eBook For Two-Dimensional Transition Metal Dichalcogenides Phase Engineering and Applications in Electronics and Optoelectronics 1st Edition

Preface xi

1 Two-dimensional Transition Metal Dichalcogenides: A General Overview 1
Chi Sin Tang and Xinmao Yin

1.1 Introduction to 2D-TMDs 1

1.2 Crystal Structures of 2D-TMDs in Different Phases 2

1.2.1 Other Structural Phases 3

1.2.2 Phase Stability 4

1.3 Electronic Band Structures of 2D-TMDs 7

1.3.1 Electronic Band Structures of the 1H, 1T, and 1T ′ Phase 8

1.3.2 Indirect-to-Direct Bandgap Transition 11

1.3.3 Spin-Orbit Coupling and Its Effects and Optical Selection Rules 13

1.4 Excitons (Coulomb-Bound Electron-Hole Pairs) 15

1.4.1 Exciton Binding Energy 16

1.4.2 Excitons and Other Complex Quasiparticles 18

1.4.3 Resonant Excitons in 2D-TMDs 19

1.5 Experimental Studies and Characterization of 2D-TMDs 20

1.5.1 Synthesis of 2D-TMDs 21

1.5.1.1 Chemical Vapour Deposition 21

1.5.1.2 Molecular Beam Epitaxy 22

1.5.2 Optical Characterization 23

1.5.2.1 Photoluminescence 23

1.5.2.2 Spectroscopic Ellipsometry 25

1.5.2.3 Raman Characterization 29

1.5.3 Electronic Bandgap 35

1.5.3.1 Angle-Resolved Photoemission Spectroscopy 35

1.5.3.2 Scanning Tunneling Spectroscopy (STS) 37

1.5.4 Conclusions 40

References 40

2 Synthesis and Phase Engineering of Low-Dimensional TMDs and Related Material Structures 61
Bijun Tang, Jiefu Yang, and Zheng Liu

