Synthesis, Characterization, and Application of Morphology-Controlled Semiconductor Nanostructures
형태가 제어된 반도체 나노구조의 합성, 분석 및 응용에 대한 연구

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dc.contributor.advisor정택동 (공동논문지도교수)-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 화학부 물리화학 전공, 2016. 2. 정택동 (공동논문지도교수).-
dc.description.abstractIn this dissertation, synthesis, characterization, and applications of morphology-controlled semiconductor nanostructures are discussed from the point of views of the physical chemistry and materials chemistry. Hyung-Bae Kim and his supervisor Du-Jeon Jang have developed four unique synthetic approaches for the preparation of morphology-controlled nanostructures: (1) the co-precursor method, (2) the defect-driven method, (3) the co-solvent method, and (4) the additive assisted method. Two heating methods of microwave-assisted methods and hydrothermal methods are selectively employed for the preparation of morphology-controlled nanostructures. The formation mechanisms of all the presented methods are delicately proposed in terms of LaMer theory. In addition, the morphology-dependent photophysical, photocatalytic, and photovoltaic properties of the prepared nanostructures have been investigated for potential applications. Brief overviews of the Chapters 1.- 5 mentioned in this dissertation are given below.
In Chapter 1, basic concepts of nanoscience especially on semiconductor nanostructures are introduced. The physical and chemical properties of nanosized anisotropic materials show the direction-dependent quantum confinement effects. The morphology-dependent properties of anisotropic nanostructures are summarized in three categories: sizes, shapes, and the surface conditions. The fundamental formation theories of nanostructures and the several factors that affect the growth kinetics of nanostructures are thoroughly explained.
In Chapter 2, the unique phenomenon of precursor-dependent shape variations of CdSe nanostructures are discussed. Spherical and branched CdSe nanostructures have been fabricated by employing two intrinsically different cadmium precursors of CdCl2 and CdO, respectively. Whereas CdCl2 precursors are polyol-soluble, CdO precursors are polyol-insoluble. We have also selectively employed two different polyol solvents having significantly different boiling temperature and viscosity. Due to the differences in synthetic conditions, each precursor has proceeded through the different growth pathways, generating the morphology-controlled CdSe nanostructures. The mechanism of precursors-dependent morphological variation of CdSe nanostructures are discussed. Combining the advantage of respective precursors, we have successfully synthesized novel structures of sphere-decorated CdSe tetrapods by using co-precursors of CdCl2 and CdO.
In Chapter 3, defect-driven synthesis of porous CdSe nanostructures having a near infrared emission at room temperature. It is worth emphasizing in that the defect-engineered preparation of nanostructures has been rarely reported. Porous CdSe nanorods have been prepared faciley via the hydrothermal treatment of CdSe∙(en)0.5 nanorods. During the hydrothermal process, various crystalline imperfections appear due to lattice mismatches between orthorhombic CdSe∙(en)0.5 and hexagonal wurzite porous CdSe nanorods and subsequently dissapear to release mismatch strains. In the self-healing defects process, point defects of atomic vacancies are heavily generated near the planar defects of twin boundaries in CdSe nanorods to produce volume defects of voids eventually. The emission of CdSe nanorods shifts to the red and decreases in intensity with the increase of surface states and selenium vacancies. The mean lifetime of emission increases with the increase of the hydrothermal-treatment time as the fractional amplitude of a surface-state-related component increases.
Chapter 4 focuses on two subjects
dc.description.abstract(1) the strategies and formation mechanisms of morphological variation of anatase TiO2 nanostuctures (Chapter 4A) and (2) their photocatalytic and photovoltaic applications (Chapter 4B). The morphologies of anatase TiO2 crystals have been varied facilely from rod-like structures to various hedgehog-like hierarchical structures via forming titanium glycerolate precursors as sacrificial templates. The morphologies of the precursors have been controlled readily under microwave irradiation by adjusting the relative solvent volumes of isopropanol and glycerol. The variation of the relative volume fractions of isopropanol and glycerol having significantly different boiling points and viscosity values has changed the nucleation and growth kinetics to control the morphologies as well as the sizes of titanium glycerolate precursors. In this studies, it has been founded that hierarchical 3D nanostructures have 5.5 times higher photocatalytic activity than rod-like 1D nanostructures, and the DSSC efficiency of hierarchical 3D nanostructures becomes as high as 5.37%, which is 50% higher than the DSSC efficiency of 1D nanostructures.
In Chapter 5, the ammonia-assisted synthesis of morphology-controlled ZnO microstructures under microwave irradiation is discussed. The morphologies and the surface conditions of ZnO microstructures have been controlled facilely via a one-pot synthetic route by varying the ammonia concentration of the reaction mixture. Ammonia affects the nucleation, growth, and hydrolysis kinetics of intermediate zinc glycerolate to induce shape variation from flower-like ZnO microstructures to various ZnO twin microstructures with the preferred exposure of ±(0001) polar planes. As-prepared ZnO microstructures are mesoporous with large specific surface areas and high specific pore volumes, which have resulted from the microwave-assisted fast hydrolysis of intermediate zinc glycerolate microstructures. Owing to the novel features of microwave, ZnO microstructures have numerous microcracks and wrinkles on their surfaces and show characteristic defect-driven orange emission, whose intensity increases with the specific surface area. The photocatalytic degradation rate constant of rhodamine B via our prepared ZnO microstructures have been founded to increase linearly with the specific surface area, the specific pore volume, and the polar-surface exposure. Our simple and rapid microwave-assisted synthetic method is considered to be beneficial to the development of morphology-controlled metal oxides that are applicable for eco-friendly waste-water treatment.
dc.description.tableofcontentsChapter 1. General Introduction 7
1.1. Nanosized and Nanostructured Materials 8
1.1.1. Anisotropic Materials: Sizes, Shapes, and Surface Effects on the Properties of Nanostructures 10
1.1.2. Preparation of Anisotropic Nanostructures 12
1.2. Principles of Microwave-Assisted Synthetic Methods and Solvothermal/Hydrothermal Synthetic Methods 5
1.3. References 20

