Novel Method for Detecting Resonant Frequency Shift in Atomic Force Microscopy

Abstract
This paper describes a simple method for detecting the resonant frequency shift caused by the forces between a sample and the tip of the cantilever in an atomic force microscope (AFM). This method is based on the fact that the impedance of a piezoelectric element reflects its mechanical resonant states and varies sensitively near the resonant frequencies as a function of frequency. A resonance shift therefore shifts the impedance curve. The forces are detected by sensing the impedance of a cantilever made of piezoelectric material which is vibrated near its resonant frequency. The tip-to-sample spacing is maintained by keeping changes in impedance constant. This method greatly simplifies the AFM, allowing us to use a scanning tunneling microscope as an AFM simply by exchanging the tip probe.

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