- 學位論文
探討奈米結構氧化鋅之電子結構與磁性
The study of electronic structures and magnetic properties of nanostructural ZnO
摘要
本論文主要探討氧化鋅的電子結構和磁性間的關連性，利用同步輻射光的特性，對氧化鋅的四種不同幾何結構樣品，奈米線(Nanowires)、奈米柱(Nanorods)、奈米仙人掌狀(Nanocactus)、奈米葉片狀(Nanosheets)來進行實驗。樣品在奈米尺寸下可以得到室溫鐵磁性，探討磁性貢獻來源就是本論文的重點。光激發螢光光譜(PL)實驗看出樣品缺陷大小，再由 X光激發發光光譜(XEOL)來探討缺陷的大小是由Zn或是O所提供;用延伸X光吸收光譜精細結構(EXAFS)來比較不同幾何形狀ZnO樣品原子結構的亂度，看是否和磁性有直接的關係；利用價電帶光電子能譜(VB-PES)觀看原子間的交互作用和電子已佔據態的多寡，O的2p和Zn的3d/4sp 軌域是否跟磁性排列大小有所關連；而探討磁性最直接的 X光磁圓偏振二相性(XMCD)，實驗結果得知，O的K-edge在磁性的貢獻遠比Zn的L3,2-edge來的大，配合理論計算結果算出磁性來源是因為Zn原子有缺陷導致磁性產生。
並列摘要
In present investigation, the origin of magnetism in ZnO nanowires, nanorods, nanocactus and nanosheets have been studied using X-ray absorption spectroscopy, X-ray magnetic circular dichroism (XMCD) and scanning photoemission microscopy (SPEM) techniques. All the ZnO nanostructure samples show room temperature ferromagnetism with slightly difference in saturation magnetization. The surface defects/ vacancies were related to the origin of magnetism in ZnO nanostructures. The presence of defects/vacancies were clearly observed in photoluminescence and Zn L3,2-edge and O K-edge X-ray excited optical luminescence studies. The increasing in density of states near Fermi level (Ef) due to surface defects/vacancies concentration was clearly observed in SPEM study. Furthermore, O K- and Zn L3,2- edge XMCD studies suggest magnetism in ZnO nanostructures is due to O 2p orbitals rather than Zn 3d orbitals.