Growth of Ba–O ultrathin films on Pt(111) followed by Ti incorporation to prepare oxide crystalline approximants and quasicrystals

Abstract In this study, three different precursor Ba–O films on Pt(1 1 1) are characterized and the oxide crystalline approximant (OCA) and oxide quasicrystal (OQC) films are prepared by annealing after Ti deposition on the films. The prepared Ba–O ultra-thin films are BaO(1 0 0)–(√2×√2)R3°:Pt(1 1 1), Ba–O:Pt(1 1 1)–(2 × 2) and Ba–O:Pt(1 1 1)–(√13×√13)R13.9°, as determined using scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The phase transformation from an OCA film to an OQC film likely follows the mechanism where Ti is reduced and its surface atomic density decreased, while Ba is oxidized. The schematic structural models of the OCA film as Ba4Ti4O10 and the OQC film as Ba12Ti5O12, where the Ba atoms form a cluster tiling, are proposed.