STRUCTURE OF THE P(2X1)-OXYGEN MO0.75RE0.25 (001) SURFACE STUDIED BY LOW-ENERGY LI+ ION-SCATTERING/

Low energy alkali ion scattering, low energy electron diffraction (LEE D) and Auger electron spectroscopy (AES) were used to study the adsorp tion of oxygen on the Mo0.75Re0.25(001) surface. Annealing to 1400 K i n a limited coverage range produces a phase with chemisorbed oxygen an d a structure characterized by a sharp p(2 x 1) LEED pattern. AES and ion scattering evidence indicates that the oxygen coverage is about 0. 8 to 1.0 ML and shows that this structure contains vacancies ordered i nto missing rows. Oxygen atoms are adsorbed near three-fold hollow sit es which result from the vacancy formation. Oxygen is found to induce loss of Re from the first and second layers in a thermally activated p lace exchange with Mo atoms. The structural features found are discuss ed and compared with previous results from oxygen adsorption on Mo(001 ) and W(001) surfaces and the effect of oxygen on the component depth profile is explained on the basis structural and thermodynamic stabili ty.