Faceting of Ru($11\bar {2}0)$ Surface: A Model System for Catalysis

We have studied NO$_{2}$-induced faceting of a Ru($11\bar {2}0)$ surface by means of low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and Auger electron spectroscopy (AES). By annealing the sample at $>$ 600 K in NO$_{2}$ (10$^{-8}$ Torr), the surface becomes fully faceted as revealed by LEED although it is rather smooth, with only two layers exposed. The faceted surface remains the same at NO$_{2}$ exposure ranging from 20 L to 12000 L and is stable for substrate temperature $T \quad <$ 850 K.The STM results confirmed the LEED observations and showed that the faceted surface consists of sawtooth ridges along the [0001] direction with typical dimensions of $\sim $5 nm in width and $>$ 100nm in length. We have found that the faceted O/Ru surface is very active for NH$_{3}$ decomposition to produce H$_{2}$ with high selectivity to N$_{2}$ at room temperature.