Chapter 2. Precursor-Dependent Shape Variation of Wurtzite CdSe Crystals in a Microwave-Assisted Polyol Process 21
2.1. Abstract 23
2.2. Introduction 25
2.3. Experimental Details 25
2.4. Results and Discussion 26
2.5. Conclusion 39
2.6. References 41

Chapter 3. Dislocation-Driven Growth of Porous CdSe Nanorods from CdSe∙(ethylenediamine)0.5 Nanorods 44
3.1. Abstract 45
3.2. Introduction 46
3.3. Experimental Details 49
3.4. Results and Discussion 51
3.5. Conclusion 64
3.6. References 65

Chapter 4. Fabrication and Application of Morphology-Controlled Anatase TiO2 Nanostructures 68
Part 4A. Morphological variation of anatase TiO2 crystals via formation of titanium glycerolate precursors under microwave Irradiation 69
4A.1. Abstract 69
4A.2. Introduction 70
4A.3. Experimental Details 73
4A.4. Results and Discussion 75
4A.5. Conclusion 90
4A.6. References 92
Part 4B. Hierarchical mesoporous anatase TiO2 nanostructures with efficient photocatalytic and photovoltaic performances 94
4B.1. Abstract 94
4B.2. Introduction 95
4B.3. Experimental Details 98
4B.4. Results and Discussion 103
4B.5. Conclusion 114
4B.6. References 115

Chapter 5. Morphology-Tunable Synthesis of ZnO Microstructures under Microwave Irradiation: Formation Mechanisms and Photocatalytic Activity 118
5. 1. Abstract 119
5.2. Introduction 120
5.3. Experimental Details 123
5.4. Results and Discussion 125
5.5. Conclusion 143
5.6. References 144

Appendices 147
A.1. List of Publications 147
A.2. List of Presentations 148

Abstract (Korean) 151
dc.format.extent5921883 bytes-
dc.publisher서울대학교 대학원-
dc.subjectDye-sensitized solar cells-
dc.titleSynthesis, Characterization, and Application of Morphology-Controlled Semiconductor Nanostructures-
dc.title.alternative형태가 제어된 반도체 나노구조의 합성, 분석 및 응용에 대한 연구-
dc.contributor.affiliation자연과학대학 화학부-
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College of Natural Sciences (자연과학대학)Dept. of Chemistry (화학부)Theses (Ph.D. / Sc.D._화학부)
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