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Dynamic atomic force microscopy (AFM) modes that operate at frequencies faraway from the resonance frequency of the cantilever (off-resonance tapping(ORT) modes) can provide high-resolution imaging of a wide range of sampletypes, including biological samples, soft polymers, and hard materials. Thesemodes offer precise and stable control of vertical force, as well as reducedlateral force. Simultaneously, they enable mechanical property mapping of thesample. However, ORT modes have an intrinsic drawback: a low scan speed due tothe limited ORT rate, generally in the low kHz range. Here, we analyze how theconventional ORT control method limits the topography tracking quality andhence the imaging speed. The closed-loop controller in conventional ORTrestricts the sampling rate to the ORT rate and introduces a large closed-loopdelay. We present an alternative ORT control method in which the closed-loopcontroller samples and tracks the vertical force changes during a defined timewindow of the tip-sample interaction. Through this, we use multiple samples inthe proximity of the maximum force for the feedback loop, rather than only onesample at the maximum force instant. This method leads to improved topographytracking at a given ORT rate and therefore enables higher scan rates whilerefining the mechanical property mapping. Keywords: atomic force microscopy(AFM); off-resonance tapping (ORT); pulsed-force mode; feedback control

Enhanced feedback performance in off-resonance AFM modes through pulse train sampling