Kelvin Probe Force Microscopy and Its Application to Evaluation of Thin Film Growth

Abstract

The surface potential distribution and the surface charge distribution are very important properties of materials, which influence various physical and chemical processes. In this paper, we describe the measurement principle of Kelvin Probe Force Microscopy (KPFM), which detects the electrostatic force between a tip and a sample surface and can measure the contact potential difference (CPD) between the work function of a tip and that of a sample surface quantitatively. The operation of KPFM is based on the dynamic mode atomic force microscopy (AFM), which uses the enhancement of the force sensitivity by oscillating the cantilever at resonance. We also describe the frequency-modulation (FM) method to measure the very weak tip-sample interaction. Finally, as a practical application of AFM/KPFM, we introduce the experimental result of the discrimination between the CaF₁ interface layer and the CaF₂ bulk layer on thin film epitaxiallly grown on Si(111) surface with high spatial resolution.