Title

Advanced In Situ TEM for Elucidating Structural Evolution and Rational Stability Design in Semiconductor Nanocrystals

Alternative Title

반도체 나노결정의 구조 변화 경로 규명 및 메커니즘 기반 안정성 설계를 위한 실시간 투과전자현미경 분석법 고도화 연구

DGIST Authors

Hyeonjong Ma ; Jiwoong Yang ; Jinsoo Kim

Advisor

양지웅

Co-Advisor(s)

Jinsoo Kim

Issued Date

2026

Awarded Date

2026-08-01

Type

Thesis

Description

In situ transmission electron microscopy, liquid-phase TEM, semiconductor nanocrystals, degradation mechanisms, surface and shell engineering, stability

Table Of Contents

I. Introduction 1
1.1 Structural Evolution and Instability of Semiconductor Nanocrystals: Conventional Characterization Methods and Their Limitations 1
1.2 In Situ Transmission Electron Microscopy for Investigating Structural Changes of Nanomaterials: Capabilities and Methodological Advances 4
1.3 Recent Progress of In Situ Transmission Electron Microscopy Using Graphene Liquid Cells (GLCs) 7
1.3.1 Introduction of GLC 7
1.3.2 Veil-Type GLC 9
1.3.3 Well-Type GLC 19
1.3.4 Liquid-Flowing-Type GLC 29
1.4 Dissertation Overview 36
1.5 References 40
II. In Situ TEM for Investigating the Phase Transformation Mechanism in Semiconductor Nanocrystals Induced by Off-Stoichiometry 63
2.1 Introduction 63
2.2 Experimental Section 65
2.2.1 Materials 65
2.2.2 Synthesis of Wurtzite-CdSe Quantum Nanosheets 65
2.2.3 Material Characterization 66
2.2.4 In Situ TEM Analysis 66
2.2.5 Ex Situ Electron-Beam Irradiation Experiment 66
2.2.6 Ex situ Thermal Heating Experiment 67
2.2.7 Calculation of Maximum Electron Transfer Energy 67
2.2.8 Density Functional Theory Calculations 67
2.3 Results and Discussion 69
2.3.1 Structural Transformation of Wurtzite 2D CdSe Quantum Nanosheets 69
2.3.2 Off-Stoichiometry-Induced Phase Transformation Mechanism in 2D Quantum Nanosheets 75
2.3.3 Atomic Scale In Situ TEM Analysis of the Phase Transformation 88
2.3.4 Unconventional Phenomena during the Phase Transformation 93
2.4 Conclusion 97
2.5 References 98
III. Development of Advanced Graphene-Based Liquid-Cell Imaging Platform for In Situ Liquid-Phase TEM under Practical Environments 108
3.1 Introduction 108
3.2 Experimental Section 111
3.2.1 Materials 111
3.2.2 Preparation of Graphene Double-Liquid-Layer Cells 112
3.2.3 Investigation of the Probabilities of the Liquid Pocket Formation 115
3.2.4 Synthesis of CdS Quantum Nanorods 115
3.2.5 Synthesis of Golds Nanorods 116
3.2.6 Synthesis of Single-Layer MoS2 and Fabrication of Single-Layer MoS2 Coated TEM Grids 116
3.2.7 In Situ Transmission Electron Microscopy 117
3.2.8 Standard Deviation Mapping 117
3.2.9 Radiolysis Simulation 118
3.2.10 Ex Situ Observation of the CdS Nanorod Degradation by Water 118
3.3 Results and Discussion 119
3.3.1 Moisture-Induced Degradation of CdS Quantum Nanorods 119
3.3.2 Development of Graphene Double-Liquid-Layer Cells 123
3.3.3 Amorphization of CdS Quantum Nanorods 132
3.3.4 Shape-Evolution of Crystalline Phases During Nanorod Degradation 139
3.3.5 Investigation of the Electron Beam Effect 146
3.4 Conclusion 152
3.5 References 153
IV. Degradation Mechanisms of Perovskite Nanocrystals and Strategy for Stability Enhancement via Surface Engineering 165
4.1 Introduction 165
4.2 Experimental Section 167
4.2.1 Materials 167
4.2.2 Preparation of CsPbBr3 PeNCs 167
4.2.3 General Characterization 168
4.2.4 In Situ Liquid-Phase TEM 169
4.2.5 Characterization of Nanocrystal Shape 170
4.2.6 In situ WAXS Analysis 172
4.2.7 XANES and Extended EXAFS Analysis 174
4.2.8 Ex Situ Characterization of Water-Induced Degradation of PeNCs 174
4.3 Results and Discussion 175
4.3.1 Water-Induced Degradation of Pristine-PeNCs 175
4.3.2 Investigation of the Effect of Surface Ligands on the Degradation Trajectories of PeNCs 186
4.3.3 Investigation on the Effect of Water Exposure on PeNCs Outside of the TEM 195
4.4 Conclusion 200
4.5 References 201
V. Degradation Mechanisms of Blue-Emitting ZnSeTe Quantum Dots and Strategy for Stability Enhancement via Shell-Geometry Engineering 212
5.1 Introduction 212
5.2 Experimental Section 214
5.2.1 Materials 214
5.2.2 Synthesis of ZnSeTe QDs 215
5.2.3 General Characterization 215
5.2.4 Fabrication of Graphene Double-Liquid-Layer Cells 216
5.2.5 Quantitative Analysis of Nanoparticle Shape 217
5.2.6 Ex Situ Characterization of ZnSeTe QDs Induced by Water Exposure 220
5.2.7 Fabrication of QLEDs Based on ZnSeTe QDs 221
5.3 Results and Discussion 222
5.3.1 Geometry-Defined ZnSeTe QDs for Water-Induced Degradation Analysis 222
5.3.2 Isotropic Degradation of Spherical ZnSeTe QDs 225
5.3.3 Geometry-Dependent Degradation of Faceted ZnSeTe QDs 232
5.3.4 Ex Situ Evidence for Water-Induced Degradation Pathways 242
5.3.5 Performance and Stability of QLEDs based on ZnSeTe QDs 246
5.4 Conclusion 249
5.5 References 250
요 약 문 262

URI

https://scholar.dgist.ac.kr/handle/20.500.11750/60744
http://dgist.dcollection.net/common/orgView/200001006958

DOI

10.22677/THESIS.200001006958

Degree

Doctor

Department

Department of Energy Science and Engineering

Publisher

DGIST

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