臺灣博碩士論文加值系統

使用低真空熱蒸鍍冷凝法製備兩組奈米鉍顆粒，以編號Bi080630及Bi081224表示。從X光螢光分析與X光繞射譜圖分析，確定樣品表面有薄薄一層氧化物(Bi2O3)，除此之外無其他雜質。透過AFM與X光繞射鑑定樣品的粒徑大小分別為5.7 nm與24.3 nm。
為了探討奈米鉍顆粒的磁特性，我們對奈米鉍顆粒進行一系列M-H量測，平均粒徑為5.7 nm與24.3 nm的奈米鉍顆粒皆觀察到自旋極化與反磁效應的現象，並利用修正過的朗之萬函數(Langevin function)以及修正反磁項(diamagnetic term)來描述其特性。本論文更進一步以壓合的方式改變奈米鉍顆粒的間距，使得奈米鉍顆粒間的交互作用影響增加，觀察到奈米鉍顆粒的自發磁性減弱。另外，也觀察到在聚合密度較低時，飽和磁化強度隨顆粒間距縮短而增強，在聚合密度較高時，飽和磁化強度則會隨顆粒間距縮短而減弱。
探討奈米鉍顆粒的自發磁性隨顆粒間距變化趨勢，受到顆粒表面的費米能量隨顆粒間距變化的影響。除此之外，奈米鉍顆粒的飽和磁化強度隨顆粒間距變化的趨勢，則受到crosslinking effect以及magnetic dipole-dipole interaction的影響。

Two sets of nano-sized bismuth powder samples were fabricated by the thermal evaporation method. The atomic force microscope image, x-ray diffraction patterns, and x-ray fluorescence pattern were used to determine the particle size and composition. AFM images and XRD patterns showed that the mean particle diameters of samples are 5.7 nm and 24.3 nm. A very thin layer of bismuth oxide covers the surface Bi particles, other then that there is no trace of impurity.
Magnetic properties were studied by magnetization measurement. The M-H curves of the 5.7 nm and 24.3 nm nanoparticles can be described by a modified Langevin function plus a modified diamagnetic term. Influence of the interparticle interactions on the magnetic characters of Bi nanoparticles is studied. The interparticle separation between Bi nanoparticles are tuned by cold press the particle assembly, indicated by packing fraction f of the assembly that ranging from 1% to 77% of the mass density of bulk Bi. The variations of the particle moment μP and the saturation magnetization Ms are investigated as well. The particle moment of the samples decreases as f is increased. The saturation magnetization of those samples with f smaller than 60 % increase as f is increased. The saturation magnetizations of those samples with f larger than 60 % decrease with increasing of f.
The variation of the particle moment is discussed by consider of the Fermi energy of the surface and core atoms in the nanoparticles. The variation of the saturation magnetization may be understood by the crosslinking effect and magnetic dipole-dipole interaction.

目 錄
論文摘要 Ⅰ
Abstract Ⅱ
致謝 Ⅲ
目錄 Ⅳ
圖目與表目 Ⅵ


第一章 簡介 1
1-1 塊材鉍之基本物理性質 1
1-2 奈米尺度下之磁特殊性質 3
1-3 實驗動機 5
參考文獻 7
第二章 樣品基本性質分析與量測儀器介紹 8
2-1 樣品製備 8
2-2 成分分析 11
2-3 粒徑分析 15
2-4 巨觀磁性量測 30
參考文獻 33
第三章 自旋極化參數分析 34
3-1 自旋極化模型 34
3-2 磁化曲線擬合分析 36
3-3 熱誘發對顆粒磁矩之影響 43
3-4 熱擾動對飽和磁化強度之影響 47
3-5 粒徑對自旋極化之影響 49
參考文獻 54
第四章 顆粒間交互作用對自旋極化參數之影響 55
4-1 樣品壓合 55
4-2 顆粒間交互作用對顆粒磁矩之影響 57
4-3 顆粒間交互作用對飽和磁化強度之影響 72
4-4 顆粒間交互作用對有效磁能之影響 79
參考文獻 85
第五章 結論 86

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