銳鈦礦奈米二氧化鈦因為具有強光催化力、化學穩定性佳、照光之後穩定、無毒及低價位的優點，是目前最重要的光觸媒材料。但是因為其能隙對應到紫外光區，在太陽頻譜中僅佔4 %左右，遠小於可見光區的51 %，所以需要透過摻雜來增加其對可見光的反應。其中，氟氮共摻雜最為有效。除此之外，透過異質接面也可以有效分離電子電洞對，增加其生命期與光催化力。
當六氟鈦銨與硼酸水溶液在特定莫爾濃度比例下，可以在玻璃基板上方成長三氟氧鈦銨圓盤狀晶體。透過玻璃基板消耗混合溶液中之氫氟酸，可以加速三氟氧鈦銨在玻璃基板上方的成長，使之大幅高於文獻中在雙十八烷基二甲基銨薄膜上之生長速度。X光繞射儀與高解析度穿透式電子顯微鏡皆顯示三氟氧鈦銨具有單晶結構。由霍氏轉換紅外光光譜儀與拉曼頻譜可得知，每個二氧化鈦八面體皆為銳鈦礦結構，且周圍皆圍繞著大量的氟與氮原子。換言之，三氟氧鈦銨具有轉換成高濃度氟氮共摻雜銳鈦礦奈米二氧化鈦顆粒之潛力。
將三氟氧鈦銨透過氧氣回火使之轉換為氟氮共摻雜銳鈦礦奈米二氧化鈦顆粒。透過不同的回火溫度可以得到不同氟氮共摻雜濃度之二氧化鈦顆粒，並且發現其對可見光有良好的吸收。如果使用發光位置為450奈米之藍光二極體做為激發光源，最高可以獲得11.2倍商用P-25之光催化力。同時也發現其電子電洞對生命期與光催化力成正比。
我們更進一步使用有機金屬化學氣相沈積法將硫化鋅或硒化鋅生長在氟氮共摻雜銳鈦礦奈米二氧化鈦顆粒上，可以形成異質接面結構。硫化鋅具有高於二氧化鈦之能隙，所以可以保留氟氮共摻雜的角色。硒化鋅之能隙非常接近太陽頻譜中最高強度，所以可以幫助二氧化鈦對光之敏感性。高解析度穿透式電子顯微鏡皆顯示硫化鋅或硒化鋅具有單晶結構。對硫化鋅或硒化鋅與二氧化鈦異質接面結構來說，其電子電洞對生命期分別由原來的65奈秒延長至207或240奈秒。它們的光催化力分別是商用P-25的1.5與2.0倍。同時也發現其電子電洞對生命期與光催化力成正比。除此之外，硫化鋅或硒化鋅對二氧化鈦表面缺陷之鈍化作用也顯示對其光催化力呈現負面影響。
SK模式之自聚性量子點結構必須在壓縮應力大於2 %以上才可以獲得。在砷化鎵基板上，高密度硒化鋅自聚性量子點結構可以在適當的硫化鋅緩衝層厚度下被獲得。為了要獲得最高密度，硫化鋅必須不受砷化鎵基板的伸張應力之影響，所以其厚度必須生長至高於130奈米左右。經過硒化鋅成長30秒後，最高密度為每平方公分4.9 x 109個。在砷化鎵基板上直接成長硒化鋅，由於兩者間晶格不匹配性僅有0.26 %，理論上不應該發現有自聚性量子點結構。但是在成長硒化鋅時加入過量的硒原料下，由於硒原子的析出作用，可以發現一些類似自聚性量子點的結構，最高密度為每平方公分4 x 108個。
高品質柱狀氧化鋅與片狀氫氧化鋅透過硝酸鋅及六亞甲基四胺水溶液生長在砷化鎵基板上。透過加入適量濃度的硝酸水溶液，可以控制柱狀氧化鋅或片狀氫氧化鋅的生長與密度。如果成長在晶格匹配之氮化鎵基板上，更可以得到直立式柱狀二氧化鋅矩陣。將片狀氫氧化鋅在笑氣中回火脫水成為氧化鋅，可以獲得更高的光催化力。

