that in gases;was ablation in crater water in 2 SC timesthat cBN and in in air steam (laser: 6 20W,30products s); times NH greater than Si pulse,20 GW/cm Al foil by 45 laser pulses; compared with drilling in air, Ablation rate was 2 times higher in water than in air; A hole of The ablated thickness was 1.1 µ m) µ m) attached by immersed into water, layer thickness 3 mm, scanned focused beam 0.2 mm/s 1-mm steady free-surface water layer over the surface, focused laser beam coated by Al foil (16 vacuum grease ( ∼ 10 immersed into liquid, covered by window,local transverse submerged jet, scanning by focused laser beam 10 and 20 mm/min In water: water layer thickness 2 mm, local transverse submerged jet immersed into free-surface water the experiment Novel features, observed phenomena, c Workpiece was Workpiece Workpiece beam Other features of µ m, µ m, µ m, µ m, ∼ 12 2 2 µ m, 0.5 µ s, 1.15–1.4 J, N:A,355-Nd:YAG, nm, µ s, 5 kHz, 1.6W 4 GW/cm KrF,248 nm, 100 Hz Workpiece KrF,248 nm, 23 ns, up to 5 J/cm dYG 1.06 Nd:YAG, 40 average 1.06 Nd:YAG, 450 60 Hz 2 ω 50 ns, spot Nd:glass, 1.064 (455–529 nm), 3–24W, spot 80 and 30 s 3 and 15 ns, spot 5–6 mm parameters Ar-ion, multiline 2 O 2 (10–30%), H (5 and 10%), 3 3 ) KNO the sample) oxygen NaNO Air, water, KOH (5–30%), Air, water Water, air Water (3-mm layer above Water, steam, vacuum, air, 4 N 3 µ m Continued , grain ( 3 O 2 µ m µ m; c-BN size 3 foil) Materials Liquids/gases in contact Laser type and Si Ceramics: Si and cBN (SC and polycrystal) Si machinedDiamond, SC and sintered by Co, with grain specimen size ≈ 25 sintered by TiN and Al Al (polished) Water Al 1100 (70 Table 4.2 Ch04-I044498.tex 12/9/2007 16: 11 Page 163 ) ( Continued Haefliger (2002) [509] Sun (2001) [508] Zhu (2001) [507] Ramanathan (2001) [463] Koh (2002) [510], Hong (2002) [511] Kim (2001) [467], (2004) [473] 2 ); 2 light ≈ 10 times higher ; having water film effect of the laser 2 µ m diameter local was weaker and ≈ 10 ≈ 10 J/cm self-focusing ); dependence of sound spectral sound 2 µ m in diameter were drilled by (Figs 4.19 and 4.20) 2 ablation rate is greatest for liquid film thickness of a was lower and shorter (50 ns vs. 100 ns in air) formation of grooves as narrow10 nm) as and 266 nm of (at depthwas depth also up observed to 200 nm (at width 450 nm) crater at the edgerate of a the ridge main crater; around at the 1000 hole Hz pulse Holes and grooves machined; atablation presence rate of was water about the 3was times not lower than adjusted in in air water); (focus rate 62 nm/pulse, more than in19 case nm/pulse of (3.1 condensed J/cm layer, peaks (3.5 and 10.6 kHz)presented on water layer thickness Measurements of sound, surface reflectionphotoacoustic and beam deflection above thecase specimen; of in water film, the ablationand rate the is threshold fluence is 20–40% lower (0.5 J/cm on surface the emitted emission than in air (for Cu up to 15 nm/pulse, 13.5 J/cm for foil); few micrometres ablation rate saturates at Holes 40–60 single-laser pulse using beam in the liquidswith (the the liquids workpiece); were best not results inusing were contact CS achieved Ablation rates of Si and Cu were about 2 times higher The desired effect was the oxidation of Al, but Water layer thickness 1.1 mm provides largest ablation 2 µ m/s (details of 2 ∼ 16 mm; µ m) by glass, scanning rate up to 33 layer over the surface or condensed from vapour water film on the surface, focused laser beam Steady free-surface water layer 0.9–1.5 mm over the specimen, steady and scanned focused laser beam (diam. ≈ 50 experiment setup presented in Kim (2004) [473]) Condensed from vapour liquid film of few micrometre thickness, laser fluence up to 1.5 J/cm micrometres thick water film on surface, condensed from steam; focused laser beam, 2.5–13.5 J/cm Height of the liquid column gap between the liquid and the sample was 4 mm Water was covered ∼ 250 nm KrF,248 nm, 23 ns 1–2.2-mm water 0.25 ps, 1 and 1000 Hz, up to 1.1 mJ dYG 1064Nd:YAG, nm, 6 ns, apertured beam 30 mW,spot KrF,248 nm, 30 ns Dozens of dYG 1064Nd:YAG, nm, 15 ns, 1 Hz, 400 mJ, initial beam diam. 4mm Ar-ion, 488 nm, up to Ti:sapphire, 790 nm, Cl 4 µ m) , acetone, 2 methanol, NaCl, NH water–isopropanol mixture (50 %vol) Air, water Air, water, Air, CS Air, water Water, air Water (15 µ m foils and 100 nm films on Si (10–150 nm) Si 316 stainless steel (0.1 mm) Cu Si, Cu,‘mould components for IC packaging’ Al: 100 Al films Ch04-I044498.tex 12/9/2007 16: 11 Page 164 [495] Ito (2003) [514] Li (2004) [466] Katayama (2003) [498] Kabashin (2003) [496] Chen (2003) [512], Lu (2004) [513] Tsuji (2003) force omments References remove in water the crater were ring patterns 2 optically from µ m in width and dome- and glove-shaped fs pulses observed ≈ 20 nm; detected : grooves 25–45 4 continuum white light chemistry µ m in depth fabricated; in solution no have been observed alignment marks on theachieving Si fine chip; considerations ablation for area andgeneration low rate particles are presented; bubbles 60–160 detectable HAZ or recast; material removalgreater rate than 3 in times air;NaCl concentrationslow 80% scanning provides at speed greatestis ablation greater rate; if aspect machined in ratio solution;discussionremoval of material Case Nd:YVO less material than inwater air; more nanosecond material pulses remove thansurfaces in are in smoother (see air; Fig. inin 4.15); at water water fs-laser ablation the ablated Craters ablated into material; Silicon melting depth was (Fig. 4.18) were found onobviously irradiated caused by surface, acoustic wave, generatedbubble oscillations due to of irregular shape andobviously there due was to molten plasma material, heating (Fig 4.16) vacuum; at fluences over 100 J/cm generated at laser ablation specimen’s rear surface displacement – peak force8 about times greater than in air Ablation threshold in water 5 times larger than in Ablation rate in water 5 times greater than in air; The purpose of the process was to open the ARL at ) 4 , 2 , also a 2 µ m/s µ m, ∼ 4 m/s) above the workpiece horizontally into stirred free-surface water, focused laser beam into water, focused laser beam, focus above the sample, 15 mJ/cm 50–150 (numerical data for case Nd:YVO striped irradiation from two crossed beams horizontally into water, steady or scanned focused laser beam, spot ≈ 20 ≈ 1.2 kJ/cm vertically into free-surface water, water layer 10 mm, rotating vessel, focused laser beam vertically into water, focused laser beam the experiment Novel features, observed phenomena, c Water layer (running Target immersed Target immersed Target immersed Target immersed Target immersed , slit 2 beam Other features of µ m, µ m, , 532 nm, 2 4 µ m) -Ti:sapphire, -Nd:YVO µ J/pulse 110 fs, 1 kHz, 60–1000 J/cm 120 fs, 10 Hz, 4 mJ, 30 min OPO, 800 nm, 8 ns, 10 Hz, 4 mJ, 30 min dYG 1.06 Nd:YAG, beam (3 25 kHz, 2.6W 1.06 Nd:YAG, 0.3–2 ms, 20–30 Hz, peak power 4–7 kW 2 ω 400 nm, 200 fs, 1 kHz, 10 2 ω 30 ns, 92 mJ 355Nd:YAG, nm, ∼ 30 ns, 58 mJ/cm parameters Ti:sapphire, 800 nm, Ti:sapphire, 800 nm, ) from 5% up to saturation Air, water Water Water Water Continued ( Materials Liquids/gases in contact Laser type and SC Si (111) Water Organic ARL on Si (60 and 300 nm) 316 stainless steel Air, water solution of NaCl, machinedIron with specimen Au Ag Table 4.2 Ch04-I044498.tex 12/9/2007 16: 11 Page 165 ) ( Continued Choo (2004) [491] Daminelli (2004) [483] Lu (2004) [513] Iwabuchi (2004) [492] Chen (2004) [515] ) reddish light brilliant light and loud sound; N particles generated 2 (more than in air),material removal and 2 of ablation pressure and bubble E ) and pulse numbers ( N ≈ 1.7 J/cm water 2–5 times lower thanpreviously in reported air in (other Chen results (2003) [512]) In water: absence of thermaldendritic damage, solidified rougher molten surface, silicon , moreremoval, no uniform shoulder material on thefluence periphery,threshold emission,at high In water: threshold of surfacematerial modification removal greater, rate lower; similarcoefficients incubation than in air; elongated100-nm-period craters; ripples on irradiatedintensities surface; ( E at low Crater with rough surface formedpiled up with on small the grains periphery (see Fig. 4.13) rate less than in(Figs air 4.11 and and more 4.12) sensitive to laser fluence colloidal Si and SiO Mechanical impact collapse jet werewere recorded of by MPa piezo magnitude; thewas transducer; ablation in force both water on 4.5 target times greater than in air Time to penetrate 0.1–0.3-mm-thick plates was in µ m, µ m 2 , 2 ≈ 3 mm, 2 µ m) or µ m, µ m), liquid layer immersed horizontally into free-surface water (spot 27 vertically into solution (spot 37 5 mm in both cases, mechanical perturbation optionally applied; focused laserup beam to 15 J/cm immersed horizontally into free-surface water, water layer mask projection irradiation, 1–2.23 J/cm 1–5000 pulses immersed into water, focused laser beam, spot 100 spot 40 100 J/cm vertically into water, focused laser beam, spot 100 vertically into water, focused laser beam Workpiece Workpiece Workpiece Target immersed Target immersed µ m, µ J N:A,266-Nd:YAG, nm, KrF,248 nm, 25 ns, 10 Hz maximum 4 ω 10 Hz 130 fs, 1–1000 Hz, 3–250 dYG 1.06 Nd:YAG, 1064Nd:YAG, nm, 20 ns, up to 20 Hz,to up 242 mJ 25–250 mJ Ti:sapphire, 800 nm, 0.1 M 4 SO 2 Na Air, water Air, water Water, water solution of (rutile, SC) Water 2 -doped SC Si Cu, Fe,Al Air, water Cu, Fe,Al, stainless steel SC Si (111), n TiO Ch04-I044498.tex 12/9/2007 16: 11 Page 166 Ren (2005) [517] Kazakevitš (2005) [516] Jia (2007) [518] formed omments References µ m fabricated; ablation conical surface relief µ m and grooves of width ≈ 30 nm, in air 1200 nm µ m depending linearly on the ;ablation rate saturation at high fluences cavity confinement increases the laser-energy rated circuits fabrication process µ m were fabricated into the sample’s surface In case of moving laser beam diameter of laser spot with period of 10–50 Craters of depth down torate 50 in water was aboutin 2 water, the times greater thancoupling to in target air; corresponds to optical breakdownlayer threshold; thickness oxidized in water Craters of diameter of 100 of 5 (see Fig. 5.23) 2 µ m, µ l/s, steady water curtain 0.6–0.7-mm thick, 72 focused beam Sample was immersed horizontally into water immersed horizontally into steady of flowing water, steady or scanned focused laser beam, spot 10–60 20–50 J/cm the experiment Novel features, observed phenomena, c Workpiece Vertical flowing 2 µ m, nm, beam Other features of µ m, W/cm 10 ≈ 80 2 10 µ m, up to developed at CLEA-LALP,Arcueil, France × ≈ 65 W/cm ding to a layer below the photoresist layer in semiconductor integ 14 up to 7 ≈ 100 fs, 1 kHz, spot 10 dYG 355Nd:YAG, nm, 5 ns, 10 Hz, spot 130 fs, 1 kHz, 0.7 mJ parameters 130 ns, 1–5 kHz, 5W average Cu-vapour, 511 nm, 20 ns, 7.5 kHz, 3W average Ti:sapphire, 800 nm, ) Air, water Water, ethanol (95%) 1,06 Nd:YAG, Continued ( Materials Liquids/gases in contact Laser type and Si (100) ZnSe (SC) Water (1.2 mm layer) Ti:sapphire, 800 machinedCu, brass (40Zn60Cu), bronze with specimen (8Sn92Cu), SC W Notations CVD – chemical vapour deposition CW – continuous wave (laser) PI – polyimide PMMA – poly(methyl methacrylate) SC – single crystalline. Table 4.2 ACCIC – a code for simulation of laser – confined target interaction, ARL – anti-reflective layer; in the article by Ito et al. [514] regar Ch04-I044498.tex 12/9/2007 16: 11 Page 167

Subtractive processing 167

4.1.3 High-power laser underwater and water-assisted cutting 4.1.3.1 Arrangements with axial symmetry The machining techniques using high-power lasers differ considerably from low-power ones. The laser beam, along with shielding gas and/or water, is fed to the workpiece through a special cutting head (Fig. 4.23). The thickness of the materials cut through may range up to 50 mm, the lasers are CW or millisecond pulsed with power up to some kilowatts. The CO2 lasers are preferentially used because of their high energetic efficiency. Water is the choice for cooling liquid for its low price and safety. Because CO2 laser light (10.6 µm) is strongly absorbed in water, a local dry zone is provided as a rule (Fig. 4.24). Cooling of the workpiece by liquid reduces heat-affected zone (HAZ), avoids the redeposition of the debris, and reduces the emission of waste gases and particles into the atmosphere. There are also applica- tions where water is already present at the workpiece, like at dismantling and repair of nuclear reactors parts [519–521].

H2O Air H2O H2O O O2 O2 2

(a) (b) (c) (d) (e) Figure 4.23 Schemes of underwater and water-assisted laser cutting. Literature examples: (a) Alfille et al. [520], (b) Matsumoto et al. [519], (c) Konagai et al. [366], (d) Haferkamp et al. [522], (e) Richerzhagen et al. [523], When CO2 lasers are used, a dry zone at the workpiece surface is needed (a), (b), (d), because water does not transmit well 10.6 µm radiation. In the case on Nd3+-based lasers (about 1 µm wavelength) light may be transmitted through water (c) or even along a water jet (e). Typical consumption of water: (d) 15 ml/min [522], (e) 50 ml/min [524].

Laser Pulsed gas flow Nozzle

Water

Workpiece

Gas Assist Water intake due to vortices gas Nozzle Vortices flow Water

Dry zone Vortices Workpiece

Figure 4.24 Schematics of CO2 laser cutting with water cooling from frontside [522]. Due to high absorption of 10.6 µm light in water, local dry zone is used. Water may be provided to the working zone using pulsed assisted gas of by vortices-induced pulsation. © Laser Zentrum Hannover, reproduced with permission. Ch04-I044498.tex 12/9/2007 16: 11 Page 168

168 Handbook of Liquids-Assisted Laser Processing

2. cw-Unter 3. cw-Atmosphäre 4.gepulst- 1.cw-Atmosphäre Wasser Leistungsregelung Atmosphäre

P = 1000 W P = 1000 W Pmax = 1000 W PLP = 1000 W h = 1000 W Pmin = 300W = 40 % f = 500 Hz Figure 4.25 V-cut contours in a 1-mm-thick X5CrNi1810 stainless steel sheet [522]. Gas: oxygen; cutting speed 3.5 m/min, CO2 laser. (1) P = 1000W,CW,cutting in ambient air; (2) P = 1000W,CW,cutting under water; (3), CW,power controlled, cutting in ambient air; (4) pulsed 500 Hz, P = 1000W, τ = 40 per cent, cutting in ambient air. P: laser beam power, τ: duty ratio. Water-assisted cutting by a CW laser provided nearly the same cut quality as cutting by pulsed lasers in gas [522]. © Laser Zentrum Hannover, republished with permission.

Figure 4.25 demonstrates the effect of water cooling on laser cut quality. Because at cut corners the beam feed rate slows down, there is a hazard of burnout of material due to excessive heat accumulation. CW laser cutting with water cooling (2) provides a better cut quality than cutting in dry gas (1), although not equally good quality as cutting by a pulsed laser beam in dry gas (4). Alternatively, the burnout may be reduced by dynamic control of the laser power (3). Under circumstances, the maximum cutting speed at the presence of water may be higher or lower than the maximum cutting speed in gas ambient. For example, Haferkamp et al. [522] report a higher cutting speed under water, while Alfille et al. [520] report a lower cutting speed for similar lasers and materials (CO2 lasers, stainless steel) (see also Table 4.3).

4.1.3.2 Arrangements with separate laser beam and water jet Such arrangements are simple and economical,because no special working head or immersion of the workpiece into liquid is needed, but a general purpose laser cutting device can be easily upgraded with a water jet.

Water jet advancing laser beam In patent US5068513 [525], a combined water jet/laser beam web slitter is described (Fig. 4.26). A high- pressure water jet is used in conjunction with a relatively low-power laser to produce a smooth cut in a travelling web. The cutting procedure produces a relatively small amount of fibre dust in the atmosphere surrounding the cutting operation. The water jet serves the travelling web into separate parts, and the laser is directed to the severed edges to burn away the protruding ends of the paper fibres to produce a uniform, smooth cut in both severed edges (original summary from Ref. [525]).

Water jet and laser beam directed to the same point Directing water jet to the fusion zone (Fig. 4.27), the cooling and melt removal effects are most pronounced, resulting in best cut quality and highest cutting speed. Alternatively, the workpiece may be immersed into water, in which case also the water jet is submerged JP11000786 [526] and JP11000787 [527]. Ch04-I044498.tex 12/9/2007 16: 11 Page 169

Subtractive processing 169

48a P 32a 46a 42a

34a

Laser 44a Water jet beam 45a 26a Web

24a 24a 28 38a 36a 40 Water 30

Figure 4.26 Schematics of a water jet slitter with laser finish (Patent US5068513 [525]).

5 7 4

5 8 1

6 6 8 3 3 9

2 9 2a 2 1 12 3a 13

11 10 (a) (b)

Figure 4.27 Combined water jet/laser beam cutting devices. After patents: (a) JP2001062652 [528], see also JP2003062683 [529], JP2002146669 [530], JP2000317659 [531]; see also (b) JP11000780 [532], see also JP 11000841 [533].

Water jet following the laser beam In the work by Schüning and Rothe [534], a water jet was used with purpose to confine the assist gas jet, increasing the gas flow velocity and improving this way the melt removal from the gap (Fig. 4.28). Because the water does not enter the fusion zone, the system is proper to be effectively used also with CO2 lasers. Water also cools the workpiece. Systems where a water jet follows the laser beam, are described also in JP11000774 [535] and JP4053699 [536]. Ch04-I044498.tex 12/9/2007 16: 11 Page 170 Black (1997) [540] Konagai (1996) [336] [539] [520], (1997) [521] Li (1999) [541] Bach (1988), [537] Haferkamp (1989) [538], Haferkamp (1990) [522] Schüning (2000) [534] Matsumoto (1992) [519] Alfille (1993) Alfille (1996) 2 ∼ 15% lower (1 mm) than in gas, 15 times more H ∼ 40% lower and (in gas jet) in order to avoid µ g/J ures, observed phenomena, comments References water jet followed laser beam surface; the laser grooved component had tensile strength than the mechanically milled one In water: the cutting speed was Burnout was greatly reduced the kerf width at exit1.5 mm side in narrower air); (1 the mmdepth cut contra of was 7 of m better than quality at at depth water 0.5 m 6 times less aerosols andunderwater cutting 40% less sedimented dross at Less burr, better tolerances; HAZat is cutting 10–20% in narrower water; thedetached plastic or layer burnt on near steelwas the was reduced cut; not the by 10–30% emission of gases the expansion of theincreasing of the gas gas flow jet velocity withinthe along the the optimized cutting gas cutting front; jet gap, allowedto a the higher gap impulse material transfer systems, in resulting deeper in levels better as conventional materialpossible efficiency cut rate quality, higher and a greater process window emission Material removal rate 10 Novel feat A groove mesh was fabricated by laser on a cylindrical A /min; 3 Local dry zone (oxygen) above the specimen; rear side in contact with200–700 water; mm/min Local dry zone orapplied water though the working head nozzle (Wasserdüse), 15 cm Local dry zone (air)0.5 and 7 m belowwater the surface; local dry 2 timeszone less (oxygen) above aerosols the and debris, workpiece Local dry zone (oxygen) Narrower and more regular kerf Local dry zone (oxygen) above the specimen; rear side in contact with50 water; mm/min different assist gases Laser beam transmitted through water, focusing lens in water experiment performed underwater. µ m, pulsed, , 1 kW,CW and , 5 kW , 0.5 kW , 0.5 and 5 kW ,5kW , 530W,pulsed , 10.6 2 2 2 2 2 2 2 Laser type and beam Other features of the 300–800W pulsed CO 1.2Nd:YAG, kW, pulsed 1–2 ms pulses and intervals 80 ns, 110W average assisted by liquids or Liquids parameters Air, water CO Water CO Water CO Water CO Water CO Water Cu-vapour, 511 nm, High-power laser machining -based glazed 3 carbon steel Water CO O # 2 Steel C45 sheets (3 mm); steel St 37-2 (3 mm, also EPO coated); X5CrNi1810; reinforced plastics ceramic tiles, 8.5 and 9.2 mm steel, 10 mm Materials Stainless steel 316, 2–8 mm stainless steel 10–30 mm; Stainless steel 304L, 10–50 mm SUS 304 austenitic stainless steel, up to 20 mm 45 machined AISI 304 stainless Al Table 4.3 Ch04-I044498.tex 12/9/2007 16: 11 Page 171

Subtractive processing 171

Laser beam

Gas jet Supporting water jet

Cutting gap modell Figure 4.28 Method of laser cutting supported with a water jet [534]. © IEEE (2000), reproduced with permission.

4.2 Liquid-Jet-Guided Laser Beam Machining

First written report about light guiding by a water jet is from 1842 [542].The phenomenon was later extensively used in illuminated fountains. In 1870, John Tyndall experimented with sunlight guiding in a stream of water. First experiment of guiding a laser beam by a water jet was obviously performed in 1976 by Amarnath Kshatriya at British Columbia Institute of Technology,Burnaby,Canada (Fig. 4.29). First materials technology report where a liquid-guided laser beam was used is obviously the article by von Gutfeld et al. [544] (Fig. 4.30). The full potential of guiding a laser beam by a liquid jet in materials processing was recognized only in 1993 by Bernold Richerzhagen at Ecole Polytechnique Fédérale de Lausanne, Switzerland [545].The essential understanding was that a water jet as thin as tens of micrometres can transmit hundreds of watts of laser power capable to cut millimetre-thick materials with high precision. The technology named Laser MicroJet® was commercialized in 1999 by Synova SA (Table 4.4). Similar methods and devices are described also in patents of other companies, WO2004094096 [546], JP2003173988 [547], JP11000780 [548], JP2004122173 [549], JP2000317661 [550], etc. (at least 40 patents were issued up to the end of year 2006). Figure 4.31 presents the typical arrangement of laser light-guiding water jet system. A laser beam is focused into a nozzle while passing through a pressurized water chamber. The low-pressure water jet emitted from the sapphire or diamond nozzle guides the laser beam via total internal reflection at the water/air interface. Stable length zb (Fig. 4.32) of a cylindrical thin jet of an inviscid incompressible liquid is given by the following relations (gravity forces and surrounding gas effects are neglected) [554]:

zb = utb, (4.9)

  1 R0 tb = ln , (4.10) βmax δ0
= σ βmax 0.34 3 , (4.11) ρR0 Ch04-I044498.tex 12/9/2007 16: 11 Page 172

172 Handbook of Liquids-Assisted Laser Processing

C B

LASER

A

Water tap Figure 4.29 Schematic of the total internal reflection demonstration using a laser and a water jet. © American Institute of Physics, (1976), reprinted with permission from Ref. [543].

- + Anode JET Cathode

re r

Nozzle (a)

Inlet Circulating pump Anode Cathode Potentiostat

Laser

Beam expander Quartz Nozzle window Drain

Electrolyte reservoir Heater stage (b) Figure 4.30 Schematics of solution jet-guided laser-enhanced electroplating experiment. © American Institute of Physics (1983), reprinted with permission from Ref. [544]. Table 4.4 Technical characteristics of water jet guided laser systems by Synova S.A. Lasers Nd:YAG, 1064, 532 or 355 nm, <100 µs Liquid Filtered and deionised water Water pressure 20–500 bar Jet speed Up to 300 m/s (at 500 bar) Orifice diameter∗ 20–150 µm Water flow rate 5–100 ml/min

∗ The diameter of the jet is some 10–20% smaller than the nozzle diameter because of the vena contracta effect [552]. Ch04-I044498.tex 12/9/2007 16: 11 Page 173

Subtractive processing 173

Z Y Laser in 632 nm Focusing objective X

Sapphire nozzle Quartz window

Water inlet X = 0 Chamber

Jet Metallic holder

Figure 4.31 Schematic of the coupling unit of laser light-guiding water jet (Synova’s Laser MicroJet®Technology). The laser light is focused onto orifice and transmitted along a the jet due to total internal reflection. The diameter of the jet is commonly 65–100 µm, the jet speed at 200 bar pressure is about 200 m/s. A 50 mm long jet is able to transport up to 700W light power, corresponding to 21 MW/cm2. Source: ‘Fig. 1 of water jet as a multimode waveguide – theoretical and experimental investigation of modal noise and beam propagation in material processing with laser microjet’ © Laser Institute of America, Orlando, Florida (2006), reproduced with permission from Ref. [551]. The Laser Institute of America disclaims any responsibility or liability resulting from the placement and use in the described manner. www.laserinstitute.org. All rights reserved.

200 Orifice diameter 100 m

150 75 m 100

50 m 50 Stable jet length (mm) Stable

250 500 750 1000 Pressure (bar)

Figure 4.32 The stable jet length measured from the nozzle inlet to the position where the first drop is formed [553]. The maximum working distance of water-jet-guided laser cutting is closely correlated to this value and varies analogously concerning nozzle diameter and pressure. © Coherent GmbH, reproduced with permission.

where u is liquid mean velocity in jet, tb is the time required for a disturbance in jet radius to grow from δ0 to R0, βmax is the frequency of most rapidly growing disturbance, R0 is the radius of the jet, δ0 is amplitude of the initial disturbance, σ is liquid surface tension, and ρ is liquid density. For practical calculations, the initial −3 −4 disturbance may be taken 10 –10 of the undisturbed jet radius R0. As reported by Spiegel et al. [555], at large energy densities, >100 MW/cm2, the transmission of 532-nm, 180-ns-laser light was reduced by Raman scattering (peak value at 653 nm) in water. For example, at 410- MW/cm2 input peak intensity, the transmission of an 8-cm-long water jet decreased by 26.7 per cent (from 86 to 63 per cent). Ch04-I044498.tex 12/9/2007 16: 11 Page 174

174 Handbook of Liquids-Assisted Laser Processing

Table 4.5 Water-jet-guided laser cutting speed dependence on silicon wafer thickness [524, 556]. Wafer thickness (µm) Cutting speed (mm/s) 100 120 200 80 300 40 500 20 700 10 1000 6 1500 3 2000 1

4.2.1 Applications and performance Water-jet-guided lasers beam technology has been developed so far for precision machining at moderate laser power, the main application areas being dicing, drilling, and slotting of semiconductor wafers (Si, GaAs, InP, and SiC), fabrication of solder masks (stencils) and endoscope parts, cutting of ferrite cores and super hard materials (silicon nitride, diamond). Table 4.5 gives an example about the efficiency of the method. Advantages of water-jet-guided lasers beam machining in semiconductor industry (in comparison with abrasive and dry laser machining): • The dissipation of harmful to photolithography and semiconductor structures particulates is extensively avoided. • No debris or microcracks left; no change in the nature of the surface material by heat damage; high-quality cut with constant width and parallel walls. • The kerf is effectively cooled, resulting in negligible heat-affected zone. • The mechanical force applied by the water jet on the work piece is very low (<0.1 N). • Water-jet-guided laser device has much lower operating costs than a corresponding diamond saw (but much higher investments).

Surface roughness

Surface roughness of water-jet-guided laser cuts in 660-µm-thick silicon is reported to be Ra 3 µm, what is at the same level that in diamond-edged blade cuts [557]. Limitations of water-jet-guided laser machining • It is hard to cut well reflecting materials; only thin foils of Cu and Au can be cut. However, thin Cu and Au coatings on absorptive materials do not matter. • It is hard to cut transparent or little absorbing materials; for example, the cutting speed is low for 99% Al2O3 ceramics, but moderate for 96% Al2O3 ceramics [558]. A list of over 200 technical articles (1996–2007) about Synova’s Laser MicroJet®technology can be found on Internet site http://www.synova.ch/pub_articles.php [559]. See also Table 4.6. 4.2.2 Molten salt-jet-guided laser beam

In patent DE10238339 [464], the use of molten salt jets (e.g. NaNO3 and KNO3) for laser light guiding was proposed. The advantages of molten salts instead of water are higher heat capacity and higher oxygen content that facilitate the removal of the material in oxidation cutting. Ch04-I044498.tex 12/9/2007 16: 11 Page 175 ) ( Continued Kshatriya (1976) [543] Richerzhagen (2001) [524] von Gutfeld (1985) [560] von Gutfeld (1983) [544] [561] Wagner (2002) ,then the 2 (at µ m µ m/s were ∼ 30 down to 3 a 2 µ m/s was achieved C) is described; the advantages ◦ ,60 2 plating rates up to technology ® ); the resistivity of achieved coatings was 2 (1–16A/cm ∼ 150A/cm Demonstration of laser lightwater guiding jet through a by water-jet-guided laser beam ismould compound proposed: first, is the removed at 29–42 MW/cm achieved are: no focusing problems; suitsmaterials for cutting of of thickness sheet in mm, R Electroplating speed up to 50 achievable (SC Si) near to bulk value of Cu Laser MicroJet copper is cut at 310 MW/cm region of plating; Novel features, observed phenomena, comments References A two-step process for singulation of IC packages , scanned 2 Laser type and beam He-Ne, 1 mW 532Nd:YAG, nm, 230–360 ns, 30–60 kHz, 0.4–1.7 mJ beam 2–10 kW/cm dYG 1064,Nd:YAG, 532, 355 nm, 15 ns – CW, 100–700W average Ar-ion, CW, Ar-ion, CW,up to 25W Jet provided a rapid re-supply of fresh ions into µ m; length µ m Nozzle and jet Nozzle diameter 0.2–0.5 mm, velocity 5–10 m/s Jet diameter 20–1000 up to 150 mm, velocity up to 450 m/s Nozzle diameter 0.35 and 0.5 mm, length 5 mm, jet velocity 10 m/s 60–100 4 Liquids parameters parameters Distilled water, 50–500 bar, ∼ 1 l/h containing Au cyanide containing CuSO Water Nozzle diameter , 3 O 2 Liquid-guided laser beam processing (examples). , SiC, 4 N 3 polyimide a.o. Materials machined Galvanic Au plating Water solution, Galvanic Cu plating Water solution, Cu,Al, Ni,Au,Ag, stainless steel, Si, Ge, GaAs, InP,Al IC packages (mould compound and Cu frame) Si Table 4.6 Ch04-I044498.tex 12/9/2007 16: 11 Page 176 [562] Battaglia (2006) [551] Spiegel (2004) [555] Couty (2004) [552] [563] Wagner (2003) Vágó (2003) ; it causes the 2 2 of water jet was µ m) saturated > 100 MW/cm (jet diameter 19 of laser light in water jet was studied ∼ 80 mm at velocities over 250 m/s Using water-jet-guided laser beam, burr-free,tapered slightly cuts without distinguishable heat-affected zone were achieved; up to 40 000hour high-quality can apertures be per fabricated in stencil masks Mode structure both experimentally and theoretically; specklesize grain around 20 mm was both predicted and observed Growth of laser-induced disturbances investigated both experimentally and bysimulation numerical using FLUENT software jet breakup length to Strong stimulated Raman scatteringobserved (653 nm) at was irradiances decrease of transmitted to thetransmission workpiece of light: an the 8-cm-long26.7% water (from jet 86% might to droppeak 63%) by intensity when of the only input 410 beam MW/cm has a Novel features, observed phenomena, comments References µ s, 2 1.2, 50 ns, 1.5 kHz, = 2 dYG 1064Nd:YAG, nm, M Laser type and beam dYG 1064Nd:YAG, nm, 0.4 25 kHz , 22W average dYG 532Nd:YAG, nm, 180 ns, 10 kHz, 10 mJ, 100W average, 90 kW peak, 1.3 GW/cm 7W average Nd:YAG, 532 nm, 20 kHz, 13W average He-Ne (for jet breakup studies) µ m, µ m, 0.03 = µ m, 5–50 MPa µ m, jet diameter µ m, 60–325 m/s Nozzle and jet 75 60 47 nm, 250 bar, stable jet length 60–80 mm 40 94–209 m/s NA C) Nozzle diameter ◦ Liquids parameters parameters Water (30 WaterWater Jet diameters 19 and Jet diameter 48 ) µ m) Water Jet diameter 50 and Continued ( Materials Cu Steel (0.4 mm) Water Nozzle 150 machined Stainless steel (150 Notations IC – integrated circuit. Table 4.6 Ch04-I044498.tex 12/9/2007 16: 11 Page 177

Subtractive processing 177

4.3 Water at Backside of an Opaque Material

Water at backside cools the workpiece, avoids the adhesion of debris and dross on the workpiece, and avoids the deposition of debris on the opposite parts. Liquid at backside is not on the laser light path, so CO2 lasers may used in conjunction with water. In Fig. 4.33, three typical configurations of water–workpiece system are shown. A modification of the arrangement in Fig. 4.33b is described in JP11058049 [564]: a frozen liquid at the backside with aim to reduce the assist gas consumption (not shown in Fig. 4.33). Water-at-backside drilling is useful for precision drilling of small holes into injection needles (WO8903274 [565]) and engine fuel injectors (WO0069594 [566]).

Laser Laser Laser Workpiece Workpiece Workpiece Gel

(a) (b) (c) Figure 4.33 Laser cutting of tubes and sheet materials with water at backside. a) Liquid protects the opposite wall of a tube from melt deposition, JP2052188 [567]; (b) Liquid prevents the adhesion of debris and dross at the backside of the workpiece, JP8132270 [568], JP2002018586 [569]; (c) Having water-containing gel at the backside of a silicon wafer, JP2004042082 [570].

4.4 Backside Machining of Transparent Materials

4.4.1 Introduction If the material to be machined is transparent to laser light, then it is possible to supply the laser beam through the workpiece. This principle has been utilized in laser soldering, cleaning (Fig. 2.2), and also in subtractive processing as described in this section. First published report about laser backside modification of a transparent material in contact with liquid is probably the article by Leonov et al. from 1975 [571]. The authors report that the damage and the optical breakdown threshold at a glass plate in contact with water were 2.5 times higher compared to these in air. Later, in 1980, Davidson and Emmony [572] studied cracking and ablation of ZnSe windows in contact with water due to CO2 laser irradiation (Fig. 4.34). The damage was attributed to the action of a shock wave, generated due to rapid expansion of water vapour. More recently (1996–1999), Ikeno, Dolgaev, Simakin and Lyalin fabricated holes and grooves in various optical materials using aqueous salt solutions and carbon suspensions for laser beam absorption enhancement (see Fig. 4.35 and Table 4.9). Interest to laser backside machining increased considerably after Wang et al. reported in 1999 that opti- cally smooth surfaces with nanometre resolution can be fabricated by this technique in hard UV-transparent materials. They used pyrene solution in acetone and an excimer laser (Fig. 4.36). Inorganic optical materials: glass, fused silica, quartz, sapphire, fluorides, diamond, etc. are hard, brittle, and thermally and chemically resistant, which makes them difficult to machine with conventional methods such as electron-beam lithography and photolithographically defined HF etching or plasma etching. These methods suffer also from low aspect ratios [575]. High aspect ratio structuring of quartz by ion track etching has been demonstrated [576], but a MeV ion accelerator is needed for implementation of it. All the mentioned micromachining methods need a vacuum system. Grinding and ultrasonic machining suffer from geometrical restrictions and unsufficient for optical devices finish (Table 4.7). Ch04-I044498.tex 12/9/2007 16: 11 Page 178

178 Handbook of Liquids-Assisted Laser Processing

Cu CO Laser mirror 2 Laser pulse

ZnSe b c a ZnSe t Water v

w Water

Figure 4.34 Scheme of experiment (a) and shock wave propagation (b) at CO2 laser irradiation of ZnSe plate in contact with water. Material’s fracture corresponded to the shock wave pattern shown in the figure. © Taylor and Francis Ltd., republished with permission from Ref. [572]. http://www.informaworld.com

Laser Beam

Vetch

Vsc Sapphire Liquid

Figure 4.35 Sketch of etching of inclined channels in sapphire by a scanned laser beam [573]. vetch, vsc are etching rate and scanning velocity respectively. Liquid: toluene with carbon suspension. Laser beam was scanned at constant speed; formation of absorptive carbon film on the surface led to self-modulation of the etching process and formation of separate channels. Laser: Cu-vapour, 510 nm, 10 ns, 8 kHz,≈0.5W average, 2 mm/s. © Elsevier. Inorganic optical materials are also difficult to machine with conventional lasers because of low absorption of the light, resulting in low surface quality. High-quality microstructuring can only be achieved by ablation withVUV-, ps-, and fs-laser pulses [577, 578]. LIBWE offers a opportunity to reach optical surface quality by conventional laser systems of low cost. In comparison with photolithographical techniques, there is no need to fabricate expensive photomasks. Laser backside etching in organic solutions (Table 4.8) needs about 10 times less energy than direct UV etching in air and the machined surfaces are smoother [579]. Main applications of liquids-assisted laser backside etching are micro-optical and microfluidic components (Figs 4.37, 4.51 to 4.54).

Considerations for the choice of liquids • Water is more safe than organic solvents. • Solubility of absorbing additives in the solvent should be as high as possible; for example, in case of pyrene, acetone is a better solvent than THF [587]. Ch04-I044498.tex 12/9/2007 16: 11 Page 179

Subtractive processing 179

Transparent material Pattern Lens mask

Pyrene KrF acetone Excimer solution Laser

Pyrene Acetone CH3COCH3

Figure 4.36 Setup for laser backside etching (LIBWE) of a fused silica by KrF laser [574]. Laser irradiation causes vaporisation and ionization of the solution in contact with the workpiece. High temperature and plasma irradiation modify the surface layer of the workpiece so that it starts also absorb the light. In steady regime the temperature of the workpiece reaches boiling point. High-pressure transient and bubble collapse-induced microjet probably contribute to the materials removal. © Elsevier.

Table 4.7 Comparison of glass and silica micromachining methods. Method Threshold fluence Processing speed Surface roughness

Micro sandblasting [584] 4–110 µm/s 30–90 nm (Ra)

Ultrasonic machining [581] 8.4 µm/s (quartz) 1.5 µm(Ra, quartz) Dry reactive plasma etching [584] 20 µm/min >10 nm Laser ablation in air, >10 J/cm2 200–300 nm/pulse >10 nm nanosecond pulses [582] Laser ablation in air, 6 J/cm2 (1.2 ps) 20–40 nm/pulse >10 nm fs/ps-pulses [582, 583] Laser ablation in air, 1 J/cm2 (157 nm) 20–40 nm/pulse 4–8 nm (r.m.s.) VUV,nanosecond pulses [580, 582] LIBWE, organic solutions [586] 0.3 J/cm2 5–30 nm/pulse 0.23–10 nm LIBWE, liquid metals [585] 1.3 J/cm2 (248 nm) Up to 600 nm/pulse 1.5–7 nm (r.m.s.) 7 J/cm2 (1064 nm)

• Halogenated hydrocarbons have reduced liquid decomposition effects (reduced incubation phenomena, less debris) [588]. • Liquid metals (Hg, Ga) do not show neither incubation effect nor produce debris, they provide high etch rate and enable the use of longer wavelength lasers [585].

Considerations for the choice of additives • High light absorption at the laser wavelength ensuring that only a micrometre-thick layer of the liquid in contact with the workpiece is heated. • Little debris from decomposition and chemical reactions. • High photostability and absence of luminescence (was the argument for choice of K2CrO4 in the work by Paraskevopoulos et al. [589]). Ch04-I044498.tex 12/9/2007 16: 11 Page 180

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Figure 4.37 Surface morphology of a calcium fluoride plate etched with 500 pulses of KrF laser at 900 mJ/cm2, using an acetone solution containing pyrene at a concentration of 0.4 mol/dm3 [574]. © Elsevier.

Table 4.8 Liquids and additives used in backside laser machining of transparent materials. Liquids Additives

Cyclohexane, tetrachloromethylene, NiSO4, CrO3, KMnO4, CrO3, FeCl3, tetrachloroethylene, benzene, toluene, cumene, KMnO4, KNO3,K2CrO4, carbon particles, t-butylbenzene, 1,2,4-trimethylbenzene, pyrene, pyranine, benzil, naphthalene, chlorobenzene, dichlorobenzene, fluorobenzene, phenanthrene, anthracene, isopropanol (IPA), tetrahydrofuran, 9-methyl-anthracene, 9,10-dimethyl-anthracene, methylmethacrylate, methyl benzoate, acetone, 9-phenyl-anthracene, fluoranthrene, Rose Bengal mercury,gallium dye, Np(SO3Na)3

Cheng et al. [590] present a table of etching thresholds, extinction coefficients and fluorescence quantum yields for 8 additives (pyrene, naphthalene, phenanthrene, anthracene, 9-methyl-anthracene, 9,10-dimethyl- anthracene, 9-phenyl-anthracene, fluoranthrene) to organic solvents.

Choice of the laser Nanosecond lasers are effective for LIBWE in organic solvents only in the UV region of wavelength. Fem- tosecond lasers are applicable also in NIR region [584]. Cheng et al. [591] succeeded in backside etching of glass with a 532-nm, 15-ns laser in conjunction with Rose Bengal dye solution in acetone. In case of liquid metals as absorbents, low-costVIS and IR lasers can be applied.

Advantages of liquids-assisted laser backside etching • Etching threshold may be 10–20 times lower than in gas. • Etching occurs well below the optical damage threshold of the materials (for example, the damage threshold of quartz is ≈20 J/cm2 for direct laser irradiation [587, 592]). • Low surface roughness in comparison with VUV and fs/ps-laser ablation in air, and with reactive plasma etching [580]. • Low debris, no microcracks. • One-step method in comparison with lithography. • Fabrication of long and bent channels is easier than in gases because of more efficient debris removal by liquid motion and debris dissolution. • There is no plasma shielding of laser light at backside etching. Ch04-I044498.tex 12/9/2007 16: 11 Page 181

Subtractive processing 181

Disadvantages of liquids-assisted laser backside etching • The surface may be contaminated by liquid and solute decomposition/reaction products like carbon,chlorine [593], and chromium oxide [573, 594, 595]. • Etching rate in organic solutions may be significantly lower than the etching rate in gas by fs/ps- or VUV lasers (Table 4.7). However, a low etching rate is an advantage in fabrication of sub micrometre features in optical materials, because the process control is easier.

Backside etching due to laser-generated hydrofluoric acid In the experiments by Murahara [596], backside etching (polishing) of fused silica occurred due to hydrofluoric acid, generated at laser irradiation of fluoroethylenepropylene in water (see Table 4.9, Murahara 2001). The chemical surface reaction is similar to this presented in Fig. 6.1.

4.4.2 Technologies, phenomenology, and etching mechanisms 4.4.2.1 Organic and aqueous solutions at backside of the workpiece Absorption of laser light For efficient coupling of laser light into a workpiece,high absorption coefficient of the liquid at laser wavelength is needed along with short heat diffusion length. Most widely used additives to organic solvents, like pyrene and pyranine start to absorb considerably only in the UV region (Figs 4.38 and 4.39), whereas used in the work by Cheng et al. [591]. Rose Bengal dye has the absorption maximum in yellow (Fig. 4.40).

Etching mechanisms Laser etching of inorganic transparent materials with organic or aqueous solutions at backside of the workpiece is supposed to proceed in the following way. (1) Absorption of light Absorption of light in solute following energy transfer to solvent and to workpiece. In pyrene, there is a strong evidence that multiphotonic absorption is the primary mechanism of absorption [574, 599, 600] (Figs 4.41 and 4.42). Typical absorption coefficients of used hydrocarbon solutions at UV wavelengths are about 104 cm−1 [590, 585], thus the heated by nanosecond-laser pulses depth is about 1 µm [479]. (2) Modifications of the workpiece surface At laser irradiation, the workpiece surface may undergo changes that enhance the light absorption. This leads to so called incubation effect (Figs 4.47 and 4.48), where ablation is absent or ablation rate is low for the first laser pulses and increases thereafter. Zimmer et al. [601] found, that at backside ablation of silica glass in pyrene/toluene solution, a surface layer of ∼30–50 nm became amorphous and its absorption coefficient at 248 nm raised up to 104–105 cm−1. Total 10–30 per cent of incident laser energy was absorbed in this modified layer. Organic solvents decompose due to laser heating (e.g. the decomposition temperature of acetone is around 700 K [587]); the decomposition products like carbon adhere on the surface and enhance its absorption (Fig. 4.49). Dolgaev et al. observed thermal decomposition of CrO3 near the solid–liquid interface resulting in forma- tion of water-insoluble of Cr2O3 suspension [595] and film of Cr2O3 [594] on the workpiece. Using carbon suspension in toluene, a thin carbon film was deposited on the workpiece, that led to self-modulation of the depth of etching of sapphire by a scanned laser beam (Fig. 4.35). Vass et al. [602] point that naphthalene methacrylate as working liquid may polymerize under action of laser light and form an absorptive layer on the surface. (3) Heat transfer and temperature rise Heat and temperature rise generated in liquid and in the absorptive surface layer is transferred into bulk of the liquid and into the workpiece, causing thermal stresses/softening of the solid, and melting/vaporization of both materials at higher temperature levels. Ch04-I044498.tex 12/9/2007 16: 11 Page 182

182 Handbook of Liquids-Assisted Laser Processing

0 Absorption (a.u.) 200 250 300

0 200 300 400 500 600 700 800 900 Wavelength (nm)

Figure 4.38 Spectrum of linear absorption of a 0.5 M pyrene/toluene solution [597]. The inset shows a more detailed view of the UV range. © Institute of Physics, reproduced with permission.

104 SO3Na 3 NAO S

) 3 − 1 SO3Na

mol 2 3 OH dm − 1 1 (cm Molar absorption coefficient 0 200 400 600 Wavelength (nm)

Figure 4.39 Optical absorption spectrum of 32 µM aqueous solutions of pyranine (8-hydroxy-1, 3,6-pyrenetrisulfonic acid trisodium salt) before (solid line) and after (broken line) irradiation with 5000 pulses from a KrF laser at fluence of 1.5 J/cm2 [598]. Reproduced with kind permission of Springer Science and Business Media.

Several researchers have calculated the temperature distribution at laser backside etching of fused silica [603– 605]. However, as shown by Zimmer et al. [601] the neglecting of light absorption in the modified surface layer of silica may lead to a considerable underestimation of the peak temperature. Considering absorption, they calculated for maximal interface temperature 6860 and 12 010 K at 950 mJ/cm2 fluence and wavelengths of 351 and 248 nm, respectively; while without absorption the maximum temperature was only 1079 K. For ◦ ◦ reference, the melting and boiling temperatures of fused silica are Tm = 1983 C and Tb = 2250 C. (4) Thermal stresses Dolgaev et al. [595] attributed the ablation of sapphire below the melting threshold to the cracking of the surface due to thermal stresses between the sapphire and formed onto it Cr2O3 layer. (5) Plasma effects High temperatures in the working zone cause thermal dissociation and ionization of solvent and target vapours. Laser heats the plasma due to inverse Bremsstrahlung absorption, and the heated plasma causes further heating of the sample. Bombardment of the workpiece by ions and electrons from plasma generates impurities, defects, defect-trapped and free electrons. In organic solvents, carbon species in plasma Ch04-I044498.tex 12/9/2007 16: 11 Page 183

Subtractive processing 183

Cl 0.6 Cl Cl O

Cl C ONa l l 0.4

NaO O O ll Absorbance 0.2

450 500 550 600 650 700 Wavelength (nm)

Figure 4.40 An absorption spectrum of 5 µM Rose Bengal (RB) in acetone [591]. The inset shows the chemical structure of RB. © Institute of Physics, reproduced with permission.

Sn

Tm

S1

T1

S0 Figure 4.41 Excitation of pyrene and photophysical process: possible mechanism for cyclic multiphotonic absorption [574]. © Elsevier.

[Pyrene]** Rapid internal Cyclic conversion [Pyrene] multiphotonic Super-heated absorption liquid Laser (pulse) [Pyrene]*

Figure 4.42 Plausible mechanism for LIBWE by cyclic multiphotonic absorption [574]. © Elsevier.

emit light from visible to extreme UV, thus capable to excite the electrons in optical materials like silica to defect or vacuum levels, giving rise to an increase of absorption of laser light by the material [606]. (6) Pressure, bubbles, and shock Rapid heating of liquid by laser generates high-pressure transients and shock waves in both the workpiece and in the liquid. Thereafter a vapour bubble starts to expand, reaching maximum size in ∼100 µs and shrinking then again [607] (Fig. 7.5). During the collapse of the bubble, a microjet forms and strikes the solid surface at speed of 100–200 m/s (Fig. 7.10). Both the pressure inside the bubble and microjet impact are believed to contribute to the modification of the material and to its removal from the workpiece [601]. Ch04-I044498.tex 12/9/2007 16: 11 Page 184

184 Handbook of Liquids-Assisted Laser Processing

0.8 0.6 M 0.4 M

0.6

0.4

0.2 Each rate (nm/pulse)

0.0 0.0 0.4 0.8 1.2 1.6 Fluence (J/cm2) Figure 4.43 Etch rate dependence on the laser fluence at backside etching of fused silica in aqueous solution of Np(SO3Na)3 by a 30 ns KrF laser [608]. Reproduced with kind permission of Springer Science and Business Media.

45

40

35

30

25

20

15 Etch rate (nm/pulse)

10

5

0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Laser Fluence (J/cm2) Figure 4.44 Etch rate vs. laser fluence of a 30 ns KrF laser etching of silica glass: () pure toluene liquid; () pyrene in acetone solution (concentration: 0.4 mol dm−3) [607]. © Elsevier.

Ding et al. [608] measured the instant velocity of the jet that formed at the collapse of an R = 0.8 mm bubble to be 200 m/s at a delay time of 100 ns. The impact pressure of the liquid jet was estimated using the formula [609]

P = ρCVjet, (4.12) where ρ and C are the density of water and the acoustic velocity in water, respectively.A jet velocity of 200 m/s corresponds to a pressure of 300 MPa. Böhme and Zimmer [610] explained by bubble size the influence of the laser spot size on the etch rate of fused silica in pyrene/toluene. Large bubbles persist a longer time and more solvent is decomposed and deposited onto surface of the workpiece, thus the etch rate should be larger for larger laser spot size. (7) Dissolution of workpiece in supercritical solution Dolgaev et al. [479] pointed to a possible hydrothermal dissolution mechanism in laser backside etching of sapphire. Vass et al. [605] observed that Ch04-I044498.tex 12/9/2007 16: 11 Page 185

Subtractive processing 185

28 180 70 BaF CaF2 2 160 quartz 24 Sapphire 60 140 20 50 120 16 40 100 80 30 12 60 20 8

Etch rate (nm/pulse) Etch rate (nm/pulse) 40 10 4 20

0 0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3.0 3.3 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 (a) Fluence (J/cm2)(b) Fluence (J/cm2)

Figure 4.45 Etch rates vs. laser fluences at LIBWE (a) for BaF2 and quartz, (b) for CaF2 and sapphire [612]. Solution: 0.4 M pyrene in acetone; laser: XeCl, 25 ns. © Elsevier.

250 Carbon Fused layer 200 silica

150 Laser Liquid medium

100

50

Etch depth after one pulse (nm) 0 0 1000 2000 3000 4000 5000 Laser fluence (mJ/cm2)

Figure 4.46 Etch depth – laser fluence dependence in case of a predeposited carbon layer on the surface [606]. Liquid: water, carbon layer thickness:  26 nm,
22 nm. Reproduced with kind permission of Springer Science and Business Media.

at lower energy densities (210 mJ/cm2) no melted silica droplets were found in the working zone, despite the etching occurred. Dissolution rates of some materials in high-temperature high-pressure water are given in Table 7.4.

Etch rate Etch rate dependence on laser fluence at LIBWE in aqueous and organic solutions is characterized by a two- slope curve (Figs 4.43 to 4.45). Similar dependencies were found also at etching of fused silica in pyrene/acetone [611], BaF2 and quartz in pyrene/acetone [612], and fused silica in naphthalene/methyl-methacrylate [605]. Vass et al. [605] found by calculations that the breaking point corresponds to the onset of melting of silica. Figure 4.46 presents the results of an experiment where a carbon layer was predeposited onto the surface of the workpiece, in order to get support to the liquid decomposition etching mechanism. In cases of metals or a solution of Rose Bengal dye in acetone at the backside of the workpiece [591], the etch depth was found to depend linearly on the laser fluence over all used range of laser fluences. Ch04-I044498.tex 12/9/2007 16: 11 Page 186

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800 C 0.4 M(Pyrene/Acetone) 700

600 B

500

400

300

200 1 2 Number of incubation pulses 100

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 Fluence (J/cm2) Figure 4.47 Number of pulses required to initiate etching of quartz [587]. © SPIE (2004), reproduced with permission from Ref. [587].

Incubation effect A characteristic feature of laser backside etching using organic solutions (both bulk and absorbed layer [592]) is that at low fluences the etching rate tends to increase with time (Figs 4.47 and 4.48).The incubation process can be explained by modification of the etched material due to high temperature and plasma irradiation (e.g. amorphization of fused silica) or by formation of an carbon layer due to decomposition of organic substances (Fig. 4.49). The raised absorption coefficient of interface confines the absorption of the laser energy into a thinner layer, which increases the magnitude of the temperature jump [587, 593, 601]. Similar phenomena have been observed also at laser etching of polymers and fused silica in air [613]. The incubation effect is greatly reduced in case of halogenated organic solvents [586, 606] and does not occur in case of liquid metals.

Surface roughness At LIBWE in organic solutions, three distinct laser fluence regions with different surface relief can be distin- guished (Fig. 4.50). In case of quartz, the mechanisms responsible for etch rate and surface profile formation are explained as follows [587]: Region 1: low fluences, low etch rates, high surface roughness. Here the laser softens the material but does not melt it. The mechanical impact of collapsing bubbles and mechanical stresses in case of a carbon deposit are responsible for high surface roughness. Region 2: intermediate fluences, low surface roughness. The melting temperature of quartz (2000 K) is reached. The higher laser-induced temperature will also generate a stronger pressure jump, compared to the lower fluences, which removes the molten material with a single-laser pulse. Region 3: high etch rates, high surface roughness. A further increase of the etch rates and surface roughness in the high fluence range may be due to plasma formation in solution. Kopitkovas et al. [587] observed that at larger pyrene concentrations the surface roughness and incubation time decreased. A possible high pyrene concentration (1.4 mol/l) was found to be beneficial for laser backside etching of quartz. Böhme et al. [614] suppose that more efficient heating of surface peaks in contrast to the valleys results in higher etch rates of first, and leads to a smooth surface this way. The smoothing effect is determined by the thermal diffusion length. On the other side, the described mechanism rounds the corners of small structures, which may be undesirable in some applications. For surface roughness of samples, backside etched in toluene vapours, see Fig. 4.61. Ch04-I044498.tex 12/9/2007 16: 11 Page 187

Subtractive processing 187

30 650 mJ/cm2 1000 mJ/cm2 A 650 650 m2 2 25 s As 100 100 m 2 As 200 200 m 2 As 100 100 m 20 2 As 30 30 m

15

10

5 Average each rate (nm/pulse)

0 1 10 100 1000 (a) Pulse number

30 650 mJ/cm2 1000 mJ/cm2 2 2 As 650 650 m As 100 100 m 25 2 As 200 200 m 2 As 100 100 m 2 20 As 30 30 m

15

10

5 Average each rate (nm/pulse)

0 1 10 100 1000 (b) Pulse number

Figure 4.48 (a) Averaged etch rate in dependence on the applied pulse number for different spot sizes determined from the final depth of the etch pits using 0.5 M pyrene/toluene. (b) Calculated ‘real’ etch rate per laser pulse. (The lines are used to guide the eyes.) Workpiece: fused silica; solution: 0.5 M pyrene in toluene; laser: KrF,30 ns [610]. © Elsevier.

Toulene: • C7H8 C (s) CyHz(g)

Acetone: • ? C3H6O C (s) CyHz(g) CO2(g)

C2Cl4: • ? - C2Cl4 C (s) CyHz(g,l) Cl

1m

(a) (b)

Figure 4.49 (a) SEM picture of a thin film around the etched area in fused silica as a result of decomposition process and (b) possible decomposition reactions of the solvents used for LIBWE processing [593]. © Elsevier. Ch04-I044498.tex 12/9/2007 16: 11 Page 188

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45 C =0.4 M(Pyrene/acetone) 40

35 Etch roughness (nm) A 30 25 20 15

Etch rate (nm/pulse) 10 1 3 5 2 0 0.8 1.2 1.6 2.0 2.4 2.8 Fluence (J/cm2)

Figure 4.50 Etch rate and surface roughness of quartz, laser backside etched using 0.4 mol/l pyrene in acetone solutions as etching media. © SPIE (2004), reproduced with permission from Ref. [587]. Application examples (Figs 4.51–4.54)

Figure 4.51 Array of micro-sized blind holes etched in fused silica by LIBWE [611]. Such arrays are useful for microtiter plates. © Elsevier.

Figure 4.52 SEM picture of a cylindrical structure etched into fused silica employing the scanning contour mask technique [611]. The bottom of the structure is very smooth as shown in the inset. © Elsevier. Ch04-I044498.tex 12/9/2007 16: 11 Page 189

Subtractive processing 189

0 –2 18 16 –4 14 12 –6 10 8 –8 6 19.3 m 4 –10 2 0 –12 m Depth ( m) –14 0 500 m 100 m 400 m –16 200 m 300 m –18 300 m 200 m 50 100 150 200 250 300 350 400 450 500 400 m 100 m Position (m) (a) (b)

Figure 4.53 (a) 3D-profilometer scan of a Fresnel lens etched in CaF2 by LIBWE using a XeCl excimer laser and (b) line scan of etched profile [612]. © Elsevier.

10 m

750 m 750 m

Figure 4.54 Confocal scanning laser microscopic image of an etched grating pattern on the surface of a fused silica plate fabricated by 400 pulses of KrF irradiation at 1.0 J/cm2 and 4 Hz using a solution of pyrene in acetone with a concentration of 0.5 mol/dm3 [615]. © Elsevier.

Deep trenches and channels Effective provision of fresh solution and removal of debris by the motion of bubbles enables etching of deep trenches and channels in transparent materials, useful for example for microfuidic devices (Figs 4.55 and 4.56). The process may be further enhanced by ultrasound agitation (Figs 4.57 and 4.58).

4.4.2.2 Backside etching with an adsorbed liquid layer on the workpiece (LESAL) Using instead of bulk liquid an adsorbed liquid layer on the workpiece (Fig. 4.59), the relaxation time of the system after laser pulse is greatly reduced.Thus, in the experiments by Böhme et al. [616] the etch rate did not depend on the laser pulse repetition rate up to 100 Hz. Another distinct feature is the occurrence of a region where the etch rate does not depend on the laser fluence (Fig. 4.60). It is believed, that in this region, higher laser fluences more intensively desorb the liquid from the surface, so that the amount of absorbed laser energy per unit area remains constant [617]. Otherwise, the etching mechanism and surface properties remain to a great extent similar as at LIBWE (Fig. 4.61). Ch04-I044498.tex 12/9/2007 16: 11 Page 190

190 Handbook of Liquids-Assisted Laser Processing

Laser-absorbing region

Organic Laser beam solution

Silica glass

Etch front by LIBWE Figure 4.55 Principle of laser backside deep wet etching of transparent materials [575]. © Institute of Pure and Applied Physics, republished with permission.

180 m

40 m

Figure 4.56 Cross-sectional SEM images of deep trenches on silica glass fabricated by the LIBWE method using 12 000 pulses at 10 Hz for a trench about 9 µm wide. A saturated pyrene/acetone solution was in contact with the silica glass plate, and a KrF excimer laser beam was irradiated at F = 1 J/cm2 per pulse. Before SEM observation, the silica plates were cut perpendicular to the deep trenches [575]. © Institute of Pure and Applied Physics, republished with permission.

Glass cuvette

50X Objective fs laser XY microstage NA 0.42 pulses

Z microstage

Water

Ultrasonic transducer

Ultrasonic cleaner

Figure 4.57 Schematics of ultrasound assisted LIBWE [584]. The negative pressure driven by ultrasonic waves generates many tiny cavitation bubbles. As these cavitation bubbles collapse, they release high-frequency energy, which detaches trapped bubbles near the entrance of the machined hole. Furthermore, the frequent growth and collapse of cavitation bubbles cause pressure fluctuations that scrape residual bubble mixtures from the channel cavity. Reproduced with kind permission of Springer Science and Business Media. Ch04-I044498.tex 12/9/2007 16: 11 Page 191

Subtractive processing 191

100 µm

µ µ Circular bentholes: t1 100 ms, t2 1 ms, 4 m/s, 33 J pulse energy. Figure 4.58 Examples of bent channels fabricated in a glass sample in contact with methanol by ultra- sound-assisted LIBWE [584]. Magnified views of vertical holes are on the right-hand side of the picture. Etching was performed by 800 nm, 100 fs, 1 kHz laser pulse packets of period t1 and of length t2. Feed rate was 4 µm/s. Reproduced with kind permission of Springer Science and Business Media.

Laser Transparent beam material Laser-induced Absorbed layer surface modification

Vaporized Air toluene

Heater

Theater Tvapour Tsample Tcondensation Figure 4.59 Principal experimental set up for LESAL processing [616]. One of the main requirements for LESAL process is that the sample temperature (Tsample) is higher than temperature for condensation of vapour medium (Tcondensation). © Elsevier.

Etch rate at 75˚C chamber temperature

100 Low fluence Saturation region 10 region High fluence region 1

0.1 Each rate (nm/pulse) 0.01

1E.3 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Laser fluence (J/cm2) Figure 4.60 Etch rates on fused silica in dependence on the laser fluence at a chamber temperature of 75◦C using an adsorbed toluene layer (the line is used for guide the eyes [592] The splitting into three fluence regions is pointed out. Laser: 248 nm, 30 ns © Elsevier. Similar dependencies were observed also at etching of sapphire and MgF2 [616]. Ch04-I044498.tex 12/9/2007 16: 11 Page 192

192 Handbook of Liquids-Assisted Laser Processing

Chamber temperature 75˚C 1000 1000

100 100

10 10

1 1

0.1 0.1 Each rate (nm/pulse) Roughness, rms (nm) RMS,interference microscope 0.01 RMS,AFM 0.01 Etch rate 1E.3 1E.3 0.01.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Laser fluence (J/cm2)

Figure 4.61 Surface roughness and etch rate of a LESAL-etched fused silica using an adsorbed toluene layer [592]. Laser: 248 nm, 30 ns. The surface roughness is lowest on the constant etch rate plateau. © Elsevier.

700 30 (a) 0.5 M pyrene/toluene 600 20 500 10 (b) 400 0 300 0.5 1.0 1.5 Gallium 200 Each rate (nm/pulse) 100

0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 Laser fluence (J/cm2)

Figure 4.62 Etch rate in dependence on the laser fluence at backside etching of fused silica using (a) 0.5 M pyrene/toluene solution and (b) gallium as absorbing metallic liquid [620]. Laser: KrF,20 ns. © Elsevier.

