Nanofretting behaviors of monocrystalline silicon (1 0 0) against diamond tips in atmosphere and vacuum

With an atomic force microscopy, the tangential nanofretting behaviors of monocrystalline silicon (1 0 0) were investigated by using spherical diamond tips under atmosphere and vacuum conditions, respectively. Different from fretting, the nanofretting damage of silicon may successively experience two progresses, the generation of hillocks and grooves, with the increase in normal load. The critical contact pressure corresponding to the transition of the damage mode was found to be close to the hardness of Si(1 0 0). Due to the absence of water and oxygen in vacuum, the tangential force in nanofretting was a little lower than that in atmosphere. Compared to those in atmosphere, the nanofretting scars in vacuum exhibited higher hillock at low load but shallower groove at high load, which could be explained as the “soft coating” effect of oxide layer on Si(1 0 0) surface.