Ti1-x Sn x O2 nanofilms: Layer-by-layer deposition with extended Sn solubility and characterization

Highlights: • High quality epitaxial rutile Ti_1-xSn_xO₂ nanofilms were grown in a layer-by-layer mode at a moderately low temperature of 400 °C. • Extended solid solubility of up to x = 0.216 has been achieved in the films for the first time despite unfavorable theoretical prediction by DFT. • Films possessed smooth interfaces and step-terraced surfaces and are optically transparent with well controlled stoichiometry. • Sn⁴⁺ ions are homogenously distributed in the films and are found to substitute Ti⁴⁺ in the lattice sites. High quality rutile Ti_1-xSn_xO₂ nanofilms were successfully grown in a layer-by-layer mode at a moderately low temperature of 400 °C using pulsed laser deposition (PLD). High solid solubility of up to x = 0.216 has been achieved in the Ti_1-xSn_xO₂ films despite theoretical prediction by Density functional theory (DFT) of large formation energy (∼5.64 eV) required for the substitutional alloy to exist at such high Sn concentration. The resultant films have smooth interfaces and step-terraced surfaces with well controlled stoichiometry and are optically transparent. Sn L₃-edge Extended X-ray absorption fine structure (EXAFS) reveals the substitution of Sn⁴⁺ in the Ti⁴⁺ lattice sites of TiO₂. The lattice spacing along [110] increases linearly with increment in x due to substitution of Sn⁴⁺ ions in the Ti lattice sites of the Ti_1-xSn_xO₂ films. X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS) show that Sn is uniformly distributed on the surface and in the bulk of the films. These results are crucial when considering Ti_1-xSn_xO₂ with suitable composition for making TiO₂ based quantum structures in advanced optoelectronic devices and solar energy materials, where high-quality crystalline thin film-substrates are important.