Nanotribology, Nanomechanics and Materials Characterization Studies and Applications to Bio/nanotechnology and Biomimetics

Prof. Bharat Bhushan Ohio Eminent Scholar and Howard D. Winbigler Professor and Director NLBB [email protected] Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics

© B. Bhushan

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 1 Micro/nanoscale studies Materials/Device Studies Bio/nanotribology Bio/nanomechanics Biomimetics • Materials/coatings Materials sci., biomedical eng., physics & physical chem. • SAM/PFPE/Ionic liquids • Biomolecular films • CNTs Techniques • Micro/nanofabrication AFM/STM Microtriboapparatus Nanoindentor

Numerical modeling and simulation

Collaborations Applications

• MEMS/NEMS • BioMEMS/NEMS • Superhydrophobic surfaces • Reversible adhesion • Beauty care products • Probe-based data storage • Aging Mech. of Li-Ion Batt.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 3 Outline • Introduction

‰ Nanotribology

‰ Examples of a magnetic storage device, MEMS/NEMS and BioMEMS/BioNEMS

• Measurement Techniques

• Results and Conclusions

‰ Surface Imaging, Adhesion, Friction and Wear

‰ Adhesion, Friction and Wear of CNTs

‰ Bioadhesion Studies

‰ Hierarchical Nanostructures for Superhydrophobicity, Self Cleaning and Low Adhesion

‰ Conclusions

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 4 Introduction Nanotribology • At most interfaces of technological relevance, contact occurs at numerous asperities. It is of importance to investigate a single asperity contact in the fundamental tribological studies.

Engineering Interface Tip - based microscope allows simulation of a single asperity contact • Nanotribological studies are needed

‰ To develop fundamental understanding of interfacial phenomena on a small scale

‰ To study interfacial phenomena in micro- or nanostructures and performance of ultra-thin films, e.g., in magnetic storage and MEMS/NEMS components

B. Bhushan, J. Israelachvili and U. Landman, Nature 374, 607 (1995); B. Bhushan, Handbook of Micro/Nanotribology, second ed., CRC Press, 1999; B. Bhushan, Introduction to Tribology, Wiley, NY, 2002; B. Bhushan, Nanotribology and Nanomechanics – An Introduction, Springer, 2005; B. Bhushan, Wear 259, 1507 (2005); B. Bhushan, Springer Handbook of Nanotechnology, second ed., Springer, 2007. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 5 Example of a Magnetic Storage Device

Diamond like carbon overcoat 3.5 nm thick

Al2O3-TiC

MR type picoslider Magnetic rigid–disk drive (Bhushan, 1996)

Liquid Lubricant 1- 2 nm

Diamondlike carbon overcoat 3-5 nm Magnetic coating 25 –75 nm Al-Mg/10 μm Ni-P, Glass or Glass - ceramic 0.78-1.3 mm

Thin–film disk

B. Bhushan. Tribology and Mechanics of Magnetic Storage Devices, 2nd ed., Springer-Verlag, NY, 1996 Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 6 Examples of MEMS/NEMS and BioMEMS/NEMS

springs

shuttle

Microgear unit can be driven at speeds up to 250,000 RPM. Various sliding comp. are shown after wear test for 600k cycles at 1.8% RH (Tanner et al., 2000) gears and pin joint

Microengine driven by electrostatically-actuated comb drive Stuck comb drive Sandia Summit Technologies (www.mems.sandia.gov) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Microfabricated commercial MEMS components

B. Bhushan. Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, 2007 Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 8 The generating points of friction and wear due to interaction of a biomolecular layer on a synthetic microdevice with tissue (Bhushan et al., 2006)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 9 CNT-based Nanostructures SWNT biosensor

The electrical resistance of MWNT Sheet the system is sensitive to the adsorption of molecules to the nanotube/electrode. Adhesion should be strong between adsorbents and (Chen et al., 2004) SWNT.

