Epitaxial Growth of Ruthenium Dioxides on Ru(0001) Surface

C.-H. Nien and M.S. Zei


The epitaxial growth of the RuO2 clusters on Ru(0001) electrode formed by electrooxidation in HClO4 solution has been studied by ex-situ reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) after emersion. The LEED pattern for the RuO2 clusters on Ru(0001) exhibits a (1 x 1) phase, while both Ru-oxide and substrate reflections are observed by RHEED, so that the crystal structure of RuO2 clusters has been determined by RHEED rather than LEED. Sample annealing at 700 Ko for 11 min sharpens the RHEED reflections facilitating the determination of the structure of RuO2 clusters. That is, the RuO2 clusters are exclusively (100) oriented, monocrystalline despite the crystal disorder, and three (100) RuO2 domains rotated by 120o with each other grown on Ru(0001). Furthermore, it is found that the crystallinity of RuO2 grains formed at +1.98 V is even worse than that at + 1.12 V. Under oxidation conditions the hydroxyl OH anions are chemisorbed on Ru(0001) electrode inducing the segregation of Ru-atoms to surface. The Ru-atoms turn to react with the OHad species to bulk hydroxide RuOH, causing surface roughening and formation of three dimensional (3D) RuO2 cluster via a Vollmer-Weber growth mode on Ru(0001).

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