THE NATURE OF THE OXIDE PHASES FORMED DURING PROGRESSIVE OXIDATION OF THE RHODIUM(111) SURFACE

The progressive oxidation of the Rh(111) surface was studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and temperature-programmed desorption (TPD). When the Rh(111) surface was oxidized in 1 Torr O2 for 10 min, the AES O/Rh ratio increased with increasing temperature and reached a maximum value at approximately 800 K. The oxide grown at this temperature had an average stoichiometry of RhO, and the LEED pattern consisted of a broadened hexagonal array of spots contracted 13% with respect to those from the Rh(111) surface. Oxidation at higher temperatures led to a decrease in the O/Rh ratio as the onset of oxide decomposition was reached. Consequently, the oxide grown at 973 K and 1 Torr had an average stoichiometry indicative of a surface suboxide with a composition near RhO0.5. This oxide yielded a well-ordered LEED pattern with approximately (8 x 8) superperiod. None of the LEED patterns observed in this study are consistent with the growth of Rh2O3(001) on the Rh surface.