Pure and cobalt-doped SnO2(101) films grown by molecular beam epitaxy on Al2O3

Abstract Pure and Co-doped epitaxial SnO 2 films grown by oxygen plasma assisted molecular beam epitaxy on r-cut α-alumina substrates were investigated by electron diffraction, X-ray photoelectron spectroscopy (XPS), and X-ray photoelectron diffraction (XPD). On hot alumina substrates (∼ 800 °C) only a submonolayer amount of Sn adsorbs, indicating a strong adhesion of the first monolayer of tin on the alumina surface. SnO 2 films grown at ∼ 400–600 °C substrate temperature exhibit a SnO 2 (101)[010]‖Al 2 O 3 (-1012)[12-10] epitaxial relationship. Subtle differences in the XPD data of SnO 2 films compared to measurements on SnO 2 (101) single crystal surfaces are consistent with the presence of a high density of stoichiometric antiphase domain boundaries in the film. These planar defects are introduced in the SnO 2 film to compensate for the more than 10% lattice mismatch between the SnO 2 films and the alumina substrate along the SnO 2 [-101] direction. Co x Sn 1− x O 2 films with a Co-cation concentration of 5–15% were also grown. XPS indicates that Co is in a 2+ oxidation state and XPD shows that tin is replaced substitutionally by Co.