Synthesis and Characterization of Two-Dimensional Nano-Materials by Chemical Vapor Deposition: Graphene and MoSe2 Film
- 주제(키워드) two-dimensional materials , Graphene , MoSe2 film , chemical vapor deposition
- 발행기관 고려대학교 대학원
- 지도교수 이철진
- 발행년도 2015
- 학위수여년월 2015. 8
- 학위구분 박사
- 학과 대학원 마이크로/나노시스템협동과정
- 원문페이지 106 p
- 실제URI http://www.dcollection.net/handler/korea/000000060383
- 본문언어 영어
- 제출원본 000045841391
초록/요약
Nanomaterials have been extensively explored due to their unique structure and excellent properties for the tremendous application potential. Nanotechnology also has become one of the essential topics in research and developing technologies for their applications. Scientists have been studying and working on various types of nanomaterials from zero to three dimensional. Among these nanomaterials, two-dimensional nano-materials appear to be the research hotspot in recent years because of its unique electronic properties, good optical properties and excellent flexibility. The deep study of various two-dimensional nano-materials has been desired to open new applications for future information technology for people’s safe and welfare. In recent years, scientists have found many kinds of nanomaterial, such as graphene, boron nitride, black phosphorus and various transition metal dichalcogenides. Since the demonstration of single layer graphite by exfoliation method in 2004 by Novoselov, Geim and co-workers, graphene has been attracting enormous attention of scientific researchers. The continuous hexagonally carbon atoms structure gives rise to some exceptional mechanical, electronic, optical and thermal properties. Based on these, graphene has been considered as a strong candidate for the applications of new generation flexible electronic devices and energy-storage materials such as batteries, super-capacitors. For different applications, the various fabrication method were explored by researchers in recent years, such as mechanical exfoliation, liquid exfoliation, epitaxy on SiC substrates, and vapor evaporate deposition, which will be described in detail in next section. The transition metal dichalcogenides (TMDs) also attract significant attention owning to their unusual electrical properties duo to low dimensionalities. TMD species with a generalized structure of MX2, where M is transition metal and X is a chalcogen, represent a large amount of untapped species with 2D structure. The bandgap of most of monolayer TMD materials is a direct bandgap, while that of multilayer TMDs transforms to indirect bandgap. This special point makes the TMD materials will be feasible for the applications of future electronics and optoelectronics, such as catalysis, chemical sensor, transistors, and energy storage applications. Atomically thin MoS2 nanosheets with large area must be prepared for so many applications. Mechanical exfoliated method can give high quality and crystallinity samples. However, it is very inefficient and not repeatable for the thickness and size. Vapor deposition techniques including physical vapor deposition and chemical vapor deposition have shown great promise to obtain TMD materials with reasonable high quality with scalable size. Very recently, some kinds of TMD films of monolayer to few layer has been obtained, and size is from triangle domains to wafer-scale. However, there are still some many kinds of untapped 2D TMD materials which need more attention to develop the fabrication method and explore the unknown properties. In this work, we demonstrated the generation of a bandgap in the bilayer graphene synthesized by plasma-enhanced chemical vapor deposition. By adjusting the growth time, the defect density and nano-crystallite size of bilayer graphene were easily controlled, affecting the bandgap of bilayer graphene and the field effect mobility of bilayer graphene field effect transistor (FET). The defect density increased with increasing growth time, whereas the nano-crystallite size decreased. The semiconducting behavior of bilayer graphene was observed by measuring the temperature-dependent conductivity. Defects generated by plasma radiation induce in-plane symmetry in graphene, thus opening a bandgap. The bandgap energies in the bilayer graphene are 90, 156, and 187 meV for growth times of 5, 10, and 30 min, respectively. The back-gate bilayer graphene FET presented the p-type semiconducting behavior and the field effect mobility of approximately 1000 cm2V-1s-1 when the bandgap energy was 156 meV. In addition, the continuous MoSe2 films on SiO2/Si substrate were fabricated by atmosphere pressure chemical vapor deposition. Optical images and low magnification TEM images indicated the large size and continuity of the films. Raman mapping and AFM demonstrated the homogeneous and thickness of samples. The HRTEM images with corresponding FFT patterns showed hexagonal lattice structure of as-grown MoSe2 film. From Raman and PL spectra analysis, the as-grown MoSe2 film showed very clear peaks and strong PL emission at room temperature, which indicated the high quality and crystallinity of the samples. Therefore, the CVD-grown large area MoSe2 film will have a strong potential in a variety of applications in the near future.
more목차
Abstract i
List of Figures iv
List of Tables xii
Table of Content xiii
Chapter 1: Introduction - 1 -
1.1 Overview of Two-Dimensional Nanomaterials - 1 -
1.2 Structure and Properties of Graphene - 5 -
1.3 Synthesis and Characterization of Graphene - 9 -
1.3.1 Productions of Graphene by Mechanical Exfoliation - 9 -
1.3.2 Synthesis of Graphene by Epitaxy on SiC Substrates - 10 -
1.3.3 Synthesis of Graphene by Chemical Vapor Deposition - 12 -
1.3.4 Characterization of Graphene - 17 -
1.4 Structure and Properties of Transition Metal Dichalcogenides - 23 -
1.5 Synthesis and Characterization of Transition Metal Dichalcogenides - 25 -
1.5.1 Production of Transition Metal Dichalcogenides by Mechanical Exfoliation Method - 25 -
1.5.2 Production of Transition Metal Dichalcogenides by Chemical Exfoliation Method - 29 -
1.5.3 Synthesis of Transition Metal Dichalcogenides by Vapor Deposition Method - 31 -
1.5.4 Characterization of Transition Metal Dichalcogenides - 34 -
1.6 Outline of Dissertation - 37 -
Chapter 2: Synthesis and characterization of Graphene by Plasma-Enhanced Chemical Vapor Deposition - 42 -
2.1 Synthesis and Characterization of Graphene by Plasma-Enhanced Chemical Vapor Deposition - 43 -
2.2 Effects of Gas Concentration - 46 -
2.3 Effects of Plasma Power and Temperature - 47 -
2.4 Effects of Synthesis Time - 49 -
2.5 Fabrication of Graphene Field Effect Transistors - 55 -
2.6 Electrical Properties of Graphene and Its Field Effect Transistors - 57 -
2.7 Brief Summary - 64 -
Chapter 3: Synthesis and characterization of Molybdenum Diselenide by Chemical Vapor Deposition - 68 -
3.1 Synthesis and Characterization of MoSe2 films by Chemical Vapor Deposition - 69 -
3.2 Effects of Source Materials Weight and synthesis time - 71 -
3.3 Effects of the Flow Rate of Carrier Gas and Reducing Gas - 72 -
3.4 Characterization of MoSe2 Films under Optimal Process - 72 -
3.5 Brief Summary - 82 -
Chapter 4: Conclusion - 85 -
List of Publications - 87 -
List of Conferences - 88 -
Acknowledgements - 89 -
