Single asperity tribochemical wear of silicon nitride studied by atomic force microscopy

Abstract

Nanometer scale single asperity tribochemical wear of silicon nitride was examined by measuring the wear of atomic force microscope tips translated against a variety of substrates in aqueous solutions. We show that the chemical nature of the substrate plays an important role: significant wear was observed only when the substrate surface is populated with appropriate metal-hydroxide bonds. Mica and calcite substrates, whose water-exposed cleavage surfaces lack these bonds, produced little if any tip wear. As a function of contact force FN and scan duration t, the length of the tips in this work decreases approximately as (FNt)0.5. We propose that pressure-induced intermediate states involving hydroxyl groups form on both the tip and the substrate; chemical reactions subsequently form transient bridging chemical bonds that are responsible for tip wear.