Microscopic structure of SrTiO3 bicrystal boundaries studied with scanningtunneling and atomic force microscopy

We studied the thermal annealing effects on the microstructure of the grain boundary of a 36.8 degrees and a 24 degrees symmetric [100] tilt SrTiO3 bi crystal. Scanning tunneling microscopy and atomic force microscopy were use d for the observation of the vacuum exposed boundary structures. Annealing the bicrystalline substrates at temperatures as low as 780 degrees C led to the formation of grooves at their boundaries. This provides direct evidenc e that the thickness depression of YBa2Cu3O7-delta films at the bicrystal b oundaries originates from the underlying grooved substrates. A simple struc tural model has been proposed to explain the 1/theta dependence of the norm alized critical currents flowing cross the grain boundaries. (C) 1998 Elsev ier Science S.A. All rights reserved.