Advanced processing and characterization of SrTiO3 single crystals and bicrystals for high-Tc superconducting film substrate

The preparation of single crystals and bicrystals of SrTiO3 and their surface treatment have been investigated to facilitate their application to the substrates of high-Tc superconducting thin films and devices. Bicrystals with different inter-crossing angles were used to elucidate the weak-link characteristics of grain boundary junctions formed in the epitaxial YBa2Cu3O7 δ films on the bicrystal substrates. Wet etching by pH-controlled ammonium fluoride solutions enabled us to finish SrTiO3 surfaces with atomically defined step-and-terrace structures. Atomically controlled two-dimensional layer-by-layer epitaxial growth was achieved by laser molecular beam epitaxy of oxide films on this atomically regulated surface.