Revealing the Mechanical Contributions to the Signal Origin in Electrochemical Strain Microscopy

Electrochemical strain microscopy (ESM) is typically applied to investigate local ionic motion by detecting surface displacement caused by an applied alternating current (AC) voltage. However, this displacement is not the only factor affecting the measured ESM signal. In this study, a strong correlation between ESM contrast and purely mechanical contrast obtained using contact resonance atomic force microscopy (CR-AFM) is demonstrated. This correlation suggests that additional nonionic mechanisms impact the ESM response. While ionic displacement typically occurs on a scale of a few pico-to nanometer and is most pronounced at low excitation frequencies, the results reveal enhanced contrast at higher frequencies, particularly when exciting the second eigenmode of the cantilever. Correlative measurements demonstrate that this contrast enhancement is present consistently in both ESM and CR-AFM data, suggesting that the mechanical properties of the tip–sample contact have a significant impact on the amplitude of the ESM signal. These findings emphasize the importance of considering mechanical contributions when interpreting ESM measurements, particularly at higher excitation frequencies.