Epitaxial Growth of Ruthenium Dioxides on Ru(0001) Surface

Abstract

The epitaxial growth of the RuO 2 clusters on Ru(0001) electrode formed by electrooxidation in HClO 4 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 RuO 2 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 RuO 2 clusters has been determined by RHEED rather than LEED. Sample annealing at 700 K o for 11 min sharpens the RHEED reflections facilitating the determination of the structure of RuO 2 clusters. That is, the RuO 2 clusters are exclusively (100) oriented, monocrystalline despite the crystal disorder, and three (100) RuO 2 domains rotated by 120 o with each other grown on Ru(0001). Furthermore, it is found that the crystallinity of RuO 2 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 OH -ad species to bulk hydroxide RuOH, causing surface roughening and formation of three dimensional (3D) RuO 2 cluster via a Vollmer-Weber growth mode on Ru(0001).