Noncontact scanning force microscopy using a direct-oscillating piezoelectric microcantilever

This article describes noncontact scanning force microscopes that make use of a new type of direct-oscillating unimorph piezoelectric microcantilever. Since the scanning force microscope system using the piezoelectric cantilever requires no external deflection detector, it is very simple, compact, and is easy to operate in comparison with the conventional system using the optical sensors. In the noncontact operation mode, the piezoelectric cantilever is more preferred to other deflection detectable cantilevers, because it can be directly oscillated by applying voltage to itself. The methods used to detect the resonance shift due to force gradients acting the tip are slope detection and frequency modulation detection. In the slope detection technique, the resonance shift is detected by measuring the change of the amplitude or phase of the induced piezoelectric current. In frequency modulation detection, the resonance shift is detected by direct measurement of the resonance frequency of the current. The piezoelectric microcantilever serves as a resonator in this technique. The constructed noncontact scanning force microscope has been used to obtain the slope detection image of the Au film surface with grains of about 50 nm diam. The measured characteristics data of the fabricated cantilevers allow us to study the dependence of minimum detectable force gradients on the lever dimensions. We have discussed the design of the cantilever for noncontact operations. (C) 1996 American Vacuum Society.