Surface potential measurement by heterodyne frequency modulation kelvin probe force microscopy in mhz range

Abstract

The chemical and physical processes on surfaces are significantly influenced by the surface potential of materials. When using the frequency modulation Kelvin probe force microscopy (FM-KPFM), which has been widely used for measuring the surface potential distribution with high spatial resolution, it is very difficult to distinguish the surface potential due to the surface state from that due to the bulk state, because the charge transfer between the surface and bulk states occurs at a low-frequency ac bias voltage in the kHz range. Here, we propose a heterodyne FM-KPFM method using a high-frequency ac bias voltage in the MHz range to distinguish the surface and bulk states. This method is based on the heterodyne effect between the mechanical cantilever oscillation and the oscillating electrostatic force. For the first time, we succeeded in achieving the atomic-resolution imaging of the surface potential on an O-rich TiO2(110) surface using the electrostatic interaction in the MHz range. Furthermore, we could measure the upward and downward band bending on the surface at the atomic scale.