Insights into fluid tapping-mode atomic force microscopy provided by numerical simulations

Abstract

In an attempt to understand the physics underlying tapping mode atomic force microscopy (TMAFM) operated in fluids, simulations of complete TMAFM experiments were performed based on a cantilever model invoking the damped driven harmonic oscillator with a single degree of freedom with parameters based on real experiments, the most important of which was a low quality factor (Q). Such a low-Q oscillator captures some of the essential features related to operation of TMAFM in fluids, when compared to real experiments. Fluid TMAFM (a low-Q system) is characterized by a highly anharmonic deflection signal when compared to operation in air (a high-Q system). Our model was able to capture this hallmark of fluid TMAFM without the inclusion of more nuanced hydrodynamic effects. Such modeling can aid in the understanding of tip-sample interactions in fluid TMAFM and in the development of techniques to extract meaningful mechanical surface properties from such interactions.