Mechanics and Computation / View source

for Atomic-Scale Friction and Wear of Single Asperities
=Robert Carpick, Ph.D.=

===April 5, 2012===

"Atomic-Scale Friction and Wear of Single Asperities"

R.W. Carpick, Professor and Chair
Mechanical Engineering and Applied Mechanics Dept., University of Pennsylvania

I will discuss recent experimental studies of nanoscale single asperity contacts that reveal surprising new behavior and insights. First, the behavior of nanoscale contacts with truly 2-dimensional materials including graphene will be discussed. Although the friction force exhibits a significant dependence on the number of 2-D layers as previously reported1, adhesion (the pull-off force) does not. However, studies as a function of scanning history reveal further complexities that arise from the combined effects of high flexibility and variable substrate interactions that occur at the limit of atomically-thin sheets. 

I will then discuss nanoscale wear. A better understanding of the physics of wear would allow the development of rational strategies for controlling it at all length scales. As well, wear is a primary limitation of devices such as micro-/nano-electromechanical systems (MEMS/NEMS).  We show that ultrastrong materials can be used to be greatly reduce nanoscale wear2-5. We have also demonstrated the ability to characterize single-asperity wear with a high degree of precision by performing in-situ wear tests inside of a transmission electron microscope.  Silicon probes of different initial radii and shape were slid against a flat diamond substrate.  The shape evolution and volume loss due to wear are well described by kinetic model based on stress-assisted bond breaking mechanisms, allowing new insights to be gained about the kinetics of atomic-scale wear6.  

1.	Lee, C., Li, Q., Kalb, W., Liu, X.-Z., Berger, H., Carpick, R.W. and Hone, J. Frictional characteristics of atomically-thin sheets. Science 328, 76-80 (2010).
2.	Lantz, M.A., Gotsmann, B., Jaroenapibal, P., Jacobs, T.D.B., O'Connor, S.D., Sridharan, K. and Carpick, R.W. Wear-resistant nanoscale silicon carbide tips for scanning probe applications. Advanced Functional Materials, on line (2012).
3.	Bhaskaran, H., Gotsmann, B., Sebastian, A., Drechsler, U., Lantz, M., Despont, M., Jaroenapibal, P., Carpick, R.W., Chen, Y. and Sridharan, K. Ultra-low nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like-carbon. Nature Nanotech. 5, 181-185 (2010).
4.	Fletcher, P.C., Felts, J.R., Dai, Z., Jacobs, T.D., Zeng, H., Lee, W., Sheehan, P.E., Carlisle, J.A., Carpick, R.W. and King, W.P. Wear-resistant diamond nanoprobe tips with integrated silicon heater for tip-based nanomanufacturing. ACS Nano 4, 3338-3344 (2010).
5.	Liu, J., Grierson, D.S., Notbohm, J., Li, S., O’Connor, S.D., Turner, K.T., Carpick, R.W., Jaroenapibal, P., Sumant, A.V., Carlisle, J.A., Neelakantan, N. and Moldovan, N. Preventing nanoscale wear of atomic force microscopy through the use of monolithic ultrananocrystalline diamond probes. Small 6, 1140-1149 (2010).
6.	Jacobs, T.D., Gotsmann, B., Lantz, M.A. and Carpick, R.W. On the application of transition state theory to atomic-scale wear. Tribol. Lett. 39, 257 (2010).
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