Epitaxial growth of tin oxide film on TiO2(1 1 0) using molecular beam epitaxy

Growth of tin oxide thin films using molecular beam epitaxy in a pyrolyzed nitrogen dioxide atmosphere on a titanium dioxide (1 1 0) substrate was investigated using X-ray photoelectron spectroscopy (XPS), electron diffraction, and atomic force microscopy (AFM). Properties of deposited films were studied for their dependence on substrate temperature and oxidation gas pressure. Analyses using XPS data revealed that tin atoms were fully oxidized to Sn⁴⁺ and SnO₂ films were grown epitaxially in deposition conditions of substrate temperatures of 627 K or higher and NO₂ pressure greater than 3×10⁻³ Pa. At a substrate temperature of 773 K, a smooth surface with atomic steps was visible in the SnO₂ films, but above or below this temperature, fine grains with crystal facets or porous structures appeared. At pressures of 8×10⁻⁴ to 3×10⁻⁴ Pa, the randomly oriented SnO phase was dominantly grown. Further decreasing the pressure, the Sn metal phase, which was epitaxially crystallized at less than 500 K, was also grown.