Near-edge x-ray absorption fine structure characterization of compositions and reactivities of transition metal oxides

Abstract

We have applied the near-edge x-ray absorption fine structure (NEXAFS) technique to characterize the systematic trends in the oxygen K edge and metal L edge features of powder materials of 3d transition metal oxides. In agreement with previous high energy electron energy loss spectroscopy data [L. A. Grunes et al., Phys. Rev. B 25, 7157 (1982)], our NEXAFS results demonstrate that the characteristic oxygen K-edge features are related to the number of d electrons in the transition metal oxides. By comparison with these model compounds data, we have applied NEXAFS to investigate the compositions and reactivities of thin oxide overlayers on several single crystal surfaces, including V(110), Mo(110), and Ni(100). We will use several examples to demonstrate the capabilities of NEXAFS, such as the determination of surface O/M stoichiometries, the differentiation between atomic and molecular oxygen species on surfaces, and the determination of reaction kinetics under in situ conditions. Finally, direct differentiation of surface and bulk compositions of metal oxides will also be discussed by comparing the NEXAFS data collected by means of the surface-sensitive electron-yield and bulk-sensitive fluorescence-yield methods.