Nanotube bioforce sensor

Force applied at the free end (Zhang et al., 2005) of nanotube cantilever is detected as the imbalance of Mechanical properties of current flowing through the nanotube ribbons, such as the nanotube bearing supporting elastic modulus and tensile the nanotube cantilever. strength, critically rely on the The deflection of nanotube adhesion and friction between cantilever involves inter-tube nanotubes. friction. (Roman et al., 2005)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Measurement Techniques

Surface Force Apparatus (SFA),1968

Scanning Tunneling Microscope (STM), 1981

Atomic Force Microscope (AFM) and Friction force Microscope (FFM), 1985

B. Bhushan, J. Israelachvili and U. Landman, Nature 374, 607 (1995); B. Bhushan, Handbook of Micro/Nanotribology, second ed., CRC Press, 1999; B. Bhushan, Introduction to Tribology, Wiley, NY, 2002; B. Bhushan, Nanotribology and Nanomechanics – An Introduction, Springer, 2005; B. Bhushan, Springer Handbook of Nanotechnology, second ed., Springer, 2007. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 11 Schematic of a small sample Schematic of a large sample AFM/FFM AFM/FFM

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 12 Results – Surface Imaging and Friction

STM images of a solvent-deposited C60 film on gold coated mica B. Bhushan et al., J. Phys. D: Appl. Phys. 26, 1319 (1993) CNN Headlines News, 3/18-3/19/93, etc. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 13 μ = 0.006

Topography and friction force maps for HOPG

J. Ruan and B. Bhushan, J. Appl. Phys. 76, 8117 (1994); Y. Song and B. Bhushan, Phys. Rev. B 74, 165401 (2006) National Public Radio, 4/12/95; Business Week, 5/1/95 etc. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 14 Friction force map and line plots of friction force profiles for HOPG. Friction force changes discontinuously with sudden jumps. This leads to saw tooth pattern and it occurs due to atomic-scale stick-slip. Can use mechanical model proposed by Tomlinson in 1929. Equilibrium position before sliding begins Stick Slip

Slip event is a AFM tip- dissipative process cantilever model Periodic interaction Sample potential surface Atomic lattice Direction of motion constant, a of sample surface The tip needs to overcome the energy barrier in order to jump from a stable equilibrium on the surface into a neighboring position. The tip remains stuck until energy stored in the spring is high enough to overcome the energy barrier. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 15 Scale effect on friction

Coefficient of Friction Nanoscale* Microscale

RMS* with Si3N4 with Si3N4 Sample (nm) tip ball Si(100) 0.14 0.06 0.47 HOPG 0.09 0.006 0.1 Natural 2.3 0.05 0.2 Diamond DLC film 0.14 0.03 0.19

*Scan area = 1 μm x 1 μm

Roughness, nano- and macroscale friction data of various samples

J. Ruan and B. Bhushan, ASME J. Tribol. 116, 389 (1994) B. Bhushan et al., ASME J. Tribol. 126, 583 (2004) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 16 Comparing the conditions of nanoscale and macroscale tests, there are at least four differences

•Contact size in FFM is small—particles are ejected readily

•Mechanical properties have size effect— properties on nanoscale are superior to the bulk properties

•Applied loads in FFM are low—elastic contact regime (little plowing)

•Small radius of tip results in lower friction

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 17 Custom piezo stages for high velocity sliding

Ultrahigh velocity stage (upto 200 mm/s) High velocity stage (upto 10 mm/s)

Schematic of experimental setup N. Tambe and B. Bhushan, J. Phys. D: Appl. Phys. 38, 764 (2005); Z. Tao and B. Bhushan, Rev. Sci. Instrum. 77, 103705 (2006) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 18 Friction force on log scale Normal load = 100 nN 60 Si (100) Viscous shear Meniscus force dominates Friction force on linear scale Friction force on log scale (low velocity) 40 dominates 60 10 Si (100) Si (100) Atomic-scale stick 40 20 slip dominates 5 20

0 0 0 60 10 60 DLC DLC DLC Phase transformation/ Friction force (nN)(nN) force force Friction Friction 40 Friction force force (nN) (nN) Friction Friction tip jump 5

Friction force force (nN) (nN) Friction Friction 40 20

0 0 0105 2 × 105 0 1 2 3 Atomic-scale stick 10 10 10 10 20 Velocity (μm/s) Velocity (μm/s) slip dominates

