The effects of thermal annealing on the microstructure at the grain boundary of a 36.8° symmetric  tilt SrTiO3 bicrystal were studied. Scanning tunneling microscopy and atomic force microscopy were used for nondestructive observation of the 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 YBa2Cu3O7-δ films at the bicrystal boundaries originates from the underlying grooved substrates. Defects characterized as holes with diameters ranging from ∼30nm to ∼200nm were also observed.
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