2.1 Introduction 61

2.2 Structure of 2D TMDs 62

2.3 Synthesis of 2D TMDs 64

2.3.1 Top-Down Method 65

2.3.2 Bottom-Up Method 66

2.4 Phase Engineering of 2D TMDs 66

2.4.1 Direct Synthesis of TMDs with Targeted Phases 68

2.4.1.1 Precursor Selection 68

2.4.1.2 Catalyst 70

2.4.1.3 Temperature Control 72

2.4.1.4 Alloying 74

2.4.2 External Factor-Induced Phase Transformation 79

2.4.2.1 Ion Intercalation 79

2.4.2.2 Thermal Treatment 81

2.5 Conclusion 82

References 83

3 Thermoelectric Properties of Polymorphic 2D-TMDs 87
H. K. Ng, Yunshan Zhao, Dongzhi Chi, and Jing Wu

3.1 Introduction to 2D Thermoelectrics 87

3.1.1 Why 2D over 3D? 88

3.1.2 Why 2D Semiconductors? 89

3.2 Thermoelectric Transport 89

3.2.1 Boltzmann Transport Equation 90

3.2.2 Scattering Parameter for Different Mechanism 92

3.2.2.1 Ionized/Charged Impurity Scattering 92

3.2.2.2 Phonons Scattering 93

3.2.2.3 Carrier–Carrier Scattering 94

3.2.2.4 Surface Roughness Scattering 95

3.3 Experimental Characterization TE in 2D 95

3.3.1 Electrical Measurements 95

3.3.1.1 FET Measurements 95

3.3.1.2 Hall Measurements 96

3.3.2 Seebeck Measurement 96

3.3.2.1 ΔT Calibration 97

3.3.2.2 V Tep Measurement 97

3.3.3 Thermal Conductivity 98

3.3.3.1 Raman Spectrometer 99

3.3.3.2 Tdtr (fdtr) 101

3.3.3.3 Thermal Bridge Method (Electron Beam Heating Technique) 102

3.3.3.4 Other Thermal Property Measurement Methods 104

3.4 Manipulation of TE Properties in 2D 106

3.4.1 Tuning of Carrier Concentration 107

3.4.2 Strain Engineering 107

3.4.3 Band Engineering 110

3.4.3.1 Layer Thickness and Band Convergence 110

3.4.4 Phase Transition 112

3.5 Future Outlook and Perspective 115

References 117

4 Emerging Electronic Properties of Polymorphic 2D-TMDs 127
Tong Yang, Zishen Wang, Jiaren Yuan, Jun Zhou, and Ming Yang

4.1 Electronic Structure and Optical Properties of 2D-TMDs 127

4.1.1 Electronic and Optical Properties of 1H-Phase 2D-TMDs 127

4.1.2 Electronic and Optical Properties of 1T-Phase 2D-TMDs 131

4.2 Polaron States of 2D-TMDs 133

4.2.1 Holstein Polarons in MoS 2 133

4.2.1.1 Experimental Characterizations of Holstein Polarons 133

4.2.1.2 Theoretical Simulations of the Spectral Functions 136

4.2.2 Asymmetric Intervalley Polaron Effects on Band Edges of 2D-TMDs 137

4.2.3 Polaron Effects on the Band Gap Size of 2D-TMDs 139

4.3 Valley Properties of 2D-TMDs 143

4.3.1 Circularly Polarized Light 147

4.3.2 External Field 148

4.3.3 Magnetic Metal Doping 148

4.3.4 Magnetic Substrate 149

4.4 Charge Density Waves of 2D-TMDs 151

4.4.1 Charge Density Waves in TMDs 151

4.4.2 Effects of CDW on Electronic Properties 154

4.4.3 Mechanisms in CDW Transitions 155

4.4.4 Manipulation of CDWs 158

4.5 Janus Structures of 2D-TMDs 159

4.5.1 Fabrication Approaches for Janus 2D TMDs 159

4.5.2 Emerging Properties of Janus 2D TMDs 160

4.5.3 Potential Applications of Janus 2D TMDs 160

4.6 Moiré Superlattices of 2D-TMDs 161

References 165

5 Magnetism and Spin Structures of Polymorphic 2D TMDs 181
Meizhuang Liu, Zuxin Chen, Jingbo Li, Yuli Huang, Kuan Eng Johnson Goh, and Andrew T. S. Wee

5.1 Two-dimensional Ferromagnetism 182

5.2 Cr-based Magnetic Materials and Device Applications 183

5.3 Polymorphic 2D Cr-based Magnetic TMDs 191

5.4 Magnetism in 2D Vanadium, Ion, Manganese Chalcogenides 200

5.5 Conclusions and Outlook 204

Acknowledgements 204

References 205

6 Recent Progress of Mechanical Exfoliation and the Application in the Study of 2D Materials 211
Yunyun Dai, Xinyu Huang, Xu Han, Jiangang Guo, Xiangfan Xu, Lei Wang, Luqi Liu, Ningning Song, Yeliang Wang, and Yuan Huang

6.1 Introduction 211

6.2 Different Ways for Preparing 2D Materials 213

6.2.1 Chemical Vapor Deposition (CVD) 213

6.2.2 Mechanical Exfoliation (ME) 213

6.3 New Mechanical Exfoliation Methods 214

6.3.1 Oxygen Plasma Enhanced Exfoliation 214

6.3.2 Gold Film Enhanced Exfoliation 218

6.4 Application of Mechanical Exfoliation Method 222

6.4.1 Electrical Properties and Devices 222

6.4.1.1 Screening of Disorders 223

6.4.1.2 Electrical Contacts of 2D Materials 225

6.4.2 Optical Properties and Photonic Devices 227

6.4.2.1 Photodetectors 227

6.4.2.2 Optical Modulators 228

6.4.2.3 Single Photon Emitters 228

6.4.3 Moiré Superlattice and Devices 230

6.4.3.1 Graphene/h-BN Moiré Superlattice 230

6.4.3.2 Twisted Graphene Moiré Superlattice 231

6.4.3.3 Twisted TMD Moiré Superlattice 231

6.4.4 Magnetic Properties and Memory Devices 232

6.4.4.1 Ferromagnetism in 2D Materials 235

6.4.4.2 Antiferromagnetism in 2D Materials 237

6.4.5 Thermal Conduction 240

6.4.6 Superconductors 244

6.4.6.1 2D Superconductors and Their Characteristics 244

6.4.6.2 Regulation Methods 247

6.5 Summary and Outlook 249

Acknowledgments 249

References 250

7 Applications of Polymorphic Two-Dimensional Transition Metal Dichalcogenides in Electronics and Optoelectronics 267
Yao Yao, Siyuan Li, Jiajia Zha, Zhuangchai Lai, Qiyuan He, Chaoliang Tan, and Hua Zhang

7.1 Field-Effect Transistors (FETs) 268

7.1.1 Homojunction-based FETs Formed by Phase Transition 269

7.1.2 Homojunction-based FETs Formed by Direct Synthesis 270

7.2 Memory and Neuromorphic Computing 272

7.3 Energy Harvesting 275

7.4 Photodetectors 277

7.5 Solar Cells 282

7.6 Perspectives 284

References 285

8 Polymorphic Two-dimensional Transition Metal Dichalcogenides: Modern Challenges and Opportunities 293
Chi Sin Tang, Xinmao Yin, and Andrew T. S. Wee

8.1 Summing up the Chapters 293

8.2 Projecting the Future: Challenges and Opportunities 295

8.3 Global Challenges and Threats 296

8.3.1 Clean and Renewable Energy Sources 297

8.3.2 Water Treatment and Access to Clean Water 299

8.3.3 Healthcare and Pandemic Intervention 302

8.3.4 Food Safety and Security 305

8.3.4.1 Agricultural Production, Sustainability, Productivity, and Protection 306

8.3.4.2 Roles of 2D-TMDs in Food Packaging and Preservation 306

8.4 Exponential Growth in Demands for Modern Computation 307

8.4.1 Deep Learning and Artificial Intelligence 307

8.4.2 Internet of Things and Data Overload 308

8.5 Conclusion 312

References 312

Index 325