0 100 102 104 106 Velocity (μm/s) Effect of velocity on friction force • Friction mechanisms vary with surfaces • At different velocity regime, different mechanisms dominate friction N. S. Tambe and B. Bhushan, Nanotechnology 15, 1561 (2004); ibid, 16, 2309 (2005); J. Phys. D: Appl. Phys. 38, 764 (2005); Appl. Phys. Lett. 86, 061906, 2005; J. Vac. Sci. Technol. A 23, 830 (2005); Ultramicroscopy 105, 238 (2005); Z. Tao and B. Bhushan, Rev. Sci Instrum. 77, 103705 (2006); J. Vac. Sci. Technol. A 25 1267(2007) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 19 Nanofriction maps

Contour map showing friction force dependence on normal load and sliding velocity.

N. S. Tambe and B. Bhushan, Appl. Phys. Lett. 86, 193102 (2005); Nature Mat. In Nanozone, Feb. 17 (2005) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 20 Nanowear map

Nanowear map for DLC illustrating effect of sliding velocity and normal load.

N. S. Tambe and B. Bhushan Scripta Mat. 52, 751 (2005); Tribol. Lett. 20, 83 (2005). Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 21 Adhesion and Friction between Individual Nanotubes Experimental Schematic MWNT tip and SWNTs suspended on a micro-trench (1) Scan of MWNT tip in (2) Ramp of MWNT tip in lateral direction across vertical direction against suspended SWNT bridge suspended SWNT bridge

Average diameter of suspended SWNT bridge is 1.43 nm The diameter of the MWNT tip is about 100 nm. Method (1) works for flexible MWNT tip while method (2) is suitable for stiff MWNT tip

B. Bhushan, X. Ling, A. Jungen, C. Hierold, Phys. Rev. B, 2008 Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Scan of MWNT tip in lateral direction across suspended SWNT bridge (A) (B) (C) Cantilever tapping amplitude 21 nm

ABC (A) Nanotubes came into contact and formed a movable junction. By analyzing the dissipated power of the vibrating cantilever, the kinetic friction between nanotube is proportional to the attenuation of the cantilever amplitude during the initial contact of nanotube:

16 nm FF = 4 ± 1 pN (B) The junction slipped to the end of the MWNT tip with the deformation of the tip. (C) The adhesive force between nanotubes forced the nanotubes to 0 Cantilever vertical deflection 2.4 µm deform more until they detached from each other. 0.8 nm

Multiplying cantilever deflection at the point of detachment with cantilever spring constant gives:

FA = 0.7 ± 0.3 nN -1.2 nm

The coefficient of kinetic friction is calculated from FF / FA : µ = 0.006 ± 0.003 Comparable to values reported on graphite on nanoscale. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 23 Bioadhesion Studies

• Study surface modification approaches - nanopatterning and chemical linker method to improve adhesion of biomolecules on silicon based surfaces.

B. Bhushan et al., Acta Biomaterialia 1, 327 (2005) ; ibid 2, 39 (2006); Lee et al., J. Vac. Sci. Technol. B 23, 1856 (2005) ; Tokachichu and Bhushan, IEEE Trans. Nanotech. 5, 228 (2006); Eteshola et al., J. Royal Soc. Interf. 5, 123(2008)

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 24 Sample preparation

STA: Streptavidin APTES:Aminopropyltriethoxysilane NHS: N-hydroxysuccinimido BSA: Bovine serum albumin

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 25 Schematic representation of deposition of streptavidin (STA) by chemical linker method

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 26 Adhesion measurements in PBS with functionalized tips

Patterned silica surface exhibits higher adhesion compared to unpatterned silica surface. Biotin coated surface exhibits even higher adhesion. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 27 Lessons From Nature (Biomimetics)

Biomimetics • Nature has gone through evolution over 3.8 billion years. It has evolved objects with high performance using commonly found materials. • Biological inspired design or adaptation or derivation from nature is referred to as biomimetics. It means mimicking biology or nature. Biomimetics is derived from a Greek word “biomimesis.” Other words used include bionics, biomimicry and biognosis. • Biomimetics involves taking ideas from nature and implementing them in an application. • Biological materials have hierarchical structure, made of commonly found materials.

