Multi-asperity nanotribological behavior of single-crystal silicon: Crystallography-induced anisotropy in friction and wear

The micro/nanotribological behaviors of monocrystalline silicon wafers – displaying various orientations and roughnesses – rubbing on metals and ceramics balls are investigated under multi-asperity low contact pressures. Whatever the ballʹs materials, results reveal a crystallography-induced anisotropy in friction due to crystallographic orientation of the wafer. This anisotropy leads to a time-dependent seizure mechanism – connected to the surface energy of the wafer itself linked to its crystal orientation. The wafer roughness mainly influences the third body generation rate and finally controls the seizure mechanism. When carbon nitride coatings are deposited on wafers, anisotropy does completely vanish: friction and wear mechanisms are instead controlled by the surrounding environment.