Design growth structures of ZnO nano/micro-crystals by thermal evaporation of Zn metal without using catalyst = 촉매를 배제한 Zn 금속의 열 기화방법으로 ZnO 나노/마이크로 결정들의 성장구조체 설계

국문 초록 (Abstract)

오늘날의 세라믹은 고전 세라믹과 파인 세라믹으로 구분할 수 있다. 파인 세라믹이란. 자연상의 재료로부터 제품을 만든 고전 세라믹과는 다르게, 자연 재료로부터 원하는 재료를 분리하여 사용하는 세라믹을 말한다. 파인 세라믹을 구분하면 원소성분, 응용분야, 특성, 구조 등으로 나눌 수 있다. 이 중에서 구조적 특성은 매우 중요하다. 동일 성분의 재료에서 구조/형상이 변함에 따라 기계적, 화학적, 물리적, 전기적, 광학적 특성이 변하며 이에 따라 여러 다른 응용분야도 적용할 수 있다. 따라서 재료의 구조/형상을 제어하는 기술은 많은 연구진들의 중요한 연구 주제이다.
ZnO는 3.37 eV의 넓은 밴드갭과 60 meV의 큰 결합에너지를 갖는 매우 중요한 다 기능성 반도체 재료이다. 알려진 바로는, ZnO는 nanowires, nanotubes, nanobelts, nanocages 등의 다양한 구조체로 만들 수 있어, 여러 분야에 응용가능성이 매우 높다. 일반적으로 유기금속 기상 증착법, 액상법, 수열합성법 등이 서로 다른 형상 및 디맨젼을 갖는 ZnO를 합성하는데 사용된다. 그러나 이 방법들은 소스 재료가 비싸고, 화학물질을 사용하여 위험하며, 공정이 복잡하다는 단점을 갖고 있다. 열 기화법은 넓게 사용되는 기술로서 기상에서 ZnO의 다양한 디맨젼 및 형상을 제작할 수 있다. 이 방법은 앞서 말한 방법들의 단점을 전부 보완한다. 그러나 이 방법은 촉매를 사용하지 않을 때 구조체 (형상, 디맨젼, 크기, 균일함) 를 제어하는데 매우 어려움이 있다. 그리고 사용된 촉매는 ZnO의 응용성을 위한 고유특성을 저하 시킨다. 따라서 ZnO의 제품 응용을 위해서는 촉매를 사용하지 않고 구조체를 디자인 할 수 있는 기술이 요구된다

다국어 초록 (Multilingual Abstract)

In general ceramics are classified into the classic and fine ceramics. The classic ceramics are derived from common, naturally occurring raw materials such as glass, cement and pottery. Whereas the fine ceramics are some element compounds, selected from naturally occurring raw materials to be used for suitable applications. The characteristic of fine ceramics can be characterized, based on are component elements, applications, properties and structures. In ceramic materials, the morphology (e.g. structure, shape, size and dimension) significantly play a role on the properties such as physical, chemical, mechanical, electronic and optical properties. Change in morphology leads to change in properties as well. Therefore, in one ceramic material, it is an important to control its morphology in term of structure, shape, size and dimension in order to obtain the properties, which are suitable for each type of applications. This is an important topic which has been extensively researched by many research groups.
Zinc oxide (ZnO) is one of the most important multifunctional semiconductors owing to its wide direct energy band gap of 3.37 eV and large exciton binding energy of ~60 meV. It has a variety of structures such as nanowire, nanotube, nanobelt, and nanocage. The one-dimensional (1-D) ZnO nanowires can be used for light-emitting diode, laser diode and photo-emitter devices due to their optical properties. Whereas the three-dimensional (3-D) ZnOs, having large surface area, are suitably used for pigment, electronic, catalytic and sensor applications.
In general, zinc oxide nanomaterials with various shapes and dimensions have been prepared using the conventional techniques such as metal-organic chemical vapor deposition, vapor transport and condensation and hydrothermal methods. However, those processes have complex and multiple steps, leading to high cost production. In addition, they deal with dangerous chemicals. Thus, a catalyst-free thermal evaporation, which is simple and non-toxic chemical technique, is another selective way for fabrication of zinc oxide with various shapes and dimensions.
This thesis presents characterization and design of nano/micro structures of ZnO using thermal evaporation without using catalyst. The 1 and 3-D ZnOs are able to be fabricated by this technique, so called a solid–vapor process. The second chapter deals with the fabrication and design of 1-D ZnOs. The quality of 1-D ZnOs in terms of verticality, density, diameter, and crystallinity was controlled by varying growth parameters such as a type of substrate and a substrate position. The third chapter deals with the fabrication and design of 3-D hexagonal hollow ZnOs with various shapes by evaporation of Zn clusters, used as template, under low pressure. The shape of 3-D hexagonal hollow ZnOs was controlled by varying a distance from downstream. A study of defect dependent optical property of 3-D ZnOs was addressed as well.
Finally, we expect that a catalyst-free thermal evaporation would be promising and selective dimensional and structural design technique for a variety of materials.

목차 (Table of Contents)

• ABSTRACT 4
• Chapter 1. Literature Review 8
• 1.1. Description of Zinc Oxide 8
• 1.1.1. Crystal structures and lattice parameters of ZnO 9
• 1.1.2. General Properties of Znic Oxide Nanostructures 12
• 1.1.3. Defect chemistry of ZnO 15
• 1.1.4. The optical properties with defects 17
• 1.2. Synthetic methods of zinc oxide nanostructure 22
• 1.2.1. Vapor-phase Growth Process 22
• 1.2.2. Solution-Phase Growth Process 30
• 1.3. Fabrication of Dimensions 31
• 1.3.1. One Dimension ZnO nanostructure : nanowire and nanorods 31
• 1.3.2. Three Dimension ZnO nanostructure : hollow shape 32
• 1.4. Effect of process parameters on the morphologies 33
• 1.5. Properties and application a of ZnO nanostructures 35
• 1.5.1. Electrical and Photoconductive Properties of ZnO Nanostructures 35
• 1.5.2. ZnO Nanostructured Based Chemical and Biological Sensors 36
• 1.5.3. ZnO nanowire-based UV photodetectors 37
• 1.6. Future work on functional ZnO nanowires 40
• REFERENCES . 44
• Chapter 2 High-quality ZnO nanowire arrays directly synthesized from Zn vapor deposition 54
• 2.1. Introduction 54
• 2.2. Experimental produce 57
• 2.3. Results and Discussion 59
• 2.3.1. Detailed structural characterization of ZnO NW arrays on the GaN/sapphire substrate 59
• 2.3.2. Influence of the substrate position on the growth behavior of the ZnO NW arrays 64
• 2.3.3. Controlled diameter and density of the ZnO NW arrays 75
• 2.3.4. Length dependent of the ZnO NW arrays as a function of the growth time and distance (l) 82
• 2.3.5. Room-temperature photoluminescence properties of the ZnO NW arrays on the GaN/sapphire substrate 86
• 2.3.6. Detailed growth mechanism for the formation of the vertically well-aligned ZnO NW arrays 93
• 2.4. Conclusions 99
• References 101
• Chapter 3 Effects of pressure and substrate positions on ZnO nanostructures during thermal evaporation of Zn Metal 113
• 3.1. Introduction 113
• 3.2. Experimental 114
• 3.3. Results and discussion 117
• 3.4. Conclusions 128
• References 129
• Chapter 4 Conclusion 133