| AVS 60th International Symposium and Exhibition | |
| Tribology Focus Topic | Monday Sessions |
| Session TR+AS-MoM |
| Session: | Bridging Scales and Characterization |
| Presenter: | R.W. Carpick, University of Pennsylvania |
| Correspondent: | Click to Email |
I will discuss recent atomic force microscopy studies of nanoscale single asperity contacts that reveal surprising new behavior and insights. First, the behavior of nanoscale contacts with truly 2-dimensional materials will be discussed. For nanoscale contacts to graphene, we find that the friction force exhibits a significant dependence on the number of 2-D layers1. Surprisingly, 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. An even stronger effect occurs when graphene is fluorinated, where experiments and simulations both show that friction between nanoscale tips and fluorinated graphene (FGr) monolayers exceeds that for pristine graphene by an order of magnitude. The results can be interpreted in the context of the Prandtl-Tomlinson model of stick-slip friction.
I will then discuss new insights into the physics of nanoscale wear. A better understanding of wear would allow the development of rational strategies for controlling it at all length scales, and would help enable applications for which wear is a primary limitation such as micro-/nano-electromechanical systems (MEMS/NEMS). We have 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. For silicon probes 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 mechanisms2. This allows new insights to be gained about the kinetics of atomic-scale wear3.
[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, 2010, 76-80.
[2] Jacobs, T.D. and Carpick, R.W. "Nanoscale Wear as a Stress-Assisted Chemical Reaction," Nature Nanotech., 8, 2013, 108-112.
[3] 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, 2010, 257-271.