Hematite α-Fe2O3(0001) in top and side view: Resolving long-standing controversies about its surface structure

J. Redondo, J. Michalička, F. Kraushofer, G. Franceschi, B. Šmid, N. Kumar, O. Man, M. Blatnik, D. Wrana, B. Mallada, M. Švec, G. S. Parkinson, M. Setvin, M. Riva, U. Diebold, J. Čechal

Faculty of Mathematics and Physics, Charles University, Praha 18000, Czech Republic
Faculty of Chemistry, University of the Basque Country, Guipuzkoa 20018, Spain
Central European Institute of Technology, Brno University of Technology, 61200 Brno, Czech Republic
Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Marian Smoluchowski Institute of Physics, Jagiellonian University, 30-348 Krakow, Poland
Institute of Physics, Czech Academy of Science, Na Slovance 2, Czech Republic

Adv. Mater. Interfaces 10 (2023) 2300602

Hematite is a common iron oxide found in nature, and the α-Fe2O3(0001) plane is prevalent on the nanomaterial utilized in photo- and electrocatalytic applications. The atomic-scale structure of the surface remains controversial despite decades of study, partly because it depends on sample history as well as the preparation conditions. Here, a comprehensive study is performed using an arsenal of surface techniques (non-contact atomic force microscopy, scanning tunneling microscopy, low-energy electron diffraction, and X-ray photoemission spectroscopy) complemented by analyses of the near surface region by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The results show that the so-called "bi-phase" termination forms even under highly oxidizing conditions; a (1 × 1) surface is only observed in the presence of impurities. Furthermore, it is shown that the biphase is actually a continuous layer distorted due to a mismatch with the subsurface layers, and thus not the proposed mixture of FeO(111) and α-Fe2O3(0001) phases. Overall, the results show how combining surface and cross-sectional imaging provides a full view that can be essential for understanding the role of the near-surface region on oxide surface properties.

Corresponding author: Jesús Redondo.

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