Nanoscale ultrasonics in liquid environment

Abstract

I report on the feasibility to implement Ultrasonic Atomic Force Microscopy techniques in liquid environments taking advantage of the mechanical diode effect. When using the mechanical diode mode, the inertia of the cantilever allows us to detect ultrasound without monitoring any particular cantilever resonance. It is shown that mechanical diode signals in liquids exhibit a similar dependence on the ultrasonic excitation amplitude and tip-sample normal force as in air. Moreover, Ultrasonic Force Microscopy on samples of biological interest such as lipid bilayers yields to reasonable contrast. In some cases, apparent mechanical-diode signals are detected out-of-contact, with the cantilever far distant from the sample surface. © 2008 IOP Publishing Ltd.