Electronic Structure of Co-doped ZnO Thin Films by X-ray Absorption and Emission Spectroscopy

Abstract

The electronic structure of Co-doped ZnO thin films, synthesized with a nominal composition of Zn1−xCoxO (x = 0.03, 0.05, 0.7, 0.10, and 0.15) by using spray pyrolysis method, has been investigated using near edge X-ray absorption fine structure (NEXAFS) measurements at the O Kand the Co L3,2-edges and using resonant inelastic X-ray scattering (RIXS) measurements at Co L3,2-edge. All the prepared Zn1−xCoxO thin films showed ferromagnetic behavior at room temperature, as measured by using an alternating gradient force magnetometer (AGFM). The intensity of the pre-edge spectral feature at the O K -edge increases with the Co concentration, which clearly reveals that there is strong hybridization of O 2p − Co 3d atoms in the ZnO matrix. Spectral features of the Co L3,2-edge NEXAFS exhibit multiple absorption peaks and are similar to those of Co ions coordinated in tetrahedral symmetry by four oxygen atoms. These results clearly demonstrate that Co is in a 2+ state, substituting at the Zn site. Co L3,2-edge RIXS measurements show that the substitution by Co atoms can explain the magnetic interaction in Co-doped ZnO.