Friction,Wear, and Aging of an Alkoxy-monolayer Boundary Lubricant on Silicon

We study the friction, wear, and aging of a model boundary lubricant, an alkoxy monolayer covalently bonded to a Si(111) surface, using an interfacial force microscope with a spherical diamond probe. The robust alkoxy bond creates a film that effectively lubricates and prevents wear of Si at stresses comparable to those found in microelectromechanical systems devices. Sliding on the monolayer over 50 nm produced friction approximately three times greater than that of sliding over molecular length scales (∼2 nm); this is attributed to deformation dynamics of the experiment. By repeated scanning over the same location, we observed wear on a level that reduces the friction by thinning and/or reordering the monolayer film.