Nanometer-scale variations in interface potential by scanning probe microscopy

The local electrical potential at individual grain boundaries and the poten tial distributions across polycrystalline samples have been measured by usi ng scanning surface potential imaging with an atomic force microscope. Indi vidual grain boundaries are isolated for measurement by micropatterning an array of contacts onto the surface of a ZnO-based varistor material. Quanti fication of the voltage dependence of the local voltage decrease and resist ivity is illustrated. Comparisons are made by using optical and electron mi croscopy and spectroscopy. On a larger scale, potential distributions are m apped in a polycrystalline ZnO-NiO system that exhibits positive temperatur e coefficient of resistivity behavior.