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G. Franceschi, F. Kraushofer, M. Meier, G. Parkinson, M. Schmid, U. Diebold, M. Riva:
"A Model System for Photocatalysis: Ti-Doped α-Fe₂O₃(1-102) Single-Crystalline Films";
Chemistry of Materials, 32 (2020), 3753 - 3764.

Hematite (α-Fe2O3) is one of the most investigated
anode materials for photoelectrochemical water splitting. Its
efficiency improves by doping with Ti, but the underlying
mechanisms are not understood. One hurdle is separating the
influence of doping on conductivity, surface states, and
morphology, which all affect performance. To address this
complexity, one needs well-defined model systems. We build
such a model system by growing single-crystalline, atomically flat
Ti-doped α-Fe2O3(11̅02) films by pulsed laser deposition (PLD). We characterize their surfaces, combining in situ scanning tunneling microscopy (STM) with density functional theory (DFT), and reveal how dilute Ti impurities modify the atomic-scale structure of the surface as a function of the oxygen chemical potential and Ti content. Ti preferentially substitutes subsurface Fe and causes a local restructuring of the topmost surface layers. Based on the experimental quantification of Ti-induced surface modifications and the structural model we have established, we propose a strategy that can be used to separate the effects of Ti- induced modifications to the surface atomic and electronic structures and bulk conductivity on the reactivity of Ti-doped hematite.

http://dx.doi.org/10.1021/acs.chemmater.9b04908

https://publik.tuwien.ac.at/files/publik_288891.pdf