High quality ammonium oxofluorotitanate discoid crystal is successfully grown on glass with an aqueous solution of ammonium hexafluorotitanate and boric acid at the molar ratio of 0.6. The concentration of hydrofluoric acid is less on the glass substrate surface and enhances the ammonium oxofluorotitanate nucleation growth. The growth rate is much higher than that grown on dioctadecyldimethylammonium. From the examinations of X-ray diffraction and high-resolution transmission electron microscopy, the crystal shows high crystalline quality and uniformity. Each titanium oxide octahedral is linked with fluorine and nitrogen atoms. Therefore, ammonium oxofluorotitanate has high potential to be thermally decomposed into high crystalline fluorine and nitrogen co-doped titanium oxide.
A simple process for the preparation of nanocrystalline anatase phase titanium oxide converted from ammonium oxofluorotitanate by thermal treatment was developed. The nanocrystalline anatase phase titanium oxide shows a large bandgap reduction due to the co-doping of high concentrations of fluorine and nitrogen. Due to the excellent nanocrystalline quality and the co-doping of higher concentrations of fluorine and nitrogen at the thermal treatment temperature of 800 OC, it is 1.3 times the photocatalytic activities of P-25 due to the visble region usage of Hg lamp light source. The 11.2 times the visible photocatalytic activities of P-25 using blue light-emitting diode as the light source is obtained from thermal treatment temperature of 600 OC. There is one to one correspondence between carrier lifetime and photocatalytic activity. As a result, a highly reactive and visible-light-driven photocatalysis is achieved.
The heterostructure of zinc selenide/titanium oxide and zinc sulfide/titanium oxide were prepared by metal-organic chemical vapor deposition on the above-prepared titanium oxide. The energy bandgap of zinc sulfide is much larger than that of titanium oxide and can act as a window for titanium oxide. It would not hinder titanium oxide absorption and preserve the role of fluorine and nitrogen co-doping. The energy bandgap of zinc selenide is near the maximum intensity of solar spectrum and acts as a sensitizer of titanium oxide. The lifetime of electron and hole pairs of heterostructure are about 240 and 207 nsec, which are longer than 65 nsec of titanium oxide prepared at 800 oC thermal treatment. Their photocatalytic activities are further improved to 2.0 and 1.5 times higher than that of commercial P-25. The photocatalysis of titanium oxide is very sensitive to the surface states. Titanium oxide surface defects can act as trapping sites for photo-induced holes and facilitate the separation of photo-induced carriers. Zinc selenide and zinc sulfide can passivate the surface well. It may say that titanium oxide surface defects removal has a negative impact.
The density, height, diameter, PL wavelength and intensity of zinc selenide self-assembled quantum dots grown on zinc sulfide/gallium arsenide with the zinc sulfide thickness from 15 to 160 nm are studied. For a fixed 30 sec zinc selenide self-assembled quantum dots growth, it cannot be formed with the zinc sulfide thickness below 15 nm due to the close lattice match between zinc sulfide and gallium arsenide. The zinc sulfide/gallium arsenide is fully lattice relaxed with the zinc sulfide thickness higher than 130 nm examined by X-ray diffraction. The higher quality and density of zinc selenide self-assembled quantum dots can be obtained on zinc sulfide/gallium arsenide with the zinc sulfide thickness far beyond its critical thickness. The maximum zinc selenide self-assembled quantum dots density of 4.9 x 109 cm-2 with the strongest photoluminescence intensity is obtained at the zinc sulfide/gallium arsenide thickness of 130 nm. Clusters are formed on the surface of zinc selenide/gallium arsenide. The selenium segregation is the main mechanism for the formation of clusters. The dislocations will enhance the selenium segregation. Higher zinc selenide cluster corresponds to higher density of dislocations. The non-spherical cluster is formed from the mergence of the two clusters.
High quality zinc oxide rods and zinc hydroxide slices are successfully grown on gallium arsenide with the aqueous solution of zinc nitrate and hexamethylenetetramine. The growth can be controlled by the appropriate nitric acid concentration incorporation in the solution. After thermal annealing, the zinc oxide slices transformed from zinc hydroxide slices can contribute much higher photocatalytic activity to 1.2 times to P-25.

