An Ordered Mixed Oxide Monolayer Formed by Iron Segregation on Rutile-TiO₂(011): Structural Determination by X-ray Photoelectron Diffraction

Abstract

Iron impurities in the rutile-TiO 2 (011) surface can result in the formation of an ordered, ternary iron− titanium oxide monolayer. Here the FeTi 2 O 5 mixed oxide monolayer predicted by DFT simulations is confirmed by synchrotron based angle scanned X-ray photoelectron diffraction (XPD) studies. The ternary oxide monolayer has been synthesized on rutile-TiO 2 (011) substrate via two different experimental pathways: first, by segregation of Fe impurities from the bulk by annealing a clean TiO 2 (011) substrate in 1 × 10 −7 mbar of oxygen at ∼450 °C and, second, by physical vapor deposition of Fe on clean TiO 2 (011) in 1 × 10 −7 mbar of oxygen at ∼450 °C. For both preparation procedures an intermixed surface oxide is formed with Fe and Ti in 2+ and 4+ charge states, respectively. The surface is characterized by high-resolution and fast X-ray photoelectron spectroscopy (XPS), XPD, and low energy electron diffraction (LEED). Multiple electron scattering simulations implemented in the electron diffraction in atomic clusters (EDAC) package were performed for comparing experimental XPD patterns with structural models. The reliability of the approach was tested on XPD pattern of reconstructed clean TiO 2 (011)-2 × 1 surface, for which a structural model exists. The XPD pattern of the monolayer ternary iron titanium oxide is compared to structural models proposed by density functional theory (DFT)-based models.

Processing and analysis of X-ray photoelectron diffraction data using IGOR Pro

“…XPD pattern) by using a suitable projection. Finally, one can compare an XPD pattern with theoretical scattering calculations and adjust the simulations to obtain the atomic configuration of the surface and near-surface regions (Muntwiler et al, 2001;Pancotti et al, 2009;Halpegamage et al, 2016).…”