Mechanical-Diode Mode Ultrasonic Friction Force Microscopy

We report on a novel technique, Mechanical-Diode Mode Ultrasonic Friction Force Microscopy, based on the study of the additional ultrasound-induced torsion of a cantilever when the cantilever tip scans in contact with a sample surface at low frequency in the presence of shear surface ultrasonic vibration of sufficiently high amplitude (lateral mechanical-diode effect). Data recorded on Si(111) are discussed. The results can be understood by considering the interaction of the tip with the lateral surface sample potential, and the presence of an ultrathin viscous liquid layer at the tip-sample contact which develops hydrodynamic pressure when sheared at ultrasonic velocities