Contents

Acknowledgment………………………………......………....................I
中文摘要……………………………………………………......……...III
Abstract………………………………………………………..….…....IV
Contents………………………………………………..……..….........VII
Figure Captions……………………………………………………...XIII
Table Captions…..…………………………………….........……...XXIV

Chapter 1
Introduction……………………………......................…………………1
1.1 Introduction………………………………………….......………....1
1.2 Background…………………………………………………….…..2
1.3 Photocatalysis………………………………………………….…..3
1.4 Semiconductor Photocatalysis……………………………………..4
1.5 Mechanism of Photocatalysis………………………..……….……5
1.6 Preparations of TiO2………………………………………….……6
1.7 Motivations…………………………………………….….……….7
1.7.1 Doping………………………………………………...…….7
1.7.2 Heterojunction…………………………………...………….8
1.8 Thesis Organization……………………………………….………10

Chapter 2
Experiments……..........................……………………………………..14
2.1 LPD Deposition Procedures……………….................…………..14
2.1.1 LPD Methode…...………………………................................14
2.1.2 Cleaning Procedures for Glass, GaAs and GaN substrates…..15
2.1.3 Preparation of Deposition Solution…………………………..17
2.1.4 Preparation of LPD-TiO2 and LPD-NH4TiOF3………..……..17
2.1.4.1 Preparation of (NH4)2TiF6 Solution…………………..18
2.1.4.2 Preparation of H3BO3 Solution……..………………...18
2.1.4.3 Growth Procedure…………………………..………...18
2.1.4.4 Basic Mechanism……………………………………..19
2.1.5 Preparation of LPD-ZnO……………………………………..19
2.1.5.1 Preparation of Zn(NO3)2 Solution…………….……...19
2.1.5.2 Preparation of C6H12N4 Solution……………………..20
2.1.5.3 Preparation of HNO3 Solution………………………..20
2.1.5.4 Growth Procedure…………………………..………...20
2.1.5.5 Basic Mechanism……………………………………..21
2.1.6 Equipments………………………………….………………..21
2.1.7 Physical and Chemical Properties………….………………...22
2.1.8 Photocatalytic activity………………………………………..23
2.1.9 Time-resolved Lifetime Measurement……......……..……...25
2.2 Growth Procedure of MOCVD…………………………………..25
2.2.1 MOCVD Methode..…………………………………………..26
2.2.2 Cold Wall System and Single Hot Zone……….……………..28
2.2.3 Simplicity, Flexibility and Versatility…………………….…..28
2.2.4 Halide-Free………………………………………….………..29
2.2.5 Stoichiometry Easily Controlled…………….………………..29
2.2.6 Low Temperature and Low Pressure Growth…….…………..30
2.2.7 Capability of Heterostructure………………………….……..30
2.2.8 Components of MOCVD……………………………………..31
2.2.9 Design of Growth Reactor…………………………..………..31
2.2.10 Reactant Gases………………………………….…………..32
2.2.11 Heating System……………………………………………..33
2.2.12 Exhaust Disposal System……………………….…………..34
2.2.13 Safety Considerations…………………………………..…..34
2.2.14 Characterization Techniques…………………………….….35
2.2.14.1 Atomic Force Microscopy (AFM).……………..…..35
2.2.14.2 Photoluminescence (PL) ………………….………..36

Chapter 3
Ammonium Oxotrifluorotitanate Discoid Crystal Prepared by Liquid-Phase Deposition…………………..…………………………..47
3.1 Introduction…………………………………………………...…..47
3.2 Growth Parameters………………………………………………..49
3.3 Characteristics of NH4TiOF3 Discoid Crystal……..……………...49
3.3.1 H3BO3/(NH4)2TiF6 ≥ 0.6……………………………..……..49
3.3.2 H3BO3/(NH4)2TiF6 < 0.6…………………….……………..52
3.4 Chemical Reaction and Growth Mechanism for LPD-TiO2 ……..55
3.5 Crystal Structure of NH4TiOxF5-2x………………………………..56

