Direct Measurement of Storage and Loss Behavior in AFM Force-Distance Experiments Using the Modified Fourier Transformation

TL;DR

This paper introduces a novel Fourier transform-based method to directly measure the storage and loss behavior of materials in AFM experiments, eliminating the need for model fitting and enabling more accurate material characterization.

Contribution

The paper presents a modified Fourier transform technique for direct, model-free measurement of viscoelastic properties in AFM force-distance data, with options for subsequent model fitting.

Findings

Enables direct measurement of storage and loss moduli without fitting models.

Provides a Fourier domain framework for common viscoelastic models.

Facilitates better selection of appropriate viscoelastic models for materials.

Abstract

Force-distance curve experiments are commonly performed in Atomic Force Microscopy (AFM) to obtain the viscoelastic characteristics of materials, such as the storage and loss moduli or compliances. The classic methods used to obtain these characteristics consist of fitting a viscoelastic material model to the experimentally obtained AFM data. Here, we demonstrate a new method that utilizes the modified discrete Fourier transform to approximate the storage and loss behavior of a material directly from the data, without the need for a fit. Additionally, one may still fit a model to the resulting storage and loss behavior if a parameterized description of the material is desired. In contrast to fitting the data to a model chosen a priori, departing from a model-free description of the material's frequency behavior guides the selection of the model, such that the user may choose the one that is most appropriate for the particular material under study. To this end, we also include modified Fourier domain descriptions of commonly used viscoelastic models.