Laser Raman Microprobing Techniques P

LASER RAMAN MICROPROBING TECHNIQUES P. Dhamelincourt, J. Barbillat, M. Delhaye

To cite this version:

P. Dhamelincourt, J. Barbillat, M. Delhaye. LASER RAMAN MICROPROBING TECHNIQUES. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-249-C2-253. 10.1051/jphyscol:1984255. jpa- 00223968

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LASER RAMAN MICROPROBING TECHNIQUES

P. Dhamelincourt, J. Barbillat and M. Delhaye

Laboratoire de Spectrochimie Infrarouge et Raman, C. N. R. S., lhziversitB des Sciences et Techniques de LiZZe, B&. C. 5, 59655 ViZZeneuve d 'Ascq Cedex, France

@sun6 - L1int6r&t de la microspectrcm6trie Raman pour l'analyse mol6culaire non destructive ainsi que 1'6volution des techniques sont pr6sentBs. Quelques exemples d'application illustrent l'exps6.

Abstract - The analytical potential of micr0Fm-w spectroscopy for non destructive mlecular analysis is presented. The evolution of the techniques and some applications are presented.

From the thof its discovery in 1928 until a few years ago Raman scattering was used as a tml for the study of bulk samples of macroscopic dimension furnishing information about fundamntal mlecular properties as well as serving an inprtant function in laboratory spectrochemical analysis /1,2/.The entry of Raman spectres- copy into the field of instumental microanalysis represents a significant opportu- nity for the field of Raman spectroscopy in that Raman scattering can provide information which up to this time has not been available from any other widely used micro analytical technique such as electron or ion microprobing techniques. Indeed these last techniques readily identify,mp out the distribution and determine the quanti- ty of elemental constituents present but do not distinguish the chemical forms of elements present as specific compound in a microsample. It is well known that Raman spectroscopy which is based on the study of the spectral distribution of inelasti- cally scattered light emitted by a sample irradiated with a mnoenergetic beam of light,is a highly spcific technique of investigating mlecular species in all phases of matter as they are fingerprinted by their vibratinal spectra. %,with Lasers as sources for excitation of Raman scattering and the ongoing develornts in instnnnen tation for the optical spectroscopy,Raman microprobing techniques have matured to the pint at wich non destructive chemical microanalysis has become routinely prac- ticable for both academic research and industrial pqses /3,4/. In the first part of this paper,I shall take stock of the evolution of the instruments which have been developed and in a second part,I shall illustrate the analytical potential of Raman microprobing techniques by exemples of analysis prformed on samples relevant to various areas of microanalysis.

I1 - EVOLIPTION OF THE INSTRWATION FOR MIwm SP~SCOPY Beteem 1973 and 1976,tw laboratories: N.B.S. Washingtown U.S.A.,and L.A.S.I.R., Lille France, developed indepently tw~types of Raman microprobe instrument.The instrument developed at N.B.S. was specially designed to analyze single micrometer size particle.Briefly,it is a conventional Laser Raman spectra~terin which the sample holder has been replaced by a state of the art fore optical system with compnents to tightly focus the Laser radiation on the particle to be analyzed and collect effi ciently the scattered light /5/:In our laboratory at Lille W proceeded differently by starting from the tool of the microscopist-the optical microscope-to create a totally new instrument /6/. The basic configuration of this instrurnent(Fig.l)results from the coupling of a conventional light microscope(with bright and dark field illu mination)to a double mnochromtor sPectromter equipped with concave holographic gratings,followed by two different detection systems(mnochanne1 and multichannel). The light microscope provides the sample stage and forms part of the mging system.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984255 JOURNAL DE PHYSIQUE

DOUBLE CONCAVE HOLOGRAPHIC GRATl NG FILTER

n I n

'ER

POINT GLOBAL MULTICHANNEL HONOCHANEL ILLUHINATION ILLUHINATION DETECTOR DETECTOP v V ILLUMlNATlON DETECTION

Fig. 1 - Diagram of Raman microprobe/microscope(M.O.L.E.)developed CMRS-Lille,illustrating modes of sample illumination and signal detection.

