ICMCTF2009 Session E5: Nano- and Microtribology Instrumentation and Characterization

Tuesday, April 28, 2009 1:30 PM in Room California
Tuesday Afternoon

Time Period TuA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2009 Schedule

Start Invited? Item
1:30 PM Invited E5-1 Nanotribology, Nanomechanics and Materials Characterization Studies and Applications to Bio/Mamotechnology and Biomimetics
B. Bhushan (The Ohio State University)

At most solid-solid interfaces of technological relevance, contact occurs at numerous asperities. A sharp atomic/friction force microscope (AFM/FFM) tip sliding on a surface simulates just one such contact. However, asperities come in all shapes and sizes which can be simulated using tips of different shapes and sizes. AFM/FFM techniques are commonly used for tribological studies of engineering surfaces at scales ranging from atomic- to microscales. Studies include surface characterization, adhesion, friction, scratching/wear, boundary lubrication, and surface potential and capacitance mapping1-5. AFMs and their modifications are also used for nanomechanical characterization, which includes measurement and analysis of hardness, elastic modulus and viscoelastic properties, and in-situ localized deformation studies. State-of-the-art contact mechanics models have been developed and are used to analyze dry and wet contacting interfaces. Experimental data exhibit scale effects in adhesion, friction, wear, and mechanical properties, and a comprehensive model for scale effects due to adhesion/deformation and meniscus effects has been developed. Generally, coefficients of friction and wear rates on micro- and nanoscales are smaller, whereas hardness is greater. Therefore, micro/nanotribological studies may help define the regimes for ultra-low friction and near-zero wear. New lubrication strategies such as the use of self-assembled monolayers promise to be very versatile and effective at these scales. To improve adhesion between biomolecules and silicon based surfaces, chemical conjugation as well as surface patterning have been used6. Friction and wear studies of biomolecules show that these act as a lubricant but wear away in AFM experiments, even when attached to the underlying substrate7. In the area of biomimetics, surface roughness present on lotus and other leaves has been measured and the surface films are characterized to understand the mechanisms responsible for superhydrophobicity (high contact angle). A model for surface-roughness-dependent contact angle has been developed and optimum distributions have been developed for superhydrophobic surfaces8-10. These fundamental nanotribological studies provide insight to molecular origins of interfacial phenomena including adhesion, friction, wear and lubrication. Friction and wear of lightly loaded micro/nano components are highly dependent on the surface interactions (few atomic layers). Nanotribological and nanomechanics studies are also valuable in the fundamental understanding of interfacial phenomena in macrostructures to provide a bridge between science and engineering. This talk will present an overview of nanotribological and nanomechanics studies and their applications.

1Bhushan, B., Israelachvili, J.N., and Landman, U., “Nanotribology: Friction, Wear and Lubrication at the Atomic Scale,” Nature, Vol. 374, 1995, pp. 607-616.

2Bhushan, B., Handbook of Micro/Nanotribology, second ed., CRC Press, Boca Raton, Florida, 1999.

3Bhushan, B. et al.., Applied Scanning Probe Methods, Vol. 1-10, Springer-Verlag, Heidelberg, Germany, 2004, ‘06, ‘07, ‘08.

4Bhushan, B., Nanotribology and Nanomechanics – An Introduction, Springer-Verlag, Heidelberg, Germany, 2005.

5Bhushan, B., Springer Handbook of Nanotechnology, second ed., Springer-Verlag, Heidelberg, Germany, 2007.

6Bhushan, B., Tokachichu, D. R., Keener, M. T., and Lee, S. C., “Morphology and Adhesion of Biomolecules on Silicon Based Surfaces,” Acta Biomat. 1, 327-341 (2005).

7Bhushan, B., Tokachichu, D. R., Keener, M. T., and Lee, S. C., “Nanoscale Adhesion, Friction and Wear Studies of Biomolecules on Silicon Based Surfaces,” Acta Biomaterialia 2, 39-49 (2006).

8Burton Z. and Bhushan, B., “Hydrophobicity, Adhesion, and Friction Properties of Nanopatterned Polymers and Scale Dependence for Micro- and Nanoelectromechanical Systems,” Nano Letters 5, 1607-1613 (2005).

9Bhushan, B., Nosonovsky, M., and Jung, Y. C., “Towards Optimization of Patterned Superhydrophobic Surfaces,” J. Roy. Soc. Interf. 4, 643-648 (2007).

10Nosonovsky, M. and Bhushan, B., “Multiscale Friction Mechanisms and Hierarchical Surfaces in Nano- and Bio-Tribology,” Mat. Sci. Eng.R 58, 162-193 (2007).

