Tribological behavior of polycrystalline and single-crystal silicon

SEM tribometric experiments were performed with polycrystalline silicon (poly-Si) vs. poly-Si and Si(111) vs. Si(111) interfaces in moderate vacuum to 850°C, complementing similar recent experiments on Si(100) vs. Si(100). All friction data agree with a hypothesis associating the wear- and thermal desorption-induced generation and cooling-induced adsorptive passivation of dangling bonds on the sliding surfaces with high and low adhesion and friction, respectively. Strong additional evidence is given for a surface re- and deconstruction-induced, temporary reduction in high temperature friction. The wear rate of the various Si vs. Si specimens (on the order of 10-12 m3 /(N m)) specific to the wide temperature range vacuum test regimen is about 104 times higher than that of unpolished PCD films sliding against themselves under multi-GPa unit loads and similar environmental conditions. In contrast, the characteristic load-carrying capacity of the high-wearing Si, regardless of its crystal structure, was found to be only ∼ 1 MPa. The wear mechanism of the various Si crystallinities was heavily influenced by the agglomeration and plowing of the wear debris particles trapped in the contact zone.