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

Transcription

1 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 B. Bhushan 1

2 Micro/nanoscale studies Materials/Device Studies Bio/nanotribology Bio/nanomechanics Biomimetics Materials sci., biomedical eng., physics & physical chem. Techniques Materials/coatings SAM/PFPE/Ionic liquids Biomolecular films CNTs AFM/STM Microtriboapparatus Nanoindentor Micro/nanofabrication 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.

3 3

4 Introduction Nanotribology Outline 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 4

5 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,

6 Example of a Magnetic Storage Device Diamond like carbon overcoat 3.5 nm thick Al 2 O 3 -TiC Magnetic rigid disk drive (Bhushan, 1996) MR type picoslider Liquid Lubricant 1-2 nm Diamondlike carbon overcoat 3-5 nm Magnetic coating nm Al-Mg/10 μm Ni-P, Glass or Glass - ceramic mm Thin film disk B. Bhushan. Tribology and Mechanics of Magnetic Storage Devices, 2 nd ed., Springer-Verlag, NY,

7 Examples of MEMS/NEMS and BioMEMS/NEMS shuttle springs gears and pin joint 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) Microengine driven by electrostatically-actuated comb drive Sandia Summit Technologies ( Stuck comb drive

8 Microfabricated commercial MEMS components B. Bhushan. Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg,

9 The generating points of friction and wear due to interaction of a biomolecular layer on a synthetic microdevice with tissue (Bhushan et al., 2006) 9

10 CNT-based Nanostructures MWNT Sheet SWNT biosensor (Chen et al., 2004) The electrical resistance of the system is sensitive to the adsorption of molecules to the nanotube/electrode. Adhesion should be strong between adsorbents and SWNT. (Zhang et al., 2005) Mechanical properties of nanotube ribbons, such as the elastic modulus and tensile strength, critically rely on the adhesion and friction between nanotubes. Nanotube bioforce sensor (Roman et al., 2005) Force applied at the free end of nanotube cantilever is detected as the imbalance of current flowing through the nanotube bearing supporting the nanotube cantilever. The deflection of nanotube cantilever involves inter-tube friction.

11 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,

12 Schematic of a small sample AFM/FFM Schematic of a large sample AFM/FFM 12

13 Results Surface Imaging and Friction STM images of a solvent-deposited C 60 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. 13

14 μ = 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, (2006) National Public Radio, 4/12/95; Business Week, 5/1/95 etc. 14

15 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 Equilibrium position before sliding begins Stick Slip AFM tipcantilever model Sample surface Slip event is a dissipative process Periodic interaction potential 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. 15

16 Scale effect on friction Coefficient of Friction Nanoscale* Microscale Sample RMS* (nm) with Si 3 N 4 tip with Si 3 N 4 ball Si(100) HOPG Natural Diamond DLC film *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) 16

17 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 17

18 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, (2006) 18

19 Friction force (nn) Friction force on log scale (low velocity) 10 Si (100) DLC 5 Friction force (nn) Friction force on log scale Normal load = 100 nn Si (100) Meniscus force dominates DLC Atomic-scale stick slip dominates Viscous shear dominates Phase transformation/ tip jump Friction force (nn) Friction force on linear scale Si (100) DLC Velocity (μm/s) 20 Atomic-scale stick slip dominates Velocity (μm/s) 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, , 2005; J. Vac. Sci. Technol. A 23, 830 (2005); Ultramicroscopy 105, 238 (2005); Z. Tao and B. Bhushan, Rev. Sci Instrum. 77, (2006); J. Vac. Sci. Technol. A (2007) Velocity (μm/s) Effect of velocity on friction force 19

20 Nanofriction maps Contour map showing friction force dependence on normal load and sliding velocity. N. S. Tambe and B. Bhushan, Appl. Phys. Lett. 86, (2005); Nature Mat. In Nanozone, Feb. 17 (2005) 20

21 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). 21

22 Adhesion and Friction between Individual Nanotubes Experimental Schematic (1) Scan of MWNT tip in lateral direction across suspended SWNT bridge (2) Ramp of MWNT tip in vertical direction against suspended SWNT bridge MWNT tip and SWNTs suspended on a micro-trench 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

23 Scan of MWNT tip in lateral direction across suspended SWNT bridge Cantilever tapping amplitude (A) (B) (C) 21 nm 16 nm 0 A B C Cantilever vertical deflection (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: F F = 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 2.4 µm deform more until they detached from each other. 0.8 nm -1.2 nm Multiplying cantilever deflection at the point of detachment with cantilever spring constant gives: F A = 0.7 ± 0.3 nn The coefficient of kinetic friction is calculated from F F / F A : µ = ± Comparable to values reported on graphite on nanoscale. 23

