我們在水相中以醋酸鎘、硫乙醯胺與硝酸成功合成出硫化鎘奈米粒子，所合成出來的菱形十二面體的直徑約為100奈米，該形狀的硫化鎘奈米粒子尚未被國際期刊發表過。我們也以相同的合成手法，透過調整醋酸鎘用量、較少量的硝酸以及較短的反應時間，成功合成出可調控尺寸的硫化鎘奈米粒子，其粒徑分別為27、52、68、81、104、116、130以及164奈米。穿透式電子顯微鏡的鑑定結果確認合成出的硫化鎘菱形十二面體表面暴露的晶面為{110}晶面，而可調控尺寸的硫化鎘奈米粒子大多為多晶結構。此外，我們也深入探討其成核與晶體成長的機制，並以可見光吸收光譜等技術監測反應的過程，藉由了解這些機制，我們得以掌握更多調控晶體尺寸與形狀的因素。我們透過吸收以及放光光譜來量測硫化鎘奈米粒子的光學性質，觀測到不論是吸收還是放光譜帶，都有隨著粒子尺寸的增大而有紅位移的現象，這展示了在量子侷限效應的範疇外，仍能觀測到半導體的光學尺寸效應。最後，我們嘗試建構了一個修正過後的能帶結構圖，用以解釋硫化鎘奈米粒子在光學上的尺寸與晶面效應。

CdS rhombic dodecahedra with sizes of ~ 100 nm have been synthesized for the first time by heating an aqueous mixture of cadmium acetate, thioacetamide (TAA), and nitric acid. We have also prepared zinc blende CdS nanocrystals with tunable sizes of 27, 52, 68, 81, 104, 116, 130, and 164 nm using the same reaction conditions but varying the cadmium acetate amount, reducing HNO3 amount and shorting the reaction time. TEM characterization confirms the {110} surfaces of CdS rhombic dodecahedra and somewhat polycrystalline CdS nanocrystals. The reaction process has been monitored using UV-vis spectroscopy. By recording the light absorption and emission spectra of these nanocrystals, their absorption and emission bands shift steadily to longer wavelengths, demonstrating again that semiconductor optical size effects are observable far beyond the expected quantum confinement dimensions. A modified band diagram for CdS nanocrystals has been constructed to clarify their optical size and facet effects.

TABLE OF CONTENTS
論文摘要 I
ABSTRACT II
TABLE OF CONTENTS III
LIST OF FIGURES V
LIST OF SCHEMES XII
Synthesis of CdS Rhombic Dodecahedra and Size-Tunable CdS Nanocrystals with a Zinc Blende Structure Showing Optical Size Effects
1 Introduction 1
1.1 Cadmium sulfide 6
1.2 Reported synthesis of CdS nanocrystals in organic phase 7
1.3 Reported synthesis of CdS nanocrystals in aqueous phase 10
1.4 Nucleation and crystal growth 13
1.5 Optical properties 14
1.6 Electrical conductivity properties 17
2 Experimental 21
2.1 Reagents 21
2.2 Instrumentation 21
2.3 One-pot synthesis of CdS rhombic dodecahedra (RD) 21
2.4 One-pot synthesis of size-tunable CdS nanocrystals 22
3 Results and discussion 24
3.1 Characterizations of CdS rhombic dodecahedra 24
3.2 Characterizations of size-tunable CdS nanocrystal 29
3.3 Previous hypothesis: reaction rate determines particle size and shape 36
3.4 Hypothesized formation mechanism 37
3.5 The size effect on optical properties 50
4 Conclusion 58
References 59

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