| 摘要: | 本計畫旨在研究稀磁半導體氧化物，包括二氧化鈦 (TiO2)、氧化鋅 (ZnO) 之奈米顆粒與薄膜。我們將深入探討該類材料在不同掺雜條件下呈現鐵磁性的機制，同時嘗試對缺陷密度、微結構、形態以及薄膜介面進行調制，以釐清自旋如何透過偏振子交換作用達成有序排列。近年來研究人員對於稀磁半導體材料之興趣持續加溫，尤其是過渡金屬氧化物系統，原因是它們在適當的掺雜下，除了呈現出鐵磁性外，其居里溫度可超過室溫，因此在自旋電子學元件的發展上與應用上深具潛力。本計畫擬針對兩種稀磁半導體氧化物系統 (TiO2與ZnO)，探索其在奈米顆粒及薄膜型態下的鐵磁性行為。在先前的研究工作中，我們發現TiO2奈米顆粒在電子自旋共振量測中呈現一些有趣的現象，尤其經過鐵、鉻與鎳掺雜後，其自旋訊號與鐵磁訊號具有某種程度的關聯，可用來探討自旋或鐵磁序化的機制。本專題計畫具有三重目標：(一) 嘗試以不同的製程與鍍膜技術將上述材料製作成奈米顆粒與薄膜，並且有系統地研究其結構特性；(二) 以電子自旋共振做為主要實驗工具，探討TiO2與ZnO鐵磁序化的機制。實驗的變因將包括溫度、掺雜物、掺雜密度、缺陷密度以及微結構的調制等，並配合結構與其他磁性分析，了解該類材料系統結構與磁性表現之關聯；(三) 藉由電子自旋共振在不同外場方向下所呈現的異向表現，研究TiO2與ZnO薄膜的異向性，並深入剖析由介面誘發的相關磁性行為。
This project is determined to study dilute magnetic semiconductor (DMS) oxides, including TiO2 and ZnO in the forms of nanoparticle and thin film. We would like to investigate the mechanism of ferromagnetic ordering displayed by these materials under different doping conditions. By tuning some experimental parameters such as defect concentration, micro-structure, morphology and interface, we hope to get deeper insight into how localized spins align themselves into ferromagnetism through the exchange interaction of bound polarons. There has been an increasing interest in the topic of dilute magnetic semiconductors in recent years, and especially in transition-metal oxide systems because when properly doped, they not only exhibit a ferromagnetic ordering, but the Curies temperature is also above room temperature. Therefore DMS materials have great potential for the development of future spintronic devices. This proposed project intends to focus on two DMS oxide systems (TiO2 and ZnO) and to study the magnetic behaviors of their nanoparticle and thin-film forms. In our preliminary study of TiO2 nanoparticles, we have found some interesting phenomena. When doped with Fe, Cr, and Ni, the ESR and FMR signals are correlated in some sense, and can therefore be used to probe the spin or ferromagnetic ordering mechanism. The aim of this proposed study has three folds: (1) to make nanoparticles and thin films of TiO2 and ZnO with various techniques, and to characterize their structural properties systematically; (2) to study the magnetic ordering mechanism of these materials, using Electron Spin Resonance (ESR) as a primary tool. The experimental variables would include temperature, dopant, doping concentration, defect concentration, micro-structure variation, etc. By carefully tuning and characterizing the structural and magnetic properties, we hope to reveal more information of how ferromagnetism correlates with the structural imperfections; (3) to explore other related magnetic issues in the thin-film type samples such as magnetic anisotropy. We would also like to explore the interface-induced effect and see how it would correspond in the anisotropic behavior of ESR signals. |