• It is estimated that the 100 largest biomimetic products had generated $1.5 billion over 2005-08. The annual sales are expected to continue to increase dramatically.

M. Nosonovsky and B. Bhushan (2008), Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer-Verlag, Heidelberg, Germany; B. Bhushan (2007), Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, Germany; B. Bhushan, Phil. Trans. R. Soc. A (in press). Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 28 Montage of some examples from nature

Montage of some examples from nature.

B. Bhushan, Phil. Trans. R. Soc. A (in press). Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 29 Hiearchical Nanostructures for Superhydrophobicity, Self-cleaning and Low Adhesion One of the crucial property in wet environments is non-wetting or superhydrophobicity and self cleaning. These surfaces are of interest in various applications, e.g., self cleaning windows, windshields, exterior paints for buildings, navigation-ships and utensils, roof tiles, textiles and reduction of drag in fluid flow, e. g. in micro/nanochannels. Also, superhydrophobic surface can be used for energy conservation and energy conversion such as in the development of a microscale capillary engine.

Reduction of wetting is also important in reducing meniscus formation, consequently reducing stiction.

Various natural surfaces, including various leaves, e. g. Lotus, are known to be superhydrophobic, due to high roughness SEM of Lotus leaf showing bump structure. and the presence of a wax coating (Neinhuis and Barthlott, 1997)

NY Times, 1/27/05; ABCNEWS.com, 1/26/05; Z. Burton and B. Bhushan, Ultramicroscopy 106, 709 (2006); B. Bhushan and Y. C. Jung, Nanotechnology 17, 2758 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Rolling off liquid droplet over superhydrophobic Lotus leaf with self cleaning ability

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Roughness optimization model for superhydrophobic and self cleaning surfaces

Wenzel’s equation:

cosθ = Rf cosθo

Droplet of liquid in contact with a Effect of roughness on contact angle smooth and rough surface

M. Nosonovsky and B. Bhushan, Microsyst. Tech. 11, 535 (2005); Microelectronic Eng. 84, 387 (2007); Ultramicroscopy 107, 969 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); US Patent pending (2005) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Formation of the composite interface

Cassie-Baxter equation:

cosθ = Rff SL cosθ 0− f LA

= RfRffcosθ0LA−+ ( cosθ 0 1)

fLA requirement for a hydrophilic surface to be hydrophobic

R f cosθ0 D fLA ≥< for θ0 90 Rf cosθ0 + 1

Y. C. Jung and B. Bhushan, Nanotechnology 17, 4970 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008); M. Nosonovsky and B. Bhushan, Microsyst. Tech. 12, 231 (2006); ibid, 273 (2006) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics In fluid flow, another property of interest is

contact angle hysteresis (θH)

Increased droplet volume θadv : Advancing contact angle

Decreased droplet volume θrec : Receding contact angle

θH = θadv - θrec

If θH is low, energy spent during movement of a droplet is small and a droplet can move easily at a small tilt angle

α : Tilt angle

f 1− fR LA (cosθrec0 − θadv0 )cos adv θθ rec ≈− for high contact angle (2 R θ + )1cos f 0 (θ Æ 180°)

Increase in fLA and reduction in Rf decrease adv − θθ rec B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, 225010 (2008); B. Bhushan, M. Nosonovsky, and Y. C. Jung, J. R. Soc. Interf. 4, 643 (2007); M. http://lotus-shower.isunet.edu/the_lotus_effect.htm Nosonovsky and B. Bhushan, Microelectronic Eng. 84, 382 (2007); Nano Letters 7, 2633 (2007); Springer-Verlag, Heidelberg (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Fabrication and characterization of nanopatterned polymers Study the effect of nano- and microstructure on superhydrophobicity Nanopatterns Micropatterns

Low aspect ratio (LAR) – 1:1 height to diameter

High aspect ratio (HAR) – 3:1 height to diameter Lotus patterned •Materials

‰ Sample ƒ Poly(methyl methacrylate) (PMMA) (hydrophilic) for nanopatterns and micropatterns

