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

The binary model system RuO2/TiO2(110) can be prepared with single crystallinity and excellent control of the morphology of the RuO2(110) nanoislands. The interface of RuO2/TiO2(110) is structurally well-defined since RuO2 grows with the same lattice constants as TiO2(110). The actual growth of RuO2 on TiO2(110) single crystals starts from square-shaped 3–4 ML thick RuO2 islands with narrow size and thickness distributions. After TiO2(110) is completely covered by RuO2, the further growth proceeds via a step flow mechanism, forming very large and flat RuO2(110) terraces with well-defined thickness. Both the flat RuO2(110) films and RuO2(110) nanoislands are very reactive toward CO oxidation, and the RuO2(110) nanoislands are robust in the redox reactions, i.e., easily recovering their morphology after reoxidation from the reduced state. The RuO2/TiO2(110) heterojunction forms a Schottky barrier of 1.4 eV which is important for photocatalysis.