Guidelines for Fast and Nondestructive Imaging in AM-AFM

TL;DR

This paper establishes guidelines for high-speed, nondestructive amplitude-modulation atomic force microscopy of fragile molecules, focusing on minimizing tip-sample interaction forces to enable faster imaging without damage.

Contribution

It provides a theoretical framework identifying force limitations and strategies to optimize imaging speed and safety for fragile biomolecules in AM-AFM.

Findings

Exciting at the resonance slope minimizes feedback error forces.

Analysis of frequency dependence helps estimate interaction forces.

Guidelines improve imaging speed while preserving sample integrity.

Abstract

Amplitude-modulation atomic force microscopy enables observation of fragile molecules at the nanometer scale. To shorten measurement times and capture dynamic molecules, increasing the frame rate is essential. Traditionally, maximum frame rates were thought to be limited by device bandwidth. However, for fragile molecules, imaging speed is often constrained by disruption from tip-sample interaction forces. Despite its significance, no comprehensive theoretical study has addressed this limitation. Here, we establish guidelines for high-speed, nondestructive AM-AFM imaging of fragile molecules. Our analysis identifies two types of forces: an impulsive force on the molecule's uphill side and a steady force linked to error saturation on the downhill side. By examining the frequency dependence of the amplitude-distance curve, we demonstrate that exciting at the resonance slope minimizes feedback error forces and allows for their easy estimation using simple equations. These findings provide valuable insights for studying fragile materials, particularly biomolecules.