KPFM and its Use to Characterize the CPD in Different Materials

Kelvin probe force microscope (KPFM), based on the Kelvin method, measures the contact potential difference (CPD) between a conducting atomic force microscopy (AFM) tip and a sample, and allows to map the work function (𝜙) of the sample. This chapter first introduces principles and theories of KPFM, as well as the effect of measurement mediums, mainly ambient and ultrahigh vacuum (UHV) conditions, on the results of KPFM. Besides present basic principles, it also highlights the potential of KPFM to gain insight into the structural and electronic properties of functional surfaces and interfaces. The chapter then describes details of KPFM instrumentation and operational principles, including comparison of the AM and FM modes, simultaneous mapping of topography, and potential (or 𝜙) positions. KPFM is adopted to characterize the electrical properties of surfaces of metals and semiconductors. In addition, KPFM also shows an interesting advantage in the study of devices including junctions, heterostructrues, field-effect transistors (FETs), and solar cells.