In order to test recently predicted ballistic nanofriction (ultra-low drag and enhanced lubricity) of gold nanocrystals on graphite at high surface speeds, we use the quartz microbalance technique to measure the impact of deposition of gold nanocrystals on graphene. We analyze our measurements of changes in frequency and dissipation induced by nanocrystals using a framework developed for friction of adatoms on various surfaces. We find the lubricity of gold nanocrystals on graphene to be even higher than that predicted for the ballistic nanofriction, confirming the enhanced lubricity predicted at high surface speeds. Our complementary molecular dynamics simulations indicate that such high lubricity is due to the interaction strength between gold nanocrystals and graphene being lower than previously assumed for gold nanocrystals and graphite.

We report a joint theoretical and experimental study of the tribological properties of gold-yttrium stabilized zirconia (YSZ) based nanocomposite coatings, with a focus on the role of nanocrystalline grain size. Nanocomposites hold great promise for space and ambient applications, on account of their ability to adapt to and exhibit low friction and wear rates in constantly varying environmental conditions. Their internal structure has been the topic of prior literature, but the impact of grain size on tribological performance has heretofore not been considered, and the surface topology has not been reported. As such, we have performed both experimental and theoretical studies, to model the impact of grain size on film stress and wear attributes, and to document surface region grain size distributions through scanning tunneling microscopy (STM) measurements of self-affine fractal scaling properties. Nanocrystalline gold crystal sizes, as determined from STM and x-ray diffraction (XRD) data are consistent with those inferred from high resolution transmission electron microscopy (HRTEM) measurements. Our modeling results associate smaller grain sizes with lower wear rates, consistent with experiments. The findings show promise for nanoscale customization of coatings so as to tailor them at the nanoscale in an application specific manner.