Chapter 4
High Photocatalytic Activity of Fluorine and Nitrogen Co-doped Nanocrystalline Anatase Phase Titanium Oxide Converted from Ammonium Oxotrifluorotitanate…………………….……………….72
4.1 Introduction…………………………………………………….…72
4.2 Growth Parameters……………………………………….……….73
4.3 Physical and Chemical Analyses of Nanocrystalline Anatase Phase TiO2 Converted from NH4TiOF3………………………….….….73
4.4 Photocatalytic Activity and Roles of F and N in Nanocrystalline Anatase Phase TiO2………………………………….….……….77
4.5 One to One Correspondence between Carrier Lifetime and Photocatalytic Activity…………………………………..…….82
4.6 Visible Photocatalytic Activity…………………………………...83
4.7 Water Splitting……………………………………………………87

Chapter 5
High Photocatalytic Activity of Heterojunction of Zinc Selenide or Zinc Sulfide Coated Titanium Oxide Particles……………………..107
5.1 Introduction………………..………………………….………...107
5.2 Growth Parameters…………..…….……………………….…...108
5.2.1 NH4TiOF3 discoid crystal…………...…….……………....108
5.2.2 MOCVD Growth ZnSe and ZnS..…………..….………....109
5.3 Physical and Chemical Analyses of ZnSe Coated Nano-scaled TiO2 Particles……………………………………..…………………..109
5.3.1 Heterojunction of ZnSe/TiO2………………...…………....109
5.3.2 One to One Correspondence between Carrier Lifetime and Photocatalytic Activity……………….…….………….....112
5.3.3 Photoinduced Hydrophilic Property……………..………..112
5.4 Physical and Chemical Analyses of ZnS Coated Nano-scaled TiO2 Particles…………………..….……….......................................113
5.4.1 Heterojunction of ZnS/TiO2…………….……….….…...113
5.4.2 One to One Correspondence between Carrier Lifetime and Photocatalytic Activity…………….……………..…….…...116
5.5 Conclusions…………….……………………………….…...116

Chapter 6
Conclusions……………………..…………………………………….132
6.1 Ammonium Oxofluorotitanate Discoid Crystal……….…....132
6.2 Fluorine and Nitrogen Co-doped TiO2 Nano-scaled Particles………..………………………………….……...132
6.3 High Photocatalytic Activity of Heterojunction of Zinc Selenide or Zinc Sulfide Coated Titanium Oxide Particles…………………………………………………....133
6.4 Nano-scaled Group II-VI Compound Semiconductor Prepared by Metal-Organic Chemical Vapor Deposition…….….…..134
6.4.1 High density ZnSe self-assembled quantum dots grown on ZnS/GaAs with ZnS buffer layer far beyond its critical thickness………………………………….....134
6.4.2 Mechanism of clusters formation on zinc selenium/gallium arsenic prepared by metalorganic vapor phase epitaxy ………………………………...134
6.5 Growth of Zinc Oxide Rods and Zinc Hydroxide Slices on Gallium Arsenide with Zinc Nitrate and Hexamethylenetetramine Aqueous Solution by Incorporating with Nitric Acid…………………………………………....135
6.6 Photocatalysis of Zinc Oxide Converted from Zinc Hydroxide Slices by Thermal Annealing …..………..……..….….......135

Appendix I
Zinc Selenide Self-assembled Quantum Dots and Clusters Prepared by Metal-Organic Chemical Vapor Deposition……………………..137

Appendix II
Growth of Zinc Oxide Rods and Zinc Hydroxide Slices on Gallium Arsenide with Zinc Nitrate and Hexamethylenetetramine Aqueous Solution by Incorporating with Nitric Acid………………………...164

Appendix III
Photocatalysis of Zinc Oxide Converted from Zinc Hydroxide Slices by Thermal Annealing………………………….……………….……176

References……………………………………………………………..193

Publication List……………………………………………………….216

Autobiography…………………………………………………....…..221


Figure Captions
Chapter 1
Figure 1.1 Semiconductors employed in photocatalysis and bandgap energies. …………….……………………………………12