Fig. 2 - Diagram of Raman microprobe(M1CRODIL 28)developed at Lille (CNRS-DILOR company)illustrating the optical scanning of sample and multichannel detection. All rrcdes of observation available in a standard optical microscope are available in the instrument.Therefore,microsaniples can be examined in situ without any more preparation than that required for white light observation.This configuration results in a versatile Raman microprobe/microscope because it permits two fundamental desof operation. - Point illumination with mnochannel detection(spectra1 We) Ey use of the bright illumination system of the microscope,the objective focuses the Laser beam into a microscopic s,pt,and the sample or the sample region of interest is mved by translation of the microscope stage into the focal volume of the beam. The light scattered by the sample is collected in the back scattering direction through the sane objective and directed onto the Ram spectrometer-Thedetector is a photmltiplier followed by a photon counter and a chart reccrrder. - Global illumination and Raman imaging system(Imaging mode). In this mcde,a larger area(from 150 to 300p in diameter)of the Wleis illmina- ted from above with partially defocused Laser radiation.For that the Laser beam is rotated to form an annular beam of light which feeds the condenser of a dark field illuminator-By selecting a frquency in the Raman spectrum characteristic of one specific component in the sample,a micrographic image is produced which indicates the distribution of this component throughout the illuminated area.This Raman line imaging is achieved by transferring through the spectrometer the optical image formed by the microscope objective onto the photocathode of the rnultichannel detctor.The spatial resolution is about lpm. This instrument has been comrcially available under the name of M.O.L.E. by Instru mts S.A., Inc., J.Y. Optical Systems Division until 1981.It is now superseded by a mcdular system,the RmorU-1000,in which a conventional macrommn spectrmeter may be fitted with an optical microscope for microRaman masurements.This is a ten- dancy against which we warn for memanufacturers to return to the early stage of laboratory expximentation by s-ly coupling microscopes to conventional mnochro- mators.Limitations of the M.O.L.E. instrument are that in the spectral mode the m- suraent times are generally too long for fragile materials and that the imaging mode lacks of sufficient sensivity and spectral resolution to reveal weak lines or to discriminate Raman features from fluorescence background.So extensive researchs have been done in our laboratory and in close collaboration with a french campany -DILOR, Lille-to find optimal procedures in order to increase both the speed of spectra recording and the Raman imaging capability-These researchs have led to a second generation of Raman microprobe which employs spectrographic dispersion with a very sensitive multichannel detector.This new instrument called MICRODIL 28 is described more in details in another paper of this session /7/.Briefly tkis instru- mt(see Fig. 2)uses a double forena>nochromtor with plane holographic gratings,followed by a spectrcgraph.Aspecially built rnultichannel detector head cooled by Peltier elemnts,combined with a digital treatment unit,is used to detect and to store signal. This detector can be operated in tvm different ways when placed at the focal plane of the spectrcgraph in order to deliver either spectral or spatial infomtion. Outputs are provided to a camputer and to digital or analog recorders.

I11 - SOME APPLICATIONS OF MICROFWWN SPECTIZOSCOPY

For some years now Ramn microprobing techniques have been extensively applied for non destructive microanalysis for both academic research and industrial purpses.1 will try here to give an overview of the kind of problems that are amenable to inves tigation by microRaman spectroscopy by presenting a few domains for which microRaman investigations have been conducted with success.

A - GEOLOGY - ANALYSIS OF FLUID INCLUSIONS IN M.INF,RALS

When a mineral forms it may trap in its defects small portions of the fluid phase from which it is growing.These fluid inclusions are real witnesses of the genesis of minerals because they have mrized conipsition and density of the original mixture. The knowledge of these two characteristics permits the geologist to retrace the chemistry and thennobarometric conditions of rock formation.Hitherto,microthenrpmetry C2-252 JOURNAL DE PHYSIQUE

was mainly the sole technique used by geologists for fluid inclusion studies.It is based upon the observation under an optical microscope equipped with a cooling-hea- ting stage of the mlting tmpratures of solid phases and the hoqeneisation tem peratures of volatile fluids along with an estimation of their volume ratio.But these measurements are often altered and then,misinterpretating fluid phase equilibria leads to incorrect conclusions about past rock formation events-Fromnow on micro Ramannin situl'measurementsof fluid inclusions in minerals have proved to be essen- tial as a complement of microthemmetry measurements in that they permit to confirm (or infirm) microthermmetric results,to detect and estimate the molar proportion of all fluids and to identify solid phases in equilibrium with fluids /8/.Mreover unique infomtion may be drawn only from Raman analysis like the detection of hydrogen and quantitatkve evaluation of free sulphate ion concentration in brine /9,10/. B - INDUS= MATERIAL CONTROL Contamination or formation of defects are problems currently encountered in the comwrcial production of materials.The chemical identification of these defects is of particular interest because it can lead to properly selected materials and processes.To illustrate these problems I have selected exemples where samples were also analyzed using other microanalytical techniques but with inconclusive results.

1 -Raman microspectroscopy in semi-conductor process sup~ort/11/. -Wafer mask defect- Glass masks contain the circuit pattern from which replicates are transferred by photochemical process to silicon wafers. A lot of glass masks which had passed visual inspection were found to result in pattern defects when used to process product wafers.A Faman spectrum of the area causing the defect,cmpred to an adjacent area exhibits a sharp line at 2330 cm-l characteristic of nitrogen gas.The defects were concluded to be due to tiny air or nitrogen gas bubbles below the surface of the glass. -Device contaminant from etching- White particles(a few micrometer in size)were de- tected on product wafers having pattern defects after etching of the silicon dioxide in a buffered hydrofluoric acid solution(HF).Secondaq ion mass spectrometry had de- tected fluorine in the defect areas.The m spectrum of the contaminant revealed it to be mnium hexafluorosilicate.

