Investigations of the valence states, cobalt ion distribution, and defect structures in Co-doped ITO films
Abstract
The valence states, the distribution of Co ions, and defect structures in the Co-doped ITO films with Co concentrations of 5-13 at.% were examined by X-ray absorption spectroscopy (XAS) at Co, K, and L-edges. The structural analyses and ab initio calculations reveal that the Co atoms are substantially incorporated into the ITO lattice and form cobalt-vacancy complexes, while partial formation of Co0 species is observed for all the films. The analyses of Co-K edge XAS reveal that the Co-O bond length RCo-O is shortened and the corresponding Debye-Waller factor (σ2) obviously increases with Co doping, implying the relaxation of oxygen environment around the substitutional Co ions. The qualitative fitting of Co L3-edge XAS further confirms the coexistence of Co0 and Co2+ in the films. The Co atoms mainly occupy the substitutional sites of In2O3 lattices with the metallic Co clusters being about 20-43 at.% for the 5, 7, and 8.5 at.% Co-doped ITO films. However, a significant fraction (∼57 at.%) of metallic Co clusters is found in the 13 at.% Co-doped ITO film.
- Publication:
-
Journal of Materials Research
- Pub Date:
- August 2018
- DOI:
- 10.1557/jmr.2018.184
- Bibcode:
- 2018JMatR..33.2336L