Figure 1.2 Energy levels for some semiconductors employed in photocatalysis with respect to the normal hydrogen electrode. …………….……..……………………………13

Chapter 2
Figure 2.1 Flow chart of LPD-NH4TiOF3 and LPD-TiO2. …….…….…38

Figure 2.2 Flow chart of LPD-ZnO and LPD-Zn(OH)2. ………………39

Figure 2.3 Schematic diagrams of the apparatus for LPD deposition. ....40

Figure 2.4 Photocatalytic examination procedure. ……………..………41

Figure 2.5 The lifetime is derived from multiexponential fittings. …….42

Figure 2.6 Various processes during an epitaxial growth. ……….……..43

Figure 2.7 (a) Illustration of the MOCVD system. (b) Cross-section of the rectangle quartz tube. ……………………..….…………….44

Figure 2.8 Vapor pressure of organometallic precursors. …………..….45

Figure 2.9 Flow chart of MOCVD. …………….……………………....46

Chapter 3
Figure 3.1 SEM surface morphologies obtained with the molar ratio of H3BO3/(NH4)2TiF6 at 3.0 before (a) and after (b) annealing, (b) 0.6 and (d) 0.15. ….……………………………………58

Figure 3.2 Morphologies of NH4TiOF3 discoid crystal observed by the SEM for (a) 15, (b) 30, (c) 45, (d) 75 and (e) 90 min growth, and (f) shows the cross section of 90 min growth with H3BO3/(NH4)2TiF6 at 0.6. ….…………………….………..59

Figure 3.3 FTIR spectrum of NH4TiOF3 discoid crystal with H3BO3/(NH4)2TiF6 at 0.6. ….………………….……..…60

Figure 3.4 XRD spectrum of NH4TiOF3 discoid crystal with H3BO3/(NH4)2TiF6 at 0.6. ….………………….………..61

Figure 3.5 Sketch of NH4TiOF3 discoid crystal and its diffraction patterns of the crystal planes labeled as ‘T’ and ‘S’ with H3BO3/(NH4)2TiF6 at 0.6. ….……………………….………62

Figure 3.6 (a) BEI and (b) TOF-SIMS mapping show the uniform composition distribution of NH4TiOF3 discoid crystal with H3BO3/(NH4)2TiF6 at 0.6. ….……………………….……..63

Figure 3.7 XRD spectrum as a function of the mole ratio of H3BO3/(NH4)2TiF6. ….…………………………………...64

Figure 3.8 SEM surface morphologies obtained with the mole ratio of H3BO3/(NH4)2TiF6 at (a) 0.6, (b) 0.5, (c) 0.4 and (d) 0.2. ….………………………………………….………….65

Figure 3.9 FTIR spectra as a function of the mole ratio of H3BO3/(NH4)2TiF6.….……………………………………66

Figure 3.10 UV-Vis spectra of different mole ratio of H3BO3/(NH4)2TiF6. …………………….……………….67

Figure 3.11 Ramam spectrum of NH4TiOF3 discoid crystal. ……..……68

Figure 3.12 Possible chemical reaction mechanism of LPD-TiO2 film...69

Figure 3.13 Possible deposition mechanism of LPD-NH4TiOF3 discoid crystal deposited on glass substrate. ….………….……..…70

Figure 3.14 Crystal structure of NH4TiOxF5-2x: (a) part of the chain built from cis corner-connected TiF6 octahedra. (b) zigzag chains of corner-connected TiF6 octahedra with ammonium ions in between. ….…………………………………………….…71

Chapter 4
Figure 4.1 XRD spectra as a function of thermal treatment temperature. The insets show the morphologies of as-deposited as grown NH4TiOF3 discoid crystal, and that of thermal treatment at 400 0C, 500 0C, 600 0C and 800 0C. ………………….……….…88

Figure 4.2 High resolution images of (a) 200 0C, (b) 400 0C and (c) 800 0C. Nano-scaled TiO2 shows the single crystalline diffraction pattern after 800 0C thermal treatment. (d) TOF-SIMS mapping shows the uniformity of TiO2 particles. ………..…89