2 -Analysis of contaminants in synthetic textile filaments /3/. Small individual filaments(typical1y 5 to 20pm in diameter)are usually used tomake textile yarns.So filament breaks caused by particulate contamination of the polymer is an hprtant problem.Inclusions in the filaments arising from particulate contamination of the feed stock polymer can be sub-divided in -Internal contamination from substances present as part of the polymer recipe or produced during polymerisation.Titanum dioxide(anti1ustre of the textile yarn),degra- ded polymer, ... carbonaceous residues... have been thus identified. -External contamination from substances acquired during the material handling processes.Packaging materials(polythene,polyvinils,... ) ,~~~)rkers'clothingfiber fragments (polyamide),airborne particles(quartz,calcite, ...)have been identified. These now routine investigations are made directly by recording through the textile filament the Raman spectra of the contaminants.

C - ANALYSIS OF AIRBORNE PAFTICLES The analysis of airborne particles in the size range 1 to 10~is wrtant in myfields of hmendeavour including concerns related to pollution monitoring, global climate rnodification,health hazard, ... FCman microprobe techniques are emi- nently suited for the characterization of microparticles of inorganic and organic 0rigin.m particular,organic cornpunds give informative,diagnostically useful spectra /12,13/.The principal species for which spectroscopic characterization is easy inclu- de the cmnminerals(silicates,oxides,carbonates,sul£ates, ... )and some organic can- pounds (pesticides,insecticides, aliphatic acids,plymers, hydrocarbons films ,peptids ..) D - MICROANALYSIS OF BIOLOGICAL TISSUES

With the advent of Raman microprobe rechniques,qreat possibilities for unique inves- ti ations a ar to be opening U in bioly~thologyand tissue research to obtain mo?ecular inqrmation at the celyular leve . croF&mm studies are generally performed on standard histological sections of biological tissues.% far these studies have been devoted to problems such as -The identification of purines and mineral pre- cipitation in tissues from organs of various animals induced by natural or patholo- gical processes /14/ -The identification of the nature of kidney stone induced by mercury and cadniun intoxication /15/ -The analysis of the process of hard tissue forn?ation(Biomineralization) /16/ -The understandting of photo-product formation in visual pigments of the vertebrate photoreceptors responsible for colour vision /17/ -The identification of microscopic foreign bodies of plywr(coming from inplanted prosthesis)for diagnosis pathology /18/.This list is not exhaustive of course as more and more studies are now being performed on biological materials. TV - CONCLUSION Wth routine detection limits well under the nancqram and high specificity the Raman microprobing technique has already beccane in mylaboratories a major microanalytical technique yielding new or more precise answers to problems left unsolved or inaonipletely solved by other techniques.With the steadily advances in instnmata- tion,experimentation and theory,the future of this technique looks very prcanising. REFERENCES 1 - LONG D.A., Raman Spectroscopy, MC Graw Hill, Inc, London (1977). 2 - HENDRA P.J., Laser Raman Spectroscopy,in vibrational spectra and stru~ture~Vol.2 Durig J. R. (Ed), Marcel Dekker, Inc. , New York, Chap. 2, (1978) 135. 3 - Applications of the bDLE Raman microprobe, L'Actualit6 Chimique, Avril (1980). 4 - ETZ E.S., Scanning electron microscopy, I (1979) 67. 5 - ROSAXD G.J. and ETZ E.S., Res. and ~evei.28 (1977) 20. 6 - DHAMELINCOURT P. et al., Anal. Chem. 2 (1979) 414 A. 7 - BARBIU&T J. et al. , The Micrddil 28: a new mltichannel Rarwn microprobe, (New microanalytical techniques session) . 8 - RAMBOZ C.C. and BENY J.M.,Contrib. Mineral.Petro1. (1983) "to be published". 9 - DUBESSY J. et al., Geochim.co~m~chim.Acta47 (1983) 1. 10 - DUBESSY J. et al., Abstacts of the 12th meeting Of International Mineralogical Association,Orl6ans ,France (1980). L1 - Private co~cation. 12 - GOYPIRON et al., Abstracts of the 2nd International Congress on Analytical Tech- niques in Environmental Chemistry,Barcelone, Spain (1981). 13 - ETZ E.S. et al., Environmental pollutants,Toribora T. et al. (m), Plenum Publi- shing Corp. (1978). 14 - BAILAN-DUFRANCAIS C. et al., Biol-Cell., 5 (1979) 51. 15 - TRUCHET M., Doctoral thesis, Paris, France (1982). 16 - GRYNPAS N.D. et al., Proc. 17th Microbeam Analysis Society Conference,Heinrich K. (Ed), San Francisco Press, San Francisco (1982). 17 - BARRY B. and MATHIES R., J. of Cell Biol. 2 (1982) 479. 18 - ABF?AHAM J.L. and FTZ E.S., Science 2 (1979) 716.