4.4.2.3 Liquid metals at backside In comparison with etching in organic and aqueous solutions, etching with metals (Hg, Ga) at backside of the workpiece has following distinctive features: no incubation effect, high etching threshold and etching rate and linear dependence of the etching rate on laser fluence (Fig. 4.62). No UV lasers are needed: a 1.06 µm Nd:YAG laser was successfully applied in the experiments by Zimmer et al. [618, 619]. The process occurs essentially the same way as in solutions: laser heats of the metal, heat is transferred by conduction to the workpiece, and molten and/or evaporated material is ejected [620]. High etching threshold was explained by high reflectivity and high thermal conductivity of the metals. For example, the reflectivity of gallium is about 80 per cent and thermal conductivity is ∼300 times higher compared to toluene. Rapid growth of the etching rate at higher fluences may originate from a change in the mechanism of the etching, for instance, due to the beginning of the gallium evaporation. Because the absorption coefficients of mercury and gallium are about 10 times higher (α>105 cm−1) than of hydrocarbon solutions, the possible modification of the absorption of the workpiece has less influence on the process and an incubation phenomenon is not observed [585]. Ch04-I044498.tex 12/9/2007 16: 11 Page 193 ) ( Continued Leonov (1975) [571] Lyalin (1999) [623] Dolgaev (1996) [593, 594] Simakin (1999) [622] Davidson (1980) [572] Dolgaev (1997) [595] Ikeno (1989) [621] s Reference(s) bent calculated on surface µ m size shock waves ); 2 2 (at spot 2 µ m; isolated decomposition of ≤ 1 mm) ) 2 and MnO 3 25–65 J/cm in ZnSe observed, ,FeO , 1.2 mm/s) 3 2 µ m were etched into glass by a O 2 cracks ∼ 0.5 correspondingly carbon film on during laser pulse was 600 K (sapphire of Cr 3 formed while scanning; surface damage O 2 and release of gas bubbles of 10–100 channels observed; C toluene tilted Grooves of depth up toby 140 4500 nm were laser etched pulses in (in glass benzene, 0.2 J/cm etched surface Circular symmetric Grooves of depth scanned beam (0.8 J/cm in water photographed peak temperature substrate with DLC film, 1.1 J/cm diameter 1.15–0.32 mm); shock pressure measuredcalculated and (up to 100 MPa at distance Drilling, beam scanning, and maskmachining projection with spatial resolution of 3 Epitaxial growth observed 0.2 mm diameter holes drilledmicrochannels into fabricated 1.5 mm plate; Threshold of ] 2 ) [all at 3 ), 2 O 2 µ m/pulse 2 mm/s 1.1 J/cm 0.2 Å/pulse (glass), 0.4 Å/pulse (fused silica), 4.5 Å/pulse (CaF Up to 300 nm/pulse = Up to 300 nm/pulse 1.1 Å/pulse (Al 40 (3 J/pulse) Etch rate Novel features, observed phenomena, comment 2 µ m, ≈ 0.5W 2 materials (LIBWE, LESAL, etc.) and related experiments. µ m, 100 ns, 2 , 10.6 2 µ m, up to 1.5 J/cm 50 J/cm Laser type and CO Cu-vapour, 510.6 nm, 20 ns, 8 kHz, spot 50 Neodymium, 40 ns average Cu-vapour, 510 nm, 10 ns, 8 kHz, Cu-vapour,10 ns, 8 510 kHz nm, Cu-vapour, 510.6 nm, 20 ns, 8 kHz, 0.2–1.5 J/cm 1ms 4 4 , 2 mol/l 1.06 Nd:YAG, (2 mol/l), (6 mol/l); (1.5 g/ml); 4 3 3 3 CrO Carbon nanoparticles (3–4 nm) (saturated) 4–5 nm carbon particles (1 mol/l) KMnO Glassy carbon particles (4–5 nm) KMnO FeCl benzene, cumene Benzene, toluene Water Toluene Water No Toluene, 2 Laser-induced backside wet etching of transparent ) 3 O , CaF 2 3 O 2 Target or etched ZnSe Fused silicaSapphire Water( α -Al NiSO Sapphire WaterGlass, fused silica, CrO Glass, fused silica, sapphire material(s) Liquids Additives beam parameters Glass K-8 Water No Al Table 4.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 194 [624, 579], (2000) [574, 625], (2001) [599],Yabe (2001) [600] [626] [627], (2000) [625],Wang (2001) [599] [579], (2000) [574, 625], (2001) [599], [600] [603] Wang (1999) Wang (1999) Wang (1999) Wang (1999) Wang 2000 [603] Wang (2000) Yabe (2001) s Reference(s) 3 µ m; from 1900 K µ m µ m, no debris or cracks µ m lines etched by mask projection µ m lines etched by mask projection; etch depth µ m lines etched by mask projection 10 (acetone/pyrene) up to 4410 Kvarious (acetone/benzil); solute at concentrations 0.1–1 mol/dm estimated maximum liquid temperatures Grooves with wavy surface etchedabsorption by mask length projection; of solution0.4 at laser wavelength was Estimated light absorption depth 0.48–2.9 10 3.5 10 ; ; ; 2 2 2 ) ) 2 2 2 , ) ) 2 2 2 2 etch threshold 0.1 J/cm etch threshold 0.24 J/cm etch threshold 0.24 J/cm etch threshold 0.74 J/cm 5–20 nm/pulse (0.16– 0.5 J/cm (0.4– 1.3 J/cm 5–25 nm/pulse (0.4–1.3 J/cm 5–25 nm/pulse (0.4–1.3 J/cm 1–15 (0.7–1.3 J/cm to the fluence 1.5 J/cm Etch rate Novel features, observed phenomena, comment 2 Laser type and KrF,248 nm, 30 ns 5–34 nm/pulse KrF,248 nm, 30 ns, 2 Hz XeCl, 308 nm, 30 ns, up to 0.5 J/cm KrF,248 nm, 30 ns, 2 Hz KrF,248 nm, 30 ns, 2 Hz KrF,248 nm, 30 ns No etching up 3 3 3 3 3 3 3 0.4 mol/dm 0,4 mol/dm Pyrene, 1 mol/dm Pyrene, 0.1– 1 mol/dm Benzil, 0.8 mol/dm No additives 0.4 mol/dm 0.4 mol/dm ) hydrofuran (THF) hydrofuran (THF) Methyl- benzoate Acetone Pyrene, Acetone Acetone Pyrene, Tetra- ) Acetone Pyrene, 2 Continued ( , LiF (single 3 2 O 2 (single crystal) Fused silica Acetone Pyrene, material(s) Liquids Additives beam parameters Target or etched PEP Quartz (c-SiO CaF Fused silica Tetra- crystal) Al Table 4.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 195 ) ( Continued [625], (2001) [599],Yabe (2001) [600] Li (2001) [631] Nikiforov (2000) [630] Simakin (2000) [628, 629] Murahara (2001) [596] Wang (2000) µ m and chemical ) etched 2 µ m and length up to of water–quartz interface; ) respectively,diameter 21 , probably due to supercritical state 2 3 µ m (at 600 J/cm 1 nm was achieved at laser fluence of diameters 4 and processing time 60 min; the 2 µ m (at 60 J/cm µ m lines etched by mask projection Bent channels 200 of the solution length up to 600 10 reflectivity decreases rapidly when pulse energyexceeds density 1000 J/cm Smooth etched surfaces; etch rategreater of than sapphire of was glass and fused silica Surface roughness 25 mJ/cm reaction where HF is, generated is similar to this in Fig. 6.1 Transient reflectivity studies ; 2 ) 2 2 etch threshold 0.045 J/cm Etch threshold 0.5 J/cm Sample was grind using FEP turntable with a water layer between; laser light irradiated the turntable through sample Up to 36 nm/pulse (0.1–0.6 J/cm 2 2 2 µ J/pulse Cu-vapour, 510.6 nm, 20 ns, 8 kHz, up to > 1.5 J/cm 100 Hz, up to 50 mJ/cm 120 fs, 1 kHz, 1–10 XeCl, 308 nm, 20 ns, 2Hz KrF,248 nm, 16 ns, up to 1 J/cm ArF,193 nm, 10 ns, Ti:sapphire, 800 nm, 3 4 CrO 2 Pyrene, 1.0 mol/dm a photochemical reaction between water and FEP) drofuran benzene, cumene, also with addition of glassy carbon particles, 3–5 nm Tetrahy- Toluene, PEP Soda-lime glass, Pyrex, sapphire Quartz WaterFused silica K Water HF (generated in Silica glass Water No Ch04-I044498.tex 12/9/2007 16: 11 Page 196 Ding (2002) [598] Ding (2002) [608] Zimmer (2002) [633] [632] Böhme (2002) [611] Dolgaev (2001) [479] Yasui (2002) s Reference(s) µ m, in surface is µ m fabricated observed, the ≈ 0.03 : in low etch rate 2 µ m wide lines in supercritical was wave studied (images gas generation µ m holes etched by mask 12 two etching regions × µ m holes of depth 25 dissolution of sapphire µ m depth; 40 × surface r.m.s. – roughness < 10 nm and if etched tetrachloroethylene, it contains phenomenon observed; 10 ≈ 2 times lower than in case of KrF laser; bubbles, microjet and shock µ m lines and 12 µ m; obviously due to pyranine decomposition high etch rate region1 the surface roughness waspresented); dye up particles to formation observed Sinusoidal gratings (period 780 nm,surface depth roughness 180 less nm, than 5phase nm grating r.m.s.) projection fabricated by projection; 0.5 etched by mask projection; no cracks or debris Distinction between region the Channelling RBS studies; at 3.5 J/cm 15 Etch rate incubation amorphous chlorine; 40 in fused silica by maskfabricated projection; by curved contour surfaces maskroughness technique; surface concentration; solution obviously contributes to high ablation rate Ablation rate had linear dependence on electrolyte ) 2 , ; 2 2 0.5 M 2 ); ); ) ) 2 2 2 2 + µ m/pulse µ m/pulse pyrene) threshold fluence < 0.5 J/cm 0.1–0.9 nm/ pulse ( < 1.3– 1.5 J/cm etch threshold 0.4–0.5 J/cm toluene Up to 2.4 (KOH, 7 mol/l); 0.24 in pure water Up to 22 nm/pulse (0.4– 1.5 J/cm Up to 16 nm/pulse (0.96 J/cm 230 nm/pulse (fluences up to 3.5 J/cm 0.02–0.12 nm/ pulse (KrF,0.6– 1.67 J/cm ≈ 0 . 1 nm/pulse ( < 1.3– 1.5 J/cm Etch rate Novel features, observed phenomena, comment 2 2 ≈ 20 ns, µ m,120 J/cm µ m, 130 ns, 1 Hz, Laser type and KrF,248 nm, 100 Hz Cr,Yb,Ho:YSGG, 2.92 spot 100 KrF,248 nm, 30 ns Up to XeCl, 308 nm, 20 ns, 5 Hz, 0.2–1.5 J/cm KrF,248 nm, 30 ns, 5 Hz; XeF,351 nm, 5 Hz KrF,248 nm, 30 ns, 5 Hz 3 3 (up to Na) 3 3 CO 3 3 2 Na 0.4 mol/dm 0.5–1.0 mol/ dm Pyrene, 0.4–0.6 mol/l 7 mol/l) 0.4–1.0 mol/ dm Pyrene, 0–0.4 mol/l ) tetrachloro- ethylene, toluene cyclo- hexane, tetrachloro- ethylene Acetone, , 2 Continued ( 2 MgF Sapphire Water KOH, KCl or material(s) Liquids Additives beam parameters Target or etched Fused silica Acetone Pyrene, Fused silica Water Pyranine, Fused silica Water Np(SO Fused silica Acetone, Fused silica, sapphire, CaF Table 4.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 197 ) ( Continued Itoh (2003) [637] Niino (2003) [636] Niino (2003) [607] Zimmer (2003) [634] Niino (2003) [607, 635] Hwang (2004) [584] Zimmer (2004) [617], Böhme (2004) [592] agitation of in liquid; µ m in length or > 200 µ m in length, but also surface roughness down to , 2 > 600 were drilled into glass using images presented; shock carbon soot generated of interface presented; grid pattern of the previous work done at AIST, µ m for Corning 7059 glass achieved; µ m in diameter and µ m features etched by mask projection of tens of micrometres in diameter, of up to at etch depth of 400 nm (Böhme (2004) [592]) summary enhances the etching thanks to bubbles removal < 10 µ m in diameter and bent and circular channels laser pulse packets, á 16 pulses, three packets every 1 s see (Wang,Ding,Yabe) in this table liquid Channels ≈ 40:1 aspect ratio,were fabricated;trapped in channels bubbles cause inhomogeneities; ultrasonic 21 0.23 nm method time-resolved images with Mask projection etching; surface roughnessetch 4 depth nm 3.7 at etch incubation effect observed Linear dependence of etchthe rate number on of laser shots; fluence and Shock wave and bubble Constant etch rate of aboutinterval 1.3 from nm/pulse 2 in to a 5 fluence J/cm expansion velocity 1400 m/s and of bubble 200 m/s Holes of 8 A short 2 ); 2 ); 2 2 µ m/s 2 ); threshold 2 in glasses (1 J/cm 0.1–30 nm/ pulse Up to 30 fluence 0.5 J/cm threshold fluence 0.19 J/cm threshold fluence 0.7 J/cm ≈ 15 nm/pulse (0.72 J/cm Up to 200 nm/pulse (0.7–7.5 J/cm 2 µ J 2 µ J 2 XeF,351 nm, 30 ns 6–10 nm/pulse KrF,248 nm, 30 ns, up to 7.5 J/cm fs laser, 800 nm, 100 fs, 1 kHz , 3–33 KrF,XeCl KrF,248 nm, 30 ns, 5 Hz, up to 1.4 J/cm KrF,248 nm, 30 ns, 1.6 J/cm 130 fs, 1 kHz, 1–10 Ti:sapphire, 800 nm, No Pyrene, 0.1–0.4 mol/l No Pyrene, pyranine (adsorbed layer) toluene, tetra- chloromethy- lene methanol, isopropanol toluene, water Acetone, Acetone, Water, THF, , PEP 2 Fused silica, different glasses Silica glass Toluene Silica glass Toluene Silica glass, quartz, sapphire, CaF Silica glass WaterFused silica No Toluene Glass Ch04-I044498.tex 12/9/2007 16: 11 Page 198 Kopitkovas (2004) [587] Kopitkovas (2004) [612] Kawaguchi (2004) [638], (2005) [639] Ding (2004) [615] Böhme (2004) [593] Vass(2004) [604] Vass(2004) [605] molten transient µ m features (numerical, 1D) µ m;time-resolved , surface roughness 2 luminescence spectra contaminated by chlorine and calculations quartz surface is amorphized images at backside laser irradia- numerically using 1D-model with ; light penetration depths estimated − 1 measured 11.1–30.4 MPa (at distances µ m; molten silica droplets observed; (not with carbon if scanned spot etched in ) 4 µ m; hole and groove arrays with 1 Cl 2 silica depth calculated temperature-varying materials properties Etch incubation investigated; recorded; plano-convex and diffractive microlens arrays fabricated in quartz Novel features, observed phenomena, comments Reference(s) 0.16 – 0.25 ranges from 5 nm to several micrometres 400–62 300 cm carbon C (1.2–60 nm in depth) and Bubble and shock wave imagespeak presented; pressure 1–0.1 mm); initial peak pressure10–200 estimated MPa Diffractive grey tone phase mask projection ofFresnel patterns; microlens etched in CaF Pressure and temperature confirm the melting mechanism of etching Surface characterization by RBS/channelling, XPS and Raman spectroscopy; shock wave and bubble 248 nm light penetration depth3.2 of 1 M solution: size fabricated,maximum depth 2.4 tion of glass–toluene interfacevelocity presented: 1.4 shock km/s, bubble wave growth velocity 200 m/s Absorption depth of solution measured: 39 2 ; 2 ; ; 2 ); 2 2 ); 3 , 2 2 – 0.8 J/cm , 3.4 J/cm – 0.4 J/cm 2 2 2 Up to 67 nm/pulse (BaF Up to 50 nm/pulse (860 J/cm 0.85 mol/dm threshold fluence between 0.11– 0.21 J/cm BaF sapphire – 2.3 J/cm CaF threshold fluences: quartz – 0.5 J/cm Etch rate mask- 2 2 2 2 KrF,248 nm, 30 ns, 5 Hz, 1.6 J/cm XeCl, 308 nm, 30 ns, 4 Hz to 1.4 J/cm 4Hz Laser type and KrF,248 nm, 20 ns, 1 J/cm 1.5 Hz 20 ns, 1.5 Hz, 0.11–0.86 J/cm defined patterns ArF,193 nm, 20 ns, ArF,193 nm, 3 3 1,3,6-trisulfonic acid trisodium salt, up to 1 M Pyrene, 0.4–1.4 M Naphthalene, 0–1.71 mol/dm Naphthalene, 0.85 mol/dm Pyrene, 0.5 M KrF,248 nm, 30 ns, up 4 Cl ) 2 tetrahydro- furan meth- acrylate meth- acrylate C Acetone Pyrene, 0.4 M XeCl, 308 nm, 25 ns, Toluene, , Continued 2 ( , BaF 2 Silica glass Water Naphthalene- sapphire, quartz Target or etched Fused silica TolueneCaF No QuartzFused silica Acetone, Methyl- Fused silica Methyl- Fused silica, quartz material(s) Liquids Additives beam parameters Table 4.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 199 ) ( Continued Zimmer (2005) [640] Böhme (2006) [597, 641] Böhme (2005) [586] Böhme (2005) [614] Cheng (2005) [590] Böhme (2005) [610] Kawaguchi (2005) [575] Kawaguchi (2005) [639] Vass(2006) [602] smoothing µ m deep follows the d on etched ripples estimated to exceed up to masks µ m wide and 420 around the etched area − 0 . 33 d (1 page) of the LIBWE and the earlier at homogeneous irradiation studied dependence on distance ≈ p bubble pressures carbon deposit review µ m for microreactors/microconcentrators Binary gratings and freeformdiscussion surfaces about fabricated; proper surface, ripple period about 120 nm work by Böhme and Zimmer (removable by oxygen plasma); relationship of surface relief Shock pressure Sinusoidal gratings (period 760 nm) etched; Focused beam scanning, trenches of10 depth about fabricated; threshold fluences for 11absorbing light- organic substances/solutions measured Maximum 75 MPa Etch rate evolution in timeperiod studied: the after incubation etch ratesizes remains the constant; etch at rate greater increases spot in silica glassfabricated with a maximum aspect ratio of 60 Micro trench about 7 A short Adherent ) 2 ), 2 2 ) ) 2 2 etch depth on pulse number given Up to 55 nm/pulse (30 ns pulses, 1.7 J/cm (1.2 J/cm ≈ 0 . 1 nm/pulse ( ≈ 0.2 J/cm threshold ≈ 0.07 J/cm 17 nm/pulse average (1 J/cm 2 2 µ J, up to ,upto80Hz 2 N:A,266-Nd:YAG, nm, KrF,248 nm, 30 ns Dependence of KrF,248 nm, 30 ns, 2 Hz; dye/KrF,248 nm, 0.6 ns, 2 Hz KrF,248 nm, 30 ns Up to 20 nm/pulse KrF,248 nm, 20 ns, 1 J/cm KrF,248 nm, 30 ns, 1 J/cm KrF, 248 nm, 25 ns,to up 1.87 J/cm 4 ω 10 ns, 78 50 kHz Dye/KrF,248 nm, 0.5 ns, 5 kHz, 20 mJ Pyrene, 0.5 mol/l Pyrene, 0.4 mol/l Naphthalene, 0.85 and 1.71 mol/l Pyrene, 0.5 mol/l saturated 0.5 mol/l 0.4 mol/l 0.5 mol/l , 4 Cl 2 tetra- chloroethy- lene C Methyl- methacrylate Fused silicaSilica glass Toluene No AcetoneFused silica Pyrene, Toluene, Fused silica Toluene, Fused silica Toluene Pyrene, Borofloat glass Acetone Pyrene, Fused silica Acetone Fused silica Toluene Pyrene, Ch04-I044498.tex 12/9/2007 16: 11 Page 200 Böhme (2006) [616] Zimmer (2006) [585] Zimmer (2006) [618], (2007) [619] Böhme (2006) [642] Böhme (2006) [597] Böhme (2006) [606] Böhme (2006) [588] ; no pulse on etched orientation halogenated does not affect the ripples 2 at interface was of laser light transient reflectivity temperature ) ∼ 2500 K (absorption coefficient of Ga: chamber temperature effect on etch rate − 1 around the etched area; ; halogenation lowers the etch rate and no incubation effects cm 5 Novel features, observed phenomena, comments Reference(s) etching process number and fluence; etched surfacer.m.s.; roughness 7 nm number and fluence; etched surface roughnessno 1.5 incubation nm; effects; almost nomaterial; rim maximum or redeposited estimated > 10 Study of repetition rate dependence of etching100 Hz; at crystal least structure up of to SiO Liquid–solid interface measurements; discussion on etch mechanisms in different fluence regions perpendicular to the electric field surface: ripple period about 550 nm, Deposits material removal mechanisms discussed; similarity with etching of virgin silica observed Comparison of etching in various incubation effects, small holes foundsmooth in etched otherwise surface solvents Almost linear dependence of etch rate on pulse Almost linear dependence of etch rate on pulse Ablation in air and in water compared; 2 2 ) ) ); ) 2 2 2 2 2 in air) ), ); thresh- ); thresh- ); thresh- 2 2 2 2 2 2 (1.5 J/cm 1.1–6.5 nm/pulse (pyrene/toluene, 0.3–0.5 J/cm Up to 230 nm/ one pulse (0.4–4.8 J/cm 600 nm/pulse (0.7– 7.5 J/cm (0.3–1.6 J/cm 600 nm/pulse, (up to 8 J/cm Up to 350 (12 J/cm Up to 300 (28 J/cm old fluence 3 J/cm old fluence 7 J/cm old 0.75 J/cm threshold fluence 1.3 J/cm (12 J/cm Etch rate KrF,248 nm, 30 ns Up to 22 nm/pulse 130 fs, 1 kHz KrF,248 nm, single pulses KrF,248 nm, 30 ns Fused silica: up to KrF,248 nm, 10 Hz Up to 27 nm/pulse, Laser type and KrF,248 nm, 10 Hz Up to 1064Nd:YAG, nm, 18 ns, 2 kHz dYG 1064Nd:YAG, nm, 73 ns, 1 kHz Ti:sapphire, 775 nm, Pyrene, 0.5 mol/l No Pyrene, 0.5 mol/l 2 F, Cl, Cl 5 5 4 H H H ) 6 6 6 fluoro- benzene, tetra- chloroethy- lene C C C (adsorbed layer) Water No Toluene Continued ( 2 Fused silica Toluene No Target or etched Fused silica, quartz, sapphire, MgF Fused silica Toluene, Fused silica coated by carbon Fused silica Toluene, Fused silica Gallium No Fused silica Gallium No material(s) Liquids Additives beam parameters Table 4.9 Ch04-I044498.tex 12/9/2007 16: 11 Page 201 Cheng (2006) [591] Böhme (2007) [620] Zimmer (2006) [643] Zimmer (2007) [601] An (2006) [644] Vass(2006) [645] µ m µ m ) 2 µ m, maximal ∼ 35-nm- aof amorphization µ m; trenches down to 65 ), according to calculations, the surface − 1 ) corresponds roughly to the boiling 2 cm 5 µ m µ m depth) –10 4 in depth andsurfaces of aspect ratio 3.6 etched; crack-free Rectangular trenches and chamberscombinations and their etched, minimal width 5 size 75 Good quality gratings having266/20, period/depth of and 154/3, 550/120pulses nm into were fused silica etchedthe surface;AFM gratings by images are of 50 presented laser layer may be heated up to 12 000 K (950 J/cm temperature of fused silica (calculations) (at 2.5 Linear dependence of etchand rate fluence;etched on surface pulse roughness 2.2 number nmincubation r.m.s.;no effects; etched surfaces waviness 20–30 Laser irradiation caused Etching of fused silica using toluene/pyrenegallium and liquid are compared; the threshold(1.3 fluence J/cm for Ga thick surface layer of silica glass10 (absorption coefficient Absorption depth 330 2 ); 2 ); ), 2 /s 2 ); 3 2 , scanned 2 2 2 µ m Up to 70 nm/pulse (6–13 J/cm Up to 650 nm/pulse (0.75–11 J/cm ≈ 100 threshold fluence 0.76 J/cm beam) (80 J/cm Ga: 620 nm/pulse (8.75 J/cm threshold 1.3 J/cm threshold fluence 5.7 J/cm diated byence interfer- pattern of two laser beams Pyrene/toluene: 35 nm/pulse (1.7 J/cm The sample was irra- 2 2 3 mm, × µ m, up to 2 µ J 100 × µ m 7.85 J/cm dYG 532Nd:YAG, and 266 nm, 10 ns, 10 Hz, 285–680 mJ/cm 532 nm, 15 ns, 5 kHz, 40–90 KrF,248 nm, 25 ns, 10 Hz, mask projection KrF,248 nm, 25 ns, 10 Hz, spot 3 600–950 mJ/cm KrF,248 nm, 20 ns, 10 Hz, spot 100 0.3 ps, 1 kHz , spot 1.5 Ti:sapphire, 800 nm, ) 3 Naphthalene (1.85 mol/dm dye, 1.2 mM (saturated) (0.5 mol/l) (0.5 mol/l) Gallium No Methyl- methacrylate – naphthalene-1,3,6-trisulfonic acid trisodium salt 3 Na) 3 Soda-lime glass Acetone Rose Bengal Fused silica MercurySilica glass No WaterFused silica (1 mm) No Fused silica TolueneFused silica Pyrene Toluene Pyrene DLC – dry laserRBS cleaning – Rutherford-backscattering spectrometry XPS – X-ray-photoelectron spectroscopy Notations PEP – poly(tetrafluoroethylene-co-hexafluoropropylene) FEP – fluoroethylenepropylene pyranine – 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodiumNp(SO salt AFM – atomic force microscpe Ch04-I044498.tex 12/9/2007 16: 11 Page 202

202 Handbook of Liquids-Assisted Laser Processing

4.5 Machining of Liquid-Containing Materials

Porous hydrophilic inorganic and organic materials contain a significant amount of water under normal con- ditions, which influences the laser machining process. If the laser light is absorbed mostly in water (e.g. of CO2 laser), the material disintegration and removal occurs mainly due to water vapours pressure and the thermal load on the matrix remains low.Thus, changes in material properties can be avoided. For example, Sugimoto et al. [646] report that at laser cutting of soaked in water marble, the formation of white lines at the cutting edges in the material was eliminated. Laser removal of water-containing coatings is described in Section 2.2.

4.5.1 Rock drilling Rock, dependent on its porosity (Table 4.10), may contain a significant amount of water, which plays a significant role at laser processing. For a decade, there has been an interest to drill gas wells by lasers. Gas wells are up to 3 km deep and replacing of drill bits takes a considerable time. It has been estimated that using lasers, a 3 km deep well can be drilled in 10 days instead of 100 days using the conventional technology. In 1995, preliminary studies about the perspectives of use of lasers for gas well drilling started at Gas Technology Institute (GTI), Des Plaines IL, USA and in 1997 first proof-of-principle experiments were carried out. In 1999, Argonne National Laboratory, Gas Research Institute and the Colorado School of Mines started joint fundamental research on laser rock drilling. A commercial product is expected in 2010–2012 [648].

Potential benefits of laser drilling of rock • More rapid rock penetration • No need to buy and install well casing • No need to replace drill bits • Faster retrieval of downhole data • Reduced on-site drilling time • Reduced environmental impact

Table 4.10 Porosity of some rocks [647]. In ambient, the pores are usually filled by water. Rock Porosity (%) Sandstone 0.5–40 Quartzite and ferruginous quartzite 0.2–20 Phyllite 0.5–0.6 Flint 1–6 Limestone 0.5–48 Marble 0.1–2.2 Granite 0.2–7.4 Copper ore 0.2–7 Ch04-I044498.tex 12/9/2007 16: 11 Page 203

Subtractive processing 203

Lasers having potential for rock drilling:

2–6-kW CO2 10.6 µm 5 kW-Yb fibre 1.04 µm 0.2–2-kW Nd:YAG 1.06 µm Energy density at workpiece 10–10 000 J/cm3 The mechanisms of material removal in rock drilling are thermal spalling, melting, and vaporization. Thermal spallation is the most effective rock removal mechanism, because smallest specific energy is needed [649].

4.5.2 Biological materials Materials of biological origin like wood, paper, food, etc. contain a significant amount of water, which deter- mines to a great extent their light absorption spectra (resembles this of water) and the material removal processes in laser machining. Examples of laser machining of some biological materials are given in the Table 4.12. For example, in the patent EP0930012 [661], a method of cutting of dough sheets into pellets by carbon dioxide laser, operating at wavelengths and wavelength bands 2000–2100 nm (especially 2064–2096 nm) is described. A jet of water steam is delivered to the cutting point together with the laser beam, so that the dough is kept moist during cutting. The method overcomes some disadvantages of commonly used punching technology: the form of the pellets can be operatively changed, the use of the dough sheet area is better, and there are no problems with sticking of the dough to the punches. Laser machining and treatment of living organisms and tissues, in vivo and in vitro, is out of the scope of this book. References to relevant literature were given in Introduction.

4.6 Laser Cleaving of Crystals in Water and of Water-Containing Crystals

4.6.1 Breaking of single-crystal silicon wafers In the article by Kurobe et al. [667] laser-induced breaking of single-crystal silicon wafers, with the backside in contact with water, was described. An Nd:YAG was used at powers up to 80W and feed rates of 0.4–20 mm/s. The use of water was reported to result in nearly twice lower crack deviation, damage depth, and branching crack length. The authors explain these benefits by the cooling effect. Water is known to assist crack propagation in glasses, oxides, fluorides, selenides, etc., but not in silicon [668, 669].

4.6.2 Cleaving of protein crystals Crystallized proteins are needed for determination of their structure by X-ray diffraction. Because the crystals may grow polycrystalline, have regions of poor crystallinity or be of improper shape, there is a need for separation of well crystallized portions. Protein crystals contain 23–90 per cent of solvent (water, acetone, etc.) and it is advantageous to perform cleaving in the same solvent. The common practice of cutting of protein crystals by micro-hand tools does often not yield good enough results because the protein crystals are soft and fragile. Cleaving of protein crystals by laser can be a favourable alternative here [670, 671]. In the studies by Kashii et al. [670] a 150 fs Ti:sapphire laser (800 nm) was found to be able to cleave millimetre-sized hen egg white lysozyme (HEWL) crystals neatly.The needed laser fluence was ∼1.5 J/cm2. The process has been referred to as fs-CACO: femtosecond laser-induced cut and cleave operation. Table 4.11 presents the essentials of selected research reports about laser machining of liquid-containing materials. Ch04-I044498.tex 12/9/2007 16: 11 Page 204 Sugimoto (1996) [646] Savina (2000) [28] Liu (1997) [650] Savina (1998) [27] Goldfarb (1997) [651] O’Brien (1999) [652] 3 > 60% ions better cut n + 0–9, were of H = + ; cement matrix ; pulse overlap 2 through water or 0–3, and [Mg(MgO) = 0–5, m = ,n 30 m was engraved; + µ m decontamination and ] × m ∼ 8 (discharge in water) and 0.8 kJ/cm 0 and 1, m O) electric discharge 3 2 choice of lasers for petroleum well O molecules to Mg = 2 (H ,n n + ablation efficiency was 0.23 mg/J atures, observed phenomena, comments References ] /h) by than of dry material was achieved; formation m 2 O) 2 quality of white lines in marble was avoided [H(MgO) formed in ablation plume; theand cluster growth nucleation obviously occurs throughMgO addition and of H caused a significant decrease ofby ablation efficiency inducingaerosol size melting; was most abundant generated Concrete independently of peak laserrange irradiance from over 0.2 a to 4.4 MW/cm possibilities of laser decommissioning of nuclear facilities was observed to melt, dehydratesand and and vaporize, while aggregate materialfractured was and found dislodged to without be melting through concrete under water; energywas consumption 1.5 kJ/cm drilling (H (discharge in concrete) Discusses the Surface layer (4–30 mm) of( ∼ 5m concrete was removed Solvated Mg and MgO clusters A wall mosaic 3.5 The goal of the work was to investigate the µ s, 2–40 Hz soaked with water Laser beam was delivered via 1 mm diameter fibre, 10 m in length, linear pulse overlap up to 90% Laser beam was fibre delivered, scanning rate 10 cm/s ( ∼ 50% overlap) electrodes 20–140 kV, 0.8–7 kJ/pulse, 4–40 Experiment was performed in vacuum the experiment Novel fe The materials were Voltage between 2 , 2–2.3 kW, 2 erials and related research (examples) (see also Table 2.6) parameters pulsed, duty 55–60% dYG 1.6Nd:YAG, kW, 0.5–1 ms, up to 800 Hz, up to 30 J, spot 0.55– 0.96 mm, up to 4.4 MW/cm CO dYG 1.6Nd:YAG, kW, 0.5 ms, 400 Hz, 2 J,0.55 spot mm 355 and 532 nm, 10 ns, 30–70 mJ Laser type and beam Other features of Liquids/their samples: 5% labile, 20%–30% hydrated bonded) Water in cement Water layer on surface No Water (chemically , O 2 2 6H · · Laser machining of liquid-containing mat 2 · ) ) 2 2 3 3 O, Mg(OH) 2 5H 4MgCO machined content Materials Mg(OH) Concrete Cement and concrete (also doped with CsCl and SrCl Concrete (60/40 sand/Portland cement weight ratio) Marble, granite Water Mg(NO Table 4.11 Ch04-I044498.tex 12/9/2007 16: 11 Page 205 ) ( Continued Lawrence (2000) [653] Chung (2005) [656], Bieri (2005) [657] Inoue (2000) [654] Robinson (2001) [29] Xu (2003) [649] Xu (2005) [655] for µ m the 2 (shale) µ mat 3 far shale, /pulse and 22 2 3 ablation of µ m at 0.81 ± 15 for numerical ± of ordinary Portland by laser beam; using laser were achieved 2 at Argonne National laboratory (see zones was around 920W/cm C-CUIP method absorption coefficient Au ink was cured µ m wavelength and 177 wavelength curing the thermal load to flexiblelow polymeric remains Printed 10.6 thermal spallation Optical cement was determined to be 470 Material removal rates up to 180 cm Reports about the research on laser radioactive concrete Savina (2000) [28]) effectiveness 180 J/cm specific energies ranged 0.5–2.2 kJ/cm Principles of simulation of laser spallation ofspallation criterion rock are is outlined; that thebeneath laser-induced the stress surface just reachesthe the rock critical strength of Berea gray sandstone and 784W/cm , scanning rate ◦ 0.5 mm/s Electric pulse between electrodes: peak voltage 950 kV, peak current 30 kA, 18–54 kJ Shield gas – nitrogen Laser beam irradiance required for producing Laser beam was applied at a incident angle of 45 µ m µ s, 0.85W,10–50 100 Hz, spot 30 No 0.5–2Nd:YAG, ms, 50–800 Hz, 1–12 J, 680–1200W Ar-ion, 514 nm, ink) Specimen immersed into water Toluene (binder of the (5.3 nm in average, 1.9%vol) in toluene Portland cement Granite Sandstone, shale, limestone Au particles Ch04-I044498.tex 12/9/2007 16: 11 Page 206 Rao (2005) [658] (2005) [659] Bybee (2006) [660] Wang by CCUP procedure;transient ) 2 mation of materials, fragmentation, multiphase problems and only the P4VP-island parts doped with atures, observed phenomena, comments References spallation of rock Reports the methodology andof results laser of simulation Scanning speed was 60–2400 mm/min; spalling, drilling, and glazing experimentsperformed; were spalling depth 2–12 mm(at was 600–6000 observed J/cm In methanol, state of P4VP50 nm there; in ablated width craters and up were to less 12 nm than in depth temperature and density profiles are presented TCPP were, ablated obviously because the swollen 2 2 2 2 24 cm × Spot 1.6–16 cm (CW), 35 (pulsed); 40–3700W/cm (CW), 115W/cm (pulsed) Samples immersed into methanol the experiment Novel fe 2 e: a FD-based numerical procedure for simulation of large defor , CW/100 and 2 N:A,532-Nd:YAG, nm, parameters 500 Hz, 50% pulsed, 3.5 and 10 kW 1 ms, 800W,spot 10 mm 2 ω 8 ns, up to 0.17 J/cm Laser type and beam Other features of -poly(4-vinylpyridine) diblock copolymer Liquids/their Liquids were not applied CO Methanol ) Continued ( -P4VP film: -P4VP –block polystyrene- machined content Concrete Materials PS- b native and TCPP doped Rock Notations PS- b CCUP (C-CUIP) procedure – CIP combined and unified procedur fluid–structure interaction CIP – constrained interpolation profile Table 4.11 TCPP – tetrakis(4-carboxyphenyl)porphine Ch04-I044498.tex 12/9/2007 16: 11 Page 207 References Kitano (2004) [663,664], Murakami (2004) [665] EP0930012 (1999) [661] Barcikowski (2006) [666] Kolar (2002) [662] µ m; laser generated pyrolysis products µ m/pulse phenomena, comments In comparison with theform punching of technology,the the dough pelletsthe can use be of operatively changed, theare dough no sheet problems area with is sticking better,punches and of there the dough to the HAZ width could be14–70 controlled in range of (aerosols and at cut surface) were identified milling of millimetre-sized protein crystalslittle with thermal damage was0.1 developed; ablation rate properties of the paper, butformation caused of yellowing; ether cross-linksthe and cellulose dehydration of was observed; theexplained yellowing by was formation ofcarbon–cellulose chromophores due interactions to A technique called PULSA for laser cutting and The treatment did not change the mechanical (examples). of the Novel features, observed Focused scanned laser beam, a steam jet is directed into the cutting zone 10–45 kJ/m Focused scanned laser beam Relative humidity of environment was 65% µ m, 2 , 125 MW 2 , , up to 2 kW Feed rate up to 5 m/s, 2 2 µ J, spot 25 parameters experiment 50 mJ/cm 2000–2100 nm peak dYG 1064Nd:YAG, nm, 6 ns, 20 Hz, 1 J/cm 193 nm,1 ns,1 kHz, 1 CO Laser type and beam Other features 39% 12% humidity (pine) Laser machining or treatment of someerials mat of biological origin machinedDough sheet Liquids Water (steam) CO Cellulose and paper HEWL crystals Solvent content Particleboard, birch plywood, pine Materials Notations HEWL – hen egg whitePULSA lysozyme – pulsed UV laserHAZ soft – abalation heat-affected zone. Table 4.12 Ch05-I044498.tex 11/9/2007 18: 50 Page 209

Chapter Five

Generation and Modification of Particles

Contents 5.1 Introduction 209 5.2 Optical Properties of Small Particles 210 5.3 Experimental Techniques of Particles Generation 213 5.4 Metal Particles 214 5.5 Inorganic Compound Particles 240 5.6 Silicon and Amorphous Carbon Particles 250 5.7 Diamond and DLC Particles and Films 250 5.8 Organic Particles 258

5.1 Introduction

Formation of small particles at laser ablation of solid in liquids is an inevitable phenomenon at both shock processing and machining. When a solid target is vaporized, the vapour tends to condensate as small particles. When ablation is carried out in liquid, the particles remain in liquid as a suspension (Fig. 5.1). Particles of 2–1000 nm in size do not settle under normal conditions and are called colloids. Aqueous colloids are called hydrosols. Using laser ablation of solids in liquids, colloidal particles of a large variety of materials has been fabricated in the recent years, in course of overall interest rise to nanoscale sciences and nanofabrication.

1ns 1ms100 ms 1ms

1mm

(a) (b) (c) (d)

Figure 5.1 Temporal sequence of physical phenomena at irradiation of solids in transparent liquids with laser pulses of fluences in range 10–100 J/cm2 (a) energy absorption; (b) plasma and shock wave formation; (c) bubble at its maximum size, condensation of vapours; and (d) relaxation. All these phenomena have been used for materials processing (scaled after Geiger et al. [469] and Tsuji et al. [672]).

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

209 Ch05-I044498.tex 11/9/2007 18: 50 Page 210

210 Handbook of Liquids–Assisted Laser Processing

Table 5.1 Liquids and their additives used at particles generation. Liquids Additives + − Water, D2O, pentane, hexane, cyclohexane, heptane, NaCl, KCl, MgCl2,AgNO3, NaBH4,I ,CN , octane, nonane, decane, chloroform, methanol, ethanol, phtalazine, citric acid, sodium citrate, dodecanethiol, ethylene glycol, diethylene glycol, 1-propanol, 2-propanol gelatine, cyclodextrines, PVP,SDS, SHS, SOS, SDBS, (IPA), isobutanol, n-hexanol, 2-ethoxyethanol, acetone, CTAB, sodium polyacrylate, tetraalkyl-ammonium liquid He II bromide salts

(The abbreviations are defined at the end ofTable 5.4)

Compared with other methods of fabrication of nanoparticles, laser ablation in liquid has following advantages: • There are no problems with the collection of the particles, compared with fabrication in gas [673]. • Compared with spark method, the target may be isolating [674]. • Laser ablation yields principally cleaner particles, because no other substances are involved in the process than the target and the liquid. For example, the chemical methods need a stabilizer as a rule that modifies the surface of the achieved particles. The main disadvantage of laser method is its small productivity (of order of some mg/h) and expensive equipment (laser). Up to today,about 20 different liquids have been used as the ablation media in particle fabrication (Table 5.1) ranging from organic solvents and water to liquid helium in fundamental research of neutral atoms and clusters. Various additives have been applied in order to control the particles size and size distribution.

Average size Laser-generated particles vary in size. The average size is calculated commonly as:

N0 diwi i dav = , (5.1)
N0 wi i πd3 w = i , (5.2) i 6

where di is the diameter of the ith particle and N0 is the total number of particles in sight [675].

Stability of colloids Colloids may aggregate as they collide with each other. In electrolyte solutions, however, the particles are carrying a charge, proportional to their ζ-potentials, that hinders them to come near to each other. The colloids are considered unstable when their ζ-potential lies between −30 and +30 mV,and stable when the ζ-potentials are more positive than +30 mV or more negative than −30 mV (see also Section 2.3.1). For example, silver colloids of size less than 50 nm are unstable in pure water [676]. Large particles may settle due to gravitation force (Eq. (4.2)).

5.2 Optical Properties of Small Particles

Optical methods, first of all total absorbance measurement and absorption spectroscopy, are convenient methods for characterization of colloidal particles. In addition, many important applications of laser-generated particles rely on their optical properties. Ch05-I044498.tex 11/9/2007 18: 50 Page 211

Generation and modification of particles 211

100 Ag Ti Au 80

Pt 60

40

Absorption (a.u.) Cu 20 Pd

0 200 300 400 500 600 700 800 900 Wavelength in vacuo (nm)

Figure 5.2 Calculated absorption spectra of some 10 nm in diameter metal hydrosols at room temperature [678]. The main absorption peak centre wavelength is determined by the dipole plasma resonance frequency (Mie resonance) and the surroundings, while the width of the peak is determined by the collision frequency of electrons in the particle, and depends on the particle size. Reproduced by permission of The Royal Society of Chemistry from Ref. [678]. Table 5.2 Interband absorption threshold energies for some metals on interest to laser particle generation [679]. Material Threshold energy (eV) Cu 2.08–2.1 Ag 3.86–3.9 Au 2.38–2.45

Figure 5.2 presents the optical absorption spectra of some important metal colloids. The sharp peak at longer wavelengths is due to electron plasma resonance, the rise of absorption at shorter wavelengths is due to interband absorption (Table 5.2). Examples of absorption spectra of nanorods and core-shell particles are presented in Figs 5.16 and 5.17. Examples of extinction spectra for spheroidal and trigonal prismatic silver nanoparticles can be found in the article by Kelly et al. [677]. Interest to silver and gold colloids is to a great extent due to their absorption maximum in visible region. Plasma resonance Plasma resonance is the collective oscillations of the free electron gas in the metal. The two lowest modes of such oscillations in case of spherical particles are presented in Fig. 5.3. The dominant peaks in Fig. 5.2 correspond to dipole resonance; the quadrupole resonance peak is for nanoparticles weak and lies at shorter wavelengths [679] (Table 5.3).

Estimation of average diameter of nanoparticles from plasma resonance peak width The dependence of the resonance peak width on particle size (smaller particles have larger peak width, a correlation graph may be found in the review by Perenboom et al. [681]) enables the determination of the mean particles size. In the 1–10 nm range, the Mie theory predicts an inverse proportional dependence of the plasmon peak width w on the particle diameter dav (intrinsic size effect): w d ∝ 0 , (5.6) av w

where w0 is a constant. Ch05-I044498.tex 11/9/2007 18: 50 Page 212

212 Handbook of Liquids–Assisted Laser Processing

Electric field L 1 Magnetic field L 1

Electric field L 2 Magnetic field L 2

Figure 5.3 Electric and magnetic fields far away from metal clusters in dipole and quadrupole resonance mode, L = 1 and 2, correspondingly [680].

Table 5.3 Plasma resonance frequencies of some important systems [679]. Geometry Plasma resonance frequency Formula number  ne2 Bulk ωp = (5.3) ε0me ωp Flat surface ωres =  (5.4) 1 + ε1 ε0

ωp Sphere (dipole resonance) ω1 =  (5.5) 1 + 2 ε1 ε0

Notations: ωp – Drude plasma frequency, n – density of electrons, e – electron charge, me – electron mass, ε0 – vacuum permettivity, ε1 – medium permettivity.

With a further increase in the diameter of the nanoparticle (>20 nm), the peak width increases again, because of more inhomogeneous polarization of the larger nanoparticles in the electromagnetic field of the incoming light and due to excitation of a higher number of different multipole modes, the so-called extrinsic size effect [682].

Estimation of the average diameter of nanoparticles from absorbance From Drude theory follows a linear dependence between absorbance and average diameter of nanoparticles [683]:

katom = f0dav, (5.7)

where f0 is a constant. The constants w0 and f0 may be determined from direct measurements of particle size with electron or scanning probe microscopes. Ch05-I044498.tex 11/9/2007 18: 50 Page 213

Generation and modification of particles 213

5.3 Experimental Techniques of Particles Generation

Main experimental setups used for laser ablation fabrication of colloids are presented in Figs 5.4–5.7.

Glass Isopropyl Graphite beaker alcohol target Laser beam Focusing 1064 nm 3.5 ns lens 10 Hz

Figure 5.4 Setup with vertical target [684]. For avoiding of crater formation and absorbance increase due to generated suspension, the target my be rotated [685]. © Elsevier.

(a) Preparation of colloids (b) Modification of colloids 1064 nm (38 J/cm2) 355 nm (4–12 mJ/pulse)

Water Silver nanoparticles

Silver plate

Figure 5.5 Setup for ablation of an horizontal target in liquid (left) and for irradiation of suspended particles (right). © The Laser Society of Japan, reproduced with permission from Ref. [686].

Laser beam

Lens –

Quartz cell

Distilled water Target holder Target

Stirring bar

Magnetic stirrer

Figure 5.6 Setup with horizontal target and stirred liquid [687]. © Elsevier. Ch05-I044498.tex 11/9/2007 18: 50 Page 214

214 Handbook of Liquids–Assisted Laser Processing

Laser beam

Lens l/2 plate Laser Splash of beam Lens suspension 53°

Splash of suspension

Suspension Suspension

(a) (b)

Figure 5.7 Setup with inclined laser beam (b), compared to conventional setup (a). The conventional system suffers from splashes at laser energies over 30 mJ/pulse. System (b) with laser beam at an angle to the surface avoids the splashes reaching the lens. At Brewster angle, also the reflection losses may be avoided. Pulse energies up to 150 mJ were applicable with this optical arrangement [688]. © Elsevier.

5.4 Metal Particles

5.4.1 Introduction Noble metals colloids (Fig. 5.8) are useful in photography, optoelectronics, catalysis, biosensing, labelling of proteins, etc. Due to plasma resonance in visible region (Fig. 5.2), the Raman scattering and other optical nonlinearities of the nanoparticles are greater here by orders of magnitude compared with those of flat surfaces. In comparison with conventional chemical methods of fabrication of noble metal colloids, in laser process the particles are clean, because no other substances but a metal target and a liquid are needed. A recent application-oriented review about photophysical and photochemical properties of metal nanopar- ticles was published by Kamat [689] and a review of using surface plasma resonance techniques in biomedical sciences by Englebienne et al. [690]. Magnetic colloids are useful in catalytic chemistry, magnetic recording, magnetorheological fluids, etc. In comparison with the common fabrication methods of magnetic particles, such as decomposition of organo- metallic precursors and mechanical milling, laser ablation is simpler and helps to avoid contamination of particles. However, when ablation is performed in oxygen-containing liquids, the surface of the particles becomes oxidized.

5.4.2 Mechanisms determining the particles size In many applications, particles of same size are of advantage, for example in SERS-based sensors [692]. In the following, the major phenomena controlling the size of small particles during laser irradiation and subsequent growth are characterized.

Dependence of the melting temperature on particles size Because the vapour pressure depends on the surface curvature (Eq. (7.57)), the melting temperature of solid particles decreases with the decrease of their size (Fig. 5.9). Ch05-I044498.tex 11/9/2007 18: 50 Page 215

Generation and modification of particles 215 Absorbance

200 300 400 500 600 700 800 900 Wavelength (nm) (a) (b)

Figure 5.8 (a) Electron micrograph and (b) optical absorption spectrum of platinum nanoparticles with an average diameter of 6 nm produced by laser ablation at 1064 nm of a platinum metal plate in pure water [691]. © Elsevier.

1.0 0 / T r T

0.95

0.9 02040 R, nm

Figure 5.9 Variation of melting temperatureTr with radius for gold particles in vacuum,T0 – melting temperature for macroscopic bodies (after Sambles [693], © Royal Society of London, reproduced with permission).

According to Sambles [693] (with reference to Reiss and Wilson [694] and Curzon [695]), the melting temperature of small particles follows the relation:   Hm ρs γsl γ l ρs (T0 − Tr ) = + 1 − , (5.8) 2M T0 r − p r ρl

with notations: Hm – latent heat of fusion, T0 – bulk melting point, Tr – melting point at radius r, ρs – density of solid, ρl – density of liquid, γl – surface energy of liquid, γsl – mean solid–liquid interfacial energy, M – molecular mass, p – relevant skin thickness. Sambles [693] gives to the parameter p an estimate p = 2.2 ± 0.5 nm. Ch05-I044498.tex 11/9/2007 18: 50 Page 216

216 Handbook of Liquids–Assisted Laser Processing

Ostwald ripening Because the solubility of smaller particles is larger than this of larger ones, mass transfer from smaller particles to larger occurs. Ostwald ripening tends to minimize the total surface area of the particle system.

Heat transfer efficiency Small particles cool faster than larger ones. Inasawa et al. [696] have shown that for a given laser fluence, there exists a critical size over which the temperature of the particle does not reach the melting temperature during the laser pulse length. This phenomenon explains the particle size reduction and narrowing of their size distribution at laser irradiation of suspensions. The time to reach the boiling temperature of the particles, t b is − ( − ) =  − 1 A B Tb Tw t b tm ln , (5.9) B A − B (Tm − Tw) where    N 2 3FM r  A = 1 − 1 − n ηε , (5.10) 4τρC r r2 p n=1

= 3Mλ B 2 , (5.11) ρCpr  tm is the time for the particle to melt, 4πr3ρ Hm  3M t = tm +   , (5.12) m F N r2 π 2 − − n ηε − π λ ( − ) r 1 1 2 4 r Tm Tw τ n=1 r

tm is the time for the particle to reach the melting temperature, given by the equation     N 2 Fr r  3Mλ T = T + 1 − 1 − n ηε × 1 − exp − t , (5.13) m w 4τλ r2 ρC r2 m n=1 p

with notations: Tw – ambient temperature, Tm – melting point of the particle, Tb – boiling point of the particle, F – laser fluence per pulse, τ – laser pulse width, M – atomic mass of the particle, ρ – density of the particle, Cp – specific heat of the particle, λ – thermal conductivity of the surroundings, r – radius  2 = 2 − − 2 of the particle, rn – radius of the nth (111) plane: r r (r nd) , d – distance between (111) planes, N – number of (111) planes included in a particle, N = 2r/d, η – fraction of the area of the plane occupied =   = 2 by metal atoms (η 0.91 for a gold (111) plane), ε – absorption coefficient of a metal atom, ε ε/επr0 NA, ε – mole absorption cross-section of the metal, NA – Avogadro’s number, r0 – bond radius of metal atoms. (111) Planes mean that the particle is modelled as being composed of n layers of equal thickness perpendicular to the laser beam axis. Particle’s size reduction occurs if the particles temperature reaches the boiling temperature, tb ≤ τ, during the laser pulse.

Surfactants Surfactants were found to control efficiently the size of laser ablation formed nanoparticles through a so-called dynamic formation mechanism [697–699]: (1) Immediately after the laser ablation, a dense cloud of metal atoms is built over the laser spot of the metal plate. As the interatomic interaction is much stronger than the interaction between a metal atom and a Ch05-I044498.tex 11/9/2007 18: 50 Page 217

Generation and modification of particles 217

surfactant molecule or a solvent molecule, metal atoms are aggregated as much as metal atoms collide mutually. (2) This initial rapid aggregation continues until metal atoms in the close vicinity are consumed almost com- pletely. As a result, an embryonic metal particle forms in a region void of metal atoms (cavity). However, the supply of metal atoms outside the region through diffusion causes the particle to grow slowly even after the rapid growth ceases. (3) This slow growth terminates when the surfaces of the particles are fully covered with surfactant molecules or the free metal atoms are consumed completely in the solution. Full covering of particles by surfactant molecules occurs when the surfactant concentration exceeds the critical micelle concentration. Using this criterion, Mafuné et al. [698] developed a formula for maximum particle radius rs growing in a surfactant solution:       3 NsS S k dsvs 1 rs (t) = = · · r0 + kVadavat − 3r0, (5.14) 4π 3 kVadava 4

where Ns is the number of surfactant molecules absorbed on particle, S is surface area occupied by one surfactant molecule on the particle, k is attachment coefficient of metal atoms by the particle (attachment 2  cross-section = kπr ), k is attachment coefficient of surfactant atoms, ds is density of a surfactant molecules in the solution, vs is velocity of surfactant molecules in the solution, da is the number density of metal atoms in the cloud of the metal atoms, va is diffusion velocity of metal atoms in the vapour, Va is volume of the metal atom, and r0 is the radius of the embryonic particle. Ionic surfactants, but also cyclodextrines were used to control the growth of laser-generated particles, reducing this way their size and size dispersion. Cyclodextrines were chosen due to their biocompatibility [700].

Effect of chlorides Bae et al. [701] found that presence of chlorides in the aqueous medium during laser ablation contributed to the reduction of the average particle size, prevented formation of large particles, and increased the formation efficiency of small nanoparticles thereby. However, the long-term stability of Ag nanoparticles formed in NaCl solution was reduced by enhanced spontaneous aggregation compared to those in neat water.

5.4.3 Modification of suspending particles by laser irradiation 5.4.3.1 Reduction in size and fragmentation Often there is a need to convert larger particles into smaller ones, enlarging this way their overall surface area (in sensing and catalysis) or increasing the density of the particles on a surface (in information storage). Particles exposed to light may loose their mass due to photodissolution and vapourization. In case of ultra- short intense pulse irradiation, particles may decay into fragments in a Coulomb explosion process. Fig. 5.10 presents some situations in particles fragmentation under the action of laser light. Lasers provide a unique possibility to reduce the size of noble metal particles due to their intense plasma resonance in visible region [702]. Figure 5.11 presents the dependence of final size of irradiated in suspension 45-nm size Au particles depending on the laser fluence. The mechanisms controlling the final size of particles were described in Section 5.4.2. Particle size reduction may occur also due to disintegration of aggregated particles, a process going on also below the melting temperature of the material [703].

Modification of particles by ps/fs-laser pulses Shorter pulses melt the particles at lower pulse energy, because the energy losses due to heat transfer from particles to liquid is smaller. According to Hodak et al. [704], the characteristic time of heat transfer from nanoparticles to liquid is about 100–200 ps. Ch05-I044498.tex 11/9/2007 18: 50 Page 218

218 Handbook of Liquids–Assisted Laser Processing

Laser beamAuCl4 Laser beam Laser beam Heated to the b.p by laser pulses (Tb.p.) Tb.p. Size reduction of larger particles Photoreduction and nucleation

Evaporation of gold atoms from the surface and cooling the particle Without particle growth Particle growth and nucleation

Aggregation of gold atoms, • Size reduction of larger particles formation of small particles. Wide size distribution • Particle growth and nucleation

(a) (b)

Narrow size and distribution (c)

Figure 5.10 Schematic of laser-induced size reduction of gold nanoparticles [696]. (a) Heated by laser pulses, gold atoms evaporate from the particle surface when the particle temperature is above the boiling point. Then the particle becomes smaller and evaporated gold atoms aggregate to form small particles. (b) With laser irradiation to gold nanoparticles, fragmented particles cannot grow because of a lack of source material, AuCl4, which causes a wide size distribution. (c) With laser irradiation into AuCl4 solution, particle growth and laser-induced size reduction occur at the same time. Fragmented particles can grow to the maximum diameter controlled by the irradiated laser fluence, which results in narrow size distribution. © Institute of Pure and Applied Physics, reproduced with permission.

50

40

30

20

m.p. b.p. Maximum diameter (nm) 10

0 102 103 104

Absorbed laser energy, Q(J/(g pulse))

Figure 5.11 Dependence of the maximum diameter of Au particles on the absorbed laser energy [702]. Notations: m.p. – melting point of the material reached; b.p. – boiling point of the material reached. Solution: water + citric acid; laser: 532 nm, 7 ns. © American Chemical Society (1999), reprinted with permission from Ref. [702].

Because of smaller mass of electrons,they gain easier energy from laser light,so that the electron temperature may considerably exceed the temperature of ions (Fig. 5.12). If a significant amount of hot electrons leave the particle, the particle may explode due to repulsive forces between the positive ions, a phenomenon called Coulomb explosion (Fig. 5.13). Ch05-I044498.tex 11/9/2007 18: 50 Page 219

Generation and modification of particles 219

6000 τ 30 ps 380 Electrons τ 5 ns

Electrons 360 4000 ions 340

2000 Temperature (K) Temperature (K) 320 ions 300 0 200 400 600 0 5 10 15 20 103 Delay time (ps) Delay time (ps)

Figure 5.12 Temporal evolution of electron temperature Te (dotted line) and ion temperature Ti (full line) calcu- lated for 20-nm Au particles excited with (a) 30 ps and (b) 5 ns laser pulses with Eabs = 2.05 mJ/pulse. © American Chemical Society (2000), reprinted with permission from Ref. [704].

e Ag Ag Ag e e Ag e e e e h e Ag e e e e Ag Ag Ag Ag Ag Ag e e e e e e Ag e

Ag nanocluster Electron ejection Transient state Fragmentation

Figure 5.13 Fragmentation of a Ag cluster with laser excitation [705]. A transient aggregate formed via the photoejection of electrons is considered to be a precursor for complete fragmentation of the particle. © American Chemical Society (1998), reprinted with permission from Ref. [705].

5.4.3.2 Melting without fragmentation It is possible to modify the shape or/and structure of the particles by melting. The corresponding changes in optical absorption spectra are expected to be applicable for optical information storage [704].

Melting of nanorods At melting,the rod-shaped particles transform into spheres,minimizing this way their surface energy (Fig. 5.14). The changes start at the middle of the rods, what is explained by poorer cooling and thus higher temperature there (Fig. 5.15). Changes in optical absorption spectra during the transformation are shown in Fig. 5.16. Shape transformation at nanoparticles at an exposure to light may occur also without melting. Jin et al. [708] observed conversion of 8-nm-sized spherical Ag nanoparticles into prisms at exposure to a fluorescent lamp light. In another study the same researchers [709] found that it was possible to control the nanoprisms size in range of 30–120 nm by the ratio of the amplitudes of two wavelengths from an Xe-lamp, the first wavelength corresponding to dipole plasmon resonance and the second to quadrupole plasmon resonance of the nanoprisms (see Table 5.4 for experimental details, Jin 2001, and 2003).

Melting of core-shell particles Laser melting of core-shell particles may also cause significant changes in their absorption spectra (Fig. 5.17) having a potential for use in optical information storage. Ch05-I044498.tex 11/9/2007 18: 50 Page 220

220 Handbook of Liquids–Assisted Laser Processing

Figure 5.14 TEM image of a gold nanorods solution after exposure to 800-nm nanosecond laser pulses [706]. The laser fluence was 0.64 J/cm2. Nanoparticles having an odd shape (φ-shape) are highlighted in the TEM image by circles. Particles of this particular shape are absent in the original starting solution, and a high abundance of this particular shape is mainly produced by irradiation with low-power nanosecond laser pulses (the length of rods was 44 nm and width 11 nm before laser irradiation). © American Chemical Society (2000), reprinted with permission from Ref. [706].

(110) (111)

(111) (001) (a)

(110) (111)

(111) (001) (b) Twin

(111)

(111) (111)

(111) (001) (c)

(111)

(111) (001)

(d) Twin

Figure 5.15 A schematic process for the structural transformation of a gold nanorod to nanodot under laser irradiation [707]. © 2000 American Chemical Society, reprinted with permission from Ref. [707].

5.4.3.3 Enlargement in size and coagulation Growth of particles may occur even at low-level light exposure due to photodissolution and Ostwald ripening. Jin et al. [708] observed a size reduction of 8 nm Ag particles at an exposure to a fluorescent lamp light with subsequent growth into prisms. Mafuné et al. [682] report that growth of gold clusters into nanoparticles continued within 2 h after the pulsed laser for the size reduction was switched off. Ch05-I044498.tex 11/9/2007 18: 50 Page 221

Generation and modification of particles 221

0.30 τ 7 ns

0.25

0.20

0.15

Absorbance 0.10

0.05

0.00 500 600 700 800 900 1000 (a) Wavelength l/nm (b)

0.30 τ 100 fs

0.25

0.20

0.15

Absorbance 0.10

0.05

0.00 500 600 700 800 900 1000 (c) Wavelength l/nm (d)

Figure 5.16 Comparison of the optical absorption data and TEM images for two gold nanorod samples irradiated by laser pulses having the same fluence (0.25 J/cm2) but different laser pulse width (7 ns (top: a, b) vs. 100 fs (bottom: c, d)) [706]. Only an optical hole burning at the laser wavelength (800 nm) and a partial melting of the gold nanorods are found when nanosecond pulses are used. Especially a high abundance of φ-shaped particles as shown in Fig. 5.14 is clearly visible. However, a complete melting of the gold nanorods into nanodots and a complete depletion of the nanorods are achieved with femtosecond laser pulses of the same energy (fluence). This result leads to the conclusion that nanosecond laser pulses are less effective in melting the gold nanorods. (The length of rods was 44 nm and width 11 nm before laser irradiation). © American Chemical Society (2000), reprinted with permission from Ref. [706].

Light may stimulate aggregation of particles by increasing van der Waals forces between them (Section 2.3.1).The effect is most pronounced at Mie resonances where interparticle energy may be enhanced by many orders of magnitude. Laser-heated particles may melt together, as shown in Fig. 5.18. Having a mixture of particles of different materials, alloy particles may be achieved. Izgalijev et al. [710] report about AgAu alloy particles formation at irradiation of a mixture Ag and Au colloids by laser light. Chandrasekharan et al. [712] observed laser-stimulated melting together of gold particles, previously aggregated through adsorbed Rhodamine 6G molecules. In some cases, the particles aggregation into nanowires and nanonetworks was observed [713–715] (Fig. 5.19).The mechanisms determining the morphology of the aggregates is not clear. Formation of networks may be controlled by surfactants in the solution (Fig. 5.20). Ch05-I044498.tex 11/9/2007 18: 50 Page 222

222 Handbook of Liquids–Assisted Laser Processing

1.0 a

b c d 0.5 Absorbance (1 cm)

0.0 300 400 500 600 700 Wavelength (nm)

Figure 5.17 Absorption spectra of AucoreAgshell particles (molar ratio Au:Ag = 1:0.5) following photoexcitation with 532 nm, 30 ps laser pulses: (a) non-irradiated; (b)–(e) Eabs = 0.13, 1.16, 4.6, and 6.7 mJ/pulse [704]. Further details of the experiment are given inTable 5.4, Hodak 2000. Reprinted with permission from J. H. Hodak,A. Hen- glein, M. Giersig, G.V.Hartland, Laser-induced inter-diffusion in AuAg core-shell nanoparticles. J. Phys. Chem. B.; (Article); 2000; 104(49): 11708-11718. © American Chemical Society (2000), Ref. [704].

TiO2 ν nh TiO2 Au

Au

Figure 5.18 Schematic diagram illustrating the fusion of TiO2/Au nanoparticles at laser irradiation [711]. © American Chemical Society (2001), reprinted with permission from Ref. [711].

Atomic transmutations observed at laser irradiation of suspended particles It is well known that even in low-temperature deuterium plasma, free neutrons are generated – laboratory neutron sources use only some kilovolt of excitation.Thus,at laser processing of materials in heavy or semiheavy water, the generation of neutrons in laser plasma or at bubble collapse is expected. The released neutrons can cause nuclear reactions in the surrounding materials. Also extraordinary high-electric fields near small metal particles at Mie resonance (Section 5.2) may contribute to nuclear reactions. Shafeev et al. [716] report about transmutation of mercury into gold in course of irradiation of mer- cury suspension in heavy water by picosecond Nd:YAG and Ti:Sapphire laser pulses of energy density of ∼1010W/cm2. The supposed nuclear reaction was:

196Hg + n → 197Hg + γ, (5.15) Ch05-I044498.tex 11/9/2007 18: 50 Page 223

Generation and modification of particles 223

(a)

(b)

Figure 5.19 TEM images of laser-generated Au networks in water [715]. (a) Preparation within an ice-bath and (b) preparation under the room temperature. The scale bar length corresponds to 50 nm. © Elsevier.

0.9

0.8 Nano- 0.7 networks 0.6

0.5 Small nanoparticles 0.4 Absorbance @ 250 nm 0.3

0.2 110100 Concentration (mM)

Figure 5.20 Typical optical absorption spectra of Pt particles irradiation products after laser excitation of the interband at 355 nm in different SDS concentrations [691]. The arrow indicates the critical micelle concentration of SDS. SDS – sodium dodecyl sulphate (C12H25OSO3Na). © Elsevier.

where γ stands for γ-photon. 197Hg decays within 2.7 days into 197Au through electron capture from its own K shell: − 197Hg (Z = 80) + e → 197Au (Z = 79). (5.16)

