Abstract
We have investigated the bimetallic Sn/Rh(111) system formed by vapor deposition of Sn on a Rh(111) single-crystal surface by applying two powerful structural probes: alkali-ion scattering spectroscopy (ALISS) and x-ray photoelectron diffraction. For initial submonolayer exposures, the surface structure responsible for the observed low-energy electron diffraction pattern is explored and its alloy nature is established. The ALISS results indicate that the formation of this surface alloy is produced by the replacement of top-layer Rh atoms by Sn atoms. The resultant alloy surface can be strictly two dimensional if the annealing temperature is high enough This surface alloy is buckled with the Sn atoms displaced upward from the Rh surface plane by In addition, x-ray photoemission spectroscopy core-level measurements have been performed on this surface alloy at grazing exit angles and these are compared with results on the analogous Sn/Pt(111) surface alloy. Binding energy shifts of and -0.6 eV for the Rh and Sn core levels, respectively, were observed for the Rh-Sn alloy compared to the pure elements. A shift of was also seen for the valence-band centroid upon alloying. From temperature-programmed desorption studies it was determined that CO adsorption is decreased on the Sn/Rh surface alloy, but with only a small (4 kcal/mol) decrease in the adsorption energy. The growth mechanism of the Sn film in the Sn/Rh(111) bimetallic system was also probed. The vapor deposition of Sn on Rh(111) at 300 K does not form epitaxial clean Sn films or pure Sn clusters but rather forms a random alloy of increasing thickness.
- Received 10 February 1997
DOI:https://doi.org/10.1103/PhysRevB.56.15982
©1997 American Physical Society