Morphology evolution in oxygen-induced faceting of Re (12-31)

The adsorption of oxygen on Re ($12\bar {3}1)$ has been studied by low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). The atomically rough Re ($12\bar {3}1)$ surface remains planar at room temperature after being exposed to oxygen. However, the O/Re ($12\bar {3}1)$ surface can undergo drastic morphological changes to become completely faceted upon annealing at 700K or higher temperatures. With low oxygen coverages ($\sim $0.5ML), the facets form ridge-like structures and grow along the ridge direction [$\bar {2}113$]. The size of the ridges grows with annealing temperatures. The typical dimensions for the ridges are $\sim $8nm wide and $>$50nm long upon annealing at 1000K. The orientations of the two facets of the ridge are identified as ($11\bar {2}1)$ and ($01\bar {1}0)$ by LEED measurements, which are consistent with kinematical simulations of the LEED patterns and confirmed by STM measurements. When the oxygen coverage is about 1ML, the ridge-like structure is found to be truncated by a third set of facets in the annealing temperature range between 900K and 1300K. The faceted O/Re surfaces may not only provide us templates to grow ordered nano-structures but also are possible candidates to study structural sensitivity in catalytic reactions.