Versatile Model System for Studying Processes Ranging from Heterogeneous to Photocatalysis: Epitaxial RuO₂(110) on TiO₂(110)

The binary model system RuO 2 /TiO 2 (110) can be prepared with single crystallinity and excellent control of the morphology of the RuO 2 (110) nanoislands. The interface of RuO 2 /TiO 2 (110) is structurally well-defined since RuO 2 grows with the same lattice constants as TiO 2 (110). The actual growth of RuO 2 on TiO 2 (110) single crystals starts from square-shaped 3–4 ML thick RuO 2 islands with narrow size and thickness distributions. After TiO 2 (110) is completely covered by RuO 2, the further growth proceeds via a step flow mechanism, forming very large and flat RuO 2 (110) terraces with well-defined thickness. Both the flat RuO 2 (110) films and RuO 2 (110) nanoislands are very reactive toward CO oxidation, and the RuO 2 (110) nanoislands are robust in the redox reactions, i.e., easily recovering their morphology after reoxidation from the reduced state. The RuO 2 /TiO 2 (110) heterojunction forms a Schottky barrier of 1.4 eV which is important for photocatalysis.