Figure 4.3 High resolution image shell and interior nano-crystal after 600 0C thermal treatment. Their corresponding diffraction patterns all show high quality single crystallinity. ………………..…90

Figure 4.4 (a) Transmittance spectra and (d) its corresponding optical absorption edges as functions of thermal treatment temperature. ………………….………………………..…..92

Figure 4.5 Diffraction patterns of the discoid crystal labeled as ‘T’ plane. Sketch of beam direction is show in (a). Different diffraction patterns of (b) NH4TiOF3, (c) TiOF2 and (d) TiO2 can be obtained after 0, 10 and 20 min electron beam impaction. ……………………………………………..……93

Figure 4.6 (a) Micro PL spectra as a function of thermal treatment temperature. (b) and (c) show more detailed micro PL spectra of as-deposited and 700 0C thermal treatment specimens, respectively. …………………………………………….…95

Figure 4.7 (a) Atomic concentrations of F and N as functions of the thermal treatment temperature. (b) More detailed of N and F doping concentrations at the temperature higher than 300 0C. …………………………………………………………96

Figure 4.8 ESCA spectra of (a) Ti, (b) O, (c) F and (d) N as functions of thermal treatment temperature. ………………….………….98

Figure 4.9 (a) Photocatalytic activity as a function of the thermal annealing temperature. (b) Lifetime of EHP as a function of cutoff wavelength examined by time resolved fluorescence spectrometers. ………………….……………….………..100

Figure 4.10 Detail ESCA spectra of (a) F and (b) N in TiO2 as functions of thermal treatment temperature. ……………….………101

Figure 4.11 Transmittance of methylene blue at 664 nm under 450 nm blue LED illumination. (b) Lifetime of EHP as a function of thermal treatment temperature. …………………………102

Figure 4.12 Lifetime of EHP as functions of excited energy and thermal treatment temperature. ………………….………………..103

Figure 4.13 Schematic diagram of energy bandgap of F and N co-doped TiO2 via NHE. ………………….………………………..104

Figure 4.14 Schematic diagram for the events of photo-generated electrons in TiO2 and its corresponding lifetime. ……..…105

Chapter 5
Figure 5.1 Optical absorption edges as functions of NH4TiOF3 thermal treatment temperature and ZnSe growth time. …................117

Figure 5.2 (a) ZnSe/TiO2 heterojunction structure of HRTEM and lattice images indicated with blue circuits The dark region is belonged to TiO2 and coated with a ZnSe shell. Its HRTEM image is shown in (b). High crystal quality of (c) twin crystal of ZnSe dots is observed on the outer shell. Moir&eacute; fringes as a result of nano-particles randomly attached to relatively large grain. Both the DP of (d) core and (e) shell show single crystal. Photocatalystic activity is as a function of ZnSe growth time as shown in (f). The corresponding lifetime of EHP is shown in the inset. (g) is the HTREM image of ZnSe coated on a discoid TiO2, which shows the uniform coverage via MOCVD growth. ...…..……………………………....121

Figure 5.3 (a) Photocatalystic activity as function of ZnSe growth time and thermal treatment temperature of NH4TiOF3. (b) Lifetime of EHP as a function of ZnSe growth time. (c) (a) Ratio of photocatalytic activity to P-25, and (b) lifetime of EHP as functions of ZnSe growth time. ………………....123

Figure 5.4 Images of MB drops on the photoinduced super hydrophilic 15-min-ZnSe/800 oC-TiO2. …............................................124

Figure 5.5 Energy bandgap diagram of ZnSe/TiO2 heterojunction structure. …......................................................................125

Figure 5.6 Energy bandgap diagram of ZnS/TiO2 heterojunction structure. ……………………………………………......126

Figure 5.7 Optical absorption edges as functions of NH4TiOF3 thermal treatment temperature and ZnS growth time. ……………..127

Figure 5.8 Heterojunction structure of ZnS/TiO2 and indicated with blue circuits. The dark region is belonged to TiO2 and coated with a ZnS shell. Both the DPs of core and shell are single crystal. …………………………………………………...128

