Control of a high-speed nanopositioner for Lissajous-scan video-rate AFM

Conventionally, raster-based trajectory is used in atomic force microscopy (AFM) for scanning applications. A triangle reference, which is one of the two input signals used to construct the raster trajectory, contains high order harmonics of its fundamental frequency that can excite the mechanical resonant modes of a nanopositioner. To achieve video-rate scanning, high-bandwidth nanopositioners with lateral dominant modes above 20 kHz are often required when using the raster-pattern in order to avoid vibrations. In this paper, we achieve video-rate scanning on a 11.3-kHz nanopositioner using a smooth scan trajectory known as Lissajous-scan pattern. The Lissajous trajectory can be constructed by tracking two monotonic sinusoidal waveforms on the lateral axes of the nanopositioner. Using the internal model (IM) controllers, good tracking performance of 2-kHz sinusoids was achieved. High-quality AFM images of a calibration specimen were successfully recorded at 18 frames/s using the proposed Lissajous trajectory and control strategies.