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

We studied the thermal annealing effects on the micro structure of the grain boundary of a 36.8° and a 24° symmetric [100] tilt SrTiO₃ bicrystal. Scanning tunneling microscopy and atomic force microscopy were used for the observation of the vacuum exposed boundary structures. Annealing the bicrystalline substrates at temperatures as low as 780°C led to the formation of grooves at their boundaries. This provides direct evidence that the thickness depression of YBa₂Cu₃O_7-δ films at the bicrystal boundaries originates from the underlying grooved substrates. A simple structural model has been proposed to explain the 1/φ dependence of the normalized critical currents flowing cross the grain boundaries. PACS nos: 61.16.Ch, 61.72.Mm, 68.35.-p, 68.35.Ct, 68.35.