The Imaging Mechanism of Atomic-scale Kelvin Probe Force Microscopy and its Application to Atomic-Scale Force Mapping

Abstract

Kelvin probe force microscopy (KPFM) using noncontact atomic force microscopy (NC-AFM) has been utilized for years and has achieved true atomic-scale resolution in the measurement of contact potential difference (CPD). However, the meaning of atomic-scale CPD images has not been clearly explained. In this paper, we propose a novel model which explains the imaging mechanism of atomic-scale KPFM. Our model shows that the cantilever oscillation induced by an AC electric field, which is applied for KPFM measurement, brings about the atomic resolution in CPD images. We show experimental evidence of our model by measuring the dependence of the cantilever oscillation and the frequency-shift signal on the tip-sample distance. We conclude that the CPD images reflect the interaction strength between the tip and the sample surface rather than the electrostatic force. Finally, we propose a novel method for force mapping based on our model.