Nanoscale dowsing with atomic force microscopy: distance and relative humidity contributions to the off-surface electrostatic response of soda lime glass

Piezoresponse force microscopy (PFM) has emerged as a tool of choice to probe ferroelectric materials through electrochemomechanical coupling at the nanoscale. However, this technique is not without its challenges, with artefacts related to electrostatic and topographical features presenting a significant obstacle to the accurate interpretation of PFM data. 

Here, we investigate the bias-dependent off-surface electrostatic response of soda lime glass, a material not traditionally associated with electromechanical activity. Unexpectedly, we observe a distinctive ferroelectric-like hysteresis behaviour that is highly dependent on both the tip-sample separation and relative humidity. We also show the dynamic nature of these interactions, through a temporal analysis of the relaxation of this electrochemomechanical response. 

While the presence of an electrostatic force is expected, we can infer that this hysteretic effect is not inherent to the pure electrostatics of the voltage application and residual surface charges in an air-water capacitor, but is probably due to the incomplete charge and discharge dynamics of the soda lime glass. The choice of tip and the control of environmental conditions are thus essential for the measurement of true electromechanical responses of ferroelectrics.