Impact of substrate corrugation on the sliding friction levels of adsorbed films

We report a quartz crystal microbalance (QCM) study of sliding friction for solid xenon monolayers at 77 K on Cu(111), Ni(111), graphene/Ni(111), and C-60 substrates. Simulations have predicted a strong dependence of phononic friction coefficient (eta) on surface corrugation in systems with similar lattice spacing, eta proportional to U-0(2), but this has never before been shown experimentally. In order to make direct comparisons with theory, substrates with similar lattice spacing but varying amplitudes of surface corrugation were studied. QCM data reveal friction levels proportional to U-0(2), validating current theoretical and numerical predictions. Measurements of Xe/C-60 are also included for comparison purposes.