Noncontact observation with van der Pol-type self-excited FM-AFM in liquid

Abstract

This study examined a probe cantilever in an atomic force microscope made to vibrate as a van der Pol-type self-excited oscillator using linear and nonlinear feedback to maintain a sufficiently small amplitude of the probe cantilever. Sample surface shape measurements were conducted based on the method proposed herein. In a liquid environment, changes in the amplitude and the equivalent natural frequency of the probe cantilever depending on the atomic force acting between the sample and the probe were investigated experimentally. Results show that even with the noncontact mode using the proposed method in liquid, observation of the sample surface shape can be performed to nanometer order, which is equivalent to the capabilities of existing techniques.