After 4 h of irradiation of an Hg suspension by 350 ps, 1.06 µm laser pulses, up to 13 per cent of mercury was converted into gold. Ch05-I044498.tex 11/9/2007 18: 50 Page 224 max λ ences Fojtik (1993) [720] Henglein (1993) [721] Neddersen (1993) [692] Eckstein (1993) [719] Hasegawa (1991) [717] Fujisaki (1993) [718] ; , – standard deviation; of st networks metal clusters SERS spectra decomposed into atoms – average size; µ m was also observed at 520 nm (Au) av = ∼ 1 chains , later particles max λ light-enhanced van derWaals forces was observed;coagulation started with of physical and chemical properties : 399 nm (Ag, water), 414 nm (Ag, of optical absorption spectra for metal max λ review ovel features, observed phenomena, comments Refer Calculation colloids, of small metal particles in solutions methanol), 521 nm (Au, water), 625 nm (Cu, water) Dependence of suspension absorption spectrafluence on presented; laser obviously due to irradiation in 16 h; atOstwald the ripening beginning of theformation growth of particle developed Stable (at least over somefabricated months) by metal ablation colloids in water; various absorbed on colloidsquality; molecules higher were pulse of energy high yieldparticles; obviously smaller which at further irradiation Laser ablation of metal targets resulted in excitation and emission spectra of the tripletof transitions Ba and Cathin in wires He of are diameter presented; growth of tangle laser ablation of targets in superfluid He (Ag) and related research (solids targets in liquids); 2–19 nm (Au) 3–4 nm (Ni) 10–50 nm, 20 nm av Clusters and atoms of Ba and Ca Aggregated particles Laser irradiation caused the colloids to aggregate Aggregated particles Stable in dark colloids aggregated in course if 2 ,up 2 , 0.5W,beam -Nd:YLF,0.2 mJ + to 200 min Lasers or otherHg-lamp, 100W, Particles size, achieved up to 30 h Ruby,694 nm, 2.3–27 J/cm Nd:YAG, 1064 nm, 10 Hz, 55 mJ dYG 1064 Nd:YAG, and 532 nm, 1 and 0.2 mJ, respectively. 2 ω area 1 mm light sources or after treatment N Ar -hexyl n sodium + polyacrylate 0.2 mM water 2-propanol, chloroform, acetone, ethanol, alcohol used for particles preparation by chemical reduction 2-propanol, water, cyclohexane methanol Superfluid liquid He (1.6 K) Liquids Aqueous solution in) vacuo of main absorption peak. Metal colloids prepared or modified by laser irradiation, Ni film 11 nm, in suspension Targets in suspension Ba, Ca Au particles, Au particles, 10 nm, Au film Ag,Au, Pt, Cu Water, acetone, wavelength ( Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 225 ) ( Continued Persson (1996) [726] Satoh (1994) [722] Sibbald (1996) [725] [703] Persson (1995) [723] Hui (1995) [724] Takami (1996) ; effect − : 400 nm -exciplexes 2 max λ − 35 to to less than and Br − by I of colloid in 20 h (in calculations modified -potential from ζ in UV–VIS region are presented 2 ,He-Ag-He-exciplexes trapped in micro- ,Ag reduces the particle mean size 2 of colloids were ,Cu 2 was confirmed by ab initio Produced by Nd:YAG-laser Ag particlesfurther were dissociated by XeCl-laser10 (308 mJ); nm, 10 linear Hz, cavities were found; formation of AgHe Irradiation caused full coagulation dark stable for several years);fractal first conglomerates particle formed; chains, optical then absorption spectra changes were explained bythe Ostwald possible ripening; mechanisms of coagulationneutralization were of Ag photon particles and/orplasmon by oscillation-enhanced surface van der Waals forces; photocoagulation was observed also inZn case colloids of Larger particles were further dissociated bylaser continuing irradiation, the dissociation wasshorter more wavelengths; effective absorption at and emissionof spectra Ca of this modification onwas plasma small resonance frequency (before irradiation), 450 nm (afterwith 15 min 355 nm irradiation light) ≈ 10 nm and changed Irradiation − 50 mV; achieved particles were stableweek at (no least aggregation one or precipitation); Emission and absorption spectraneutral and atoms, dynamics also of residing atbubbles microscopic were He investigated Surface µ m-sized -exciplexes 2 Clusters and particles 9 nm mode (15 min irradiation with 355 nm) Neutral atoms, clusters, and particles 20 nm mean and particles; Ag atoms, clusters AgHe 2 ∼ 20 mJ -Nd:YAG, -Nd:YAG, 2 ω 532 nm (less effective) High-pressure Hg-lamp, 100W with water filter and 355 nm,pulsed, 10 and 20 Hz, 10–20 mJ Nd:YAG, 1064 nm, 10 Hz, 55 mJ ≈ 15 min pulsed, 10 and 20 Hz, 10–20 mJ 532,355, and 266 nm, pulsed, 10 Hz 3 ω 355 nm, 10 ns, 60 mJ/cm , 3 , and 4 NaBH He II (1.7 K) 532 Nd:YAG, 2-propanol, chloroform solution of AgNO He II (1.6 K) 532 Nd:YAG, nm, SDS Acetone, ethanol, Aqueous Water 8nm Ga, In mode Ca, Cu,Ag He II (1.7 K) Nd:YAG, Au colloids, Ag, Mg,Yb,Al, Ag Ag particles, 19 nm Ag Ch05-I044498.tex 11/9/2007 18: 50 Page 226 ences Procházka (1997) [728] Procházka (1997) [729] Hui (1997) [730], (1999) [731] [727] Srnová (1998) [733] Hui (1998) [732] Takeuchi (1997) neutral of of 406 nm = max photochemical process λ ) enhances the coagulation 3 395 nm were produced by laser = max λ M NaCl) residing in He bubbles are presented − 4 10 × ovel features, observed phenomena, comments Refer Colloids prepared in water andstable NaCl at solution least were for asolution year; precipitated prepared within in 1 phtalazine day;of SERS-activities colloids and deposited onto surface particles studied (water), 410 nm (phtalazine added), 398(7 nm particles yield and provides smallertheir size, aggregation; but metalation causes of aon free laser base fabricated porphyrin particlesstable was in faster time and (at more produced least particles. 10 months) that on chemically SERS-active colloid/adsorbate systems prepared directly by laser ablation insolution; colloid-adsorbate an (bpy adsorbate or (phtalazine) tppz)glass films and on Cu/C-grids fabricated; Eu atoms Laser irradiation promotes the high-concentration colloids; acetone was detectedirradiated in solution, obviouslywhere in Au particles get electrons from 2-propanol Neutral Mg and Be atoms dissociation of laser-ablated metal particlessuperfluid He; in the LIF spectraare of explained Mg by and formation Bemetal of atoms atoms solid He around the Smaller laser fluence yieldslarger smaller particles particles; initially fragment uponNaCl laser additive irradiation; (but not NaNO av M) − 4 10 × Eu atoms and particles Results of spectroscopic investigations (LIF) Mg and Be atoms and particles 18 nm mean 10 nm mean 13–14 nm mean (7 12.3–14.8 nm (in water) -ion, 514 and + Nd:YAG, 1064 nm, 40 ps, 1 Hz, 40 mJ Lasers or other Particles size, achieved dYG 532Nd:YAG, or 355 nm, pulsed, 10 and 20 Hz, 10–20 mJ Nd:YAG, 1064 nm, 40 ps, 1 Hz, 40 mJ 488 nm, up to 1.8W,up to 20 h Nd:YAG, 1064 nm, 20 ns, 10 Hz, 10–30 mJ light sources or after treatment N Ar M − 5 NaCl − 4 10 0.7 mM M + 10 + + − 5 M NaCl × (liquids 10 7 − 2 3 + + 10 × NaCl,water phtalazine water phtalazine –7 2-propanol 0.2–5 mM and NaNO He II He II ( ∼ 1.6 K) Nd:YAG? optionally stirred) Liquids Water,water Water, water Water Water ) Continued ( < 10 nm, in suspension Targets Eu Mg, Be Au particles Ag Ag Ag Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 227 ) ( Continued Fujiwara (1999) [737] Kamat (1998) [705] Jeon (1998) [734] Chang (1999) [738] Kurita (1998) [736] [702] Takami (1999) Yeh (1999) [735] in leads along changed 580 nm 400 nm ≈ = ; at 1064 nm excitation) of size less than max max φ -shaped λ λ trans during irradiation from 531.5 to 517 nm max fused photoejection of electrons λ exceeded the Au melting rod-to-sphere conversion into spherical particles temperature excitation) an incomplete photoannealing long (532 nm) for 1 min, and30 min fragmented again during Laser irradiation of particlesphotoexcitation by of ps-pulses electrons causes and thisabsorption way to plasmon bleach; to particles fragmentation (seewavelength Fig. (532 5.13); nm longer instead ofpreferentially 255 nm) the causes fragmentation of largerirregularly or shaped particles their bent and twistedrepresenting forms an nanostructures, probably early stage ofshape the transition; the rod-to-sphere restructuring ofstarts the from Au the nanorods centre portion of the particle process was observed resulting in Formed particles were spherical causes mainly a (SP Non-spherical particles of size 20–50 nm some minutes 10 nm, obviously due tothermal melting and radiation vaporization; measurements indicatedparticles that the temperature.; shift of during irradiation Longer laser wavelength and smalleryielded fluence smaller particles; colloids stability:in prepared water – several months,iso-propanol in – methano l–1day,in at least 6 months; Stable colloids (at least overacetone a formed week) at achieved; laser ablation; About 10 nm particles At 532-nm laser irradiation (SP independent av 5–20 nm (355 nm, 18 ps, 10 Hz, 1.5 mJ, 3 min) ≈ 12 nm of starting size 16.3–32.9 nm (water), 12.4–17.4 nm (iso-propanol) Cu particles 10–150 nm achieved 2 2 2 ≈ 18 ps, ≈ 6ns -Nd:YAG, -Nd:YAG, -Nd:YAG, 2 ω 532 nm, 18 ps, 1.5 mJ 2 ω 532 nm, up to 60 mJ, up to 120 min 2 ω 532 nm, 10 Hz, 7 ns, up to 800 mJ/cm Xe-lamp, 250W, > 300 nm filtered 355Nd:YAG, and 532 nm, 2–3 mJ Nd:YAG, 355 nm, dYG 1064Nd:YAG, or 532 nm, 247 and 397 mJ/cm 532Nd:YAG, and 1064 nm, 6 ns, up to 10 Hz, up to 67.4 mJ/cm dYG 532Nd:YAG, and 1064 nm, 10 Hz 2 citric acid, citric sodium citrate + + + Solution used for particles generation by chemical reduction agitated acid iso-propanol Solution used for particles generation by chemical reduction, under N Electrolyte solution used for preparation of nanorods anaerobic conditions Water, methanol, Water Water av 10.5–29.4 nm 40–60 nm 5–50 nm ≈ 10 nm diam., ≈ 50 nm length, also silica-covered and micelle- stabilized CuO powder 2-propanol under particles Ag Au particles, Ag particles, Au particles Au rods, e.g. TNA-capped Au Ch05-I044498.tex 11/9/2007 18: 50 Page 228 ences McGrath (1999) [741] Link (1999) [739] Mafuné (2000) [697] Link (1999) [740] [742] Mafuné (2000) [698] Tsuji (2000) ; 2 12); ; size = femtosecond 400 nm = (355 nm), 0.8 J/cm 2 max 12 are more favourable µ J), the λ particles continue to grow ≥ rods transformation to spheres transient grating experiments to near-spherical particles n metal ions formation theory for particle maximum radius µ J) or the nanorod aspect ratio (1.9–3.7) ovel features, observed phenomena, comments Refer for providing stable particles; Optical absorbance studies, the observations support themechanism particles through size reduction dependent reactivity was explained bytime longer of heating large particlesheated and state that longer they maintain their irradiation melts the nanorods of comparable volumes while thefragment nanosecond them pulses to smallerhigh near-spherical energies particles; at (mJ), fragmentation isthe also femtosecond observed irradiation; for a mechanismthe involving rate of energyof deposition electron–phonon as and compared phonon–phonon to relaxation theprocesses is rate proposed to determineof the the final laser-exposed fate nanorods, thatfragmentation is, melting or Pump-probe investigations; is a photothermal process, transformationleast time 30–35 ps, is independent at of(5–20 the power used Dependence of colloid absorbancewavelength, spectra fluence, and on focusing laser studies; particle generation thresholds: 0.5 J/cm (532 nm) particles size can beconcentration; controlled SDS in 7–15 with nm by SDS Nearly spherical particles formed;stability abundance was and greatest at 0.01 M SDS ( n Dependences of colloid parametersparameters on studied; process less particles wereheptane produced solution; in obviously particles formsingle within laser a shot; presented; in pure water, the until precipitate within a day At moderate energies (e.g. 40 15.9 nm av, mostly spherical particles ≈ 10 nm 5.3–16.2 nm average (90 mJ, 0.05–0.003 M SDS) 5–30 nm µ m µ J, spot 2 2 µ m µ m, 10 min -Nd:YAG, -Nd:YAG, -Nd:YAG, 2 ω 532 nm, 10 ns, < 90 J/cm 2 ω 532 nm, 15 ns, 10 Hz Lasers or other Particles size, achieved 100 fs, 1 kHz, up to 1 mJ, spot 25 OPO, 800 nm, 7 ns, 10 Hz, up to 20spot mJ, 25 400 nm, 100 fs, 500 Hz, 20 100 355, Nd:YAG, 532, and 1064 nm, 5–9 ns, 10 Hz, up to 1.4 J/cm 2 ω 532 nm, 10 Hz, up to 90 mJ,spot 1– 3mm light sources or after treatment N Ti:sapphire,800 nm, Ti:sapphire, 8, 10, Na) + 1 = 4 − 2 n n H SO + n 25 Na, + + 3 H and CN 12 + 12, 16) additives OSO Electrolyte solution used for preparation of nanorods Electrolyte solution used for preparation of nanorods I 0.003–0.1 M SDS (C 0.003–0.05 M SDS (C heptane dodecanethiol Liquids Water, also with Water Water Water ) Continued ( diameter, 31 nm length; and 11 nm diameter, 44 nm length Targets 10.2 nm diameter, 28.6 nm length) 5–100 nm Au rods, 8 nm Au rods, (e.g. Au,Ag suspensions, Ag Ag Ag Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 229 ) ( Continued Hodak (2000) [704] Kapoor (2000) [744] Link (2000) [706] Niidome (2000) [743] Chandrasekharan (2000) [712] due into > 10 mJ/ melt -radiolysis; the γ ≈ 10–15 nm, various shell shape change and fragmentation and spherical particles formation were prepared by radiation chemistry φ -shaped particles; for fs-pulses, the alloying φ -shaped particles formed at low fluences Co source), core size 60 thickness; occurred at 5–6 mJ/pulse andpulse fracturing for at 5 ns pulses;4 in mJ/pulse, correspondingly; case dissipation of of 30 energy psabsorbed pulses in at 75 nm 1 particles and melting occurs of in particles 100–200 was ps; observedlower temperatures to than start the at expected(is much melting depending point oncomplete particle alloying size); of at particlespulses needs used hundreds fluences, of the laser Particles were prepared by particles underwent in course of laserspectra irradiation; transient of absorption Cu particles on ps-scale presented Laser irradiation caused the nanorods to spherical and energy threshold for particletimes melting lower was as found for 100 ns-pulses;more fs-pulses homogeneous provide (in sense particlesshape) size colloidal and solution; at ns-pulsemuch irradiation (Figs 5.14 and 5.16) Core-shell particles ( to more effective absorption of 1064 nm light Fusion of particles was explainedparticle by clusters; the formation energy of gainedabsorbed from photons the is dispersedthe as neighbouring excess heat particles, thus into theper energy particle loss in clusters is lower of separate particles 20 nm av, some 200 nm Growth of particles is accelerated at large sizes, 5–20 nm 2 ,up 2 – 2 2 2 ≈ 0.4 cm to 45 min 10.2 J/cm OPO, 800 nm, 7 ns, 0.64–16.7 J/cm 6–8 ns, 10 Hz, up to 360 mJ, beam size 100 fs, 1 mJ, 0.2 mJ/cm dYG 532Nd:YAG, nm, ≈ 18 ps, 4 mJ, 10 Hz, 5–30 min 355 Nd:YAG, and 532 nm, 35 ps, 10 Hz, unfocused, 8 mJ/cm 532 nm, 5 ns, beam diameter 5mm 532 nm, 30 ps, 10 Hz, beam diameter 4 mm T:sapphire, 800 nm, Cyclohexane, stirred 1064 Nd:YAG, nm, ammonium bromide salts solution used for particles preparation, stirred containing gelatine used for particles preparation Aqueous solution Aqueous solution Aqueous solution Tetraalkyl- av , Ag core-shell 3.2 nm DT-passivated 44/11 nm Rh6G-capped Au nanoparticles ≈ 2nm Cd and Cu particles in solution particles, both Au and Ag core Au particles, Au Ag nanorods Ch05-I044498.tex 11/9/2007 18: 50 Page 230 ences Link (2001) [745] Poondi (2000) [746] Chen (2001) [715] Chen (2001) [747] Link (2000) [707] Hodak (2000) [704] – 2 ) Care 3 ◦ formed threshold and twisted and Ni(NO 3 melting networks nanowires formed, diameter of wires 6 nm, structure a singleAu nanorod was in average 60 fJ at both particles; the thresholds for alloying and ovel features, observed phenomena, comments Refer band optical absorption (atmelting 800 nm), energy for laser wavelengths precursors for Ni andwas Cu; the 150–1100W,beam power diameter of 3 laserinteraction and beams time 6 mm, 1–3 min; sphericalbut pure porous Ag dual particles, phase Niachieved and Ni oxide particles were thinner; laser melting at 1064the nm twisted affected nanorods selectively with aspecta ratio hole of into 6 distribution (burning histogram) Cross-linked networked nanorods fcc-polycrystalline Au; wires prepared at 0 Laser irradiation below the induces point and linetwins defects, mostly and (multiple) stacking faults, whichthat are drives the the precursor nanorods tointo convert the their more {110} stable facets {100}hence and minimize {111} their facets surface and surface energy,followed by reconstruction and diffusion, leadingφ -shaped through particles to spheres (Fig. 5.15) Laser heating transformed core-shell≈ 60 particles nm (up in to size) afteralloyed some pulses intofragmentation homogeneous are many times lower(1 for and 30 4 ps mJ) pulses than for 5 ns pulses (5–6 and 12 mJ) 5 min) temporarily colloid As estimated from the changes in SPR longitudinal Average size of starting particlesAg: 16.8 was nm; Au: at 13.7 nm, beginning of irradiation (at The liquids contained AgNO Ni Ni av 1–5 nm (Ag) and 0.4–1.2 nm (Ni oxide) spherical particles;Ag nanotubes ≈ 5nm dependent on metals ratio 2 2 ,upto 2 µ m, CW µ m, pulsed , 2 -Nd:YAG, µ J 10.64 Nd:YAG, 1.064 30 Lasers or other Particles size, achieved 100 fs, 1 mJ/cm OPO, 800 nm, 7 ns, 250 mJ/cm and 820 nm, 100 fs, 1 mJ/cm 532 nm, 0.245 J, up to 25 min 2 ω 532 nm, 10 Hz, 5 min CO 532 nm, 5 ns, 10 Hz, up to 12.8 mJ; 532 nm, 30 ps, 10 Hz, up to 6.7 mJ light sources or after treatment N T:sapphire, 800 nm, T:sapphire, 410 used for particles preparation used for particles preparation used at particle synthesis diethylene glycol, 2-ethoxy-ethanol solution of salts used at particle synthesis Liquids Aqueous solution Aqueous stirred Water ) Continued ( Au core-shell Targets 44/11 nm (average length/diameter) Ni, Cu, Nb Ethylene glycol, particles Au nanorods Aqueous solution Au nanorods, Ag Au and Ag colloids Aqueous solution Au Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 231 ) ( Continued Mafuné (2001) [675] [687] Lee (2001) [749] [751] Jin (2001) [708] Mafuné (2001) [683] Kapoor (2001) [748] Simakin (2001) [750] Abid (2001) Tsuji (2001) ; 395 nm = ), 455 nm 2 max nanoprisms λ ‘rosary’ ensembles of size transformed 2 -radiolysis; the relating the optical of the particles while high γ 510 nm (96 mJ/cm theory ≈ 220 nm (Cu) shape transformation and fragmenta- = alloying max disk-shaped particles achieved, λ 2 ; ) 2 517 nm 400 nm (Ag), = ≈ in course of laser irradiation max max Particles generation threshold at 532pulse; nm irradiation was of 7.2 produced mJ/ byby 1064 532 nm nm particles reduced theirλ size down 5 nm; (Ag), 520 nm (Au) average diameters 20 nm (Au),thickness 60 nm some (Ag), nm; at 32 J/cm Benzenethiol SERS spectra in Aucolloids and recorded; Ag the ablated surfacebe of an Ag efficient proved to SERS-active substrate; into smaller particles which grew into Spherical nanoparticles of 8 nm optical absorption spectrum calculatedelement by solution finite of Maxwell equations (16 mJ/cm approach exponentially a stable size,fluence which dependent; was a laser absorbance to particle average diameter,(Eq. presented (5.7)) Low fluences cause fluences cause removal of silverphoto-oxidation layer due to Colloid absorbance dependence onfluence, laser and wavelength, target relative positionλ studied; Particles were prepared by particles underwent tion At laser irradiation, the particle size was found to Au particles formed ) 2 v a v a (Ag, 532 nm), (Ag), (Au) v v a a av av Nanoprisms, thickness 15.6 nm, side 10–60 nm 4.6–14.4 nm 31 nm (Ag, 1064 nm) 4.1–6.2 nm (840–280 mJ/cm 12 nm 15 nm (Pt) Disk-shaped particles At 10–20 J/cm 15 nm 18 nm Alloying 2 2 2 2 2 2 < 90 J/cm -Nd:YAG, µ m, up to 532 nm, 35 ps, 10 Hz, unfocused, 6–10 mJ/cm dYG 532Nd:YAG, and 1064 nm, 10 ns, 80 mJ, 532 nm, 10 ns, 10 Hz, up to 1.05 J/cm Fluorescent lamp, 45W,350–700 nm, 70 h and 1064 nm, 5–9 ns, 10 Hz, 0.1–1 J/cm Nd:YAG, 1064 nm, 6 ns, 10 Hz, 5–40 mJ Cu-vapour, 510.6 nm, 20 ns, 15 kHz, spot 10 32 J/cm 532Nd:YAG, nm, 5 ns, 10 Hz, 15–96 J/cm gelatine 355 Nd:YAG, and SDS, SDS,10 mM 2 ω + + + 0.1–10 mM used for particle synthesis flowing Stirred water 355, Nd:YAG, 532, of salts used for particle synthesis Aqueous solution Aqueous solution Water Water Water Water Water, stirred or ≈ 8nm av nm (Pt) v a av , prepared by 1064 nm laser ablation 8nm particles, 23.4 nm Pt,Tl particles, 25 Au Au colloids, Ag, Cu Ag,Au Ag,Au Ag nanoparticles, Au core – Ag shell Ch05-I044498.tex 11/9/2007 18: 50 Page 232 ences Mafuné (2002) [754] Dolgaev (2002) [753] Compagnini (2002) [755] Kamat (2002) [689] Brause (2002) [676] Mafuné (2002) [682] Chen (2002) [752] in range particles 2 particles Cl nanoparticles formed and at Au 1 . 04 alloy 525 nm (Au, ;Au colloids coagulated = size can be controlled max λ flat disks 524 nm (Au), 405 nm (Ag) 399–393 nm (as ablated); = = max λ max at ablation in chloroform; solid films due to cluster attachment to nanoparticles λ of metal nanoparticles photophysical and 520 nm = ovel features, observed phenomena, comments Refer max water), 390 nm (Ag, water) 393–404 nm (during irradiation of suspension) Review photochemical properties; thereby of laser-induced fragmentation and fusion of Au,Ag, andTiO grow again and mutual aggregation; the growthon depends SDS crucially concentration Laser fragmentation of nanoparticles: itdemonstrated,that was particle 1.7–5.5 nm by laserλ fluence and SDS concentration; ablation in dichloroethane also TiCirradiation formed; of further Au particles reducedchanged their their shape size to and in 30 days; amorphous; further irradiation oflowers suspension the first particles size, butdue then to the particles size coagulation; rises critical(coagulation again lower onset) size for Ag clusters≈ 50 nm; in water was XPS studies revealed formation of spherical AuPd respectively AgPd formed compounds with embedded Au particles fabricatedSOG, PMMA, with and PS; As-ablated particles were of irregular size and At ablation of Ti in water also TiO Average size of starting particlesAg: 16.8 was nm, Au: Pd: 13.7 4.8 nm, nm; at laser irradiation mostly Within 2 h after laser fragmentation the av M M ≈ 6nm (Ti) − 4 − 4 10 10 av as ablated; × × at continued (Au in (Ag) av av av av SDS); 1.7 nm (0.05 M SDS) SDS); 1.7 nm (0.05 M SDS) 3530 nm 63 nm irradiation, then size rises again) < 80 nm (Au), 60 nm (Ag), 35 nm 3.4 nm (9 3.4 nm (9 12 nm ethanol), 20 nm ≈ 4 nm (AuPd), (AgPd), metal ratio dependent 2 2 2 2 -Nd:YAG, -Nd:YAG, µ m, 1–4 J/cm dYG 532Nd:YAG, nm, 10 Hz, 0.32–1.2 J/cm 2 ω 532 nm, 10 Hz, up to 1 J/cm Cu-vapour, 510.5 nm, 20 ns, 15 kHz, spot 50 355Nd:YAG, and 532 nm, 10 Hz, up to 130 mJ 2 ω 532 nm, 5 ns, 10 Hz, 0.2–1 J/cm dYG 532Nd:YAG, nm, 5 ns, 10 Hz, 0.245 J, beam diameter 7.5 mm,up to 55 min Lasers or other Particles size, achieved light sources or after treatment N SDS (up SDS (up + + -heptane to 0.05 M) to 0.05 M) isobutanol (for Ti) chloroform, n used at particle synthesis, stirred Liquids Ag), ethanol, Aqueous solution ) Water (for Au and Water Water Water Water, ethanol, Continued ( av av Pd and Pd colloid targets) 8nm in SDS soln. 8nm in SDS solution. mixtures Targets Au,Ag,Ti (scanned Au particles Au particles Ag Au,Ag Ag Au Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 233 ) ( Continued [714] [756] Bae (2002) [701] [495] Mafuné (2003) [758] Mafuné (2003) [699] Mafuné (2003) [757] Tsuji (2003) Tsuji (2002) Tsuji (2003) 400 nm > 600 days ≈ M; at higher Pt colloid 400 nm max − 5 µ m; wires had ; stable colloids λ 2 formation = 10 400 nm formation was × ≈ particles, in case of max λ max λ nanowire nanowebs (length up to 500 nm) form ); as result of Au ); at irradiation with 532 nm, 2 2 (1 p.) of the work by Tsuji et al. Tsuji (2003) [713] nanonetworks , 2 review Colloids prepared by shorter wavelengthsmaller, obviously were due to fragmentationinduced of by particles self-absorption; Particle fragmentation and was observed; length of wires up to 1 irregular shape; formation of wirespossible was due obviously to absence of foreign substances in water Particle generation threshold 1 J/cm SDS concentration the particlesnanoparticles were fragmented; are size reduced inSDS a solution more under concentrated irradiationwhereas of nanonetworks a are less formed intense inconcentrated laser, a SDS less solution undermore irradiation intense of laser a Particles were prepared by 1064pure nm water laser (2.5 ablation J/cm in at SDS concentration less than 4 Using fs-laser mostly non-spherical ns-laser spherical; formationmuch efficiency lower than using in fs-laser case of ns-laser; 4.3 J/cm Particles were prepared by 1064pure nm water laser (2.4 ablation J/cm in (particles grow slowly); greatest abundanceSDS at and 0.01 colloid M stabilityparticles is due to charging of the in SDS solution, in pure water the half-life observed: Pt particles were soldered together by mixture laser irradiation 5 mM NaCl provides highestproduction; efficiency NaCl of additive reduces particles thecolloids; stability postirradiation of by 355 nmlight unfocused reduced the particle size; A short Au joints , 2 355 nm) 0.01 M (1064 nm, (5 J/cm → (water), 3 nm 12 nm + SDS) av av av → − 4 1064 10 = × SDS) 41 nm mean (fs-laser), 27 nm mean (ns-laser) 29 nm ( λ ≈ 2nm 6.2 nm av (water 3 26.4 nm 5 mM NaCl) , , 2 2 2 2 2 2 2 -Nd:YAG, -Nd:YAG, 2 ω 532 nm, 10 Hz, spot 0.023 mm Nd:YAG, 1064 nm, 5 ns, 10 Hz, spot 1 mm, 6.4 J/cm 532, 255 nm, 12 mJ, 36 J/cm 532 nm, 10 Hz, spot 0.023 mm 5 kHz, 4 mJ, 10 min 800 nm, 120 fs, 10 Hz, 4 mJ, 30 min OPO, 800 nm, 8 ns, 10 Hz, 4 mJ, 30 min dYG 1064, Nd:YAG, 532 nm, 10 Hz, up to 3 J/cm 2.2 J/cm up to 5 J/cm Nd:YAG, 355 nm, 7 ns Ti:sapphire, SDS, SDS + + NaCl, up + SOS, or SDBS, stirred to 30 mM Stirred waterStirred water 1064, Nd:YAG, 2 ω Stirred water 355 Nd:YAG, nm, (0.1 M) Water, water Water Water Water, water av ) and av av ) Pt particles (6 nm 20.7 nm 10–100 nm Pt Ag Ag Au (20 nm Au particles, Ag Ag colloids, Ch05-I044498.tex 11/9/2007 18: 50 Page 234 ences Simakin (2003) [765], (2004) [766], Izgaliev (2004) [767] Bozon-Verduraz (2003) [673], Simakin (2003) [765], (2004) [766] Mortier (2003) [759] Compagnini (2003) [760], (2004) [761] Kabashin (2003) [496], (2004) [764] Kabashin (2003) [762, 763] ) 2 and of opti- alloyed ≈ 30 days; disk shaped theory elongated particles h); 2 ≈ 4 nm; particles 3 continued to grow 5 carbon atoms in the > 5 J/cm -CD solution → β particle/(cm 12 two Gaussian distributions , pointing to –0.5 M) no particles were formed 790 (10 − 4 → 640 565 nm (in pure chloroform); in CTAB 20 nm; stability time of Au particles = = = ovel features, observed phenomena, comments Refer max max av alkane chain); at fluences Hybrid Au-Ag particles were convertedparticles; to PVP 0.1 g/l enhancesbut the 0.5 alloying g/l rate, inhibits itSimakin (the (2004) experimental [766] conditions and in somewhat Izgaliev different) (2004) [767] were cal absorption spectrum evolution2003 presented publications) (only in in acetone and ethanol somewhat smaller andparticles spherical were achieved; PVP additionreduced to the ethanol average size downgeneration to rate 10 but different gold complexes; obviouslyafter immediately ablation gold ions are formed of the colloid Au particlesd changed to disk-shaped solutions (10 were formed with aspect ratioscarbon 4.2–6.5 atoms (at in 10–5 alkane chain) λ Particle formation threshold inthan water 5 in times vacuum; size larger distributiondecomposed function into may be two different mechanisms In water:as fabricatedAg particles were λ Colloids fabricated in pure water and started to precipitateand in stable some (at days; most least small 45at days) ablation colloids in were 10 mM achieved Au particles elongated;at further irradiation (35 J/cm ) 2 ), rises av 2 (10 mM av (in -hexane, (Ag in water) (1000 J/cm av (60 J/cm ≈ 10 nm ( n ) av maximum 2 av -CD) to 125 formed, av 8nm 1 J/cm 4nm 60 nm abundance ≈ 30 nm pure chloroform, by dynamic light scattering) 2.1–2.3 nm β Au-Ag-alloy particles 2 µ m 2 2 2 -Nd:YAG, Cu-vapour, 510.6 nm, 20 ns, 15 kHz, 30–50 spot, 9–9.4 J/cm Lasers or other 50Nd:YAG, Hz, Particles size, achieved 5–15 mJ, 10 min 2 ω 532 nm, 5 ns, 10 Hz, up to 200 J/cm 800 nm, 110 fs, 1 kHz, 0.8 mJ 800 nm, 110 fs, 1 kHz, 60–1000 J/cm Cu-vapour, 510.6 nm, 20 ns, 15 kHz, up to 35 J/cm light sources or after treatment N Ti:sapphire, Ti:sapphire, + + PVP + -CD) γ , β 0.1 g/l Chloroform, chloroform CTAB (up to 0.5 M) Linear alkanes having 5–10 carbon atoms cyclodextrines ( α , 0.1–10 mM vessel (also with PVP additive), acetone, moving cuvette 1 mm/s ethanol Liquids Water, water Water in a rotating Water, ethanol Water, ethanol, ) Continued ( Targets Mixture of Au and Au Au Au Au Ag,Au Ag colloids Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 235 ) ( Continued Pfleger (2003) [768] Jin (2003) [709] Chen (2003) [769] [672] Inasawa (2003) [696] Callegari (2003) [770] Tsuji (2004) ), 2 of laser ;by size was theory µ s (18 J/cm ) contributes to of Ag may be a reason for bimodal size distribution of laser ablation process; in first ; laser irradiation of chemically av ) ); a semi-quantitative 2 10 km/s observed; bubble growth 2 having jet and size particles, dependent of light photodissolution in range 30–120 nm by the wavelengths nanoprisms µ s (36 J/cm 300 particle size reduction into dual-beam irradiation by two differentbeams, unimode wavelength growth was achieved: the controlled ratio, first wavelength corresponding toplasmon dipole resonance and the secondquadrupole to plasmon resonance; obviously exciting quadrupole plasmon mode inhibitsgrowth the bimodal Spherical particles formed; 1064 nmthan is 532 nm more efficient for particleparticles generation; was coercitivity 230 of Oe, muchobviously due more to that antiferromagnetic of cobalt bulk oxide cobalt, core av , fluence dependent), size ofones chemically was prepared 36.1 nm prepared particles reduced their size(260–75 mJ/cm to 7.5–13.3 nm µ s a vertical velocity 400 m/s; bubble lifetime 200 size reduction presented (Eqs (5.9)–(5.13)) 532 nm the average diameter2 was reduced times; about air ( dissolvedreduction of atmospheric particle gases size, bothat at fragmentation; generation irradiation and of chemicalparticles prepcipitate by 532 nm reduced theirto average size 15 nm; from 45 Due to irradiation thevarious spherical shape particles grew into wavelength (various filters were used):octaheders, cubes, tetraheders, prisms; all prisms hadthickness the same 7 nm At irradiation spherical particles transformed After fragmentation first by 1064 nm and thereafter by The size of photoreduced particles was 8.3–17.7 nm Time-resolved imaging av av (air, av av maximum abundances at 70 and 150 nm, thickness 9.8 nm (constant) 30 nm 1064 nm), 49 nm (Ar, 1064 nm), 6 nm in chloroform ≈ 80 nm 17 nm Triangular nanoprisms, Various shapes, size 2 2 < 0.2W, Xe-lamp, 150W, 550 nm pass filtered, beam power 50 h dYG 532Nd:YAG, and 1064 ns, 6 ns, 10 Hz XeCl, 308 nm, up to 260 mJ/cm Fluorescent tube, 20W, 350–700 nm, 1h Nd:YAG, 1064 nm, 10 ns, 18 and 36 J/cm dYG 532 Nd:YAG, and 1064 nm, 7 ns, 10 Hz, up to 60 min Solutions where the particles were prepared Stirred water under air or Ar, chloroform Solutions where the particles were prepared the particles were prepared vessel Water in a rotating av prepared hydrosol photo- and chemically reduced 4.8 nm Co Ag foil, chemical Au particles, Ag particles, Ag particles Solutions where Ag,Au, Si Water Ch05-I044498.tex 11/9/2007 18: 50 Page 236 ences Ganeev (2004) [774], (2005) [775] Karavanskii (2004) [773] Mafuné (2004) [691] Kazakevich (2004) [772] Shafeev (2004) [771] esu; − 8 formed, 8.7 mM (rods, 10 = × /W,nonlinear oxide shells , |≈ 5 2 cm/W (at was observed at (3) cm − 9 | χ various shaped 10 − 13 formed × 10 generation av × 3 25 ns; nonlinear optical − 1 . 5 of colloid solution estimated i t (405 nm) ≈ 1.5 nm particles were formed with CuZn core; at ovel features, observed phenomena, comments Refer nonlinear refractive index 397.5 nm, 1.2 ps) absorption of aqueous colloidsnonlinear changes optical in transmission 48 h to ensuring the stability ofoptical colloid properties solution; nonlinear of achieved colloidswavelength 532 studied nm, at absorption coefficient at surfactant concentration greaterparticles than of CMC, size for SDS and 0.5 mM for SHS) nano- networks In water no particles afterthe laser colloids ablation in were acetone found; resonance and peak ethanol at have Cu 580 nm, plasma surrounded in by acetone glassy carbon Cu were particles achieved;irradiation of CuZn in water yieldedCuZn particles also containing metal besides oxides andcore-shell hydroxides, in ethanol further irradiation of CuZn particles Zn was removed spheres, elliptical, etc.), after sedimentation formonths mostly 0.5 spherical particles remained in solution; third-order susceptibility form Z-scan measurements was ablation of Ag due toparticles; light obviously Ag interaction particles with Ag causeof the SH, and generation SH performs thedue fragmentation to of SPR particles Second harmonic Achieved Ag particles obviously had At low surfactant concentrations ( < CMC As fabricated particles were of (0.1 M av ≈ 1.5 nm SDS) 5–10 nm (Cu in ethanol), 20–60 nm (CuZn in ethanol) 4–400 nm (as fabricated in EG), 5–10 nm (after 0.5 month) 9–16 nm max (Au), 4.6–6.4 nm max (Ag) , µ m, 2 , 2 2 2 2 2 -Nd:YAG, dYG 355Nd:YAG, nm, spot 0.03 cm ≈ 3.3 J/cm Lasers or other Particles size, achieved Nd:YAG, 1.06 130 ns, 1–5 Hz, 200 J/cm up to 30 min 810 nm, 120 fs, 1 kHz, 0.5 mJ, spot 0.1 mm 510.6 nm, 20 ns, 15 kHz, up to 34 J/cm 2 ω 532 nm, 9 ns, 10 Hz, 20 J/cm Cu-vapour, 511 nm, 20 ns, 7.5 kHz, ≈ 30 J/cm light sources or after treatment N Ti:sapphire, SDS or SHS, + stirred, 278 K ethanol, also with PVP additive (0.1 g/l) Stirred ethylene glycol (EG), water, or ethanol (95%), acetone, diethylene glycole Liquids Water Water and Water, ethanol Cu-vapour, Water, ethanol ) av Continued ( Pt particles,6 nm Targets Cu, CuZn (60–40%) Au,Ag Ag Ag Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 237 ) ( Continued [686] [780] Compagnini (2004) [776] Pyatenko (2004) [685] Chen (2004) [778] Chen (2004) [777] [779] Tsuji (2005) Tsuji (2005) Tsuji (2005) , 2 ); at 2 wires and refractive of the max were observed, dielectric constant λ , laser irradiation of 2 540 nm (pure and Co, while CoO particles = 4 , larger particles were achieved 2 O max 3 > 150 mJ/cm λ nanoparticles were produced wires and sheets , probably due to the 4 410–420 nm (Ag colloids) O 507 nm ( + 0.01 M DDT) (1 J/cm 3 = nanoprisms and nanorods → max λ 1.3478; dielectric constant decreases with ; -decane) Spherical nanoparticles achieved, n particles fragmentation and formationcrystalline of cf. Jin 2003 [709] In water, Co formation of Ag fusion of particles; at lower fluences, 50–100 mJ/cm Using decane with DDTsingle additive, mostly crystalline spherical and stablecolloids over several achieved; weeks from all materials; in hexane,produced Co from nanoparticles Co were laser fluence 30 J/cm Laser light spot sizestudied; influence small in spot range sizes 0.6–1.3 mm providemonths stable colloids over Spherical particles achieved; 532 nmfor is particles more production effective than 1064also nm; CoO besides phase Co, found(less by XRD; than coercivity of 100 bulk Oe Co);formed, is obviously ethanol due less to particlesgeneration lower were threshold of bubbles colloidal solution absorption 405 nm;by measured Kretschmann type SPR sensor of the colloidal solutionindex was 1.8167 and increasing Ag nanoparticle concentration (approximate formula given) were dominantly produced from CoO Spherical Ag particles were producedlaser by ablation 1064 of nm Ag plate;colloids additional (355 irradiation nm, 4–12 of mJ/pulse, 10 min)particles reduced size and causedsheets formation of Ag At higher fluences Ag colloid caused the particles fragmentation and ), 2 av (in decane (water, av (at spot size (after (after in pure decane, av av av av 2 av av 5nm 5nm 1 J/cm 0.7 mm) 4.2 nm 18.7 nm 532 nm), 11.8 nm (ethanol, 532 nm) Down to 2 with DDT,1 J/cm 30 nm ablation), down to 14 nm additional irradiation 12 mJ/p) , 2 2 , 5 min , 10 min 2 2 2 -Nd:YAG, -Nd:YAG, -Nd:YAG, Nd:YAG, 1064 nm, 350 mJ 10 min 3 ω 355 nm, 10 Hz, 30 mJ, 60 min 2 ω 532 nm, 10 ns, 10 Hz, up to 340 mJ/cm 532Nd:YAG, nm, 5 ns, 10 Hz, up to 30 J/cm Nd:YAG, 1064 nm, 10 ns, 10 Hz, 38 J/cm 3 ω 355 nm, non-focused, 50–150 mJ/cm dYG 532 Nd:YAG, and 1064 nm, 7 ns, 10 Hz, up to 30 J/cm SDS + (70 mM) hexane, stirred pentane to decane, pure and with DDT additive (up to tens of mM) (rotating vessel) Alkanes from Water and Water Water Water Water, ethanol, powder 4 O 3 suspensions av ,prepared by laser ablation Co Co, CoO, and Co Ag, rotating Water Au Ag Ag Ag colloid, 20 nm Ch05-I044498.tex 11/9/2007 18: 50 Page 238 References (2005) [784] Sylvestre (2005) [700] Kil (2005) [781] (2005) [783] Burakov (2005) [782] (2006) [785] Tarasenko Tarasenko Tarasenko , 2 level, 523–530 nm agglomerates = sound max λ µ s; postirradiation caused both ) were formed at nanodisc 2 µ s) laser pulses, av ); the crystallographic 2 contained 10% more Zr than correspondingly; size reduction of and formation of right-angled 2 ; at high fluences obviously plasma ≈ 0.4 mm above the target surface, probably agglomerates observed; optical absorption ZrVFe powder observed, 1400–1500 nm in size, consisting of fragmentation particle size distribution function; self-focusing emission intensity and removed mass were largest nanowire ovel features, observed phenomena, comments to spectra for all achieved colloids presented and discussed Single or two shifted ingreatest Ag time particles (1–30 production efficiencyand (2–3 smallest times) particles sizeof at Ag shift colloids 5–10 by 532 nm, 0.35 J/cm Studies of postirradiation of532, achieved 400, colloids and by 800 266, nm laser0.5, 0.1, light and for 0.6 J/cm 5 min at fluences 0.1, single particles and transformation of structure of generated particlesthe was starting the same material that of Particles aggregates small Ag particles fragmentation and growth ofstable particles; Ag some colloid days, in in acetonecolloids water at only least optical several extinction months; spectra for presented Cu the target; smallest particles (71highest nm laser fluence (20.3 J/cm heats/melts the target andejects subsequent molten bubble material collapse from the surface; Bimodal plasma at focal point due to both particles fragmentation andchainswas growth/ observed formation At subsequent irradiation with 532 nm light, 0.3 J/cm Achieved av av ) 2 av , (Ag, ≈ 7nm ≈ 10 nm (532 nm, ), av 2 av 50 nm formed > (two shifted pulses) (266 nm, 16 J/cm 71–110 nm log-normal distribution ≈ 20 nm acetone, single pulse 1064 nm), 15–50 nm as prepared by 1064 nm, by 532 nm agglomerates of disc-like particles d 20 nm (main peak), 60 nm (second peak); focal point on surface 15 nm 95 J/cm 2 2 ), 2 , 2 µ m, 2 2 ) and 2 2 at waist 2 532 nm (10–250 J/cm 0.5–5 GW/cm 10 ns, 10 Hz 800 nm, 120 fs, 1 kHz, spot 6 880 J/cm Lasers or other Particles size, achieved up to 0.1 J/cm and 1064 nm, 10 Hz, 50 mJ, up to 5 J/cm 266 Nd:YAG, and 532 nm, 15 ns, 10 Hz, up to 0.5 J/cm 532 Nd:YAG, and 1064 nm, 10 Hz, 50 mJ, 0.5–5 GW/cm 266Nd:YAG, nm (5–40 J/cm dYG 532Nd:YAG, nm, 8 ns, 10 Hz, 100–300 mJ, up to 20.3 J/cm light sources or after treatment N Ti:sapphire, Ti:sapphire,400 nm, ) vessel Solution where the particles were fabricated, including gelatine as surfactant Ethanol Acetone Water, rotating Water, acetone 532 Nd:YAG, Water , 7 . 2 Continued ( Fe 35 . 8 V 57 Targets Liquids 10–30 nm Zr sintered, rotating 12/min Au Ag, Cu Ag colloids Ag Au Table 5.4 Ch05-I044498.tex 11/9/2007 18: 50 Page 239 [786] Shafeev (2006) [716] Bugayev (2006) [419] Tsuji (2006) ; µ J, µ J µ J, 300 Hz, photo-reduction ofAg particles diameter of prismatic, rod a.o. shape of photo-oxidation ; (iii) Nd:YAG: 90 ps, 40 mJ, Hg-enriched (52%) Hg, the 2 196 -ions and following − Ag crystals W/cm ; (iv) Nd:YAG: 350 ps, 350 12 2 10 ; (ii) Ti:sapphire: 120 fs, 1 kHz, 900 2 × transmutation of Hg into, Au obviously due to ; W/cm laser light or by fluorescent lamp light in 0.2 mM 2 2 13 W/cm 8 W/cm 10 Hg (0.15%). In case of 10 × of silver ions, although Agat crystals irradiation were found of also colloids in pure water (at 810 nm), 2 196 conversion amounts to 13% (350pulses, ps 4 h) Nd:YAG-laser the generation of thermalwas neutrons observed; during using laser Hg exposure ofthe natural conversion isotopic of composition, Hg into Au is close to the content of their growth was explained by with twin planes by Cl NaCl solution yielded 10 Hz, 10 10 Irradiation of achieved colloid by50 mJ/cm 355 and 532 nm, 6 ns, ∼ 60 nm was observed duringof laser the shock material peening Laser beam parameters: (i) CVL: 20–30 ns, 10 kHz, 100 2 BrN 42 Au trans- H → 19 bromide), C 10–100 nm, spherical (as ablated in water) ∼ 60 nm, spherical Spherical nanoparticles formation with 10 nm, Hg mutation observed , , 2 2 µ m, µ m, Na) 3 SO Nd:YAG 1064 nm, 10 Hz, 36 J/cm 10 min scanned beam Cu-vapour, 510 and 578 nm 405 nm 1.06 Nd:YAG, 90 ps 1.06 Nd:YAG, 350 ps dYG 12Nd:YAG, ns, 4 Hz, 0.8 J, spot 1 mm, 100 J/cm 4 Ti:sapphire, 810 or ) 4 H 6 C Na) Na) 3 , 25 3 NaSO 2 H SH] 33 C) SO 12 11 ◦ H OSO ) 17 2 16 25 H 8 H NaCl, − 10 12 (CH + 3 O(RTor 2 KCl, and MgCl 0.2 mM water D frozen, Water, Water -octyl sulfonate (C n -bipyridine -dodecylbenzene sulfonate (C  n Inconel 600, 316L Hg suspensions (dispersed ultrasonically) Ag Rh6G – Rhodamine 6G CMC – critical micelleLIF concentration – laser-induced fluorescence CVL – copper vapour laser SDS – sodium dodecyl sulfate (C SDBS – SHS – sodium hexadecyl sulphate (C SOS – sodium CD – cyclodextrines bpy – 2,2 PVP – polyvinylpyrrolidone DT,DDT – dodecanethiol [CH tppz – 2,3,5,6-tetrakis(2’-pyridyl)pyrazine SOG – spin on glass PMMA – polymethylmetacrylate PS – polystyrene CTAB – cetyltrimethylammonium bromide (hexadecyltrimethylammonium Abbreviations: TNA – thionicotinamide Ch05-I044498.tex 11/9/2007 18: 50 Page 240

240 Handbook of Liquids–Assisted Laser Processing

5.5 Inorganic Compound Particles

Inorganic nanoparticles (Fig. 5.21) are efficient in catalysis and sensors due to their large surface/bulk ratio (TiO2, SnO2). They may be useful also as luminophores (Eu2O3), semiconducting quantum dots (ZnSe, CdSe) and hard, high-temperature conductivity materials (BN). Table 5.7 gives an overview of the related experimental research up to the end of 2006. Laser ablation of zinc and some selenide and oxide materials in water has resulted in growth of differently shaped nanostructures in the ablation zone (Figs 5.22–5.25).There is a strong evidence that the process proceeds through formation of a water solution of the starting or intermediate (ZnO) materials. High temperatures generated by laser are known to enhance the dissolution of many solids in water (Table 7.4). The growth is most intense at the bottom of an ablation groove, obviously because both temperature and solute concentration remain high there for a sufficient time. The growth obviously occurs after the laser pulse, else the fragile structures would be broken by laser- induced shock and flow. At ablation of same or similar materials in air,no growth of such structures has been observed. In comparison with hydrothermal growth under static conditions (Table 5.5) the laser-induced growth is faster by many orders of magnitude.

5.5.1 Hydrothermal growth It is probable that the growth of nanorods and nanoplatelets in laser ablation zone in water occurs via an hydrothermal route:the solid starting material dissolves in laser-heated water and the solute crystallizes thereafter

200 nm

Figure 5.21 The TEM morphologies of the prepared by laser ablation c-BN nanocrystals with diameters of 30–80 nm [787]. Target: h-BN, ambient: acetone; laser: 532 nm, 10 ns. © Elsevier.

1 µm

Figure 5.22 ZnO columnar single crystals, 500–600 nm long and 200 nm wide, formed by pulsed laser ablation of Zn in deionized water at 80◦C [788]. © Elsevier. Ch05-I044498.tex 11/9/2007 18: 50 Page 241

Generation and modification of particles 241

Figure 5.23 SEM image of the ablation crater and ZnSe nanowires. Liquid: water; laser: 800 nm, 150 fs, 220 µJ, 2000 pulses (courtesy by Tianqing Jia, The Institute for Solid State Physics, The University of Tokyo, Japan; and State Key Laboratory of Optoelectronic Materials and Technologies, Zhongshan University, China. Read more in the article by Jia et al. [518].

2 µm

(a)

Zinc hydroxide layers DS molecules layers 26.52 Å 38.8 Å 34.5°

(b)

Figure 5.24 TEM image and SAED pattern (a) of organic/inorganic nanocomposite produced by laser ablation of Zn target in 0.01 M SDS solution at 100 mJ/pulse [789]. The drawing (b) shows the schematic structure of model of the nanocomposite. Laser: 355 nm, 5–7 ns. SAED – selected area electron diffraction; SDS – sodium dodecyl sulphate (C12H25OSO3Na). © The Laser Society of Japan, reproduced with permission from Ref. [789].

Figure 5.25 PZT platelets grown at laser ablation of PZT ceramics (Pz 26, Ferroperm A/S) under water [790]. Laser: Nd:YAG, 1.064 µm, 180 ns, 1000 Hz; spot diameter about 50 µm, fluence 59 J/cm2 (0.6 GW/cm2) scanning speed 0.16 mm/s, number of passes – 4. Ch05-I044498.tex 11/9/2007 18: 50 Page 242

242 Handbook of Liquids–Assisted Laser Processing

Table 5.5 Hydrothermally fabricated single crystalline platelets (conventional hydrothermal processes).

Material Reaction time Size of synthesized Reactants and temperature platelets Reference

◦ PbTiO3 H2O,TiO2, KOH 200 C; 15 h ≈10 µm Peterson (1999) [792] Pb(CH3COO)2 · 3H2O ◦ PbTiO3 H2O,TiO2, KOH (or NaOH, 150 C; 24 h ≈0.3 µm Chien (1999) [791] or RbOH), Pb(NO3)2 ◦ SnS H2O, SnCl2 · H2O, Na 2S, 200 C; 48 h ≈7 µm Zhu (2005) [796] thioglyeolic acid

Table 5.6 Examples of materials synthesized or grown by hydrothermal techniques [797]. Material class Examples Growth rate

Single oxides SiO2,TiO2, ZrO2, HfO2,Cu2O, BeO, Bi2O3,Al2O3, 2.5 mm per day (SiO2) ZnO, Fe2O3

Perovskite type mixed oxides A(Ti, Zr)O3, where A = Ca, Sr, Ba, Pb, Bi

Carbonates CaCO3, MnCO3, FeCO3, CdCO3, NiCO3, 0.2 mm per day (CaCO3)

Phosphates AlPO4 (berlinite), GaPO4 0.5 mm per day (AlPO4)

Hydroxyapatites A10(BO4)6X2, where A = Ca, Sr, Ba, Fe, Pb, Cd and = 3− 3− 3− 3− 2− BO4 PO4 ,VO4 , SiO4 ,AsO4 ,CO3 ; = − − − 2− X OH ,Cl ,F ,CO3 Silicates, zeolites, germanates, fluorides, sulphides, tungstates, molybdates, titanates, tantalates, neobates, selenides, aluminates, antimonites and antimonates, ferrites

Piezoelectric materials Li2B4O7, Pb(Zr,Ti)O3

Laser hosts YVO4, GdVO4 + 4+ 5+ Nonlinear optical crystals KTiOPO4 (KTP), LiB3O5,{K } [Ti ]O [P ]O4 1.8 mm per week (KTP)

Superconductors YBa2Cu3O7−δ,Bi2Sr2CaCu2O8+δ,

Superionic conductors Li4B7O12Cl, LiH2B5O9

into regular-shaped structures. This hypothesis is supported by the fact that, for example, platelet growth has often been observed at solution synthesis of similar materials under static conditions: in hydrothermal synthesis of PbTiO3 [791, 792], in chemical coprecipitation synthesis of Bi4Ti3O12 [793], and also in molten salt synthesis of Bi4Ti3O12 [794]. Growth of Al2O3 platelets was observed at calcination of boehmite in an HF aqueous solution [795] However, the aspect ratio of platelets (up to 50) has remained smaller by 1–2 orders of magnitude compared to this in laser-assisted process (aspect ratios up to 500). Laser-assisted growth is also much faster (∼10 µm/s) than chemical coprecipitation growth (∼10 µm/h) [793] or the hydrothermal growth (∼10 nm/h) [791, 792]. Table 5.5 summarizes the main conditions and results of some hydrothermal synthesis processes of nanoplatelets. Note that the ordinary methods need, as a rule, foreign substances in the solution while laser ablation-induced growth may occur in pure water. Table 5.6 presents further examples of materials, whose growth may accur at laser irradiation of corresponding solids in water. Table 5.7 presents a chronological reference of the research about inorganic compound particles preperation by laser ablation of solids in liquids. Ch05-I044498.tex 11/9/2007 18: 50 Page 243 ) ( Continued Sugiyama (2002) [801] [802] Liu (2001) [800] References Dolgaev (2002) [753], Simakin (2003) [765], (2004) [766] Zhang (2002) [803] [765] Dawson (2001) [711] Anikin (2002) Wang (1998) [798] Yang (2000) [799], 2 + to Eu 3 + formed and at ablation ≈ 10 nm diameter spherical 1 . 04 phenomena, comments in range 2–1050 nm transformed into particles with a narrow size distribution; the size 10 nm approximately corresponds to both the surface energy/cohesion energy and cooling/collisions balance Crystalline nanoparticles were achieved in all liquids (wasproved in not case of DMSO) carbon spherules of size 70–2800boron nm, grains and carbon fibres in dichloroethane also TiC formed observed Most part of achieved powdersheet- was and sphere-shape graphite particles volume grows 6–8 times Novel features, observed At laser irradiation the particles Achieved: encapsulated in boron At ablation of Ti in water also TiO av (Yang (CdS) Well-crystalline particles achieved Simakin (2003) av av av av ≈ 10 nm 50 nm (2000) [799]) 25 and 150 nm (maxima) 35 nm up to 100 nm Due to laser irradiation fusion the < 5 nm Reduction of Eu , 4 , N 4 3 N 4 3 -C β N x , 3 4 multicore N , spherical 3 2 2 ZnSe, CdSe 10–20 nm cubic-C Particles particles CdS, ZnSe 40 nm graphite-C α -C composite Non-crystalline europium oxide achieved Size Au-shell TiC,TiO TiO TiO , 2 W/cm 2 2 10 by laser ablation of solids in liquids. µ m N:A,532-Nd:YAG, nm, N:A,532-Nd:YAG, nm, µ m, 4 J/cm µ m, 4 J/cm Cu-vapour, 510.6 nm, 20 ns, 15 kHz, spot 50 dYG 1064Nd:YAG, nm, 10–15 ns, 1 Hz, 0.5–1 J up to 45 min 2 ω 8 ns, 10 Hz Cu-vapour, 510.6 nm, 20 ns, 10 kHz, spot 20–80 Cu-vapour, 510.5 nm, 20 ns, 15 kHz, spot 50 dYG 532Nd:YAG, nm, 18 ps, 10 Hz, 2–3 mJ, 5 min XeCl, 308 nm, 15 ns, 5 Hz, unfocused beam 2 ω 10 ns, 5 Hz, 10 Lasers 2 under N atmosphere isobutanol, diethylene glycole, ethanol, DMSO Dichloroethane water, ethanol used for particles preparation, flowed solution used for particles preparation, stirred 1–2 mm layer Anhydrous ethanol, Aqueous solution Ammonia solution, Water, acetone, Water or aqueous Inorganic compound particles prepared C Ethanol 4 . 3 2 particles, particles, 2 2 O 2 Poly-B SC Ni-doped ZnSe, CdS Eu CdS, ZnSe Acetone 10–40 nm 2 nm and 170–1050 nm TargetsGraphite, polycrystalline Liquids Au-capped TiO TiO Ti Table 5.7 Ch05-I044498.tex 11/9/2007 18: 50 Page 244 References Ganeev (2003) [804] Liang (2003) [807] Ganeev (2003) [805] Liu (2003) [808] Ganeev (2003) [806] [787] Wang (2003) ) − 3 ≈ 1000 times /W,nonlinear 2 20 m Ni 80 − 18 10 × formed with diameters − 7 . 5 with oxygen vacancies near the 2 − x -scan at 1064 nm, 25 ns, 10 Hz, Stable within 1 month, thereafter sedimentation of small crystalsobserved; was nonlinearity parameters of colloid given for ns- and ps-pulses Fabricated in 10 mM SDSstable colloid more was than 1 week;were the obviously particles non-stoichiometric SnO Single crystalline Ag surface nanorods typically 30–50 nm and lengths 300–500 nm absorption coefficient 1 cm/GW (by Z volume part of nanoparticles 10 Nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of colloid solutions determined by Z-scan technique; the nonlinear refractive index of CdS colloidgreater was than that of bulk material solution discussion of c-BN formation mechanism Novel features, observed av av ), 3 S 2 Size phenomena, comments 2.5–6 nm (CdS) 10 nm < 10 nm Nonlinear refractive index of colloid 2–3 nm 30–80 nm XRD and FTIR spectra presented; 4–12 nm (As ) nanorods − 5 20 10 , CdS (volume 2 − x Ni 3 3 3 × S S S 80 2 2 2 part of particles 3–5 Particles c-BN achieved As As As Ag 2 µ m W/cm W 10 10 N:A,532-Nd:YAG, nm SnO N:A,532-Nd:YAG, nm, N:A,532-Nd:YAG, nm, dYG 1064Nd:YAG, nm, 20 ns, 10 Hz, 15 mJ, focused beam, 15 min Nd:YAG, 1064 nm, 25 ns, 12.5 Hz, spot 100 2 ω dYG 1064Nd:YAG, nm, 25 ns, 2Hz 2 ω 10 ns, 5 kHz, 10 2 ω 10 ns, 5 Hz, 10 Lasers SDS + saturated 3 ) (1 and 10 mM) aqueous solution, 1–2 mm layer Acetone AgNO Water Water, water Continued ( glass Water , CdS Water 3 3 3 S S S 2 2 2 Targets Liquids h-BN, rotating Sn Ni As As As Table 5.7 Ch05-I044498.tex 11/9/2007 18: 50 Page 245 ) ( Continued Liang (2004) [813] Liang (2004) [810] Iwabuchi (2004) [492] Liu (2004) [809] [814] Sasaki (2004) [811], Liang (2004) [812] Tsuji (2004) 3 filament multilayer wormhole- , morphologies gel was 2 O, the filament 2 spindle-like in SDS solution; 3 and not spherical 2 C 2 ◦ consisting of Ag particles formed at 10 mM + 1.3 H µ m 3 2 > 1 week, in pure water and ≈ 1 particles were formed (less in plumes were grown at 4 3 ( ≈ 30 nm thick) achieved; at O O 3 2 Co particles of well-crystalline anataseTiO were formed nanostructures exhibiting tube-, rod-, or platelet-like Nanodendrites nanoparticles (50 nm av) and achieved; Mg(OH) diameter 1 mM SDS unstable amorphous particles were formed, but transformed to anatase and grew in size (8annealing nm at av) 500 after 3 h SDS, stable solid–liquid interface organic liquids); formation mechanisms discussed achieved, diameter 1–5 nm Spherical LiCoO In 4 weeks after fabrication In pure water, Mg(OH) deposits were found on thebottom, composed vessel’s of both rutileanatase TiO and SDS concentration near themicelle critical concentration (8.6 mM); only at 10 mM SDS fabricatedstable particles over 1 were week; atin ablation pure of water Zn ZnOH/SDS plates ablation of Pt/TiO Ag AnataseTiO Well-crystalline particles achieved when ), 2 ) 4 av , :6nm : 2 nm, O 2 3 3 10 nm, < spherical Features size down to some nm 10–200 nm (LiCoO 3nm elongated and spherical SnO (in both pure water and SDS solution) < 10 nm (Co TiO 2 , 4 2 O , 3 3 3 3 ,Co O 2 2 2 cassiterite SnO spherical Brucite Mg(OH) and Ag nanoplumes (0.01 M SDS) LiCoO Anatase TiO Ag nanodendrites Anatase TiO TiO , 2 2 W/cm µ m, 7 2 N:A,355-Nd:YAG, nm, 355-Nd:YAG, nm, N:A,532-Nd:YAG, nm, N:A,266-Nd:YAG, nm, 355-Nd:YAG, nm, dYG 1064Nd:YAG, (130 ns) and 355 nm (10 ns), 1–10 Hz, 200 J/cm 3 ω 7–8 ns, 10 Hz, spot 1 mm, 60 min 3 ω 10 Hz, spot 1 mm,maximum 150 mJ > 120 min 2 ω 10 ns, 3 Hz, 10 4 ω 10 Hz, spot 40 100 J/cm 3 ω 6 ns, 10 Hz, focused, 30 mJ, 60 min 3 SDS SDS + + SDS + (1–10 mM), (1–50 mM), stirred (1–100 mM), aqueous solution Saturated AgNO cyclohexane Water Water Water, water Water, water Water, methanol, µ m 2 2 3 ) suspension (rutile, SC) Ni Mg LiCoO powder (3 av TiO Ti, Sn, Zn, Pt, TiO Ti Ch05-I044498.tex 11/9/2007 18: 50 Page 246 Sasaki (2005) [789] Usui (2005) [816] Usui (2005) [817] References Lalayan (2005) [815] Tsuji (2005) [779] , and /SDS 4 2 > 1 O studies Chen (2005) [818] 3 and Co, 4 ,Co 3 O 3 -Zn(OH) O 2 β quenching of hexagonal crystal provided highest exciton used: CTAB (cationic), 3 particles were prepared (6 pp., 7 figs., 32 refs.) of 3 review phenomena, comments In water spherical ZnOformed; particles in SDS, oxide nanomaterials fabrication at liquids; in gas, Fe luminescence and lowest green luminescence, probably due to the occupation of O defects of theof surface ZnO by the Oof in LDA carboxyl groups multilayer plates symmetry formed with thickness of inorganic layer 4.6 Å; diffuse reflectance and PLboth spectra particles recorded; exhibited UV emission In hexane, Co nanoparticles were produced from Co BaTiO while CoO particles were dominantly produced from CoO Surfactants SDS (anionic), LDA (amphoteric), OGM (non-ionic); LDA at mmol/dm colloid in water unstable (PL degradation in some days), in ethanol more than 1 year;sizes particle calculated from PL spectra Novel features, observed A AIST by laser ablation in gases and in av (CdS), (GaAs), av av µ m for Size In water up to micrometers, mostly < 10 nm, for round particles, ≈ 2 plates 12–33 nm 20–80 nm Melted surface 3nm both in ethanol 2 nm /SDS /SDS 2 2 -Zn β (in water spherical /SDS (cassiterite), 4 (anatase), 2 2 2 O 2 3 -Zn(OH) -Zn(OH) octagonal multilayer plates multilayers Co ZnO, in SDS solution (OH) from all materials), Co and CoO in hexane Particles CeO SnO β multilayer plates particles In SDS solnution β GaAs, CdS achieved 2 , 2 , 2 , 6.7 J/cm 2 N:A,355-Nd:YAG, nm, N:A,355-Nd:YAG, nm, N:A,355-Nd:YAG, nm, 3 ω 10 Hz, 30 mJ, 60 min 60 min 3 ω 5–7 ns, 10 Hz, spot 1.5 mm dYG 5–40Nd:YAG, kJ/cm 3 ω 7 ns, 10 Hz, 6.7 J/cm 355Nd:YAG, nm TiO (total dose?) 60 min dYG 1064Nd:YAG, nm, 33 ps, 30 mJ Lasers , 3 3 3 ) solution of SDS, 10 mmol/dm solutions of surfacts. 0.1–10 mmol/dm solution of SDS, 10 mmol/dm stirred rotating vessel acetone Water and water Water and water Water and hexane, Water Continued ( 4 2 O 3 Zn Zn Co,CoO,and Co powder suspensions Sintered CeO Targets Liquids GaAs, CdS Water, ethanol, Ti, Sn, Zn Water and water Table 5.7 Ch05-I044498.tex 11/9/2007 18: 50 Page 247 ) ( Continued Liang (2005) [819] Ganeev (2005) [820, 821] Ganeev (2005) [822, 775] Liu (2005) [823] -scan Z of particles of c-BN from neutral /W (at 2 particles µ J (0.9 ps cm c-BN 2 theory studies by esu → − 14 − 9 /W (at 532 nm), 10 2 10 × cm × state − 15 − 7 . 5 3 |≈ 2 10 S 2 (3) × to acidic (anatase) were achieved only at 10 mM SDS solution, thewere other mostly amorphous; optical band gap of well crystalline particles 3.34 eV; solutions changed during ablation pulses); third-order susceptibility of GaAs particles at| χ 795 nm and time-varied absorption; for 10-nm particles self-defocusing start-up time 8 ns; opticalonset limiting for particles inglycol ethylene and water 5–8 Optical nonlinearity 1064 nm, 25 ns) on temperature (1000–5000 K) and pressure (4–40 GPa) are presented nucleation at laser irradiationin of liquids BN is presented; calculated dependences of critical radiusnuclei of and probability of phase transition h-BN Narrowest particle size distribution and best stability innonlinear case optical of parameters xylol; were 2–3 orders of magnitudethan greater of bulk materials; nonlinear refractive indexes of solutions: CdS 4 A thermodynamic As Well crystalline TiO av , − 5 av : 4.5 nm 3 10 S 2 × av,volume ratio 4 3nm spheroidal (10 mM SDS) 5–200 nm (in ethylene glycol), up to 10 nm (in silicon oil) CdS: 2 nm As − 4 10 × particles, ≈ 2 3 2 S spherical 2 CdS respectively Cubic BN (c-BN) ≈ and slightly non- stoichiometric GaAs (gallium-rich particles), volume ratio As TiO , 2 , 15 min 2 N:A,355-Nd:YAG, nm, N:A,532-Nd:YAG, nm, Nd:YAG, 1064 nm, 20 ns, 10 Hz, 30 J/cm 3 ω 10 Hz, 150 mJ, 60 min 2 ω 9 ns, 10 Hz, 20 J/cm 15–45 min ethanol solution of SDS, 1–100 mM ethylene glycol, silicon oil, stirred oun,xylol, Toluene, Water and water glass 3 S 2 -BN Water GaAs water Water, ethanol, CdS crystalline, h As Ti Ch05-I044498.tex 11/9/2007 18: 50 Page 248 Zeng (2005) [824] Golightly (2006) [825] Ichikawa (2006) [788] Ryu (2007) [826] - -hexane, 2:1 ( n n 3:1 (water = = were achieved; hydrothermal growth > 40 nm); in phenomena, comments References Below CMC of SDS (8ZnO mM), particles formed;over CMC, core–shell particles SDS depressesinitially the formed oxidation Zncharacterization of particles; results the of colloids by HRTEM,PL,FT-IR,and opti- cal absorptionpresented spectroscopy are in addition, amorphous carbon deposit formed Surfactants inhibited the growth of the crystals, LGA more strongly (LGA: 3.6–180 mM, CTAB: 1.4–140 mM); hypothesis proposed hexane < 50 nm) and Ti:C were incorporated into particles, into smaller particlesextent; to Ti: a impurities greater ratiosfor example were Ti:O Photoluminescence peak of suspension was blue-shifted by about 40–50 nm; opticalof bandgap particles was4.7 eV estimated to be Novel features, observed The elements present in solvents av , av av Size 18–45 nm Rods fabricated in water had diameter 200 nm, length 600–800 nm ≈ 5– 20 nm dependent on solvent and laser fluence 24 nm C ◦ , spheri- 4 C SC hexagonal ◦ ZnO and Zn core– ZnO shell spherical particles rods (Fig. 5.22) spherical, at 60 and 80 Particles ZnO, at 40 containing particles, dependent of the solvent;TiC,TiO, and TiH phases found CaMoO cal, polycrystals achieved Ti, O, C, and H N:A,355-Nd:YAG, nm, N:A,532-Nd:YAG, nm, 266-Nd:YAG, nm, Nd:YAG, 1064 nm, 10 ns, 10 Hz, 70 mJ, spot30 2 min mm, 3 ω 7 ns, 10 Hz, 3.2 J, spot 1 mm, 40 min 2 ω 10 Hz, 20–100 mJ, spot 1 mm, 30–60 min 4 ω 8 ns, 10 Hz, 0.1 J, spot ≈ 1 mm, 120 min Lasers LDA + -hexane n SDS C ◦ + ) (0.1–100 mM) or CTAB; up to 40–80 ethanol, Water Water, water Water Continued ( 4 Targets Liquids Zn Zn CaMoO (ceramics) Ti rod,rotating Water, 2-propanol, Table 5.7 Ch05-I044498.tex 11/9/2007 18: 50 Page 249 Kawaguchi (2007) [828] Jia (2007) [518] Tsuji (2007) [827] C. [816]. ◦ at 25 3 battery electrodes µ m of diameter and of particles occurred only µ m length was observed at mol/dm µ m/s − 4 10 Fusing at 532 nm laser wavelength atdiation irra- at least 10 min;with in the contrast source particles, the fused together particles exhibited a faint ferromagnetic component up to at least 300 K Growth of wurzite ZnSe- nanorods of 50–150 0.5–3 the sides of the ablationgrowth crater; rate the of the nanorods1–3 was composed of achieved particles studied 90% of microparticles were converted to nanoparticles; rate capacity of × ; OGM: 1.1 3 10–100 nm At irradiation with 150 mJ pulses mol/dm − 3 10 4 × O 2 particles ;LDA:1.8 4 3 O ) 3 − Nearly LiMn Fused together Au- Fe ZnSe-nanorods mol/dm COO OH) 2 8 − 3 ) 2 10 CH 2 × ) CH 3 2 (CH + echnology,Japan (OCH N ; SDS: 8.1 11 ) 3 11 2 ) 2 Na) DC – dodecyl sulfate (CH 3 3 (CH BrN) 3 mol/dm 42 H dYG 1064Nd:YAG, nm, 6 ns, 10 Hz, 30 and 150 mJ, 60 min 1064 nm, 10 Hz, 20 mJ, up to 40 min 130 fs, 1 kHz, 0.7 mJ − 4 OSO 19 25 10 H × 12 SO 2 ) 3 Water Water solution 532 Nd:YAG, and 4 O 3 4 O µ m 2 : SDS – sodium dodecyl sulfate (C LiMn suspension, particles size 5 colloids (tens of nm) ZnSe (SC) Water (1.2 mm layer) Ti:sapphire, 800 nm, Au and Fe Critical micelle concentrations: CTAB: 9.2 HRTEM – high-resolution transmission electronPL microscope – photoluminescence FT-IR – Fourier transform infrared (spectroscopy) OGM – octaethylene glycol monododecyl ether (CH LDA – lauryl dimethylaminoacetic acid betaine (CH CTAB – cetyltrimethylammonium bromide, (C Notations ∗ DMSO – dimethylsulfoxide (CH AIST – National Institute of Advanced Industrial Science and T Ch05-I044498.tex 11/9/2007 18: 50 Page 250

250 Handbook of Liquids–Assisted Laser Processing

5.6 Silicon and Amorphous Carbon Particles

Silicon nanoparticles have applications as ultraviolet photodetectors and visible light sources/lasers. Carbon particles (Fig. 5.26) have gained interest for their nonlinear optical properties. For example, carbon suspensions are efficient optical limiters for nanosecond pulses, for protection of human eyes and of optical sensors against high-power laser irradiation. The limiting occurs via production of bubbles and its onset is around 1 J/cm2 for carbon particles in water [829]. At laser ablation of solid carbon in liquids, formation of polyynes has been observed as well. Polyynes are believed to serve as novel 1D-conducting materials,‘molecular wires’ [830]. Table 5.8 presents a chronological reference of the research about silicon and amarphous carbon particles preparation. Formation of diamond particles and films (including diamond-like carbon (DLC)) in liquids- assisted laser processes is overviewed in Section 5.7.

(a) (b)

Figure 5.26 High-resolution SEM images of the carbon particles formed at laser ablation of graphite in isopropyl alcohol: (a) a nanostructured particle and (b) a micron-sized particle [684]. Laser: 1064 nm, 3.5 ns, 1 J/cm2. © Elsevier.

5.7 Diamond and DLC Particles and Films

Laser-energized liquid-assisted diamond synthesis may occur in several ways: • By laser irradiation of organic liquids or organic liquid–solid interface. • By laser ablation deposition having an organic liquid target (Fig. 5.27). • By laser irradiation of solid carbon or carbon suspensions in a liquid. • By laser irradiation of a liquid containing a dissolved organic gas (e.g. methane in water). Laser synthesis of diamond is an alternative to other low-pressure diamond synthesis methods like CVD and flame, featuring locality,good controllability,and little consumption of starting materials [841]. Besides diamond, formation of DLC in the same processes is likely (see Table 5.9). Graphite may be converted into diamond by driving the material into the pressure/temperature region where diamond is the only stable form of carbon (Fig. 5.28). The calculated probabilities of phase transfor- mations in dependence of temperature and pressure are presented in Figs 5.29 and 5.30. Laser synthesis of diamond occurs in the region 3500–4500 K, ∼10 GPa above the graphite–diamond boundary. Mechanisms determining the crystallographic form of laser-synthesized diamond are discussed in the article by Yang et al. [845] Graphite tends to transform into such form of diamond whose structure is close to the structure of graphite (minimal displacement of atoms needed for transformation): thus the hexagonal graphite lattice is changed into a hexagonal diamond lattice, and the rhombohedral graphite lattice is changed into a cubic diamond lattice. Although hexagonal diamond is metastable, it could be kept when it is prepared in dynamic methods such as the shock-wave method or explosive method, or by laser method; where the quenching rate is high [846, 798]. There is also evidence that hexagonal graphite may transform into cubic diamond via a rhombohedral graphite intermediate [846]. Similarly, conversion of organic compounds into diamond in a laser-driven process is easier if the carbon atoms in the molecules of the starting compound are arranged similar way as the atoms in diamond, like in Ch05-I044498.tex 11/9/2007 18: 50 Page 251 ) ( Continued References Dolgaev (2002) [753] Fojtik (1993) [720] Ogale (1992) [831] Gaumet (1996) [832] Chen (1997) [833] Chen (2002) [834] Tsuji (2002) [835] and n main ;C able 5.9). bubbles n 8, 10, 12, 14 = n ; in liquid the yield 10, 12, 14, 16 formed generation observed; = and other n detected , 70 2 sound ,C H n gases 60 C > 2 is smaller than in vapour with laser irradiation produced µ m in diameter) in toluene n , n in hexane; shorter laser wavelengthstarting and particle concentration of 4 mg/ml provided greatest effective for polyyenes formation; polyynes formation paths discussed in benzene and toluene; Crystal size was almostlaser independent fluence; on in case ofwater PVP the additive particle in size wassmaller about 10% unidentified clusters Novel features, observed Benzene was used as afor reactive trapping molecule the laser-inducedreactions C phenyl radicals were identified: the Polyynes product is phenylacetylene of C surface achieved; ablation crater was deeper than in air (several yielded C lower density cores formed; tiny and audible produced Partly crystallized spherical carbon particles were achieved of size 20–50 nm av av 60–84 nm 1–3 nm Ablation of suspended carbon particles lids in liquids (diamond and DLC particles and films: see T 2 H n n C Carbon Up to 400 nm Spherical structures with dense shells C Diamond 5–20 nm Diamond particles on graphite Particlestype Particles size phenomena, comments 2 2 µ m, (film 2 2 Nd:YAG, , single pulse 2 2 W/cm µ m, 1–2 J/cm 10 1064 nm, 1 ms, both focused or non-focused targets), 500 J/cm (carbon suspension) Ruby,694 nm, 2.3–27 J/cm 266,Nd:YAG, 532, and 1064 nm, 6 ns, 10 Hz, 10 1.06 Nd:YAG, 16 ns, 10 Hz, 0.7 J, up to 6000 shots pulsedNd:YAG, Cu-vapour, 510.5 nm, 20 Carbon ns, 15 kHz, spot 50 35 355,Nd:YAG, nm 532 and 1064 nm, 5–9 ns, 10 Hz, 0.2 J/cm Ruby,694 nm, 30 ns, 20 J/cm Lasers benzene vapour Benzene, toluene, hexane, stirred c-hexane, toluene surfactant additives) ethanol, dichloroethane Benzene (3–4 mm layer) Water, 2-propanol, Water Water (also with Carbon and silicon particles fabricated by laser irradiation of so µ m, C (film and suspension) Graphite Benzene (under Ar), Carbon black, 25 nm in suspension GraphiteSi Water Graphite particles, 75 suspended in liquid Si film c-hexane TargetsGraphite (pyrolytic) Liquids Table 5.8 Ch05-I044498.tex 11/9/2007 18: 50 Page 252 References [837] Chen (2004) [829] Chen (2004) [838] Pearce (2004) [674] Tabata (2004) Tsuji (2003) [836] ) and 2 radicals 2 at 532 nm 2 are obviously 8, 10, 12, 14, 16 8, 10, 12 were formed, = 60 = n ,n ≈ 0.3 J/cm , 2 2 H H n n C C ; dependence of polyynes yield on 2 being dominant in all cases; C H 8 n polymerized and hydrogenated to formC formed; ablation of graphite particles yielded less and shorter polyynes C stable in timeachieved;probablyTHF polymerizes (over onto 3particles months) surface; colloid Novel Novel features, observed Graphite particles andpolyynes hydrogen-capped Polyynes Most of particles were ofof graphite; diamond some (in both liquids);plasma, atomic detected H by in optical spectroscopic, may be responsible for diamond growth Photostable (at least up to 12 J/cm Photostable colloids achieved; average graphitic domain size estimatedRaman from spectra was 1.56 nm;limiting optical setup various experimental parameters studied produced from C av av 6.5 nm 15 nm 2 2 H H n n C C Particlestype Particles size phenomena, comments 2 2 , non-focused, , 5 min 2 2 , 30 min 2 N:A,532-Nd:YAG, nm, 532-Nd:YAG, nm, 60 min dYG 266,Nd:YAG, 355, 532, and 1064 nm, 5–9 ns, 0.2 J/cm 2 ω ≈ 7 ns, 20 Hz, 1.3 J/cm 2 ω 10 ns, 10 Hz, spot 0.5 mm, up to 66 J/cm 1064 nm, 7 ns, 10 Hz, 0.8 J/cm 532Nd:YAG, and 1064 nm, 7 ns, 10 Hz, 1 J/cm Lasers ) Hexane, methanol (stirred) Ethanol under Ar, free surface liquids (THF) Water, rotating vessel 532 Nd:YAG, and Continued ( 60 suspension Diamond particles, 5 nm in diameter Graphite Water, cyclohexane Glassy (vitreous) carbon Glassy carbon Tetrahydrofuran TargetsC Liquids Table 5.8 Ch05-I044498.tex 11/9/2007 18: 50 Page 253 [830] Kitazawa (2005) [684] Miyazaki (2006) [840] [839] Tsuji (2006) Wang (2005) nets , 2 H µ m 2n µ m particles µ m size and C ≈ 20 ≈ 2 polyynes particles of composed of small particles; particles of of diamond nucleation and growth 4–8 were formed, the measured = absorbance, abundance, and Raman spectra are presented for different experimental conditions (starting materials, solvents, and laser wavelengths); the yield of polyynesdecreasing increased laser with wavelength; largest distributions of long-chain polyynes were achieved at ablation of graphitearomatic in hydrocarbons; formation mechanisms of polyynes are discussed size were formed; FTIR, PL, PLE, and Raman studies Rose-shaped cracknel-shaped n Hydrogen-capped of short wires no crystallinity was developed observed for small particles;5 were covered after laser irradiation by at laser ablation of graphitepresented; at in temperatures liquids up toand 5000 pressures K up to 30sizes GPa are the predicted particles to be25–250 nm in range Almost no morphological changes were Theory µ m µ m, ≈ 2 ≈ 20 2 H 2n C , 2 , 2 ,up 2 , 30 min 2 W/cm 8 to 20 min 3.5 ns, 30 Hz, 1 J/cm 355,Nd:YAG, 532 and 1064 nm, 7 ns, 10 Hz, up to 250 mJ/cm non-focused, 60 min Nd:YAG, 266, 355, 532, and 1064 nm, 5–9 ns, 10 Hz, 40 mJ, 0.2 J/cm 10 Benzene, toluene, hexane, cyclohexane, methanol, hexafluorobenzene, perfluorooctane, perflu- orodecaline (stirred) Water, stirred µ m powder 60 Graphite Isopropyl alcoholGraphite 1064 Nd:YAG, nm, Carbon black particles suspension, 14 nm – 5 av Graphite, coal or C in suspension Notation PVP – polyvinylpyrrolidone Ch05-I044498.tex 11/9/2007 18: 50 Page 254 Shafeev (1999) [850] Xiao (1995) [842] Singh (1993) [849] [844] Lu (1998) [847] Xiao (1995) [841] Sharma (1993) [848] Wang (1999) poly- , 2H- and vapour to substrate 2 O 2 /H bondings was 2 adhesion 3 sp promote the diamond growth − ) to toluene did not result in doped carbon 3 with a large amount of for range 1000–5000 K, 0–20 GPa (see Figs 5.29 features, observed phenomena, comments References solid–liquid interfaces films mixture (200 mbar);120 nm film thick film deposition obtainedhydroxyl after ions 12 rate OH 000 laser 0.1 pulses; Å/pulse; obtained, deposition rate was 0.1with Å/pulse; in a comparison PMMA target, noin particulates the were deposited found films 6H-hexagonal and ohmic contacts;(ClAuPPh adding organometallic substances Simultaneous with carbon deposition etchingsubstrate of and the generation ofthe suspended carbon particles dots observed; and lines had good Probability of graphite toprobability diamond as transformation function of temperaturecalculated and pressure and 5.30); formation of nanometre-sizedirradiation diamond in at liquids laser is explained by high nucleation rate DLC film Mostly graphitic particulates formed,formation but also mechanism diamond; probably includesbreaking preferential of C − H bonds inhydrogen formation cyclohexane and atomic types along a smalldiamond fraction in of hexane, cubic obviously phase becausemolecule formed; the no does structure not of mach the diamond lattice Some nm Four laser pulses: cubic diamond, 10 pulses: cubic Glassy carbon dots and lines 20–50 nm In cyclohexane and decalin a mixture of hexagonal 500 nm cubic Ablation/deposition performed in O Particles size Novel adiation of liquids and , 2 , 2 × 2 , focused 2 ≈ 4 J/cm steady or scanned beam 220 mJ, spot 2 5mm 20 pulses at each point 2 pulses KrF,248 nm, 20 ns, 5 Hz, XeCl, 308 nm, 30 ns, 1–4 J/cm 220 mJ, focused beam KrF,248 nm, 23 ns, 1 Hz, 1–10 J/cm Cu-vapour, 510.6 nm, 20 ns, 8 kHz, up to 1 J/cm Lasers ArF,193 nm, 10 Hz, ArF,193 nm, 10 Hz, -hexane oil (a polyphenyl ether) 2 mm layer) Benzene (3 mm layer) Santovac 5 vacuum oil (a polyphenyl ether) Cyclohexane (2–3 mm layer) Cyclohexane, decalin, n Liquids Toluene ( ≈ C Santovac 5 vacuum ◦ Diamond and diamond-like carbon (DLC) formation by laser irr ∼ 600 Targets Cu, SC (100) and polycrstalline Si (100) Stainless steel (above the liquid surface) Si (100) Si, SC W Table 5.9 Ch05-I044498.tex 11/9/2007 18: 50 Page 255 ) ( Continued Hidai (2000) [851] [846], [798] Simakin (2000) [628, 629] [852] Simakin (1999) [622] Lyalin (1999) [623] Wang (1998) Wang (2002) Yang (2001) con- of the temperature intermediate rhombohedral 100 nm, probably due ≈ ; dependence of the were transparent in the fraction in deposited films amounted to phase 3 sp Focused laser beamwater irradiation resulted in oftaining formation methane 7.2 wt% of solution hydrogen granulartransmittance in of DLC a film, focusedthe laser defocus beam distance by water was on studiedvariation as of well, the five-fold transmittance was observed Intergrowth diamond crystals achieved withcubic both and hexagonal structure, graphiteto conversion diamond occurs via metastable graphite to heating it by laserand periodic beam detachment following of graphitization the film due to thermal stresses Backside of the substrates infilm contact with deposition liquid took irradiated; placeetching along the of the substrate;was no observed; film optical microhardness breakdown 50–70 or GPa; film plasma thickness saturates at Obtained particles consistedgraphite; a of new Raman 5% linesurface, diamonds 926/cm, of was the and found, irradiated obviously originating 95% from nano-diamonds thickness saturated at 100 nm, despitethe the surface ablated depth increased; of calculated peak sapphire-film-liquid structure during laser pulse was 600 K 60–70% depending onexcellent the adherence, precursor; thevisible and films have microhardness showed of 50-70 GPa The Well adherent and stable in DLC films were achieved; film 3 sp µ m µ m thick µ m Hydrogen DLC film; particles size in film 30 nm Diamond parti- cles, 300 nm (for example) DLC film 100 formed on surface, 70% DLC film ∼ 100 bonds Diamond parti- cles, 30 nm av DLC film100 80– , , 2 2 ,upto 2 ; liquid–solid 2 W/cm µ m, up to 10 30 Hz, 150 mJ, 20 min Cu-vapour, 510.6 nm, 20 ns, 8 kHz, spot 50 Cu-vapour, 510.6 nm, 20 ns, 8 kHz, up to > 1.5 J/cm 532Nd:YAG, nm, 10 ns, 5 Hz, 250– 350 mJ Nd:YAG, 532 nm, 10 ns, 5 Hz, 10 1.5 J/cm Cu-vapour, 510.6 nm, 20 ns, 8 kHz, 0.2–1.5 J/cm scanned focused beam 0.3–3 mm/s 25 min, scanned beam up to 1.2 mm/s 45 min interface was irradi- ated through the substrate ArF, 193 nm, 23 ns, dissolved + methane (at 350 kPa) benzene, cumene, containing carbon particles (3–4 nm) benzene, cumene, also with addition of glassy carbon particles, 3–5 nm layer 1–2 mm layer Benzene, toluene, also with glassy carbon or diamond particles (4–5 nm) added Acetone, Toluene, Toluene, Water Water, 1–2 mm 2 , CaF 3 O 2 Glass, fused silica, Glass, fused silica, sapphire Soda-lime glass, Pyrex, sapphire Glass Graphite (polycrystalline) Graphite (polycrystalline) Al Ch05-I044498.tex 11/9/2007 18: 50 Page 256 Simakin (2002) [853] [856] Hidai (2002) [854] Shi (2005) [855] Wang (2005) ) 2 Pd-doped ∼ 3 J/cm , 2 ; in case of laser irradiation of nanodiamond to the liquid resulted in 2 features, observed phenomena, comments References which served as seed layer for subsequent CVD multiwall carbon nanotubes films copper deposition; efficiency of DLCdiffusion film barrier as for Cu was demonstrated by formation at laser ablationcalculated of graphite radia in of water; phase critical transition nuclei probabilities are and presented at graphite–diamond temperatures up to 5000formation K of and diamond pressures particles 7–21 GPa; predicted of to size be most 3–5 favourable nm around 12 was GPa and 4500 K of the gas neardiameters the liquid 50–200 nm surface, DLC were achieved particles of by benzene was irradiatedprovided enhanced by DLC laser deposition light; attip; near-field the needle effect deposited in liquidthicker films than were those rougher deposited and inKrF-laser benzene (248 nm, vapour 23 by ns, spot 0.1 cm Glass–liquid interface was irradiatedaddition through of the Pd(acac) glass; The achieved particles consisted of DLC, covered The tip of a W needle (10 nm in radius) covered Thermodynamic calculations µ m thick DLC particles, 200–700 nm Diamond DLC film (graphitic), cluster size 34 nm DLC film ∼ 100 on surface Particles size Novel , 2 2 ; 2 µ m CW,spot 150 30 Hz, 40–150 mJ, 20 min scanned focused beam 0.5 mm/s 0.72–1.09 MW/cm Cu-vapour, 510.6 nm, 20 ns, 8 kHz, 0.5 J/cm Lasers Ar-ion, 514.5 nm, ArF,193 nm, 23 ns, additive) 2 dissolved + methane (up to 72 mg/l) Benzene Benzene, toluene (also with Pd(acac) Liquids Water Water ) Continued ( – triphenylphosphine complex of Au – palladium acetylacetonate 3 2 Targets No Graphite Glass W Pd(acac) Notations ClAuPPh CVD – chemical vapour deposition Table 5.9 Ch05-I044498.tex 11/9/2007 18: 50 Page 257

Generation and modification of particles 257

Heating wires rotating motor thermocouples excimer laser beam liquid target focusing lens

viewing window reactive gas cooling water

substrate gravity vacuum pump

Figure 5.27 Laser ablation deposition of diamond films using a liquid target [842]. An high viscosity, low-vapour pressure liquid-like vacuum oil is needed for this process (see also Section 6.3.2). © American Institute of Physics (1995), reprinted with permission from Ref. [842].

50

G J 40 Diamond

30 F

I E 20 Pressure (GPa) H CW D B Liquid 10 A PLIIR C HTHP Graphite 0 0 1000 2000 3000 4000 5000 6000 Temperature (K)

Figure 5.28 P,T phase and transition diagram for carbon as understood from experimental observations. Solid lines represent equilibrium phase boundaries [843]. A: commercial synthesis of diamond from graphite by catalysis; B: P/T threshold of very fast (less than 1 ms) solid–solid transformation of graphite to diamond; C: P/T threshold of very fast transformation of diamond to graphite; D: single crystal hexagonal graphite transforms to retrievable hexagonal-type diamond (shock-wave synthesis); E: upper ends of shock compression/quench cycles that con- vert hex-type graphite particles to hex-type diamond; F: upper ends of shock compression/quench cycles that convert hex-type graphite to cubic-type diamond; B, F, G: threshold of fast P/T cycles, however generated, that convert either type of graphite or hexagonal diamond into cubic-type diamond; H, I, J: path along which a single crystal hex-type graphite compressed in the c-direction at room temperature loses some graphite characteristics and acquires properties consistent with a diamond-like polytype, but reverses to graphite upon release of pressure. Notations: SW – shock waves; HTHP – high temperature high pressure; PLIIR – pulsed laser-induced liquid–solid interfacial interaction. © Elsevier.

cyclic and aromatic compounds. Cyclohexane, decaline, and benzene are favourable compounds for diamond synthesis, because only breaking of relatively weak C–H bonds is needed to get free carbon rings. Abstracted atomic hydrogen and formed in solvents OH-radicals have known to contribute to the nucleation of diamond as well [847]. Ch05-I044498.tex 11/9/2007 18: 50 Page 258

258 Handbook of Liquids–Assisted Laser Processing

2.01010 10 2

5 10 3 1.51010 5 10 10 3 10

4

4 1.01010 10

5 Pressure (Pa) S line B– 3 10 0.5 10 3 4 4 10 2

3 10 10 10 10 5 10 5 0 1000 2000 3000 4000 5000 Temperature (K)

Figure 5.29 Schematic illustration of the probability of phase transformation in the pressure–temperature diagram [844]. The B–S line is the Berman–Simon line. The curves above and below the B–S line are fd and fg, respectively. fd – probability of the transformation from graphite to diamond; fg – probability of the transformation from diamond to graphite. © Institute of Physics, reproduced with permission.

103

10 4 c b 105 a 106

107 d f 108

109

1010

1011

1012 3500 3000 2500 2000 1500 1000 500 Temperature (K)

Figure 5.30 fd–T curves of diamond formation probability: (a) P = 6 GPa. (b) P = 8 GPa and (c) P = 10 GPa [844]. © Institute of Physics, reproduced with permission.

