Observation of the origin of d0 magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

• Published in: Nanoscale Vol. 6; no. 15; p. 9166
• Main Authors: Singh, Shashi B, Wang, Yu-Fu, Shao, Yu-Cheng, Lai, Hsuan-Yu, Hsieh, Shang-Hsien, Limaye, Mukta V, Chuang, Chen-Hao, Hsueh, Hung-Chung, Wang, Hsaiotsu, Chiou, Jau-Wern, Tsai, Hung-Ming, Pao, Chih-Wen, Chen, Chia-Hao, Lin, Hong-Ji, Lee, Jyh-Fu, Wu, Chun-Te, Wu, Jih-Jen, Pong, Way-Faung, Ohigashi, Takuji, Kosugi, Nobuhiro, Wang, Jian, Zhou, Jigang, Regier, Tom, Sham, Tsun-Kong
• Format: Journal Article
• Language: English
• Published: England 07.08.2014
• Subjects: Fourier Analysis; Luminescence; Magnetics; Nanostructures; Nanotechnology - methods; Nanowires; Oxygen - chemistry; Spectrophotometry; Surface Properties; Temperature; Tin Compounds - chemistry; X-Ray Absorption Spectroscopy; X-Rays; Zinc Oxide - chemistry
• ISSN: 2040-3372
• DOI: 10.1039/c4nr01961j

Efforts have been made to elucidate the origin of d(0) magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO.