Surface potential at surface-interface junctions in SrTiO3 bicrystals

An analytical approach to the quantification of electrostatic force microscopy and scanning surface potential microscopy images of systems with electric potential inhomogeneity has been developed in order to determine the interface potential in a donor-doped Sigma5 SrTiO3 grain boundary. The voltage dependencies of the electrostatic force gradient and surface potential verify the solutions. The distance dependencies of force gradient and surface potential were used to quantify the potential at the grain boundary-surface junction and the depletion width. Both measurements yield the same properties despite the difference in imaging mechanisms. The interface potential is shown to result from local charge rather than from a local variation in dielectric constant. The amount of charge implied by an interface potential of 30 mV would render detection of associated defects impossible, but these results represent a lower limit in intrinsic bulk grain boundary potential.