Noise Rejection Mode Imaging of Atomic Force Microscope

This paper presents an imaging mode of atomic force microscope (AFM) that is robust to the environmental acoustic noise. AFM operations are sensitive to external disturbances including acoustic noise, as disturbances to the probe-sample interaction directly results in distortions in the sample images obtained. Although conventionally passive noise cancellation has been employed, the passive-noise apparatus limits the function of AFM and its use in emerging applications. Moreover, residual noise still persists. In this work, we propose a noise rejection mode (NRM) of AFM imaging to avoid and eliminate the acoustic-caused disturbance to the imaging process. Contrary to other existing AFM imaging modes, in the proposed NRM approach, the set-point of the feedback loop for tracking the sample topography is adjusted online such that the AFM system is insensitive and thereby, robust to the environmental noise. Then, a feedforward controller is augmented to counter act the noise-caused vibration in the feedback loop. Both the set-point adjustment and the feedforward noise cancellation are implemented through finite-impulse-response (FIR) filters. Experimental examples are presented and discussed to illustrate the proposed technique.