Piezoelectric Sensor for Detecting Force Gradients in Atomic Force Microscopy

This paper presents a piezoelectric sensor for detecting force gradients in the noncontact atomic force microscope (AFM). To simplify the force gradient detecting system of the noncontact AFM, the direct sensing cantilever with a ZnO piezoelectric film has been developed. The signal related to the vibration amplitude of the cantilever end is measurable by detecting the charge induced by the piezoelectric effect. The gradient of the force between the tip of the vibrating cantilever driven by an external oscillator and the sample modifies the vibration amplitude of the lever, hence inducing a change of the piezoelectric charge signal. We have adapted the transfer matrix method for calculating the change of the piezoelectric charge due to the gradient of the force. The piezo-electric signal trace has been recorded as a function of sample displacement. We have converted the recorded data to force gradients using a transfer matrix.