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