2:10 PM E5-3 Nanotribology of WSC and MoSeC Self-Lubricant Coatings
T. Polcar (SEG-CEMUC University of Coimbra & Czech Technical University - Prague, Czech Republic); M. Evaristo (University of Coimbra, Portugal); R. Colaço (Instituto Superior Tecnico, Portugal); A. Cavaleiro (University of Coimbra, Portugal)
Transition metal dichalcogenides alloyed with carbon (TMD-C), namely WSC and MoSeC, deposited by magnetron sputtering were thoroughly studied with respect to their structure, mechanical and tribological properties. It was shown that TMD-C represented a new class of self-lubricating coatings maintaining low friction (below 0.05) in different environments, such as dry and humid air, elevated temperature or contact pressure. The coatings exhibited extremely high load-bearing capacity connected with remarkable low friction coefficient and wear rate. The unique tribological properties were attributed to two predominant features: (1) the formation of a thin tribolayer consisting of pure transition metal dichalcogenide (TMD) with basal planes optimally oriented for the low friction, i.e. parallel to the coating surface, and (2) the reorientation of the disordered TMD platelets under sliding. In this study, a nanotribometer (pin-on-plate) and atomic force microscope (AFM) with lateral force measurement (LFM) have been used to evaluate the nanotribology of selected TMD-C coatings. The friction under different contact pressure has been evaluated and compared with the macroscopic friction obtained on a standard pin-on-disc tribometer. The wear tracks have been characterized either by depth sensing methods or Raman spectroscopy, in order to determine the possible structural transformations in the contact. Moreover, the same techniques have been applied to the macroscopic wear tracks, where nanotribology helped to characterize the frictional properties of tribolayer.
2:30 PM E5-4 Micro-Tribological Performance of Metal/ MoS2 Lubricants
P. Stoyanov, R. Chromik (McGill University, Canada); J.R. Lince (The Aerospace Corporation)
Solid lubricant coatings with co-sputtered metal and MoS2 have shown favorable macrotribological properties at a wide range of contact stresses and humidity levels. These materials are also candidates for microcontacts and micro-electromechanical systems (MEMS), but their performance at this scale is poorly understood. For this study, microtribological properties of Au/ MoS2 and Ti/ MoS2 coatings, with varying metal additives of 0-80 at.% and 0-10 at.% respectively, were examined using a nanoindentation instrument. Titanium and gold were chosen for this study as metal additives due to their different influence on the mechanical properties of the coating. The hardness, H, and reduced modulus, E, of the coatings varied with the different additives and increased with increasing the metal composition. Au/ MoS2 coatings had H = 1-2 GPa and E = 40-90 GPa, whereas the hardness and the reduced modulus for Ti/ MoS2 was 5-6 GPa and 100-120 GPa respec tively. Reciprocating microscratch tests were performed with spherical diamond tips with radii between 10 µm and 100 µm. A range of normal loads were used between 0.2 mN and 5.0 mN. Characterization of the wear track and transfer films was performed using a micro-Raman spectrometer and an atomic force microscope. Friction measurements were analyzed with a contact model that contains the Hertzian elastic term and a plowing component. Non-linear fitting with the model revealed a variation in the two friction components at higher contact stresses with respect to the different metal concentration (i.e. the plowing component decreases with increasing the metal additive). These results were correlated to the mechanical properties, difference in the transfer film formation, and the surface of the wear track.
2:50 PM Invited E5-5 Application of Diamond-Like Nanocomposite Coatings for Microsystems Tribology1
S. Prasad (Sandia National Laboratories); T. Scharf (The University of North Texas)

A variety of fabrication methods are available to build Microsystems: bulk micromachining, surface micromachining (SMM), LIGA (German acronym for Lithography, Galvanoformung und Abformung), and meso-scale machining. Microsystems fabricated by LIGA and meso-scale machining are more amenable to applying thin films and coatings to mitigate friction and wear. The major focus of this presentation will be the on tribological issues associated with structures created in the LIGA process, specifically electroformed metal structures with dimensions of 0.01 to several mm, and thickness up to 500 µm. Diamond-like nanocomposite (DLN) coatings processed from siloxane precursors by plasma enhanced chemical vapor deposition are well known for their low friction and wear behavior.

In this study, we have examined the feasibility of applying these coatings on the sidewalls of LIGA-fabricated microsystems parts. Novel tribological tests were designed to evaluate the frictio n behavior of coated parts in planar-sidewall and sidewall-sidewall contacts, in regimes relevant to MEMS. Friction coefficients of DLN coated LIGA parts ranged from an extremely low value of 0.02 in dry nitrogen to 0.2 in air with 50% RH, with minimal amounts of wear in both environments.