5.8 Organic Particles

Laser ablation of organic materials in liquids has been used for fabrication of phthalocyanine and its metal derivatives particles. These materials possess useful photoconductive and semiconductive properties and are applied for sensors, bioprobes, and organic microdevices. The common methods of fabrication of particles of these materials are evaporation and reprecipitation. Laser ablation of bulk materials in liquids presents a simple way to control the size and molecular aggregation structure of the particles [857]. Nanoparticles of some materials cannot be fabricated another way, for example of quinacridone particles of size below 50 nm [858] (Table 5.10). Ch05-I044498.tex 11/9/2007 18: 50 Page 259 Li (2004) [862] (2003) [860] Li (2003) [861] Sugiyama (2006) [858] (2002) [857] (2000) [859] Tamaki Tamaki Tamaki , 2 at 580 nm; achieved C increased the ◦ 2 , fluence up to 120 mJ/cm 2 -form and by 580 nm, β -form γ of ; as fabricated particles were structurally 2 2 at 355 nm and 15 mJ/cm 2 atures, observed phenomena, comments References optical abstraction spectra iswavelengths shifted towards longer crystalline phase of the particles efficiency of particles generation; surfactantsthreshold lowered fluence the of particle generation metastable, a phase transformation occurred in some days colloid stable at least fornanoparticles 1 were of month; prepared by> 50 355 mJ/cm nm irradiation up to 30 min; thresholds30 mJ/cm for particle modification: Laser spot size typically 23 mm months were achieved; phase transitionsirradiations of are Pc likely due to laser In pure water VOPcbut nanoparticles were stable associated at in leastlowering some 2 the months temperature days, if down to surfactants 5 were added; StableVOPc nanoparticle colloids achieved;threshold fluence ≈ 20 mJ/cm Novel fe At higher concentrations of surfactants the Q-band in Thermal diffusivity of the liquid determines the size and Transparent colloid solutions stable for at least several H) 9 , av O) 2 , 20 min); , 30 min) 2 2 2 (580 nm, (355 nm, CH av av av av 2 O(CH 20 nm 90 mJ/cm 180 min) ≈ 100 nm (VOPc, 340 mJ/cm 60–100 nm (VOPc, 0.4–0.01 mM surfactants) 50 nm 98 mJ/cm 60 nm hexagonal 49/17 nm (mean width/height) 50 nm Size Triangular 60/19 nm 4 H 6 for CC 2 2 ) 3 ,up 2 , 2 (CH 2 2 2 CCH 2 mm, up 3 -Nd:YAG, -Nd:YAG, 4 ns, -Nd:YAG, ) 3 × to 80 mJ/cm 3 ω 4 ns, 20 Hz, spot 2 up to 180 min to 80 min 5 Hz, up to 68 mJ/cm XeF,351 nm, 30 ns, 5 Hz, 30 mJ/cm XeF,351 nm, 30 ns, 5 Hz, up to 340 mJ/cm 3 ω 20 Hz, spot 2 × mm, 80 mJ/cm 355 nm, ns-pulses OPO, 580 nm, 7 ns, 10 Hz 10 min Lasers Na) 3 SO (SDS 25 + H 12 or Igepal CA-630) ethanol, 1-propanol, ethyl acetate water SDS (1–16.4 mM) and Igepal CA-630 (0.184–0.41 mM) Water, stirred XeF,351 nm, 30 ns, Water, methanol, Water, Water Water solutions of Water, stirred 3 ω Organic colloids prepared by laser ablation in liquids. µ m and 1– µ m in suspension – quinacridone par- powder (few tens of µ m) floated in water floated in liquid by stirring FePc powders in suspension Target materialsanthracene, perylene, Liquids pyrene, abd coronene powders in suspension FePc powder in suspension β ticles, 0.2 10 VOPc crystalline VOPc powder VOPc, CuPc, VOPc, CuPc, FePc, Notations FePc – iron phthalocyanine CuPc – copper phthalocyanine SDS – sodium dodecyl suphate (C Igepal CA-630 – octylphenoxy polyethoxy ethanol ((CH Table 5.10 VOPc – vanadyl phthalocyanine, oxo(phthalocyaninato) vanadium Ch06-I044498.tex 11/9/2007 18: 51 Page 261

CHAPTER SIX

Surface Modification, Deposition of Thin Films, Welding, and Cladding

Contents 6.1 Surface Modification 261 6.2 Deposition and Transfer of Thin Films 262 6.3 Welding and Cladding Under Water 277

6.1 Surface Modification

6.1.1 Modification of surfaces of inorganic materials Laser irradiation may modify the surface of a solid by melting and vaporizing it, or/and by inducing chemical reactions between the solid and the ambient. In a liquid, there are two main differences in comparison with gases or vacuum: (a) Cooling rate of the laser melted zone is faster which may result in metastable phases; (b) The density of chemical species (e.g. oxygen and nitrogen) is greater in liquid than in gas, thus the reaction efficiency is greater. Using lasers, the modification of surfaces can easily be performed locally without a need for masks.

Laser-induced quenching in water Much research has been done in quenching of laser melted silicon in water. In comparison with air ambient, in water the quench rate was ∼30 per cent higher (for 270 nm deep melts, 4 ns laser pulses). After irradiation of single crystalline silicon under water, perfect epitaxy was obtained with no surface oxidation or changes in surface morphology. Si regrowth velocities over 7 m/s were observed, but the critical for formation of amorphous silicon quench rate 15 m/s was not achieved [863–865] (see also Table 6.1, Polman 1988 and 1999). In conventional nanosecond laser melting of solids in gas or vacuum, the solidification velocity v can be estimated by: λ ∂T v = · , (6.1) H ∂z where ∂T/∂z is the temperature gradient in the solid just behind the interface, H is the enthalpy of melting, and λ is the thermal conductivity of the solid [863].

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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A review of laser reactive quenching at liquid–solid interface has been published by Kanetkar and Ogale [866].

Oxidation and nitriding At laser-induced high temperatures, inert under normal conditions liquids like water and liquid nitrogen, dissociate, liberating chemically reactive species. In Table 6.1, some examples of corresponding research are presented (see also the review by Kanetkar and Ogale [866]). In the articles by Imai et al. [867], and Watanabe and Sameshima [868] some examples of aftertreatment of laser irradiated materials by water are presented (see Table 6.1).

6.1.2 Modification of surfaces of organic materials Fluorocarbon polymers like PTFE possess excellent chemical and thermal stability,low wettability,low electrical conductance, small dielectric losses up to very high frequencies, etc., which makes them useful in many applications. On the other hand, high chemical stability hinders, for example, their joining with other materials, needed for example in fabrication of electronic printed boards. Adhesion and biocompatibility of fluorocarbon polymers can be improved by treatment in plasma, but also by irradiation by UV light in water or aqueous solutions (see Table 6.2). Using of UV light, thereby from lasers, avoids the need for a vacuum system and enables selective treatment without masks. Besides lasers and liquids, excimer lamps and nitrogen or ammonia gases have given similar results [874, 55]. The principle of PTFE hydrophilization is shown in Fig. 6.1. Surface irradiation by UV (excimer) laser light at presence of water leads to replacement of surface fluorine atoms by OH-groups, and liberation of hydrofluoric acid (which in turn may be used for etching of silica as described by Murahara [596]) (see Table 4.9, Murahara 2001).

H2O + [CF2]n + hν(193 nm) → [CFOH]n + HF.

6.2 Deposition and Transfer of Thin Films

6.2.1 Laser ablation deposition in water vapour Laser ablation deposition in water vapour has found to be beneficial in fabrication of bio-compatible hydrox- ylapatite coatings on implants, and of TiO2 passivating films on silicon solar cell structures [881] (Table 6.3). A schematic representation of PLD is shown in Fig. 6.2. Focused pulsed laser light (usually from an excimer laser because of short pulse and high absorption) irradiates the target and causes explosive vaporization of the material. The ejected material condenses on a substrate placed some centimetres away. In case of laser pulse length in nanoseconds, the chemical composition of the coating closely resembles the composition of the target [882]. Apatites, in particular hydroxylapatite Ca10(PO4)6(OH)2 (also named hydroxylapatite or HA), have chem- ical composition and structure similar to the calcium phosphate phase of the bone and the tooth mineral [883]. Hydroxoapatite is the material of choice for biologically compatible coatings on metal substrates, implants and prostheses for orthopaedics, neurosurgery, and dentistry [884]. It is the most stable calcium phosphate in contact with the body fluids [885]. HA coatings may be fabricated by sputtering, plasma and flame spraying, electrophoretic deposition, electrolysis, RF sputtering, ion beam deposition, powder sintering, etc. [886]. The commonly used method is plasma spraying, but it suffers from pores in the coatings [887]. Laser ablation deposition has attracted as a method for achieving pore-free well-crystalline HA coatings. For PLD of HA, the targets were made of compressed HA powder, the laser fluences at the target were 1.5–3.5 J/cm2, and the substrate was heated up to some hundreds of degrees of Celsius. For the deposi- tion of coatings of some micrometres thick, 10 000–20 000 laser pulses at 193 and 248 nm wavelength were Ch06-I044498.tex 11/9/2007 18: 51 Page 263 (1987) ( Continued ) [863, 864] Imai (1999) (2000) [871] Jendrzejewski Polman (1989) cases 2 vity (1988) 3 ater [867] ace Polman comments References water; quench enriched was observed; laser O and Fe:NH ; results of oxide Patil (1987) 2 of related previous the sample’s 1 − x 2 µ m was observed review accelerate the rearrangement µ m) Al layered structures in LN µ m became C, and WC 2 case a multiphase composite comprised ∼ 30 6 -Fe-N austenite, respectively found, in ; an increase of hardness down γ H β -W 6 C, 3 rate may be enhanced by 30% for deep by nitrogen to the depth of 270–330 (in Ar gas 400–500 Processed surface studied by CEMS, XRD, RBS, Ogale Si regrowth velocities over 7 m/s were observed Metastable Fe oxide was formed of W characterization by CEMS, XRD, RBS, andare XPS presented and discussed [869] XPS and TEM; transient reflectionsin measurement cource of process; in Fe:H [870] led to dimeric metastable solid solution vapour was found to of sol–gel films , leading densificationand of crystallization silica of titaniaof and silica–titania phase gel separation films surface layer FeO and the W:C irradiation of+ Fe research with 94 references is also presented of physical phenomena at liquid–solidare interface presented; a short At laser irradiation in LN TEM-micrographs, and a thorough discussion [865] 2 irradiated area ∼ 6 mm in diameter (down to 270 nm) melts if irradiated in Light conducted throughquartz guide Physical diffusor phenomena atwithout solid–liquid focussing; interf were studied by transient electrical conducti and optical reflectivity measurements; Experiments were Irradiation caused densification and crystallization bath and scanned 0.17–2 cm/s immersed into LN Sample was See Polman (1988) [863] In addition to the results presented in Polman or Polman (1988) [864] (1988) [863, 864], calculated reflectivities, performed in vacuum of sol–gel films; subsequent exposure to w the experiment N ovel features, observed phenomena, iation under liquids and related research (examples). 2 2 2 2 µ m, ∼ 130 kW/cm , 10.6 2 532 nm, 4 ns Laser or other light source Other features of and 15 J/cm up to 15 J/cm Low pressure Hg-lamp, 4.9 eV,1.4 mW/cm 4 ns, up to 28 mJ 2 , Ruby,694 nm, 30 ns, 3 C, ◦ (60–180 nitrogen (77 K) 1 kW, 1–72 h) Air, water 2 ω -Nd:YAG, Air, water Ruby,694 nm, 30 ns, 10 Al layer Water, NH Modification of inorganic materials surfaces by laser irrad + (40 nm),+ B Fe layer benzene, LN sol–gel coatings with water vapour Materials Fe,W,Fe Si (100) Si (100) and SOS Air, waterSilica, titania 532 2 ω -Nd:YAG, and nm, The coatings Synchrotron, 6–20 eV 38HMJ steel Ar, liquid CO processed Environment and beam parameters Fe (foil) silica-titania were saturated 4.7 4 ω -Nd:YAG, eV Table 6.1 Ch06-I044498.tex 11/9/2007 18: 51 Page 264 (2003) [873] Haefliger (2002) [867] [818] Chen (2005) Watanabe rate (2002) [509] SNOM (2002) [872] vating − 2 nm in Haefliger 4 N cm 3 ; 14 of the metal of width down Haefliger 10 ions in the × − 2 nanocrystalline 3 + cm 12 10 local corrosion × Al oxide lines exposed to water µ m thick 10 amorphous layer formed 2 2 rosion in water convection transport mobility of oxygenand in due water to the increased of Al films formed , crystallite size 50–150 nm N ovel features, observed phenomena, comments References oxide; grooves formation was also observed irradiation and then at 20–25 kJ/cm (as crystallized) to 3.2 ;vapour as result of aftertreatment by vapour, silicon films was reduced from 1 C ◦ µ m/s was obviously due to increased diffusivity and was used for laser beam focusing rate up to 33 immersed into a diameter were formed at aluminized Si below by laser by glass, scanning to 266 nm were obtained, increased oxidation SNOM tip was Protrusions of up to 30 nm height and 38 illuminated from oxide layer followed by tips drop of water, as result of laser heating destruction of passi into water and 1.3 MPa for 3 h the density of defect states in the crystallized Aftertreatment in Amorphous Si layers were crystallized by laser Water was covered Electrically insulating Water-immersion Al electrode film was patterned by laser- Target immersed At 6–15 kJ/cm , vapour was 2 2 µ m µ m, ∼ 250 nm spot 2.5 spot CW,up to 17 mW, micro-objective assisted cor up to 30 mW, 30 ns, 280 mJ/cm 50 shots in vacuum performed at 260 (total dose?) up to 30 mW, Nd:YAG, Laser or other light source Other features of 10 and 15 s spot 10 5–40 kJ/cm Ar-ion, 488 nm, Ar-ion, 488 nm, µ m) Ar-ion, 488 nm, Environment and beam parameters the experiment Water (15 Water Water vapour XeCl, 308 nm, ) ( Continued 2 4 N 3 SU-8 and glass) on glass films on PDMS, 120 nm) on (25 nm films) 10–150 nm) Materials Sintered processed Poly-Si Si CeO Al (films Al (coating Water Al ( ∼ 60 nm Water Notations CEMS – conversion-electron Mössbauer spectroscopy XRD – X-ray diffraction RBS – Rutherford-backscattering spectrometry XPS – X-ray-photoelectron spectroscopy SOS – silicon on sapphire SNOM – scanning near-field opticalPDMS microscope – poly(dimethylsiloxane) CW – continuous wave SU-8 – a kind of high-viscosity photoresist Table 6.1 TEM – transmission electron microscopy Ch06-I044498.tex 11/9/2007 18: 51 Page 265 ences [875, 876] Huang (1999) [874] (2001) (1995) [877] [879] Murahara Heitz (1996) Hatao (1997) Lou (1998) Hopp (2003) [880] [878], 2 and 3 2 , 3000 pulses) Murahara 2 ; adhesion surface (minimum contact (treatment in from hydrophobic the 275 times/up 2 if treated in 1% ◦ hydrophilic, surface if treated in aminoethanol ◦ of fluorocarbon resin was improved (treatment in water), respectively, 2 ) (minimum contact angle with water 2 hydrophilic surface of FEP solution) ); the bond strength to epoxy resin 3 3 BO 3 N ovel features, observed phenomena, comments Refer OH functional groups; the tensileof shear modified strength surface PTFEstainless bonded steel by was epoxy 12 resin MPa to where abstraction of fluorine atoms and introduction of nitrogen, oxygen, andatoms hydrogen occurred; the modifiedhigher surface absorption layer showed in the UV–VIS spectral region to 98 kgf/cm B(OH) 490 times/up to 55 kgf/cm of PTFE became hydrophilicto and replacement oleophilic , due of surface F atoms by CH strength of FEP to epoxy resin was increased due to laser treatment from 0.2 to 110 kg/cm to epoxy resin to hydrophilic 509 was increased from 2 to 26.2 kg/cm H (1% NaAlO angle with water was 28 Laser irradiation converted the PTFE surface Laser treatment in water (25 mJ/cm Laser irradiation in liquidsconverted (but the not PTFE in surface air) from hydrophobic to hydrophilic and triethylene-tetramine; the bond strengthepoxy resin to Uverapid 20 wasup increased to 100–200 9 times, MPa (when treated in triethylene-tetramine) Adhesive strength Treatment resulted in experiment up to 90 min plate using FEP turntable resulted in plate by fused silica with a water layer between; laser by fused silica irradiated through PTFE (transmission became down to 30 light irradiated the turntable through the sample window Liquid was covered As result of laser irradiation, Irradiation time Liquid layer was Sample was grind interface was laser Liquid was covered PTFE–liquid 51%) iation under liquids and related research (examples). , covered by silica 2 , , 2 2 2 , 2 , 2 * (172 nm); 2 * (146 nm) 2 Laser or other light source Other features of and Xe pulse tens of nanoseconds, 10–20 mW/cm up to 50 mJ/cm 10 ns, 100 Hz, up to 4000 pulses 1500 pulses Kr 20–30 mJ/cm 10 Hz, 10–535 mJ/cm ∼ 8 mJ/cm ArF,193 nm, 2 4 H 2 (1.8%, up to 25 mJ/cm 3 (1.2%) up to 4000 pulses ,NaOH, up to 2500 shots , NaAlO 3 3 4 and N -hexafluoropropylene) 3 BO µ m layer) up to 3000 pulses 3 Environment and beam parameters the CuSO 50 B(OH) solution of 1,2-diamino-ethane, 20 ns, up to of B(OH) solutions of triethylene-tetramine H Air, amino-ethanol, ArF,193 nm, Water solution ArF,193 nm, Water and water XeCl, 308 nm, Water Vacuum,gaseous Excimer lamps Modification of organic materials surfaces by laser irrad µ m) NH µ m) PTFE (film) (10–1000 resin (50 Materials processed PTFE, FEP Fluorocarbon Water and waterPTFE ArF,193 nm, FEP PTFE PTFE – poly(tetrafluoroethylene) Notations FEP –co poly(tetrafluoroethylene- Table 6.2 Ch06-I044498.tex 11/9/2007 18: 51 Page 266

266 Handbook of Liquids-Assisted Laser Processing

H2O H F ArF laser F OH F CCCC F F F PTFE FFFF C C C F F F

Fluorocarbon Figure 6.1 Principle of the photochemical reaction providing the replacement of F atoms by OH functional groups. © SPIE (2001), reproduced with permission from Ref. [596].

Plasma Window plume Rotating target

t° Heater

Substrate To vacuum Water pump vapour Figure 6.2 Schematics of pulsed laser deposition (abbreviated as PLD or LAD). Because a focused laser beam acts only on a small area of the target, the latter is rotated for even consumption of the material and for avoidance of formation of craters. The substrate may be heated in order to improve the adhesion and crystallinity of the deposited film. The irradiation densities of the target are some joules per centimetre square.

needed [888]. A 0.5 mbar water vapour pressure in the chamber was found to yield the best coatings (highly crystalline) [888]. Regarding other materials, only TiO2 coatings fabrication by PLD in water vapour ambient has been reported [881]. 0.55 mbar vapour pressure was found to yield best passivating films for silicon solar cells.

6.2.2 Laser ablation deposition using a liquid target Pulsed laser ablation deposition has established as a method for fabrication of high purity thin films of compound materials without little declination from the composition of the target. It is also easy to fabricate multilayer films by in situ target changing. However, PLD suffers from target deterioration (craters and cones formation) and from particulates in the deposited film. The particulates originate from droplets ejected from the molten target. Both of these problems can be avoided by using a liquid target. In this way,the focused laser beam ablates always a smooth surface and, hence, target deterioration is completely prevented without target rotation. Further, splashing can be avoided by using a viscous liquid [842]. For example, a liquid GaAl target was used by Willmott et al. [896], Fig. 6.3, for fabrication of AlGa films, from considerations that ablation of solid Al produces easily droplets and because liquid GaAl target has less impurities than a sintered target. (see also Table 6.4) Ch06-I044498.tex 11/9/2007 18: 51 Page 267 ( Continued ) Cotell (1993) (1995) [884] Jelínek Fernández- C ◦ C) , ◦ and temporal Serra (1998) using Pradas (1998) and a slow above 700 good C and ◦ : a fast shock the films at µ m were µ m were deposited; Bagratashvili C and 700 ◦ C and high water ratio; surface ◦ µ m HA films were deposited; ovel features, observed phenomena, comments References evolution of HA laser ablation plume was investigated; [889] three distinct components were identified deposition of hydroxylapatite was observed at [885] except if deposited at high temperatures (780 various deposition conditions are presented; deposition rate was around 0.1 nm/pulse; the (1996) [887] wave generating component including Ca and micrometre-size particulates component degree of hydroxylation and bestproperties) crystalline were achieved at waterpressure vapour of 0.5 mbar and low water content ambient Coatings of thickness 0.2–1.2 0.4–1 HA coatings of thickness of 2–3 and residual gas pressure are presented N ArF laser; in case of KrF laser, best films (highest [888] , He,Ar, or Kr In water vapour-enriched inert gas environments, 2 chamber was performed in vacuum chamber, environment (Ar 600–700 was bubbled water vapour flow 0.7–10 sccm) the adhesion of the films was generally flow 9–18 sccm, micrographs and XRD spectra of bath at rate 10 sccm tetracalcium phosphate at temperatures performed in water vapour pressure 0.1 mbarpressure in vacuum P ions, a intermediate faint component 0.15–1.5 mbar; number of laser deposited; pureshots HA 15 000 phase was obtained Scanned laser through a water temperatures between 400 O pressure 2–100 Pa(no gases added) and chemical composition of films on laser fluence, distance between target and substrate beam, residual gas dependence of the density of macroparticles Ar/water vapour best crystallinity films were achieved at The deposition was Optical emission intensity and spectrum, Water vapour ◦ ◦ 2 2 2 2 , , 2 2 ∼ 200 mJ, 2.2 mm, × 10 Hz, 3.5 J/cm 2.6 J/cm incident angle 45 ∼ 2 J/cm KrF,248 nm, KrF,248 nm, 30 ns, 10 Hz, incident angle 45 Laser or other light source Other features of 0.4 300 mJ, spot 0.5–10 J/cm C) 20 Hz, ◦ C) ◦ C) 10 Hz, 3.5 J/cm ◦ (200–780 Si (RT–800 (575 fused silica 10 Hz, 3–7 J/cm Substrates and beam parameters the experiment Ti-6Al-4V, KrF,248 nm, Ti-6Al-4V, KrF,248 nm, 30 ns, The deposition was Laser ablation deposition in water vapour (examples). HA and HA HA (powderpellet) No HA (powder Ti-6Al-4V ArF,193 nm, pellets) HA (sintered Ti-6Al-4V, KrF,248 nm, Targets pellet) natural apatite Ti (RT) 20 ns, 10 Hz, Table 6.3 Ch06-I044498.tex 11/9/2007 18: 51 Page 268 Serra (1999) [891] [883] Fernández- Pradas (2000) [892] Serra (1999) [890] Doeswijk (1999) [881] Arias (1998) µ s); the C O, the ◦ 2 2 /Si interface 2 µ m were deposited; µ m and of surface C and 10 Pa H ◦ µ m were fabricated; coatings : 600 nm, velocity 2.3 km/s y O were composed of HA and a-TCP; O 2 x ovel features, observed phenomena, comments References Deposition in 0.55 mbarprovide lowest water density of vapour states was at TiO found to coatings contained crystalline phasescalcium, rich as in CaO and Tetra CP;45 coatings Pa deposited H at Images of laser plumerevealed obtained that in species water are vapour confinedgas by leading the to background thewave formation at of 0.1 a mbar planar and0.2 shock a mbar; spherical in both shock cases wavereactions at the with presence the of background chemical atmospherethe leads formation to of calciumthe oxide dominant radicals emissive that species become in the plume HA coatings of thicknessthe dependence of of 0.85 thevapour coatings pressure composition was on investigated water byspectroscopy FT–IR plume components was investigated byphotography high-speed at different wavelengths: (i)(ii) Ca: 520 atomic nm, oxygen (O): 777(iii) nm, velocity Ca 20 km/s, and the largest lifetime ofoptimal charge laser carriers fluence at (27.8 target was 2 J/cm deposited at substrate temperatures under 400 HA coatings of thicknessroughness of of 1–4 0.4 were amorphous; at over 500 scratch test results are presented as well N The dynamics of found in Serra (1998) [889] laser ,Ar, or water vapour 2 environment or water vapour (0.1 and 0.2 mbar) environment Pressures of water vapour: 0.15–0.8 mbar O Ne or water vapour environment (0.1 mbar) environment (10–45 Pa) Water vapour Vacuum,Ne (0.1 mbar) 2 2 2 , incident , incident , 18 000 shots 2 2 ◦ ◦ 3.1 mm, × 2.6 J/cm KrF,248 nm, 30 ns, spot 0.8 355Nd;YAG, nm, 10 ns, 1.5 J/cm angle 45 angle 45 Laser or other light source Other features of 10 Hz, 0.8 J/cm dYG 355Nd;YAG, nm, 10 ns, 10 Hz, 73 mJ, 3.1 J/cm KrF,248 nm, up to 6 J/cm ArF,193 nm, 20 ns, C) ◦ C) ◦ C) ◦ -Si (100), Pyrex No (20–600 Si (100); (485 p glass; (300 Substrates and beam parameters the experiment ( Continued) (SC, 2 HA (powder pellet) HA (powder pellet) No HA (powder pellet) Ti-6Al-4V HA (sintered) Ti-6Al-4V, Targets rotating target) TiO Table 6.3 Ch06-I044498.tex 11/9/2007 18: 51 Page 269 [893] Jiménez (2004) [895] [894] Arias (2002) Arias (2003) (as low as O dissociation by 2 ∼ 125 nm/pulse O 2 of deposited coatings was at lower temperatures was measured in dependence of in the coatings (higher H − electric discharge , crystalline HA coatings C), due to both the higher incorporation ambient, the ablation rate was ◦ 2 and in Ar close to that in H of OH Using could be obtained determined at target-substrate distancesthe 9–48 mm; coatings were more homogeneousdistances, while at at greater shorter distancesalso the contained coatings undesired phases and surface damage 300 HA ablation rate the kind of ambientwater gas vapour and the its ablation pressure; for rate122 nm/pulse sinks (15 linearly Pa) from toO 108 nm/pulse (80 Pa); in the ionization current) andand the ionization higher of mobility the(provided particles by on the the electron substrate bombardmentcoating of during the its growth) Thickness distributions l/s); DC , or water vapour · 2 environment (45 Pa) environment (45 Pa, 25 Pa discharge 0–60 mA environment (15–80 Pa) Ar, O Water vapour Water vapour 2 2 2 3.2 mm, 1.6 J/cm 3.2 mm, 0.9 J/cm 2 × × 20 Hz, spot 1.4 20 Hz, spot 1.4 20 Hz, 1.2 J/cm (OH) ArF,193 nm, 20 ns, 6 ) 4 C) ArF,193 nm, 20 ns, (PO ◦ 10 2 ) 4 C) ◦ (Po 3 HA (sintered) Si (111)HA (sintered) ArF,193 nm, 20 ns, No HA (sintered) Ti (300–460 Notations HA – hydroxylapatite, hydroxyapatite, Ca XRD – X-ray diffraction DC – direct current RT – room temperature ( ∼ 20–25 SC – single crystalline FT-IR – Fourier transform infraredCP spectroscopy – Calcium phosphate TCP – tricalcium phosphate, Ca Ch06-I044498.tex 11/9/2007 18: 51 Page 270 Franghiadakis (1999) [899] Xiao (1995) [842] Sankur (1989) [897] Götz (1997) [898] Xiao (1995) [841] particles C ◦ bondings for solid In); diamond 3 2 sp of the ions ejected from (100 mJ/cm 2 of liquid In ablation by 15 ns , but above the threshold, the ablation 2 with a large amount of deposited from molten Ge on 300 ) obviously promote the diamond growth − threshold fluence ovel features, observed phenomena, comments References was obtained after 12 000deposition laser rate pulses; was film 0.1 Å/pulse;(OH hydroxyl ions DLC film Ge films 120 nm thick film containing cubic Kinetic energy distribution the targets was studies byprobable TOF kinetic technique; energy the has most valueselectronvolts for of several singly tens charged of ions,factor and exceeding was 2 larger for by doubly a charged ions was obtained, deposition rate wasincomparison 0.1 with Å/pulse; a PMMAparticulates target, no were found in the deposited films with 0.5 ps laser pulsesthe the same ablation for threshold both was 2.5 solid mJ/cm and liquid metal, substrates were smooth, single crystallineat and RT epitaxial; dense, low stress, bulkvery refractive low index, optical and absorption filmsof were liquid achieved; Ge use targetgeneration completely and elilminated ejection the of particulates pulses was 30 mJ/cm was more efficient for liquid In N The flow 2 2 (examples). O 2 /H 2 3 sccm Deposition was performed in vacuum vapour mixture (200 mbar) Experiment was performed in vacuum Experiment was performed in vacuum performed in O Experiment was performed in vacuum chamber, O Ablation/deposition 2 2 ), 5mm 2 × ) and 0.5 ps 2 , 100–120 J/cm 2 (up to 19 mJ/cm 10 Hz, spot 0.3 mm KrF,248 nm, 15 ns (up to 180 mJ/cm KrF,248 nm, 25 ns;ArF, 193 nm, 17 ns; 1–8 J/cm 220 mJ, focused beam Laser or other light source Other features of 220 mJ, spot 2 CO ArF,193 nm, 10 Hz, ArF,193 nm, 10 Hz, C) ◦ C ◦ Si (100), ∼ 600 Stainless steel (above the liquid surface) No No GaAs, NaCl (25–300 Substrates and beam parameters the experiment Laser ablation deposition using liquid targets and related research Santovac 5 vacuum oil (a polyphenyl ether) Santovac 5 vacuum oil In (solid 300 K, and liquid 600 K) Si, Ge (molten and solid), Cu (solid) Targets Molten Ge Si, CdTe, Table 6.4 Ch06-I044498.tex 11/9/2007 18: 51 Page 271 [900] (2000) [896] Kiso (2002) [901] Tóth (1999) Willmott N 1 − x optical Ga as the of thickness x 2 < 0.001–0.16 AL/s; , though control 3 ∼ 1 m/s), in case of Bi and emission intensity N (0001) films ∼ 1.2 s for Sn and Bi, 1 − x ; laser irradiation excites of material ejection from 2 Ga x ∼ 0.3 and µ m (75 000 laser pulses) were up to 3.37 achieved, without the need forbuffer a layer; the GaN growth or AlN ratethe ranged crystallographic and opticalfilms properties were of found the to be superior using N of the film thickness and, in the case of Al nitriding source compared to NH surface waves (radial velocity also droplets emission; relaxation timesprocesses of were wave respectively also control of the stoichiometry,wasto high poorer reevaporation due rates ofphysisorbed unreacted, Ga atoms between laser pulses targets are presented; the velocitythe of ablated the plume front was of approximatelySn 6 and km/s Bi for at both 5.5 J/cm emission spectra of Ga plume dependence on laser fluenceexperimental are presented; results were compared with 1D-simulation of heat flow,takingheat into of account vaporization the andthat recoil pressure; most it of was the found substrate ablated not particles in are the transferred formneutral to of atom, the an except excited at ion and but near an the excited target High-speed photographs Deposited film thickness was up to 140 nm; GaN (0001) and Al 3 µ s, molecules or NH 2 ∼ 400 17 10 × Experiment was performed in vacuum Pulsed N ambient, 2.5 Experiment was performed in vacuum per pulse; non-wetting glass-ceramic crucibles were used for molten targets 2 2 2 1.6 mm, up × to 5.5 J/cm 0.5 up to 5.5 J/cm KrF,248 nm, 17 ns, 8 and 12 Hz, spot size 0.1 and 0.15 mm, 3.5–6.4 J/cm ArF,193 nm, 18 ns, spot ArF,193 nm, 20 ns, 10 Hz, C ◦ C) ◦ 2 640–740 Molten Sn, Bi No Molten Ga,Al-Ga Si (111), Molten Ga SiO Notations RT – room temperature ( ∼ 20–25 DLC – diamond-like carbon AL – atomic layer TOF – time of flight Ch06-I044498.tex 11/9/2007 18: 51 Page 272

272 Handbook of Liquids-Assisted Laser Processing

ϩV i KrF LT 248 nm

ϩV PV LT i Si (111)

KrF 248 nm PV

LT LF LT CR

CC EE RS i Si AI2O3 TF (a) (b) ϩV Figure 6.3 Schematics of liquid-target pulsed laser deposition systems used for the production of GaN and AlxGa1−xN thin films: (a) Plan view of the horizontal geometry, (b) side view of the vertical geometry. The labelling is as follows: PV: pulsed valve; CC: ceramic crucible; LT: liquid target; LF: laser focus spot on target; RS: radiation shield;TF: tungsten filament; CR: ceramic ring; E: Pt-coated Ti electrode. Due to space problems heating was provided by passing current through the Si wafer. Non-wetting glass-ceramic crucibles were used for molten targets. © American Institute of Physics (2000), reprinted with permission from Ref. [896].

Diamond and diamond-like carbon (DLC) films fabrication by laser ablation of carbon-containing liquids is described in Section 5.7.

6.2.3 Laser ablation deposition using frozen target Frozen gas targets If nitrogen-containing compound films are desired in laser ablation deposition, the ablation is commonly performed in nitrogen gas ambient. However, due to low density of nitrogen atoms in the gas, the films may remain nitrogen deficient. The use of frozen nitrogen target enables to compensate the nitrogen deficit, and generate chemically activated species (excited N2 and H), which promote the bonding in the films [902] (Fig. 6.4). For deposition of carbon and carbide films, frozen acetylene and methane targets have been used as carbon source (see Table 6.5).

Frozen solution targets (MAPLE) MAPLE means Matrix-Assisted Pulsed-Laser Evaporation. The technique was developed for deposition of thin films of biomaterials, materials which are too fragile for direct laser ablation deposition. In addition, the technique was proved to be useful for deposition of nonlinear optical organic materials, conductive polymers, luminescent organic substances, etc. MAPLE involves dissolving or suspending the functional material in a volatile solvent, freezing the mixture to create a solid target, and using a low fluence pulsed laser to evaporate the target for deposition of the solute inside a vacuum system (Fig. 6.5). Ch06-I044498.tex 11/9/2007 18: 51 Page 273

Surface modification, deposition of thin films, welding, and cladding 273

Gas inlet

Refrigerator Mass flow controller

Capillary

Turbo molecular pump Substrate holder Condensed gas

Substrate

Window

Lens

Excimer laser Figure 6.4 Schematic view of the synthesis chamber with a frozen nitrogen target [902]. Gaseous nitrogen is constantly supplied onto cold target and is frozen there. © Elsevier.

MAPLE suits for fabrication of biomaterial thin films ranging from biocompatible polymers like polyethylene glycol (PEG) to complex living micro-organisms such as eukaryotic cells [911]. The target is a frozen matrix consisting of a volatile solvent (e.g. water, methanol, chloroform, etc.) and a low concentration, <1 wt. per cent, of the film material. The solvent and solution concentration are selected so that the polymer/organic material of interest can dissolve to form a dilute, particulate free solution and also so that the majority of the laser energy is initially absorbed by the solvent molecules and not by the solute. At laser irradiation the solvent vaporizes and the expanding vapour plume carries the solute onto substrate placed some centimetres away from the target [910] (Tables 6.6 and 6.7). Patterning can be achieved with a contact shadow mask, feature sizes down to 20 µm are possible. MAPLE technique has been proven to provide better thickness control of polymer and biomaterials films as traditional aerosol,dip coating,or spin coating processes. In comparison with vacuum evaporation,conventional PLD, and in situ polymerization techniques, MAPLE is less substance specific [910].

6.2.4 Forward transfer from solution (LIFT, MDW) LIFT technique – laser induced forward transfer – is an alternative to MAPLE for fabrication of biomaterial thin patterned films. In LIFT,the target is a thin solution film on a transparent substrate at room temperature and is irradiated by laser from backside (Fig. 6.6). The process is also called MAPLE Direct Write (MWD) (Table 6.8). The functional solute material (e.g. proteins, DNA, cells, tissue) is imbedded in a matrix and spread on a transparent ribbon blank. A laser pulse strikes this material through the ribbon, thermally exciting part of the matrix material. The thermal expansion propels the materials to the substrate. The matrix function is to Ch06-I044498.tex 11/9/2007 18: 51 Page 274 References Niino (2000) [907], Niino (2001) [908] Ishiguro (1999) [902] Hiroshima (1997) [904, 905] Niino (2002) [909] Ishiguro (1998) [906] Hanabusa (1995) [903] C (ArF laser, ◦ C ◦ were deposited polycrystalline hexagonal film ablation are ); a KrF laser produced DLC 2 on HOPG and Si plates 2 cm 2 C) at laser fluence up to ◦ mixture yielded amorphous 4 and/or BN films x CH were formed film on Si yielded C and 400 4 4 + ◦ NbN 2 N 3 formed on a quartz substrate placed atomic nitrogen was produced in a containing nanometre-sized diamond embryos and total number of shots 18 000; frozen without the need of any post-thermal 2 and Si 4 µ m thick N 3 presented; multi-photon ionization process C–N films without splashing particles ∼ 2 targets provided higher nitrogen concentration in the films DLC films 40 mm apart from the17 target; nm/min deposition at rate RT was and 13 nm/min at 300 apart from laser ablation target 3.8 J/cm DLC films were deposited onto Si (100)30 mm substrate distance located from at the target onto MgO (100), Si (100)substrates and (300 Corning 7059 glass SiC films annealing, but Si splashes wereablation found of in N the film: films at substrate temperature above 200 Results of studies of solid N C power density 900 MW/vm Ablation of CH (0.1 Torr) 2 Deposition was performed in vacuum Other features of Deposition was performed in vacuum at substrate temp. RT,573 K, 873 K and 1173 K Deposition was performed in vacuum or in N Experiment was performed in vacuum Deposition was performed in vacuum deposited onto glass, Si and rock salt substrates, 15 mm apart from targets in vacuum the experiment Novel features, observed phenomena, comments The films were ablation 2 ,up 2 2 , incident , 18 000 shots 2 ◦ KrF,248 nm KrF,248 nm, 14 ns, 5 Hz KrF,248 nm, 14 ns, 5 Hz, 3.9 J/cm 12 ω -Nd:YAG, and 5 Hz, spot 1 mm, 3–7 J/cm 4 ω -Nd:YLF,263 nm, 8 ps, 10 Hz, 5 J/cm angle 45 8 ps, 10 Hz, 1.5–10 J/cm to 8000 pulses Laser type and ArF,193 nm, 14 ns, 10 Hz ArF,193 nm 4 2 4 4 +CH (10 K) 4 ω -Nd:YLF,263 nm, 2 2 2 2 C) ◦ Solid N Solid acetylene (1–2 mm) Solid CH Solid N Solid N ( ∼ 10 K) and/or CO (12 K) (1–2 mm) mixture (16 K) (3 mm, 10 K) Laser ablation deposition from frozen targets (examples). -BN Solid N h Cu Cu Target’s Nb and Graphitic carbon Solid CH Si (100) Cu Cu substrates Targets beam parameters Notations HOPG – highly orientedDLC pyrolytic graphite – diamond-like carbon RT – room temperature ( ∼ 20–25 Table 6.5 Ch06-I044498.tex 11/9/2007 18: 51 Page 275

Surface modification, deposition of thin films, welding, and cladding 275

Desorbing solvent and macromolecules Incident UV laser pulse

Volatile solvent Cooled, rotating pumped away Substrate MAPLE target

Gate valve

Turbo pump

Figure 6.5 Schematic diagram of the MAPLE deposition system [910]. The process is carried out in vacuum or in low-pressure inert gas/water vapour. © Elsevier.

Table 6.6 Processing conditions for deposition of thin films of chemoselective polymers and carbohydrates by MAPLE [910].

Laser wavelength (nm) 248 or 193 for polymers, 193 for carbohydrates Laser power (W) ∼0.02 Laser spot size on the target (cm2) ∼0.4 × 0.1 Laser fluence on the target (J/cm2) 0.05–0.25 Laser repetition rate (Hz) 2–5 Target size (diameter in cm) ∼2.5 Target to substrate distance (cm) 5 Substrate type NaCl, Si,Au/Si and quartz (SAW) Substrate temperature (◦C) Room temperature (25◦C) System base pressure prior to deposition (Torr) 10−5

Background gas during deposition Ar or Ar/H2 Background pressure during deposition (Torr) 5 × 10−2 (50 mTorr) Deposition rate (Å/laser pulse) 0.03–0.05 Typical film thickness (nm) 20–50 Typical deposition time (min) 20–50 Ch06-I044498.tex 11/9/2007 18: 51 Page 276 Piqué (1999) [910] [911] Piqué (2002) [912] Mercado (2005) [914] (2005) [913] Wu (2001) Toftmann µ m; (for PEG 2 of previous research with a µ m) were fabricated overview of previous research with a table atures, observed phenomena, comments References overview Deposition ambient:Ar or Arvapour,50 saturated mTorr;50–100-nm with thick water films were deposited; it was possible to depositchemical polymers changes without and withcontrol; submonolayer a thickness short table of process parameters is presented 250- µ m dots of immobilizeda HRP,in the polymer form composite (500 of nm)(polyurethane, 20 with a protective coating Deposition ambient: vacuum; only Alq3 underwent some degradation during deposition, thecompounds other did not suffershort any chemical changes; a of deposited materials andpresented deposition conditions is Deposition rate was 0.3–1.1 ng/cm Depositions were conducted in Arpermeation at chromatography 100 (GPC) mTorr; gel with refractive index (RI) detection revealed ato significant 95%) change in molecular (up weightprocess; of severe PLGA non-uniformity during of deposition achievedsupport films the spallation mechanism of MAPLE concentration in water 0.5–4 wt%);particle the structures film of had achemical particle structure size of up the tothe deposits 5–10 un-irradiated was close PEG to that of 2 xamples). 2 , angle , ◦ 2 2 2 , , , 2 2 2 ◦ spot 0.05 cm 6 ns, spot size 0.8–1.9 mm 1–15 Hz, 0.1–0.4 J/cm 5 Hz, 0.1–1 J/cm 2.5–10 J/cm 10–500 mJ/cm 0.4–2 GW/cm of incidence 45 angle of incidence 45 1–20 Hz, 10–500 mJ/cm beam parameters Novel fe ArF,20 ns; 1–5 Hz, sition (MAPLE) (e evaporation depo Si (111) and NaCl KrF,248 nm, 30, or Si Si (100), NaCl KrF,248 nm, 25 ns, Substrates Laser type and Glass, fused silica ArF,193 nm, 20 ns, for films C) C) Quartz, Si 355 3 ω -Nd:YAG, nm, ◦ ◦ C) Cto ◦ ◦ sted pulsed-laser alcohol (100–200 K) − 160 (220–240 K) NPP); water (for ppy), glycerole/ phosphate buffer (for BSA); ( − 40 Chloroform ( ∼ 120 K) Tert-butyl Water ( − 20 Water ( − 50 -glycolide) Frozen matrix-assi -(4-nitrophenyl)-(L)-prolinol N Compounds Matrix SXFA polymers Glucose, sucrose, dextran PEG, HRP/PEG Water NPP,ppy,Alq3, BSA Chloroform (for PEG PLGA Notations MAPLE – matrix-assisted pulsed-laserSXFA evaporation – fluoroalcoholpolysiloxane NPP – BSA – biotinylated bovine serumppy albumin – polypyrrole PEG – polyethylene glycol PLGA – poly (lactide- co HRP – horseradish peroxidase Table 6.7 Alq3 – tris-(8-hydroxyquinoline) aluminium Ch06-I044498.tex 11/9/2007 18: 51 Page 277

Surface modification, deposition of thin films, welding, and cladding 277

Laser pulse

Transparent Laser transferred ‘ribbon’ material

Material to Objective Micromachined be deposited channel

Substrate

Figure 6.6 Schematic diagram of the LIFT (MDW) process [911]. Material to be deposited is pre-coated on a quartz plate and is transferred using a single laser pulse onto a receiving substrate placed parallel and in close proximity to the target film (distance ∼100 µm) under air or vacuum conditions. © Elsevier.

minimize the irradiation damage to the film material and to softly desorb the solute material. The matrix can also be an adhesion promoter, or an immobilization medium. The spatial resolution of the deposited patterns of 10 µm can be routinely achieved. By translating the substrate with respect to the laser any features can be directly written. Laser transfer is a ‘clean’, one step process, not limited to oligomer structures [911, 915–917]. A preferential application of LIFT has been the fabrication of protein patterns for biosensors. Protein-based biosensors consist usually of a dot array of proteins immobilized onto a solid substrate and capable of binding specifically to a target biomolecule. Detection of the bound analyte can subsequently be performed using various methodologies such as fluorescent, immunoenzymatic, and chemiluminescent labelling techniques. Such sensors are used for rapid detection and identification of proteins as required for many biomedical applications such as clinical diagnostics,drug discovery,and proteomic analysis. Commonly,protein microarrays are fabricated by pin microspotting, ink-jet printing, or photolithography. Laser transfer technique serves as an alternative to these techniques being simple and rapid [916].

6.3 Welding and Cladding Under Water

Welding and cladding in contact with liquids is not known to bring along any benefits, but there may be a need to do these operations under water at repair of underwater constructions (e.g. offshore platforms, floating structures and nuclear reactors) [918–922]. Compared with the other underwater welding methods, underwater laser welding is characterized by its low-heat input, which is a key to reduce the sensitivity of stainless steel to stress corrosion cracking [923]. Laser underwater welding is commonly performed using a local dry zone, but can be in principle carried out also without it (Fig. 6.7). However, at welding the temperature rises up to 10 000◦C what causes thermal dissociation of water. The gas bubble at underwater welding is estimated to contain up to 80 per cent of hydrogen that dissolves easily in melt and causes brittleness of the weld joint [502]. Szelagowski and Sepold [924] report about welding of 6-mm thick St 52-3 (A440) steel in contact with water by 4-kW CO2-laser at pressures 0.5–2.5 bar. The incorporated hydrogen amounted 15–20 ml/100 g weld. In order to avoid the entering of water into the welding zone, special welding heads have been developed (Fig. 6.8). However, the local dry zone may not guarantee an hydrogen-free weld. At a 32-kW Nd:YAG welding of HTS material at feed rate of 22 mm/s having water depth of 460 mm and He shield gas,Whitney and Rhoads [929] measured diffusible hydrogen concentration in wet welds to be about 150 times higher than in dry welds (3.3–6.4 ml of hydrogen per 100 g of wet welded metal; contra only 0.02 ml in dry weld). An increase in tensile strength and hardness throughout the weld was observed as well in the wet case [929]. Ch06-I044498.tex 11/9/2007 18: 51 Page 278 Karaiskou (2003) [915] Serra (2004) [916] Fernández-Pradas (2004) [917] [911] Wu (2001) µ m 100 µ m in size) × µ m µ m were fabricated µ m; protein -lysine coated glass slides L ∼ 50 µ m in diameter containing 40 cells features, observed phenomena, comments References vel were deposited onto glass on nylon coated glass surface Starting film thickness was 10 microarrays with dot size were fabricated on a poly- Patches of 150 were transferred; banana tissue (containingenzyme) PPO paste was transferred ontoresulting a microelectrodes stable biosensor for dopamine Starting film thickness was 250microarrays nm; with DNA spot size of 100 Microarrays of DNA droplets (55–65 (examples). 2 2 2 µ J, spot µ J, spot ClH 3 µ m, 0.8 J/cm µ m NO dYG 355Nd:YAG, nm, 10 ns, 10 40 0.1–0.4 mJ/cm 355Nd:YAG, nm, 10 ns, 10 40 KrF,248 nm, 0.5 ps, 10 mJ, 110 mJ/cm 11 sition (MDW, LIFT) H 4 Ti Ti + + hydrochloride, C film (60 nm) Fused silica ArF,193 nm. 20 ns, film (60 nm) Glass Glass Quartz Substrate for Laser type and 8 O 2 N 16 H SDS 10 + induced forward transfer depo + Hydrogel (for cells), mineral oil (for banana tissue) PBS mixed with glycerol EDTA glycerol Liquid/matrix starting film beam parameters No Tris-HCl, 1 mM Water assisted laser Liquids- graphite + powder Eukaryotic cells, banana tissue pallidum 17 kDa protein antigen Compounds Lambda phage DNA Salmon sperm DNA or cells Treponema Notations LIFT – laser induced forwardPBS transfer – phosphate buffered salineSDS solution – sodium dodecyl sulphate DNA – desoxyribonucleic acid PPO – polyphenoloxidase enzyme EDTA – ethylenediaminetetraacetic acid, C Table 6.8 Tris-HCl – 2-Amino-2-(hydroxymethyl)-1,3-propanediol, Ch06-I044498.tex 11/9/2007 18: 51 Page 279

Surface modification, deposition of thin films, welding, and cladding 279

Laser beam

v Capillary in water

Water

Weld bead Workpiece

Molten material Capillary in workpiece Figure 6.7 Laser wet welding under water layer [924]. The focused laser beam of intensity of ∼106 W/cm2 impinges onto a metallic surface and delivers its energy to the metal. The material will be heated locally to temperatures above the boiling point resulting in a vapour or plasma filled capillary. Through this capillary the laser beam enters the metal and delivers its energy to deeper areas. The process can be carried out even using a CO2-laser; although water is opaque at 10.6 µm wavelength, high-intensity laser beam can ‘bore’ a hole into the water. Reproduced by permission TWI Ltd.

Laser beam

Shielding Gas

Fiber cable Filler

Laser torch

Shieldig water tube Shielding gas tube

Feeding wire (a)

Auxiliary gas Shielding gas Water curtain Working Sensor Working gas gas

Funnel- shaped lamella rings

Substrate

Workpiece (c) (b) Figure 6.8 Devices for underwater laser welding and cladding, developed at (a) Ishikawajima-Harima Heavy Industries, Ltd. (IHI) [925, 926]; (b) Bremer Institut für angewandte Strahltechnik (BIAS) [927] and (c) Hitachi Ltd. [928, 927]. Republished with permission of Atomic Energy Society of Japan. Ch07-I044498.tex 11/9/2007 18: 54 Page 281

CHAPTER SEVEN

Physics and Chemistry of Laser–Liquid–Solid Interactions

Contents 7.1 Laser Beams and Their Propagation 281 7.2 Phase Change Phenomena 288 7.3 Optical Breakdown of Liquids and Plasma 295 7.4 Shock Waves in Liquids and Solids 302 7.5 Laser-Induced Reactions of Carbon with Organic Solvents and Water 306 7.6 Behaviour of Oxides in High Temperature Water and Water Vapour 308

7.1 Laser Beams and Their Propagation

Nomenclature x, y, z – Cartesian coordinates r, θ √– cylindrical coordinates, r2 = x2 + y2, θ = sin y/x i = −1 – imaginary unit ε – dielectric permittivity, ε = εr ε0 −12 ε0 – dielectric permittivity of vacuum, ε0 = 8.8541878176 × 10 F/m εr – relative dielectric constant (permittivity) µ – magnetic permeability, µ = µrµ0 −7 2 µ0 – magnetic permeability of vacuum, µ0 = 4π × 10 N/A (by definition) µr – relative magnetic permeability λ – wavelength k = 2π/λ – wave number√ c – speed of light, c = 1/ εµ √ c0 – speed of light in vacuum, c0 = 1/ ε0µ0 = 299 792 458 m/s (convention) ν – frequency of light ω – angular frequency of light, ω = 2πν E – electrical field vector E(r, z) – electrical field amplitude E0 = E(0, 0) – electrical field amplitude at z = 0, r = 0 H – magnetic field vector H(r, z) – magnetic field amplitude H0 = H(0, 0) – magnetic field amplitude at z = 0, r = 0 P0 – total power transmitted by the beam; for pulses: the maximum total power I0 = I(0, 0) – irradiance power density (intensity of the light) at z = 0, r = 0

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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F0 = F(0, 0) – fluence at z = 0, r = 0 Ep – energy of the laser pulse = τ – pulse duration, full-width half maximum (FWHM), I(τ/2) √I0/2 = = τe – half of the pulse duration, at level 1/e, I(τe) I0/e, τe τ/2 √ln 2 2 2 τe2 – half of the pulse duration at 1/e level, I(τe2 ) = I0e , τe2 = τ/ 2ln2 w – beam radius (locus of E(z, r) = E(z, 0)/e or H(z, r) = H(z, 0)/e,orI(z, r) = I(z, 0)/e2; contains 86.5% of the beam energy = = = 2 w0 – waist radius (focal spot diameter), w0 w(z 0); I(0,√w0) I(0, 0)/e we – waist radius defined by I(0, w√e) = I(0, 0)/e, we = w0/ 2 zR – Rayleigh length, w(±zR) = 2 · w0 b – confocal parameter (depth of focus), b = 2 zR R – wavefront curvature ζ(z) – Gouy phase shift θdiv – divergence – total angular spread of the beam (full-width diffraction angle), = 2θdiv q(z) – complex beam parameter M 2 – beam quality parameter, beam propagation factor, M 2-factor.

7.1.1 Properties of Gaussian beams

TEM00 beam relations (isotropic, linear medium; SI units)

Gaussian TEM00 beam (diffraction limited beam) is the most frequently used approximation of low-power laser beams. However, the beams from high-power lasers may significantly differ from the Gaussian one. Complex amplitude of electrical field (V/m): w −r2 r2 E (r, z) = E 0 exp exp −ikz − ik + iζ(z) (7.1) 0 w (z) w2 (z) 2R (z) Complex amplitude of magnetic field (A/m): w −r2 r2 H (r, z) = H 0 exp exp −ikz − ik + iζ(z) (7.2) 0 w (z) w2 (z) 2R (z)

Energy density (J/m3): 1 W = ε ε E2 + µ µ H 2 (7.3) 2 0 r 0 r in vacuum: 2 2 W = ε0E = µ0H (7.4) Intensity (power density perpendicular to the wavefront) (W/m2) (Figs 7.1 and 7.2): = 1 × ∗ I 2 Re E H , (7.5) w 2 −2r2 I (r, z) = I 0 exp (7.6) 0 w (z) w2 (z) Beam radius: z 2 w (z) = w0 1 + (7.7) zR Ch07-I044498.tex 11/9/2007 18: 54 Page 283

Physics and chemistry of laser–liquid–solid interactions 283

1.0

b I(r, 0) w(z) I 2w 0 0 w0 1/e z 0 div 1/e 2 r z R 0 we w0

Figure 7.1 Intensity distribution in a TEM00 Gaussian beam in the waist region.

z

Figure 7.2 Beam radius dependence on z-coordinate of threeTEM00 Gaussian beams having the same wavelength, but different divergences.

Rayleigh length: π · w2 z = 0 (7.8) R λ Confocal parameter (depth of focus): b = 2zR (7.9) Wavefront curvature: z 2 R (z) = z 1 + R (7.10) z Divergence (rad): w0 λ θdiv = arctan = arctan (7.11) zR πw0 Total angular spread of the beam: = 2θdiv (7.12) Gouy phase shift (rad): z ζ (z) = arctan (7.13) zR Complex beam parameter (m−1):

1 = 1 = 1 − λ i 2 (7.14) q (z) z + izR R (z) πw (z) Total power of the beam (W): I I (0, z) P = πw2I = πw2 0 = πw2 (z) (7.15) 0 e 0 0 2 2 Ch07-I044498.tex 11/9/2007 18: 54 Page 284

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Power transmitted through a circle of radius r = w(z): 2 P (z) = 1 − e P0 ≈ 0.865P0 (7.16)

Real laser beam

For laser beams containing besides TEM00 also higher modes:

2 θreal = M θdiv. (7.17)

Gaussian laser pulse For a laser pulse of both Gaussian spatial and Gaussian temporal shape, (spatial length of the pulse is much −2 greater than zR)[Wm ]: w 2 −2r2 −t2 ( ) = 0 I r, z, t I0 exp 2 exp 2 , (7.18) w (z) w (z) τe Intensity on the beam’s axis, [W m−2]: 2P t 2 2P t 2 ( ) = 0 − = 0 − · . . . I 0, z, t 2 exp 2 2 exp 4ln2 (7 19)(7 20) πw (z) τe2 πw (z) τ

Integral relations for single Gaussian pulses Peak intensity [W m−2] from peak fluence [ J m−2] or pulse energy [ J]: √ √ F 2 ln 2F Ep 2Ep 4 ln 2Ep I = √ 0 = √ 0 = = = (7.21) 0 3/2 2 3/2 2 3/2 2 πτe πτ π we τe π w0 τe π w0 τ Pulse energy [ J] from peak fluence [ J m−2] or peak intensity [W m−2]:

π3/2 2τ = 2 = 1 2 = 3/2 2 = 1 3/2 2 = √I0wo Ep πwe F0 πw0 F0 π I0we τe π I0wo τe (7.22) 2 2 4 ln 2 Peak fluence [ J m−2] from peak intensity [W m−2] or pulse energy [ J]: √ √ πI τ E 2E = π τ = √ 0 = p = p F0 I0 e 2 2 (7.23) 2 ln 2 πwe πw0

Region where the power density exceeds a predetermined value Pth [930] (Fig. 7.3) 1 2E π1/2w2 = p 0 − 2 4 zth π w0 , (7.24) λ Pthτe w2 (z) 2E ( ) = p rth z ln 3 2 2 , (7.25) 2 Pthπ / τeP (r, z, t)

Volume where P > Pth: zth zth 2E = π 2 = π 2 ( ) p . Vth 2 rthdz w z ln 3 2 2 dz (7.26) 0 0 Pthπ / τew (z) Ch07-I044498.tex 11/9/2007 18: 54 Page 285

Physics and chemistry of laser–liquid–solid interactions 285

r th Vth z z th z th

Figure 7.3 Surface of constant power density near the waist of a Gaussian beam.

Time (measured from the laser pulse peak) when laser power in a point (r, z) reaches P > Pth: 2E 2r2 = τ p − . tth e ln 3 2 2 2 (7.27) Pthπ / τew (z) w (z)

7.1.2 Reflection of light (normal incidence) Reflectivity of a vacuum–medium interface

(n − 1)2 + k2 R = , (7.28) (n + 1)2 + k2 where n is the refractive index indicating the phase velocity and k is the extinction coefficient: 1 n2 = · ε2 + ε2 + ε , (7.29) 2 1 2 1 1 k2 = · ε2 + ε2 − ε . (7.30) 2 1 2 1

ε1 and ε1 are the components of the complex dielectric permittivity,

ε = ε1 + iε2. (7.31) k is related to the (linear) absorption coefficient a by 2ωk a = . (7.32) c

Reflectivity and transmittance of an interface between two media

When light is propagating from a medium with refractive index n0 to another medium with refractive index n1, the reflectivity R and transmittance T is given as I n − n 2 R = r = 0 1 (7.33) I0 n0 + n1 I T = t = 1 − R, (7.34) I0 where I0 is the incident, Ir is the reflected, and It is the transmitted light intensity. Reflectivity of still water surface to visible light at normal conditions and normal incidence is about 2 per cent. Ch07-I044498.tex 11/9/2007 18: 54 Page 286

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Reflectivity of two parallel interfaces (e.g. air–water–solid) For light with coherence length smaller than that the distance between the interfaces,

= T1T2τ T 2 , (7.35) 1 − R1R2τ

where T1 is the transmittance of the interface 1, R1 is the reflectance of the interface 1,T2 is the transmittance of the interface 2, R2 is the reflectance of the interface 2, and τ is the transmittance of the medium between the interfaces. According to calculations by Kim and Lee [467], a water layer on aluminium increases the overall surface absorptivity from 0.08 to 0.108.

Reflectivity of liquid–plasma interface

The reflectivity at the liquid–plasma interface, Rlp, can be calculated in frames of Drude model as [931, 259] n − n 2 + k − k 2 = pl l pl l Rlp 2 2 , (7.36) npl + nl + kpl + kl

√ ε + ε2 + ε2 where n = , (7.37) pl 2 ε kpl = , (7.38) 2npl 2  ωp ε = 1 − , (7.39) ω2 + γ2 2  ωp ε = γ , (7.40) ω ω2 + γ2 2 nee ωp = , (7.41) meε0 8kBTe γ = npσc (7.42) πme

where ε and ε are the real and imaginary parts of the dielectric function of plasma, ω is the laser frequency, ε0 is the dielectric constant of vacuum, e is the electron charge, ωp is the plasma frequency, npl and kpl are the real and imaginary parts of the refractive index of plasma, nl and kl are those for liquid, respectively, ne and np are electron and particle density, respectively, γ is the electron-particle collision frequency, and σc is electron-particle collision cross-section.

Light pressure Light (or acoustic) pressure on an interface perpendicular to the propagation direction of the light (sound) is given by I p = W (1 + R) = (1 + R) , (7.43) c where W is the energy density, I is the intensity of light (sound), and R is the reflection coefficient. Ch07-I044498.tex 11/9/2007 18: 54 Page 287

Physics and chemistry of laser–liquid–solid interactions 287

2 2 In vacuum: p = ε0E (1 + R) = µ0H (1 + R) . (7.44)

7.1.3 Propagation of Gaussian beams Transformations of a Gaussian beam in a paraxial linear optical system may conveniently be described by the ABCD-method. Below,an example of finding geometrical relations for a laser beam focused onto a workpiece in liquid is given. If the window is absent, the parameter g should be taken equal to zero (Fig. 7.4). The ABCD-matrix for the interval between the beam waists w0 and wwp (interval a-b-g-h)isgivenas product of the ABCD-matrices of homogeneous intervals and interfaces [932]: ⎡ ⎤ 10 AB 1 h 10 1 g 1 b 1 h 1 a = · ng · · ⎣ 1 ⎦ · · 1 · CD 01 0 01 0 01 − 1 01 nl ng F ⎡ ⎤ b g hF g h ab ag ahF ⎢ 1 − − − a + b + + − − + ⎥ ⎢ F ngF nl ng nl F ngF nl ⎥ = ⎣ ⎦. (7.45) − F 1 − aF nl nl nl Using complex beam parameter q defined for a medium with refractive index n as

1 1 λ = − i 0 , (7.46) q R (z) nπw2 (z)

the parameters q0 and qwp at the locations 0 and wp are related as:  Aq + B 1 C + D 1 q0 = 0 =  . qwp + or (7.47) Cq0 D qwp A + B 1 q0

Taking into account that in our model at the boundaries of the interval a-b-g-h, R(z) =∞(Eq. (7.10)), from (7.46) follows: 1 =− λ0 i 2 , (7.48) q0 πw0 and 1 =− λ0 i 2 , (7.49) qwp nlπwwp

Focusing Beam expander n1 ng lens (optional) Laser w0

wwp F

hg b a

Figure 7.4 Propagation of a Gaussian beam in a model system of liquids-assisted laser processing. In comparison with focusing in air, in liquid the focus spot lies more away from the laser. Ch07-I044498.tex 11/9/2007 18: 54 Page 288

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Using (7.47), λ D C − i 0 2 λ πw2 πw C − iλ D −i 0 = 0 = 0 0 . (7.50) 2 − λ0B 2 − nlπwwp A i 2 πw0 A iλ0B πw0 The equations for real and imaginary parts of (7.50) are: 2 4 + 2 = Re: π w0 AC λ0BD 0, (7.51)

2 4 2 − 2 2 − 2 2 2 − = Im: π w0 A λ0B π nlw0 wwp (AD BC) 0. (7.52) Equations (7.45), (7.51), and (7.52) relate the geometrical and material parameters of the model a, b, g, h, w0, wwp, λ, F, nl, ng.

7.2 Phase Change Phenomena

7.2.1 Overall phenomenology On nanosecond–microsecond time scale, a typical laser-generated transient at a liquid–solid interface looks like in Fig. 7.5. Immediately after laser energy absorption the leading front of excitation may be regarded 1D; later spherical. Decay phase of the bubble is presented in more detail in Fig. 7.6. Nomenclature r1, r2 – liquid–vapour interface curvatures in two perpendicular planes containing the normal to the interface T – thermodynamic temperature T0 – ambient temperature Tv – temperature of the vapour Tvl – temperature difference across liquid–vapour interface p0 – ambient pressure pg – gaseous phase (vapour) pressure pl – ambient liquid pressure ρ, ρ1 – density of the liquid

(a)Toluene (b) (c) Silica loquid glass Shock Shock Shock wave wave wave

Laser Bubble beam 200 m 200 m 200 m

(d) (e) (f)

Bubble 200 m 200 m 200 m

Figure 7.5 Time-resolved optical micrographs of laser ablation of toluene liquid through a glass plate at the delay times of (a) 100 ns, (b) 500 ns, (c) 1.2 µs, (d) 10 µs, (e) 50 µs, and (f) 100 µs [607]. Laser: 248 nm, 30 ns, 1.6 J/cm2 pulse−1. © Elsevier. Ch07-I044498.tex 11/9/2007 18: 54 Page 289

Physics and chemistry of laser–liquid–solid interactions 289

40 s delay

400 s delay

800 s delay

Figure 7.6 Bubble decay at laser ablation of alumina under water [469]. © Elsevier.

ν1 – special volume of liquid σ – surface tension σˆ – accommodation coefficient, ranges 0.02–0.04 for water and lower alcohols [933] α – vaporization coefficient m – particle (atom or molecule) mass Hv – latent heat (enthalpy) of vaporization per unit mass  qi – heat flux across liquid–vapour interface Vlv – change of molecular volume at vaporization, Vlv = Vv − Vl J – nucleation rate (number of nuclei per unit volume and time) αl – thermal diffusivity of the liquid −23 kB – Boltzmann’s constant, kB = 1.3806505(24) × 10 J/K Rg – universal gas constant, Rg = 8.3144 kJ/(kg mol K).

7.2.2 Vaporization from free liquid surfaces Equilibrium vapour pressure (saturated vapour pressure) Clausius–Clapeyron equation (defines the slope of the vapour pressure curve):

dp Hv = . (7.53) dT T Vg − Vl

Saturated vapour pressure: Hvm T0 ps (T) = p0 exp 1 − (7.54) RgT0 T

Dependence of vapour pressure on surface curvature Pressure difference across a curved liquid–vapour interface is given by the Laplace equation (Young–Laplace equation): 1 1 Pg − Pl = σ − . (7.55) r1 r2 Ch07-I044498.tex 11/9/2007 18: 54 Page 290

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Vaporization/condensation rate Hertz–Knudsen equation:  m j =ˆσ [ps (TR) − pv], (7.56) 2πRgTR where j is the intensity of vaporization or condensation (particles per unit area), M is the liquid molar mass, TR is the temperature at the vapour–liquid interface, and ps is the saturation vapour pressure corresponding to the temperature TR. Velocity of surface recession at vaporization [934] ∂x Hvm 1 1 m ≈ αpb exp − × √ . (7.57) ∂t x=0 kB Tb T ρl 2πmkBT

Heat flux to the liquid–vapour interface [554]  ˆ 2  = 2σ Hv m − Pv Vlv qi 1 Tvl. (7.58) 2 −ˆσ Tv Vlv 2πRgTv 2Hv Heat transfer coefficient of a liquid–vapour interface:   = qi hi . (7.59) Tvl

7.2.3 Nucleation of vapour bubbles Definitions Homogeneous nucleation – nucleation in the interior of a uniform substance. Heterogeneous nucleation – nucleation at interfaces or inclusions. Critical nucleus size – nuclei of size smaller than critical shrink spontaneously, and of greater size grow spontaneously. Critical nucleation rate Jcr – rate of nucleation of critical nuclei. Binodal (vapour pressure curve) – the line on the phase diagram where the liquid and vapour are the thermodynamically stable phases. Spinodal – locus of states of infinite compressibility (∂p/∂V )T = 0; spinodal is the boundary of unstable and metastable regions on state diagram. Fluctuations in density,however small they are, will grow spontaneously. Kinetic spinodal (cloud line) – locus in the phase diagram, where the lifetime of metastable states becomes shorter than a relaxation time to local equilibrium. If the surface tension is known, the physical boundary of metastable states in this approach is completely determined by the equation of state only,(i.e. by the equilibrium properties of the system). Fisher limit – homogeneous nucleation limit derived by Fisher [935]; depends on the size of the volume under consideration and the duration of the applied stress. Phase explosion (Explosive boiling) – sharp increase of homogeneous nucleation in a superheated liquid. Homogeneous nucleation Homogeneous nucleation of vapour bubbles occurs if the state of the liquid crosses a certain curve in the pressure–temperature diagram (Fig. 7.7). Different theories predict different nucleation limits; in case of heating by nanosecond and shorter laser pulses, the kinetic spinodal is closest to the observed nucleation onset. Homogeneous nucleation rate (nuclei per time and volume unit) is given by [554]: 3σ 16πσ3 = − J N0 exp 2 , (7.60) πm 3kBTl ηpsat − pl Ch07-I044498.tex 11/9/2007 18: 54 Page 291

Physics and chemistry of laser–liquid–solid interactions 291

50 25 C.P. Binodal C.P. H2O Spinodal 20 0 Kinetic spinodal Nucleation limit 15 (Skripov) 50 Nucleation limit (Zheng) 10 100 Binodal Kinetic spinodal

Pressure (MPa) Spinodal 5 Nucleation limit 150 (Skripov) H O Nucleation limit 0 2 (Zheng) Fisher’s theory 200 5 300 400 500 600 700 560 580 600 620 640 Temperature (K) Temperature (K)

Figure 7.7 Calculated pressure of liquid water along the binodal, spinodal, and kinetic spinodal as a function of temperature [936]. The dotted curve corresponds to the nucleation limit in Fisher’s theory, the circles indi- cate experimental data of Skripov and Chukanov, and the triangles indicate the experimental data of Zheng recalculated in P −T coordinates with the analytic equation of Soul and Wagner. © Elsevier. ∼ νl where η = exp pl − psat (Tl) . (7.61) RT l Feder et al. [937] and Dömer and Bostanjoglo [938] presented an improved formula for nucleation rate for phase explosion situations, taking into account the presence of a Knudsen layer at the liquid–gas interface. The liquid, superheated to a temperature T, was assumed to be exposed to the recoil pressure 0.54 ps(T)of atoms evaporating into a Knudsen layer, with ps(T) being the saturated vapour pressure at temperature T. The equilibrium temperature TE is then determined by ps(TE) = 0.54 ps(T). The vapour was approximated by an ideal gas. Then the stationary homogeneous nucleation rate of critical bubbles becomes    ρ (T) 2σ H 16πk Tσ3 ˙ = − v − B N exp exp 2 , (7.62) 0.54 m πm kBT 3 0.54ps (T) g

where Hv(T) is the atomic evaporation enthalpy, T  g = Hv T dT. (7.63) Tg

However, in laser processing situations, for example in cleaning, the exact value of nucleation rate is of minor influence on the experimentally observable nucleation threshold, because the exponential rise of the nucleation rate with superheating leads to an extremely sharp increase over many orders of magnitude within a narrow temperature interval [80]. In water and lower alcohols under typical circumstances, for example, a temperature increase of 1oC causes the nucleation rate to increase three orders of magnitude [554].

Heterogeneous nucleation Heterogeneous nucleation rate is given by [554]: N 2/3 (1 + cos θ) 3Fσ 1/2 16πFσ3 = 0 − J exp 2 , (7.64) 2F πm 3kBTl ηpsat − pl Ch07-I044498.tex 11/9/2007 18: 54 Page 292

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20

15

10

5 Distance from the Au surface (nm) 0

90 ps 115 ps 140 ps 165 ps

Figure 7.8 Snapshots from the molecular dynamic (MD) simulation of 24 water layers on a Au(111) surface suddenly heated to 1000 K. The time between successive frames is 25 ps. © American Chemical Society (2001), Reprinted with permission from Ref. [939].

1 where F = F (θ) = 2 + 3 cos θ − cos3 θ , (7.65) 4 2/3 where θ is the contact angle of the liquid at the interface and N0 is the number of molecules per unit area at the interface. 22 −3 −1 In laser cleaning, a nucleation rate Jcr = 10 m s was measured at Si–water interface [80]. Likely to homogeneous nucleation, also here an exponential increase over many orders of magnitude in a very narrow temperature interval is observed, giving rise to a relatively sharp nucleation threshold [80]. At intense short pulse irradiation of a solid–liquid interface, no vapour bubbles, but a continuous vapour layer formation is observed and predicted by MD-simulations (Figs 2.37, 2.38, and 7.8).

7.2.4 Bubble dynamics Bubble in an infinite space Bubbles created in bulk liquid by laser pulses or by cavitation, expand and shrink periodically as shown in Fig. 7.9. In many liquids, thereby in water and in alcohols, the bubble emits a short light pulse (sonoluminescence) and shock wave every time it collapses. Dynamics of a spherical bubble much smaller than the sound wavelength is given by Rayleigh–Plesset equation [941]: d2R 3 dR 2 1 4η dR 2σ + = − − ( ) − − R 2 pg P0 P t , (7.66) dt 2 dt ρl R dt R

with notations: ρl is the density of the liquid, pg is the pressure in the gas, assumed to be spatially uniform, P0 is the background static pressure (usually 1 bar), P(t) is the pressure in the neighbourhood of the bubble, η is the shear viscosity,and σ is the surface tension of the gas–liquid interface. The bubble growth velocity becomes [554] dR 2 [T − T (P )] H ρ = 0 s 0 · v v . (7.67) dt 3 Ts (P0) ρl Ch07-I044498.tex 11/9/2007 18: 54 Page 293

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Bubble Shock wave

R

t

Figure 7.9 Bubble pulsation in a bulk liquid. Every time the bubble collapses, a short light pulse (∼150 ps) and a shock wave are generated in many liquids, thereby in water. After Isselin et al. [477] and Brujan [940].

Equation (7.66) does not consider the energy dissipation through heat conduction, viscosity,etc. Leiderer et al. [80] achieved better match with experiment by 2 2 3γ d R + 3 dR = 1 R0 − t − R 2 pmax exp p0 , (7.68) dt 2 dt ρl R τ

where γ is the polytropic exponent. The energy loss was accounted by the relaxation time τ; τ =∞ corresponding to the adiabatic model.

Bubble at a heated surface Carey [554] gives a formula for bubble growth on a heated surface (constant temperature): √ = −1/6 R(t) 0.470 Ja Prl αlt, (7.69)

[T0 − Ts (P0)]Cplρl where Ja is the Jakob number, Ja = , (7.70) ρvHv ν and Pr is the Prandtl number, Pr = , (7.71) α where ν is the kinematic viscosity and α is the thermal diffusivity. Heat transfer controlled growth of a hemispherical bubble on a heated surface has been analysed numerically by Robinson and Judd [942]. Veiko et al. [156] present a differential equation for the equilibrium shape of a bubble on an heated surface, taking into account the wetting angle.

Bubble decay at interfaces When a bubble collapses at a solid boundary, a liquid jet, directed to the boundary develops (Fig. 7.10). At millimetre-size bubbles the jet velocity ranges up to 200 m/s (depends on bubble radius and on the distance to the wall) and can cause damage even of hard materials (cavitation erosion) [471, 943]. Ch07-I044498.tex 11/9/2007 18: 54 Page 294

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t

Figure 7.10 Collapse of a gas/vapour bubble near a rigid boundary. Schematically after Blake et al. [946]. The jet diameter is about one-tenth of the bubble initial diameter. As the investigations by Tomita and Shima [947] indicate also hemispherical bubbles generate a liquid jet at solid boundary.

Liquid jet is formed also at bubble (gravitational) detachment from a heated surface [944] and at bubble collapse near a free liquid surface [945]. The impact pressure of the liquid jet is given by the formula [609, 477]:

ρlCl · ρsCs P = · vjet, (7.72) ρlCl + ρsCs

where (ρlCl), (ρsCs) are, respectively, the acoustical impedances of water and solid material. For a perfectly rigid wall an assumption (ρlCl)  (ρsCs) can be made. Thus Eq. (7.72) becomes:

P = ρl · Cl · vjet. (7.73)

Chen et al. [948] measured the microjet impact pressure 320–490 MPa for laser pulse energy in range of 5–22 mJ (iron in water; laser: 1064 nm, 30 ns). Bubbles collapse induced flow near a solid boundary was investigated by Ohl et al. [19]. The tangential to boundary flow velocities were highest during the time interval of jet impact and ranged up to ≈10 m/s at maximum bubble size of 2 mm.

