Friction and wear of diamond-silicon nano-systems: Effect of moisture and surface roughness

Many micro/nano-electro-mechanical systems have components in relative contact motion. This paper carries out a molecular dynamics analysis to understand how moisture and slider surface roughness influence the friction and wear behaviour of a nano-system. The nano-sliding was between a rough diamond slider and monocrystalline silicon (1 0 0) surface with a thin water layer. The TIP4P model was used to describe the water. The Lennard-Jones interactions were used for the pairs of unlike molecules. It was found that the wear of silicon increases with the slider roughness. The water molecules can get into the cavities of damaged zones, leading to a thick layer of amorphous silicon. Under higher roughness conditions, the presence of water alters the friction characteristics by reducing the silicon-diamond contact area, but has no significant effect on the overall wear. It was demonstrated that surface-surface interactions are important to friction and adhesion, and that wear occurs as the distortion of a few top layers of silicon atoms when the roughness exceeds critical amplitude.