Even for macroscopic interfaces, the actual contact between surfaces occurs at a level of minute asperities that are anywhere from nm to µm in size. Studies at a level of an individual asperity can therefore provide fundamental understanding of specific contributions to friction, which otherwise may be difficult to isolate from each other. Such studies are now possible using the Atomic Force Microscopy (AFM), where the surface, the counter-surface, and the environment can be very well controlled. Because of the small contact sizes that are amenable to AFM measurements and thanks to the ability of our group to carry our large-scale molecular dynamics simulations, it is now possible perform simulations and experiments on the same materials systems and on the same length scales [7, 8]. Nanoscale friction measurements are also important directly for nanotechnology applications. Due to the high surface-to-volume ratio of nanoscale devices, surface forces (adhesion and friction) can become dominant and, for instance, lead to undesirable stiction (i.e., sticking of surfaces of two device components that were meant to be disjoint). Prof. Szlufarska’s group carries out AFM experiments to test properties of new classes of materials (e.g., ultrastable molecular glasses and nanostructured ceramics) and to test predictions made in our molecular simulations on the same materials systems.
[7] M. Mishra, P. Egberts, R. Bennewitz, I. Szlufarska “Friction model for single asperity elastic-plastic contacts”, Phys. Rev. B 86, 045452 (2012)
[8] I. Szlufarska, M. Chandross, R. W. Carpick, “Recent Advances in Single-Asperity Nanotribology”, J. Phys. D: Appl. Phys. 41, 123001 (2008)
Fig.3: (Left) Schematic of a typical AFM (Courtesy of Dr. David Grierson) (Center)A scratch made in AFM experiments on a single crystal SiC with ultrananocrystalline diamond tip. (Right) Depth profile across the groove shown in the center image.