The implementation of contact mode Kelvin probe force microscopy (cKPFM) utilizes the electrostatic interactions between tip and sample when the tip and sample are in contact with each other. Surprisingly, the electrostatic forces in contact are large enough to be measured even with tips as stiff as 4.5 N/m. As for traditional noncontact KPFM, the signal depends strongly on electrical properties of the sample, such as the dielectric constant, and the tip properties, such as the stiffness. Since the tip is in contact with the sample, bias-induced changes in the junction potential between tip and sample can be measured with higher lateral and temporal resolution compared to traditional noncontact KPFM. Significant and reproducible variations of tip-surface capacitance are observed and attributed to surface electrochemical phenomena. Observations of significant surface charge states at zero bias and strong hysteretic electromechanical responses at a nonferroelectric surface have significant implications for fields such as triboelectricity and piezoresponse force microscopy.
Keywords: HfO2; charge storage; electrostatics; scanning probe microscopy; thin films.