Relict microbubbles After a bubble decays near a solid boundary, many microbubbles with initial radii between 5 and 150 µm remain for hundreds of microseconds [10, 949]. The next laser-induced pressure transient forces these bubbles to collapse, causing a plurality of small cavitation erosion pits over an extended area around the initial bubble epicentre [477]. The lowering of acoustical cavitation threshold by relict microbubbles is called memory effect in cavitation. Antonov et al. [950] observed that also after optical breakdown in bulk water the breakdown threshold for successive pulses remained ∼3 times lower than the initial threshold (Nd:YAG-laser, 15 ns). The initial threshold recovered in a day. According to Bunkin and Bunkin [951], if a liquid with dissolved gas contains small amounts of electrolytes (in concentrations of ∼0.01 ppm), whose ions have surface-active properties, under equilibrium conditions it should contain stable microbubbles of a free gas (called ‘bubbstons’). Thus, after optical breakdown the water decomposition products may form long-live bubbstons that lower the breakdown threshold for successive pulses.

Chemical reactions induced by bubble collapse Temperature in collapsing bubbles is estimated to rise up to 6000–20 000 K [952], which causes the dissociation of the liquid. According to Mason and Peters [953], the following reactions occur at bubble collapse in pure water: . . H2O → HO + H . + → . H O2 HO2 . 2HO → H2O2 . → + 2HO2 H2O2 O2 Ch07-I044498.tex 11/9/2007 18: 54 Page 295

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7.3 Optical Breakdown of Liquids and Plasma

Nomenclature ne – electron density ρv – electron density in valence band (of the liquid) ρc – electron density in conduction band (of the liquid) ni – ion density na – density of neutral atoms gi – partition function for single ionized atoms ga – partition function for neutral atoms −31 m, me – electron mass, 9.1093826(16) × 10 kg −23 kB – Boltzmann’s constant, kB = 1.3806505(24) × 10 J/K h – Planck’s constant, h = 6.6260693(11) × 10−34 Js
– Dirac’s constant,
= h/2π = 1.054 571 628(53) × 10−34 Js T – thermodynamic temperature Tp – plasma temperature; it is assumed here Tp = Te = Ti ν – frequency ω – angular frequency −12 ε0 – dielectric permittivity of vacuum, ε0 = 8.8541878176 × 10 F/m c – speed of light In dielectric liquids, which are of main interest in laser processing, the ionization (plasma formation) is possible by (1) direct ionization of the liquid by multiphonon or tunnel ionization, and/or by (2) cascade ionization (avalanche ionization) via inverse Bremsstrahlung absorption. The latter mechanism needs one or more ‘seed’ electrons generated by thermal ionization of impurities or by multiphonon ionization, depending on the purity of liquid (after Sollier et al. [260]).

7.3.1 Photoionization of a dielectric liquid For photon energies below the ionization potential (for water, E = 6.5 eV), free electrons have to be generated by multiphoton or tunnel ionization. The time-averaged ionization rate for a field with angular frequency ω and intensity I acting on an electron density ρv − ρc in the ground state is given by Keldysh equations [954]     3/2 dρ 2ω 1 + γ2 mω ˜ c = × γ
Q ,
dt photo 9π γ ω ⎧ ⎫ ⎪   ⎪ ⎨⎪ K √ γ − E √ γ ⎬⎪ ˜ 1+γ2 1+γ2 × (ρv − ρc) exp −π + 1 × , (7.74) ⎪
ω ⎪ ⎩ E √ 1 ⎭ 1+γ2

where ⎧ ⎫ ⎪ γ γ ⎪ ∞ ⎨⎪ K √ − E √ ⎬⎪ π 1+γ2 1+γ2 Q (γ, x) = × exp −πn ⎪ ⎪ 2K √ 1 n=0 ⎩ E √ 1 ⎭ 1+γ2 1+γ2 π (2 x + 1 − 2x + n) ×  (7.75) 2K √ 1 E √ 1 1+γ2 1+γ2 Ch07-I044498.tex 11/9/2007 18: 54 Page 296

296 Handbook of Liquids-Assisted Laser Processing

Here x represents the integer part of the number x, K and E denote elliptic integrals of the first and second kinds, and  denotes the Dawson probability integral,

z  (z) = exp y2 − x2 dy. (7.76) 0 At room temperature the initial steady-state free electron density in the conduction band resulting from the Boltzmann distribution is negligible. Thus, the steady-state electron density in the ground state corresponds to 23 −3 the total electron density ρv = 6.68 × 10 cm [955]. The Keldysh parameter γ and the effective ionization potential ˜ for creating an electron–hole pair in condensed matter exhibiting a band structure (e.g. water) are given by  ω cε m γ = 0 (7.77) e 4I

and    2 1 + γ2 1 ˜ = E  . (7.78) π γ 1 + γ2 where I is irradiance and is bandgap energy.

7.3.2 Cascade ionization (avalanche ionization) As soon as free electrons exist in the interaction volume,they gain kinetic energy through inverse Bremsstrahlung absorption of photons and can generate further free electrons through impact ionization once their energy exceeds the critical energy.The ionization rate per electron participating in the cascade is then given by (case electron-ion inverse Bremsstrahlung) [955]: 1 e2τ m ω2τ ηei =  I − c , (7.79) IB 2 2 + ˜ ω τ 1 cn0ε0mc 3 2 M

where τ is the time between collisions, c is the vacuum speed of light, I is irradiance, and n0 is the refractive index of the medium at frequency ω. The masses of the electron and the liquid molecules are m and M, respectively. For large irradiances, the cascade ionization rate is proportional to I (afterVogel et al. [956]). Net absorption coefficient for electron-ion inverse Bremsstrahlung is given by [957, 959]  n2e6g m
ω aei = e e 1 − exp − , (7.80) IB 3
3 2 6ε0c ω me 6πkBTp kBTp where g is average Gaunt factor √ 3
ω
ω g (ω, Te) = exp K0 , (7.81) π 2kBTe 2kBTe

where K0(x) is the modified Bessel function. ei Alternatively, aIB may be expressed as [958] 2
ω ei ≈ · 3 Znine − − aIB C λ 1 exp , (7.82) Tp kBTp √ 2 2e6 where C ≈ √ √ ≈ 1.37 × 10−35 when λ is in micrometers. 4 3/2 3 3π
c me kB Ch07-I044498.tex 11/9/2007 18: 54 Page 297

Physics and chemistry of laser–liquid–solid interactions 297

The electron-atom inverse Bremsstrahlung absorption coefficient is given by Wu and Shin [259]  e2n n σ 8k T aea = e i c B e , (7.83) IB πmcv2 πm where c is the speed of light in vacuum and ni is the total number of ions. 7.3.3 Photoionization absorption coefficients of atoms Photoionization absorption coefficients of atoms produced by thermal dissociation of the liquid, may be calculated as [259, 957]   ∞ 3 − 1 θ 2 −θ a = 7.9 × 10 22 i,a n exp a,i  , (7.84) pi 2 a 2 Z nhν ga kBT p 1 − 1 n n=n1 where  n = integer θi,a hν . (7.85)

and θa,i is ionisation potential of particle i. Equation (7.85) states that the lower limit in summations is determined from the condition that the photon energy is greater than the binding energy of the electron in the atom. The total absorption coefficient at is the sum of the electron-ion and electron-atom inverse Bremsstrahlung absorption coefficients and of photoionization absorption coefficient, = ei + ea + at aIB aIB api. (7.86) 7.3.4 Thermal ionization Near laser heated surface, the generation of plasma by thermal ionization is the usual case. Equilibrium electron and ion concentrations in plasma are expressed by Saha’s equation [959]: 3 2πm k T 2 neni = 2gi e B p − θi 2 exp , (7.87) na ga h kBTp

where θi is ionisation energy of atom i, gi is the electronic partition function of ion, gi = 1, and ga is the electronic partition functions of atom, given by ∗ n θ 1 g = 2n2 exp − i 1 − , (7.88) a k T n2 n=1 B p where √ ∗ Z 3 np n =∼ , (7.89) a0 and a0 is the Bohr radius.

7.3.5 Diffusion loss of electrons from the plasma The diffusion loss of electrons depends on the shape of the plasma region. In bulk liquid, the plasma region may be considered elliptical (Fig. 7.3). In the model of Kennedy [955], the ellipsoid was approximated with a = 2 cylindrical volume with radius w0 (beam waist radius) and length zR πw0 /λ (Rayleigh length of the laser beam). This led to the following expression for the diffusion rate per electron 2 2 2τεav 2.4 1 ηdiff = + . (7.90) 3me ω0 zR

The same equation may be applied also in case of irradiation of a solid surface in liquid, using instead zR the actual thickness of the plasma. Ch07-I044498.tex 11/9/2007 18: 54 Page 298

298 Handbook of Liquids-Assisted Laser Processing

7.3.6 Recombination loss At calculation of optical breakdown in water,Vogel et al. [956] used for the recombination rate an empirical value determined by Docchio through inspection of the decay of the plasma luminescence [960], ρ d C =− × −9 3 × 2 2 10 cm /s ρc . (7.91) dt rec In reality, recombination of free electrons in water is not a one-step process but consists in hydration of the electron within about 300 fs and subsequent decay of the hydrated state that has an average lifetime of ≈300 ns [961].

7.3.7 Thermal conductivity of the plasma

The plasma electron conductivity λe can be calculated by the Spitzer–Härm expression [962], 2 3/2 (k T )5/2 k λ = δ 20 √ B e B , (7.92) e T π me4Z (ln )

where ln  is the Coulomb logarithm, 3  =  , (7.93) 3 3 3 2e kBTe πne

Z is the average charge of ion and δT = 0.225 when Z = 1. When <1, the Spitzer–Härm expression is not valid, and thermal conductivity can be calculatedas [963]    √ −1 5 2 k (k T )5/2 52 16 2 λ = √B B e + e 4 , (7.94) 2 π meZe R 15 15 Z

1 η − 1 − ln η 1 where R = · , η = , (7.95) 2 (1 − η)2 λ2 λ λ = D , (7.96) bc

kBT λD = , (7.97) 2 2 4πe ni Z + Z

Ze2 bc = . (7.98) 3kBT

7.3.8 Rate equation for free electrons

The time evolution of the electron density ρc in the conduction band of a liquid under the influence of the laser light is in generic form given by [964, 956] dρc = dρc + dρc + dρc + dρc + dρc dt dt photo dt therm dt casc dt diff dt rec ρ ρ = d c + d c + − − 2 ηcascne ηdiff ne ηrecne . (7.99) dt photo dt therm Ch07-I044498.tex 11/9/2007 18: 54 Page 299

Physics and chemistry of laser–liquid–solid interactions 299

Definitions of the terms: 1st term:production of free electrons mediated by the strong electric field in the laser focus (photoionization via multiphoton and tunnelling ionization). 2nd term: production of free electrons by thermal ionization. 3rd term: production of free electrons by cascade ionization. 4th term: diffusion loss of free electrons. 5th term: recombination loss of free electrons. The cascade ionization rate ηcasc and the diffusion loss rate ηdiff are proportional to the number of already 2 produced free electrons, while the recombination rate ηrec is proportional to ρc , as it involves an interaction between two charged particles (an electron–hole pair) (citation fromVogel et al. [956]). One speaks of optical breakdown when a critical free electron density of 1018 − 1020 cm−3 is exceeded during the laser pulse [260].

7.3.9 Internal energy density of electrons and particles in plasma [965, 259]

3 E = n k T + n θ (7.100) e 2 e B e i i 3 E = n k T + n E (7.101) p 2 p B p p,0 l,diss

where summation in (7.100) is over all particles in the plasma, θi is the ionisation energy of atom i in plasma, and El,diss is the total dissociation energy for the molecule of the liquid.

7.3.10 Energy balance equation for electrons Electrons gain energy by absorption of the laser light and loose energy by collision with atoms and ions, via conduction, radiation, and plasma expansion. For a water-confined plasma of thickness L at a solid surface, the energy balance equation for electrons was given by Wu et al. as follows [259]:

d (LU ) e = I 1 − R [1 − exp (−a L)] + I 1 − R exp (−a L) R dt wp t wp t c 3  − k T − T v n L − q − q − (1 − R ) σT 4 − 1 − R σT 4 2 B e p tr e cdc cdw c e wp e − Pe uw,pre + uwev + uc,pre + ucev , (7.102)

2me vtr =  , (7.103) mp,avenpσc 8kBTe πme

with notations: L is the thickness of plasma layer, Ue is the energy density for electrons, I is the laser power  density, Rlp and Rlp are the liquid–plasma interface reflectivity to laser and plasma radiation, respectively,  Rc and Rc are the solid surface reflectivity to laser and plasma radiation, respectively, σ is the Stefan–Boltzmann constant, Pe is the partial pressure of electrons, at is the total absorption coefficient, and qcdc and qcdw are the heat flux conducted from plasma to the solid surface and liquid surface, respectively, vtr is the electron-particle energy transfer frequency, mp,ave is the average particle mass, σc is the electron-particle collision cross section, uw,pre and uwev are the pressure- and evaporation-caused receding velocities of the liquid surface and uc,pre and ucev are the pressure- and evaporation-caused velocities of the solid surface. Ch07-I044498.tex 11/9/2007 18: 54 Page 300

300 Handbook of Liquids-Assisted Laser Processing

7.3.11 Heat flux conducted from plasma to adjacent matter [966, 967, 259] Wu and Shin [259] used in simlation of laser peening in water confinement the relation Te − Tm kBTe qc = min λe , fnekBTe , (7.104) 0.5L me

where Tm is the temperature of the adjacent medium, and f is a dimensionless number ∼0.03–0.1 [966]. The total pressure of plasma P is the sum of the electron partial pressure and the particle partial pressure

P = Pe + Pp = kBTene + kBTpnp, (7.105) where the subindex p denotes particles. Plasma models used for simulation of laser peening were described in Section 3.3.6.1.

7.3.12 Dependence of optical breakdown threshold on laser pulse length Calculated and measured optical breakdown thresholds for bulk water are presented in Fig. 7.11. Optical breakdown is a stochastic process and it depends on hard to avoid particulate impurities in the liquid; at low laser fluences it may not occur at every laser pulse. The fluence, at which breakdown occurs at every pulse, may be 10 times higher than the minimum fluence at which breakdown becomes possible [968]. Table 7.1 presents a comparison of optical breakdown thresholds of some common solvents.

7.3.13 Factors affecting the breakdown threshold in liquids Optical breakdown thresholds in liquids are lowered by suspending particles [969, 930] and by dissolved gases [970, 971]. Bunkin and Lobeev [968] studied the probability of Nd:YAG-laser breakdown in water in dependence on temperature and on dissolved electrolyte concentration. According to Kennedy et al. [972] the impurities

105 1014

104 ) ) 2 2 1013 103

102 1012 101

100 1011 Breakdown threshold (J/cm 101 Breakdown threshold (W/cm

102 1010 1014 1013 1012 1011 1010 109 108 Pulse duration (s)

Figure 7.11 Optical breakdown thresholds for bulk water. The circles are experimental data in W/cm2. Solid 21 13 lines are calculated dependencies for 800 nm wavelength using critical electron density ρcr = 10 cm . AfterVogel et al. [956]. Ch07-I044498.tex 11/9/2007 18: 54 Page 301

Physics and chemistry of laser–liquid–solid interactions 301

Table 7.1 Relative to water optical breakdown thresholds in various liquids for Nd:YAG-laser pulses (calculated from the data by Bunkin and Lobeev [968]).

Liquid Ith/Ith, water Water 1.00 Heptane 0.4 Ethanol 0.47 Benzene 0.36 Carbon tetrachloride 0.28

in water affect the breakdown thresholds for pulse lengths greater than 10–100 ps, but not for shorter pulses (1064 nm wavelength). For pure water, the calculations by Vogel et al. [956] showed that laser wavelength starts to influence the breakdown threshold only beginning from 1 to 10 ps pulse length.

7.3.14 Temperatures and pressures at laser breakdown and ablation in water Figures 7.12 and 7.13 and Table 7.6 present some examples of temperatures of laser beakdown and processing plasmas. Data on plasma pressures can be found in Figs 3.16–3.18 and in Table 7.6. Figure 7.14 shows the spatial distribution of luminescence of a laser-induced plasma at a solid–liquid interface. Compared with laser plasmas in air or in vacuum, the confined plasmas by liquids or solids have higher temperature, density,and pressure. The results of some experimental work on laser-generated plasmas at solid–liquid interfaces and in sus- pensions are summarized in Table 7.6. The observations of Sakka et al. [974, 470] have shown that the typical plasmas occurring at laser processing in liquids are neither thin nor dense – there is a broadened line spectrum with self-absorption reversed dips on a continuous background.

20 000

10 000 Plasma temperature (K) Plasma temperature

5000 0.1 1 10 100 1000 Laser pulse energy (mJ)

Figure 7.12 Measured maximum plasma temperature as a function of laser pulse energy at optical breakdown in bulk water. Schematically after Kennedy et al. [972]. Ch07-I044498.tex 11/9/2007 18: 54 Page 302

302 Handbook of Liquids-Assisted Laser Processing

15 000 Ramp-up, z 0 Ramp-up, z 100 nm Pamp-down, z 0 Ramp-down, z 100 nm Rectangular, z 0 10 000 Rectangular, z 100 nm t 30 ns

5000 Temperature, T(r,z,t) (K)

0 0 0.2 0.4 0.6 0.8 1 Radius, r (mm)

Figure 7.13 Calculated by an analytical model radial temperature distributions at a distance z = 0 and z = 100 nm over a laser irradiated iron target in water. Laser: τ = 30 ns, Pave = 50W,spot size r0 = 1 mm; pulse shapes: ramp-up, ramp-down, and rectangular [384]. © Elsevier.

21 ns 40 ns

60 ns 80 ns

100 ns

0.5 mm

Figure 7.14 A series of images of the light-emitting region generated by the irradiation of a pulsed Nd:YAG-laser to a graphite target in water. Exposition time for each frame was 13 ns. A white broken line indicates a rough estimation of the position of the target surface [973]. © Elsevier.

7.4 Shock Waves in Liquids and Solids

Nomenclature ρ0 – density ahead the shock front ρ – density behind the shock front m˙ – mass flux of the material passing through the shock wave p0 – pressure ahead the shock front p – pressure behind the shock front e0 – specific internal energy ahead the shock front e– specific internal energy behind the shock front Us – shock velocity up – particle velocity behind the shock front Ch07-I044498.tex 11/9/2007 18: 54 Page 303

Physics and chemistry of laser–liquid–solid interactions 303

u0 – relative to shock front particle velocity ahead the shock front, u0 =−Us u – relative to shock front particle velocity behind the shock front, u = up − Us h – enthalpy ht – total enthalpy v0 – specific volume ahead the shock front v – specific volume behind the shock front εxx – xx-component of the strain tensor σxx – xx-component of the stress tensor µ, λ – Lamé constants.  – Grüneisen coefficient (Mie-Grüneisen coefficient) Shock waves in liquid-assisted laser processing are commonly considered as a discontinuity of material prop- erties, density,pressure, particle velocity,and internal energy in the space. This is justified by circumstance that the shock front width in liquids and solids is of order of only few angstroms. The properties of matter at both sides of the shock front are related by following conservation relations [975]: Conservation relations Conservation of mass: ρ0Us = ρ Us − up =˙m (7.106) Conservation of linear momentum:

p − p0 = ρ0Usup (7.107) Conservation of energy: 1 pu = ρ U u2 + e − e (7.108) p 0 s 2 p 0 For solids, the last two equations may be written also (for shock propagating in x-direction) [976]

σxx = p0 + ρ0Usup (7.109) 1 ρ U e − e + u2 = σ u (7.110) 0 s 0 2 p xx p Rankine–Hugoniot relations (Conservation relations in moving with shock front coordinates)

ρu = ρ0u0 (7.111) + 2 = + 2 p ρu p0 ρ0u0 (7.112) p + + 1 2 = p0 + + 1 2 e u e0 u0 (7.113) ρ 2 ρ0 2 Bernoulli’s equation 1 1 h + u2 = h + u2 = h (7.114) 2 0 2 0 t Hugoniot equation 1 e − e = p − p (v − v) (7.115) 0 2 0 0 Rayleigh equations − 2 2 = 2 2 = 2 2 =−p p0 ρ0Us ρ0u0 ρ u (7.116) v − v0 Ch07-I044498.tex 11/9/2007 18: 54 Page 304

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4 Snay & Rosenbaum (1952) Rice & Walsh (1957) 12 Nagayama et al (2002 Bloom & Keeler (1974) Sound speed at 1pm & 20C 11 Ref. [977] (Flyer impact method) Linear fit of all data 3 10

9

Water8 Iron 2 7 Shock velocity (km/s) velocity Shock Shock Velocity (km/s) Velocity Shock

Linear fit of all data 6 D 1471 1.956u 1 5 0 0.2 0.4 0.6 0.8 1 12345 Particle velocity (km/s) Particle velocity (km/s) (a) (b)

Figure 7.15 (a) Shock velocities as a function of particle velocity for water. © American Institute of Physics (2004), reprinted with permission from Ref. [977]. (b) Shock velocities as a function of particle velocity for iron [978]. Open circles are the reprocessed Los Alamos standards data. Filled circles are the two stage light–gas gun data. Experimental uncertainties lie within the symbol size. Dashed line is linear fit and solid line is quadratic fit. © American Institute of Physics (2000), reprinted with permission from Ref. [978].

Gain in the kinetic energy per unit mass of the material by the passage of the shock wave in the laboratory frame coordinates: 1 1 U 2 = (u − u )2 = p − p (v + v ) (7.117) 2 p 0 2 0 0 Loss in the kinetic energy per unit mass of the material by the passage of the shock wave in shock front-fixed coordinates: 1 1 u2 − u2 = p − p (v + v ) (7.118) 2 0 2 0 0 Shock impedance

Z = ρ0Us (7.119) In liquids and solids, the relation between shock and particles velocity can often be approximated by a linear function (cf. Fig. 7.15 and Table 7.2).

Us = C0 + Sup, (7.120) where C0 is speed of the sound ahead the shock wave. Using Eq. (7.120) and jump conditions at the shock front, the Hugoniot pressure and internal energy may be expressed as [273, 976]

ρ C2η p = 0 0 , (7.121) (1 − Sη)2 ηp e = , (7.122) 2ρ0 where V ρ η = 1 − = 1 − 0 . (7.123) V0 ρ Ch07-I044498.tex 11/9/2007 18: 54 Page 305

Physics and chemistry of laser–liquid–solid interactions 305

Table 7.2 Relation between shock and particles velocities for some liquids [979, 980].

Liquid Shock velocity (m/s)

Acetone Us = 1940 + 1.38 up

Ethanol Us = 1730 + 1.75 up

Ether Us = 1700 + 1.46 up

Ethylene glycol Us = 2150 + 1.55 up

Mercury Us = 1750 + 1.72 up

Liquid oxygen Us = 1880 + 1.34 up

Water Us = 1483 + 1.79 up

(Mie)–Grüneisen equation of state Equation of state for shock-compressed bodies with linear Us(up) relationship (Eq. 7.120) can be derived from Mie–Grüneisen equation  (V ) p (V ) = p (V ) + e (V ) − e (V ) , (7.124) 0 V 0 using modified Rankine–Hugoniot relation (achieved through elimination of up and Us from Eqs (7.106) and (7.108)), 1 e − e = (V − V ) p + p , (7.125) 0 2 0 0 where V ≡ 1/ρ. Combining Eqs (7.121), (7.124), and (7.125) yields 2 ρ0C0 η η p = p0 (1 − η) + · 1 − + ρ0 (e − e0) . (7.126) (1 − Sη)2 2 In this expression, it is assumed that the shocked matter is in hydrostatic compression; for solids it means that the shock pressure is much larger than the yield strength of the material. Elastic–plastic shock waves in a solid (propagating in x-direction)

Elastic shock wave: σxx = (λ + 2µ) εxx (7.127)

σyy = σzz = λεxx (7.128) If yielding occurs behind the elastic precursor wave, the shock yield stress Y is

Y = 2µεxx (7.129) and hydrostatic pressure at the wavefront 1 2 p = σ + σ + σ = λ + µ ε . (7.130) 3 xx yy zz 3 xx Leonov et al. [571] calculated the shock pressure at laser irradiation of glass–water interface using the formula by Zaharov [981] Ea r0 1 p (r) =  ln 2  , (7.131) Vf r ln r r0

valid if r > df , where r0 = df /2, df is the diameter of the focus spot, Ea is the absorbed laser energy, Vf is the focal volume, and  ≈ 1.5 is Grüneisen coefficient. The shock speed in adiabatic compression approximation Ch07-I044498.tex 11/9/2007 18: 54 Page 306

306 Handbook of Liquids-Assisted Laser Processing

is given by 2 ( ) ( ) U r = p r 1 − , (7.132) 2 2 ρ 2 ρ 2 1/n C0 ρ0C0 − 0C0 + 0C0 1 n p (r) n where the factor n ≈ 7 is valid for water. Models of shock propagation at laser peening were described in the section 3.3.6.2.

7.5 Laser-Induced Reactions of Carbon with Organic Solvents and Water

7.5.1 Reactions of carbon with organic solvents Amongst other possible chemical reactions occurring at liquids-assisted laser processing of solids, the reactions of carbon with organic solvents and water have been studied more extensively. Wakisaka et al. [982] proposed the following reaction schemes between graphite and benzene vapours (A) or liquid benzene (B) at laser irradiation. Reproduced by permission of The Royal Society of Chemistry. The conditions of the experiment are given in Table 7.6:Wakisaka (1993).

Condition A

H C2 C1 C1 C2 CCH

Intermediate 1

Condition B CH3

H C1

C1 CH3 CH3 CH3 C2H5 Intermediate 2 CH C1 3

CH3 CH3 Gaumet et al. [983] have identified the following reactions between carbon clusters of different sizes with benzene. The main reaction product was phenylacetylene. Reproduced by permission of The Royal Society of Chemistry.

H C2

C1 C2 C CH (1)

Intermediate 1 Phenylactetylene

(A) Cn addition to benzene (linear and cyclic)

CH3 * toluene C1* +

CCH phenylacetylene * C2* + CH CH2 styrene Ch07-I044498.tex 11/9/2007 18: 54 Page 307

Physics and chemistry of laser–liquid–solid interactions 307

C CCH3 1-phenylprop-l-yne * C3* +

Indene

CCCCH

1-phenylbuta-1,3-diyne * C4* +

naphthalene

(B) Reaction between Cn

C8H2 C12H2

H(CCCCCC)2 HH (C C)4 H

(C) Reaction between aromatic rings

biphenylene biphenyl

McGrath et al. [984] detected a number of gaseous and liquid reaction products generated by laser irradiation of graphite suspensions in toluene and benzene (Table 7.3):

Table 7.3 Reaction products of laser irradiation of graphite in toluene and benzene [984]. A carbon suspension made from 25 nm diameter particles was used: 133 mg/l for benzene and 200 mg/l for toluene. The amount of gaseous products are expressed as a percentage of the total gas amount of moles. Laser: 1064 nm, 10 ns, 650 mJ, 6000 pulses.

Graphite + benzene Graphite + toluene Gaseous Gaseous products products (%) Liquid products (%) Liquid products

H2 (94.6) 1-Methylene H2 (92.6) 1,2-Dimethylbenzene

CH4 (2.2) H-indene CH4 (4.9) 1-methylene-2- propenybenzene

C2H2 (2.9) naphthalene C2H2 (2.2) 1-propynylbenzene

C2H4 (0.3) biphenyl C2H4 (0.2) 1-methylnaphthalene biphenylene C2H6 (0.1) naphthalene acenaphthylene 2-ethenylnaphthalene 1-methytriphenylene biphenyl 1,1-methylenebisbenzene 4-methyl-1,1-biphenyl biphenylene bibenzyl 2,2-dimethylbiphenyl 9H-fluorene Ch07-I044498.tex 11/9/2007 18: 54 Page 308

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7.5.2 Reactions of carbon with water The studies by Chen et al. [833] revealed the main reactions at 1.06-µm laser irradiation of carbon suspension in water:

C + H2O → H2 + CO,

CO + H2O → H2 + CO2. McGrath et al. [984] identified both gaseous and liquid products generated in a suspension of 25-nm diameter carbon particles in water by a laser beam of 1064 nm, 10 ns, 650 mJ, and 6000 pulses (percentage is of the total molar amount of gas produced). Gaseous products: CO (68%), H2 (25%), C1 (2.0%), C2 (4.4%), C3 (0.2%), and C4 (0.4%). GC-MS was used to detect individual hydrocarbons which were determined to be methane (CH4), ethane (C2H6), ethene (C2H4), ethyne (C2H2), propene (C3H6), 1,2-propadiene (C3H4), 1-propyne (C3H4), 1-buten- 3-yne (C4H4), and 1,3-butadilyne (C4H2). The main product in each hydrocarbon group is highlighted in italics (citation from McGrath et al. [984]). Liquid products: Carboxyl (R-COOH) and ester (R-COO-R) functional groups, arene carbon, alkenes, and alkynes were detected by 13C NMR technique.

7.6 Behaviour of Oxides in High Temperature Water and Water Vapour

It was pointed out by Dolgajev et al. [479] and Hidai and Tokura [478] that at laser ablation in water the hydrothermal dissolution of solids may play an important role. When the temperature and pressure of water rise from normal to supercritical values, the solubility of many oxides, commonly machined by laser, rises several hundred-fold [985, 797] (Table 7.4).

Table 7.4 Solubility of some oxides in pure water at 500◦C and 1000 atm (100 MPa). (After Matson and Smith [986]).

Oxide Solubility (ppm)

UO2 0.2

Al2O3 1.8

SnO2 3.0 NiO 20

Nb2O5 28

Ta 2O5 30

Fe2O3 90 SeO 120

SiO2 2600

GeO2 8700 Ch07-I044498.tex 11/9/2007 18: 54 Page 309

Physics and chemistry of laser–liquid–solid interactions 309

Table 7.5 Generation and thermodynamic data on some metal and silicon hydroxides [988].

◦ D298 Geometry ◦ ◦ rH298 r S298 (M—OH) of M—OH Group Reaction (kJ/mol) (J/mol K) (kJ/mol) bond

VIII ½Fe2O3(s) + 653 213 334 Linear ½H2O(g) = Fe(OH)(g) + ½O2(g) 669 229 318 Bent

½Fe2O3(s) + H2O(g) = 324 102 411 Bent Fe(OH)2(g) + ¼O2(g)

IB CuO(s) + ½H2O(g) = 400 145 260 Linear Cu(OH)(g) + ¼O2(g) 429 161 230 Bent

IIB ZnO(s) + H2O(g) = 201 55 300 Bent Zn(OH)2(g)

IIIA ½Al2O3(s) + 779 199 549 ½H2O(g) = Al(OH)(g) + ½O2(g)

½Al2O3(s) + 498 134 566 ½H2O(g) = AlO(OH)(g)

½Al2O3(s) + H2O(g) = 572 121 458 Al(OH)2(g) + ¼O2(g)

½Al2O3(s) + 3/2H2O(g) = 188 −7.3 487 Al(OH)3(g)

½Ga2O3(s) + 550 211 428 Linear ½H2O(g) = Ga(OH)(g) + ½O2(g) 570 224 408 Bent

IVA SiO2(s) + ½H2O(g) = 675 190 297 Linear SiO(OH)(g) + ¼O2(g) 718 188 254 Bent

SiO2(s) + H2O(g) = 260 62 436 Linear SiO(OH)2(g) 317 64 408 Bent

SiO2(s) + 2H2O(g) = 45 −76 487 Bent Si(OH)4(g)

Many oxides form volatile hydroxides by reaction with water vapour. Even the moisture in laboratory air could create high volatility hydroxides and oxy-hydroxides during high-temperature exposure [987] (Tables 7.5 and Fig. 7.16). Tables 7.6 and 7.7 present essentials of some selected experimental and theoretical work on laser-liquid-solid interactions, having importance to several kinds of materials processing. Ch07-I044498.tex 11/9/2007 18: 54 Page 310

310 Handbook of Liquids-Assisted Laser Processing

Temperature (K) 1800 1600 1400 1200 4

Si(OH)4 A 6

Si(OH)4 K 8

SiO(OH)2A SiO(OH)2K 10 Log (P, atm) Log (P,

SiO(OH) K 12

14 5.5 6.0 6.5 7.0 7.5 8.0 8.5 10 000/T (K)

Figure 7.16 Calculated vapour pressure of Si–OH species over SiO2 with x(H2O) = 0.37 and P(total) = 1 bar [988]. The lines labelled K were calculated from thermodynamic functions taken from Krikorian’s estimates based on the pseudo halide behaviour of the hydroxyl group. The lines labelled A were calculated from the thermodynamic functions taken from Allendorf’s et al. ab initio calculations. The vapour pressure of SiO(OH) (g) from Allendorf’s calculations was too low to appear on this graph. © Elsevier. Ch07-I044498.tex 11/9/2007 18: 54 Page 311 ) ( Continued Gaumet (1996) [832] Sakka (2000) [470] Saito (2002) [973] Ueno (2001) [989] [982] Chen (1997) [833] References Wakisaka (1993) 2was > (traces) n 4 , 6 H n 2 H 2 ,C 4 ,C 2 ≈ 7500 K, reactions with phenyl ; lifetime of line in plasma at 10–20 ns ,CH 2 n ,CO − 3 2 H 2 cm ,N 2 ,C 20 2 10 clusters; C ≈ n plasma temperature , − 3 cm density of carbon atoms ≈ 100 ns , biphenyl, diphenylacetylene 4 21 700–1100 MPa 10 -C 6 × H 6 of solids in liquids. smaller than in vapour (see also Section 7.5) Reaction products identified by massphenylacetylene, chromatography: xylene, ethylbenzene, styrene, C Reaction products identified by gas chromatography: CO, H Optical emission spectra atpulse 29–1000 ns presented; mass from the spectrography study laser reaction of products in liquid; thedensity early is stage estimated plasma emissions pressure radical are listed: the mainphenylacetylene; reaction in product liquid was the yield of C Benzene was used as athe laser-induced reactive C molecule for trapping (concentrations given), O Plasma emission images atpulse 21–1080 ns in from air the and laser estimated at 21–100 ns in water presented; 6.7 Fluid dynamics observed by high-speedup camera to 20 Mfps andpeak by pressures reflectance up of to a 10PVDF-sensor; probe MPa transient beam; were reflectance measured data by are compared with theoretical predictions of temperature rise and bubble nucleation ,upto 2 2 C ◦ features of Novel features, observed ses at laser irradiation Sample immersed horizontally intosurface free liquid, focused laser beam water, focused laser beam, 10 J/cm into circulating liquid, covered by window horizontally into water, covered by window,20 0.52 GW/cm the experiment phenomena, comments Target immersed into Workpiece immersed Target immersed µ m, 2 2 2 W/cm -Nd:YAG, 532 nm, 10 13 ns, spot 5 mm, beam parameters 2 ω 10 ns, 10 Hz, 22 mJ 0.05–1.4 J/cm dYG 532Nd:YAG, nm, ∼ 1064Nd:YAG, nm, 20 ns Nd:YAG,266, 532, and 1064 nm, 6 ns, 10 Hz, 10 1.06 Nd:YAG, 16 ns,10 Hz,0.7 J,up to 6000 shots 1064Nd:YAG, nm, 20 ns, fluence ≈ 8–9 J/cm -hexane, carbon Liquids/gases in vapour n tetrachloride Ar), benzene Air, water Water Water, benzene, Some experimental research of physical–chemical proces Graphite Benzene Materials contact with Laser type and Other irradiated specimen Graphite Benzene (under Carbon black, 25 nm in suspension Graphite, Poly-BN Si, Hg Graphite Air, water Table 7.6 Ch07-I044498.tex 11/9/2007 18: 54 Page 312 Saito (2003) [992] McGrath (2002) [984] Sakka (2002) [991] Sakka (2002) [990] References ;in 4 Swan 2 2 ≈ 6000 K to C 2 1 of C 5000 K during S) changes at 2 ≈ 100 ns) P– hydrocarbons; the 2 2 = 3 of C to C was the main gas product 1 2 at 20–80 ns from the laser ≈ 4000 K ( t rotational temperature 0) to = vibrational temperature ≈ 1000 ns; rotational temperature is more reliable and CO were the main reaction products along 2 numerous hydrocarbons ranging from C Evolution of tiny gas bubblesH observed; in water, with small amounts of C up to for laser ablation plume in liquids than vibrational Optical emission spectra pulse recorded; 396 nm Al line ( Optical emission spectra in 535–575 nm (C Optical emission spectra inSwan 512–518 nm band (C tail region) recordedfrom at laser 150–1200 pulse; ns band region) recorded at 50–500pulse; ns from laser main liquid product in toluenebenzene was biphenyl, along bibenzyl with and numerous in aromatic polycyclic hydrocarbons in smaller concentrations (Table 7.3); possible reaction paths discussed toluene and benzene H the whole time interval; thermalcavity cooling is of slower than the the gas collapse of the cavity 40–50 ns from absorption lineanalytical to model emission of line; plasmacalculated transients plasma presented; temperature varies from ≈ 7000 K ( t 2 2 2 ≈ 1.2 kJ/cm features of Novel features, observed ≈ 1 mm spot, ≈ 10 J/cm µ m, into circulating water, focused laser beam, 7.2–10.4 J/cm water, focused laser beam, horizontally into free surface water, water layer 15-mm, focused laser beam, spot ≈ 87 the experiment phenomena, comments Target immersed Target immersed into Target immersed ≈ 1mm ≈ 70 mJ beam parameters dYG 1064Nd:YAG, nm, 100 ps, focused and unfocused 40 fs, unfocused dYG 1064Nd:YAG, nm, 20 ns dYG 1064Nd:YAG, nm, 20 ns 1064Nd:YAG, nm, 10 ns, 10 Hz, 650 mJ, beam diameter 1064Nd:YAG, nm, 20 ns, Ti:sapphire, 780 nm, Liquids/gases in benzene Water Water, toluene, ) ( Continued Materialsirradiated contact with specimen Laser type and Other Graphite Water Carbon suspension, 13–75 nm Graphite Air, water Al Table 7.6 Ch07-I044498.tex 11/9/2007 18: 54 Page 313 Lang (2006) [107] Sakka (2005) [993] Tsuji (2004) [672] ∼ 40 m/s µ s ) 2 µ s (36 J/cm parameter introduced; self-absorption of ∼ 50 m/s (97 nm film) to ∼ 5 MPa; ejection velocity of liquid film ), 300 2 µ s a vertical jet 10 km/s observed; bubble growth Dynamics of liquid filmrecorded at by laser-heated optical surface reflectivity was withresolution; estimated 2 nm, with 0.2 ns aid ofcalculations temperature initial vapour pressure (atlift-off) liquid was film varied from (227 nm film); Further analysis of resultsself-absorption by Saito 2003 [992]; plasma emission is considerable in water first velocity 400 m/s; bubble lifetime 200 (18 J/cm Time-resolved imaging of laser ablation process; in Condensed from vapour film (97–227 nm) on surface 2 , spot 2 several mm dYG 1064Nd:YAG, nm, 10 ns, 18 and 36 J/cm dYG 532Nd:YAG, nm, 7 ns, 138 mJ/cm GraphiteSi Air, water wafer IPA Ag,Au, Si Water Ch07-I044498.tex 11/9/2007 18: 54 Page 314 References Geretovszky (1996) [994] Sollier (2001) [260] Dou (2001) [939] [384] Wu (2005) [259] Thorslund (2003) ratio to ns and during LSP experiments at water confined LSP is for laser wavelengths from 355 to 1064 nm of solids in liquids. ; the calculations give insight into plasma parameters as 2 transmission of breakdown plasma in water mathematical model of pressure generation 3D-numerical calculations of temperatureirradiated distribution interface at laser below liquid vaporization threshold presented the density of species,α , light water–plasma interface transmission, thermal reflectivity and to energy internal balance energy was investigated theoretically and pulse length offound 25 ns; to at be 1064 nm dominated theby by breakdown multiphoton avalanche process ionization, ionization but was at 355 and 532 nm described; the model considers thehomogeneous processes and to two-temperatures laser be beam 1D,electron-ion the absorption and plasma due electron-atom IB andHertz–Knudsen photoionization surface only,and evaporation; the modelagreement was with in experimental good data1–10 at GW/cm 532 and 1064 nm, 0.6–25 Molecular dynamics simulation of water0 on to suddenly 1000 K heated surface from describes on water time superheating internal and 0–400 film ps; lift-off the (Fig. simulation 7.8) temperature, pressure, and thermal stresses forand ramp-up, rectangular ramp-down, laser pulses, including(see confined Fig. ablation 7.13 with for coating calculated temperatures) A Analytical models in cylindrical coordinates for LSP plasma The ses at laser irradiation specimen; scanned laser beam Other features Water layer over Liquids/gases in of the system molecular layers) contact with target under study Results, comments Water Water Water (6, 12 or 24 Water Some theoretical research of physical–chemical proces Targets glass Fe, SS304 Au (111) Tungsten film on Table 7.7 Ch08-I044498.tex 12/9/2007 17: 21 Page 315

CHAPTER EIGHT

Liquids and Their Properties

Contents 8.1 Introduction 315 8.2 Properties of 100 Selected Liquids 332 8.3 Properties of Water 379

8.1 Introduction

About 70 different neutral liquids have been used in laser materials processing, Tables 8.1 and 8.2, the most frequently used liquid being water, following with alcohols.Water is also often a constituent of materials. Many materials like oxides have adsorbed water on their surfaces under normal conditions. The codes and synonyms of 100 selected liquids from the first three classes in Table 8.1 are presented in Table 8.6, their molecular structures in Table 8.7, and properties in Table 8.8. The main physical properties of some important to laser processing metals, semiconductors, oxides and other inorganic compounds are also given in this chapter,Tables 8.3 and 8.4. The composition of sea water is given in Table 8.5.

Table 8.1 Classes of liquids used in laser materials processing.

Inorganic Liquefied or Molten or liquid metals liquids Organic liquids frozen gases and semi-conductors Molten salts

H2O Hydrocarbons Ar Bi KNO3 D2O Halocarbons He Ga,Al-Ga NaNO3 H4N2 Alcohols CH4 Ge NaCl Ethers CO2 Hg NH4Cl Esters NH3 In Ketones N2 Si Amines O2 Sn Carbon disulphide Freones DMSO Silicon oil Vacuum oil

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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316 Handbook of Liquids-Assisted Laser processing

Table 8.2 Liquids used in laser processing classified by the processes.

Process Liquids Additives

Cleaning Water, ethanol, methanol, IPA, NaCl, methanol, acetone ethanol, IPA Shock processing Water No

Front-side machining Water, heptane, perfluorocarbons, H2O2, NaCl, CaCl2, NaNO3, KNO3, benzene, o-xylol, p-xylol, ethanol, Na2SO4,K2SO4, CuSO4, KOH, glycerine, ether, DMSO, DMFA, N2H4, methanol, ethanol, isopropanol, soapy liquid nitrogen, molten NaCl, NH4Cl, additives, saccharose NaNO3 and KNO3

Back-side machining Cyclohexane, tetrachloromethylene, NiSO4, CrO3, KMnO4, CrO3, FeCl3, tetrachloroethylene, benzene, toluene, KMnO4, KNO3,K2CrO4, carbon cumene, t-butylbenzene, 1,2,4- particles, pyrene, pyranine, benzil, trimethylbenzene, chlorobenzene, naphthalene,phenanthrene,anthracene, dichlorobenzene, fluorobenzene, 9-methyl-anthracene, 9,10-dimethyl- isopropanol (IPA), tetrahydrofuran, anthracene, 9-phenyl anthracene, methylmethacrylate, methyl benzoate, fluoranthrene, Rose Bengal dye, acetone, mercury,gallium Np(SO3Na)3

Generation of metal water, D2O, pentane, hexane, NaCl, KCl, MgCl2,AgNO3, NaBH4, particles cyclohexane, heptane, octane, nonane, I+,CN−, phtalazine, citric acid, decane, chloroform, methanol, ethanol, sodium citrate, dodecanethiol, gelatine, ethylene glycol, diethylene glycol, cyclodextrines, PVP,SDS, SHS, SOS, 1-propanol,2-propanol (IPA),isobutanol, SDBS, CTAB, sodium polyacrylate, n-hexanol, 2-ethoxyethanol, acetone, tetraalkyl-ammonium bromide salts liquid He II

Generation of inorganic Water, hexane, dichloroethane, toluene, Ammonia,AgNO3, SDS, compound particles xylene, ethanol, 2-propanol (IPA), LDA, CTAB ethylene glycol, diethylene glycole, isobutanol, acetone, DMSO, silicon oil Generation of carbon Hexane, cyclohexane, perfluoro-octane, and silicon particles (not perfluorodecalin, benzene, diamond or DLC) hexafluorobenzene, toluene, methanol, 2-propanol (IPA), tetrahydrofuran (THF) Generation of diamond Hexane, cyclohexane, decalin, benzene, Carbon or diamond particles, dissolved and DLC particles and toluene, cumene, acetone, vacuum oil methane (in water), Pd(acac)2 films (a polyphenyl ether) Generation of organic Water, methanol, ethanol, 1-propanol, SDS, Igepal CA-630 particles ethyl acetate

Surface modification Water, benzene, aminoethanol, H3BO3, B(OH)3, NaOH, NaAlO2, 1,2-diaminoethane, triethylene- CuSO4 tetramine, NH3, liquid nitrogen Ablation deposition Ga,Al-Ga, Ge, In, Sn, Bi, Si, from liquid targets vacuum oil (a polyphenyl ether)

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Liquids and their properties 317

Table 8.2 (Continued)

Process Liquids Additives

Ablation deposition Acetylene, N2,CH4,CO2 from frozen targets (inorganic compounds) Ablation deposition Water, chloroform, tert-butanol, from frozen targets glycerole, phosphate buffer (MAPLE) Forward transfer Water, glycerine, mineral oil Tris–HCl, EDTA, PBS, SDS deposition (LIFT)

Notations DLC – dry laser cleaning LIFT – laser induced forward transfer Np(SO3Na)3 – naphthalene-1,3,6-trisulphonic acid trisodium salt PVP – polyvinylpyrrolidone SDS–CnH2n+1OSO3Na SHS – sodium hexadecyl sulphate, C16H33NaSO4 SOS – sodium n-octyl sulphonate, C8H17SO3Na SDBS – n-dodecylbenzene sulphonate, C12H25C6H4SO3Na CTAB – cetyltrimethylammonium bromide (hexadecyltrimethylammonium bromide), C19H42BrN + − LDA – lauryl dimethylaminoacetic acid betaine, CH3(CH2)11N (CH3)2CH2COO Pd(acac)2 – palladium acetylacetonate Igepal CA-630 – octylphenoxy polyethoxy ethanol (CH3)3CCH2(CH3)2CC6H4O(CH2CH2O)9H Tris-HCl – 2-Amino-2-(hydroxymethyl)-1,3-propanediol, hydrochloride, C4H11NO3ClH EDTA – ethylenediaminetetraacetic acid, C10H16N2O8 PBS – phosphate buffered saline solution

Table 8.3 Properties of some metals and elemental semiconductors [995–998]

6 ρα× 10 Cp λ Tm Tb Hm Hvap nkR kg/m3 K−1 J/kg K W/m K ◦C ◦C kJ/kg kJ/mol (400 nm) (400 nm) (400 nm) Al 2700 23.1 897 237 660.32 2519 397 291 0.49 47.86 0.9243 Be 1850 11.3 1825 200 1287 2471 877 292 2.90 3.13 0.537 Cr 7150 4.9 449 93.7 1907 2671 404 342 1.50 3.62 0.691 Co 8860 13.0 421 100 1495 2927 275 Cu 8960 16.5 385 401 1084.62 2562 208.7 307 1.28 2.14 0.489 Ga 5910 371 40.6 29.76 2204 80.2 270 Au 19 300 14.2 129 317 1064.18 2856 63.7 343 1.66 1.94 0.371 In 7310 32.1 233 81.6 156.60 2072 28.6 232 Fe 7870 11.8 449 80.2 1538 2861 247.3 340 1.83 3.04 0.58

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318 Handbook of Liquids-Assisted Laser processing

Table 8.3 (Continued)

6 ρα× 10 Cp λ Tm Tb Hm Hvap nkR kg/m3 K−1 J/kg K W/m K ◦C ◦C kJ/kg kJ/mol (400 nm) (400 nm) (400 nm) Mg 1740 24.8 1023 156 650 1090 349 128 Hg 13 533.6 140 8.34 −38.83 356.73 11.4 59.1 Mo 10 200 4.8 251 138 2623 4639 390.7 590 3.03 3.22 0.550 Ni 8900 13.4 444 90.7 1455 2913 298 375 1.62 2.39 0.479 Nb 8570 7.3 265 53.7 2477 4744 323 Pd 12 000 11.8 246 71.8 1554.9 2963 157.3 361 Pt 21 500 8.8 133 71.6 1768.4 3825 113.6 469 1.73 2.85 0.556 Ag 10 500 18.9 235 429 961.78 2162 104.8 258 0.17 1.95 0.848 Ta 16 400 6.3 140 57.5 3017 5458 202.1 Sn 7260 22.0 228 66.6 231.93 26.2 59.2 296 Ti 4510 8.6 523 21.9 1668 3287 295 426 W 19 300 4.5 132 174 3422 5555 284.5 824 3.39 2.41 0.464 V 6000 8.4 489 30.7 1910 3407 422 Zn 7140 30.2 388 116 419.53 907 112 114 Si 2329 2.6 700 130 1412 Ge 5323.4 5.9 310 58 937 C 3515 0.8 520 600 3547

Table 8.4 Properties of some inorganic compounds [999–1001]. SC – single crystalline, subl – sublimes, decp – decomposes, expl – explods.

6 ρα× 10 Cp λ Tm Tb Hm Compound kg/m3 K−1 J/kg K W/m K ◦C ◦C kJ/mol NaCl 2165 801 1465 28.158

NH4Cl 1530 sublimes decp 520 165.7

Na2SO4 2680 884 1689 23.849

LiNO3 2380 254 25.5

NaNO3 2260 310 expl 537 16

KNO3 2109 337 decp 400 12

Al2O3 3980 6.5 ∼25 2047 2980 ◦ ◦ SiO2 (SC) 2651 (0 C) 0.55 1.6 (500 C) 1423 2950

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Liquids and their properties 319

Table 8.4 (Continued)

6 ρα× 10 Cp λ Tm Tb Hm Compound kg/m3 K−1 J/kg K W/m K ◦C ◦C kJ/mol

Fe2O3 5240 1565 CuO 6480 1326 11.80 ZnO 5610 4.0 25.2 1975 subl 52.3

TiO2 (rutile) 4250 9.0 9 1867 2500–3000

SnO2 (cassiterite) 6950 1630 subl 1800–1900

Co3O4 6110 decp 900

ZrO2 5760 8.0 1.5 2710 ∼5000 MgO 3581 60.0 (27◦C) ∼2852 ∼3600 78

CeO2 7650 2400 3500

Si3N4 3190 2.5 17 subl 1900 c-BN 3487 1.2 ∼600 740 2973 sublimes SiC 3220 5.3 84 2760 AlN (SC) 3255 5.27 600 285 3000 decomposes ZnSe (SC) 5420 1517 CdS (SC, hexagonal) 4820 1750 subl 980

Table 8.5 Major composition of sea water (salinity 35‰) [1002]

Concentration Constituent g/kg

Na+ 10.77 Mg2+ 1.29 Ca2+ 0.4121 K+ 0.399 Sr2+ 0.0079 Cl− 19.354 − SO2 2.712 4 − HCO3 0.1424 Br− 0.0673 F− 0.0013 B 0.0045 Ch08-I044498.tex 12/9/2007 17: 21 Page 320 -heptylhydride n tet, Freon 14, ylene, naphthene s in Table 8.8. trichloride, omethylene , isooctane , trichloromethane ide, ethylene dichloride, EDC, -dipropylmethane, n .7 and propertie -Pentane, 1,3-dimethyl propane, diethyl methane -Hexane -Heptane, n n n CFC-14 trichloroethene,TCE Petroleum benzin, petroleum spirit, mineral spirits, ligroine, naphtha petroleum Freon 150 203-624-3 Cyclohexylmethane 200-872-4 Trifluoromethane, fluoryl, Freon 23, HFC-23 265-151-9 232-453-7 Beilstein EG/EC 878165 202-046-9 Decahydronaphthalene 493-02-7 493-01-6 109-66-078-78-4 969132110-54-33 203-692-4 1730723142-82-5 201-142-8 1730733540-84-1 Iso-pentane, isopentane 203-777-6 1730763287-92-3 205-563-8 1696876110-82-7 208-759-1 Isobutyltrimethylmethane 1900195108-87-2 206-016-6 1900225mix. 91-17-8 Pentamethylene, cyclopentyl cis 203-806-2trans hexahydrobenzene, hexameth 75-25-275-09-267-66-3 173104856-23-5 200-854-6 1730800 Tribromomethane 200-838-9 173104275-46-7 Methylene chloride, chlor 200-663-8 1098295 Methylidyne trichloride 200-262-8 Carbon tetrachloride, carbon 79-01-6 1736782 201-167-4 Trichloroethylene, ethylene 101316-46-5; 64742-49-0 CAS Reg. No. Reg. No. number Common synonyms yoliquids. Molecular structure is presented in Table 8 2 3 3 3 CH 3 2 2 ) CH CH CH Cl 107-06-2 605264 203-458-1 Ethylene chlor 3 3 4 5 2 3 ) ) ) CH 2 2 2 )CH 2 3 CCl 2 CH CH 2 3 2 3 18 ) 3 (CH CH (CH (CH C(CH 10 12 11 Cl 3 4 3 3 3 3 3 2 H H H H 5 6 6 10 (CH Linear molecular CH CH CH CH CH CH(CH C C C C CHBr CH CHCl CCl CHF ClCH ClCH 2 2 3 3 3 Cl ganic solvents, waters and cr 18 3 12 12 14 16 18 10 12 14 Cl 4 4 2 H H H H H H H H H H HCl 5 5 6 7 8 5 6 7 10 2 2 C C C C C C CHBr CHCl CHF (mostly alkanes) Composition formula

IUPAC Name

Nomenclature of 100 selected or Number

12 Pentane 2-Methylbutane34 Hexane C 5 Heptane 2,2,4-Trimethylpentane6 C 7 Cyclopentane 8 Cyclohexane 9 Methylcyclohexane Decalin C 10 Petroleum ether*11 Bromoform 12 mixture of hydrocarbons Dichloromethane13 Chloroform 14 Tetrachloromethane CH 15 CCl Fluoroform 16 1,2-Dichloroethane17 1,1,2-Trichloroethene C C

Class Hydrocarbons aromatic) (not Halocarbons Table 8.6 Ch08-I044498.tex 12/9/2007 17: 21 Page 321 ) ( Continued ydro- , styrol obenzene obenzene ylene tetrachloride, perfluorohexane, opylbenzene, ortho-xylol meta-xylol para-xylol -hexane, perflexane, PP1, FC72 cyanide -Chlorobenzene perchloroethylene, tetrachloroethene, PERC, PCE o α - Methylnaphthalene n perfluoro- naphthalene, perfluorodecahydronaphthalene isopropylbenzol, cumol α - Chloronaphthalene 2067113 206-192-4 Perfluorodecalin, octadecafluorodecah 60433- 60433-11-6 108-90-7 605632462-06-6 203-628-5 Phenyl chloride 1236623 207-321-7 Phenyl fluoride, monofluor 127-18-4355-42-0 1361721 204-825-9 eth Tetrachloroethylene, 1802113306-94-5 206-585-0cis Tetradecafluorohexane, trans 12-7 71-43-295-50-1 969212120-82-1 200-753-7 Cyclohexatriene, benzol 606078 956819392-56-3 202-425-9 204-428-0 1,2,4-TCB 1683438108-88-3 206-876-2 Hexafluorobenzene, perfluor 100-42-5 63576095-47-6 1071236108-38-3 203-625-9 Methylbenzene, toluol 202-851-5106-42-3 1815558 Phenylethylene, vinylbenzene 60544198-82-8 202-422-2 1,2-Dimethylbenzene, 1901563 203-576-3 1,3-Dimethylbenzene, 203-396-5 1236613 1,4-Dimethylbenzene, 90-12-0 202-704-5 2-Phenylpropane, isopr 506793 201-966-8 2 2 ) 3 2 2 2 CH 2 ) ) ) 3 3 3 3 3 2 3 CCl ClCH 90-13-1 970836 2019673 Cl Cl Cl F CNCH CH 100-47-0(CH (CH 506893(CH 202-855-7CH(CH Phenyl 7 7 18 6 5 4 3 5 5 5 5 4 4 4 5 2 14 6 F H H F H H H H H F H H H H H H H 6 10 6 6 6 6 6 6 6 6 6 6 6 6 6 10 10 CCl C C C C C C C C C C C C C 2 3 Cl C ClCl C Cl FC NC 7 10 4 18 6 5 4 3 5 5 8 8 10 10 10 12 14 6 F H H Cl F H H H H H F H H H H H H H 2 6 10 6 6 6 6 6 6 7 7 8 8 8 8 9 10 11 C C C C C C C C C C C C -Xylene -Xylene -Xylene Tetrachloroethene 6-Tetradecafluoro- hexane 6,7,7,8,8,8a- Octadecafluorodecalin Hexafluorobenzene o m p

18 1,1,2,2- 19 1,1,1,2,2,3,3,4,4,5,5,6,6, 20 1,1,2,2,3,3,4,4,4a,5,5,6, 21 Benzene 22 Chlorobenzene23 1,2-Dichlorobenzene24 1,2,4-Trichlorobenzene25 C C C Fluorobenzene26 1,2,3,4,5,6- 27 Benzonitrile C 28 Toluene 29 Styrene 30 31 32 33 Cumene 34 1-Chloronaphthalene35 1-Methylnaphthalene C C

aoabn ntaromatic) (not Halocarbons derivatives their hydrocarbons, Aromatic Ch08-I044498.tex 12/9/2007 17: 21 Page 322 -butyl -butyl n tert -trifluoroethyl alcohol yl alcohol, β in, 1,2,3-propanetriol , β , -nitrilotriethanol, -propanol, propyl alcohol,  β n ,2  benzyl alcohol, benzene 2-methyl-1-propanol, monoethylene glycol, glycol, grain alcohol, EtOH hydroxyethane, -butyl alcohol iso-propanol, isopropanol, isopropyl -octanol, alcohol C-8, capryl -butanol, butyl alcohol, yl alcohol, n sec n xymethane, methyl alcohol, wood alcohol, -butanol, 2-methyl-2-propanol, -propyl alcohol methanol, phenyl carbinole monoethanolamine, MEA carbinol, MeOH alcohol, dimethyl carbinol, IPA tert alcohol, trimethyl carbinol MEG isobutanol, iso-butanol tris (2-hydroxyethyl)amine,TEA alcohol, octyl alcohol alcohol n Beilstein EG/EC 56-81-5 635685 200-289-5 Glycerol, glycerine, glycer 78-92-2 773649 201-158-5 2-Butanol, 78-83-1 1730878 201-148-0 Isobutyl alcohol, CAS Reg. No. Reg. No. number Common synonyms N 102-71-6 1699263 203-049-8 Triethanolamine, 2,2 3 2 OH 141-43-5 505944 205-483-3 Ethanolamine, 2-aminoeth OH 71-23-8 1098242 200-746-9 1-Propanol, propanol, ) OH 107-21-1 505945 203-473-3 Ethylene glycol, 2 2 2 2 OH 71-36-3 969148 200-751-6 1-Butanol, OH 111-87-5 1697461 203-917-6 1-Octanol, 3 7 OH 100-51-6 878307 202-859-9 Phenyl methanol, ) ) CH CH CH(OH) 2 CH 2 2 OH 75-89-8 1733203 200-913-6 Trifluoroeth CH CH(OH) 2 2 2 2 2 2 2 CHOH 67-63-0 635639 200-661-7 2-Propanol, CHCH COH 75-65-0 906698 200-889-7 2 2 3 OH 64-17-5 1718733 200-746-9 Ethyl alcohol, CH ) ) ) CH OH5 67-56-1 1098229 200-659-6 Hydro CH OH (CH CH 5 (CH 3 3 3 CH 2 3 3 2 3 3 3 3 3 H H 2 6 CH Linear molecular HOCH HOCH OH (HOCH CH 3 OCF 2 3 3 OCH OCH OO (CH NO (CH OCH OC O F NO NH OCH OO (CH OC OCH 6 6 3 7 8 8 8 10 10 10 10 15 8 18 4 H H H H H H H H H H H H H H 2 2 2 2 3 3 3 4 4 4 4 6 7 8 CH C C C C C C C Composition formula )

amino]ethanol IUPAC Name Continued

( Number

36 Methanol 37 Ethanol 38 Ethane-1,2-diol39 2,2,2-Trifluoroethanol40 C 2-Aminoethanol C 41 Propan-1-ol C 42 Propan-2-ol 43 Propane-1,2,3-triol44 Butan-1-ol C 45 Butan-2-ol 46 2-methylpropan-1-ol47 C 2-Methylpropan-2-ol48 C 2-[Bis(2-hydroxyethyl)- 49 Phenylmethanol50 Octan-1-ol C

Class Alcohols Table 8.6 Ch08-I044498.tex 12/9/2007 17: 21 Page 323 ) ( Continued -oxybisethane  -butyl ether, tert -butyl ether monobutyl ether, -butyl ester dioxide, dioxane, n yl 2-methylpropenoate, ylene oxide, yl ester, formic acid, , Clorius, Niobe oil yl ether, 2-methoxyethyl ylglycol, ethylene glycol, yl phenyl ether -dihydroxydiethyl ether,  ether, di- n 2,2 monoethyl ether,ethyl cellosolve, monomethyl ether, methyl glycol, ether, ethyl ether, 1,1 -oxydiethanol, diglycol, bis(2-hydroxyethyl)  -Butyl methyl ether, methyl -Butyl acetate, acetic acid -dioxane, dioxacylohexane, glycolethylether, ether, DEG,TL4N ethylene glycol butyl ether, butyl cellosolve 2,2 1,4-epoxybutane, oxacyclopentane,THF tert MTBE, DRIVERON® methacrylic acid methyl ester, MMA n p 1,4-diethylene dioxide, 1,4-dioxacyclohexane dimethyl ether, monoglyme, DME formic acid methyl ester ether, dimethyl diglycol, dimethyldiglycol, bis(2-methoxyethyl) ether, Diglyme methyl cellosolve, 2ME, EGMM cellosolve® 111-76-2 1732511 203-905-0 Butyl glycol, ethylene glycol 109-99-9 102391 203-726-8 tetrameth Tetrahydrofuran, 123-91-1 102551 204-661-8110-71-4 Diethylene oxide, ethylene 1634-04-4 1209237 203-794-9 1730942 Dimethyl glycol, dimeth 216-653-1 100-66-3 506892107-31-3 202-876-1141-78-6 Methoxybenzene, meth 173462380-62-6 203-481-7 Methyl 506104 methanoate, meth 123-86-4 205-500-4 605459 Acetic acid ethyl ester 93-58-3 201-297-1 1741921 Methyl methacrylate, meth 204-658-1 1072099 202-259-7 Benzoic acid methyl ester 111-96-6 1736101 203-924-4 Diethylene glycol dimeth 109-86-4110-80-5 1731074 203-713-7 Ethylene 1098271 glycol 203-804-1 Ethyl glycol,2EE 2 3 2 ) O 111-46-6 969209 203-872-2 Diethylene glycol, 5 3 2 2 2 2 3 O 142-96-1 1732752 205-575-3 Dibutyl ether, butyl ) ) 2 H 2 ] 3 CH 2 OCH O 60-29-7 1696894 200-467-2 Diethyl ether, 3 2 CH CH 5 2 2 ) 3 3 2 2 ) ) 2 3 H CH 2 2 6 2 2 COCH CH O 3 3 2 OCH O O COOCH CH ) OCH 2 (CH 5 8 8 5 OCH (CH OH OCH ) OC COOC =C(CH COO(CH 3 3 3 3 3 3 2 3 2 3 3 2 3 3 H H H H 2 4 4 6 COOCH CH OH C OH (HOCH CH CH C CH OCH (CH CH HCO CH CH CH CH C 2 3 2 2 3 2 2 2 2 2 2 2 O O O OO (CH OO (CH O [CH O O OC O OCH O O O O 8 10 10 14 8 8 10 10 12 14 8 18 4 8 8 12 8 H H H H H H H H H H H H H H H H H 3 4 4 6 4 4 4 4 5 6 7 8 2 4 5 6 8 C C C C C C C C C C Hydroxyethoxy)ethanol propane methoxyethoxy)ethane enoate

51 2-Methoxyethanol52 2-Ethoxyethanol C 53 2-(2- C 54 2-Butoxyethanol55 Oxolane C 56 1,4-Dioxane 57 Ethoxyethane 58 1,2-Dimethoxyethane59 C 2-Methoxy-2-methyl- 60 1-Methoxy-2-(2- 61 Anisole 62 1-Butoxybutane63 Methyl formate64 C Ethyl acetate 65 Methyl 2-methylprop-2- C 66 Butyl acetate 67 Methyl benzoate C

te alcohols Ether Ethers Esters Ch08-I044498.tex 12/9/2007 17: 21 Page 324 -methyl-2- N yl ketone, ethyl methyl , dimethyl ketone ocarbol isobutylacetone, isopentyl opyl ketone , methyl isobutyl ketone, acid amide, methane amide, -pyrrole, 1-methyl-2-pyrrolidone, m ketone cyanide,ACN yl-2-pyrrolidinone, -Dimethylformamide, formic acid -Dimethylacetamide, acetic acid N N , , -methyl-2-pyrrolidone, M-PYROL®, NMP ketone, MEK 1,2-ethanediamine, ethylenediamine N N Diazane, diamide, levoxine isobutyl methyl ketone, isopropylacetone, MIBK methyl ketone, methyl isoamyl ketone, isoamyl methyl ketone, MIAK dimethylamide, DMF,DMFA dimethylamide, DMAC pyrrolidinone, N Amide C1, Beilstein EG/EC 67-64-178-93-3 635680107-87-9 741880 200-662-2 Propanone, 2-propanone 201-159-0 506058 2-Butanone,108-10-1 methyl eth 203-528-1 2-Pentanone, methyl pr 110-12-3 605399 203-550-1 506163 4-Methyl-2-pentanone 75-12-7 203-737-8 5-Methyl-2-hexanone, 75-52-5 505995 200-842-0107-15-3 1698205 Formic amide, formic 200-876-668-12-2 Mononitromethane, nitr 605263 203-468-6127-19-5 1,2-Diaminoethane, 605365 200-679-5 1737614 204-826-4 302-01-2 110-86-1 103233 203-809-9 Azabenzene, azine CAS Reg. No. Reg. No. number Common synonyms 2 2 2 ) 3 2 2 NH 2 2 3 CH ) 3 2 3 3 2 CH 2 2 2 3 CHCH CHCH (=O) 108-94-1 385735 203-631-1 Pimelic 2 2 COCH N NO 872-50-4 106420 212-828-1 1-Meth ) ) CH NH COCH 5 COCH 10 COCH NO CN 75-05-8CON(CH 7418575 200-835-2 Methyl 9 3 3 2 2 3 3 3 2 3 3 3 H H H H 2 6 5 5 Linear molecular CH COCH CH CH NH NH 2 2 OCH OC OO (CH (CH OCH OC NCH N NO HCON(CH NO CH NC NO C 2 6 8 10 10 12 14 NONO HCONH 3 8 7 9 5 9 3 3 N H H H H H H H H H H H H 4 3 4 5 6 6 7 2 2 3 4 5 5 C C C CH CH C C H C C C Composition formula ) - - N N , ,

N N one Dimethylmethanamide Dimethylethanamide IUPAC Name Continued

( Number

68 Acetone 69 Butan-2-one 70 Pentan-2-one 71 Cyclohexanone72 4-Methylpentan-2-one73 C C 5-Methylhexan-2-one C 74 Formamide 75 Nitromethane 76 Acetonitrile 77 Ethane-1,2-diamine78 C 79 80 Pyridine 81 1-Methylpyrrolidin-2- 82 Hydrazine

Class irgncompounds Nitrogen Ketones Table 8.6 Ch08-I044498.tex 12/9/2007 17: 21 Page 325 bisulphide, 2 marsh gas , light water, hydrogen oxide sulphoxide, methylsulphoxide, DMSO Carbon sulphide 231-168-5 231-110-9 231-147-0 231-098-5 231-172-7 232-148-9 Deuterium oxide, water-d EINECS Polydimethylsiloxane, polysilicone oil 215-605-7 231-783-9 231-956-9 7440-59-7 7440-01-9 7440-37-1 7439-90-9 7440-63-3 7789-20-0 7732-18-5 2050024 231-791-2 Water, ordinary water 75-15-0 109829363148-62-9 200-843-6 Carbon disulphide, carbon 1333-74-0 7782-39-0 7727-37-9 7782-44-7 124-38-974-82-8 1900390 204-696-9 1718732 200-812-7 Methyl hydride, biogas, n O-] 2 ) 3 SO 67-68-5 506008 200-664-3 Dimethyl 2 ) 3 4 2 [-Si(CH CS CH 2 OS (CH 6 2 4 2 ,O O O H 2 2 2 2 2 2 2 2 D H D He N O Ne Kr Xe CH N Ar

83 Methanedithione84 Methylsulphinylmethane85 C CS Silicone oil*, 586 cSt Oxidane (water*)87 Heavy water* 88 Sea water* 89 H Hydrogen 90 Deuterium 91 Helium 92 Nitrogen 93 Oxygen 94 Neon 95 Argon 96 Krypton 97 Xenon 98 Carbon dioxide99 Methane 100 Air* CO

iufe gases Liquefied Misc. Water Other common name. * Ch08-I044498.tex 12/9/2007 17: 21 Page 326

326 Handbook of Liquids-Assisted Laser processing

Table 8.7 Molecular structure of 90 liquids, listed in Table 8.6.

Pentane 2-Methylbutane Hexane

C5H12 109-66-0 C5H12 78-78-4 C6H14 110-54-3

CH3 H3C CH3 H3C CH3 CH3 H3C

1 2 3

Heptane 2,2,4-Trimethylpentane Cyclopentane

C7H16 142-82-5 C8H18 540-84-1 C5H10 287-92-3

CH3 CH3

H3CCH3 H3C CH3 CH3

4 5 6 Cyclohexane Methylcyclohexane cis-Decalin

C6H12 110-82-7 C7H14 108-87-2 C10H18 493-01-6

H

CH3 H

7 8 9a trans-Decalin Bromoform Dichlromethane

C10H18 493-02-7 CHBr3 75-25-2 CH2Cl2 75-09-2

H Br Cl

Cl Br Br H 9b 11 12

Chloroform Tetrachloromethane Fluoroform

CHCl3 67-66-3 CCl4 56-23-5 CHF3 75-46-7

F Cl Cl

Cl Cl Cl F F Cl Cl

13 14 15

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 327

Liquids and their properties 327

Table 8.7 (Continued)

1,2-Dichlroethane 1,1,2-Trichloroethene 1,1,2,2-Tetrachloroethene C2H2Cl2 107-06-2 C2HCl3 79-01-6 C2Cl4 127-18-4

Cl Cl Cl Cl Cl Cl Cl Cl Cl

16 17 18

1,1,1,2,2,3,3,4,4,5,5,6,6,6- cis-1,1,2,2,3,3,4,4,4a, trans-1,1,2,2,3,3,4,4,4a, Tetradecafluorohexane 5,5,6,6,7,7,8,8,8a- 5,5,6,6,7,7,8,8,8a- Octadecafluorodecalin Octadecafluorodecalin C6F14 355-42-0 C10F18 60433-11-6 C10F18 60433-12-7

F FFFFF F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F 19 20aF F F F 20b F F F F Benzene Chlorobenzene 1,2-Dichlorobenzene C6H6 71-43-2 C6H5Cl 108-90-7 C6H4Cl2 95-50-1

Cl

Cl Cl

21 22 23

1,2,4-Trichlorobenzene Fluorobenzene 1,2,3,4,5,6- C6H3Cl3 120-82-1 C6H5F 462-06-6 Hexafluorobenzene C6F6 392-56-3

Cl F F

F Cl Cl F F

F 24 25 26 F Benzonitrile Toluene Styrene C7H5N 100-47-0 C7H8 108-88-3 C8H8 100-42-5

CH2

N CH3

27 28 29

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 328

328 Handbook of Liquids-Assisted Laser processing

Table 8.7 (Continued)

o-Xylene m-Xylene p-Xylene C8H10 95-47-6 C8H10 108-38-3 C8H10 106-42-3

CH3 H3C

H3CCH3 CH3 CH3

30 31 32

Cumene 1-Chloronaphthalene 1-Methylnaphthalene C9H12 98-82-8 C10H7Cl 90-13-1 C11H10 90-12-0

Cl CH3 CH3

CH3

33 34 35

Methanol Ethanol Ethanol-1,2-diol CH4O 67-56-1 C2H6O 64-17-5 C2H6O2 107-21-1

H3C OH HO H3C HO OH

36 37 38

2,2,2-Trifluoroethanol 2-Aminoethanol Propan-1-ol C2H3F3O 75-89-8 C2H7NO 141-43-5 C3H8O 71-23-8

F

H2N H3C OH OH OH F

39 40 41 Propan-2-ol Propane-1,2,3-triol Butan-1-ol C3H8O 67-63-0 C3H8O3 56-81-5 C4H10O 71-36-3

OH OH H C OH HO OH 3 H3C CH3

42 43 44

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 329

Liquids and their properties 329

Table 8.7 (Continued)

Butan-2-ol 2-Methylpropan-1-ol 2-Methylpropan-2-ol C4H10O 78-92-2 C4H10O 78-83-1 C4H10O 75-65-0

OH OH CH3

CH3 OH CH H3C H C 3 3 H3C CH3

45 46 47

2-[Bis(2-hydroxyethyl)- Phenylmethanol Octan-1-ol amino]ethanol C7H8O 100-51-6 C8H18O 111-87-5 C6H15NO3 102-71-6

OH OH OH H3C OH N

OH

48 49 50

2-Methoxyethanol 2-Eethoxyethanol 2-(2-Hydroxyethoxy)- C3H8O2 109-86-4 C4H10O2 110-80-5 ethanol C4H10O3 111-46-6

OH H C OH 3 H3C O HO OH O O

51 52 53

2-Butoxyethanol Oxolane 1,4-Dioxane C6H14O2 111-76-2 C4H8O 109-99-9 C4H8O2 123-91-1

O O HO O CH3 O

54 55 56

Ethoxyethane 1,2-Dimethoxyethane 2-Methoxy-2-methyl- C4H10O 60-29-7 C4H10O2 110-71-4 propane C5H12O 1634-04-4

CH3 O CH3 O H3C O CH O 3 H3C

CH3 H3C CH3 57 58 59

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 330

330 Handbook of Liquids-Assisted Laser processing

Table 8.7 (Continued)

1-Methoxy-2- Anisole 1-Butoxybutane (2-methoxyethoxy)ethane C7H8O 100-66-3 C8H18O 142-96-1 C6H14O3 111-96-6

CH3 H C CH 3 O 3 H3C O CH O O O 3

60 61 62

Methyl formate Ethyl acetate Methyl-2-methylprop- 2-enoate C2H4O2 107-31-3 C4H8O2 141-78-6 C5H8O2 80-62-6 O O H2C O H O H3C O CH3 O CH3 H3C CH3 63 64 65

Butyl acetate Methyl benzoate Acetone C6H12O2 123-86-4 C8H8O2 93-58-3 C3H6O 67-64-1

O O O

OCH3 H3C O CH 3 H3C CH3

66 67 68 Butan-2-one Pentan-2-one Cyclohexanone C4H8O 78-93-3 C5H10O 107-87-9 C6H10O 108-94-1

O O CH 3 O CH3 H C 3 H3C

69 70 71

4-Methylpentan-2-one 5-Methylhexan-2-one Formamide C6H12O 108-10-1 C7H14O 110-12-3 CH3NO 75-12-7

CH H3C O 3 O

CH3 H4C NH H3C CH3 H 2 O 72 73 74

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 331

Liquids and their properties 331

Table 8.7 (Continued)

Nitromethane Acetonitrile Ethane-1,2-diamine CH3NO2 75-52-5 C2H3N 75-05-8 C2H8N2 107-15-3

O H N H3C N 2 NH H3C N 2

O

75 76 77

N,N-Dimethylmethanamide N,N-Dimethylethanamide Pyridine C3H7NO 68-12-2 C4H9NO 127-19-5 C5H5N 110-86-1

O O

CH3 CH3 H N H3C N N

CH3 CH3 78 79 80 1-Methylpyrrolidin-2-one Hydrazine Methanedithione C5H9NO 872-50-4 H4N2 302-01-2 CS5 75-15-0

CH3 SCS N H2NNH2

O

81 82 83

Methylsulfinylmethane Silicone oil Oxidane (water) C H OS 67-68-5 2 6 H2O 7732-18-5

CH3 O O Si O S H H H3C CH3 CH3 n

84 85 86 Heavy water Carbon dioxide Methane D2O 7789-20-0 CO2 124-38-9 CH4 74-82-8

H O OOC 2 2 H H H H H

87 98 99 Ch08-I044498.tex 12/9/2007 17: 21 Page 332

332 Handbook of Liquids-Assisted Laser processing

8.2 Properties of 100 Selected Liquids

Most important physical and chemical properties, and references to optical spectra of 100 liquids, used or of potential importance in laser materials processing, are given in Table 8.8. All properties correspond to liquids of maximum possible purity. In case of many different values for the same property in the same source, one of the middle values was chosen. The properties of sea water are for 35–40 ‰ of salinity. All parameters are given at normal conditions, 298.15 K (25◦C) and 1.01325 bar (1 atmosphere), unless noted with *. * and ** and *** denote that measurement conditions or composition of the substance are specified at the references below.