Like many solid lubricating materials, DLN coatings exhibited non-Amontonian friction behavior; with coefficient of friction (COF) decreasing with an increase in Hertzian contact stress. The main mechanism responsible for low friction and wear is governed by the interfacial sliding between the DLN coating and the friction-induced transfer film on the counterface. This interfacial shear strength, computed from COF-inverse Hertzian contact stress plots, was found to be 9 Mpa in dry nitrogen and 78 Mpa in humid air. Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) analysis of the interfaces (wear tracks and transfer films) was used to gain a fundamental understanding of tr ibochemical phenomena. The role of finite element analysis and novel characterization techniques (e.g., FIB, EBSD, Micro-impact testing) to evaluate the surface coatings for microsystems technology will be discussed.

1Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

3:30 PM E5-7 Nanotribological Properties of Topographically-Chemically Modified Silicon Surfaces
D.C. Pham, R.A. Singh, K. Na, S. Yang, E.-S. Yoon (Korea Institure of Science and Technology, Korea)
This work reports on the effect of combination of topographical and chemical modifications on the nano-scale adhesion and friction properties of the silicon surface. Silicon wafers (100) were patterned into nanopillars by MEMS fabrication process. The patterned surfaces were then chemically treated by coating thin diamond-like carbon (DLC) film (thickness 20 nm) using a plasma-assisted chemical vapor deposition method. The morphology and hydrophobicity of modified surfaces were investigated by scanning electron microscopy (SEM) and a water contact angle analyzer. The surfaces were tested for their adhesion and friction properties at nanoscale using an atomic force microscope (AFM). Borosilicate balls with two different sizes mounted on silicon nitride triangle cantilevers were used as tips. Results showed that the combined surface modification of patterning and DLC coating significantly increased hydrophobicity of silicon surface. Both the topographical and chemical mod ifications reduced the adhesion and friction forces; however, it was observed that a combination of these two kinds of modifications was more effective in reducing these forces. The physically reduced area of contact through patterning and the lower interfacial energy of DLC coating together contributed to the reduction in the adhesion and friction of the silicon surfaces with the combined modifications. It was also observed that these adhesion and friction forces increased with the tip size.
3:50 PM E5-8 Nano-Tribological Properties of Undulated Ultra Thin Diamond Patterns
D.-S. Lim, S.K. Lee, J.H. Kim (Korea University, Korea)

Surface roughness controlled ultra thin nano crystalline diamond film was fabricated on Si(100) surface1. To simulate MEMS and NEMS patterned surface, 800 nanometer and 1 micrometer wide lines with 200 nanometer wide space pattern were prepared on Si(100) substrate by E-Beam lithography and RIE process. ESAND (Electrostatic Self-assembly of Nano Diamond) seeding process was employed to initiate nano crystalline diamond growth. For seeding procedure, negatively charged substrate surface was covered with cationic polymer (PMMA) monolayer, and anionic polymer (PSS) coated cationic nano diamond particles were spontaneously attached on the substrate. Through this process, undulated nanocrystalline diamond pattern was successfully formed by conventional hot filament CVD system. The roughness of deposited surface was controlled by regulating the size of seeding nano diamond particles. Crushing nanodiamond aggregates and dispersion of nano diamond solution was performed in attrition milling system. AFM probe was used for the wear test and surface profiling of nanocrystalline diamond coatings. 2D frictional coefficient mapping by LFM (Lateral Force Microscopy) scanning showed low friction coefficient (< 0.1) on line patterned diamond surface, and higher friction coefficient (> 0.3) on narrow area adjacent to undulated pattern edges. With prolonged LFM scanning, the high coefficient of friction was decreased down to below 0.1. The morphology of nanocrystalline diamond was analyzed with Raman spectroscopy.

1J.H.Kim, S.K.Lee, O.M.Kwon, and D.S.Lim, “Ultra Thin CVD Diamond Film Deposition by Electrostatic Self-Assembly Seeding Process with Nano Diamond Particles”, Accepted for Publication in Journal of Nanoscience and Nanotechnology (2007).

4:10 PM E5-9 Nanotribology of Multilayered Nano Thin Films by Molecular Dynamics Simulations
J.-C. Huang, C.-C. Cho (Tungnan University, Taiwan)
The molecular dynamics simulation method was used to investigate the tribological characteristics of multilayered nano thin films. The NVT ensemble principle and COMPASS potential function were employed in the simulation. The multilayered nano thin film contained the Cu and Ni thin films in sequence. The nano tribological phenomena of the Cu/Ni multilayered nano thin film was studied under diamond tool in vacuum and water environments. It was concluded that the nanotribology behavior of Cu/Ni multilayered nano thin film differed under different environments.
Time Period TuA Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2009 Schedule