24 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) 24

25 Sample preparation STA: Streptavidin APTES:Aminopropyltriethoxysilane NHS: N-hydroxysuccinimido BSA: Bovine serum albumin 25

26 Schematic representation of deposition of streptavidin (STA) by chemical linker method 26

27 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. 27

28 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 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). 28

29 Montage of some examples from nature Montage of some examples from nature. B. Bhushan, Phil. Trans. R. Soc. A (in press). 29

30 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. SEM of Lotus leaf showing bump structure. Various natural surfaces, including various leaves, e. g. Lotus, are known to be superhydrophobic, due to high roughness 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, (2008)

31 Rolling off liquid droplet over superhydrophobic Lotus leaf with self cleaning ability

32 Roughness optimization model for superhydrophobic and self cleaning surfaces Wenzel s equation: cosθ = R f cosθ o Droplet of liquid in contact with a smooth and rough surface Effect of roughness on contact angle M. Nosonovsky and B. Bhushan, Microsyst. Tech. 11, 535 (2005); Microelectronic Eng. 84, 387 (2007); Ultramicroscopy 107, 969 (2007); J. Phys.: Condens. Matter 20, (2008); US Patent pending (2005)

33 Formation of the composite interface Cassie-Baxter equation: cosθ = R f cosθ f f SL 0 LA = R cos θ f ( R cosθ + 1) f 0 LA f 0 f LA requirement for a hydrophilic surface to be hydrophobic f R cosθ for θ < 90 f 0 LA 0 R f cosθ0 + 1 Y. C. Jung and B. Bhushan, Nanotechnology 17, 4970 (2006); B. Bhushan and Y. C. Jung, J. Phys.: Condens. Matter 20, (2008); M. Nosonovsky and B. Bhushan, Microsyst. Tech. 12, 231 (2006); ibid, 273 (2006)

34 In fluid flow, another property of interest is contact angle hysteresis (θ H ) Increased droplet volume Decreased droplet volume θ adv : Advancing contact angle θ rec : Receding contact angle θ H = θ adv - θ rec If θ H 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 θ adv θ rec R f 1 f LA 2( R (cosθ f rec0 cosθ 0 cosθ + 1) Increase in f LA and reduction in R f decrease adv0 ) for high contact angle (θ 180 ) θadv θ rec B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, (2008); B. Bhushan, M. Nosonovsky, and Y. C. Jung, J. R. Soc. Interf. 4, 643 (2007); M. Nosonovsky and B. Bhushan, Microelectronic Eng. 84, 382 (2007); Nano Letters 7, 2633 (2007); Springer-Verlag, Heidelberg (2008)

35 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 Poly(methyl methacrylate) (PMMA) (hydrophilic) for nanopatterns and micropatterns Hydrophobic coating for PMMA 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, (2008);

36 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 R f 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.

37 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 PF 3 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 (PF 3 ) (SAM) B. Bhushan and Y. C. Jung, Ultramicroscopy 107, 1033 (2007); J. Phys.: Condens. Matter 20, (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, (2008); Mater. Sci. Eng.:R 58, 162 (2007) ; Langmuir 24, 1525 (2008)

38 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 If δ H δ ( 2P D) R 2 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, (2008)

39 Contact angle, hysteresis, and tilt angle on patterned Si surfaces with PF 3 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, (2008)

40 The critical radius of droplet for the transition increases with the pitch based on both the transition criterion and the experimental data.

41 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.

42 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, (2008); Ultramicroscopy (in press); Langmuir (in press); Koch et al., Soft Matter (in press)

43 Fabrication of nanostructure and hierarchical structure Recrystallization of wax tubules Nanostructure Self assembly of the Lotus wax deposited by thermal evaporation 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, (2008); Ultramicroscopy (in press); Langmuir (in press); Koch et al., Soft Matter (in press)

44 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)

45 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.

46 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. 46

47 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. 47

48 References Bhushan, B., Israelachvili, J. N. and Landman, U. (1995), "Nanotribology: Friction, Wear and Lubrication at the Atomic Scale, Nature 374, 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, Bhushan, B. (2009), Biomimetics Lessons from Nature: An Overview, Phil. Trans. R. Soc. A (in press). 48

49 Question 1 Questions & Anwers

50 Question 2 Questions & Anwers

51 Question 3 Questions & Anwers

52 Question 4 Questions & Anwers

53 Question 5 Questions & Anwers

54 Question 6 Questions & Anwers

55 Question 7 Questions & Anwers

56 Question 8 Questions & Anwers