IN-SITU SURFACE CHARACTERIZATION OF SRTIO3(100) SUBSTRATES AND HOMOEPITAXIAL SRTIO3 THIN-FILMS GROWN BY MOLECULAR-BEAM EPITAXY AND PULSED-LASER DEPOSITION

The topmost atomic layer of SrTiO3 (STO) substrates was investigated b y in situ low-energy ion scattering spectroscopy (LEISS). After mechan ochemical polishing, the topmost layer of the STO substrate consisted of SrO and TiO2 planes. It was dominantly stabilized with TiO2 planes after the STO substrate was treated with a pH-controlled NH4F-HF(BHF) solution. STO thin films were deposited on the BHF-treated STO substra tes by the molecular beam epitaxy (MBE) and pulsed laser deposition (P LD) methods. STO films were confirmed to have topmost layers with TiO2 planes by the MBE method, and SrO planes by the PLD method. We also i nvestigated the effects of the deposition conditions and surface treat ments, and confirmed that the TiO2 plane was more stable on the STO ho moepitaxial film surface. Furthermore, the BHF-treated STO substrates greatly improved the thickness dependence of Tc of heteroepitaxial YBa 2Cu3Ox (YBCO) ultra-thin films. (C) 1998 Elsevier Science B.V. All rig hts reserved.