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 F_(N) and scan duration t, the length of the tips in this work decreases approximately as (F_(N)t)~(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.
展开▼
