Coherent Phonon Generation in the Process of Friction

After the pioneering friction experiments on an atomic scale by Mate, McClelland, Erlandson and Chiang in 1987 it seems well established that the origin of the dissipation during the process of friction is the generation of phonons by a stick-slip mechanism. Less clarity exists about the type of phonons generated. In this paper we show that — besides high frequency molecular vibrations — also low frequency (MHz) ultrasonic waves including surface acoustic waves are expected to be excited in the process of friction. Vice versa, the friction force can probably be strongly modified by ultrasonic waves incident on the interface between two sliding solids.