Correlation between drive amplitude and resonance frequency in electrochemical strain microscopy: Influence of electrostatic forces

Abstract

Electrochemical strain microscopy (ESM) is based on the detection of the surface deformation of electrochemical materials induced by local electrical excitation via an AFM tip. Here, we compare the two common excitation methods, dual ac resonance tracking and band excitation, for resonance–amplified electrochemical strain microscopy. By means of these methods, we characterize two different materials, a mixed electronic-ionic conductor and a pure solid state ion conductor. We find a significant correlation between the resonance frequency and ESM drive amplitude. We performed numerical simulations taking into account the complex interplay of sample-tip interactions, contact mechanics, and cantilever dynamics. These simulations predict a positive amplitude-frequency correlation for pure Vegard strain and negative correlations for local tip/sample and non-local cantilever/sample electrostatic forces. These results are important for the quantitative interpretation of ESM-based images.