Investigation of electrical and mechanical characteristics of the two-dimensional nanomaterials/polymer systems
- 주제(키워드) 2D nanomaterials , crack , polymer system
- 주제(DDC) 621.042
- 발행기관 아주대학교
- 지도교수 박지용
- 발행년도 2022
- 학위수여년월 2022. 2
- 학위명 박사
- 학과 및 전공 일반대학원 에너지시스템학과
- 실제URI http://www.dcollection.net/handler/ajou/000000031660
- 본문언어 영어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
In this paper, we discussed the mechanical properties of two-dimensional nanomaterials and polymer substrate systems and the electrical properties of polymer dielectric materials. Graphene and Molybdenum disulfide (MoS2) were synthesized by Chemical Vapor Deposition (CVD) method, and the CVD parameters for synthesizing into a single layer were optimized. The synthesized two-dimensional nanomaterial was investigated by Optical Microscopy (OM), Atomic Force Microscopy (AFM), and Raman spectroscopy. In addition, in order to measure the electrical properties of the synthesized two-dimensional nanomaterial, it was fabricated as a FET device, and electron mobility of about 1000 cm2/Vs for graphene and about 2 cm2/Vs for MoS2 was measured using a probe station. First, the two-dimensional nanomaterial synthesized by CVD is transferred onto a poly (methyl methacrylate) (PMMA) substrate, and then the PMMA is swollen using methanol or ethanol. We found that strain caused by the expansion of the PMMA layer caused cracks on the surface of the transferred 2D nanomaterial. In the case of graphene, a rectangular pattern was used, and as the length of the width increased, we confirmed that more cracks were generated in the vertical direction (the long direction of the rectangle). In the case of MoS2, cracks were mainly generated in the zig-zag direction where bonding was relatively weak because each flake grew as single crystalline, and we confirmed that there is a minimum area for accumulating the strain required for crack formation. In addition, by introducing fracture mechanics, we confirmed that the difference in elastic modulus in the laminated structure of heterogeneous materials can accelerate crack formation. And when the two-dimensional nanomaterial/PMMA device was immersed in alcohol, through in-situ IV measurement, we verified that the crack formation occurred simultaneously with the swelling. In addition, the crack pattern according to the change of the surface state of the two-dimensional nanomaterial was observed, and the possibility of new nanostructure creation or applications such as sensors and fuses was suggested through re-transfer and PDMS imprint. Next, we describe the electrical properties of the ion gel synthesized from poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) according to the mass ratio. Characteristics were measured and applied as dielectric material to flexible graphene FET. We developed a mass ratio of ion gel that best maintains electric double layer capacitance (EDLC) properties of ionic liquid without losing flexibility through capacitance and impedance measurement and compared the measured and calculated results by deriving an equivalent circuit of the device. In addition, we applied the graphene FET fabricated on PET substrate as a gate dielectric material to prove that it works without losing the electrical properties of graphene even when strain is applied.
more목차
Chapter 1 1
Introduction 1
Chapter 2 6
Theorical background 6
2.1 Introduction of Two-dimensional nanomaterials 6
2.1.1 Graphene 6
2.1.2 Molybdenum disulfide 13
2.2 Synthesis of Two-dimensional nanomaterials 16
2.2.1 Exfoliation of 2D nanomaterials 16
2.2.2 Chemical Vapor Deposition (CVD) 21
2.3 Device fabrication and characterization 26
2.3.1 Transfer of nanomaterials 26
2.3.2 Device fabrication 29
2.3.3 Characterization of Graphene & MoS2 33
2.4 Fracture mechanics 37
2.4.1 Basic principles of fracture mechanics 37
2.4.2 Fracture mechanics in thin film 40
2.5 References 45
Chapter 3 52
Mechanical failures of two-dimensional nanomaterials on polymer systems 52
3.1 Introduction 52
3.2 Experimental section 55
3.2.1 Synthesis of 2D nanomaterials 55
3.2.2 Preparation of 2D materials on PMMA substrates 55
3.2.3 Swelling of PMMA film and characterizations 56
3.3 Results and discussion 57
3.3.1 Preparation of PMMA expansion 57
3.3.2 Observation of crack generation in 2D nanomaterials 59
3.3.3 Analysis of crack in 2D nanomaterials 67
3.3.4 Fracture mechanics approach of crack generation 69
3.3.5 In-situ investigation of crack propagation 72
3.4 Conclusion 75
3.5 References 76
Chapter 4 81
Investigation and application of mechanical failure of 2D nanomaterials/polymer system by surface treatment 81
4.1 Introduction 81
4.2 Experimental methods 83
4.2.1 Synthesis of 2D nanomaterials 83
4.2.2 Preparation of 2D materials on PMMA substrates 83
4.2.3 Swelling of PMMA film and characterizations 84
4.2.4 PDMS imprint 84
4.3 Results and discussion 85
4.3.1 Re-transferred 2D nanomaterials 85
4.3.2 PDMS imprint 89
4.3.3 Surface ozone treatment of 2D nanomaterials 92
4.4 Conclusions 95
4.5 References 96
Chapter 5 98
Electrical properties of ion gels based on PVDF-HFP applicable as gate stacks for flexible devices 98
5.1 Introduction 98
5.2 Experimental Section 101
5.2.1 Materials and preparation of ion gel 101
5.2.2 Electrode fabrication and impedance measurement 101
5.2.3 Graphene growth and transfer 101
5.2.4 Flexible graphene FET fabrication and measurement 102
5.3 Results and discussions 103
5.3.1 Device for ion gel measurement of electrical properties 103
5.3.2 Capacitance measurement of ion gel 104
5.3.3 Impedance measurement of ion gel 106
5.3.4 IV characteristic of flexible graphene FET with ion gel 109
5.4 Conclusions 111
5.5 References 112
Chapter 6 117
Summary and future work 117
6.1 Summary 117
6.2 Future work 119
List of publications 120
