Effect of atomic-scale surface roughness on friction: a molecular dynamics study of diamond surfaces

Abstract We have examined by molecular dynamics simulations the friction which arises when two hydrogen-terminated diamond (111) surfaces are placed in sliding contact. In particular, the effects of load, crystallographic sliding direction, and substitution of surface hydrogen groups by methyl groups on the friction coefficient μ were investigated. For the hydrogen-terminated system, it is possible to have μ approximately equal to zero for certain sliding directions, while μ increases with increasing load for other sliding directions. However, when methyl groups are substituted for some surface hydrogen atoms μ generally increases with increasing load for all sliding directions examined. In this case, the directional anisotropy of μ is less than for the hydrogen-terminated system.