Surface studies of YBa2Cu3O7-x -matching oxide substrates and interfaces

Crystallographic changes as a result of heat-treatment at 700-900 deg. C are found for SrTiO3(100), MgO(100) and LaAlO3(100). The p(2x2) reconstruction of the SrTiO3(100) and the superstructures on MgO(100) and on LaAlO3(100) thus observed are suggested to be induced by segregation of impurities to the surface. The surface charge-effects which disturb electron- and photon-impact experiments with these insulators are removed by heat-treatments. Deposition of copper results in formation of copper islands on SrTiO3(100) and on LaAlO3(100). Yttrium forms islands on LaAlO3(100) and grows in a layer-by-layer mode on SrTiO3(100) and on MgO(100). An yttrium 1x1 epitaxy is observed on the MgO(100) surface, which is suggested to be an YO superstructure. Oxidation of the 1x1 Y/MgO(100) systems diminishes the charge-effects and improves all diffraction and spectroscopic measurements. This may be due to the formation of metallic states around the Fermi level when the film is oxidized. An in situ synthesized YBa2Cu3O7 thin film on SrTiO3(100) compared to a thick epitaxial YBa2Cu3O7-x(001) film on MgO(100) reveals differences in surface electronic structures but not in surface stoichiometries. (au) 18 refs