AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP27
Adsorbate-Induced Faceting of Atomically Rough Re Surfaces

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: H. Wang, Rutgers University
Authors: H. Wang, Rutgers University
W.H. Chen, Rutgers University
A.S.Y. Chan, Rutgers University
T.E. Madey, Rutgers University
Correspondent: Click to Email
We report faceting of atomically rough Re(12-31) and (11-21) surfaces induced by oxygen or ammonia using AES, LEED, STM and synchrotron-based high resolution X-ray photoemission spectroscopy (HRSXPS). Faceting is driven by thermodynamics (anisotropy of surface free energy) but is controlled by kinetics of surface diffusion. The Re(12-31) surface undergoes faceting once the oxygen coverage exceeds 0.5 monolayer (ML) and the surface is annealed at @>=@700K. The morphology of the surface depends on oxygen coverage and adsorption temperature, ranging from long sawtooth ridges to complex structures exposing some of the following five different facets: (11-21),(01-10),(10-10),(01-11) and (10-11). For Re(11-21), adsorption of oxygen at room temperature followed by annealing causes the surface to become partially faceted with (01-10) and (10-10) facets forming zigzag chains. Under oxidation conditions, i.e. dosing a large amount of oxygen at high temperatures (900-1000K), the (11-21) surface is completely covered by four facets identified as (01-10), (10-10), (01-11) and (10-11). In contrast, after exposure to ammonia at 700K, the Re(11-21) surface only shows a (1x2) reconstruction and remains planar (ammonia dissociates on Re, and only N remains on the surface at T>700K). By exposure to ammonia at 900K, the Re(11-21) surface becomes completely faceted, forming 2-sided ridge-like structures; the orientations of the ridge sides are different from any of those found in oxygen-induced faceting of Re(12-31) and Re(11-21). Our work demonstrates that it is possible to tailor the surface morphology by choosing appropriate adsorbate and annealing conditions, which in turn provides different but related model systems to study structural sensitivity in catalytic reactions as well as potential templates to grow nanostructures.