Novel Reciprocal Self-Sensing Techniques for Tapping-Mode Atomic Force Microscopy

We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively. A microcantilever, which can be batch fabricated through a standard microelectromechanical system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for actuation and deflection sensing. The setup enables the elimination of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. The voltage to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough which degrades the dynamic range of the sensors significantly. A feedforward control technique is employed to cancel the feedthrough and increase the dynamic range from less than 1 dB to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for TM-AFM imaging.