Abstract
High-quality Sn-doped In2O3 (ITO) films were grown epitaxially on yttria stabilized zirconia (111) with oxygen-plasma assisted molecular beam epitaxy (MBE). The 12 nm thick films, containing 2–6% Sn, are fully oxidized. Angle-resolved x-ray photoelectron spectroscopy (ARXPS) confirms that the Sn dopant substitutes In atoms in the bixbyite lattice. From XPS peak shape analysis and spectroscopic ellipsometry measurements it is estimated that, in a film with 6 at.% Sn, ∼1/3 of the Sn atoms are electrically active. Reflection high energy electron diffraction (RHEED) shows a flat surface morphology and scanning tunneling microscopy (STM) shows terraces several hundred nanometers in width. The terraces consist of 10 nm wide orientational domains, which are attributed to the initial nucleation of the film. Low energy electron diffraction (LEED) and STM results show a bulk-terminated (1 × 1) surface, which is supported by first-principles density functional theory (DFT) calculations. Atomically resolved STM images are consistent with Tersoff–Hamann calculations that show that surface In atoms are imaged bright or dark, depending on the configuration of their O neighbors. The coordination of surface atoms on the In2O3(111)–1×1 surface is analyzed in terms of their possible role in surface chemical reactions.
Highlights
High-quality Sn-doped In2O3 (ITO) films were grown epitaxially on yttria stabilized zirconia (111) with oxygen-plasma assisted molecular beam epitaxy (MBE)
After studying the dependence of the calculated bulk properties on the density functional, i.e. local density approximation (Perdew Wang functional) (LDA (PWC)) [18] versus Perdew Burke Ernzerhof (PBE) [19] and scalar relativistic treatment all-electron-non-relativistic versus density functional semicore pseudopotential (DSPP) [20] and scalar relativity with DMol3 [21, 22], it was found that the PWC-DSPP lattice constant comes closest to the experimental one (0.2%), as expected
Following a recipe given by Ohta et al [2], the Yttria stabilized zirconia (YSZ)(111) substrate was prepared by annealing in air at a temperature of 1350 ◦C for about 40 min
Summary
High-quality Sn-doped In2O3 (ITO) films were grown epitaxially on yttria stabilized zirconia (111) with oxygen-plasma assisted molecular beam epitaxy (MBE). Reflection high energy electron diffraction (RHEED) shows a flat surface morphology and scanning tunneling microscopy (STM) shows terraces several hundred nanometers in width. Low energy electron diffraction (LEED) and STM results show a bulk-terminated (1 × 1) surface, which is supported by first-principles density functional theory (DFT) calculations. Yttria stabilized zirconia (YSZ) is an ideal substrate for ITO growth, as it exhibits cube-on-cube epitaxy and a small lattice mismatch with In2O3. We have used oxygenplasma assisted molecular beam epitaxy (MBE) to grow high-quality single crystalline ITO films on YSZ(111). Activated oxygen is necessary for fully oxidizing the film; growth in a background of molecular oxygen resulted in non-stoichiometric films.
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