Definitions of the properties (More detailed definitions and further explanations for all properties are given in the Glossary.)

E Hazard codes: Highly F Flammable B Biohazard O Oxidizing Extremely F+ Flammable

Xn Harmful C Corrosive R Radioactive Xi Irritant

Dangerous for T Toxic E Explosive N the T+ Very Toxic environment F Molar mass Molar mass M (g/mol) 3 G Molar volume Liquid molar volumeVliq (cm /mol) H Density ρ Density ρ (kg/m3) Idρ/dT Temperature coefficient of density dρ/dT (kg/m3 K) J Melting point (K) Atmospheric (1.01325 bar) freezing/melting point Tm (K) ◦ ◦ K Melting point ( C) Atmospheric (1.01325 bar) freezing/melting point Tm ( C) L Hm Enthalpy change of atmospheric melting (kJ/mol) M Heat capacity Heat capacity at constant pressure Cp liq(J/mol K) N Diffusion coefficient Diffusion coefficient D (10−5 cm2/s) O Heat conductivity Heat conductivity λ (J/s m K) P Surface tension Surface tension γ (N/m) Q Dynamic viscosity, η Dynamic viscosity η (kg/m s) R d(ln η)/dT Temperature coefficient of dynamic viscosity d(ln η)/dT (10−2 K−1) S Relaxation time Orientational relaxation time τ (ps) T Thermal expansion Volumetric thermal expansion coefficient β (K−1) −1 U Isothermal Compressibility Isothermal compressibility κT (kPa ) −1 V Adiabatic compressibility Adiabatic compressibility κS (kPa ) W Sound velocity Longitudinal sound velocity vL (m/s) X Acoustic impedance Acoustic impedance Z (Pa s/m); (1 Mrayls = 1MPas/m) Y US absorption ultrasound absorption coefficient (10−15 s2/m), near 25◦C at 104–107 MHz Z Acoustic non-linearity Acoustic non-linearity parameter B/A AA Shock velocity Shock velocity Us (m/s) at shock pressures close to 10 GPa AB Boiling point (K) Atmospheric (1.01325 bar) boiling point Tb (K) Ch08-I044498.tex 12/9/2007 17: 21 Page 333

Liquids and their properties 333

◦ ◦ AC Boiling point ( C) Atmospheric (1.01325 bar) boiling pointTb ( C) ◦ AD Superheat temperature Attainable atmospheric superheat temperature Tsh ( C) AE Nucleation rate Homogeneous bubble nucleation rate J (cm−3 s−1) AF Hb Enthalpy of vaporization at Tb (kJ/mol) AG Evaporation rate Evaporation rate, ER, BuOAc AH Vapour density Vapour density (vs. air) AI Vapour pressure Vapour pressure (kPa) AJ Antoine equation parameter A Antoine equation parameter A (SI system of units) AK Antoine equation parameter B Antoine equation parameter B (SI system of units) AL Antoine equation parameter C Antoine equation parameter C (SI system of units) AM Saturation concentration Saturation concentration in air (g/m) AN Flash point Flash point (◦C) AO Ignition temperature Ignition temperature (◦C) AP Explosion range Vapour explosion range (vol% in air) AQ Critical temperature (K) Vapour/liquid critical temperature Tc (K) ◦ ◦ AR Critical temperature ( C) Vapour/liquid critical temperature Tc ( C) AS Critical pressure Vapour/liquid critical pressure Pc (bar) 3 AT Critical volume Vapour/liquid critical molar volume Vc (cm /mol) AU Critical compressibility factor vapour/liquid critical compressibility factor Zc = Pc · Vc/(R · Tc) =− AV Pitzer acentric factor Pitzer acentric factor ω log10(Pvp/Pc)T/Tc = 0.7 AW Electrical conductivity Electrical conductivity σ ( −1 cm−1) AX Dipole moment Molecular dipole moment D (Debyes), 1 Debye = 3.162 × 10−25 (Jm3)1/2 N AY Polarity parameter Solvent polarity parameter ET AZ Dielectric constant Dielectric constant relative to vacuum ε BA 1000 × dlnε/dT Temperature coefficient of dielectric constant, 1000 × dlnε/dT (K−1) −6 3 BB Magnetic susceptibility Molar magnetic susceptibility χm (10 cm /mol) BC Index of refraction Index of refraction nD at 589 nm BD 1000 × dnD/dT Temperature coefficient of the index of refraction −1 1000 × dnD/dT (K ) BE Kerr coefficient Kerr coefficient B (10−9 cm−1 esE−2); 1 esE = 300 V/cm; Bs = Kerr coefficient of CS2 BF Scattering coefficient Light scattering coefficient R90, relative to benzene BG Depolarization factor Light depolarization factor u × 102 BH IR spectrum Spectrum number in the Sadtler handbook [1003] BI IR/Raman Spectrum Spectrum number in the Raman/IR Atlas [1004] BJ UV–VIS Spectrum Spectrum number in the Perkampus UV–VIS Atlas [1005] BK UV cut-off point UV cut-off point (nm) BL UV 5% absorption UV 5% absorption point (nm) BM Ionization energy Gas phase ionization energy (eV) BN Hf (0) Standard state enthalpy of formation Hf (0) (kJ/mol) BO Gf (0) standard state Gibbs energy of formation for gas Gf (0) (kJ/mol) BP Hildebrandt parameter Hildebrandt solubility parameter δ (MPa1/2) BQ Oxygen solubility Oxygen solubility xg (mole fractions) BR Nitrogen solubility Nitrogen solubility xg (mole fractions) BS CO2 solubility Carbon dioxide solubility xg (mole fractions) BT Solubility in water Solubility in water (g/l) BU Riddick reference Substance number in Riddick handbook [1006] BV Marcus reference Substance number in Marcus handbook [1007] BW Poling reference Substance number in Poling handbook [1008] Ch08-I044498.tex 12/9/2007 17: 21 Page 334

334 Handbook of Liquids-Assisted Laser processing

Table 8.8 Properties of 100 selected liquids listed in Table 8.6

Substance Property code (PC) → EF G H

Molar mass M Molar volume Vliq Density ρ No. Formula or name CAS Reg. No. Hazard codes (g/mol) (cm3/mol) (kg/m3)

1 C5H12 109-66-0 F+ Xn N 72.150 115.22 621.39

2 C5H12 78-78-4 F+ Xn N 72.150 116.46 614.2

3 C6H14 110-54-3 F Xn N 86.177 131.59 654.84

4 C7H16 142-82-5 F Xn N 100.204 147.47 679.46

5 C8H18 540-84-1 F Xn N 114.231 166.07 687.81

6 C5H10 287-92-3 F 70.134 94.73 740.45

7 C6H12 110-82-7 F XnN 84.161 108.75 773.89

8 C7H14 108-87-2 F Xn N 98.188 128.35 765.06

9 C10H18, mix 91-17-8 C N 138.253

9a C10H18, cis 493-01-6 C N 138.253 154.83 892.88

9b C10H18, trans 493-02-7 C N 138.253 159.66 865.96 10 Petroleum 64742-49-0 F+ Xn N 0.645–0.665 ether 101316-46-5

11 CHBr3 75-25-2 T N 252.73 2877.9

12 CH2Cl2 75-09-2 Xn 84.932 64.53 1316.78

13 CHCl3 67-66-3 Xn 119.377 80.68 1479.70

14 CCl4 56-23-5 T N 153.822 97.07 1584.36

15 CHF3 75-46-7 70.014 51.66*

16 C2H4Cl2 107-06-2 T F 98.96 79.45 1246.37

17 C2HCl3 79-01-6 T 131.39 1451.4*

18 C2Cl4 127-18-4 Xn N 165.83 1614.32

19 C6F14 355-42-0 338.044 198.91*

20 C10F18, mix 306-94-5 462.08 1.917*

20a C10F18, cis 60433-11-6 462.08

20b C10F18, trans 60433-12-7 462.08

21 C6H6 71-43-2 F T 78.114 89.41 873.60

22 C6H5Cl 108-90-7 Xn N 112.558 102.22 1100.9

23 C6H4Cl2 95-50-1 Xn N 147.00 1300.33

24 C6H3Cl3 120-82-1 Xn N 181.45

25 C6H5F 462-06-6 F Xi 96.10 1013.14*

26 C6F6 392-56-3 F 186.05 1607.32

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 335

Liquids and their properties 335

Table 8.8 (Continued)

Substance Property code (PC) → EF G H

Molar mass M Molar volume Vliq Density ρ No. Formula or name CAS Reg. No. Hazard codes (g/mol) (cm3/mol) (kg/m3)

27 C7H5N 100-47-0 103.12 1000.6

28 C7H8 108-88-3 F Xn 92.141 106.87 862.19

29 C8H8 100-42-5 Xn 104.15 901.22

30 C8H10 95-47-6 Xn 106.167 121.25 875.94

31 C8H10 108-38-3 Xn 106.167 123.47 860.09

32 C8H10 106-42-3 Xn 106.167 123.93 856.61

33 C9H12 98-82-8 Xn N 120.194 140.17 857.43

34 C10H7Cl 90-13-1 162.62 1193.82*

35 C11H10 90-12-0 Xn N 142.200 139.37* 1016.76

36 CH4O 67-56-1 F T 32.042 40.73 786.37

37 C2H6O 64-17-5 F 46.069 58.68 784.93

38 C2H6O2 107-21-1 Xn 62.07 1110.0

39 C2H3F3O 75-89-8 Xn 100.04 1373.6*

40 C2H7NO 141-43-5 C 61.08 1012.7

41 C3H8O 71-23-8 F Xi 60.096 75.14 799.60

42 C3H8O 67-63-0 F Xi 60.096 76.92 781.26

43 C3H8O3 56-81-5 92.09 1255.9

44 C4H10O 71-36-3 Xn 74.123 91.96 805.75

45 C4H10O 78-92-2 Xi 74.123 92.35 802.41

46 C4H10O 78-83-1 Xi 74.123 92.91 797.8

47 C4H10O 75-65-0 F Xn 74.123 94.88 775.45*

48 C6H15NO3 102-71-6 149.19 1119.6

49 C7H8O 100-51-6 Xn 108.140 1041.27

50 C8H18O 111-87-5 Xi 130.230 158.37 821.57

51 C3H8O2 109-86-4 T 76.09 960.24

52 C4H10O2 110-80-5 T 90.12 925.20

53 C4H10O3 111-46-6 Xn 106.12 1116.4*

54 C6H14O2 111-76-2 Xn 118.17 896.25

55 C4H8O 109-99-9 F Xi 72.107 81.71 889.2*

56 C4H8O2 123-91-1 F Xn 88.106 85.29* 1027.97

57 C4H10O 60-29-7 F+ Xn 74.123 104.75 707.82

(Continued) Ch08-I044498.tex 12/9/2007 17: 21 Page 336

336 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

Substance Property code (PC) → EF G H

Molar mass M Molar volume Vliq Density ρ No. Formula or name CAS Reg. No. Hazard codes (g/mol) (cm3/mol) (kg/m3)

58 C4H10O2 110-71-4 F T 90.126 104.56 863.70

59 C5H12O 1634-04-4 F Xi 88.15

60 C6H14O3 111-96-6 T 134.17 938.4

61 C7H8O 100-66-3 108.14 989.32

62 C8H18O 142-96-1 Xi 130.23 764.1

63 C2H4O2 107-31-3 F+ Xn 60.053 62.14 966.4

64 C4H8O2 141-78-6 F Xi 88.106 98.55 894.55

65 C5H8O2 80-62-6 F Xi 100.12 943.31*

66 C6H12O2 123-86-4 116.160 132.51 876.36

67 C8H8O2 93-58-3 Xn 136.15 1079.01*

68 C3H6O 67-64-1 F Xi 58.080 73.94 784.40

69 C4H8O 78-93-3 F Xi 72.107 90.13 799.7

70 C5H10O 107-87-9 F 86.134 107.33 801.5

71 C6H10O 108-94-1 Xn 98.144 945.2*

72 C6H12O 108-10-1 F Xn 100.161 125.81 796.3

73 C7H14O 110-12-3 Xn 114.19

74 CH3NO 75-12-7 T 45.04 1129.15

75 CH3NO2 75-52-5 Xn 61.040 53.96 1131.28

76 C2H3N 75-05-8 F Xn 41.05 776.49

77 C2H8N2 107-15-3 C 60.10 893.1

78 C3H7NO 68-12-2 T 73.09 943.87

79 C4H9NO 127-19-5 T 87.12 936.337

80 C5H5N 110-86-1 F Xn 79.101 80.88 978.24

81 C5H9NO 872-50-4 Xi 99.13 1025.9

82 H4N2 302-01-2 32.045 31.79*

83 CS2 75-15-0 F T 76.14 1255.5

84 C2H6OS 67-68-5 78.13 1095.37

85 [-Si(CH3)2O-]n 63148-62-9

86 H2O 7732-18-5 18.015 18.07 997.0474

87 D2O 7789-20-0 20.028 18.13 1104.36

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Liquids and their properties 337

Table 8.8 (Continued)

Substance Property code (PC) → EF G H

Molar mass M Molar volume Vliq Density ρ No. Formula or name CAS Reg. No. Hazard codes (g/mol) (cm3/mol) (kg/m3) 88 Sea water

89 H2 1333-74-0 2.016 28.39* 70.721*

90 D2 7782-39-0 4.0282 24.41* 163.94* 91 He 7440-59-7 4.0026 32.54* 125.01*

92 N2 7727-37-9 28.014 34.84* 807.14*

93 O2 7782-44-7 31.999 27.85* 1141.8* 94 Ne 7440-01-9 20.180 16.76* 1207.7* 95 Ar 7440-37-1 39.948 29.10* 1397.1* 96 Kr 7439-90-9 83.800 34.63* 2416.3* 97 Xe 7440-63-3 131.290 42.91* 2947.2*

98 CO2 124-38-9 44.010

99 CH4 74-82-8 F+ 16.0428 35.54* 422.7* 100 Air 28.958 875.99*

(PC) → IJKLM N O Melting Melting Heat Diffision Heat

dρ/d T point Tm point Tm Hm capacity coefficient conductivity 3 ◦ −5 2 No. (kg/m K) (K) ( C) (kJ/mol) Cpliq ( J/molK) D (10 cm /s) λ ( J/sm K)

1 −0.975 143.43 −129.72 8.40 167.19 5.62 2 −1.02 113.26 −159.89 5.16 164.80 4.85 3 −0.891 177.84 −95.31 13.07 195.43 4.21 0.123* 4 −0.840 182.59 −90.56 14.03 224.98 3.11 5 −0.824 165.80 −107.35 9.04 238.55 2.42 0.0967* 6 −0.986 179.28 −93.87 0.61 126.80 7 279.69 6.54 2.63 156.20 1.41 8 146.56 −126.59 6.75 184.50 9 9a −0.760 230.14 −43.01 232.00 0.46 9b −0.749 242.75 −30.40 228.50 10 <193 <−80 11 −2.61 282.35 9.2 1.58

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338 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → IJKLM N O Melting Melting Heat Diffision Heat

dρ/d T point point Hm capacity coefficient conductivity 3 ◦ −5 2 No. (kg/m K) Tm (K) Tm ( C) (kJ/mol) Cpliq ( J/molK) D (10 cm /s) λ ( J/sm K)

12 −1.80 176.00 −97.15 4.60 100.00 3.78 13 −1.857 209.74 −63.41 8.80 113.80 2.31 14 −1.931 250.33 −22.82 3.28 131.60 1.32 0.00028* 15 117.96 −155.19 16 −1.44 237.65 −35.5 8.84 126.30 1.72 17 −1.649 187.15 −86 18 −1.646 251.15 −22 19 186.05 −87.1 20 273.15 0 20a 20b 21 −1.051 278.68 5.53 9.95 135.95 2.16 22 −1.081 227.90 −45.25 9.61 150.80 2.35 23 −1.112 256.15 −17 24 256.15 −17 25 1.18 231.15 −42 11.31 146.36 26 2.278 ≈277 3.7−4.1 11.585 221.610 1.61 27 −0.88 260.15 −13 28 −0.929 178.16 −94.99 6.95 157.29 2.59 0.1296 29 −0.8739 242.15 −31 30 −0.840 247.97 −25.18 13.60 188.07 1.61 31 −0.855 225.28 −47.87 11.57 188.44 2.56 32 −0.873 286.41 13.26 16.81 181.66 2.75 33 −0.853 177.12 −96.03 7.79 213.30 1.68 34 −0.77 270.7 −2.45 35 −0.727 242.69 −30.46 6.94 224.40 36 −0.9321 175.49 −97.66 3.18 81.08 2.32 0.21* 37 −0.856 159.05 −114.1 5.01 112.25 1.01 0.170* 38 −0.70 260.15 −13 0.261* 39 229.65 −43.5

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Liquids and their properties 339

Table 8.8 (Continued)

(PC) → IJKLM N O Melting Melting Heat Diffision Heat

dρ/d T point point Hm capacity coefficient conductivity 3 ◦ −5 2 No. (kg/m K) Tm (K) Tm ( C) (kJ/mol) Cpliq ( J/molK) D (10 cm /s) λ ( J/sm K)

40 −0.78 283.65 10.5 0.05 41 −0.79 147.00 −126.15 5.20 143.73 0.65 0.158* 42 −0.82 183.65 −89.5 5.38 154.40 0.65 0.141* 43 −0.615 291.15 18 0.310* 44 −0.76 183.35 −89.8 9.28 177.06 0.51 0.153* 45 −0.80 158.50 −114.65 199.00 46 −0.76 165.15 −108 183.00 0.139* 47 −1.032 298.55 25.4 6.79 220.10 0.51 0.115* 48 −0.55 294.15 21 49 −0.74 257.80 −15.35 8.97 50 −0.81 257.65 −15.5 302.40 0.14 0.160* 51 −0.780 188.15 −85 52 −0.70 173.15 −100 53 −0.72 263.15 −10 54 −0.66 203.15 −70 55 −1.01 164.61 −108.54 8.54 124.10 0.141* 56 −1.128 284.15 11 12.85 154.50 1.01 57 −1.154 156.86 −116.29 7.27 172.60 6.1 58 204.15 −69 59 164.55 −108.6 60 −1.06 209.15 −64 61 −0.932 236.15 −37 1.35 62 −0.86 178.15 −95 63 −1.56 174.15 −99 119.70 64 −1.20 189.55 −83.6 10.48 170.60 2.77 0.143* 65 −1.16 225.15 −48 66 −1.02 199.65 −73.5 14.59 228.40 0.137* 67 −0.955 261.15 −12 68 −1.12 178.50 −94.65 5.69 126.60 4.77 0.1791* 69 −0.84 186.51 −86.64 8.44 158.90 0.150*

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340 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → IJKLM N O Heat Heat Melting Melting capacity Diffision conductivity

dρ/d T point point Hm Cpliq ( J/molK) coefficient λ ( J/sm K) 3 ◦ −5 2 No. (kg/m K) Tm (K) Tm ( C) (kJ/mol) [kJ/kg k] D (10 cm /s) [mW/mK]

70 −0.98 196.34 −76.81 10.63 184.5 71 −0.89 242.15 −31 0.89 72 −0.78 189.15 −84 73 199.15 −74 74 275.15 2 75 −1.377 244.60 −28.55 106.80 2.11 0.203* 76 −1.078 227.45 −45.7 4.85 77 −0.88 284.15 11 78 −0.72 212.15 −61 1.61 79 253.15 −20 0.174* 80 −0.99 231.43 −41.72 8.28 132.70 1.49 81 −0.92 249.15 −24 0.78 0.190* 82 274.68 1.53 12.66 96.8 83 161.55 −111.6 4.11 84 −0.99887 291.65 18.5 0.76 85 86 273.15 0 6.01 75.29 2.272 0.610 87 276.96 3.81 6.38 84.35 2.109 0.595 88 89 13.83 −259.32 0.12 [9.711]* [71.6]* 90 18.63 −254.52 0.20 [7.503]* 91 2.15 −271 [5.242]* [18.7]* 92 63.15 −210 0.72 [2.042]* [133.2]* 93 54.36 −218.79 0.44 [1.699]* [152.0]* 94 24.56 −248.59 [1.861]* [125.7]* 95 83.80 −189.35 [1.078]* [128.5]* 96 115.77 −157.38 [0.5218]* [89.0]* 97 161.25 −111.9 [0.3484]* 98 216.58 −56.57 9.02 99 [3.49]* [188.7]* 100 [1.937]* [139.9]*

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Liquids and their properties 341

Table 8.8 (Continued)

(PC) → PQ R S T U V

Dynamic viscosity Surface η g/m s) Thermal Isothermal Adiabatic tension [kinematic, d(ln η)/d T Relaxation expansion compressibility compressibility 2 −2 −1 −3 −1 −1 −1 No. γ (N/m) mm /s] (10 K ) time τ (ps) β (10 K ) κT (GPa ) κS (GPa )

1 0.01548 0.225 0.84 1.610 2.180 1.5955 2 0.01446 0.215 0.93 2.450 3 0.01794 0.2942 0.86 7.4 1.391 1.706 1.3180 4 0.126* 0.3967 1.05 1.440 1.2043* 5 0.01832 0.504* 1.20 6 0.02188 0.416 1.347 1.358 7 0.02465 0.898 1.75 10 1.220 1.140 0.8220 8 0.02329 0.685 9 9a 0.03218 3.381 2.23 0.867 9b 0.03015 2.128 0.865 10 11 0.04510* 1.741* 1.29 12 0.02789* 0.4043* 0.93 8 1.391* 1.026 13 0.02653 0.5357 1.00 7.4 1.26* 0.9980* 0.7571* 14 0.02613 0.9004 1.42 4.5 1.229 1.0799 0.747 15 16 0.03223 0.730* 1.27 6.9 1.141* 0.846* 17 0.0288 0.532 0.91 1.17 18 0.03130 0.798* 1.04 1.02 0.555* 19 20 [2.66]* 20a 20b 21 0.02820 0.6028 1.27 16 1.213 0.9660 0.67826 22 0.03296* 0.799* 1.15 10.3 0.990 0.731* 0.771 23 0.02684* 1.324 1.44 0.85* 24 1.83

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342 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → PQR S T U V Surface Dynamic Thermal Isothermal Adiabatic tension viscosity d(ln η)/d T Relaxation expansion compressibility compressibility −2 −1 −3 −1 −1 −1 No. γ (N/m) η (g/m s) (10 K ) time τ (ps) β (10 K ) κT (GPa ) κS (GPa )

25 0.02647* 0.517* 1.25 5.6 1.92 26 0.02164 0.860 2.05 42 1.412 27 0.03843* 1.237 1.51 37.9 0.531* 28 0.02792 0.5525 1.15 7.4 1.067 0.9115 0.696 29 0.0323* 0.696 1.42 30 0.02949 0.756 1.36 9.6 0.952 0.8105 0.636 31 0.02810 0.581 1.19 0.981 0.8621 0.667 32 0.02776 0.605 1.21 0.956 0.8588 0.673 33 0.02768 0.739 1.35 0.893 34 0.04104* 2.940 0.699 35 0.03980* 3.10* 36 0.02230 0.5513 1.32 53 1.196 1.248 1.028 37 0.02232* 1.0826 1.91 143 1.096 1.153 0.9460 38 0.04849* 13.759* 205 0.626* 39 1.543* 2.57 40 0.04889* 19.346 4.14 0.79* 41 0.02345* 1.9430 2.37 430 1.004 1.026 0.849 42 0.02096* 2.0436 2.92 290 1.064 1.332* 1.066* 43 0.0633* 945 0.520* 0.219* 44 0.02467* 2.5710 2.55 480 0.948 0.942 0.866 45 0.02337* 2.998 3.96 500 1.024 46 0.02298* 3.3330 3.24 800 0.95 0.950* 47 0.02002* 4.438 2.80 1.325* 48 613.6 7.78 0.53* 49 0.03996* 4.650* 3.30 0.75* 50 0.02692* 7.363 3.59 1360 0.827 0.764 51 0.02928* 1.60 2.53 0.95* 52 0.0282 1.85 2.70 0.97*

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Liquids and their properties 343

Table 8.8 (Continued)

(PC) → PQR S T U V Surface Dynamic Thermal Isothermal Adiabatic tension viscosity d(ln η)/d T Relaxation expansion compressibility compressibility −2 −1 −3 −1 −1 −1 No. γ (N/m) η (g/m s) (10 K ) time τ (ps) β (10 K ) κT (GPa ) κS (GPa )

53 0.0485* 30 4.69 470 0.635* 54 0.0274 3.15 0.92* 55 0.0264 0.460 1.04 2.87 1.138* 56 0.03280 1.087* 1.77 1.115* 0.738 0.539 57 0.01650 0.242* 1.01 2.18 1.654 58 0.02461* 0.455 1.06 3.6 1.19* 59 60 0.0296 0.989 1.57 61 0.03500* 0.789* 1.51 9.6 0.951* 62 0.02199* 0.602* 63 0.02462* 0.328 0.94 64 0.02375* 0.426 1.10 4.35 1.39* 0.8987* 65 0.0285* 0.6322* 66 0.02509* 0.7375* 1.34 1.17* 0.8390* 67 0.03814* 1.673* 2.09 0.876* 68 0.02268 0.3029 0.95 3.34 1.43* 1.324 1.025* 69 0.02397* 0.378 1.09 10 1.19* 1.188 70 0.02509* 0.489* 1.13 1.092 71 0.03505* 1.810* 2.01 10.4 0.955* 0.5391* 72 0.02329* 0.5463 1.34 0.116* 73 74 0.05815 3.302 2.62 37.4 0.775* 0.399* 75 0.03719* 0.614 1.17 1.24* 0.59* 76 0.02825 0.341 0.96 3.21 1.368* 1.07* 77 0.04077* 1.54 2.55 1.024 0.508 0.416* 78 0.03642 0.802 1.22 10.4 1.00* 79 0.03243* 0.927 1.19 16 80 0.03633 0.884 1.53 7.27 1.070*

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344 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → PQRS T U V Surface tension Dynamic Thermal Isothermal Adiabatic γ (N/m) viscosity d(ln η)/d T Relaxation expansion compressibility compressibility −2 −1 −3 −1 −1 −1 No. [dyne/cm] η (g/m s) (10 K ) time τ (ps) β (10 K ) κT (GPa ) κS (GPa )

81 0.0407 1.666 1.88 82 1.64 83 0.03225* 0.363* 0.72 4.5 1.218* 0.950 84 0.04298 1.991 1.93 4.7 0.928* 0.52 85 86 0.07198 0.8909 2.21 9.45 0.25705 0.4524 0.4477 87 0.07187 1.095 0.1722 0.4736 0.4625 88 0.9654 89 0.00194* 0.0134* 90 91 0.0032* 92 0.1507* 93 0.01320* 0.1954* 94 0.1247* 95 [10.53]* 0.2612* 96 0.4011* 97 98 99 0.1178* 100 0.1640*

(PC) → W X Y Z AA AB AC Sound Acoustic Ultrasound Acoustic Shock Boiling Boiling velocity impedence absorption non-linearity velocity point point −15 2 ◦ No. vL (m/s) Z (Mrayls = MPa s/m) (10 s /m) B/A Us (m/s) Tb (K) Tb ( C)

1 1020 0.634 309.22 36.07 2 300.99 27.84 3 1112 0.728 60 9.9* 5540* 341.84 68.69 4 1131 0.768 10.0* 371.57 98.42

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Liquids and their properties 345

Table 8.8 (Continued)

(PC) → W X Y Z AA AB AC Sound Acoustic Ultrasound Acoustic Shock Boiling Boiling velocity impedence absorption non-linearity velocity point point −15 2 ◦ No. vL (m/s) Z (Mrayls = MPa s/m) (10 s /m) B/A Us (m/s) Tb (K) Tb ( C)

5 372.39 99.24 6 322.38 49.23 7 1248 0.966 192 10.1* 353.93 80.78 8 374.09 100.94 9 9a 124 468.92 195.77 9b 460.42 187.27 10 30−80 11 918 2.642 262 422.65 149.5 12 1070 1.409 779 312.79 39.64 13 979 1.449 363 334.33 61.18 14 926 1.467 546 3510* 349.79 76.64 15 191.11 −82.04 16 1193 1.487 356.7 83.55 17 1028 360 87 18 1036 1.672 394 121 19 508 329.75 56.6 20 415 142 20a 20b 21 1306 1.141 850 9.2* 4100* 353.24 80.09 22 1273 1.401 147 9.3* 404.91 131.76 23 132 453 180 24 110 486.65 213.5 25 1273 357.884 84.734 26 353.405 80.255 27 464 191 28 1328* 86 4120* 383.79 110.64 29 418 145 30 1331.5 1.166 63 417.59 144.44

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346 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → W X Y Z AA AB AC Sound Acoustic Ultrasound Acoustic Shock Boiling Boiling velocity impedence absorption non-linearity velocity point point −15 2 ◦ No. vL (m/s) Z (Mrayls = MPa s/m) (10 s /m) B/A Us (m/s) Tb (K) Tb ( C)

31 1343* 412.34 139.19 32 1334* 411.53 138.38 33 65 425.52 152.37 34 532.15 259 35 517.84 244.69 36 1076 0.846 30 9.6* 5510* 337.69 64.54 37 1207 0.947 52 10.5* 5630* 351.80 78.65 38 1658 1.840 9.7* 470.75 197.6 39 346.75 73.6 40 1724 1.746 166 444.15 171 41 1222* 10.7* 370.93 97.78 42 1170* 355.39 82.24 43 1904 2.391 4580* 563.15 290 44 81 10.7* 390.88 117.73 45 1240 0.995 372.66 99.51 46 1212 0.967 153 381.04 107.89 47 355.49 82.34 48 633.15 360 49 79 10.2* 478.46 205.31 50 468.33 195.18 51 398.15 125 52 408.15 135 53 1586 ≈518 242−247 54 ≈442 168−170 55 339.12 65.97 56 1376 1.414 117 374.50 242−247 57 985 0.697 45 5400* 307.59 168−170 58 358.15 85 59 328.45 55.3 60 ≈433 155−165

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Liquids and their properties 347

Table 8.8 (Continued)

(PC) → W X Y Z AA AB AC Sound Acoustic Ultrasound Acoustic Shock Boiling Boiling velocity impedence absorption non-linearity velocity point point −15 2 ◦ No. vL (m/s) Z (Mrayls = MPa s/m) (10 s /m) B/A Us (m/s) Tb (K) Tb ( C)

61 44 429.15 156 62 ≈415 140−143 63 49 304.90 242−247 64 1085 0.971 350.21 168−170 65 374.15 101 66 399.12 125.97 67 472.15 199 68 1174 0.921 26 9.2* 5370* 329.22 56.07 69 352.71 79.56 70 375.39 102.24 71 73 428.59 155.44 72 389.15 116 73 417.15 144 74 1622 1.831 39 483.15 210 75 1300 1.471 374.35 101.2 76 1290 1.002 354.75 81.6 77 389.15 116 78 426.15 153 79 ≈438 165−166 80 1415 1.384 388.37 115.22 81 475.15 202 82 386.65 113.5 83 1149 1.443 2068 319.65 46.5 84 462.15 189 85 >410 >140 86 1498 1.494 21 5.0* 3910* 373.15 100 87 1400 1.546 374.55 101.4 88 1531 5.25* 89 1098* 11800* 20.345 −252.805 90 876* 10970* 23.264 −249.886

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348 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → W X Y Z AA AB AC Sound Acoustic Ultrasound Acoustic Shock Boiling Boiling velocity impedence absorption non-linearity velocity point point −15 2 ◦ No. vL (m/s) Z (Mrayls = MPa s/m) (10 s /m) B/A Us (m/s) Tb (K) Tb ( C)

91 177* 4.2221 −268.928 92 851* 6.6* 5090* 77.237 −195.913 93 905* 4644* 90.062 −183.088 94 595* 27.061 −246.089 95 831* 6052* 87.169 −185.981 96 691* 119.62 −153.53 97 639* 164.78 −108.37 98 839* 99 1340* 111.51 −161.64 100 865* 78.9 −194.25

(PC) → AD AE AF AG AH AI AJ Superheat Nucleation Evaporation Vapour Vapour Antoine temperature rate J Hb rate density pressure equation ◦ −3 −1 −1 No. Tsh ( C) (cm s ) (kJ mol ) BuOAc vs. air (kPa) parameter A

1 145 104−1018 25.79 2.48 68.33 5.97786 2 138 10−107 24.69 2.6 91.7 5.92023 3 182 100−1020 28.85 8.9 ∼3 20.17 6.00091 4 213.5 106−1018 31.77 3.5 6.09 6.02167 5 215.3 30.79 3.9 6.5 5.92885 6 180 106 27.30 ∼2 42.4 6.04584 7 218.5 106 29.97 2.9 13.04 5.96407 8 237.2 31.27 3.4 6.1 5.94790 9 4.76 9a 41.00 0.10 6.00019 9b 40.20 0.164 5.98171 10 2.5 11 8.7 0.79 6.15631 12 179.9 28.06 14.5 2.9 58.10 6.07622 13 173 100 29.24 10.45 4.1 25.97 5.96288 14 25* 1000 29.82 6.0 5.32 15.36 6.10445

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Liquids and their properties 349

Table 8.8 (Continued)

(PC) → AD AE AF AG AH AI AJ Superheat Nucleation Evaporation Vapour Vapour Antoine temperature rate J Hb rate density pressure equation ◦ −3 −1 −1 No. Tsh ( C) (cm s ) (kJ mol ) BuOAc vs. air (kPa) [mmHg] parameter A

15 2.43 16 31.98 4.46 3.4* 11.11* 6.28356 17 4.46 4.5 6.307 6.15298 18 2.10 5.83 2.462 6.10170 19 136.6 106 20 78.7 17.5 [6.6]* 20a 20b 21 225.3 100−1018 30.72 5.1 2.77 12.7 6.02232 22 250 100 35.19 3.86 1.567 6.30963 23 0.15 5.1 0.171 6.19518 24 >6 25 31.20 10.48 6.07698 26 191.7 10−106 31.670 10.733* 6.14231 27 0.1* 5.87121 28 253.5 100 33.18 1.90 3.2 3.8036 6.08540 29 3.6 0.841 6.34792 30 36.24 3.7 0.88 6.13072 31 235 35.66 3.7 1.1 6.13785 32 35.67 3.7 1.2 6.11140 33 37.50 4.1 0.61 6.06588 34 0.052* 35 46.00 0.00895 6.16082 36 186 10–1018 35.21 2.10 1.11 16.937 7.20519 37 190.9 10–104 38.56 1.60 1.59 7.870 7.16879 38 <0.01 2.1 0.0117 6.83995 39 3.5 10.09 5.9656 40 2.1 0.048* 6.86290 41 222.5 10–1018 41.44 0.86 2.1 2.798 6.87613 42 200 106 39.85 2.30 2.1 5.775 6.86618

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350 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → AD AE AF AG AH AI AJ Superheat Nucleation Evaporation Vapour Vapour Antoine temperature rate J Hb rate density pressure equation ◦ −3 −1 −1 No. Tsh ( C) (cm s ) (kJ mol ) BuOAc vs. air (kPa) parameter A

43 3.1 0.00033* 44 245.0 100–1018 43.29 0.43 2.55 0.910 6.54743 45 40.75 0.81 2.6 2.317 6.35457 46 437.2 10 41.82 0.62 2.55 1.527 6.50091 47 39.07 1.30 2.5 5.637 6.35648 48 5.14 <0.0013* 7.67989 49 3.7 0.015 50 313 104 46.90 <0.01 4.5 0.010 5.88511 51 0.52 2.62 1.3 6.8334 52 0.38 3.1 0.71 6.9440 53 <0.001 2.14 0.00060 6.67111 54 0.07 4.1 0.114 55 29.81 4.72 2.5 21.60 6.79696 56 34.16 2.42 3 4.95 57 147 100–1019 26.52 33 2.6 71.622 6.05115 58 36.69 4.99 3.1* 6.40* 5.7736 59 3.1 60 0.36 4.6 0.45 61 3.7 0.472 6.17595 62 4.48 0.898 5.930185 63 150 10 27.92 2.1 78.06 6.29529 64 31.94 3.90 3* 12.600 6.18799 65 3.5 5.1 66 36.28 0.98 4 1.664 6.151445 67 4.86 0.05258 6.60743 68 181.7 10–1018 29.10 5.59 2 30.806 6.25478 69 31.30 3.8 2.49 12.079 6.18444 70 33.44 2.50 3 4.720 6.13925 71 0.29 3.4 0.64 6.103304

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Liquids and their properties 351

Table 8.8 (Continued)

(PC) → AD AE AF AG AH AI AJ

Superheat Nucleation Hb Evaporation Vapour Vapour Antoine temperature rate J (kJ mol−1) rate BuOAc density pressure equation ◦ −3 −1 −1 −2 −1 6 No. Tsh ( C) [k] (cm s ) [kJ kg ][kgms 10 ] vs. air (kPa) [mbar] parameter A

72 34.49 1.62 3.5 2.51 6.0976 73 3.94 74 1.55 3.96 75 33.99 1.3 2.1 4.888 6.399073 76 224 106 1.41 11.84 6.24747 77 2.07 1.75* 78 0.20 2.5 0.49 6.2334 79 3 0.17 6.88718 80 35.09 2.72 2.7* 6.18595 81 <0.1 3.4 0.0445 82 25.20 1* 83 168 2.67 48.21 6.06684 84 2.7 0.0800 6.72167 85 >1 86 270 106−1015 40.66 [100**] 0.62 3.165 8.07131** 87 41.46 88 [31.12] 89 [27.9]* 100 0.89 0.07* 90 1.23 0.07 91 [4.55]* 107 0.08 0.14 92 [110] 1 5.58 0.97 93 [134.1] 1 6.82 1.105* 94 1.71 0.7* 95 [130.8] 100 6.43 1.38* 96 [182.5]* 105 9.08 2.899* 97 [254.1]* 105 12.57 4.560* 98 1.52 99 [167.6]* 105 0.55 100 [205.1] 1.00

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352 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → AK AL AM AN AO AP AQ Antoine Antoine Saturation Flash Ignition Explosion Critical equation equation concentration point temperature range temperature No. parameter B parameter C (g/m3)(◦C) (◦C) (vol% in air) (K)

1 1064.84 232.012 1689* −48 c.c. 285 1.4–8 469.70 2 1022.88 233.460 −57 c.c. 420 1.3–7.6 460.39 3 1171.17 224.408 563* −22 c.c. 240 1.0–8.1 507.60 4 1264.90 216.544 196* −4 c.c. 215 1–7 540.20 5 1253.36 220.241 239* −12 c.c. 410 1–6 543.90 6 1142.30 233.463 1470* −42 380 1.5–8.7 511.60 7 1200.31 222.504 357* −18 260 1.2–8.3 553.50 8 1270.763 221.416 192* −4 c.c. 260 1.1–6.7 572.19 9 58 255 0.7–4.9 9a 1594.460 203.392 703.60 9b 1564.683 206.259 678.00 10 <−21c.c. 250 0.8–7.4 11 1511.50 214.959 12 1070.07 223.24 1549* 605 13–22 510.00 13 1106.94 218.552 1027* 536.50 14 1265.632 232.148 754* >982 556.30 15 298.97 16 1341.37 230.05 350* 13 c.c. 412.6–440 6–11.4 17 1315.04 230.0 145* 410 7.9-100 18 1386.90 217.52 126* 19 448.7 20 20a 20b 21 1206.53 220.91 319* −11 555 1.4–8 562.05 22 1556.6 230 27 c.c. 590 1.3–11 632.40 23 1649.55 213.314 8* 66 c.c. 640 2.2–12 24 2* 99 c.c. 571 2.5–6.6 25 1248.083 221.827 −15 c.c. 630 1.3- 8.9 560.09 26 1219.410 214.525 516.78

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Liquids and their properties 353

Table 8.8 (Continued)

(PC) → AK AL AM AN AO AP AQ Antoine Antoine Saturation Flash Ignition Explosion Critical equation equation concentration point temperature range temperature No. parameter B parameter C (g/m3)(◦C) (◦C) (vol% in air) (K)

27 1436.72 181.0 70 550 1.4–7.2 28 1348.77 219.976 110* 4 c.c. 535 1.2–8 591.75 29 1629.2 230 25.6* 31 c.c. 480 1.1–8.9 30 1479.82 214.315 29* 30 465 1.0–7.6 630.30 31 1465.39 215.512 35* 25 ∼525 1.1–7 617.00 32 1451.39 215.148 38* 25 c.c. 525 1.1–7 616.20 33 1464.17 208.207 22* 31 c.c. 420 0.8–6.0 631.00 34 35 1826.948 195.002 122 529 772.00 36 1581.993 239.711 11 c.c. 455 5.5–36.5 512.64 37 1552.601 222.419 105* 12 c.c. 425 3.5–15 513.92 38 1818.591 178.651 0.15* 111 c.c. 410 1.8–12.8 39 952.466 166.587 33 8.4–28.8 40 1732.11 186.215 92.5 410 3.4–27 41 1441.705 198.859 46* 15 c.c. 360 2.1–13.5 536.78 42 1360.131 197.592 105* 12 c.c. 425 2–12.7 508.30 43 ∼180 o.c. 400 0.9 44 1338.769 177.042 20* 30 340 1.4–11.3 563.05 45 1171.891 169.955 52* 24 390 1.4–9.8 536.05 46 1295.197 175.787 36* 28 c.c. 430 1.6–12 547.78 47 1107.060 172.102 122* 14 c.c. 490 2.3–8.0 506.21 48 2962.73 186.750 190 325 3.6–7.2 49 0.56* 101 435 1.3–13 715.00 50 1264.322 130.73 ∼90 270 0.8 652.50 51 1711.2 230 33* 37 325 2.5–20 52 1801.9 230 18* ∼40 c.c. 235 1.8–15.7 53 1897.637 161.067 0.12* 140 c.c. 345 0.7–22 54 5* 63–64 230 1.1–10.6 55 1557.06 260.05 557* −21.5 c.c. 215 1.5–12.4 540.20 56 149* 11 c.c. 300 1.7–25.2 587.00

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Table 8.8 (Continued)

(PC) → AK AL AM AN AO AP AQ Antoine Antoine Saturation Flash Ignition Explosion Critical equation equation concentration point temperature range temperature No. parameter B parameter C (g/m3)(◦C) (◦C) (vol% in air) (K)

57 1062.409 228.183 1776* −41 180 1.7–36 466.70 58 1217.03 230 200* −6 c.c. 200 1.6–10.4 537.00 59 −28 c.c. 460 1.65–8.4 60 51 190 1.4–17.4 61 1489.502 203.573 6* 43 c.c. 475 0.34–6.3 62 1302.768 191.669 25 185 0.9–8.5 63 1125.2 230.56 1569* −28 440 5–23 487.20 64 1224.673 215.712 336* −4 c.c. 460 2.1–11.5 523.20 65 10 430 2.1–12.5 66 1368.051 203.9298 62* 25 c.c. 370 1.4–7.5 579.00 67 1974.6 230 82 c.c. 510 8.6–20 68 1216.689 230.275 533* <−20 c.c. 465 2.6-12.8 508.10 69 1259.223 221.758 310* −4 514 1.8-11.5 536.80 70 1309.592 214.561 52* 7 449 1.5–8.2 561.10 71 1495.511 209.5517 19* 43 430 1.3–9.4 653.00 72 1190.69 195.45 82* 14 460 1.2–8.0 574.60 73 43 o.c. 455 1.4–8.8 74 0.24* 175 o.c. 500 2.7-19.0 75 1441.610 226.939 90* 35.6 c.c. 418 7.3-63.0 588.00 76 1315.2 230 163* 2 c.c. 524 3.0–17 77 29* ∼36 c.c. 400 2.5-16.3 78 1537.78 210.39 12* 58 c.c. 410 2.2–16 79 1889.10 221.0 12* 70 400 1.7-11.5 80 1386.683 216.469 65* 17 c.c. 550 1.7-12.4 620.00 81 91 c.c. 245 1.3–9.5 82 653.01 83 1168.623 241.534 1244* −30 95 1–60 84 1962.05 225.892 8.0* 95 o.c. 301 1.8-63.0 85 86 1730.63** 233.426** 22.9 647.14

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Liquids and their properties 355

Table 8.8 (Continued)

(PC) → AK AL AM AN AO AP AQ Antoine Antoine Saturation Flash Ignition Explosion Critical equation equation concentration point temperature range temperature No. parameter B parameter C (g/m3)(◦C) (◦C) (vol% in air) (K)

87 643.89 88 89 33.19 90 38.34 91 5.1953 92 126.193 93 154.581 94 44.4918 95 150.6633 96 209.433 97 289.734 98 304.12 99 998◦F 15 190.55 100 132.5168

(PC) → AR AS AT AU AV AW AX Critical Critical Critical Critical Pitzer Electrical Dipole temperature pressure volume compressibility factor acentric conductivity, σ moment D ◦ 3 −1 −1 No. Tc ( C) Pc (bar) Vc (cm /mol) Zc = Pc · Vc/(R · Tc ) factor ( cm ) (Debyes)

1 196.55 33.70 311.00 0.268 0.252 2 × 10−8* 0.0 2 187.24 33.81 308.30 0.272 0.229 0.1 3 234.45 30.25 368.00 0.264 0.300 <10−14 0.085 4 267.05 27.40 428.00 0.261 0.350 <10−14 0.0 5 270.75 25.70 469.70 0.266 0.304 0 6 238.45 45.08 260.00 0.276 0.0 7 280.35 40.73 308.00 0.273 0.211 ∼7 × 10−16 0.3 8 299.04 34.71 368.00 0.268 0.235 <10−14 0.0 9 9a 32.00 480.00 0.265 0.276 0.0 9b 32.00 480.00 0.272 0.303 0.0 10

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Table 8.8 (Continued)

(PC) → AR AS AT AU AV AW AX Critical Critical Critical Critical Pitzer Electrical Dipole temperature pressure volume compressibility factor acentric conductivity, σ moment D ◦ 3 −1 −1 No. Tc ( C) Pc (bar) Vc (cm /mol) Zc = Pc · Vc/(R · Tc ) factor ( cm ) (Debyes)

11 <2 × 10−6 0.99** 12 236.85 61.00 4.3 × 10−9 1.8 13 263.35 55.00 240.00 0.296 <1 × 10−8 1.1 14 283.15 45.57 276.00 0.271 4 × 10−16* 0.0 15 25.82 48.36 133.00 0.259 0.267 1.6 16 4 × 10−9 1.8 17 8 × 10−10* 0.8*** 18 0.0555* 0*** 19 175.55 18.70 573.20 0.274 0.513 0.0 20 20a 20b 21 288.90 48.95 256.00 0.268 0.210 4.43 × 10−15 0.0 22 359.25 45.20 308.00 0.265 0.251 7 × 10−9 1.6 23 3 × 10−9 24 25 286.94 45.505 354.1 1.48 26 243.63 32.73 335.1 0.255 0.396 0 27 5 × 10−6 28 318.60 41.08 316.00 0.264 0.264 8 × 10−14 0.4 29 30 357.15 37.32 370.00 0.263 0.312 6.7 × 10−14 0.5 31 343.85 35.41 375.00 0.259 0.327 8.6 × 10−14 0.3 32 343.05 35.11 378.00 0.259 0.322 7.6 × 10−14 0.1 33 357.85 32.09 434.70 0.261 0.326 0.8 34 35 498.85 36.00 462.00 0.259 0.348 0.5 36 239.49 80.97 118.00 0.224 0.565 1.5 × 10−7 1.7 37 240.77 61.48 167.00 0.240 0.649 1.35 × 10−7 1.7 38 0.000116 39

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Liquids and their properties 357

Table 8.8 (Continued)

(PC) → AR AS AT AU AV AW AX Critical Critical Critical Critical Pitzer Electrical Dipole temperature pressure volume compressibility factor acentric conductivity, σ moment D ◦ 3 −1 −1 No. Tc ( C) Pc (bar) Vc (cm /mol) Zc = Pc · Vc/(R · Tc ) factor ( cm ) (Debyes)

40 0.00110 41 263.63 51.75 219.00 0.254 0.629 9.17 × 10−7* 1.7 42 235.15 47.62 220.00 0.248 0.665 5.8 × 10−6 1.7 43 ∼6 × 10−6 44 289.90 44.23 275.00 0.260 0.590 9.12 × 10−7* 1.8 45 262.90 41.79 269.00 0.252 0.574 <1 × 10−5* 1.7 46 274.63 43.00 273.00 0.258 0.590 1.6 × 10−8 1.7 47 233.06 39.73 275.00 0.260 0.613 2.66 × 10−6* 1.7 48 49 441.85 43.00 0.390 1.7 50 379.35 28.60 490.00 0.258 0.594 1.39 × 10−5* 2.0 51 1.09 × 10−4* 52 9.3 × 10−6* 53 5.86 × 10−5* 54 4.32 × 10−5* 55 267.05 51.90 224.00 0.259 0.0045-9.3 × 10−6* 1.7 56 313.85 51.70 238.00 0.255 5 × 10−13 0.0 57 193.55 36.40 280.00 0.263 0.281 <3 × 10−14* 1.3 58 263.85 270.64 59 60 61 1 × 10−11 62 63 214.05 60.00 172.00 0.255 0.000192* 1.8 64 250.05 38.30 286.00 0.252 0.361 <1 × 10−7* 1.9 65 66 305.85 30.90 412.80 0.253 0.407 1.6 × 10−6** 1.8 67 0.00137* 68 234.95 47.00 209.00 0.233 0.307 4.9 × 10−7 2.9 69 263.65 42.10 267.00 0.252 0.322 3.6 × 10−7* 3.3 70 287.95 36.90 301.00 0.238 0.346 2.5

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358 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → AR AS AT AU AV AW AX Critical Critical Critical volume Critical Pitzer Electrical Dipole 3 temperature pressure Vc (cm /mol) compressibility factor acentric conductivity, σ moment D ◦ 3 −1 −1 No. Tc ( C) Pc (bar) [kg/m ] Zc = Pc · Vc/(R · Tc ) factor ( cm ) (Debyes)

71 379.85 40.00 0.299 5 × 10−16 72 301.45 32.70 340.60 0.256 0.351 <5.2 × 10−6* 2.8 73 74 <2 × 10−5* 75 314.85 58.70 173.00 0.208 5 × 10−7 3.1 76 6 × 10−8 77 9 × 10−6 78 6 × 10−6 79 80 346.85 56.70 254.00 0.267 0.242 4.0 × 10−6 2.3 81 1–2 × 10−6 82 379.86 147.00 101.10 0.282 3.0 83 0.37 84 2 × 10−7 85 86 373.99 220.64 55.95 0.229 0.344 1.2 × 10−6* 1.854 87 370.74 216.71 56.26 0.228 1.9 88 42.9 × 10−3* 89 −239.96 13.152 66.95 0.303 −0.214 0.0 90 −234.81 16.653 57.71 0.312 −0.175 0.0 91 −267.95 2.2746 58.22 0.301 −0.382 0.0 92 −146.96 33.978 89.47 0.289 0.037 0.0 93 −118.57 50.43 73.37 0.288 0.022 0.0 94 −228.66 26.786 41.87 0.312 −0.039 0.0 95 −122.49 48.6 75.24 0.291 −0.004 0.0 96 −63.72 55.1 92.30 0.288 −0.00313 0.0 97 16.58 58.4 119.47 0.286 0.00336 0.0 98 30.97 73.74 94.07 0.274 0.225 0.0 99 −82.60 45.992 [162.65] 0.286 0.011 100 −140.63 37.860 84.53

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Liquids and their properties 359

Table 8.8 (Continued)

(PC) → AY AZ BA BB BC BD BE Polarity Dielectric 1000 ×d Magnetic Index of Kerr coefficient −9 2 parameter constant, ln ε/dT susceptibility refraction 1000 × dnD/dTB(10 /cm esE ) N −1 −6 3 −1 No. ET ε (K ) χm (10 cm /mol)* nD (K ) {ratio B/Bs}

1 0.009 1.841* −2.00 −63.0 1.3547 −0.552 5.5* 2 1.8275 −0.70 −64.4 1.3509 −0.570 3 0.009 1.8799 −1.90 −74.1 1.3723 −0.520 6.6* 4 0.012 1.9246* −1.68 −85.4 1.3851 −0.506 7.6* 5 1.940* −1.67 −98.3 1.3890 −0.494 6.2* 6 1.96875* 7 0.006 2.02431* −1.82 −68.2 1.4235 −0.538 5.9* 8 2.020* 9 −106.7 1.4788 −0.440 22* 9a 0.015 2.197 −1.15 9b 2.172 10 11 4.39* −2.42 −82.6 1.595 −0.550 {−0.86}* 12 0.309 8.93 −8.50 −46.6 1.421 −0.600 {−0.36}* 13 0.259 4.806* −3.68 −59.3 1.442 −0.590 −308* 14 0.052 2.2288 −2.06 −66.8 1.457 −0.558 8.4* 15 16 0.327 10.37 −5.08 −59.6 1.442 −0.540 17 0.160 3.42* −65.8 1.475 −0.568 18 2.280 −2.02 −81.6 1.503 −0.530 19 1.251 20 1.313 20a 20b 21 0.111 2.27401 −2.03 −54.8 1.4979 −0.640 41.0 22 0.188 5.621 −3.00 −69.6 1.521 −0.592 1050* 23 0.225 9.93 −4.47 −84.4 1.549 −0.458 24 −106.5 1.571 25 0.194 5.42 −58.3 1.462 0.500 26 1.374 0.558

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Table 8.8 (Continued)

(PC) → AY AZ BA BB BC BD BE Polarity Dielectric 1000 ×d Magnetic Index of Kerr coefficient −9 2 parameter constant, ln ε/dT susceptibility refraction 1000 × dnD/dT B (10 /cm esE ) N −1 −6 3 −1 No. ET ε (K ) χm (10 cm /mol)* nD (K ) {ratio B/Bs}

27 25.20 −3.62 −65.2 1.525 −0.506 28 0.099 2.3807 −2.35 −66.1 1.4941 −0.560 71.4* 29 2.4257* −68.0 1.5440 −0.519 30 2.568* −2.38 −77.8 1.5030 −0.500 134* 31 2.3742* −1.89 −76.6 1.4946 −0.516 75* 32 0.074 2.2699* −1.62 −76.8 1.4933 −0.514 75* 33 2.3833* −89.3 1.4889 −0.510 34 5.04 35 2.915* 36 0.762 32.66 −6.08 −21.4 1.3265 −0.383 {0.3}* 37 0.654 24.55 −6.22 −33.5 1.3594 −0.400 {0.24}* 38 37.7 −5.16 −38.9 1.4306 −0.240 39 −7.24 1.2907 40 0.651 37.72 −42.1 1.452 −0.340 41 0.617 20.45 −6.50 −45.2 1.3837 −0.372 {−0.78}* 42 0.546 19.92 −7.14 −45.7 1.3752 −0.410 {∼0.73}* 43 42.5 44 0.586 17.51 −7.71 −56.1 1.3974 −0.390 {−1.13}* 45 0.506 16.56 −9.90 −57.3 1.3953 −0.364 46 0.552 17.93 −8.60 −57.2 1.3939 −0.390 {−1.37}* 47 0.389 12.47 −14.60 −57.4 1.3852 −0.740 {1.54}* 48 29.36 1.483 −0.200 49 13.1* −4.89 −71.8 1.5384 −0.396 {−4.77}* 50 10.34* −9.44 −102.2 1.4276 −0.400 {−2.36}* 51 0.657 16.93 −11.58 −60.3 1.4002 −0.380 52 29.6* 1.4057 −0.400 53 0.713 31.69* −13.67 1.4461 −0.280 54 9.30 55 0.207 7.58 −3.94 1.4050 −0.440 56 0.164 2.209 −1.80 −51.1 1.4203 −0.460 {0.02}*

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Liquids and their properties 361

Table 8.8 (Continued)

(PC) → AY AZ BA BB BC BD BE Polarity Dielectric 1000 ×d Magnetic Index of Kerr coefficient −9 2 parameter constant, ln ε/dT susceptibility refraction 1000 × dnD/dT B (10 /cm esE ) N −1 −6 3 −1 No. ET ε (K ) χm (10 cm /mol)* nD (K ) {ratio B/Bs}

57 0.117 4.335* −5.00 −55.1 1.3495 −0.560 −62* 58 7.20 −5.69 −55.2 1.3781 −0.304 59 0.124 60 0.244 −85.8 1.4058 −0.408 61 4.33 −5.90 −72.2 1.5143 −0.500 112.3* 62 0.071 3.083* −50.1* 63 8.5* −13.50 1.3415 −0.440 64 0.228 6.02 −5.70 −54.1 1.3698 −0.490 65 2.9* 66 5.01* −6.50 −77.4 1.3918 −0.470 67 6.59* −3.20 −81.6 1.514 −0.460 68 0.355 20.56 −4.72 −34.0 1.3560 −0.544 {5.05}* 69 0.327 18.51* −4.77 −45.6 1.3769 −0.480 1382* 70 15.38* −4.49 −57.4 1.3885 −0.469 71 0.281 16.10* −3.73 −62.0 1.4500 −0.212 1400* 72 0.269 13.11* −5.07 −70.0 1.3936 −0.430 711* 73 74 111.0* −15.10 −23.1 1.446 −0.144 75 0.481 35.87* −4.35 −20.9 1.379 −0.450 76 0.460 35.94 −4.16 −27.6 1.341 −0.496 77 0.349 12.9 −17.90 −45.5 1.454 −0.547 78 0.386 36.71 −5.12 −38.8 1.428 −0.460 79 0.377 37.78 −6.09 −56.1 1.435 −0.560 80 0.302 12.91 −4.88 −48.5 1.507 −0.550 {6.32}* 81 0.355 32.2 −61.7 1.467 −0.500 82 −4.95 1.469 83 0.065 2.643* −2.34 −42.2 1.624 −0.674 355* 84 0.444 46.45 −43.9 1.477 −0.358 85 86 1.000 78.304 −4.53 −12.9 1.33286 −0.644 {1.23}

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Table 8.8 (Continued)

(PC) → AY AZ BA BB BC BD BE Polarity Dielectric 1000 ×d Magnetic Index of parameter constant, ln ε/dT susceptibility refraction 1000 × dnD/dT Kerr coefficient N −1 −6 3 −1 −9 2 No. ET ε (K ) χm (10 cm /mol)* nD (K ) B (10 /cm esE )

87 78.06 1.32828* 88 89 1.226* 1.1093* ** 3.45* 90 91 1.0492* 92 1.434* 8.00* 93 1.4837* 1.219* ** 20* 94 1.188* 95 1.52* 96 97 98 14* 99 1.6758* 100 1.445*

(PC) → BF BG BH BI BJ BK BL Scattering Depolarization IR/Raman UV-VIS coefficient factor IR spectrum spectrum spectrum UV cut-off UV 5% 2 No. R90 u × 10 (Sadtler) (Schrader) (Perkampus) point absorption

1 7.3 2 A1-05 200* 230* 2 5.6* 3 A1-13 3 0.298 8.0 7 A1-02 M/4 200* 225* 4 8.7 13 A1-03 M/3 195* 230* 5 5.6 21 A1-04 M/6 205* 230* 6 11.1 1 195* 220* 7 0.217 5.6 6 E1-01 M/5 195* 8 11.1* 12 205* 9 17.6 24 200* 250* 9a 25 E12-02 9b 26 E12-01 10 34 226*

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Liquids and their properties 363

Table 8.8 (Continued)

(PC) → BF BG BH BI BJ BK BL Scattering Depolarization IR/Raman UV-VIS coefficient factor IR spectrum spectrum spectrum UV cut-off UV 5% 2 No. R90 u × 10 (Sadtler) (Schrader) (Perkampus) point absorption

11 279 A2-03 330* 12 31.0 248 A2-40 M/12 230* 245* 13 0.357 20 249 A2-04 M/11 245* 260* 14 0.323 6 250 A2-02 M/10 260* 15 A2-48 16 252 A2-18 230* 250* 17 268 >400 18 269 C1-10 290* 320* 19 20 20a 20b 21 1.00 43 35 F1-01 M/13 280* 295* 22 1.46 57.5 244 F1-03 285* 310* 23 261 F3-01 295* 350* 24 F7-01 350* 25 225 FI-02 26 229 27 68 301 F1-06 300* 28 1.12 48 36 F1-08 285* 315* 29 56 60 F1-50 30 1.29 49.7 37 F3-07 290* 325* 31 1.30 50.6 38 F4-05 290* 32 1.61 56.4 39 F5-02 290* 33 41 F1-33 34 78 247 35 36 0.146 4.9 64 A3-03 M/1 205* 240* 37 0.178 5.6 65 A3-11 M/2 205* 240* 38 103 A3-01

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364 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → BF BG BH BI BJ BK BL Scattering Depolarization IR/Raman UV-VIS coefficient factor IR spectrum spectrum spectrum UV cut-off UV 5% 2 No. R90 u × 10 (Sadtler) (Schrader) (Perkampus) point absorption

39 190* 40 362 41 0.180 5.8 66 A3-08 210* 250* 42 0.168 3.9 67 M/19 210* 240* 43 107 A3-39 205* 44 0.191 9.3 68 A3-06 205* 245* 45 69 A3-05 260* 285* 46 0.182 5.5 70 200* 250* 47 4.1* 71 48 49 1.02 58.6 96 F1-41 50 0.307 93 51 9 200* 270* 52 A4-06 210* 280* 53 6 A4-11 54 55 70 J3-08 M/9 220* 280* 56 13.4* 80 J7-01 M/14 220* 290* 57 0.280 7 86 A4-01 M/18 215* 255* 58 A4-02 220* 59 85 60 64 61 60.0 F1-15 62 91 A4-04 210* 63 0.351 260* 64 66 255* 280* 65 66 255* 275* 67 68 0.257 23.1* 38 B2-01 M/16 330* 340* 69 16.6 43 B2-11 330* 345*

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Liquids and their properties 365

Table 8.8 (Continued)

(PC) → BF BG BH BI BJ BK BL Scattering Depolarization IR/Raman UV-VIS coefficient factor IR spectrum spectrum spectrum UV cut-off UV 5% 2 No. R90 u × 10 (Sadtler) (Schrader) (Perkampus) point absorption

70 19.6 71 54 E1-02 72 55 B2-02 335* 375* 73 330* 350* 74 75 24 B11-01 380* >400* 76 27 B9-01 M/17 195* 200* 77 40 A7-09 78 34 B6-01 270* 300* 79 35 B6-03 268* 80 46 53 I7-01 M/15 305* 345* 81 37 I1-07 260* 82 83 4.15 62 92 O-01 380* 84 28 B13-01 M/8 265* 330* 85 86 0.0546 8.8 1 O-02 185* 190* 87 O-03 88 89 90 91 92 93 94 95 96 97 98 99 100

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366 Handbook of Liquids-Assisted Laser processing

Table 8.8 (Continued)

(PC) → BM BN BO BP BQ BR BS

Ionization Hildebrandt Oxygen Nitrogen CO2 solubility energy  Hf (0) Gf (0) parameter solubility xg solubility xg xg (mole No. (eV) (kJ/mol) (kJ/mol) δ (MPa1/2) (mole fractions) (mole fractions) fractions)

1 10.28 −146.76 −8.65 0.00205 0.00145 0.01258 2 10.32 −153.70 −13.86 3 10.13 −166.92 0.15 14.9 0.00198 0.00138 0.01207 4 9.93 −187.80 8.20 0.00217 0.00135 0.0119 5 9.98 −224.01 14.21 0.002529 0.001533 0.01387 6 10.33 −77.10 38.92 7 9.88 −123.10 32.26 16.8 0.00123 0.000761 0.00759 8 9.64 −118.10 64.30 0.001599 0.000946 0.00934 9 9a 9.32 −169.20 85.60 9b 9.32 −182.10 74.20 10 11 10.50 12 11.33 −95.40 −68.84 13 11.37 −102.93 −70.09 19.0 0.000425 0.0128 14 11.47 −95.81 −53.53 17.6 0.001200 0.000641 0.0107 15 13.86 −693.30 −658.80 16 11.07 −126.78 −70.20 20.0 17 9.46 18 9.326 19 −2973.99 −2722.34 20 0.00390 20a 20b 21 9.24378 82.88 129.75 18.8 0.000810 0.000445 0.00912 22 9.07 51.09 98.36 19.4 0.0007884 0.000427 0.00982 23 9.06 24 9.04 25 9.20 −145.39 0.001508 26 9.90 −991.69 0.002418 0.0232*

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Liquids and their properties 367

Table 8.8 (Continued)

(PC) → BM BN BO BP BQ BR BS

Ionization Hildebrandt Oxygen Nitrogen CO2 solubility energy  Hf (0) Gf (0) parameter solubility xg solubility xg xg (mole No. (eV) (kJ/mol) (kJ/mol) δ (MPa1/2) (mole fractions) (mole fractions) fractions)

27 9.73 28 8.828 50.17 122.29 0.000923 0.000539 0.0105 29 8.464 30 8.56 19.08 122.05 31 8.55 17.32 118.89 32 8.44 18.03 121.48 33 8.73 4.00 139.05 34 8.13 35 7.96 115.20 216.40 36 10.84 −200.94 −162.24 29.6 0.0004122 0.000273 0.00635 37 10.48 −234.95 −167.73 26.0 0.000583 0.000357 0.00689 38 10.552 29.9 39 11.49 40 8.96 41 10.22 −255.20 −159.81 0.000406 0.00762 42 10.17 −272.70 −173.32 0.0007745 0.000466 43 0.00009 44 9.99 −274.60 −150.17 23.3 0.0007894 0.000461 0.00883 45 9.88 −292.75 −167.71 46 10.02 −282.90 −167.40 21.7 0.000854 0.000482 0.00697 47 9.90 −325.81 −191.20 48 7.9 49 8.26 −72.38 18.20 50 −356.90 −116.59 0.001132 0.000657 0.01277 51 10.13 0.0100 52 9.97 53 54 55 9.40 −184.18 −79.57 18.6 0.000816 0.000521 0.027 56 9.19 −314.70 −180.20 20.5 0.000616 0.000237

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Table 8.8 (Continued)

(PC) → BM BN BO BP BQ BR BS

Ionization Hildebrandt Oxygen Nitrogen CO2 solubility energy  Hf (0) Gf (0) parameter solubility xg solubility xg xg (mole No. (eV) (kJ/mol) (kJ/mol) δ (MPa1/2) (mole fractions) (mole fractions) fractions)

57 9.51 −250.80 −120.70 58 9.3 −342.80 59 9.24 60 9.8 61 8.20 62 9.44 63 10.835 −352.40 −294.90 64 10.01 −444.50 −328.00 18.6 0.000871* 0.0230 65 10.06 66 9.92 −485.30 −312.10 67 9.32 68 9.703 −217.10 −152.60 20.2 0.0008399 0.000542 0.0187 69 9.52 −238.60 −146.50 0.001011 70 9.38 −259.20 −138.20 0.001112 71 9.16 −230.12 −90.87 20.3 0.000855 72 9.30 −286.40 −135.10 73 9.284 74 10.16 39.3 75 11.08 −74.70 −6.90 0.000201* 76 12.20 24.3 77 8.6 78 9.13 24.8 0.0164 79 9.20 80 9.26 140.37 190.55 21.9 0.000458 0.000250 0.0119 81 9.17 82 8.1 95.40 159.38 0.0000072 83 10.073 20.4 0.000439 0.000222 0.00328 84 9.10 24.5 85 86 12.621 −241.81 −228.42 47.9 0.0000229 0.0000118 0.000615

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Liquids and their properties 369

Table 8.8 (Continued)

(PC) → BM BN BO BP BQ BR BS

Ionization Hildebrandt Oxygen Nitrogen CO2 solubility energy  Hf (0) Gf (0) parameter solubility xg solubility xg xg (mole No. (eV) (kJ/mol) (kJ/mol) δ (MPa1/2) (mole fractions) (mole fractions) fractions)

87 12.6395 −249.20 −234.53 0.0000118 88 89 15.42593 90 15.46658 91 24.58741 92 15.581 93 12.0697 94 21.56454 −393.51 −394.38 95 15.759 96 13.99961 97 12.12987 98 13.777 99 12.61 −74.52 −50.45 100

(PC) → BT BU BV BW Solubility in Riddick Marcus Poling No. water (g/l) reference reference reference

1 0.36* 5 20 166 2 0.048* 6 30 167 3 0.0095* 10 40 216 4 0.05* 16 60 259 5 0.00056 27 80 310 6 0.156 4 148 7 0.055* 9 50 197 8 0.014* 15 247 9 0.006* 9a 32 220 356 9b 33 357 10 0.01* *** 11 3.2* 351 1730

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Table 8.8 (Continued)

(PC) → BT BU BV BW Solubility in Riddick Marcus Poling No. water (g/l) reference reference reference

12 20* 315 1540 20 13 8* 316 1600 18 14 0.8* 317 1650 13 15 19 16 8.7* 319 1560 58 17 1* 336 1630 18 0.16* 337 1660 19 1460 180 20 1490 20a 20b 21 1.770* 38 120 187 22 0.4* 307 1530 186 23 326 1580 24 0.049* 1640 25 1.54* 288 1500 26 Insoluble* 293 1510 178 27 10* 395 2130 28 0.52* 39 130 234 29 0.24* 75 200 30 0.18* 40 140 274 31 41 150 275 32 0.2 42 160 276 33 Insoluble* 44 180 326 34 312 35 0.0258 47 367 36 In all proportions 78 240 27 37 In all proportions 79 250 66 38 1000* 134 490 39 475 450

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Liquids and their properties 371

Table 8.8 (Continued)

(PC) → BT BU BV BW Solubility in Riddick Marcus Poling No. water (g/l) reference reference reference

40 478 1920 41 In all proportions* 80 260 96 42 81 270 97 43 147 44 77* 82 280 130 45 125* 83 300 133 46 85* 84 290 131 47 85 310 132 48 In all proportions* 481 1940 49 40* 115 400 235 50 0.3* 112 370 314 51 464 470 52 In all proportions* 465 480 53 In all proportions* 469 560 54 466 55 170 740 118 56 172 770 122 57 69* 151 660 134 58 159 710 135 59 26* 60 162 720 61 1.5–1.7* 175 800 62 10* 156 63 300* 224 1240 61 64 85.3* 232 1270 124 65 15* 255 66 7* 238 1290 211 67 0.158* 258 1380 68 189 920 89 69 292* 190 930 117 70 43* 192 940 154

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Table 8.8 (Continued)

(PC) → BT BU BV BW Solubility in water (g/l) [mole fractions] Riddick Marcus Poling No. {vol/vol} reference reference reference

71 90* 194 1000 195 72 18–20* 196 980 204 73 5.4* 74 440 2190 75 105* 380 2140 25 76 385 2070 77 415 1790 78 442 2210 79 In all proportions* 445 2250 80 431 1950 143 81 1000 449 2280 82 2570 449 83 2.1* 451 2330 84 1000* 462 2400 85 86 0 230 440 87 418 88 89 [0.00001411] 438 90 [0.00001460] 416 91 [0.000006997] 450 92 [0.00001183] 455 93 [0.00002293] 460 94 [0.000008152] 458 95 [0.00002519] 1 96 [0.00004512] 453 97 [0.00007890] 468 98 [0.000615] 31 99 [0.00002552] 26 100 {0.0292} Ch08-I044498.tex 12/9/2007 17: 21 Page 373

Liquids and their properties 373

Simple analytical expressions, with up to 5 constants, of temperature dependencies of the properties of many organic solvents are given in Riddick handbook [1006]: viscosity, surface tension, heat of vaporization, and heat capacity; and in Poling handbook [1008]: vapour pressure and vapour heat capacity.

