원자 분해능 TEM에 의한 그래핀-관련 2차원 물질의 물성 및 구조 분석 = Property and Structural Analysis of Graphene Related Materials by Atomic Resolution TEM|RISS 상세보기

다국어 초록 (Multilingual Abstract)

Although graphene and graphene-related materials have various industrial applications, their theoretical properties have not been fully realized. In general, the properties of a material are determined by its elements and its structural make-up. Thus, the goal of this study is to identify and determine the properties of graphene and graphene-related materials to advance the characterizations of carbon materials.
First, the correlation between the thickness and oxidation degree of graphene Oxide (GO) samples fabricated by various oxidation processes was revealed using a combination of macroscopic and microscopic analyses. The degree of oxidation of GO varies depending on the manufacturing process, which is crucial to determine the characteristics of graphene after reduction. Four GO specimens were prepared with different manufacturing processes; subsequently, their degree of oxidation was evaluated by X-ray photoelectron spectroscopy (XPS). The d-spacing of each specimens classified by the degree of oxidation was measured via X-ray diffraction (XRD) and transmission electron microscopy (TEM). Additionally, through comparative analysis between layers with atomic force microscopu (AFM) and Raman spectroscopy, it was confirmed that the degree of oxidation was directly proportional to the thickness as well as the d-spacing of GO.
Secondly, in this thesis presents and analyzes the efficient reduction and defect healing mechanisms through pulsed wire discharge (PWD) process in a GO dispersed in an organic solvent. The energy generated during the electric explosion allows the organic solvent to serve as a carbon precursor for simultaneous reduction and defect healing within one process. To investigate the reduction efficiency of solution-based PWD method and property changes due to structural recovery, two different conductive media such as copper wire and carbon fiber were used for explosion control. The copper wire acted as a very efficient conducting medium for the reduction of GO result in very low oxygen content of less than 1 % in the GO after reduction, while the carbon fiber produced non-metal contaminated reduced graphene oxide (rGO), exhibiting excellent electrical conductivity. Electrical conductivity results of the prepared rGO powder revealed that, under the same density conditions of 0.5 g/cc, carbon fiber exhibited higher conductivity (2057.6 S/m).
Third, we present a method for measuring defect density using scanning transmission electron microscopy (STEM)-based electron energy loss spectroscopy (EELS) for graphene and graphene-related two-dimensional materials. The electron energy structure of carbon atoms varies according to the irradiation direction of the electron beam or the direction of the sample facing electron beam. It can be detected mainly through the change of π* and σ* peaks at the carbon K-edge. This tendency is apparent in the π* peak, which also has information about the sp2 bonding direction. Since graphene is a single-layer sp2 hybrid structure with a clear electron energy structure, the intensity ratio between π* and σ* peaks for an ideal graphene would be 1:3, which is the same for the π/σ bond ratio. Since graphene and its generated defects are considered different materials, changes occur in the electronic energy structure. These results enable numerical analysis, interpretation, and imaging of defects in 2D carbon materials to provide a deeper meaning behind the spectroscopic results obtained from the specimens.
In summary, this thesis suggests the methods for process, measurement, and analysis of graphene-related materials, which will provide additional insight to the field of materials science.

번역하기

목차 (Table of Contents)

Table of Contents i
List of Tables iii
List of Figures iv
Abstrarct ix

Table of Contents i
List of Tables iii
List of Figures iv
Abstrarct ix
1. General introduction 1
2. Background 3
2.1. Graphene and graphene-related materials 3
2.1.1. Graphene 3
2.1.2. CVD graphene 3
2.1.3. Graphene oxide 4
2.1.4. Reduced graphene oxide 4
2.2. Defects of graphene 5
2.2.1. Stone-wales defect 5
2.2.2. Ad-atom and vacancy defect 5
2.2.3. Grain boundary defect 6
2.3. Pulsed wire discharge 6
2.4. Electron energy loss spectroscopy 7
2.4.1. Bonding structure of graphene 7
2.4.2. Electron energy loss spectroscopy 9
2.4.3. Energy loss near edge structure 9
3. A study on the analysis method to investigate the correlation between oxidation degree characteristics and thickness of graphene oxide 11
3.1. Introduction 11
3.2. Experimental 13
3.2.1. Sample preparation 13
3.2.2. Characterization 15
3.3. Results and discussion 16
3.4. Conclusion 33
4. Single Process of Pulsed Wire Discharge for Defect Healing and Reduction of Graphene Oxide 34
4.1. Introduction 34
4.2. Experimental 37
4.2.1. Sample preparation 37
4.2.2. Purification 39
4.2.3. Characterization 40
4.3. Results and discussion 42
4.4. Conclusion 63
5. Defect Density Measurement and Calculation for Graphene-Related Materials Using the STEM-EELS Method 65
5.1. Introduction 65
5.2. Experimental 67
5.2.1. Sample preparation 67
5.2.2. Characterization 69
5.3. Results and discussion 70
5.4. Conclusion 88
6. Summary 89
Reference 92
국문초록 104
Acknowledgements 106

참고문헌 (Reference)

1. Diamagnetism of graphite, J. W. McClure, 104 666–671, , 1956

2. Band structure of graphite, P. R. Weiss, J. C. Slonczewski, 109 272–279, , 1958

3. The band theory of graphite, P. R. Wallace, 71 622–634, , 1947

4. Raman spectroscopy in graphene, M. A. Pimenta, L. M. Malard, M. S. Dresselhaus, G. Dresselhaus, 473 (5-6) 51-87, , 2009

5. The chemistry of graphene oxide, S. Park, R. S. Ruoff, D. R. Dreyer, C. W. Bielawski, 39, , 2010

6. The reduction of graphene oxide, S. Pei, H.-M. Cheng, 50 (9) 3210-3228, , 2012

7. Two-dimensional atomic crystals, D. Jiang, A. K. Geim, F. Schedin, K. S. Novoselov, 10451–10453, , 2005

8. Two-dimensional atomic crystals, T. J. Booth, V. V. Khotkevich, K. S. Novoselov, D. Jiang, A. K. Geim, S. V. Morozov, F. Schedin, 102 (30) 10451-10453, , 2005

9. Self healing of defected graphene, X. Wu, T. Xu, J. Chen, T. Shi, D. Yu, L. Sun, T. Cai, 102 (10) 103107, , 2013

10. Structure of Graphite Oxide Revisited, A. Lerf, H. He, J. Klinowski, M. Forster, 102 (23) 4477–4482, , 1998