Investigations of the valence states, cobalt ion distribution, and defect structures in Co-doped ITO films
- PDF / 683,451 Bytes
- 6 Pages / 584.957 x 782.986 pts Page_size
- 1 Downloads / 194 Views
Zhonghua Wu Beijing Synchrotron Radiation Facility (BSRF), Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 1040049, China
Jiwen Liu and Yukai Ana) Key Laboratory of Display Materials and Photoelectric Devices, Ministry of Education, Tianjin Key Laboratory for Photoelectric Materials and Devices, National Demonstration Center for Experimental Function Materials Education, School of Material Science and Engineering, Tianjin University of Technology, Tianjin 300384, China (Received 17 February 2018; accepted 24 May 2018)
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 (r2) 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 Co21 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. I. INTRODUCTION
Recently, diluted magnetic semiconductors (DMSs) have triggered considerable study for their potential applications in spin-based magnetic devices.1,2 Since Dietl et al. predicted that oxide-based DMSs can possess ferromagnetic order at room temperature (RT).3 A number of transition-metal (TM) doped oxide semiconductors, such as ZnO,4,5 TiO2,6,7 and In2O3,8,9 have been reported to exhibit high-temperature ferromagnetism. Especially, indium tin oxide (ITO, or Sn-doped In2O3) with good electrical conductivity, high optical transparency, and wide band-gap (3.75 eV) has been considered as a promising host material of DMSs for achieving RT ferromagnetism. However, the origin of RT ferromagnetism for the In2O3-based DMSs still remains controversy. Intrinsic ferromagnetism and its mechanisms in this system have been reported in many literature studies.10–12 Whereas some groups suggest that the second magnetic phase such as TM metal clusters or TM oxides can be considered as the origin of observed ferromagnetic ordering. For example, Subías et al. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.184
conclude that the observed ferromagnetism in highdoped In2O3 and ITO films is due to the formation of metallic Co clusters.13 Jiang et al. attributed the RT ferromagnetism in Fe/Sn-codoped In2O3 powders to the precipitated Fe3O4 impurity.14 Kohiki et al. attributed the observed RT ferroma
Data Loading...
