ULTRASOUND INDUCED LUBRICITY IN MICROSCOPIC CONTACT

A physical effect of ultrasound induced lubricity is reported. We stud ied the dynamic friction dependence on out-of-plane ultrasonic vibrati on of a sample using friction force microscopy and a scanning probe te chnique, the ultrasonic force microscope, which can probe the dynamics of the tip-sample elastic contact at a submicrosecond scale. The resu lts show that friction vanishes when the tip-surface contact breaks fo r part of the out-of-plane vibration cycle. Moreover, the friction for ce reduces well before such a break, and this reduction does not depen d on the normal load. This suggests the presence on the surface of a l ayer with viscoelastic behavior. (C) 1997 American Institute of Physic s.