Inverting dynamic force microscopy: From signals to time-resolved interaction forces

TLDR

Transient nanoscale surface forces govern friction, flow, deformation, and wetting, and dynamic AFM can resolve them on sub‑microsecond, nanometer scales. The study aims to complete dynamic AFM by performing full spectral analysis of the AFM signal. They invert the AFM signal formation to measure the time‑resolved force at the tip via full spectral analysis. The method provides data‑driven insight, revealing that typical imaging applies peak forces over 200 nN—about 100 times stronger than covalent bonds—without requiring prior interaction assumptions.

Abstract

Transient forces between nanoscale objects on surfaces govern friction, viscous flow, and plastic deformation, occur during manipulation of matter, or mediate the local wetting behavior of thin films. To resolve transient forces on the (sub) microsecond time and nanometer length scale, dynamic atomic force microscopy (AFM) offers largely unexploited potential. Full spectral analysis of the AFM signal completes dynamic AFM. Inverting the signal formation process, we measure the time course of the force effective at the sensing tip. This approach yields rich insight into processes at the tip and dispenses with a priori assumptions about the interaction, as it relies solely on measured data. Force measurements on silicon under ambient conditions demonstrate the distinct signature of the interaction and reveal that peak forces exceeding 200 nN are applied to the sample in a typical imaging situation. These forces are 2 orders of magnitude higher than those in covalent bonds.