Video-Rate Lissajous-Scan Atomic Force Microscopy

Raster scanning is common in atomic force microscopy (AFM). The nonsmooth raster waveform contains high-frequency content that can excite mechanical resonances of an AFM nanopositioner during a fast scan, causing severe distortions in the resulting image. The mainstream approach to avoid scan-induced vibrations in video-rate AFM is to employ a high-bandwidth nanopositioner with the first lateral resonance frequency above 20 kHz. In this paper, video-rate scanning on a nanopositioner with 11.3-kHz resonance frequency is reported using a smooth Lissajous scan pattern. The Lissajous trajectory is constructed by tracking two sinusoidal waveforms on the lateral axes of the nanopositioner. By combining an analog integral resonant controller (IRC) with an internal model controller, 1-and 2-kHz single tone set-points were successfully tracked. High-quality time lapsed AFM images of a calibration grating recorded at 9 and 18 frames/s without noticeable image distortions are reported.