Data sources for numerical values The numbers of the liquids are in italic NA – not available b.p. – (atmospheric) boiling point

E (safety codes) – [Merck [1009]]: 1–14, 16–18, 21–26, 28–33, 35–42, 44–47, 49–60, 62–65, 67–81, 83, 99

F (molar mass) – [Poling et al. (2001) [1008]]: 1–9, 12–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55, 56, 57, 58, 63, 64, 66, 68–72, 75, 80, 82, 86, 87, 89–98; [NIST [1010]]: 11, 16, 18, 20, 23, 24–27, 29, 34, 38–40, 43, 48, 51, 52, 53, 54, 59–62, 65, 67, 73, 74, 76–79, 81, 83, 84; [Jacobsen et al. (1997) [1011]]: 90, 91, 95, 99, 100

G (liquid molar volume) – [Poling et al. (2001) [1008]]: 1–9, 12–16, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 50, 55–58, 63, 64, 66, 68–70, 72, 75, 80, 82, 86, 87, 89–99 * at temperature: 15 [−60◦C]; 19, 35, 56, 82 [20◦C]; 89 [20 K]; 90 [22.7 K]; 91 [4.3 K]; 92 [78 K]; 93 [90 K]; 94 [27 K]; 95 [90 K]; 96 [120 K]; 97 [165 K]; 99 [90.68 K]

H (density) – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25–58, 60–72, 74–81, 83, 84, 86; [Mackanos et al. (2003) [1012]]: 20; [Nakamura et al. (1995) [1013]]: 87; [Jacobsen et al. (1997) [1011]]: 89–97, 100; [Cryogenic Fluids Databook (2002) [1014]]: 99 * at temperature: 17 [30◦C]; 20 [NA]; 25 [30◦C]; 34 [20◦C]; 39 [22◦C]; 47 [30◦C]; 53, 55, 65 [20◦C]; 67 [30◦C]; 71 [20◦C]; 89 [20.345 K]; 90 [23.264 K]; 91 [4.2163 K]; 92 [77.237 K]; 93 [90.062 K]; 94 [27.061 K]; 95 [87.169 K]; 96 [119.62 K]; 97 [164.78 K]; 99 [111.5 K]; 100 [78.569 K]

I (temperature coefficient of density) – [Riddick et al. (1986) [1006]]: 1–6, 9, 11–14, 16–18, 21–23, 25–38, 40–57, 60–72, 75–78, 80, 81, 84

J (melting point in K) – [Poling et al. (2001) [1008]]: 1–9, 12–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–45, 47, 49, 50, 55, 56, 57, 63, 64, 66, 68–70, 72, 75, 80, 82, 86, 87, 89–98; [NIST [1010]]: 35; rest calculated J = K + 273.15

K (melting point in ◦C) – [Merck [1009]]: 10, 11, 16, 17, 18, 23, 24, 29, 8–40, 43, 46, 48, 51, 52, 53, 54, 58–62, 65, 71, 73, 74, 76–79, 81, 83, 84; [ChemExper [1015]]: 20; [Sigma-Aldrich [1016]] – 25–27; [Liquid Synthetic Air [1017]]: 100; rest calculated K = J − 273.15

L (enthalpy change of atmospheric melting) – [Poling et al. (2001) [1008]]: 1–8, 12–14, 16, 21, 22, 28, 30–33, 35–37, 41, 42, 44, 47, 49, 55–57, 64, 66, 68–70, 80, 82, 86, 87, 89, 90, 92, 93, 98; [Riddick et al. (1986) [1006]]: 25, 26

M (heat capacity at constant pressure) – [Poling et al. (2001) [1008]]: 1–9, 12–14, 16, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 50, 55–57, 63, 64, 66, 68–70, 75, 80, 82, 86, 87; [Riddick et al. (1986) [1006]]: 25, 26; [Jacobsen et al. (1997) [1011]]: 89–97, 100; [Cryogenic Fluids Databook (2002) [1014]]: 99 * at temperature: 89 [20.345 K]; 90 [23.264 K]; 91 [4.2163 K]; 92 [77.237 K]; 93 [90.062 K]; 94 [27.061 K]; 95 [87.169 K]; 96 [119.62 K]; 97 [164.78 K]; 99 [111.5 K]; 100 [78.569 K]

N (diffusion coefficient) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16, 21, 22, 26, 28, 30–33, 36, 37, 40–42, 44, 47, 50, 56, 57, 61, 64, 68, 71, 75, 76, 78, 80, 81, 83, 84 [Eisenberg and Kauzmann (1969) [1018]]: 86, 87 [Horita and Cole (2004) [1019]]: 88 Ch08-I044498.tex 12/9/2007 17: 21 Page 374

374 Handbook of Liquids-Assisted Laser processing

O (heat conductivity) – [Riddick et al. (1986) [1006]]: 3, 5, 14, 28, 36–38, 41–44, 46, 47, 50, 55, 64, 66, 68, 69, 75, 79, 81; [IAPWS (1998) [1020]]: 86, 87; [Cryogenic Fluids Databook (2002) [1014]]: 89, 91–96, 99, 100 * at temperature: 3, 5 [37.8◦C]; 14 [23◦C]; 36 [20◦C]; 37, 38, 41–44, 46, 47, 50 [37.8◦C]; 55 [20◦C]; 64, 66 [37.8◦C]; 68, 69 [20◦C]; 75 [37.8◦C]; 79 [22.2◦C]; 81 [38◦C]; 89 [20.23 K]; 91 [4.208 K]; 92 [77.2 K]; 93 [90.07 K]; 94 [27.05 K]; 95 [87.16 K]; 96 [119.6 K]; 99 [111.5 K]; 100 [78.9 K]

P (surface tension) – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25–38, 40–47, 49–58, 60–72, 74–81, 83, 84; [IAPWS (1994) [1021]]: 86, 87; [Flynn (2005) [1022]]: 89, 95 * at temperature: 4 [37.8◦C]; 9 [20◦C]; 11 [24.8◦C]; 12, 16, 22, 23 [20◦C]; 25 [30◦C]; 27 [27◦C]; 29, 34, 35, 37, 38 [20◦C]; 40, 41 [20◦C]; 42 [30◦C]; 43–46 [20◦C]; 47 [26◦C]; 49 [20◦C]; 50 [24.73◦C]; 51 [41.0◦C]; 53, 58 [20◦C]; 61 [20◦C]; 62 [30◦C]; 63–67 [20◦C]; 69 [24.8◦C]; 70, 71 [20◦C]; 72 [23.7◦C]; 75, 77 [20◦C]; 79 [30◦C]; 83 [20◦C]; 89 [b.p.]; 95 [90 K]

Q (dynamic viscosity) – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25–58, 60–72, 74–81, 83, 84; [Mackanos et al. (2003) [1012]]: 20; [IAPWS (2003) [1023]]: 86; [IAPS (1982) [1024]]: 87; [Siedler (1986) [1025]]: 88 (salinity 40‰); [Cryogenic Fluids Databook (2002) [1014]]: 89, 91–96, 99, 100 * at temperature: 5 [20◦C]; 9 [20◦C]; 11 [30◦C]; 12 [27.61◦C]; 16, 18 [30◦C]; 20 [NA]; 22 [20◦C]; 25 [30◦C]; 35 [20◦C]; 38, 39, 49, 56 [30◦C]; 57 [20◦C]; 61, 62 [30◦C]; 65, 66 [20◦C]; 67 [30◦C]; 70 [20◦C]; 71 [30◦C]; 83 [20◦C]; 89 [20.23 K]; 91 [4.208 K]; 92 [77.2 K]; 93 [90.07 K]; 94 [27.05 K]; 95 [87.16 K]; 96 [119.6 K]; 99 [111.5 K]; 100 [78.9 K]

R (temperature coefficient of dynamic viscosity) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16–18, 21–33, 36, 37, 39, 40–42, 44–53, 55–58, 60, 61, 63, 64, 66–72, 74–84, 86

S (orientational relaxation time) – [Marcus (1998) [1007]]: 3, 7, 12–14, 16, 21, 22, 25–28, 31, 36–38, 41, 42, 44–46, 50, 53, 55, 57, 58, 61, 64, 68, 69, 71, 74, 76, 78–80, 83, 84, 86

T (thermal expansion coefficient) – [Riddick et al. (1986) [1006]]: 1, 3, 6, 7, 9, 12–14, 16–18, 21–23, 25, 26, 28, 30–32, 34, 36–38, 40–58, 61, 64, 66–69, 71, 72, 74–78, 80, 83, 84, 86; [Nakamura et al. (1995) [1013]]: 87 * at temperature: 9 [NA]; 12, 13 [NA]; 16 [20◦C]; 23 [NA]; 38 [20◦C]; 40 [55◦C]; 43 [20◦C]; 47 [30◦C]; 48 [55◦C]; 49 [NA]; 51, 52–54 [20◦C]; 55, 56 [NA]; 58 [NA]; 61 [NA]; 64 [20◦C]; 66 [20◦C]; 67 [NA]; 68 [20◦C]; 69 [NA]; 71, 72 [NA]; 74, 75 [NA]; 76 [20◦C]; 78 [NA]; 80 [NA]; 83 [20◦C]; 84 [NA]

U (isothermal compressibility) – [Riddick et al. (1986) [1006]]: 1–4, 6, 7, 12–14, 16, 21, 22, 28, 30–33, 36, 37, 41–44, 50, 56, 68–70, 74–77, 83, 84, 86; [Rodnikova et al. (2003) [1026]]: 87 * at temperature: 13 [20◦C]; 16 [30◦C]; 22 [20◦C]; 42 [40◦C]; 43 [20◦C]; 74 [NA]; 75 [20◦C]; 76 [NA]

V (adiabatic compressibility) – [Riddick et al. (1986) [1006]]: 1, 3, 4, 7, 13, 14, 18, 21, 22, 27, 28, 30–32, 36, 37, 41, 42, 44, 46, 56, 64, 66, 68, 71, 77; [Nakamura et al. (1995) [1013]]: 86, 87 * at temperature: 4 [30◦C]; 13 [35◦C]; 18 [20◦C]; 27 [35◦C]; 42 [35◦C]; 46 [35◦C]; 64 [30◦C]; 66 [30◦C]; 68 [35◦C]; 71 [35◦C]; 77 [30◦C]

W (sound velocity) – [RSHydro [1027]]: 1, 3, 4, 7, 11–14, 16–18, 21, 22, 25, 28, 30–32, 36–38, 40–43, 45, 46, 53, 56, 57, 64, 68, 74–76, 80, 83, 86, 87, 89, 99 [Jacobsen et al. (1997) [1011]]: 89–97, 99, 100 * at temperature: 28 [20◦C]; 31, 32 [20◦C]; 41, 42 [20◦C]; 89 [20.345 K]; 90 [23.264 K]; 91 [4.2163 K]; 92 [77.237 K]; 93 [90.062 K]; 94 [27.061 K]; 95 [87.169 K]; 96 [119.62 K]; 97 [164.78 K]; 98 [−37◦C]; 99 [111.51 K]; 100 [78.569 K]

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Liquids and their properties 375

Y (ultrasound absorption coefficient) – [Marcus (1998); [1007] near 25◦C, 104–107 MHz]: 3, 7, 9, 11–14, 21–24, 28, 30, 33, 36, 37, 40, 44, 46, 49, 56, 57, 61, 63, 68, 71, 74, 83, 86

Z (acoustic non-linearity parameter) – [Beyer (1974) [1028]]: 3, 4, 7, 21, 22, 36–38, 41, 44, 49, 68, 86, 88 (salinity 35‰), 92 * at temperature: 3, 4 [30◦C];7 [30◦C];36, 37 [20◦C];38 [30◦C];41 [20◦C];44 [20◦C];49 [30◦C];68 [20◦C]; 24 [30◦C]; 86 [20◦C]; 88 [20◦C]; 92 [b.p.]

AA (shock velocity) – [Marsh (1980) [979]]: 89, 90, 92, 93, 95; [Rice and Walsh (1957) [1029]]: 86; [Schaaffs (1967) [1030]]: 3, 14, 21, 28, 36, 37, 43, 57, 68 * at temperature: 3 [32◦C]; 14 [22◦C]; 21 [16◦C]; 28 [15◦C]; 36 [24◦C]; 37 [26◦C]; 43 [18◦C]; 57 [32◦C]; 68 [26◦C]; 86 [20◦C]; 89, 90 [20 K]; 92 [75 K]; 93 [NA, density 1202 kg/m3]; 95 [NA, density 1400 kg/m3] at shock pressure:3 [9.57 GPa];14 [7.39 GPa];21 [52.4 kbar];28 [52.1 kbar];36 [10.95 GPa];37 [11.04 GPa];43 [7.66 GPa];57 [9.61 GPa];68 [10.58 GPa];89 [6.480 GPa];90 [12.964 GPa];92 [10.601 GPa];93 [11.499 GPa]; 95 [26.054 GPa]

AB (atmospheric boiling point in K; at 1013 hPa) – [Poling et al. (2001) [1008]]: 1–9, 12–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55, 56, 57, 58, 63, 64, 66, 68–72, 75, 80, 82, 86, 87; [NIST [1010]]: 16; [Jacobsen et al. (1997) [1011]]: 89, 90, 92–99; [Cryogenic Fluids Databook [1014]]: 91; [Flynn (2005) [1022]]: 100; rest calculated:AB =AC + 273.15

AC (boiling point in ◦C; at 1013 hPa) – [Merck [1009]]: 10, 11, 17, 18, 23, 24, 29, 38–40, 43, 48, 51, 52, 53, 54, 59–62, 65, 68, 73, 74, 76–79, 81, 83, 84; [Riddick et al. (1986) [1006]]: 25, 26; [Sigma-Aldrich [1016]]: 27, 85 (0.002 mm Hg(lit.)); [ChemExper [1015]] −20, 35; [Horita and Cole (2004) [1019]]: 88; [Liquid Synthetic Air [1017]]: 100; rest calculated:AC =AB − 273.15

AD (attainable superheat temperature) – [Skripov et al. (1988) [1031]]: 1–8, 12, 13, 19, 21, 22, 28, 31, 36, 37, 41, 44, 57, 68, 83, 86, 95; [Avedisian (1985) [1032]]: 14, 26, 42, 46, 50, 63, 76, 89, 91–93, 96, 97, 99 * at pressure: 14 [−27.6 MPa]; 89 [149 kPa]; 91 [100 kPa]; 96 [400 kPa]; 97 [500 kPa]; 99 [400 kPa]

AE (bubble nucleation rate) – [Avedisian (1985) [1032]]: 1–4, 6, 7, 13, 14, 19, 21, 22, 26, 28, 36, 37, 41, 42, 44, 46, 50, 57, 63, 68, 76, 86, 89, 91–93, 95–97, 99

AF (enthalpy change of atmospheric boiling) – [Poling et al. (2001) [1008]]: 1–9, 12–14, 16, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 50, 55–58, 63, 64, 66, 68–70, 72, 75, 80, 82, 86, 87, 89–97; [Mackanos et al. (2003) [1012]]: 20; [Riddick et al. (1986) [1006]]: 25, 26; [Flynn (2005) [1022]]: 100

AG (evaporation rate) – [Riddick et al. (1986) [1006]]: 3, 12–14, 16–18, 21, 23, 28, 36–38, 41, 42, 44–47, 50–58, 60, 64, 66, 68–72, 75, 78, 81; [Sartori (2000) [1033]]: 86 ** 86 at RH 45%, kg/m2 s106

AH (vapour density vs. air) – [Sigma-Aldrich [1016]]: 1–18, 20–24, 28–33, 36–85, 89–92, 94, 95, 98, 99; [Padfield (1996) [1034]]: 86; [Flynn (2005) [1022]]: 93, 96, 97 * at temperature: 16 [20◦C]; 58, 64 [20◦C]; 82 [37◦C]; 89 [21◦C]; 93 [21.1◦C]; 94, 95, 96, 97 [21◦C]

AI (vapour pressure) – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25–58, 60–72, 74–81, 83, 84; [Mackanos et al. (2003) [1012]]: 20 [Greenwood and Earnshaw (1997) [1035]]: 86; [Kennish (1989) [1036]]: 88 (salinity 35‰) * at temperature: 16 [20◦C]; 20 [NA]; 26 [24◦C]; 28 [28,2◦C]; 34 [60◦C]; 40 [20◦C]; 43 [50◦C]; 48 [20◦C]; 58 [20◦C]; 77 [26.51◦C]; 80 [24.8◦C] Ch08-I044498.tex 12/9/2007 17: 21 Page 376

376 Handbook of Liquids-Assisted Laser processing

AJ, AK, AL (Antoine equation parameters A, B, C); temperature in ◦C, pressure in Pa – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25–33, 35–42, 44–48, 50–53, 55, 57, 58, 61–64, 66–72, 75, 76, 78–80, 83, 84; [Antoine-Gleichung [1037]]: 86 ** Pressure in mmHg

AM (saturation concentration) – [Merck [1009]]: 1, 3–8, 12–14, 16–18, 21, 23, 24, 28–33, 37–38, 41, 42, 44–47, 49, 51–58, 61, 63, 64, 66, 68–72, 74–80, 83, 84; [Padfield (1996) [1034]]: 86 (calculated using the formula therein) * at temperature: 1, 3–8 [20◦C];12–14 [20◦C];16–18 [20◦C];21 [20◦C];23, 24 [20◦C];28–32 [20◦C];37–38 [20◦C]; 41–42 [20◦C]; 44–47 [20◦C]; 49 [20◦C]; 51–58 [20◦C]; 61 [20◦C]; 63–64 [20◦C]; 66 [20◦C]; 68–70 [20◦C]; 71 [NA]; 72 [20◦C]; 74–80 [20◦C]; 83, 84 [20◦C]

AN (flash point) – [Merck [1009]]: 1–9, 10 (boiling range 40–60◦C), 16, 21–25, 27–33, 35–81, 83, 84 o.c. – open cup method, c.c. – closed cup method.

AO (autoignition temperature) – [Merck [1009]]: 1–10, 12, 14, 16, 17, 21–25, 27–33, 35–38, 40–81, 83, 84, 99

AP (explosion limit) – [Merck [1009]]: 1–10, 12, 17, 18, 21–25, 27–33, 36–81, 83, 84, 99

AQ (critical temperature, K) – [Poling et al. (2001) [1008]]: 1–9, 12–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 48, 50, 55, 56, 57, 58, 63, 64, 66, 68–72, 75, 80, 82, 86, 87, 98 [Riddick et al. (1986) [1006]]: 25, 26; [ Jacobsen et al. (1997) [1011]]: 89–97, 100; [Cryogenic Fluids Databook (2002) [1014]]: 99; rest calculated:AQ =AR + 273.15

AR (critical temperature, ◦C) – calculated:AR =AQ – 273.15

AS (critical pressure) – [Poling et al. (2001) [1008]]: 1–9, 12–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55, 56, 57, 63, 64, 66, 68–72, 75, 80, 82, 86, 87, 98; [Riddick et al. (1986) [1006]]: 25, 26; [ Jacobsen et al. (1997) [1011]]: 89–97, 100; [Cryogenic Fluids Databook (2002) [1014]]: 99

AT (critical volume) – [Poling et al. (2001) [1008]]: 1–9, 13–15, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 50, 55, 56, 57, 58, 63, 64, 66, 68–70, 72, 75, 80, 82, 86, 87, 98; [Riddick et al. (1986) [1006]]: 25, 26; [ Jacobsen et al. (1997) [1011]]: 89–97, 100; [Cryogenic Fluids Databook (2002) [1014]]: 99

AU (critical compressibility factor) – [Poling et al. (2001) [1008]]: 1–9, 13–15, 19, 21, 22, 26, 28, 30–33, 35–37, 41, 42, 44–47, 50, 55, 56, 57, 63, 64, 66, 68–70, 72, 75, 80, 82, 86, 87, 89–99

AV (Pitzer acentric factor ω) – [Poling et al. (2001) [1008]]: 1–5, 7–9, 15, 19, 21, 22, 26, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 57, 64, 66, 67–70, 72, 80, 86, 98, 99; [Jacobsen et al. (1997) [1011]]: 89–97

AW (electrical conductivity) – [Riddick et al. (1986) [1006]]: 1, 3, 4, 7, 8, 11–14, 16–18, 21–23, 27, 28, 30–32, 36–38, 40–47, 50–57, 61, 63, 64, 66–69, 71, 72, 74–78, 80, 81, 83, 84; [Pashley et al. (2004) [1038]]: 86; [Siedler (1986) [1025]]: 88 (salinity 35‰) * at temperature: 1 [19.5◦C];14 [18◦C];17 [NA];18 [20◦C];41 [18◦C];44, 45 [NA];47 [27◦C];50 [23.1◦C]; 51 [20◦C]; 52 [NA]; 53, 54 [20◦C]; 55 [NA]; 57 [NA]; 63 [17◦C]; 64 [NA]; 67 [22◦C]; 69 [NA]; 72 [35◦C]; 74 [NA]; 86 [22◦C]; 88 [15◦C, salinity 35‰] ** 85%

AX (molecular dipole moment) – [Poling et al. (2001) [1008]]: 1, 2, 4, 6–9, 12–16, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55–57, 63, 64, 66, 68–70, 72, 75, 80, 82, 87, 89–98; [Riddick et al. (1986) [1006]]: 3, 5, 11, 17, 18, 25, 26; [Suresh and Naik (2000) [1039]]: 87 * at temperature: 17 [NA]; ** in benzene; *** in tetrachloromethane Ch08-I044498.tex 12/9/2007 17: 21 Page 377

Liquids and their properties 377

AY (solvent polarity parameter) – [Reichardt (2003) [1040]]: 1, 3, 4, 7, 9, 12–14, 16, 17, 21–23, 25, 28, 32, 36, 37, 40–42, 44–47, 51, 53, 55–57, 59, 60, 62, 64, 68, 69, 71, 72, 75–81, 83, 84, 86

AZ (dielectric constant) – [Riddick et al. (1986) [1006]]: 1–9, 11–14, 16–18, 21–23, 25, 27–38, 40–58, 61–72, 74–81, 83, 84, 86; [Greenwood and Earnshaw (1997) [1035]]: 87; [Flynn (2005) [1022]]: 89, 91–95, 99, 100 * at temperature: 1, 4–9 [20◦C]; 11 [20◦C]; 13 [20◦C]; 17 [∼16◦C]; 29–33 [20◦C]; 35 [20◦C]; 49, 50 [20◦C]; 52 [24◦C];53 [20◦C];57 [20◦C];62, 63 [20◦C];65 [NA];66, 67 [20◦C];69–71 [20◦C];72 [20◦C];74 [20◦C]; 75 [30◦C]; 83 [20◦C]; 89, 91–95, 99, 100 [NA]

BA (temperature coefficient of dielectric constant) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16, 18, 21–23, 27, 28, 30–32, 36–39, 41, 42, 44–47, 49–51, 53, 55–58, 61, 63, 64, 66–72, 74–80, 82, 83, 86

BB (magnetic susceptibility) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16–18, 21–25, 27–33, 36–38, 40–42, 44–47, 49–51, 56–58, 60, 61, 64, 66–72, 74–81, 83, 84, 86 * temperatures not given

BC (index of refraction) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16–19, 20–33, 36–42, 44–53, 55–58, 60, 61, 63, 64, 66–72, 74–84; [Harvey et al. (1998) [1041]]: 86; [Smithsonian Physical Tables (2003) [1042]]: 87; [Flynn (2005) [1022]]: 89, 93 * at temperature: 87 [20◦C]; 89 [b.p.]; 93 [b.p.]; ** ‘long wavelengths’

BD (temperature coefficient of the index of refraction −dlnn/dT) – [Marcus (1998) [1007]]: 1–5, 7, 9, 11–14, 16–18, 21–23, 25–33, 36–38, 40–42, 44–53, 55–58, 60, 61, 63, 64, 66–72, 74–81, 83, 84, 86

BE (Kerr coefficient) – [Landolt Börnstein (1963) [1043]]: 1, 3–5, 7, 9, 11–14, 21, 22, 28, 30–32, 36, 37, 41, 42, 44, 46, 47, 49, 50, 56, 57, 61, 62, 68, 69, 71, 72, 80, 83, 86, 89, 92, 93, 98 * at temperature/wavelength: 1, 3–5 [20◦C/546 nm]; 7 [19◦C/546 nm]; 9 [20◦C/546 nm]; 11 [17.7◦C/red]; 12 [18◦C/white]; 13, 14 [20◦C/546 nm]; 21 [589.3 nm]; 22 [20◦C/546 nm]; 28 [20◦C/546 nm]; 30–32 [20◦C/589 nm];36 [NA/580 nm];37 [17.0◦C/white];37 [17.5◦C/red];42 [19◦C/580 nm];44 [18.5◦C/red]; 46 [19◦C/red]; 47 [18.3◦C/red]; 49 [20◦C/red]; 50 [20.1◦C/red]; 56 [20.2◦C/white]; 57 [20◦C/586 nm]; 61 [20◦C/586 nm]; 62 [22◦C/586 nm]; 68 [18.7◦C/white]; 69 [22◦C/546 nm]; 71 [19◦C/546 nm]; 72 [22◦C/546 nm]; 80 [NA/red]; 83 [20◦C/546 nm]; 86 [20◦C/yellow]; 89 [19.91 K/546 nm]; 92 [77.4 K/ 546 nm]; 93 [−183◦C/520 nm]; 98 [20.9◦C/546 nm/78.9 bar/0.314 g/cm3]; Bs = Kerr coefficient of carbon disulphide (CS2)

BF (light scattering coefficient, relative to benzene) – [Fabelinski (1968) [1044]]: 3, 7, 13, 14, 21, 22, 28, 30–32, 36, 37, 41, 42, 44, 46, 49, 50, 57, 63, 68, 83, 86 6 6 Absolute scattering coefficients: benzene – R90 · 10 = 48.2 (435.8 nm), R90 · 10 = 16.3 (546.1 nm); water: 6 6 R90 · 10 = 3.08 (435.8 nm), R90 · 10 = 1.05 (546.1 nm) [Fabelinski (1968) [1044]].

BG (depolarization factor) – [Fabelinski (1968) [1044]]: 1, 3–7, 9, 12–14, 21, 22, 27–32, 34, 36, 37, 41, 42, 44, 46, 49, 57, 61, 69–70, 80, 83, 86; [Landolt Börnstein (1963) [1043]]: 2, 8, 56, 47, 68 *at temperature: 2 [NA]; 8 [NA]; 56 [20◦C]; 47 [NA]; 68 [NA]

BH (IR spectrum) – Spectrum code in Sadtler handbook [1003]

BI (IR/Raman spectrum) – Spectrum code in Schrader handbook [1004]

BJ (UV–VIS spectrum) – Spectrum code in Perkampus handbook [1005]. Many references to UV-spectra are given in book by Hirayama [1045] Ch08-I044498.tex 12/9/2007 17: 21 Page 378

378 Handbook of Liquids-Assisted Laser processing

BK (ultraviolet cut-off point) – [Reichardt (2003) [1040]]: 1, 3–5, 7–9, 11–14, 16, 18, 21, 27, 28, 30, 36, 37, 39, 42–44, 55–57, 62–64, 66, 68, 75, 76, 78, 80, 81, 83, 84; [Phillips [1046]]: 6, 22, 23, 30, 41, 45, 46, 51, 52, 69, 72, 73, 86; [CRC Handbook 1995/1996 [995]]: 10, 32, 58, 79 * Temperature not given

BL (ultraviolet 5% abs. point) – [Phillips [1046]]: 1, 3–6, 9, 12, 13, 16–18, 21–24, 28, 30, 36, 37, 41, 42, 44–46, 51, 52, 55–57, 64, 66, 68, 69, 72, 73, 75, 76, 78, 80, 84, 86 * temperature not given

BM (ionization energy) – [NIST [1010]]: 1–9, 11–18, 21–25, 27–42, 44–49, 51, 52, 55–84, 86–88, 89–99

BN (standard state enthalpy of formation) – [Poling et al. (2001) [1008]]: 1–9, 12–16, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55–58, 63, 64, 66, 68–72, 75, 80, 82, 86–87, 94, 99; [Riddick et al. (1986) [1006]]: 25, 26

BO (standard state Gibbs energy of formation) – [Poling et al. (2001) [1008]]: 1–9, 12–16, 19, 21, 22, 28, 30–33, 35–37, 41, 42, 44–47, 49, 50, 55–57, 63, 64, 66, 68–72, 75, 80, 82, 86–87, 94

BP (Hildebrandt solubility parameter) – [Reichardt (2003) [1040]]: 3, 7, 13, 14, 16, 21, 22, 36–38, 44, 46, 55, 56, 64, 68, 71, 74, 76, 78, 80, 83, 84, 86

BQ (oxygen solubility) – [Fogg and Gerrard (1991) [1047]]: 1, 3–5, 7, 8,14, 19–22, 28, 36, 37, 42, 44, 46, 50, 55, 56, 64, 68–71, 80, 83; [Dias et al. [1048]]; 19; [CRC handbook 1995/1996 [995]]: 86 * at temperature 64 [20◦C]

BR (nitrogen solubility) – [Fogg and Gerrard (1991) [1047]]: 1, 3–5, 7, 8, 13, 14, 21, 22, 28, 36, 37, 41, 42, 44, 46, 50, 55, 56, 68, 75, 80, 82, 83; [Battino et al. (1984) [1049]]: 86, 87 * at temperature: 75 [298 K]

BS (carbon dioxide solubility) – [Fogg and Gerrard (1991) [1047]]: 1, 3–5, 7, 8, 13, 14, 21, 22, 26, 28, 36, 37, 41, 43, 44, 46, 50, 51, 55, 64, 68, 78, 80, 83; [CRC handbook 1995/1996 [995]]: 86 * at temperature: 26 [297.98 K]

BT (solubility in water) – [Merck [1009]]: 1–14, 16–18, 21, 22, 24–29, 30, 32–33, 35, 38, 41, 44–46, 48–50, 52, 53, 57, 59–67, 69–73, 75, 81, 83, 84; [CRC handbook 1995/1996 [995]]: 89–99; [Liquid Synthetic Air [1017]]: 100 * at temperature: 1 [16◦C]; 2 [20◦C]; 3, 4 [20◦C]; 7, 8 [20◦C]; 9 [NA]; 10 [20◦C]; 11 [30◦C]; 12–14 [20◦C]; 16–18 [20◦C]; 21, 22 [20◦C]; 24 [20◦C]; 25 [30◦C]; 26–29 [20◦C]; 30 [20◦C]; 33 [20◦C]; 38 [20◦C]; 41 [20◦C]; 44–46 [20◦C]; 48–50 [20◦C]; 52, 53 [20◦C]; 57 [20◦C]; 59 [10◦C]; 60–66 [20◦C]; 67 [30◦C]; 69–73 [20◦C]; 75 [20◦C]; 79 [20◦C]; 83, 84 [20◦C] ** litre per litre; *** boiling range 40–60◦C

BU Substance no. in Riddick handbook [1006]

BV Substance no. in Marcus handbook [1007]

BW Substance no. in Poling handbook [1008] Ch08-I044498.tex 12/9/2007 17: 21 Page 379

Liquids and their properties 379

8.3 Properties of Water

If not specified else, the data below are for pure light water at normal conditions and in SI units.

Transmission of light by water (Fig. 8.1)

10 m

1 m Pure water, 298 K

100 mm

10 mm

1 mm

100 µm

10 µm

Absorption length ∆ 1 µm

10 nm

1 nm µ µ (a) 100 nm 1 m Light wavelength in vacuum 10 m 100 J 10 1 0.1

Pulse energy 0.01 157 248 308 511 694 1054 1540 2900 10 600 193 351 755 2010 2940 Lasers wavelength (nm) (b) 266 355 532 800 1064

Figure 8.1 Transmission spectrum of pure liquid water (a) and the common lasers wavelengths (b). The spectrum was calculated from the data in [1050, 1051]. Laser data are from Laser Specification Tables [1052].

Table 8.9 Linear absorption of light in an homogeneous medium.

Distance travelled by Amount of absorbed Amount of light in medium light transmitted light

0.0101  ≈ 1%  0.01 = 1% 0.99 = 99% 0.0202  ≈ 2%  0.02 = 2% 0.98 = 98% 0.0513  ≈ 5%  0.05 = 5% 0.95 = 95% 0.0105  ≈ 10%  0.1 = 10% 0.9 = 90% 0.0223  ≈ 20%  0.2 = 20% 0.8 = 80% 0.0693  ≈ 70%  0.5 = 50% 0.5 = 50% 1.000  ≈ 100%  0.632 = 1 − 1/e = 0.368 = 1/e = 36.8% 63.2% Ch08-I044498.tex 12/9/2007 17: 21 Page 380

380 Handbook of Liquids-Assisted Laser processing

Raman spectrum of water (Fig. 8.2)

H2O

21°C 50°C 100°C

Intensity 150°C 200°C 250°C 300°C

2600 2800 3000 3200 3400 3600 3800 4000 Raman shift (cm−1)

Figure 8.2 Raman spectrum of liquid H2O in the O—H stretching region [1053]. The peak to the right is v1 symmetric stretching mode, while the peak to the left is due to the 2v2 overtone and the O—H stretching mode of two (or more) hydrogen-bonded H2O molecules [1054]. © American Chemical Society (1982), reprinted with permission from Ref. [1053].

Phase diagram of water (Fig. 8.3)

1012 Ice XI Ice X

Ice VII Ice VIII 109 Ice VI Supercritical Ice V fluid Ice II Liquid Critical point Pressure (Pa) 106 Ice Ih Vapour

103 200 300 400 500 600 700 800 Temperature (K)

Figure 8.3 Phase diagram of water © Martin Chaplin, redrawn with permission from M. Chaplin, Water Structure and Behaviour [1055]. Ch08-I044498.tex 12/9/2007 17: 21 Page 381

Liquids and their properties 381

Equations of state of water and steam Tait’s equation of state At large pressures (shock compression), the simpleTait’s equation is often used: [980]
 p + A ρ n w = . (8.1) p0 + Aw ρ0

For water below 2.5 GPa: Aw = 296.3 MPa and n = 7.415.

IAPWS formulations International Association for the Properties of Water and Steam (IAPWS) has issued two formulations for the properties of water and steam: (a) IAPWS-95 for general and scientific use [1056] and (b) IAPWS-IF97 for industrial use. [1057–1059] The IAPWS-95 formulation for scientific use is a fundamental equation with 69 empirical constants for specific Helmholtz free energy f . The thermodynamic properties of water and steam are expressed through derivatives of Helmholtz free energy with respect to the density,pressure, and temperature. IAPWS-95 is valid in range 100 Pa to 1000 MPa and 0–1000◦C. The IAPWS-IF97 formulation for industrial use is a set of fundamental equations having 10–52 empirical constants for specific Gibbs or Helmholtz free energy (dependent of the temperature–pressure region). IAPWS- IF97 is valid in ranges 0–800◦C,0–100 MPa and 800–2000◦C,0–10 MPa. Free computer codes for calculation of thermodynamic properties are available. IAPWS has also formulations for dynamic viscosity,thermal conductivity,surface tension, static dielectric constant, and refractive index of water over a large interval of temperatures and pressures.

Dependence of some thermophysical properties of water on temperature Dependence of some thermophysical properties of water on temperature is shown in Figure 8.4.

Some simple analytical formulations Density of water [1061] (253–383 K) [g/ml].

ρ = a + bT + c/(0.0362 − 0.0004099T)2, (8.2)

where a = 1.367, b =−0.000984, c =−0.0005669. Surface tension of water [1058] (valid from triple to critical point) σ = 235.8(1 − θ)1.256[1 − 0.625(1 − θ)], (8.3) σ∗

where θ = T/T* with σ* = 1 mN/m and T* = Tc. Viscosity of water [1062] (0–100◦C) [◦C, millipoises]  − η 1 + 120 = 2.1482[(t − 8.435) + 8078.4 + (t − 8.435)2] (8.4)

Heat capacity of water [994] (RT to ∼100◦C) [(J/kg K):

− − − c =−2.42139 × 10 8T 3 + 2.68536 × 10 5T 2 − 9.68137 × 10 3T + 2.13974 (8.5)

Heat conductivity of water [994] (RT to ∼100◦C) [(W/m K):

− − λ =−0.58180 + 6.357044 × 10 3T − 7.9662523 × 10 6T 2 (8.6) Ch08-I044498.tex 12/9/2007 17: 21 Page 382

382 Handbook of Liquids-Assisted Laser processing

1.005 1.6

1.000 Density 1.4 Relative (g/ml) viscosity 1.995 1.2

1.990 1.0

1.985 0.8

1.980 0.6

1.975 0.4

1.334 76 74 Surface tension 1.332 (dyne/cm) 72

1.330 70 68 Refractive 1.328 index 66 1.326 64

1.500 50 49 1.480 Sound velocity Isothermal (m/s) 48 compressibility ϫ Ϫ6 1.460 47 ( 10 , 1/bar)

1.440 46 45 1.420 44 1.400 43

600 6.6 500 6.4 400 6.2 300 Thermal 6.0 Thermal 200 expansivity conductivity Ϫ6 5.8 100 (ϫ10 , 1/K) (mW/cm/K) 5.6 0 0 10 20 30 40 50 60 70 0 10 20 30 40 50 60 70 Temperature (°C) Temperature (°C)

Figure 8.4 Dependence of some thermophysical properties of water on temperature in the range 0–70◦C. © Society for Applied Spectroscopy, republished with permission from Ref [1060]. Saturated vapour pressure (0–70◦C) [hPa]:
 17.5043 · T Magnus formula : E (T) = E · exp , (8.7) w 0 241.2 + T ◦ T is temperature in C, E0 = E(T0) = 611 hPa. Ch08-I044498.tex 12/9/2007 17: 21 Page 383

Liquids and their properties 383

90 4.21 Thermal 85 Dielectric 4.20 capacity constant 80 (J/g/°C) 75 4.19 70 4.18 65 60 4.17

200 15.0

Vapor pressure Ionization 150 14.5 (mmHg) constant 14.0 (pKw) 100 13.5 50 13.0

0 12.5 Temperature (°C) 300 4.4

250 Enthalpy 4.2 Entropy (J/g) (J/g/K) 200 4.0

150 3.8 100 3.6 50 3.4 0 0 10203040506070 010203040506070 Temperature (°C)

Ϫ250 Ϫ300 Free energy Ϫ350 (J/g) Ϫ400 Ϫ450 Ϫ500 Ϫ550 Ϫ600 010203040506070 Temperature (°C)

Figure 8.4 (Continued)

Index of refraction of water [1063, 1064] (200–1100 nm, 25◦C, λ in nanometres):

− − − n(λ) = 1.31279 + 15.762λ 1 − 4382λ 2 + 1.1455 × 106λ 3 (8.8)

Thermal dissociation (autoionization) of liquid water + − Liquid water dissociates into hydrogen ion (proton) and hydroxyl ion: H2O ↔ H + OH .The degree of dis- + − + sociation is commonly characterized by the ionization product Kw, defined by Kw = [H ][OH ], where [H ] Ch08-I044498.tex 12/9/2007 17: 21 Page 384

384 Handbook of Liquids-Assisted Laser processing

1000 ϭ pKw 8 800

600 9

400 10 Pressure, MPa 11 200 12 14 16

0 0 200 400 600 800 1000 Temperature, ЊC

Figure 8.5 Ionization product of water at high temperatures and pressures. Values at curves are pKw = −log10(Kw). © Martin Chaplin, Redrawn with permission from M. Chaplin, Water Structure and Behaviour [1055].

100

H2O H O

H2 10Ϫ1 O 2 OH

10Ϫ2 Molar fractions 100 kPa 10Ϫ3

10Ϫ4 1500 2000 2500 3000 3500T, K 4000

Figure 8.6 Molar fraction of species of the dissociation of water at thermodynamic equilibrium as a function of temperature starting from pure steam at a pressure of 105 Pa. At higher pressures the maxima will be shifted towards higher temperatures. From the article by Häussinger [1066]. © Wiley-VCH Verlag GmbH & Co KGaA, republished with permission.

and [OH−] are the concentrations of the corresponding ions. Because the proton H+ hydrates immediately,a + − + more real description of the ionization process would be: H2O+H2O ↔ H3O + OH , and Kw = [H3O ] − + [OH ]. H3O is named hydronium ion. Instead of Kw, its decadic logarithm log10Kw =−pKw is often used −14 (Fig. 8.5). At a standard temperature and pressure Kw has a value of 1 × 10 .

Thermal dissociation of water vapour Above 2000 K, water vapour starts to dissociate remarkably (Fig. 8.6). The composition of dissociated water vapour as a function of temperature and pressure can be calculated by the formulae in the article by Friel and Goetz [1065]. Ch08-I044498.tex 12/9/2007 17: 21 Page 385

Liquids and their properties 385

The degree of water dissociation as a function of temperature is [1066]: 2000 K 0.69 mol% 2300 K 2.64 mol% 2700 K 10.35 mol% 3000 K 22.4 mol% 3500 K 57.43 mol% The concentrations of free electrons and ions in thermally ionized water and other liquids can be calculated by Saha formula (Eq. (7.87)). At atmospheric pressure, significant ionisation sets in at about 12 000 K; excited atomic hydrogen and oxygen exist in region 3000–16 000 K. References-I044498.tex 11/9/2007 19: 2 Page 387

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Thermal-fluid phenomena induced by nanosecond-pulse heating of materials in water. Trans ASME J HeatTransfer 2001; 123(6):1123–1132. 990. Sakka T,Takatani K, OgataYH, et al. Laser ablation at the solid–liquid interface: transient absorption of continuous spectral emission by ablated aluminium atoms. J. Phys D:Appl Phys 2002; 35:65–73. 991. Sakka T, Saito K, Ogata YH. Emission spectra of the species ablated from a solid target submerged in liquid: vibrational temperature of C2 molecules in water-confined geometry. Appl Surf Sci 2002; 197–198:246–250. 992. Saito K, Sakka T, Ogata YH. Rotational spectra and temperature evaluation of C2 molecules produced by pulsed laser irradiation to a graphite-water interface. J Appl Phys 2003;. 94(9):5530–5536. 993. Sakka T,Saito K, OgataYH. Confinement effect of laser ablation plume in liquids probed by self-absorption at C2 Swan band emission. J Appl Phys 2005; 97: 014902. 994. Geretovszky Zs, Kelemen L, Piglmayer K. Temperature distribution in multilayers covered by liquid layer and processed by focused laser beam. Appl Surf Sci 1996; 106:422–428. 995. CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data,Editor-in-chief David R. Lide; Associate Editor: H. P. R. Frederikse, 76th ed., Boca Raton: FL, CRC Press, 1995. 996. Paquin RA. Properties of metals. In: Bass M,Van Stryland EW,Williams DR, eds. Handbook of optics, 2nd edn. New York:McGraw-Hill; 1995, Chapter 35. 997. Semiconductors on NSM. Online. Available: http://www.ioffe.rssi.ru/SVA/NSM/Semicond/ 998. Iida T.The physical properties of liquid metals. Oxford: Clarendon; 1988. 999. Ohring M.The materials science of thin films. Boston:Academic; 1992. 1000. Perry DL, Phillips SL. Handbook of inorganic compounds. Boca Raton: CRC; 1995. 1001. Meyer RJ, Pietsch EHE, Kotowski A, Becke-Goehring M. (eds.) Gmelin handbook of inorganic and organometallic chemistry, 8th edn. Berlin: Springer; 1990–1997. 1002. Morgan JJ,StummW.Water(properties). In:Kirk-Othmer Encyclopedia of chemicaltechnology,4th edn,vol. 25. NewYork: Wiley; 1998:382–405. 1003. [Anonymous]. Infrared spectra handbook of common organic solvents. Sadtler Research Laboratories; 1983. 1004. Schrader B. Raman/infrared atlas of organic compounds. Weinheim:VCH;1989. 1005. Perkampus H-H. UV-VIS atlas of organic compounds, 2nd edn. part 2, Spectra D1/1-M19. Weinheim:VCH;1992. 1006. Riddick JA, BungerWB, SakanoTK. Organic solvents. Physical properties and methods of purification, 4th edn. (Techniques in Chemistry, vol. 2). NewYork:Wiley; 1986. 1007. MarcusY.The properties of solvents. Chichester:Wiley; 1998. 1008. Poling BE, Prausnitz JM, O’Connell JP.The properties of gases and liquids, 5th edn. Boston: McGraw-Hill; 2001. 1009. Merck Chemicals. Online. Available: http://www.merck.de/servlet/PB/menu/1001796/index.html 1010. NIST Chemistry WebBook. Online. Available: http://webbook.nist.gov/chemistry 1011. Jacobsen RT,Penoncello SG, Lemmon EW.Thermodynamic properties of cryogenic fluids. NewYork:Plenum; 1997. References-I044498.tex 11/9/2007 19: 2 Page 421

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1012. Mackanos MA,Jansen ED,Shaw BL,et al. Delivery of midinfrared (6 to 7-µm) laser radiation in a liquid environment using infrared-transmitting optical fibers. J Biomed Optics 2003; 8(4):583–593. 1013. Nakamura M,Tamura K, Murakami S. Isotope effects on thermodynamic properties: mixtures of x(D2OorH2O) + (1–x)CH3CN at 298.15 K.Thermochim Acta 1995; 253:127–136. 1014. Cook P,Hands BA. Cryogenic fluids databook, 1st edn. Leatherhead: British Cryoengineering Society; 1015. ChemExper Chemical Directory. Online. Available: http://www.chemexper.com/ 1016. Sigma-Aldrich Corporation. Online. Available: http://www.sigmaaldrich.com 1017. Liquid Synthetic Air, Safety Data Sheet. BOC Gases. Online. Available: http://www.wessingtoncryogenics.co.uk/ Liquid%20Air%20Data%20Sheet.pdf 1018. Eisenberg D, Kauzmann W.The structure and properties of water. London: Oxford University; 1969. 1019. Horita J, Cole DR. Stable isotope partitioning in aqueous and hydrothermal systems to elevated temperatures, In: Palmer DA,Fernández-Prini R,Harvey AH,eds. Aqueous systems at elevated temperatures and pressures: physical chemistry in water, steam and hydrothermal solutions. Amsterdam: Elsevier; 2004:277–319. 1020. Revised release on the IAPS formulation 1985 on the thermal conductivity ofordinary water substance. IAPWS; 1998. 1021. IAPWS Release on surface tension of ordinary water substance, September 1994. IAPWS; 1994. 1022. Flynn TM. Cryogenic engineering, 2nd edn. NewYork:Dekker; 2005. 1023. IAPWS Revised release on the IAPS formulation 1985 for the viscosity of ordinary water substance.Vejle:IAPWS; 2003. 1024. Release on viscosity and thermal conductivity of heavy water substance, September 1982. IAPS; 1982. 1025. Siedler P. Physical properties (general) of sea water. In: Landolt Börnstein, numerical data and functional relationships in science and technology, new series. Group II: atomic and molecular physics, vol. 5/3a. Springer-Verlag, Berlin a.o.; 1986:223–262. 1026. Rodnikova MN,Val’kovskaya TM, Kartzev VN, et al. About elasticity of spatial H-bond network in liquids, J Mol Liquids 2003; 106:219–222. 1027. RSHydro www-page:Sound Speeds inWater,Liquids and Materials. Online. Available:http://www.rshydro.co.uk/ sound-speeds.shtml 1028. Beyer RT. Nonlinear acoustics. Washington,DC: US Naval Sea Systems Command; 1974:101. 1029. Rice MH,Walsh JM. Equation of state of water to 250 kilobars. J Chem Phys 1957; 26(4):824–830. 1030. Schaaffs W. Molecular acoustics. In: Landolt Börnstein, Numerical data and functional relastionships in science and technology,new series. Group II: atomic and molecular physics, vol. 5. Berlin: Springer; 1967:254. 1031. SkripovVP, Sinitsyn EN, Pavlov PA, et al.Thermophysical properties of liquids in the supercritical (superheated) state.New York:Gordon and Beach; 1988. 1032. Avedisian CT. The homogeneous nucleation limits of liquids. J Phys Chem Ref Data 1985; 14(3):695–729. 1033. Sartori E. A critical review on equations employed for the calculation of the evaporation rate from free water surfaces. Solar Energy 2000; 68(1):77–89. 1034. PadfieldT.Equations describing the physical properties of moist air. Online.Available:http://www.natmus.dk/cons/ tp/atmcalc/atmoclc1.htm 1035. Greenwood NN, Earnshaw A. Chemistry of the elements, 2nd edn. Oxford: Butterworth Heinemann; 1036. Kennish MJ, ed. Practical handbook of marine science. Boca Raton: CRC; 1989. 1037. Antoine-Gleichung. Wikipedia. Online. Available: http://de.wikipedia.org/wiki/Antoine-Gleichung 1038. Pashley RM, Rzechowicz M, Pashley LR, et al. De-gassed water is a better cleaning agent. J Phys Chem B 2004; 109:1231–1238. 1039. Suresh SJ,NaikVM. Hydrogen bond thermodynamic properties of water from dielectric constant data. J Chem Phys 2000; 113:9727–9732. 1040. Reichardt C. Solvents and solvent effects in organic chemistry, 3rd edn. Weinheim:Wiley-VCH;2003. 1041. Harvey AH, Gallagher JS, Levelt Sengers JMH. Revised formulation for the refractive index of water and steam as a function of wavelength, temperature and density, J Phys Chem Ref Data 1998; 27:761–774. 1042. Forsythe WE. Smithsonian physical tables, 9th edn. NewYork:Knovel; 2003. 1043. Bechmann R, Capeller U, Hellwege AM, et al., eds. Landolt Börnstein, Zahlenwerte und Funktionen aus Physik, Chemie, Astronomie, Geophysik und Technik, 6th edn. II Band: Eigenschaften der Materie in ihren Aggregatzuständen. 8. Teil Optische Konstanten. Berlin: Springer; 1963:5–815. 1044. Fabelinskii IL. Molecular scattering of light. NewYork:Plenum; 1968. 1045. Hirayama K. Handbook of ultraviolet and visible absorption spectra of organic compounds. NewYork:Plenum, 1967. 1046. G. F. Phillips, 3.8.7. UV-visible spectroscopy. Online. Available: http:// kayelaby.npl.co.uk/chemistry/3_8/3_8_7/ .html 1047. Fogg PGT, Gerrard W. Solubility of gases in liquids. A critical evaluation of gas/liquid systems in theory and practice. Chichester:Wiley; 1991. 1048. Dias AMA, Freire M, Coutinho JAP, et al. Solubility of oxygen in liquid perfluorocarbons. Online. Available: symp15.nist.gov/pdf/p193.pdf References-I044498.tex 11/9/2007 19: 2 Page 422

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1049. Battino R, Rettich TR, Tominaga T. The solubility of nitrogen and air in liquids. J Phys Chem Ref Data 1984; 13(2):563–600. 1050. Sowers BL, Birkhoff RD,Arakawa ET. Optical absorption of liquid water in the vacuum ultraviolet. J Chem Phys 1972; 57(1):583–584. 1051. Hale GM, Querry MR. Optical constants of water in the 200-nm to 200-µm wavelength region. Appl Opt 1973; 12(3):555–563. 1052. Laser specification tables (Buyers Guide 2001). Laser focus world 2000; 36(12)(Suppl.):66–286. 1053. Ratcliffe CI, Irish DE. Raman studies of liquid water up to 300◦C. J Phys Chem 1982; 86(25);4897–4905. 1054. Bernath PF. Spectra of atoms and molecules. NewYork:Oxford University; 1995. 1055. M. Chaplin,Water Structure and Behavior. Online. Available: http://www.lsbu.ac.uk/water/index2.html 1056. WagnerW,Pruß A. The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance general and scientific use. J Phys Chem Ref Data 2002; 31(2):387–535. 1057. WagnerW,Cooper JR,DittmannA,et al.The IAPWS industrial formulation 1997 for the thermodynamic properties of water and steam. J Eng GasTurbines Power 2000; 122(1):150–180. 1058. WagnerW,KruseA. Properties of water and steam,Zustandsgrößen vonWasser undWasserdampf. Berlin:Springer;1998. 1059. Parry WT,Bellows JC, Gallagher JS, et al. ASME international steam tables for industrial use. NewYork:ASME; 2000. 1060. Lin J, Brown CW. Universal approach for determination of physical and chemical properties of water by near-IR spectroscopy. Appl Spectrosc 1993; 47(10):1720–1727. 1061. Dougherty RC, Howard LN. Equilibrium structural model of liquid water: Evidence from heat capacity, spectra, density,and other properties. J Chem Phys 1998; 109(17):7379–7393. 1062. Dorsey EN. Properties of ordinary water-substance. NewYork:Reinhold; 1940. 1063. Quan X, Fry ES. Empirical equation for the index of refraction of seawater. Appl Opt 1995; 34:3477–3480. 1064. Huibers PDT. Models for the wavelength dependence of the index of refraction of water. Appl Opt 1997; 36(16):3785–3787. 1065. Friel PJ, Goetz RC. The composition and enthalpy of dissociated water vapor. J Phys Chem 1960; 64:175–177. 1066. Häussinger P. Hydrogen. In: Elvers B, RounsavilIe JF, SchulzG, eds. Ullmann’s encyclopedia of industrial chemistry, vol. A13. Weinheim:VCH;1989:297–438. 1067. Maxwell Garnett JC. Colours in metal glasses and in metallic films. PhilTrans R Soc Ser A 1904; 203:385–420.

Further Reading

1. Drawin HW. Thermodynamic properties of the equilibrium and nonequilibrium states of plasmas. In: Venugopalan M, ed. Reactions under plasma conditions, New York:Wiley; 1971:53–284. Diagram of composition of water plasma from 2 to 30 kK (Fig. 15b on page 97). 2. Yang GW. Laser ablation in liquids: applications in the synthesis of nanocrystals. Prog Mater Sci 2007; 52:648–698. A review article. Glossary-I044498.tex 11/9/2007 18: 56 Page 423

Glossary

ABAQUS A commercial general-purpose finite element program, designed primarily to model the behaviour of solids and structures under externally applied loading. Ablation Material ejection by laser light irradiation due to several mechanisms such as photothermal heating, boiling, optical breakdown, plasma formation, (chain) chemical reaction, etc. Absorbance, Aλ In spectroscopy,the absorbance Aλ is defined as

Aλ =−log(I/I0), where I is the intensity of light at a specified wavelength λ that has passed through a sample (transmitted light intensity) and I0 is the intensity of the light before it enters the sample (or incident light intensity). Absorption (of light or sound) Conversion of the transmitted energy into another form, usually thermal. Absorption coefficient, a A measure of the attenuation caused by absorption of energy that results from its −ax passage through a medium, for a plane wave in homogeneous medium I = I0e (Beer–Lambert law). ACCIC A code for simulation of laser-confined target interaction, developed at CLEA-LALP,Arcueil, France. Accommodation coefficient The ratio of the average energy actually transferred between a surface and impinging gas molecules scattered by the surface,to the average energy,which would theoretically be transferred if the impinging molecules reached complete thermal equilibrium with the surface. Acoustic impedance, Z The ratio of the amplitude of the sound pressure p and the amplitude of the particle velocity v of an acoustic wave, p Z = = ρ · c, v where ρ is the density of the medium and c is the speed of sound. Reflected power at an interface of two media with acoustic impedances Z1 and Z2 is expressed by
 P Z − Z 2 refl = 2 1 . Pinc Z2 − Z1 The acoustic impedance of air is ≈0.0004 Mrayls (MPa s/m). Acoustic nonlinearity parameter, B/A Ratio of the coefficients A and B in the Taylor expansion of the dependence of the pressure p on the density ρ of a fluid for the isentropic case B C p = p + As + s2 + s3 + ..., 0 2! 3!

where p0 notes the equilibrium pressure and s = (ρ − ρ0)/ρ0, where ρ0 is the equilibrium density. Sound speed dependence on parameter s is expressed as 

  B C v2 = v2 1 + s + s2 + ... . 0 A 2A

Usually the terms beginning with s2 will be neglected and the nonlinear acoustic properties will be determined by B/A only.

Handbook of Liquids-Assisted Laser Processing © 2008 Elsevier Ltd. ISBN-13: 978-0-08-044498-7 All rights reserved.

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424 Glossary

Due to sound speed dependence on pressure,sinusoidal wave will transform into sawtooth one in an acoustically nonlinear medium:

Adiabatic compressibility A measure of the relative volume change of fluid or solid as a response to a pressure change at constant entropy,
 1 ∂V κS =− , V ∂p S where V is volume and p is pressure. The inverse of the compressibility is called the bulk modulus. Adiabatic exponent, γ Material parameter defined by     v ∂2e 1 a2 v ∂p γ = = = =− 2 , p ∂v S pKs pv p ∂v S

where v – volume, p – pressure, e – internal energy, Ks – compressibility, a – speed of sound. AIST National Institute of Advanced Industrial Science and Technology,Tsukuba, Japan. Alcohol An organic compound in which a hydroxyl group (—OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is CnH2n+1OH. Aliphatic compounds Organic compounds in which carbon atoms are joined together in straight or branched chains as opposed to aromatic compounds which include a benzene ring. Alkanes Acyclic saturated hydrocarbons comprising a long chain of carbon linked together by single bonds. Alkanes are aliphatic compounds. The general formula for alkanes is CnH2n+2. Alkyl A univalent radical containing only carbon and hydrogen atoms arranged in a chain.The general formula for alkyles is CnH2n+1. ANSYS A commercial multiphysics finite element simulation program. Antoine equation Widely used approximation of the dependence of vapour pressure p on temperature T:

B log p = A − , T − C where A, B, and C are constants. Antoine equation is useable from the triple point up to the reduced temperature of 0.85 (T = 0.85Tc). ARL Anti-reflective layer (anti-reflective coating), a thin opaque coating having high optical absorbance, or a quarter-wavelength low-index layer suppressing reflected light due to destructive interference of light reflecting from the top and from the bottom of the ARL. Aromatic compound An organic chemical compound that contains aromatic rings (arenes) like benzene, pyridine, or indole. Aromaticity A chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger that would be expected by the stabilization of conjugation alone. Attainable atmospheric superheat temperature Highest temperature to which the liquid may be heated without boiling. The attainable superheat temperature is determined by the homogeneous nucleation rate. Impurities in liquids lower the attainable superheat temperature because they serve as bubble nucleation centres. Barkhausen noise Noise in the magnetization or magnetic flux density of a ferromagnet when the magnetizing force applied to it is changed. Bauschinger effect The decrease in flow stress shown by materials when the direction of plastic deformation is reversed (e.g. first in compression, then in tension). Glossary-I044498.tex 11/9/2007 18: 56 Page 425

Glossary 425

Beam quality parameter, M 2 Is the ratio of the laser beam’s multimode diameter-divergence product to the ideal diffraction limited (TEM00) beam diameter-divergence product. It can also be given by the square of the ratio of the multimode beam diameter to the diffraction-limited beam diameter,
 D ·  D 2 M 2 = m m = m . d0 · 0 d0

In the equation above, Dm is the measured beam waist diameter, m is the measured full-angle divergence, d0 is the theoretical ‘imbedded Gaussian’ beam diameter, and 0 is the theoretical diffraction-limited divergence. Beer–Lambert law States that in any medium that is absorbing light, the decrease in intensity I per unit length z is proportional to the instantaneous value of I,

dI(z) =−αI(z), dz where α is the absorption coefficient of the material for that wavelength of electromagnetic radiation. The −αz solution of this equation is I(z) = I0e , Beilstein Registry Number (BRN) Numeric identifier of chemical substances used in Beilstein Information System.The Beilstein Registry Number is the accession number of the substance record in CrossFire Beilstein/ Gmelin and in the Beilstein Online database. Bessel beam A beam of electromagnetic radiation with complex field amplitude ψ distribution ψ(r, t) = i(k cos αz−ωt) 2 2 J0(k sin αρ)e , where J0 is the Bessel function, k is the wavenumber, ρ = x + y , α is a parameter, and ω is the angular frequency. BFV (back free velocity) The velocity of target’s free back side. Binodal Curve on state diagram where the phase change occurs. Bohr radius, a0 Smallest possible radius of the orbit for the electron, orbiting the hydrogen nucleus; −11 a0 = 5.291772108(18) × 10 m. Boiling point The boiling point of a liquid is the temperature at which the liquid and vapour phases are in equilibrium with each other at a specified pressure. Therefore, the boiling point is the temperature at which the vapour pressure of the liquid is equal to the applied pressure on the liquid. Bremsstrahlung Electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. ◦ Brewster’s angle, θB Angle of incidence that produces a 90 angle between the reflected and refracted ray. When p-polarized light strikes a surface at Brewster’s angle, it propagates without reflection losses. θB = arctan (n2/n1), where n1 and n2 are the refractive indices of the two media. BSTOA (beta solution treated and overaged) A heat treatment of an alloy first at temperature where only β-phase exists with subsequent rapid cooling following a second heat treatment at intermediate temperatures up to the times when the meanwhile increased hardness starts to decrease again. Bulk modulus, B The inverse of the compressibility; B = 1/κ. Capillary condensation Multilayer adsorption in porous solids or in a gap from a vapour reaching a situation at which pore spaces are (gap is) filled with liquid separated from the gas phase by menisci. Capillary force Surface tension originating force between two bodies connected by a liquid bridge. Capillary wave A wave travelling along the interface between two fluids, whose dynamics are dominated by the effects of surface tension. The wavelength of capillary waves are typically less than about a centimetre. CAS Registry Number (CASRN) Numeric identifier of chemical substances allocated by CAS (Chemical Abstracts Service). Cavitation Forming of cavities in the liquid due to a sudden pressure decrease. Chlorinity A measure of the chloride content, by mass, of seawater (grams per kilogram of seawater, or per mille) (see also salinity). CMC See critical micelle concentration. Compressibility factor, Z It is defined as: pV Z = m RT Glossary-I044498.tex 11/9/2007 18: 56 Page 426

426 Glossary

where p – pressure, Vm – molecular volume, R – universal gas constant, T – temperature. Ideal gases at low temperatures have Z = 1. At higher pressures the real gases have Z > 1. Critical compressibility factor Zc is the compressibility factor at critical point. Conjugated system A chemically conjugated system is a system of atoms covalently bonded with alternating single and multiple (e.g. double) bonds (e.g. C=C C=C C) in a molecule of an organic compound. Contour method A method for determination of residual stresses. The part containing residual stresses is cut in half along a straight line, and the deformations of the cut surface are used to compute the initial residual stress field. The advantage of contour method is its simplicity. Correlated plasma Synonym for coupled plasma (see strongly coupled plasma). Coulomb explosion Disintegration of a body due to Coulomb repulsion between the positive ions after binding electrons ejection. Coupling parameter of plasma See strongly coupled plasma. Coverage, Fc In laser processing defined as follows: Fc = (AsNp)/At, where At is the area to be processed, As is the beam spot area, and Np is the cumulative number of laser pulses. Creep The tendency of a material to move or to deform permanently to relieve stresses. Critical compressibility factor (critical coefficient), Zc See compressibility factor. Critical micelle concentration, cM (CMC, c.m.c.) Concentration of the surfactant in a solution above which the surfactant molecules spontaneously form micelles. Critical molar volume See vapour/liquid critical parameters. Critical pressure See vapour/liquid critical parameters. Critical temperature See vapour/liquid critical parameters. CW (continuous wave) Applied to lasers generating essentially steady (not pulsed) light. Debye lengthThe scale over which mobile charge carriers (e.g. electrons) screen out electric fields in plasmas and other conductors. In a plasma, the Debye length is  ε k /e2 λ = 0 B , D + 2 ne/Te ij j nij/Ti

where ε0 is vacuum permittivity, kB is Boltzmann’s constant, e is the electron charge, Te and Ti are the temperatures of the electrons and ions, respectively, ne is electrons density, nij is the density of atomic species i, with positive ionic charge je. Deep rolling A cold work deformation process used to improve the fatigue strength and smoothen the surface of metals by hydrostatically seated spherical rolling element. Deep rolling provides 2–3 times deeper plastically affected zone than shot peening. Defervescence See superheating. Degeneracy The number of different arrangements of the system which have the same energy. Degenerated plasma Plasma is called degenerate if the electron temperature is less than EF/kB,

EF Te < , kB

where EF is the Fermi energy for electrons, and kB is the Boltzmann’s coefficient.

 2
2 3 3 EF = ne , 8me π

where
= h/2π, h is Planck’s constant, me is the mass of electron, and ne is the density of electrons. Density The ratio of an object’s mass to its volume. For non-ordered liquids, the density decreases with the increasing temperature (e.g. liquid argon shrinks 12 per cent on freezing). Density anomaly (increase of density ◦ with the increasing temperature) has been observed for example in water (density maximum at 3.984 C),D2O ◦ (density maximum at 11.185 C), Ge15Te 85, and liquid silica. = Depolarization factor Depolarization factor of an ellipsoid with semiaxes a, b and c is given as Lx ∞ abc + + ≡ 0 2(s+a2)3/2 (s+b2)1/2 (s+c2)1/2 ds, while Ly and Lz are obtained by performing cyclic changes. Lx Ly Lz 1. See also light depolarization factor. Glossary-I044498.tex 11/9/2007 18: 56 Page 427

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DGTPM Diffractive gray tone phase mask. Diamond-like carbon (DLC)Amorphous carbon materials with significant amounts of sp3 hybridized carbon atoms. Dielectric constant, ε (dielectric permittivity) A measure of the polarizability of materials by electric field, D = εrε0E, where εr is the relative permittivity and ε0 is the permittivity of the vacuum; D is the electrical displacement and E is the electrical field. εr is a scalar if the medium is isotropic or a 3-by-3 matrix (tensor) otherwise. Diffusion coefficient (self-diffusion coefficient) The diffusion coefficient of species (atoms, molecules, etc.) in the absence of a chemical potential gradient. Discrete element method (DEM) A family of numerical methods for computing the motion of a large number of particles. In case on molecules, ions or atoms, Coulomb force, Pauli repulsion, and van der Waals force are considered, usually by appropriate potential distributions. DLC Dry laser cleaning:microparticles removal from solid surfaces by laser irradiation without applying liquids of steam to surface. DLC See diamond-like carbon. DR See deep rolling. Dynamic viscosity, η The ratio of shear stress τ between the fluid layers to the velocity gradient, ∂u/∂y,in the direction perpendicular to the layers, ∂u τ = η . ∂y EG/EC number Numeric identifier of chemical substances allocated by the Commission of the European Communities. Eigenstrain Non-stress strain. Elastic precursor Because shock wave velocities in liquids and solids are generally lower than elastic wave velocities, the shock waves are preceded by an elastic wave known as the elastic precursor. Electrical conductivity (specific conductivity), σ Proportionality constant between electrical current density and electrical field strength, j = σE (Ohm’s law). In anisotropic materials, electrical conductivity is a second- rank tensor. Electrical conductivity of liquids is often an indicator of their purity. Electrical double layer A layer with different from bulk electrolyte charge distribution at an interface consisting of a surface charge layer (i.e. a 2D-distribution of one type of ions) and a diffuse charge layer (counter-ions distributed over the space region next to the surface). Electrical double layer force Force between two particles or between a particle and a solid surface in an electrolyte solution due to the double layer charges. Electrical double layer forces are often repulsive. Electro-optical effect Optical effect caused by the applied steady or a low-frequency electric field. When the constant relative permittivity, εr is expanded into a power series of the amplitude of the electric field (E), the linear term in E represents the Pockels effect. The quadratic field-dependent term is known as the dc Kerr effect. Electrostatic image force Force between an electrically charged body and an uncharged plane surface. The force can be calculated by replacing the plane by an image of the body,at an equal distance from the plane and having opposite charge. Electrostriction Decrease in dimension of a substance in an electric field. EMV gauge Electromagnetic displacement gauge, the operation relies on change of magnetic flux due to change of current carrying loop area. Enthalpy Also called heat content, is the sum of the internal energy of a thermodynamic system plus the energy associated with work done by the system on the atmosphere which is the product of the pressure times the volume, H = U + PV, where H is the enthalpy, U is the internal energy, P is the pressure of the system, and V is the volume. Enthalpy of melting (standard enthalpy change of fusion, heat of fusion, latent heat of fusion) The amount of thermal energy which must be absorbed or lost for a definite quantity of a substance, for example 1 kg of 1 mol to change states from a solid to a liquid or vice versa and constant temperature. Enthalpy of vaporization (heat of vaporization, latent heat of vaporization) The amount of thermal energy required to vaporize a definite quantity,for example 1 kg of 1 mol of a liquid at constant pressure and constant temperature. Glossary-I044498.tex 11/9/2007 18: 56 Page 428

428 Glossary

Ester Organic compounds in which an organic group R’ replaces a hydrogen atom (or more than one) in an oxygen acid. An oxygen acid is an acid whose molecule has an —OH group from which the hydrogen (H) can dissociate as an H+ ion.

Ether Chemical compound which contains an ether group – an oxygen atom connected to two (substituted) alkyl groups (e.g. diethyl ether): Evaporation rate, in BuOAc units Relative to n-butyl acetate evaporation time as compared by Shell Auto- maticThin Film Evaporator. Another commonly used reference liquid is ether. The liquids with small BuOAc evaporate more intensively. Extinction Reduction of the intensity of light of a directly transmitted beam in the media. Extinction coefficient, c (attenuation coefficient) A measure of reduction of the intensity of a light beam travelling through a medium, due to both absorption and scattering: ln(I/I ) c = a + b =− 0 , x where x – length of light path, I – intensity of light after distance, I0 – initial intensity of light, a – absorption coefficient, and b – scattering coefficient. Extinction coefficient, k Imaginary part of the complex index of refraction: n˜ = n − ik, where n is the index of refraction. Extinction coefficient k relates to absorption coefficient a as 2ωk a = , c where ω is the angle frequency of the light and c is the speed of light. fs-CACO Femtosecond laser-induced cut and cleave operation. Flash point The minimum temperature at which the equilibrium vapour of a liquid in admixture with air at normal pressure will be ignited by an external ignition source applied in a specified manner over the surface of the liquid. Fluorescence Spontaneously emitted radiation that ceases immediately after the exciting radiation is removed. Fractal dimension A statistical quantity that gives an indication of how completely a fractal appears to fill space, as one zooms down to finer and finer scales. There are several definitions of fractal dimension, for example the Hausdorff dimension, Rényi dimension. In applications, usually the packaging (box-counting) dimension is used. Freezing point The temperature at which a substance changes its state from liquid to solid. In the presence of nucleating substances the freezing point of liquids is the same as the melting point, in the absence of nucleators it may be substantially lower, for example water can supercool to −42◦C (231 K) before freezing. Helium does not freeze at all at normal pressure, even at absolute zero. Fresnel lens A lens comprising a set of concentric annular sections (Fresnel zones):

FWHM Full-width half maximum. Gaussian beam (named after mathematician Carl Friedrich Gauß) A beam of electromagnetic radiation with electric (or magnetic) field complex amplitude E distribution is

 w −r2 r2 E(r, z) = E 0 exp exp −ikz − ik + iζ(z) , 0 w(z) w2(z) 2R(z)

where w0 is a parameter (waist radius), 
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k is the wavenumber,   z 2 R(z) = z 1 + 0 , z and
 z ζ(z) = arctan . z0 Gibbs energy (Gibbs free energy) The energy portion of a thermodynamic system available to do work, G ≡ H − TS. Grüneisen coefficient (Mie–Grüneisen coefficient),  It is defined as   V ∂2e V ∂T V β  =− =− = , T ∂v∂S T ∂V S CVKT

where V – volume, T – temperature, e – internal energy, S – entropy, β – thermal expansion, CV – heat capacity, KT – compressibility. Halocarbons Organic compounds containing covalently bonded fluorine, chlorine, bromine, or iodine. HAZ (heat affected zone) Region in material having permanent changes in the structure due to applied heat during processing (e.g. by laser beam). Heat capacity (specific heat capacity; specific heat), c Rate of change of temperature T as heat Q is added to a body at the given conditions and state (without phase change) of the body (foremost at constant temperature or constant pressure, cT and cp): ∂Q c = . dT ρcp is called ‘volumetric heat capacity’, where ρ is the density. Heat conductivity coefficient (coefficient of thermal conductivity), λ Rate of heat flow dQ/dt due to the temperature gradient dT/dx through a homogenous solid through an area A normal to the direction of heat flow dQ/dt =−λAdT/dx under steady state conditions and when the heat transfer is dependent only on the temperature gradient. Heat transfer Transfer of thermal energy through the process of conduction, convection, and radiation.These processes may occur singly or in conjunction. Heat transfer coefficient A measure of interface thermal resistance, defined as Q h = , AT where Q is the heat flux, A is area, and T is temperature jump across the interface. HEL See Hugoniot elastic limit. Hildebrandt solubility parameter, δ A measure of solvent polarity, is defined as square root of the cohesive energy density,  E δ = c , Vm

where Ec is cohesive energy, and Vm molar volume. If the solvent and the solute have close parameters δ, then usually the solute dissolves well in the solvent. 0 As the cohesive energy is Ec = vH − RT , the solubility parameter may be expressed also as:  0 − Hvp RT δ = , V

0 where Hvp is the heat of vaporization at normal pressure. Glossary-I044498.tex 11/9/2007 18: 56 Page 430

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Hole drilling method (incremental hole drilling method) A stress release method for determination of the residual stress field in solids. A hole is incrementally drilled into material while the surface strain is measured by strain gauges. The strain vs. depth data is then used to compute the stress profile. Hugoniot data Shock velocity Us vs. particle velocity up data. Hugoniot elastic limit Compressive yield strength of a material under a shock condition. HV (Vickers hardness) A method for measuring of surface hardness of materials using square-based diamond pyramid as an indenter. Suits well for spatially resolved hardness (microhardness) measurements. HVOF (high velocity oxy-fuel) A thermal spray technology for materials coating by powders where the powder is heated and carried by oxygen flame of propylene, hydrogen, propane, or kerosene. Hydrocarbon A chemical compound that consists only of the elements carbon (C) and hydrogen (H). Hydrocarbons contain a backbone consisting of carbon atoms, called a carbon skeleton with hydrogen atoms attached to that backbone. IAPWS (International Association for the Properties of Water and Steam) An international non-profit associ- ation of national organizations concerned with the properties of water and steam, particularly thermophysical properties and other aspects of high-temperature steam,water,and aqueous mixtures that are relevant to thermal power cycles and other industrial applications (www.iapws.org/). Ignition temperature (autoignition temperature)The lowest temperature at which a chemical will spontan- eously ignite in a normal atmosphere, without an external source of ignition, such as a flame or spark. The ignition temperature decreases as the pressure increases or oxygen concentration increases. Index of refraction (refractive index), n Ratio of the speed of light in vacuum to the phase velocity of light in the medium, n ≡ c/vphase. For light absorbing substances a complex index of refraction is defined as

c2k2 4πσ n2 = = ε + i, ω2 ω where k is the wavenumber, ω is the angular frequency, ε is the electric permittivity, and σ is the electrical conductivity. It is common to specify the refractive indexes of materials for yellow sodium light (the D line, 589 nm), nD. Index of refraction of air at sea level is about 1.000292. Inverse Bremsstrahlung Absorption (IBA) Absorption process of electromagnetic radiation (e.g. laser light), whereas the energy of electromagnetic radiation is converted into kinetic energy of charged particles, for example electrons or ions in the plasma; inverse effect to Bremsstrahlung. Ionic strength It is defined as 1 I = c z2, 2 i i where ci is the molarity concentration of ith ion present in the solution and zi is its charge. Summation is done for all charged particles present in the solution. Ionization energy (ionization potential) The minimum energy required to remove an electron from the ground state of the isolated gaseous atom or molecule. Isoelectric point pH value at which the zeta potential of a substance is zero. Colloids are least stable near the isoelectric point. Isothermal compressibility, κT A measure of the relative volume V change of fluid or solid as a response to a pressure p change at constant temperature T,
 1 ∂V κT =− . V ∂p T IUPAC International Union of Pure and Applied Chemistry. Kerr coefficient (Kerr constant), K The proportionality factor in relation n = λKE2, where n is the change of the index of refraction, λ is the light wavelength, and E is the electric field strength (see also Kerr effect). Some polar liquids, such as nitrotoluene (C7H7NO2) and nitrobenzene (C6H5NO2) exhibit very large Kerr constants. Kerr effect (Kerr electro-optic effect, DC Kerr effect, quadratic electro-optic effect, QEO effect) A change in the refractive index of a material in response to an electric field. Under the influence of the applied Glossary-I044498.tex 11/9/2007 18: 56 Page 431

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field, the material becomes birefringent, with different indexes of refraction for light polarized parallel to or perpendicular to the applied field. The difference in index of refraction, n, is given by:

n = λKE2,

where λ is the wavelength of the light, K is the Kerr constant, and E is the amplitude of the electric field. Ketone A ketone is either the functional group characterized by a carbonyl group (O=C) linked to two other carbon atoms or a chemical compound that contains this functional group. A ketone can be generally represented by the formula: R1(CO)R2.