‰ Hydrophobic coating for PMMA ƒ Perfluorodecyltriethyoxysilane (PFDTES) (SAM)

Z. Burton and B. Bhushan, Nano Letters 5, 1607 (2005); Y. C. Jung and B. Bhushan, Nanotechnology 17, 4970 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008); Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Contact angle on micro-/nanopatterned polymers • Different surface structures: film, Lotus, LAR, HAR • Hydrophobic film, PFDTES, on PMMA and PS surface structures

LAR HAR Lotus

Rf 2.1 5.6 3.2 • In hydrophilic surfaces, contact angle decreases with roughness and in hydrophobic surfaces, it increases. • The measured contact angles of both nanopatterned samples are higher than the calculated values using Wenzel equation. It suggests that nanopatterns benefit from air pocket formation. Furthermore, pining at top of nanopatterns stabilizes the droplet. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Fabrication and characterization of micropatterned silicon

Transition for Cassie-Baxter to Wenzel regime depends upon the roughness spacing and radius of droplet. It is of interest to understand the role of roughness and radius of the droplet.

Optical profiler surface height maps of patterned Si with PF3 • Different surface structures with flat-top cylindrical pillars:

‰ Diameter (5 µm) and height (10 µm) pillars with different pitch values (7, 7.5, 10, 12.5, 25, 37.5, 45, 60, and 75 µm)

•Materials

‰ Sample – Single-crystal silicon (Si)

‰ Hydrophobic coating – 1, 1, -2, 2, -tetrahydroperfluorodecyltrichlorosilane (PF3) (SAM)

B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, 225010 (2008); B. Bhushan, M. Nosonovsky, and Y. C. Jung, J. R. Soc. Interf. 4, 643 (2007); Y. C. Jung, and B. Bhushan, Scripta Mater. 57, 1057 (2007); J. Microsc. 229, 127 (2008); Langmuir 24, 6262 (2008); M. Nosonovsky and B. Bhushan, Ultramicroscopy 107, 969 (2007); Nano Letters 7, 2633 (2007); J. Phys.: Condens. Matter 20, 225009 (2008); Mater. Sci. Eng.:R 58, 162 (2007) ; Langmuir 24, 1525 (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Transition criteria for patterned surfaces

• The curvature of a droplet is governed by Laplace eq. which relates pressure inside the droplet to its curvature. The maximum droop of the droplet

− D)P2( 2 δ ≈ R If δ ≥ H Transition from Cassie-Baxter regime to Wenzel regime

• Geometry (P and H) and radius R govern transition. A droplet with a large radius (R) w.r.to pitch (P) would be in Cassie-Baxter regime. Y. C. Jung, and B. Bhushan, Scripta Mater.57, 1057(2007); Y. C. Jung, and B. Bhushan, J.Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Contact angle, hysteresis, and tilt angle on patterned Si surfaces with PF3

Droplet size = 1 mm in radius

• For the selected droplet, the transition occurs from Cassie-Baxter regime to Wenzel regime at higher pitch values for a given pillar height. B. Bhushan, and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); Y. C. Jung, and B. Bhushan, J. Microsc. 229, 127 (2008); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, 225010 (2008)Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics • The critical radius of droplet for the transition increases with the pitch based on both the transition criterion and the experimental data. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Structure of ideal hierarchical surface

• Based on the modeling and observations made on leaf surfaces, hierarchical surface is needed to develop composite interface with high stability.

• Proposed transition criteria can be used to calculate geometrical parameters for a given droplet radius. For example, , for a droplet on the order of 1 mm or larger, a value of H on the order of 30 μm, D on the order of 15 μm and P on the order of 130 μm is optimum. • Nanoasperities should have a small pitch to handle nanodroplets, less than 1 mm down to few nm radius. The values of h on the order of 10 nm, d on the order of 100 nm can be easily fabricated. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Fabrication and characterization of hierarchical surface

Fabrication of microstructure

• Microstructure

‰ Replication of Lotus leaf and micropatterned silicon surface using an epoxy resin and then cover with the wax material

B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir (in press); Koch et al., Soft Matter (in press) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Fabrication of nanostructure and hierarchical structure

