In Situ Surface Characterization of SrTiO3 (100) Substrates for Well-defined SrTiO3 and YBa2Cu3O7-x Thin Film Growth

Abstract
The topmost atomic layer of SrTiO3 (STO) substrates was investigated using in situ low-energy ion scattering spectroscopy (LEISS) for ultra-thin YBa2Cu3O7- x (YBCO) film growth. The topmost layer of a STO substrate after mechanochemical polishing consisted of SrO and TiO2 planes. The topmost layer was dominantly stabilized with a TiO2 plane after the STO substrate was treated with a p H-controlled NH4F–HF(BHF) solution. It was confirmed that the topmost layer of STO thin films deposited on STO substrates was affected by the surface structure of the STO substrates. Furthermore, the dependence of T c of heteroepitaxial YBCO ultra-thin films on thickness was better for BHF-treated STO substrates than for other substrates.