Effects of Surface Roughness on the Kinetic Friction of SiC Nanowires on SiN Substrates

The effects of surface roughness on the kinetic friction between SiC nanowires and SiN substrates were investigated by use of experimental testing and numerical modelling. The experimental measurements showed that the shear stress, or the frictional force per unit projected contact area, was significantly affected by the substrate roughness, decreased from 0.38 to 0.02 MPa for the increase in roughness from 0.5 to 23 nm. A power-law relationship between frictional stress and surface roughness was found. The numerical modelling based on the lowest energy principle and the Monte Carlo method revealed that the substrate effect was through the variation in the number of contact asperities between a nanowire and a substrate, which was much fewer on a rougher surface. The real contact area also exhibited a power-law dependence on the substrate roughness. The frictional forces normalized using the real contact areas obtained from the simulation were reasonably consistent, varying from 127 to 166 MPa for the five substrates of different roughnesses.