Recrystallization of wax tubules

• Nanostructure

‰ Self assembly of the Lotus wax deposited by thermal evaporation ƒ Expose to a solvent in vapor phase for the mobility of wax molecules • Hierarchical structure

‰ Lotus and micropatterned epoxy replicas and covered with the tubules of Lotus wax B. Bhushan et al., Soft Matter 4, 1799 (2008); Appl. Phys. Lett. 93, 093101 (2008); Ultramicroscopy (in press); Langmuir (in press); Koch et al., Soft Matter (in press) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Static contact angle, contact angle hysteresis, tilt angle and adhesive force on various structures

• Nano- and hierarchical structures with tubular wax led to high static contact angle of 167º and 173º and low hysteresis angle on the order of 6º and 1º. • Compared to a Lotus leaf, hierarchical structure showed higher static contact angle and lower contact angle hysteresis.

B. Bhushan, Y. C. Jung, A. Niemietz, and K. Koch, Langmuir (in press) Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Self-cleaning efficiency of various surfaces

• As the impact pressure of the droplet is zero or low, most of particles on nanostructure were removed by water droplets, resulting from geometrical scale effects. • As the impact pressure of the droplet is high, all particles which are sitting at the bottom of the cavities between the pillars on hierarchical structure were removed by the water droplets. Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics Conclusions

• AFM/FFM has been developed as a versatile tool for fundamental studies in nanotribology, nanomechanics and material characterization.

• It has been successfully used for studies of surface imaging, adhesion, friction, scratching/wear, lubrication, measurement of mechanical and electrical properties, and in-situ localized deformation studies.

• Examples of nano/biotechnology and biomimetics research are presented.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 46 Acknowledgements

• Financial support has been provided by the Office of Naval Research, National Science Foundation, the Nanotechnology Initiative of the National Institute of Standards and Technology in conjunction with Nanotribology Research Program, and industrial membership of NLBB. • The self assembled monolayers (SAMs) were prepared by Dr. W. Eck and Prof. M. Grunze at University of Heidelberg, Germany, and Drs. P. Hoffmann and H. J. Mathieu of EPFL Lausanne, Switzerland. • Some of the patterned samples were provided by Dr. E. Y. Yoon of KIST Korea and Drs. P. Hoffmann and L. Barbieri of EPFL, Lausanne, Switzerland. • The BioMEMS/BioNEMS studies were carried out in collaboration with Prof. S. C. Lee of OSU Medical School. • Physik Instrumente provided high speed piezo stages. • Last but not the least, contributions by my past and present students and visiting scientists is gratefully acknowledged.

Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics 47 References • Bhushan, B., Israelachvili, J. N. and Landman, U. (1995), "Nanotribology: Friction, Wear and Lubrication at the Atomic Scale,” Nature 374, 607-616. • B. Bhushan (1999), Handbook of Micro/Nanotribology, second ed., CRC Press, Boca Raton, Florida. • Bhushan, B. (2001), Modern Tribology Handbook, Vol. 1 & 2, CRC, Boca-Raton, Florida. • Bhushan, B. (2002), Introduction to Tribology, Wiley, New York. • Bhushan, B., Fuchs, H., et al. (2004, ’06, ’07, ’08, ‘09), Applied Scanning Probe Methods, Vol. 1-13, Springer-Verlag, Heidelberg, Germany. • Bhushan, B. (2007), Springer Nanotechnology Handbook, second ed., Springer- Verlag, Heidelberg, Germany. • Bhushan, B. (2008), Nanotribology and Nanomechanics – An Introduction, second ed., Springer-Verlag, Heidelberg, Germany. • Bhushan, B. (2008), “Nanotribology, Nanomechanics and Nanomaterials Characterization” Phil. Trans. R. Soc. A 366, 1351-1381. • Bhushan, B. (2009), “Biomimetics – Lessons from Nature: An Overview”, Phil. Trans. R. Soc. A (in press).

Nanoprobehttp://mecheng.osu.edu/nlbb Laboratory for Bio- & Nanotechnology and Biomimetics 48 Questions & Anwers

• Question 1 Questions & Anwers

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