Real time reduction of probe-loss using switching gain controller for high speed atomic force microscopy

In this article, a switching gain proportional-integral-differential controller is used to reduce probe-loss affected regions in an image, obtained during tapping mode operation. Switching signal is derived from the "reliability index" signal, which demarcates regions where the tip has lost contact with the sample (probe-loss), within couple of cantilever oscillation cycles, thereby facilitating use of higher than optimal controller gain without deteriorating on-sample performance. Efficacy of the approach is demonstrated by imaging calibration sample at tip velocity close to 240 μm/s and plasmid DNA at tip velocity of 60 μm/s indicating significant reduction of probe-loss areas and recovery of lost sample features.