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題名: 一維氧化鋅奈米結構中摻雜效應對結構、光學及磁學特性的影響
Doping effect on the structural, optical and magnetic properties of one dimensional ZnO nanostructures
作者: 游家和
貢獻者: 電機工程研究所
關鍵詞: 溶膠凝膠法
氧化鋅
奈米線
化學水熱沉積法
螢光光譜
磁滯曲線
磁矩
日期: 2011-06
上傳時間: 2013-11-20T08:23:08Z
摘要: 本論文主要是利用溶膠凝膠法製備氧化鋅晶種層於Si基板上，並使用化學水熱成長法在氧化鋅晶種層上浸泡成長出摻雜釤氧化鋅與摻雜鋁氧化奈米線。探討溶液中不同摻雜濃度(1mM, 2mM, 4mM)及不同奈米線浸泡成長時間(1 h, 1.5 h, 2 h)對奈米線之晶體結構、表面微結構、光學及磁學特性之影響。
製備的奈米線經由X-ray繞射結果分析其晶格結構及晶粒大小，結果顯示製備的摻雜釤氧化鋅與摻雜鋁氧化鋅奈米線結構皆為纖鋅礦結構，且結晶方向皆有很高的c軸取向，另外也沒有觀察到二次相的產生。
本論文藉由掃描式電子顯微鏡觀察薄膜表面形態，結果顯示摻雜釤元素會抑制氧化鋅奈米線的成長，奈米線長度由長變短、緻密度由濃密變稀疏。相對的摻雜鋁元素會促進奈米線快速的生長，奈米線長度由短變長、緻密度由稀疏變濃密。
所有樣本經由螢光光譜量測，摻雜釤氧化鋅與摻雜鋁氧化鋅奈米線在紫外光區皆可以觀察到一個明顯的放射峰，且有摻雜的樣本會在綠光（約520 nm）及黃光區（約600 nm）各觀察到一個明顯的放射峰。隨著摻雜濃度的增加，綠光及橘光放射峰有明顯的增強；且紫外光區放射峰也隨著摻雜濃度的增加而減弱。相關的結果顯示因摻雜元素的存在會輕微扭曲晶格結構而減弱紫外光放射強度，同時因而造成的氧空缺及鋅間隙使得綠光及黃光的放射增強。
最後對摻雜釤氧化鋅與摻雜鋁氧化鋅奈米線經磁滯曲線磁性量測，發現所有樣本皆具有室溫下的磁性，且磁矩隨著摻雜的比例增加而增加。室溫磁性的存在是因為受到氧空缺及鋅間隙束縛的載子，在外加磁場磁化束縛載子時由其間耦合磁矩所形成。因此隨著摻雜量增加，氧空缺及鋅間隙增加時，導致磁矩因而隨著增加。
The purpose of the thesis is to fabricate the ZnO seed layer on Si substrate by sol-gel method and to grow samarium-doped zinc oxide and aluminum-doped zinc oxide nanowires on the seeded Si substrate by hydrothermally chemical growth method. In this study, the effect of doping concentration (1mM, 2mM and 4mM) and growth time (1 h and 1.5 h) on the crystallization, microstructure, optical and magnetic properties will be discussed.
The crystal structure of the samarium-doped zinc oxide and aluminum-doped zinc oxide ZnO nanowires was examined by XRD spectra. The results show that all of the nanowires exhibited the same wurtzite hexagonal structure and no structural was disturbance caused by the substitution of samarium or aluminum for zinc in the nanowires. Besides, no traces of Sm oxides and Al oxides related secondary phases were detected by the XRD analysis.
Morphological characterization was observed by a field emission scanning electron microscopy (FE-SEM JEOL JSM-6700F). The results showed that the growth rate of samarium-doped zinc oxide nanowires is restrained and the length of nanowires is decreased by the doping of samarium. In contrary, the growth rate of aluminum-doped zinc oxide nanowires is enhanced and the length of nanowires is increased by the doping of aluminum.
The PL spectra of the nanowires were measured with excitation of the 325 nm He-Cd laser. For all samples, a strong UV emission and a weak broad green-yellow emission were observed. With the increase of samarium and aluminum doping concentration, the intensity of UV emission decreases. This result shows that the impurity may limit the radiative efficiency of the nanowires, which can also result in the quenching of UV emission. In addition, the green-yellow emission enhanced slightly with the increase of samarium and aluminum doping concentration which indicates the increase of oxygen vacancies and zinc interstitial in the nanowires.
The hysteresis loop and magnetization processes were recorded by AGM at room temperature. Ferromagnetic behavior was observed for all compositions. Single crystal ZnO material was thought to be nonmagnetic material. However, during hydrothermal fabrication process, defects such as oxygen vacancies and Zn interstitials can be easily introduced. Band electron, which is locally trapped by oxygen vacancy or Zn interstitial, occupies an orbital overlapping with the d-shells of Zn neighbors. The sp-d exchange interactions between the band electrons and the localized d electrons of Zn couple the individual moments and lead to ferromagnetism of the nanowires. Hence, the enhancement of ferromagnetism of the nanowires is observed due to the doping of samarium and aluminum and correspondingiy increase with defects induced by the increase of doping concentration.
描述: 指導教授:楊尚霖
顯示於類別:[電機工程系(含碩士班)] 學位論文

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