Scanning tunneling microscopy, spectroscopy and tunneling-induced light emission on donor-doped BaTiO3

Donor-doped (0.2 mol% La) polycrystalline BaTiO3 has been studied by scanning tunneling microscopy, scanning tunneling spectroscopy, and detecting the tunneling-induced photon emission. A characterization of the grain boundaries was the main aim of our measurements. They were identified by differences in the surface morphology of neighboring grains. The width of the grain boundaries was estimated to be in the order of less than 20 nm. Within the limits of the lateral resolution of the measurements, which was estimated to be of the same magnitude, distinct differences between grains and grain boundaries could not be detected in the photon emission. The results of spectroscopic measurements are discussed in terms of the band structure.