We recently developed a method to directly actuate a cantilever in aqueous solutions by electrostatic force [K.-I. Umeda et al., Appl. Phys. Express 3, 065205 (2010)]. However, the cantilever was actuated by surface stress in a low frequency regime. We solved this problem by applying amplitude-modulated high-frequency electric fields, which actuates the cantilever solely by electrostatic force. The time variations of the self-oscillation frequency of a cantilever and the Au(111) surface images by frequency-modulation atomic force microscopy using acoustic, photothermal, and the improved electrostatic actuation methods were compared, which demonstrates the advantages of the last method such as stability and simplicity in instrumentation.
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