Figure 5.9 Photocatalystic activity as a function of ZnS growth time. The corresponding lifetime of EHP is shown in the inset. .........129

Figure 5.10 HTREM image of ZnS coated on a discoid TiO2, which shows the uniform coverage via MOCVD growth. ….....130

Figure 5.11 (a) Photocatalystic activity as function of ZnS growth time and thermal treatment temperature. (b) Lifetime of EHP as a function of ZnS growth time. ……………………………131

Appendix I
Figure 7.1 AFM 3D ZnS surface images of (a) 0, (b) 15, (c) 57, (d) 103, (e) 130 and (f) 160 nm on GaAs. ………..….……………..148

Figure 7.2 XRD spectra of ZnS on GaAs as a function of ZnS thickness. ………………………………………………….149

Figure 7.3 AFM (a) 2D and (b) 3D ZnSe QDs images on (i) 15, (ii) 57, (iii) 103, (iv) 130 and (v) 160 nm ZnS/GaAs for a fixed 30 sec ZnSe growth. ………..…………………………………….151

Figure 7.4 Density of ZnSe QDs as a function of ZnS thickness for a fixed 30 sec ZnSe growth. ……………………………..….152

Figure 7.5 Diameter and height of ZnSe QDs as functions of ZnS thickness. ………………………………………………...153

Figure 7.6 PL spectra of ZnSe QDs as a function of ZnS thickness. ……..……..………………………………….154

Figure 7.7 Emission energy of ZnSe QDs as functions of ZnS thickness and ZnSe QD size. ………………………………………...155

Figure 7.8 Density and diameter of clusters as functions of the flow rate of H2Se. ……………………………………………………156

Figure 7.9 (a) AFM images, (b) and (c) SEM morphologies of ZnSe clusters and (d) without cluster formation. ………………158

Figure 7.10 Size distribution of clusters. ……………………………...159

Figure 7.11 EDXA in SEM with 3 kV low acceleration voltage shows the compositions of ZnSe epilayer and clusters in at %. …....160

Figure 7.12 (a) cross-sectional HRTEM image (b) the formation model of clusters (c) compositions as a function of the depth in ZnSe. ..……………………………………………………161

Figure 7.13 PL intensity as a function of the flow rate of H2Se. ……...163

Appendix II
Figure 8.1 SEM surface morphologies of ZnO-related materials grown on GaAs substrate without and with the incorporation of HNO3 (a) 0, (b) 1.0, (c) 2.0 and (d) 5.0 ml. ………………………….170

Figure 8.2 XRD spectra as a function of the volume of HNO3. ………171

Figure 8.3 SEM images of growth evolution of ZnO rods. …………...172

Figure 8.4 (a) HRTEM and electron diffraction patterns of ZnO rod. (b) HRTEM image of ZnO rod shows the lattice fringes and the electron diffraction pattern of ZnO rod. ……………….….173

Figure 8.5 Micro PL spectrum of ZnO rod. …………………………...174

Figure 8.6 Freestanding ZnO rods on GaN/sapphire as 1 ml HNO3 incorporation with (a) 2 and (b) 18 h growth time. ……….175

Appendix III
Figure 9.1 SEM surface morphologies for the incorporation of (a) 0, (b) 1.0 and (c) 2.0 ml after thermal annealing. ...……………..184

Figure 9.2 XRD spectra for the incorporation of (a) 0, (b) 1.0 and (c) 2.0 ml HNO3 before and after thermal annealing…….……....186

Figure 9.3 SEM surface morphologies of ZnO rods (a) before and (b) after thermal annealing. ………………………………….187

Figure 9.4 FTIR spectra of ZnO rods before and after thermal annealing. ……………………………………………...…188

Figure 9.5 Micro PL spectra for the incorporation of (a) 0, (b) 1.0 and (c) 2.0 ml before and after thermal annealing. ...……………...190

Figure 9.6 Photocatalytic activities for the incorporation of (a) 0, (b) 1.0 and (c) 2.0 ml HNO3 before and after thermal annealing. ...192

Table Captions
Table I Lifetime of EHP in TiO2. ..……………………………...…….106

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