Nanoscale variation in electric potential at oxide bicrystal and polycrystal interfaces

Scanning surface potential microscopy (SSPM), has been used to measure spatial variations in grain boundary properties in SrTiO3 and ZnO. Experimental measurements of a Fe-doped SrTiO3 Σ3 bicrystal are compared to finite element calculations to quantify the effects of tip geometry and sample-tip separation. Experimental and numerical treatments include realistic tip interactions and lateral inhomogeneity in sample properties. A procedure for extracting actual interface potentials from separation dependence is proposed. Both the sign and magnitude of the grain boundary potential barrier measured with SSPM agree with macroscopic measurements. For experimentally available tips, the effect of tip geometry was found not to contribute to uncertainty. In application to polycrystalline materials, the voltage dependence of individual interface properties has been determined in micropatterned, ZnO-based, polycrystalline varistor devices.