Kinematic viscosity, ν The ratio of dynamic viscosity to the density of the fluid, η ν = . ρ Knudsen layer The gas layer near a gas–liquid phase interface not in translational equilibrium.The translational equilibrium is achieved within a few mean free paths (thickness of the Knudsen layer) by collisions between particles. LAD Laser assisted deposition (of thin films). LALP Liquid-assisted laser processing (also Laboratoire pour l’Application des Lasers de Puissance, France). LAPR Laser-assisted particles removal (from solid surfaces). Laser peening See laser shock processing and peening. Laser shock processing Treatment of solid materials by laser-generated mechanical impacts. The main application of laser shock processing is laser peening. Lennard-Jones potential (L-J potential, 6–12 potential) Interatomic/intermolecular potential expressed by   σ 12 σ 6 V (r) = 4ε − , r r

where ε is the depth of the potential well, σ is the (finite) distance at which the potential is zero, and r is the distance between atoms or molecules. Alternatively,Lennard-Jones potential can be written as   r 12 r 6 V (r) = ε min − 2 min , r r √ 6 where rmin = 2σ is the distance at the minimum of the potential. LESAL (laser etching using a surface adsorbed layer) A laser machining method of transparent materials using a thin layer adsorbed onto the back side of the material that absorbs the laser radiation and causes the etching of the material surface. LIBS (laser-induced breakdown spectroscopy) A technique for elemental analysis utilizing laser excitation (including vaporization and plasma generation) of elemental emission spectra. LIBWE (laser-induced backside wet etching) A technique of machining of transparent to laser light materials at which the opposite to laser beam side of the material is in contact with an absorbing of laser light liquid. The laser energy absorbed in contacting the solid layer of the liquid is transferred to the liquid–solid interface where the material removal takes place. It is used for fine machining of optical materials. LIFT (laser-induced forward transfer) also called MWD (MAPLE direct write) A technique of fabricating of patterned thin films of organic materials.The starting material film (target) is backside irradiated by laser beam (fixed, scanned of patterned); the irradiated parts of the film are propelled onto a substrate located ∼0.1 mm away from the target. A matrix material of the target (liquid of frozen liquid) enhances the film transfer and protects the functional material form excessive heat. Glossary-I044498.tex 11/9/2007 18: 56 Page 432

432 Glossary

Light depolarization factor Ratio of the perpendicular and parallel-scattered intensities at right angles,
 I⊥ u = . III =π/2 The light depolarization factor reflects the anisotropy of the substance. Light scattering coefficient, R90 It is defined by 2 I90 L R90 = , I0 V ◦ where I90 – intensity of the light scattered at an angle 90 to the direction of the incident light, I0 – intensity of the incident light, L – distance between scattering volume and observation point, and V – scattering volume. In the Table 8.8 the R90 values are given relative to benzene. The absolute scattering coefficient ◦ −6 ◦ of benzene at 546.1 nm and 25 CisR90 = 15.6–17.6 × 10 /cm. For water at 435.8 nm and 25 C, R90 = 4.3 cm−1 × 10−6/cm. (The values in literature scatter considerably.) LIPAA (laser-induced plasma-assisted ablation) A technique for dry laser backside etching of transparent materials, where the etching is induced by the plasma, generated by laser beam irradiation of a opaque target near (some hundreds of µm) the backside of the workpiece. The technique enables micromachining of brittle optical materials without cracking. LLNL Lawrence Livermore National Laboratory. LLSC (liquid-assisted laser shock cleaning) Combination of steam laser cleaning (SLC) with laser shock cleaning (LSC) where the surface to be cleaned is first covered by a liquid film and then subjected to laser heating and shock wave simultaneously. LP Laser peening, often a synonym to laser shock processing. LP-PLA Liquid-phase pulsed laser ablation. LPPC, LPwC Laser peening without protective coating. LSC (laser shock cleaning)A technique of removal of particles from solid surfaces due to a shock wave generated in gas (air) above the surface to be cleaned. The shock wave is commonly generated by gas breakdown by a focused pulsed laser beam. LSP (laser shock processing, laser peening) Treatment of solid parts by laser ablation-generated mechanical impulses. LULI Laboratoire d’Utilisation des Lasers Intenses, Ecole Polytechnique, Palaiseau, France. Magnetic susceptibility, χv (volume magnetic susceptibility, volumetric magnetic susceptibility, bulk mag- netic susceptibility) A measure of the degree of magnetization of a material in response to an applied magnetic field, M = χvH, where M is the magnetization and H is the magnetic field strength. µ χv = µr − 1 = − 1, µ0

where µr is the ratio of the magnetic permeability of a specific medium µ to the permeability of free space µ0. MALDI (matrix-assisted laser desorption/ionization) A technique of ionization of molecules with the purpose of their mass spectrometric analysis. The matrix absorbs the most of the laser light and also protects the fragile molecules from being destroyed by laser beam. MAPLE (matrix-assisted pulsed-laser evaporation) Laser deposition using a frozen matrix consisting of a solution of a polymeric organic compound dissolved in a relatively volatile solvent. Marangoni flow (thermocapillary surface flow,Rayleigh–Benard–Marangoni flow) Surface tension gradient- driven flow,a liquid flow from regions of low surface tension to the regions of high surface tension. Marangoni flow is often the major cause of liquid convection at laser processing. Maxwell-Garnett effective medium theory (as applied to a bubbly liquid) According to the theory, the ensemble of small bubble and the liquid can be treated as a single medium with an effective dielectric constant,   3f (εl − εv) εeff = εl 1 − , 2εl + εv + f (εl − εv) where εl is the dielectric√ constant of liquid, εv is the dielectric constant of vapour, f denotes the volume fraction of the bubbles. εeff = n, where n is the conjugate of complex refractive index of the bubble medium Glossary-I044498.tex 11/9/2007 18: 56 Page 433

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[1067]. The theory was used to interpret the interferometric measurements of bubble layer thickness in steam laser cleaning by Kim et al. [88]. Megasonic cleaning Cleaning of surfaces from particulate using agitated by 800–2000 kHz acoustic waves liquid. Melting point The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid.The melting point of a pure substance is always higher than the melting point of that substance when a small amount of an impurity is present. The more impurity is present, the lower the melting point. Liquid CO2 forms only at pressures above 5.11 atm; at atmospheric pressure, it passes directly between the solid phase (dry ice) and the gaseous phase in a process called sublimation. MIC Metal Improvement Company. Micelle An aggregate of surfactant molecules with the hydrophilic ‘head’ regions in contact with surrounding solvent, sequestering the hydrophobic tail regions in the micelle centre.

Mie–Grüneisen equation of state An equation of state particularly useful at high pressure, relates the density and pressure of compressive matter in an adiabatic process:
 2 ρ0C0 η η p = p0 (1 − η) + · 1 − + ρ0 (e − e0) (1 − sη)2 2

where   ρ V ∂T β η = − 0  =− · = ρ 1 , · · , 0, ρ T ∂V S κ ρ cV ρ0 is the density, C0 is the speed of the sound,  = 0 is the (dimensionless) Grüneisen coefficient in normal state, e − e0 is specific internal energy, s is linear Hugoniot slope coefficient s = Us/up (see Hugoniot data), β is volumetric thermal expansion coefficient, κ is isothermal compressibility, and cV is heat capacity at constant volume. For water, s = 1.79 and  = 1.65. Molar magnetic susceptibility, χm It is defined as M χ = χ , m v ρ where M is the molar mass and ρ is the density of the substance. Negative values of magnetic susceptibility of liquids inTable 8.8 indicates, that the liquids are diamagnetic. In non-uniform magnetic field these liquids are driven in direction opposite to the field gradient. Molar mass The mass of one mole of a chemical element or chemical compound. Molar volume (molecular volume) The volume occupied by one mole, numerically equal to the molecular weight divided by the density. Mole The amount of substance of a system which contains as many elementary entities as there are atoms in 12 g of carbon 12, where the carbon 12 atoms are unbound, at rest and in their ground state. Molecular dipole moment, p (dipole moment of molecule) A measure of the torque τ exercised by electric field E on molecules, τ = p × E. Table 8.8 presents the modules of permanent dipole moments of molecules. Dipole moments values of molecules in liquid and in gas phase are close. Molecular dynamics method (MD) See discrete element method. Momentum trap A solid plate in contact with the backside of laser-shocked sample, in purpose to avoid wave reflecting from backside of the sample. MWD (MAPLE direct write) See LIFT. Glossary-I044498.tex 11/9/2007 18: 56 Page 434

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Normal temperature and pressure 20◦C (293.15 K) and 1 atm (101 325 Pa) Nucleation The onset of a phase transition in a small region. The phase transition can be the formation of a bubble or of a crystal from a liquid or a droplet from vapour. Numerical aperture, NA A dimensionless number that characterizes the range of angles over which the system can accept or emit light. For objectives and lenses, NA is defined as NA = n sin θ, where n is the index of refraction of the medium (gas or liquid) and θ is the half-angle of the maximum cone of light that can enter or exit the objective or the lens. OKO See optical Kerr effect. OPO (optical parametric oscillator) An parametric oscillator which oscillates at optical frequencies. In laser materials processing, OPO is used as a generator of coherent light whose wavelength can be tuned in wide range (e.g. 0.7–5 µm). Optical breakdown Catastrophic breakdown in a transparent medium by a strong electromagnetic field. Optical Kerr effect (OKE,AC Kerr effect) Double refraction (birefringence) in liquids or solids induced by an electric field of radiation. Optical Kerr effect is partly responsible for the self-focusing of intense laser light in liquids. Orientational correlation function (of molecules) It is defined as

N N

µi (0) µj (t) M(0) M(t) i j γ(t) = = M(0) M(0) N N µi (0) µj (0) i j

where M(t) is a vector sum of N polar molecules with dipole moment µi (t) in unit volume at time t. Orientational relaxation time, τR (rotational relaxation time, rotational correlation time) Time con- stant used in the approximation of the first-order orientational correlation function γ(t): γ(t) ∝ exp[−t/τR]. τR corresponds to the time of decay of anisotropy of a liquid induced by an external field (e.g. by polarized light). Ostwald ripening In this book, the growth of larger crystals from those of smaller size which have a higher solubility than the larger ones. Due to Ostwald ripening the total surface area of the particle system will be reduced. Particle image velocimetry (PIV) An optical method used to measure velocities and related properties in fluids. The fluid is seeded with particles, and velocity information is calculated from the images of these particles. Partition function Number of possible states of a closed thermodynamical system as a function of temperature, volume, total energy,or chemical potential. Most of the thermodynamic variables of the system (of a substance) can be calculated from the partition function. PAZ Plastically affected zone. Peening A cold work process in which the surface of the cold metal is expanded, thereby relieving tensile stresses and/or inducing compressive stresses. Peening also encourages strain hardening of the surface metal. Perfluorocarbons Organic non-toxic compounds derived from hydrocarbons by replacement of all hydrogen atoms by fluorine atoms. PFC See perfluorocarbons. Phase explosion (explosive boiling) Sharp increase of homogeneous nucleation in a superheated liquid. Phase grating A diffraction grating with all lines transparent but of alternating optical thickness. Phase mask An optical mask where the patterns are formed by areas of alternating optical thickness. Phosphorescence Spontaneously emitted radiation that may persist for long periods, typically from seconds to milliseconds. Note: In molecular terms the term designates luminescence involving the change in electron spin multiplicity, typically from triplet to singlet or vice versa. The luminescence from a quartet state to a doublet state is also phosphorescence. Pitting corrosion A localized form of corrosion by which cavities or ‘holes’ are produced in the material. Pitting is considered to be more dangerous than uniform corrosion damage because it is more difficult to detect, predict, and design against. Pitting potential The ‘pitting potential’ corresponds to the potential at which the current starts to increase on the anodic scan. The ‘repassivation potential’ corresponds to the potential at which the current becomes Glossary-I044498.tex 11/9/2007 18: 56 Page 435

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negligible on the reverse (cathodic) scan. The more anodic the ‘pitting potential’, the less subject to pitting the sample. A ‘repassivation potential’ close to the ‘pitting potential’ indicates that the sample is capable of reprotecting itself easily after pitting. Pitzer acentric factor (acentric factor), ω It is defined as
 p ω =−log s − 1, p c Tr=0.7

where ps – saturation pressure of vapour, pc – critical temperature, Tr – reduced temperature. Acentric factor is a measure for the temperature dependence of the vapour pressure. For unpolar substances, the dependence of vapour pressure near critical point on the inverse temperature is nearly linear with the slope ω. PIV See particle image velocimetry. PLA Pulsed laser ablation. PLAL Pulsed laser ablation in liquid medium. Plasmon Collective oscillations of the free electron gas at optical frequencies. PLD Pulsed-laser deposition. PLIIR Pulsed-laser-induced liquid–solid interfacial interaction. PLIRQ Pulsed-laser-induced reactive quenching. Polyyne Organic compound with alternating single and triple bonds. Polyynes are believed to serve as novel 1D-conducting materials,‘molecular wires’. p-polarization Polarization of the electrical field (of light) is parallel to the mirror symmetry plane. PULSA Pulsed-UV laser soft ablation. PVDF Polyvinylidene fluoride, a high performance piezoelectric polymer, –(CH2CF2)n–. Radicals Atomic or molecular species with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions. Reduced temperature The ratio of the temperature of a substance to its critical temperature, Tr = T/Tc. Reflectivity Ratio of the intensity of the reflected light from a surface to that of the incident light. Repassivation potential See pitting potential. RH (relative humidity) Ratio of the partial pressure of water vapour in a gaseous mixture of air and water to the saturated vapour pressure of water at a given temperature. RMS(r.m.s.) Root mean square value of a function, for example of surface roughness,        2 Rq = h x, y − h x, y , where h is the local height of the surface topography. RT (room temperature) An indoor temperature of from ∼20◦Cto25◦C. Salinity The total amount of dissolved solids in seawater in parts per thousand (‰) by weight when all the carbonate has been converted to oxide, the bromide and iodide to chloride, and all organic matter is completely oxidized. These qualifications result from the chemical difficulty in drying the salts in seawater. In practice, salinity is not determined directly but is computed from chlorinity,electrical conductivity,refractive index, or some other property with a relationship to salinity that is well established. Salinity S and the total dissolved salts  in seawater are related to chlorinity Cl by

S = 0.03 + 1.805Cl respectively  = 0.07 + 1.811Cl.

Saturation concentration in air The concentration of vapour of a liquid in the air in equilibrium with the liquid. SAW (surface acoustic wave) An acoustic wave travelling along the surface of a material with an amplitude that typically decays exponentially with the depth of the substrate. SC (single crystalline, monocrystalline) Applied for materials having essentially regular crystalline structure over the entire specimen volume. Scattering A phenomenon in which the direction, frequency, or polarization of the wave is changed when the wave encounters discontinuities in the medium, or interacts with the material at the atomic or molecular level. Glossary-I044498.tex 11/9/2007 18: 56 Page 436

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Scattering coefficient (dissipation coefficient), b The fractional decrease in intensity of a beam of electro- magnetic radiation or particles per unit distance traversed, which results from scattering rather than absorption (see also Extinction coefficient). SCC See stress corrosion cracking SCE (saturated calomel electrode) A reference electrode based on the reaction between elemental mercury and mercury (I) chloride (Hg2Cl2,‘calomel’). Self-defocusing Defocusing effect of a laser beam by the refractive index change due to the laser light itself. Self-focusing Focusing effect of a laser beam by the refractive index change due to the laser light itself. SERS (surface enhanced Raman spectroscopy) A kind of Raman spectroscopy whereas the Raman signal is enhanced by local electromagnetic field enhancement by surface plasmon resonance at metal nanoparticles or rough metal surfaces.The increase in Raman scattering intensity by as much as 14 orders of magnitude enables detection of submonolayer amounts of absorbents. Shear viscosity See viscosity. Shock impedance It is defined by Z = ρ0Us, where ρ0 is the equilibrium density and Us is the shock velocity. Shock velocity, Us Velocity of propagation of the shock wave front. In an ideal gas,  γ + 1 P U = · , s 2 ρ

where γ is the ratio of specific heats at constant pressure and constant volume, P is shock pressure, and ρ is the equilibrium density of the gas. In liquids and solids, the shock velocity is lower than the sound velocity. Shock wave A mechanical wave of large amplitude, across which pressure or stress, density, particle velocity, temperature, and related properties change in a nearly discontinuous manner. Unlike acoustic waves, shock waves are characterized by an amplitude-dependent wave velocity. Shock waves are often generated at laser interaction with matter, and may cause chemical reactions in fluids and permanent structural changes in solids. Shot peening A cold work process used to produce a decorative finish and to modify mechanical properties of metals by impacting a surface with metal shots or glass beads. SHYLAC (Simulation Hydrodynamique Lagrangienne des Chocs) A computer code for hydrodynamic simulation of fluid motion and shock wave propagation, developed at LCD-ENSMA Poitiers, France. Skin depth Depth at which the amplitude of electromagnetic field, usually of high frequency, decreases to 1/e of the incident amplitude. SLC See steam laser cleaning. Slitting method (crack compliance method) A method for determination of residual stresses in solids. The general procedure for the slitting method is to gradually extend a slit into the specimen surface and measure near-slit strain as a function of slit depth. The strain vs. depth data are then used to compute the variation of the pre-slit residual stress component normal to the slit face with depth from the surface (i.e. the stress profile). SOG (spin on glass)Thin layer of glass deposited by spin-on of liquids precursors (usually silicates or siloxanes). The glass forms after thermal cure (hundreds of ◦C) of the spinned-on film. Solubility of gases in liquids, xg The maximum quantity of solute that can dissolve in a certain quantity of solvent or quantity of solution at a specified temperature. In Table 8.8 the solubilities are expressed in mole fractions, ng xg = , ng + ns

where ng and ns are the number of moles of gas and of solvent, respectively. Solubility may be characterized also by Ostwald coefficient:
   Vg L21 T, p = , Vl equil

where Vg is the volume of the dissolved gas, Vl – total volume of the liquid solution after equilibrium is reached. An increase in temperature decreases both the solubility and rate of solution of gases. For gaseous solutes, an increase in pressure increases solubility. Glossary-I044498.tex 11/9/2007 18: 56 Page 437

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Solvatochromic dyes Dyes which change colour according to the polarity of the liquid in which they are dissolved (e.g. phenolbetaine). Solvent polarity (polarity of solvent) The capacity of a solvent for solvating dissolved charged or neutral, apolar of dipolar, species. The solubility of the species is the better the more similar the interaction forces between the particles of the solvent and the interaction forces between the particles of the solute are, for example polar substances dissolve better in polar solvents and vice versa. N Solvent polarity parameter, ET (normalized polarity parameter) It is defined as

− − . N = ET(solvent) ET(TMS) = ET(solvent) 30 7 ET , ET(water) − ET(TMS) 32.4

−3 whereTMS is tetramethylsilane. ET (kcal/mol) is defined as ET = h · c ·˜ν · NA = 2.859 · 10 ·˜ν, where h is the Planck’s constant, c is the speed of light, ν˜ is the wavenumber of the light producing the electronic excitation, and NA is Avogadro’s number. N Tetramethylsilane and water are used in the definition of ET as extreme reference solvents. The definition of solvent polarity parameter by molar energy transition energy ET origins from the practice to measure solvent polarity using solvatochromic dyes. SP (shot peening) See LSP. Speed of sound, v Speed of propagation of plane sound waves. The speed of sound in an ideal gas is expressed by  cp v = RT . cv √ For most of the liquids, the speed of sound may be estimated by v = K/ρ, where K is the bulk modulus and ρ is the density. Near normal temperature, the speed of sound in liquids generally decreases with the increase of temperature. In contrast, in water the speed of sound near normal temperature increases with the increase temperature, and reaches maximum at 74◦C and decreases with further increase of temperature. Spinodal Locus of states of infinite compressibility (∂p/∂V )T = 0; spinodal is the boundary of unstable and metastable regions on state diagram. Spinodal decomposition Phase separation in a mixture of two partly miscible liquids due to diffusion 2 2 instability in a region of (∂ g/∂x )p,T < 0, where g is the free energy of mixing, and x is the concentration. s-polarization Polarization of the electrical field (of light) is perpendicular to the mirror symmetry plane (from the German ‘senkrecht’). SPR See surface plasmon resonance. Standard state The state of a pure substance in its thermodynamically most stable state at standard temperature and pressure (commonly at 298.15 K and 101326 Pa). Standard state enthalpy of formation The enthalpy change for the forming of the compound, in its standard state, from its constituent elements in their standard states (e.g. C, S, O2,H2). Standard state Gibbs energy of formation The Gibbs energy changes for the forming of the compound, in its standard state, from its constituent elements in their standard states. Standard temperature and pressure 0◦C (273.15 K) and 100 000 Pa (IUPAC since 1997).There are different definitions in use in different sources. Steam laser cleaning A process for microparticles removal from solid surfaces by laser irradiation assisted by applying steam to surface. Stereolithography An additive freeform fabrication process relying on laser solidification of liquid photopolymers. Stimulated Brillouin scattering Scattering process due to the sound wave generated by photoirradiation. Stimulated light scattering Scattering process due to material response created by light irradiation. In spon- taneous light scattering, radiation is diffracted as a Fourier component of a spontaneous statistical fluctuation of material response. In analogy with classical light scattering, light can be scattered by temporal and spatial modulation of material response induced by light. When the light scattering is stimulated by an optically created grating, it is one of the transient grating spectroscopies. Stimulated Raman scattering Scattering process due to molecular vibration produced by light irradiation. Glossary-I044498.tex 11/9/2007 18: 56 Page 438

438 Glossary

Stimulated Rayleigh scattering Scattering process due to temperature fluctuation of the medium generated by light irradiation. Strain hardening See work hardening. Stress corrosion cracking (SCC) The cracking induced from the combined influence of tensile stress and a corrosive environment. The impact of SCC on a material usually falls between dry cracking and the fatigue threshold of that material. The required tensile stresses may be in the form of directly applied stresses or in the form of residual stresses. Stress corrosion cracks propagate over a range of velocities from about 10−3 to 10 mm/h, depending upon the combination of alloy and environment involved. (http://www.corrosion- doctors.org/Forms/scc.htm), SCC can be effectively suppressed by LSP conversion of surface residual tensile stresses to compressive ones. Strongly coupled plasmas Plasmas which exhibit Coulomb interaction energies comparable to or greater ∗ 2 than the kinetic energy,that is, the coupling parameter  is greater than unity,where  = (Z e) /rkBT. Here r is average the ion separation, Z∗ the effective ion charge, and T the temperature. The properties of such plasmas, including their equations of state and transport coefficients are predicted to deviate significantly from those of classical plasmas. √ Sublayer flow Laminar boundary layer flow of thickness δ = ν/ τ/ρ in a turbulent flow. ν – kinematic viscosity, τ – shear stress, ρ – density. Supercritical state The state of a substance above the critical temperature and critical pressure. In supercritical state, the boundary between gas and liquid disappears and the substance acts like a gas in some ways and like a liquid in some ways. Superheating (boiling retardation, boiling delay) Heating of liquids to a temperature higher than its standard boiling point, without actually boiling. The superheated state of liquids is metastable state. Superheating of liquids and molten solids is rather common in laser processing of materials due to short heating time. Surface contour method See contour method. Surface plasmon resonance (SPR) Resonance oscillation of surface plasmons. Nanoparticles of noble metals exhibit strong ultraviolet-Visible SPR absorption bands. Surface tension A property of liquids arising from unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and has properties resembling those of a stretched elastic membrane. Dependence of surface tension on temperature of solute concentration gives rise to Marangoni flow. Surface tension coefficient, γ Free energy F per unit area of new surface formation at constant temperature; γ = dF/dA. Surfactant Wetting agents that lower the surface tension of a liquid, allowing easier spreading, and lower the interfacial tension between two liquids. TAB circuits Tape Automated Bonding integrated electronic circuit. Taylor factor, M The ratio of accumulated slip to macroscopic deformation. It is given by:  γi M = i , ε

where γ is the amount of slip on slip system i, and ε is the macroscopic strain imposed on the material. Temperature coefficient of density, ∂ρ/∂T Derivative of the density with respect to temperature. Temperature coefficient of dielectric constant, ∂ ln ε/∂T – relative derivative of the dielectric constant with respect of the temperature, 1 ∂ε ∂ ln ε = . ε ∂T ∂T Temperature coefficient of the index of refraction, ∂n/∂T Derivative of the index of refraction with respect to temperature. Temperature coefficient of viscosity, ∂η/∂T Derivative of the viscosity with respect to temperature. Thermal conductivity, λ Tensor quantity relating the heat flux, Jq, to the temperature gradient, Jq = −λ grad T. Glossary-I044498.tex 11/9/2007 18: 56 Page 439

Glossary 439

Thermal diffusivity, α The ratio of thermal conductivity λ to volumetric heat capacity ρcp: λ α = , ρcp

where ρ is the density and cp heat conductivity at constant pressure. Thermal diffusivity characterizes the capability of matter to spread the heat: ∂T (r, t) = α∇2T (r, t) ∂t Substances with high thermal diffusivity rapidly adjust their temperature to that of their surroundings. Thermal expansion coefficient, α (linear thermal expansion coefficient) Fractional change in linear dimensions L of a body per degree of temperature change, 1 ∂L α = . L ∂T For liquids the volumetric thermal expansion coefficient β is commonly used. It measures the fractional change in density as temperature increases at constant pressure

 1 ∂V 1 ∂ρ β = =− , V ∂T p ρ ∂T p where T is the temperature, V is the volume, ρ is the density,derivatives are taken at constant pressure p. Thermal piston effect Modulated heat flow from a heated condensed phase into an adjacent gas layer,causing thermally modulated expansion and contraction of the gas layer over a thickness approximately equal to the thermal diffusion length. The modulated gas layer expansion acts as a piston that drives acoustic waves into the gas column. Transient grating spectroscopy See stimulated light scattering. TWIN-LIBWE Two-beam interferometric laser induced backside wet etching. Ultrasound absorption coefficient, a The acoustic pressure amplitude p(x) of the progressive ultrasound wave of initial acoustic pressure amplitude p(0), at a distance x for a non-diverging beam, in any uniform medium, is described by the relationship: − p(x) = p (0) e ax.

Ultraviolet 5 per cent absorption point, L0 Light wavelength in ultraviolet region at which the absorbance of a substance on a 10 mm path reaches the value 0.05 (relative to water). Ultraviolet cut-off point, L1 Light wavelength in ultraviolet region at which the absorbance of a substance on a 10 mm path reaches the value 1.0 (relative to water). van der Waals force A relatively weak attractive force between atoms or non-polar molecules caused by polarization induced in each particle by the presence of other particles. Vaporization coefficient The ratio of the rate of vaporization of a solid or liquid at a given temperature and corresponding vapour pressure to the rate of vaporization that would be necessary to produce the same vapour pressure at this temperature if every vapour molecule striking the solid or liquid were absorbed there. Vapour explosion range (vapour flammable range) The range of a gas or vapour concentration that will burn or explode if an ignition source is introduced. Vapour/liquid critical compressibility factor, Zc It is defined as

pcVm,c Zc = ; RT c

Zc is close to 3/8 = 0.375 (equals to 3/8 for a van der Waals fluid). Vapour/liquid critical parameters The critical temperature, Tc, of a substance is the temperature above which distinct liquid and gas phases do not exist. As the critical temperature is approached, the properties of Glossary-I044498.tex 11/9/2007 18: 56 Page 440

440 Glossary

the gas and liquid phases become the same. Above the critical temperature, there is only one phase: that of supercritical fluid. The critical pressure is the vapour pressure at the critical temperature. The critical molar volume is the volume of one mole of material at the critical temperature and pressure. Vapour pressure Pressure exerted by the vapour when in equilibrium with the liquid or solid phase. The temperature dependence of vapour pressure of liquids is commonly expressed by the Antoine equation. Vena contracta effect Contraction in the edges of the flow streamlines as they move through an orifice. VISAR (Velocimetry Interferometer System for Any Reflector) A Doppler effect-based surface velocity measurement system, designed for measurement of shock transients. Viscosity A measure of the resistance of a fluid to deform under shear stress. With rising temperature the viscosity of liquids decreases. Work hardening An increase in mechanical strength of materials due to plastic deformation. In metallic solids, work hardening is due to increase of dislocations density. Yield strength The stress at which a material exhibits a specified deviation from proportionality of stress and strain. Z-scan (in optics) a technique for measuring the strength of the Kerr nonlinearity of a material, relying on self-focusing.The sample is scanned along the optical axis through the focus of a focused light beam. Intensity- dependent refractive index change affects the propagation of the beam what will be detected (e.g. by a small aperture light detector). The method is an easy and relatively simple way for measuring nonlinear absorption coefficients as well as nonlinear refractive indices for a wide variety of optically interesting materials. In neutron diffraction A technique for avoiding the influence of partial filling of the gauge volume by scanning the sample in a direction normal to the incident and diffracted beams; used for example in residual stress measurement. ζ-potential Electrical potential at the shear plane of a particle in electrolyte solution. The zeta potential of a particle can be calculated by 2εζf (ka) U = , e 3η where Ue is the electrophoretic mobility, ε is the dielectric constant of the sample, ζ is the zeta potential, ka is the ratio of particle radius to double layer thickness, η is the viscosity of the solvent, and f(ka) is Henry’s function. For particles in polar media the maximum value of f(ka) is 1.5 (Smoluchowski approximation) and for particles in non-polar media the minimum value of f(ka) is 1 (Hükel approximation). Electrophoretic mobility is defined as follows: v U = , e E where v is the particle’s velocity and E is the electric field strength. Ions inside of the shear plane (sliding surface) will accompany with a moving particle. Colloids of particles with zeta potentials in range −30 to +30 mV are considered unstable. Zeta potentials are commonly determined by electrophoretic light scattering. Subject-Index-I044498.tex 12/9/2007 14: 27 Page 441

Subject Index

ABAQUS 102, 103, 119, 122, 125, 126, 128, 130, 136, anti-reflective coating (ARL) 424 137, 138, 423 anti-reflective layer (ARL) 424 ABCD-method 287–288 Antoine equation 424, 440 Ablation 14, 15, 31, 63, 65, 92, 110, 124, 126, 144, 145, ARL – anti-reflective coating 424 147. 148, 149, 150–151, 153, 156, 161, 162, 163, 166, aromatic compound 250, 257, 424 177, 178, 182, 196, 209, 216, 224, 236, 240, 243, 251, aromaticity 424 254, 259, 262, 301–302 artificial neural network (ANN) 131 ablation, efficiency 66, 149–151, 158–166, 204 atomic nitrogen 274 ablation mask, liquid 156, 157 atomic transmutations 222–223 ablator (protective coating), in laser peening 77, 78 attainable superheat temperature 424 absorbance 110, 212, 228, 231, 439 attenuation coefficient 428 absorption 3, 5, 46, 78, 88, 94, 110, 132, 177, 178, 179, autofocusing (self-focusing) 153 181, 183, 203, 224, 296, 299, 379 autoignition temperature 376, 430 absorption coefficient 91, 181, 186, 192, 285, 296, 297 avalanche ionization 93, 123, 295, 296–297, 314 absorption of light in plasma 91, 296, 297 acceleration, of laser heated particles and substrates 37–38 back free velocity (BFV) 116, 139, 425 ACCIC code 93, 119, 126, 139, 161, 423 Barkhausen noise 76, 424 accommodation coefficient 289, 423 Bauschinger-effect 78, 424 acentric factor 355, 356, 357, 358, 435 beam quality parameter M 2 282, 425 acoustic emission 33, 147 Beer–Lambert law 425 acoustic emission at laser cleaning 33 Beilstein Registry Number (BRN) 425 acoustic impedance 70, 108, 344, 345, 346, 347, 348, 423 Berman–Simon line 258 acoustic nonlinearity parameter 332, 344, 345, 346, 347, Bernoulli’s equation (shock wave) 303 348, 423–424 Bessel beam 425 acoustic pressure 13 beta solution treated and overaged (BSTOA) 135, 425 acoustical (acoustic) impedance 294, 423 BFV – back free velocity 116, 425 acoustical signals 64, 159 bimodal particle size distribution function 238 adhesion map 27, 28 binary gratings 199 adhesion of particles 17–30 binodal 290, 425 adhesion resisting moment 43 biological materials 203, 207 adhesion, thermodynamic work of 18 biosensors 277 adhesive strength, of fluorocarbon resins 265 Bohr radius 297, 425 adiabatic compressibility 424 boiling delay 438 adiabatic exponent 424 boiling point 425 adsorbed liquid layer technique (LESAL) 189–192, 431 boiling retardation 438 aeroplane components, shock processing of 103 boiling, explosive 290, 434 aggregated particles 217, 224 boundary flow 43, 294 aggregation, of nanoparticles 221 Bradley’s model 26 agitation by ultrasound 30, 189, 190, 191 Bremsstrahlung 88, 94, 182, 295, 296, 297, 425, 430 AIST 197, 246 Brewster’s angle 214, 425 alcohol 12, 52, 57, 144, 161, 224, 253, 276, 322 Brillouin scattering, stimulated 437 aliphatic compounds 424 BRN – Beilstein Registry Number 425 alkanes 237, 424 BSTOA – beta solution treated and overaged 425 alkyl 424 Bubble 37, 43, 53, 57, 145, 147, 148, 150, 158, 159, 164, amorphization, of silica 186 183, 184, 186, 189, 193, 196, 197, 198, 225, 226, 238, ANN, artificial neural network 131 250, 267, 277, 292, 293, 294, 312 anodic oxide 65, 66, 67 bubble collapse induced flow 13–14, 43, 294 ANSYS 136, 139, 424 bubble dynamics 3, 65, 292–294 441 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 442

442 Subject Index

bubble generation rate 42, 43, 147, 148, 237 CMC – critical micelle concentration 234, 236, bubble-growth induced pressure 40, 51, 53 248, 426 bubble growth velocity 43, 50, 52, 57, 158, 198, 235, 292, coagulation, of nanoparticles 20, 220, 232 313 coagulation, of particles by laser irradiation 221, 225, 226 bubble nucleation threshold 37, 39–40, 45, 50 cohesion energy 17–18, 243 bubble pressure 183, 199, 292 colloid 6, 20, 209, 210, 221, 224, 225, 226, 229, 230, 231, bubble, decay at interfaces 293–294 233, 234, 237, 239, 244, 248, 259, 440 bubble, hemispherical 293 colloids, aggregation 224 bubble, nucleation of 39, 51, 52, 290, 311, 333 colloids, magnetic 214 bubbles discharge rate 148 colloids, noble metals 214 bubbles oscillation 153, 164, 292–293 colloids, stability 210, 227, 233 bubbles, ultramicroscopic metastable 50 complex beam parameter 282, 283, 287 bubbston 294 compressibility 424, 425 Bueckner’s superposition principle 75 compressibility factor 425, 439 bulk modulus 424, 425 compressibility,isothermal 430, 433 BuOAc units 333, 348, 349, 350, 351, 428 compression, hydrostatic 305 burnout 168, 170 concrete, laser machining of 204, 206 confinement medium (tamper) 69–70, 91 capillary condensation 18, 22, 425 confocal parameter 282, 283 capillary condensed liquid, volume of 22 conjugated system 426 capillary condensed water, effect in cleaning 45, 52, 53 constitutive relations, of solids 93, 101 capillary force 12, 22, 28, 56, 425 contact hardness 28 capillary pressure force 22, 28 contact potential 19 carbon deposit 186, 199, 248, 254 contact radius, of a particle 25, 26, 27, 28, 29, 43 carbon, phase diagram 257 contour method 75–76, 130, 137, 426 CAS Registry number (CASRN) 425 convection, convective flow 147, 148, 159 cascade ionization 295, 296–297, 299 core-shell particles 219, 229, 230, 236, 248 CASRN – CAS Registry number 425 corrosion 3, 5, 6, 11, 69, 103, 116, 118, 119, 120, 121, 126, cathodic polarization (of oxide layer) 15, 66 135, 264, 277 cavitation 6, 12, 61, 69, 71, 292, 294, 425 corrosion, pitting 123, 434 cavitation bubbles 147, 190 Coulomb explosion 217, 218, 426 cavitation impact 60, 145 Coulomb force 19 cavitation, memory effect 294 Coulomb’s friction law 103 CCUP (C-CUIP) procedure 205 Coulomb logarithm 298 cement, Portland 204, 205 coupling parameter of plasma 121, 438 channels, fabrication of 178, 191 coverage, of laser impacts 104, 105, 114, 131, 426 chemical bond force 17, 19–20 crack compliance method 74–75, 436 chemical machining 72, 74 crack front contour 87 chlorinity 425 crack propagation 87, 138, 203 cladding, underwater 277, 279 Clausius-Clapeyron equation 289 creep 30, 70, 426 cleaning by acoustic waves in liquid 13 critical compressibility factor 426 cleaning by supercritical solution 16 critical micelle concentration (CMC, cmc) 217, 245, cleaning by water decomposition products 16 249, 426 cleaning efficiency 45, 50, 56, 60, 62, 64 critical molar volume 426, 440 cleaning threshold 12, 44–45, 46, 52, 53, 54, 55, 56, 58, 60 critical nucleation rate 290 cleaning, backside by laser 12–13 critical nucleus 256, 290 cleaning, by bubble collapse induced flow 13–14 critical pressure 426 cleaning, by laser ablation/spallation in liquid 14–15 critical radius of nuclei 247, 256 cleaning, ice-assisted 17 critical temperature 39, 59, 426 cleaning, by liquid-assisted laser shock 13, 43, 432 curvature method 74 cleaning, steam laser 12, 13, 33, 432, 437 cut quality 143, 168, 170, 204 cleaving, of crystals 203 CW – continuous wave 426 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 443

Subject Index 443

Dawson probability integral 296 droplet, on surface 12, 52, 59 DC Kerr effect 427, 430 droplets, light focusing in 59 debris, at laser machining 143 Drude plasma frequency 212 Debye-Hückel inverse double-layer thickness 23 Drude theory 212 Debye length 426 dry laser cleaning (DLC) 12, 317, 427 decommissioning, of nuclear facilities 204 dry reactive plasma etching 179 decomposition, of chemical substances 186, 214 Dugdale stress 28 decontamination, of nuclear facilities 204 Dupré energy 18 deep rolling (DR) 70, 71, 84, 127, 128, 131, 426 Dupré equation 17 defervescence 426 dynamic viscosity 427 defocus distance 255 degenerated plasma 426 EG/EC number 427 dehydroxylation of silica surface 16–17, 68 eigenstrain 86, 87, 134, 136, 137, 427 DEM – discrete element method 427 ejection force, in steam laser cleaning 42–43 densification, of porous materials 141 elastic modulus, combined 25, 122, 125 density 381, 426, 438 elastic precursor 117, 305, 427 depassivation of electrodes 63 elastic–plastic shock wave 106, 128, 305 depolarization factor, of light 432 deposition of debris 177 elasto-plastic body 82, 136 deposition, by laser ablation (LAD, PLD) 31, 257, electrical discharge machining (EDM) 74, 75 262, 266, 272 electrical conductivity 427 desorption of metal ions 48 electrical double layer 23, 427 DGTPM 427 electrical double layer force 23, 427 diamond, formation probability 254, 258 electrochemical dissolution 150 diamond-like carbon (DLC) 254–256, 427 electroless metal deposition 147 dielectric constant 427 electromagnetic force 80 dielectric permittivity 427 electro-optical effect 427 dielectrophoretic force 19 electrophoretic light scattering 440 diffraction limited beam 282, 425 electrophoretic mobility 440 diffractive gray tone phase mask (DGTPM) 198 electroplating 7, 175 diffusion coefficient 427 electrostatic forces 19, 23 diffusion loss, of electrons 297 electrostatic image force 19, 427 ‘Dip and tap’ method 30, 31 electrostriction 427 dipole moment, of molecule 433 enbrittlement, hydrogen induced 15, 277 discrete element method (DEM) 427 embryonic nucleation 40, 51 dislocation density 69, 88, 111, 124, 130, 133 EMV gauge 79–80, 121, 427 dislocations 69, 106, 107, 109, 113, 119, 123, 131, energy-coupling efficiency 149 133, 142, 159 engine fuel injectors 177 dismantling, of nuclear reactors 167 enthalpy 427 displacement measurement 79–80, 80–81 enthalpy of melting 427 dissociation length, of hydrogen bond 20 enthalpy of vaporization 427 dissolution, electrochemical 150 equations of state (EOS) 100, 433 dissolution, of workpiece in supercritical water 147, 150, ester 428 184, 185 etch rate 144, 150, 153, 158, 160, 179, 184, distribution function of particle size, bimodal 238 185, 186, 187, 188, 189, 191, 192, 195, 196, divergence, of laser beam 283, 425 197, 199, 200 DLC – diamond-like carbon 254, 427 ether 428 DLC – dry laser cleaning 12, 317, 427 evaporation rate 290, 428 Doppler shift 80 exciplexes 225 double-layer force 23, 24, 25 explosive boiling 290, 434 double layer, electrical (electrochemical) 427 explosives 37, 43, 105, 141, 250, 262 double-layer thickness, Debye–Hückel inverse 23, 24 extinction 211, 238, 428 dough, machining by laser 207 extinction coefficient 36, 66, 180, 428 drag force on spheres 147 extrinsic size effect 212 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 444

444 Subject Index

fatigue damage 145, 159 heat of vaporization 148, 427 fatigue life 84, 87, 106, 108, 114, 116, 118, 122, 124, 127, heat transfer 181, 216, 429 128, 131, 138 heat transfer coefficient 39, 57, 290, 429 fatigue strength, of laser shocked bodies 86, 87, 108 heavy water 222 Fermi level 19 HEL 97, 127, 430 films, diamond 11, 250, 257 helium, liquid 210 films, DLC 250, 254, 255, 256, 270, 272, 274 Helmholtz free energy 100, 381 Fisher limit 290 hen egg white lysozyme (HEWL) 203, 207 flash point 428 Henry’s function 440 flexure strength 151 Hertz model 25 fluorescence 76, 428 Hertz theory 25, 26 fluorescent lamps 219, 220, 239 Hertz–Knudsen equation 94, 290 fluoropolymers 262 Hertz–Knudsen theory 92 flyers 70, 141 heterogeneous nucleation 37, 290, 291–292 forward transfer, laser induced (LIFT,MDW) 273, 277, HEWL 203, 207 278, 317, 431 HFF 24 fractal dimension 130, 428 high velocity oxy-fuel (HVOF) 142, 430 fragmentation, of nanoparticles 232 Hildebrandt solubility parameter 429 freezing point 428 history,of steam laser cleaning 56 Fresnel lens 189, 428 Hogg-Healy-Fuerstenau (HFF) equations 24 fretting fatigue 136 hole drilling method 74, 75 430 friction velocity 44 homogeneous nucleation 290–291, 424 frozen gas and liquid layers, removal of 15–16 Hooke’s law 99 frozen target 272–273, 274, 317 Hugoniot data 430 fs-CACO 203, 428 Hugoniot elastic limit (HEL) 92, 97, 98, 430 FWHM, definition of 428 Hugoniot equation 303 Hugoniot slope coefficient 81, 100, 102 gas well drilling 202 HV – Vickers hardness 430 Gaussian beam, characteristics 282–285 HVOF 142, 430 Gaussian beam, propagation 287–288 HYADES code 134 Gaunt factor 296 Hükel and Smoluchowski approximations 440 Gibbs energy 429, 437 hydrocarbon 56, 181, 308, 312, 430 Gibbs free energy 429 hydrofluoric acid, laser-generated 181 Gouy phase shift 283 hydrogen, in materials 15, 277 gratings, fabrication of 196 hydrogen bond force 19–20, 54 gratings, binary 199 hydronium ion 384 gratings, sinusoidal 196 hydrophilic surface 265 gravitational settling velocity 147 hydrophilization, of fluoropolymers 262, 266 Grüneisen coefficient 429 hydrosols 209 Grüneisen equation of state 100, 305, 433 hydrostatic pressure (shock wave) 305 Grüneisen parameter 100 hydrothermal dissolution 184, 308 hydrothermal growth 240, 242–249 halocarbons 429 hydrothermal reactions 149, 162, 308–310 halogenated hydrocarbons 179 hydroxides, volatile 309 halogenated solvents 200 hydroxoapatite (hydroxylapatite) 262, 267 Hamaker constant 18, 20, 21 hydroxyl groups, on silica surface 16 hardening 101, 102, 120, 124, 127, 128, 150, 440 HAZ 167, 429 heat affected zone (HAZ) 167, 429 IAPWS 381, 430 heat capacity 381, 429 ice, dry 433 heat capacity,specific 429 ice, removal of layers 15 heat capacity,volumetric 429 ice-assisted laser particles removal 17 heat conductivity coefficient 429 ignition temperature 430 heat flux to the liquid-vapour interface 290 image force 19 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 445

Subject Index 445

impulse momentum, generated by confined plasma 91, 92 laser beam,TEM00 282, 283, 425 incident angle of laser beam, in peening 129 laser induced forward transfer (LIFT,MDW) 273, 277, incremental hole drilling method 74, 75, 430 278, 431 incubation 150, 159, 196 Laser MicroJet 171, 175 incubation effect 150, 181, 186, 200 laser peening (LP) 71, 86, 88, 103, 104, 112, 120, 131, index of refraction 34, 149, 236, 237, 244, 430, 438 133, 431 inertial force, in laser cleaning 39, 57 laser peening without protective coating (LPwC) information storage, optical 219 77–78, 79, 432 injection needles 177 laser peening, fibre-delivered laser beam 104 injectors, of engine fuel 177 laser shock peening (LSP) 77, 78, 88, 105 ink, curing of 205 laser shock processing 8–9, 69, 431 interference, of high-intensity laser beams 88 LASNEX code 94, 129 interferometric probe 33, 34 latent heat of vaporization 427 intrinsic size effect 211 layer removal method 74 inverse Bremsstrahlung (IB) 88, 94 Lennard–Jones potential 26, 29, 431 inverse Bremsstrahlung absorption (IBA) 182, 295, LESAL 189, 191, 192, 431 296, 430 LIBS 431 ionic strength 23, 430 LIBWE 178, 179, 431 ionization, multiphonon 295 LIBWE, ultrasound assisted 190, 191 ionization, tunnel 295 LIF 119, 226 ionization energy 430 LIFT 273, 277, 278, 431 ionization potential 295, 296, 430 light depolarization factor 432 ionization, avalanche 93, 123, 295, 296–297, 314 light pressure 105, 286–287 ionization, cascade 92, 295, 296–297, 299 light scattering coefficient 432 ionization, thermal 295, 297 linear bulk viscosity stress 102–103 isoelectric point 23, 24, 430 linear equation of state 101 isothermal compressibility 430 LIPAA 432 IUPAC 430 liquid as an ablation mask 156, 157 liquid disc, formation in laser cleaning 56 jet stability 173 liquid film, dynamics on heated surface 61, 62, 313 jet, formation at bubble collapse 13, 14, 165, 294 liquid film, thickness measurement 31, 163 jet, liquid 171, 294 liquid helium 210 JKR model 26–27 liquid jet guided laser beam 171–176 Johnson, Kendall and Roberts adhesion model 26–27 liquid metals 179, 192 Johnson-Cook (plasticity) law 101, 127 liquid nitrogen 144, 262 liquid optics 156, 157 liquid target 257, 266, 270, 272 Keldysh equations 295 LLNL 117, 129, 432 Keldysh parameter 296 LLSC 13, 14, 432 Kelvin radius 22 longitudinal waves, elastic and plastic 95, 98 Kerr coefficient (Kerr constant) 430 LP 112, 123, 131, 432 Kerr effect (Kerr electro-optic effect) 430–431 ketone 431 LPPC, LPwC 135–136, 432 kinematic viscosity 431 LP-PLA 432 Knudsen layer 291, 431 LPwC 78, 79, 86, 138, 432 Kramer’s formula 88 LSC 13, 432 LULI 432 luminescence 147, 198, 246, 301, 434 LAD 266, 431 LALP 2, 3, 4, 431 Laplace equation 289 machining, from backside by laser 177 LAPR 431 machining, from frontside by laser 143 laser ablation, steam-assisted 146 machining, having water at backside 177 laser beam, diffraction limited 282 magnetic force 25 laser beam, Gaussian 282, 284, 287, 428 magnetic measurement of stress 76 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 446

446 Subject Index

magnetic susceptibility 432 nanoparticles, aggregation of 221, 232, 258 magnetic susceptibility,molar 433 nanoparticles, alloyed 230, 232, 234 magnetization 432 nanoparticles, average size 228, 230, 232, 233 MALDI 432 nanoparticles, carbon 193 MAPLE 272–273, 275, 276, 432 nanoparticles, coagulation 220 MAPLE Direct Write (MWD) 273, 431, 433 nanoparticles, core-shell 219, 222, 236, 248 Marangoni convection (Marangoni flow) 148, 432 nanoparticles, diamond 11, 250 Matrix-assisted pulsed-laser evaporation (MAPLE) nanoparticles, disk-shaped 231 272–273, 275, 276, 432 nanoparticles, DLC 250 Maugis and Dugdale adhesion model 27–28 nanoparticles, dynamic formation mechanism 216 Maugis–Pollock adhesion model 28–29 nanoparticles, enlargement in size 220 Maxwell–Garnett effective medium theory 49, 432 nanoparticles, extrinsic size effect 212 MD model 27–28 nanoparticles, fabrication 210 MDW 273, 277, 278 nanoparticles, fragmentation by laser 232 megasonic cleaning 43, 433 nanoparticles, fusion of 222, 229, 232 melting point 428, 433 nanoparticles, heat transfer from 217 memory effect in cavitation 294 nanoparticles, interband absorption 211 mercury lamp, use of 192, 224, 239 nanoparticles, intrinsic size effect 212 metal ions, desorption 5, 48 nanoparticles, magnetic 11, 214 metals, physical properties 317–318 nanoparticles, melting by laser 219 metastable compound 50, 259 nanoparticles, melting temperature 214 metastable ultramicroscopic bubbles 50 nanoparticles, Mie resonance 37, 221, 222 micelle 217, 245, 426, 433 nanoparticles, modification by laser 217–218 microbubbles 160, 294 nanoparticles, of noble metals 214, 217 microfuidic devices 189 nanoparticles, of inorganic compounds 240, 243 microjet, at bubble collapse 145, 179, 183, 294 nanoparticles, optical absorption spectra 215 microlens, fabrication of 198 nanoparticles, optical nonlinearity of 214 microreactors, fabrication of 199 nanoparticles, optical properties 210–212 micro-sandblasting 179 nanoparticles, organic 241, 258, 259 microscale laser impacts 93 nanoparticles, Raman scattering at 214 microtiter plates, fabrication of 188 nanoparticles, rod-shaped 219 Mie resonance 20, 37, 211 nanoparticles, shape transformation of 219 Mie–Grüneisen coefficient 102, 429 nanoparticles, φ-shaped 220 Mie–Grüneisen equation of state 100, 102, 103, 305, 433 nanoparticles, of silicon 250 Moiré interferometry 77 nanoplatelets 240, 242 molar magnetic susceptibility 433 nanoplatelets, multilayer 245, 246 molar mass 433 nanoprisms 219, 231, 235, 237 molar volume 433 nanorods 228, 230, 237, 240 mole 433 nanowires 230, 233, 241 molecular dipole moment 433 neutron diffraction 73–74, 440 molecular dynamics method (MD) 29, 123, 292, 433 neutrons, generation of 239 molecular volume 433 nitriding 72, 262, 271 molten salt 174, 242 nitrogen, atomic 274 momentum trap 78, 108, 433 nitrogen, liquid 144, 158, 262 MP model 28–29 nitrogen, solid film 272, 274 multi-axial contour method 137 nonlinear refractive index 236, 244, 247 multiphonon ionization 92, 93, 274, 295 normal temperature and pressure 434 multiphotonic absorption 181, 183 normalized polarity parameter 437 MWD 273, 431, 433 notched test sample 87 nuclear reactions 222 nuclear reactor components, laser maintenance of 103 nanocomposite, organic/inorganic 241 nucleation 39, 40, 51, 204, 290–292, 434 nanodendrites 245 nucleation, of vapour bubbles 290–292 nanonetworks 221, 233 nucleation rate, critical 290 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 447

Subject Index 447

nucleation threshold, of bubbles 50, 291 PFC 434 nucleation, heterogeneous 291–292 phase change, liquid-gas 289–290 nucleation, homogeneous 290–291 phase explosion 290, 291, 434 numerical aperture 434 phase grating 434 phase mask 434 phase mask, diffractive gray tone (DGTPM) 427, 434 OKO 434 phosphorescence 434 oleophilic surface 265 photoacoustic deflection 35, 50 OPO 434 photodeflection 49 optical breakdown 295–302, 434 photodissolution 217, 220, 235 optical breakdown, threshold 177, 300, 301 photoelastic coatings 77 optical information storage 219 photoenhanced van der Waals force 20–21 optical matching 149 photoexcitation of electrons 227 optical materials, machining of 177, 178 photo-oxidation 231, 239 optical nonlinearity 247 piezoelectric polymers 79 optical nonlinearity,of nanoparticles 214 piezoelectric probe 33, 34 optical reflectance probe 35 piezoelectric quartz transducer 79 optically smooth surfaces, fabrication of 177 piezospectroscopy 76 orientational correlation function 434 pitting corrosion 434 orientational relaxation time 434 pitting potential 434–435 Ostwald coefficient 436 Pitzer acentric factor 435 Ostwald ripening 216, 434 PIV 13, 434 overlapping impacts, in laser peening 83 PLAL 435 oxidation by laser 262 plasma 69, 81, 88–95, 110, 297, 299, 300, 301 oxidation cutting 174 plasma pressure, experiment 81, 82, 88, 90, 92, 301 oxide layers, removal by laser 11, 14–15, 63 plasma pressure, theories 81–95 oxides, physical properties 308–314 plasma resonance 211, 212, 214 oxides, solubility in water 308 plasma, coupling parameter 426 plasma, degenerated 426 paper, machining by laser 203, 207 plasma, self-absorption parameter 313 particle image velocimetry (PIV) 13, 61, 434 plasma, strongly coupled 438 particle, deformation of 25–30 plasma, thermal conductivity of 298 particle, long-time stability of the contact with plasma, transmission of light by 92 a surface 30 plasmons 435 particle, magnetized 25 plastically affected depth 85 particle, ray tracing in 38 PLD 262, 266, 435 particle, rough 19 PLIIR 257, 435 particles covered surfaces, preparation of 30 polarity of solvent 429, 437 particles, electrophoretical deposition 31 polarization effects, at laser cutting 15 particles, laser ablation deposition 31 polarization force, in particle adhesion 19 particles, plastic deformation of 28 polymerization, of working liquids 181 particles, removal efficiency 13, 44, 45 polyvinylidene fluoride (PVDF) 79, 435 particles, removal threshold 44–45 polyynes 250, 251, 252, 253, 435 partition function 434 pores, porosity 141, 202 passive film 123, 150 porosity,residual, at shock compression 141 PAZ 110 Portland cement, machining of 205 peening methods, comparison of 71 powder compacting 141 peening, by shots 70 p-polarization 435 peening, by laser shock 77–103 pressurized water reactors (PWR) 138 peening, ultrasonic by shots 70, 71 probe, interferometric 33, 34 peening, ultrasonic by strikers 70 probe, optical reflectance 35, 36 peening, water cavitation 70 probe, piezoelectric 33, 34 perfluorocarbons (PFC) 434 probe, surface plasmon 34, 36 petroleum well drilling 204 protective coating (ablator), in laser peening 77, 78, 81 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 448

448 Subject Index

protective coatings, water-soluble 144 rock, machining 202–203 protein crystals 203, 207 rod-shaped nanoparticles 219 protein microarrays, fabrication of 277 Rose Bengal dye 180, 181, 183, 185 pull-off force, of a particle at cleaning 26, 27, 29 rough particles, adhesion of 19 PULSA 207, 435 pump-probe investigations 228 PVDF 79, 121, 311, 435 Saha’s equation 297 PWR 138 salinity 319, 332, 435 pyranine 180, 181, 316 salts, molten; properties: 315, use: 174 pyrene 177, 180, 181, 182, 183, 184, 185, 186, 316 saturation concentration of vapours in air 333, 376, 435 SAW 52, 435 scale removal by laser shock in liquid 16 QEO effect 430–431 scattered light, measurement of 34, 35 quadratic bulk viscosity 103 scattering, definition 435 quadratic electro-optic effect 430–431 scattering coefficient, of light 333, 377, 432 quartz pressure transducer 79 scattering of light by bubbles 150 quench rate 261 scattering, stimulated Raman 176, 437 quenching, laser induced 261–262, 263 scattering, stimulated Rayleigh 438 quotidian equation of state 100–101 SCC 103, 120, 121, 135, 436, 438 SCE 436 radicals, generation of 251, 252, 435 SHOCKLAS 134 Raman scattering 214, 437 sea water, composition of 319 Raman spectroscopy,for stress measurement 76 self-absorption parameter, of plasma 313 Raman spectroscopy,surface enhanced 224, 226, 231, 436 self-defocusing 436 Raman-active material 76 self-diffusion coefficient 332, 373, 427 Rankine–Hugoniot relations 303 self-focusing (autofocusing) 144, 153, 163, 238, 436 rate equation, for free electrons 298–299 self-modulation, of the laser etching process 177, 178 Rayleigh equations, of shock wave 303 SERS 224, 226, 231, 436 Rayleigh length 283 settling velocity of particles, gravitational 147 Rayleigh wave (surface wave) 82, 83 shear flow,linear 43 Rayleigh–Benard–Marangoni flow 432 shear stress, in fluid 44 Rayleigh–Plesset equation 292 shear viscosity 436 reactive quenching, laser induced 7, 261–262, 263 shock cladding 140 recombination loss, of electrons in plasma 92, 298 shock forming 140 redeposition of debris, at dry laser machining 167 shock impedance 304, 436 reduced temperature 435 shock measurement techniques 79 reflected light, for laser cleaning monitoring 77 shock pressure 79, 81–82, 83, 107, 305 reflection of light, theory 285 shock pressure, laser generated 69, 81, 115 reflectivity,measurement at laser processing 263 shock pressure, measurement 79 refractive index 15, 34, 36, 153, 237, 381, 430 shock propagation, in laser peening 82, 95 refractive index, nonlinear 153, 236, 244 shock wave 11, 13, 16, 49, 69, 77, 78, 90, 105, 117, 120, regrowth velocity,of melted silicon 261, 263 123, 134, 147, 150, 177, 178, 197, 302, 436 relaxation methods, for residual stress determination 77 shock wave, conservation relations 303 relaxation time, orientational of molecule 332, 374, 434 shock wave, elastic–plastic 305 release waves, in laser peening 82 shock velocities, in iron and in water 304 repassivation potential 435 shock velocities, in liquids 305 residual stresses, formation 71 shock velocity 94, 134, 159, 304, 332, 375, 436 residual stresses, measurement techniques 70, 72, 73 shock yield stress 305 Reynolds number, shear 44 shot peening 70, 71, 122, 436 ring core method 74, 75 SHYLAC code 102, 436 ring patterns, formation at laser melting 153 silica fibre lightguide, use of 122 ripples, formation at laser melting 153 silicon surface, oxidized 19 river line patterns 87 silicon, amorphous, temperature dependence of optical rock, porosity 202 properties 36 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 449

Subject Index 449

silicon, crystalline, temperature dependence of optical superheat (superheating) temperature 39, 43, 57, 58, 333, properties 36 375, 424, 438 sin2 ψ technique 72–73, 74 superheated liquid 43, 50, 290–292 sinusoidal gratings, fabrication of 196 superheated state 39, 290–292 skin depth, of light penetration 198, 436 superheating 57, 58, 291, 438 SLC 12, 13, 31, 32, 33, 44, 436, 437 surface acoustic waves (SAW) 52, 435 slip-twinning transition 133 surface contour method 75–76, 438 slitting method 74, 75, 126, 129, 436 surface enhanced Raman spectroscopy (SERS) 224, 226, SOG 232, 436 231, 436 sol-gel film, treatment of 263 surface hardness, changes at laser processing 69, 88, 108, solid nitrogen 65 112, 113, 118 solidification velocity 261 surface modification, by laser 261–262 solubility of gases in liquids 436 surface plasmon probe 34, 36 solubility of oxides in water 308 surface plasmon resonance (SPR) 36, 236, 438 solvatochromic dyes 437 surface recession at vaporization 290 solvent polarity 429, 437 surface roughness, of laser etched surfaces 162, 186, 188, solvent polarity parameter 333, 377, 437 192, 195 sonoluminescence 292 surface roughness, of laser shocked surfaces 88 spallation 14, 15, 102, 276 surface tension 332, 374, 438 spalling, thermal 203, 205 surface tension force 22 specific heat capacity 429 surface wave focusing, in laser peening 83 speed of sound 437 surface waves, laser-induced 38–39 spin on glass (SOG) 232, 436 surfaces, optically smooth, fabrication of 177 spinodal 290, 291, 437 surfactants 216–217, 246, 248, 259 spinodal decomposition 437 susceptibility,third order 236, 244, 247 Spitzer–Härm expression 298 synchrotron diffraction, in residual stress measurements 73 s-polarization 437 SPP 34, 36 TAB circuit, cleaning of 438 SPR 36, 236, 438 Tait’s equation of state, of water 381 standard state 437 tamper layer (confinement medium) 69–70 standard state enthalpy of formation 333, 378, 437 target, frozen 272, 274 standard state Gibbs energy of formation 333, 378, 437 target, liquid 257, 266, 270, 272 standard temperature and pressure 437 Taylor factor 135, 438 steam laser cleaning (SLC) 12, 13, 31, 32, 33, 44, 437 TEM00 beam 282, 283 steam laser cleaning, optical effects in 37 temperature transients at laser cleaning 39 steam laser cleaning, phenomenology 37 thermal conductivity 438 steam laser cleaning, universal threshold 45 thermal conductivity,coefficient of 429 steam-assisted laser ablation 146 thermal conductivity,of plasma 298 Steinberg–Cochran–Guinan model 101–102 thermal diffusivity 439 stereolithography 6, 437 thermal expansion coefficient 374, 439 stimulated Brillouin scattering 437 thermal expansion coefficient, volumetric 332, 439 stimulated light scattering 437 thermal expansion, effect in laser cleaning 12, 33, 37 stimulated Raman scattering 176, 437 thermal ionization 297 Stokes formula 147 thermal piston effect 439 strain gauge 75, 126, 129 thermal spalling 203, 205 strain hardening 438 thermal stresses 127, 182 stress corrosion cracking (SCC) 103, 120, 121, 135, 438 thermocapillary surface flow 432 stress relaxation, of laser shocked bodies 74, 75, 131, 136 thermoprotective coating 124 strongly coupled plasma 119, 438 Thomas–Fermi statistical model 100 sublayer flow 438 three-point bending machine, use of 87 supercritical solution, in cleaning 16 transient grating experiments 228 supercritical state 195, 438 transient grating spectroscopy 439 supercritical water 147 transient reflectivity,of laser irradiated interfaces 195, 200 Subject-Index-I044498.tex 12/9/2007 14: 27 Page 450

450 Subject Index

transmutations, atomic 222–223 volumetric heat capacity 429 transparent materials, machining of 177 volumetric thermal expansion coefficient 100, 332, 439 trenches, fabrication of 147, 190 von Mises yielding criterion 95, 97, 128, 136 tunnel ionization 295 vortices, at underwater laser cutting 167 TWIN-LIBWE 439 twinning at laser shock processing 107 water (jet) cavitation peening 70 water decomposition 16, 68, 294, 383–384, 422 ultrashort laser pulses (in laser machining) 143, 179 water decomposition, use for cleaning of surfaces 16, 17 ultrasonic measurement of stress 72, 76 water jet, uses in laser machining 174 ultrasonic peening by strikers 70 water jet guided laser beam 171–176 ultrasonic shot peening 70 water vapour, thermal dissociation of 384–385 ultrasound absorption coefficient, of liquids 439 water, autoionization of 383–384 ultrasound agitation 189 water, equations of state of 381 ultrasound assisted LIBWE 190, 191 water, optical properties of 379 ultrasound velocity measurements 124 water, physical properties of 381 ultraviolet 5% absorption point, of liquids 378, 439 water, sea 319 ultraviolet cut-off point, of liquids 378, 439 water, state diagram of 380 underwater cladding 277, 279 water, thermal dissociation of 383–384 underwater cutting 167, 170 water, thermophysical properties of 382–383 underwater welding 277, 279 waviness, induced by laser irradiation 125 universal threshold of steam laser cleaning 45 web slitter 168, 169 welding, underwater 277, 279 van der Waals force 20, 439 work hardening 100, 101, 117, 121, 127, 128, 440 van der Waals force, photoenhanced 20–21 vaporization rate 290 vaporization coefficient 439 X-cut quartz, use of 79 vaporization, enthalpy of 333, 427 X-ray diffraction, use in residual stress measurements vapour explosion range, of solvents 333, 439 72–73 vapour flammable range, of solvents 439 vapour pressure, theory 289, 333, 440 yield strength 86, 102, 106, 107, 129, 400 vapour pressure, dependence on surface curvature 289 yield strength, dynamic 117, 128, 136 vapour pressure, equilibrium 289 Young–Laplace equation 289 vapour pressure, of volatile hydroxides 309–310 vapour supply methods 31–32 vena contracta effect 172, 440 zeta potential 23, 440 VISAR interferometry 80–81, 83, 440 z-scan; optical: 247, 440 neutron 74, 440 viscosity,definition 440 viscosity,dynamic 332, 374, 381, 427 viscosity,kinematic 431 φ-shaped nanoparticles 221, 227, 229, 230 volatile hydroxides, properties 309–314 ζ-potential 23, 440 Liquids-I044498.tex 12/9/2007 14: 31 Page 451

Liquids

Numbers of the liquids as used in Chapter 8 are in italic 2EE monoethyl ether (52) 2-ethoxyethanol (52) 1,1,1,2,2,3,3,4,4,5,5,6,6,6-tetradecafluoro-hexane (19) 2ME (51) 1,1,2,2,3,3,4,4,4a,5,5,6,6,7,7,8,8,8a-octadecafluorodecalin 2-methoxy-2-methyl-propane (59) (20) 2-methoxyethanol (51) 1,1,2,2-tetrachloroethene (18) 2-methoxyethyl ether (60) 1,1,2-trichloroethene (17) 2-methyl-1-propanol (46) 1,1
-oxybisethane (57) 2-methyl-2-propanol (47) 1,2,3,4,5,6-hexafluorobenzene (26) 2-methylbutane (2) 1,2,3-propanetriol (43) 2-methylpropan-1-ol (46) 1,2,4-TCB (24) 2-methylpropan-2-ol (47) 1,2,4-trichlorobenzene (24) 2-pentanone (70) 1,2-diaminoethane (77) 2-phenylpropane (33) 1,2-dichlorobenzene (23) 2-propanol (42) 1,2-dichloroethane (16) 2-propanone (68) 1,2-dimethoxyethane (58) 1,2-dimethylbenzene (30) 4-methyl-2-pentanone (72) 1,2-ethanediamine (77) 4-methylpentan-2-one (72) 1,3-dimethyl propane (1) 1,3-dimethylbenzene (31) 5-methyl-2-hexanone (73) 1,4-diethylene dioxide (56) 5-methylhexan-2-one (73) 1,4-dimethylbenzene (32) 1,4-dioxacyclohexane (56) acetic acid dimethylamide (79) 1,4-dioxane (56) acetic acid ethyl ester (64) 1,4-epoxybutane (55) acetic acid n-butyl ester (66) 1-butanol (44) acetone (68) 1-butoxybutane (62) acetonitrile (76) 1-chloronaphthalene (34) ACN (76) 1-methoxy-2-(2-methoxyethoxy)ethane (60) air (100) 1-methyl-2-pyrrolidinone (81) alcohol C-8 (50) 1-methyl-2-pyrrolidone (81) amide C1 (74) 1-methylnaphthalene (35) anisole (61) 1-methylpyrrolidin-2-one (81) argon (95) 1-octanol (50) azabenzene (80) 1-propanol (41) azine (80)

2-(2-hydroxyethoxy)ethanol (53) benzene (21) 2,2,2-trifluoroethanol (39) benzene methanol (49) 2,2,4-trimethylpentane (5) benzoic acid methyl ester (67) 2,2
,2

-nitrilotriethanol (48) benzol (21) 2,2
-dihydroxydiethyl ether (53) benzonitrile (27) 2,2
-oxydiethanol (53) benzyl alcohol (49) 2-[bis(2-hydroxyethyl)-amino]ethanol (48) biogas (99) 2-aminoethanol (40) bis(2-hydroxyethyl) ether (53) 2-aminoethyl alcohol (40) bis(2-methoxyethyl) ether (60) 2-butanol (45) bromoform (11) 2-butanone (69) butan-1-ol (44) 2-butoxyethanol (54) butan-2-ol (45) 451 Liquids-I044498.tex 12/9/2007 14: 31 Page 452

452 Liquids

butan-2-one (69) dioxacylohexane (56) butyl acetate (66) dioxane (56) butyl alcohol (44) DMAC (79) butyl cellosolve (54) DME (58) butyl ether (62) DMF (78) butyl glycol (54) DMFA (78) DMSO (84) capryl alcohol (50) DRIVERON® (59) carbinol (36) carbon bisulfide (83) EDC (16) carbon dioxide (98) EGMM (51) carbon disulfide (83) ethane-1,2-diamine (77) carbon sulfide (83) ethane-1,2-diol (38) carbon tet (14) ethanol (37) carbon tetrachloride (14) ethanolamine (40) Cellosolve® (52) ether (57) CFC-14 (14) ethoxyethane (57) chlorobenzene (22) ethyl acetate (64) chloroform (13) ethyl alcohol (37) chloromethylene (12) ethyl cellosolve (52) clorius (67) ethyl ether (57) cumene (33) ethyl glycol (52) cumol (33) ethyl methyl ketone (69) cyclohexane (7) ethylene chloride (16) cyclohexanone (71) ethylene dichloride (16) cyclohexatriene (21) ethylene dioxide (56) cyclohexylmethane (8) ethylene glycol (38) cyclopentane (6) ethylene glycol butyl ether (54) cyclopentyl (6) ethylene glycol dimethyl ether (58) ethylene glycol monobutyl ether (54) decahydronaphthalene (9) ethylene glycol monomethyl ether (51) decalin (9) ethylene tetrachloride (18) DEG (53) ethylene trichloride (17) deuterium (90) ethylenediamine (77) deuterium oxide (87) EtOH (37) diamide (82) diazane (82) dibutyl ether (62) FC72 (19) dichloromethane (12) fluorobenzene (25) diethyl ether (57) fluoroform (15) diethyl methane (1) fluoryl (15) diethylene glycol (53) formamide (74) diethylene glycol dimethyl ether (60) formic acid (63) diethylene oxide (56) formic acid amide (74) diglycol (53) formic acid dimethylamide (78) diglyme (60) formic acid methyl ester (63) dimethyl carbinol (42) formic amide (74) dimethyl diglycol (60) freon 14 (14) dimethyl glycol (58) freon 23 (15) dimethyl ketone (68) freon 150 (16) dimethyl sulfoxide (84) dimethyldiglycol (60) glycerin (43) dimethylglycol (58) glycerine (43) di-n-butyl ether (62) glycerol (43) Liquids-I044498.tex 12/9/2007 14: 31 Page 453

Liquids 453

glycol (38) methanedithione (83) glycolethylether (56) methanol (36) grain alcohol (37) methoxybenzene (61) methyl 2-methylprop-2-enoate (65) heavy water (87) methyl 2-methylpropenoate (65) helium (91) methyl alcohol (36) heptane (4) methyl benzoate (67) hexafluorobenzene (26) methyl cellosolve (51) hexahydrobenzene (7) methyl cyanide (76) hexamethylene (7) methyl ester (63) hexane (3) methyl ethyl ketone (69) HFC-23 (15) methyl formate (63) hydrazine (82) methyl glycol (51) hydrogen (89) methyl hydride (99) hydrogen oxide (86) methyl isoamyl ketone (73) hydroxyethane (37) methyl isobutyl ketone (72) hydroxymethane (36) methyl methacrylate (65) methyl methanoate (63) IPA (42) methyl phenyl ether (61) isoamyl methyl ketone (73) methyl propyl ketone (70) isobutanol (46) methyl tert-butyl ether (59) iso-butanol (46) methylbenzene (28) isobutyl alcohol (46) methylcyclohexane (8) isobutyl methyl ketone (72) methylene chloride (12) methylidyne trichloride (13) isobutylacetone (73) methylsulfinylmethane (84) isobutyltrimethylmethane (5) methylsulfoxide (84) isooctane (5) MIAK (73) isopentane (2) MIBK (72) iso-pentane (2) mineral spirit (10) isopentyl methyl ketone (73) MMA (65) iso-propanol (42) monoethanolamine (40) isopropanol (42) monoethylene glycol (38) isopropyl alcohol (42) monofluorobenzene (25) isopropylacetone (72) monoglyme (58) isopropylbenzene (33) mononitromethane (75) isopropylbenzol (33) M-PYROL® (81) m-pyrrole (81) krypton (96) MTBE (59) m-xylene (31) levoxine (82) light water (86) N,N-dimethylacetamide (79) ligroine (10) N,N-dimethylethanamide (79) N,N-dimethylformamide (78) marsh gas (99) N,N-dimethylmethanamide (78) MEA (40) naphtha petroleum (10) MEG (38) naphthene (7) MEK (69) n-butanol (44) MeOH (36) n-butyl acetate (66) meta-xylene (31) n-butyl alcohol (44) meta-xylol (31) n-dipropylmethane (4) methacrylic acid methyl ester (65) neon (94) methane (99) n-heptane (4) methane amide (74) n-heptylhydride (4) Liquids-I044498.tex 12/9/2007 14: 31 Page 454

454 Liquids

n-hexane (3) PP1 (19) niobe oil (67) propan-1-ol (41) nitrocarbol (75) propan-2-ol (42) nitrogen (92) propane-1,2,3-triol (43) nitromethane (75) propanol (41) N-methyl-2-pyrrolidinone (81) propanone (68) N-methyl-2-pyrrolidone (81) propyl alcohol (41) NMP (81) p-xylene (32) n-octanol (50) pyridine (80) n-pentane (1) n-propanol (41) sea water (88) n-propyl alcohol (41) sec-butyl alcohol (45) silicone oil (85) o-chlorobenzene (23) styrene (29) octadecafluorodecahydronaphthalene (20) styrol (29) octan-1-ol (50) octyl alcohol (50) TCE (17) ordinary water (86) TEA (48) ortho-xylene (30) tert-butanol (47) ortho-xylol (30) tert-butyl alcohol (47) oxacyclopentane (55) tert-butyl methyl ether (59) oxidane (86) tetrachloroethene (18) oxolane (55) tetrachloroethylene (18) oxygen (93) tetrachloromethane (14) o-xylene (30) tetradecafluorohexane (19) tetrahydrofuran (55) para-xylene (32) tetramethylene oxide (55) para-xylol (32) THF (55) PCE (18) TL4N (53) p-dioxane (56) toluene (28) pentamethylene (6) toluol (28) pentan-2-one (70) tribromomethane (11) pentane (1) trichloroethene (17) PERC (18) trichloroethylene (17) perchloroethylene (18) trichloromethane (13) perflexane (19) triethanolamine (48) perfluorobenzene (26) trifluoroethyl alcohol (39) perfluorodecahydronaphthalene (20) trifluoromethane (15) perfluorodecalin (20) trimethyl carbinol (47) perfluorohexane (19) tris(2-hydroxyethyl)amine (48) perfluoro-n-hexane (19) petroleum benzin (10) vinylbenzene (29) petroleum ether (10) petroleum spirit (10) water (86) phenyl carbinole (49) water-d2 (87) phenyl chloride (22) wood alcohol (36) phenyl cyanide (27) phenyl fluoride (25) xenon (97) phenyl methanol (49) xylene (30,31,32) phenylethylene (29) xylol (30,31,32) phenylmethanol (49) pimelic ketone (71) α-chloronaphthalene (34) polydimethylsiloxane (85) α-methylnaphthalene (35) polysilicone oil (85) β, β, β-trifluoroethyl alcohol (39)