臺灣博碩士論文加值系統

由於在室溫下奈米矽可以產生很強的光激發光，因而引起廣泛地研究與討論。過去這幾年來，科學家也發現奈米矽在空氣中予以表面氧化處理之後，它將產生更強的紅光。 本研究係以熱蒸鍍系統製備奈米矽，並探討四種不同形式的奈米矽材料的發光機制，分別為矽奈米粒子、矽奈米團塊、以及經由氫氟酸和醋酸處理後的矽奈米團塊。
本實驗中，藉由X光繞射圖(XRD) 計算奈米矽之平均粒徑大小，由穿透式電子顯微鏡(TEM)觀察其尺寸分佈。另外，從掃瞄式電子顯微鏡(SEM)和原子力電子顯微鏡(AFM)影像可得知其球型凝團情況。在分析表面鍵結情況方面，係從傅式轉換紅外光譜(FTIR)著手，而吸收能隙資訊的量測，則是藉助於紫外-可見光吸收光譜分析儀(UV-visible light spectroscopy)。
就奈米矽光激發光實驗而言，分四個部分作討論。在第一部份，工作壓力小於1torr時，矽奈米粒子在空氣下會產生較強的紅光。由於矽奈米團塊表面較其晶粒勻稱，故以其團塊取代晶粒進行後續之研究。第二部分則是針對在0.5torr工作壓力下製作的矽奈米團塊做其表面特性的研究。經由氣氛週期循環式光激發光的分析後，在空氣下所量測的結果迥異於氧氣和氮氣氣氛下的現象，且其強度的改變是不可逆的。推測除了物理吸附(空氣吸附)外，微弱的化學吸附(空氣氧化)可能是影響關鍵所在。另外，經由水浸泡處理後，其光激發光強度為其原來之兩倍，這是因為水的表面吸附使其表面產生新的電子電洞對再結合機制，因而導致其發光變強。經由時效處理後，由於材料本身的自然氧化也會使得強度增強許多。除此之外，光激發光的雷射功率大小亦會影響其表面結構及其發光特性。
第三部分，藉由氫氟酸去除矽表面的氧化物，進而探討其空氣氧化對其表面光激發光的影響。經由氫氟酸處理之後，光激發光光譜呈現藍移現象，這是因為奈米矽氧化的表面被去除之後所表現的本質光譜。一旦暴露在空氣下氧化後，光激發光光譜則紅移回到之前氧化情況下的穩定波長。第四部分的實驗，係經由醋酸浸泡處理，由於其增強矽表面的Si-O 鍵結，促使其發光增強。

The study of Si nanostructures is a very active field of research because of their strong room temperature photoluminescence. In recent years, a strong red luminescence has been often observed after surface oxidization in air. In this study, Si nanomaterials were prepared by a thermal evaporation system, and four kinds of Si nanomaterials, nanoparticles, nanoclusters, nanoclusters with HF treatment, and nanoclusters with CH3COOH treatment, were studied.
The average size and size distribution of Si nanoparticles were determined by XRD and TEM, respectively. From the SEM and AFM images, the spherical aggregation was observed. The surface bonding was be analyzed from the FTIR spectroscopy, and the absorption band gap was examined by UV-visible light spectroscopy.
Four parts of PL experiment were conducted. In the first part, the Si nanoparticles showed a strong red light emission in air when the Ar working pressure was less than 1torr. The second experiment was focused on nanoclusters prepared at 0.5 torr Ar, and their surface effect was examined. After the cyclic PL analysis, the characteristic of PL in air was different from that in O2 or N2. The change in PL intensity was not reversible in this cycling. Besides the physisorption (air adsorption), the weak chemisorption (air oxidization) might be the factor to cause this difference. After water treatment, the PL intensity of Si clusters was twice as high as that of untreated clusters. This proves that the adsorption of water could help Si clusters to emit higher PL intensity, which is due to the creation of a new set of recombination traps confined in the clusters. From the aging experiment, it could be concluded that the samples were naturally oxidized after exposure to air and this oxidization might enhance the intensity. By changing the laser power, the relationship between the magnitude of laser power and the level of oxidization of Si nanoclusters was established.
The third part of experiment was to remove the surface oxide SiOx by etching with HF and to study the influence of air oxidization on the PL properties. After the HF solution treatment, the PL showed a blue shift caused by the core of Si nanoparticles. However, after air exposure, the PL slowed a red shift and the intensity was increased, implying that the air oxidization played an important role in PL. Finally, after the CH3COOH solution treatment, the intensity of PL increased due to the stronger Si-O bond on the surface of Si nanoclusters.

摘要
Abstract
誌謝
Table of contents
Chapter Ⅰ Introduction 1
1. Nanomaterials 1
2. Preparation of nanomaterials 1
3. Si nanomaterials 3
4. Applications of Si nanomaterials 5
Chapter Ⅱ Literature Review 6
1. Luminescence from Si-based materials 6
(1) Porous Si 6
(2) Si nanoclusters 9
(3) Si quantum wells 9
(4) Si quantum wires 12
(5) Si quantum dots 12
2. Photoluminescence mechanisms 15
(1) Quantum confinement model 15
(2) Surface localization model 19
3. Oxidization effect 19
4. Aging effect 27
5. Laser power effect 27
6. Adsorption effect 27
(1) Adsorption of O2 / N2 27
(2) Adsorption of H2O 31
(3) Adsorption of other gases 36
7. Acids effect 36
Chapter Ⅲ Experimential Procedures 38
1. Preparation of Nanoclusters 38
2. Surface Treatment 38
(1) HF solution treatment 38
(2) CH3COOH solution treatment 38
(3) Water treatment 40
3. Characterization of Nanoclusters 40
(1) Transmission Electron Microscopy (TEM) 40
(2) X-ray Diffraction (XRD) 40
(3) Scanning Electron Microscopy (SEM) 42
(4) Atomic Force Microscopy (AFM) 42
(5) Fourier Transform Infrared (FTIR) Spectroscopy 42
(6) UV-Visible Light Spectroscopy 43
(7) Photoluminescence (PL) Measurement 44
Chapter Ⅳ Results and Discussion 49
1. Si nanoparticles 49
(1) TEM and XRD patterns 49
(2) UV-visible light spectroscopy 49
(3) PL analyses 49
A. Particle size effect 49
B. Air effect 54
2. Si nanoclusters 54
(1) SEM and AFM morphologies 54
(2) FTIR analysis 58
(3) PL analyses 58
A. Clusters effect 58
B. Air effect 61
C. Gas adsorption effect 61
D. Water effect 66
E. Age effect 69
F. Laser power effect 69
3. Si nanoclusters with HF treatment 74
(1) SEM and AFM morphologies 74
(2) FTIR analysis 78
(3) UV-visible light spectroscopy 78
(4) PL analyses 78
A. HF effect 78
B. Air effect 83
4. Si nanoclusters with CH3COOH treatment 83
(1) SEM and AFM morphologies 83
(2) FTIR analysis 86
(3) UV-visible light spectroscopy 86
(4) PL analyses 86
A. CH3COOH effect 86
B. Air effect 92
Chapter Ⅴ Conclusions 94
1. Si nanoparticles 94
2. Si nanoclusters 94
3. Si nanoclusters with HF treatment 95
4. Si nanoclusters with CH3COOH treatment 96
References 97

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