Exploring responsivity, sensitivity and resolution in amplitude modulated AFM: a study of global behavior and parameter influences

TL;DR

This paper clarifies key AFM concepts like sensitivity and resolution and explores how system parameters affect their behavior.

Contribution

A clear definition of sensitivity, resolution, and responsivity in AFM and a model showing how parameters influence global system behavior.

Findings

Analytical equations for amplitude and phase as functions of tip-sample distance were derived.

System parameters like damping ratio and excitation frequency significantly influence sensitivity.

A self-developed setup was used to validate results and measure amplitude distance curves.

Abstract

In atomic force microscopy, sensitivity is one of the most important characteristics as in many measurement applications. Nevertheless, in literature different meanings of the terms sensitivity and resolution can be found. The same holds for the connectected quantity responsivity. Far more, there is no literature showing globally how different system and process parameters influence sensitivity. In this work we want to make a clear definition of these term in the context of AFM. Additionally, we present the global behavior of the AFM cantilever-sample system in terms of responsivity, noise, and sensitivity. An analytical model is derived that shows this system behavior. This is achieved by finding simple analytical equations for amplitude and phase as functions of the tip-sample distance assuming small amplitudes. Furthermore, the derived equations are scaled to reduce the amount of parameters and get a more generalized form. The scaled equations are analyzed to show the influence of system parameters like damping ratio, excitation frequency and sample parameters on the global system behavior. With that, parameter for best sensitivity can be found. For larger amplitudes where the analytical model is not valid, a numerical model solved with numerical continuation is used to gain further results showing the difference between non-contact and intermittent mode. For validation, we show experimental amplitude distance curves measured with a self-developed setup. This setup is a new possibility to measure amplitude distance curves in an open and flexible environment without the need of having a commercial AFM system.

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