Oxygen adsorption on MoN precovered Fe-3.5%MoN(100) single crystals

Abstract

The two-dimensional MoN surface compound has been prepared on the Fe 3.5%MoN(100) surface by means of surface cosegregation of molybdenum and nitrogen. The MoN precovered Fe-3.5%MoN(100) surface shows a sharp (1 × 1) low energy electron diffraction (LEED) pattern. The structure of the MoN surface compound has been determined by X-ray photoelectron diffraction to consist of a single MoN surface layer plus an additional Mo subsurface layer. AES and LEED have been utilized to study the dissociative oxygen adsorption on the MoN precovered Fe-3.5%MoN(100) surface. The experiments have been conducted at oxygen pressures ranging from 5 × 10 −9 to 1 × 10 −6 mbar and temperatures between 400 and 550°C. It has been found that chemisorbed oxygen atoms replace nitrogen atoms of the MoN surface compound and cause a reduction of the Mo surface concentration. After ∼ 100 l O 2 the initial exchange process is largely completed and leads to an oxygen and molybdenum rich (Mo x Fe 1 − x )(O y N 1 − y ) surface phase. The (Mo x Fe 1 − x )(O y N 1 − y ) covered substrate shows a sharp (1 × 1) LEED pattern indicating epitaxial stabilization of the (Mo x Fe 1 − x )(O y N 1 − y ) surface phase on the Fe-3.5%Mo(100) surface. It is shown that the structure of the (Mo x Fe 1 − x )(O y N 1 − y ) surface phase is related to the (100) plane of the rocksalt structure. Further oxidation causes the formation of inhomogeneous iron oxide layers on MoN precovered and sputter cleared Fe-3.5%MoN(100) surfaces as well.