Local impedance imaging and spectroscopy of polycrystalline ZnO using contact atomic force microscopy

Abstract
A current detection scanning probe technique is developed that quantifies frequency-dependent local transport properties. The approach, referred to as nanoimpedance microscopy/spectroscopy (NIM), is based on impedance spectroscopy with a conductive atomic force microscopy(AFM) tip. NIM is applied to study the quality of a tip/surface contact and transport behavior of individual grains and grain boundaries in polycrystallineZnO. Impedance spectra were measured in the frequency range 40 Hz to 110 MHz, and the grain boundaryproperties are studied by nonlinear fitting of experimental data to an equivalent circuit. Two-terminal measurements are performed in the vicinity of a single ZnOgrain boundary and the Cole–Cole plot indicates two major relaxation processes attributed to grain boundary relaxation and tip/surface contact.