Effect of normal vibration on friction in the atomic force microscopy experiment

We studied the effect of periodic normal (out-of-plane) surface vibrations on friction in an atomic force microscope experiment. Vibration frequency was varied in the range of 1-100 kHz, and vibration amplitude was varied in the range of a few nanometers. We observed a reduction of a few orders of magnitude in friction coefficient due to the periodic vibrations. Friction reduction is over a wide range of vibration frequencies and amplitudes. Very low values (of the order of 0.01) of friction coefficient were measured. Our numerical simulation based on a minimalist modeling qualitatively agrees with the experimental results. Based on numerical simulations, a mechanism of friction reduction and/or increase with normal vibrations is proposed. (c) 2006 American Institute of Physics.