Magneto-thermoelectric effects in magnetic metallic thin-films

It was the purpose of this thesis to evaluate two-dimensional (2D) magneto-thermoelectric (MTE) phenomena in thinner regime. Mostly this work was motivated by the recent discovery of MTE properties in transition metal dichalcogenides (TMD). In general, TMD thin films have attracted much attention due to their very good electrical, optical, and electrochemical properties. However the total amount of studies of the MTE in TMD is rather small compared to the other properties, such as electric, opto-electric, and catalyst. Hence, in this thesis, we aimed to evaluate the MTE properties in TMD materials. Before we started to measure TMDs, we established a measurement platform and studied MTE properties in ferromagnetic CoFeB, and Weyl semimetal Co2MnGa.:1. Introduction a. Physical background i. Seebeck Effect ii. Anomalous Hall Effect and Anomalous Nernst Effect iii. Mott relation 2. Sample Preparation and evaluation a. Physical vapor deposition b. Mechanical Exfoliation c. Patterning Process 3. Data Evaluation 4. State of the art in Transition Metal Dichalcogenids a. Introduction b. TMD in use c. Magneto-thermoelectric properties in TMD 5. Magneto-thermoelectrical properties in CoFeB thin film a. Introduction b. Results and Discussion c. Conclusion 6. Anomalous Nernst and Anomalous Hall effect in Co2MnGa thin film a. Introduction b. Results and Discussion c. Summary 7. Anomalous Hall effect in exfoliated VS2 flake a. Introduction b. Experiment c. Results and Discussion d. Summary 8. Summary Acknowledgement and Reference

Transition Metal Dichalcogenide Photodetectors

Two Dimensional (2D) materials has triggered to have transition metal dichalcogenides (TMDCs) emerging as a new class of materials that can control or interact with light to convert the photons to electrical signals for its attractive applications in photonics, electronics and optoelectronics. 2D materials along with gapless Graphene interact with light over the wavelength region of the different spectral regions having the short wavelength of the UV and extreme UV, Visible, near IR, mid IR and THz due to excellent light absorption, enabling ultrafast and ultrasensitive detection of light in photodetectors. Next generation photodetectors are possible promising candidates for high sensitivity and TMDCs based photodetectors are the heart of the multitude of technologies to understand the principle of photodetection mechanisms and device performances. Phototransistors/photoconductors show wide varied detection performances with responsivities ranging from 10−7 A/W - 107 A/W on single or few layer TMDCs having response time between 10−5 s to 103 s. The semiconducting TMDCs like MoS2, MoSe2, WS2, WSe2 and ReS2 are gaining suitable applications in optoelectronic devices and the device design, mechanism and enhancing the performance of photodetectors are introduced and discussed systematically in this chapter. In spite of the growing demands on TMDC based devices the origin of the photoresponse characteristics is attractive and encouraging to understand and provide a path to the subject of investigation and guidelines for the future development of this rapidly growing field

Beyond Graphene: Monolayer Transition Metal Dichalcogenides, A New Platform For Science

Following the isolation of graphene in 2004, scientists quickly showed that it possesses remarkable properties. However, as the scientific understanding of graphene matured, it became clear that it also has limitations: for example, graphene does not have a bandgap, making it poorly suited for use in digital logic. This motivated explorations of monolayer materials “beyond graphene”, which could embody functionalities that graphene lacks. Transition metal dichalcogenides (TMDs) are leading candidates in this field. TMDs possess a wide variety of properties accessible through the choice of chalcogen atom, metal atom and atomic configuration (1H, 1T, and 1T’). Similar to graphene, monolayer TMDs may be produced on a small scale through mechanical exfoliation, but useful applications will require development of reliable methods for monolayer growth over large areas. In this thesis, I report our group’s recent progress in the chemical vapor deposition (CVD) of high quality, large area, monolayer TMDs under a 1H atomic configuration, which were integrated into high-quality biosensor arrays. These devices were incorporated in a flexible platform and were used for electronic read out of binding events of molecular targets in both vapor and liquid phases. I also report our findings on the CVD growth of monolayer TMDs in the 1T’ atomic configuration and measurements of their physical properties. 1T’ TMDs have been labeled the holy grail of materials due to theoretical predictions that they are 2D topological insulators; however they remain relatively unexplored due to the difficulty of monolayer growth and their lack of stability in air. Through careful passivation techniques, we were able to stabilize the as-grown monolayer 1T’ TMD flakes and perform the first characterizations on the structure. Lastly, in-plane 2D TMD heterostructures are promising material systems that combine the unique properties of each TMD. I discuss our results on the synthesis and study of 1H TMD heterostructures and unique 1H/1T’ TMD heterostructures. TMDs, with its many different accessible physical properties, coupled with the large variety of applications, have been classified as the leading nanomaterials in the realm “beyond graphene”

Heterojunction Hybrid Devices from Vapor Phase Grown MoS2_{2}

We investigate a vertically-stacked hybrid photodiode consisting of a thin n-type molybdenum disulfide (MoS$_{2}$) layer transferred onto p-type silicon. The fabrication is scalable as the MoS$_{2}$ is grown by a controlled and tunable vapor phase sulfurization process. The obtained large-scale p-n heterojunction diodes exhibit notable photoconductivity which can be tuned by modifying the thickness of the MoS$_{2}$ layer. The diodes have a broad spectral response due to direct and indirect band transitions of the nanoscale MoS$_{2}$. Further, we observe a blue-shift of the spectral response into the visible range. The results are a significant step towards scalable fabrication of vertical devices from two-dimensional materials and constitute a new paradigm for materials engineering.Comment: 23 pages with 4 figures. This article has been published in Scientific Reports. (26 June 2014, doi:10.1038/srep05458

Electronic Structure of Transition Metal Dichalcogenides and Molecular Semiconductors

Zweidimensionale (2D) Übergangsmetalldichalcogenide (TMDCs) gehören zu den attraktivsten neuen Materialien für optoelektronische Bauelemente der nächsten Generation. Um die überlegene Funktionalität der mit TMDCs verbundenen Bauelemente zu realisieren, ist ein umfassendes Verständnis ihrer elektronischen Struktur, einschließlich, aber nicht beschränkt auf die Auswirkungen von Defekten auf die elektronischen Eigenschaften und die Ausrichtung der Energieniveaus (ELA) an den TMDCs-Grenzflächen, unerlässlich, aber derzeit nicht ausreichend. Um einen tieferen Einblick in die elektronischen Eigenschaften von TMDCs und den damit verbundenen Grenzflächen in Kombination mit molekularen Halbleitern (MSCs) zu erhalten, untersuchen wir i) die fundamentale Bandstruktur von Monolagen (ML) TMDCs und die durch Schwefelfehlstellen (SVs) induzierte Renormierung der Bandstruktur, um eine solide Grundlage für ein besseres Verständnis der elektronischen Eigenschaften von polykristallinen dünnen Filmen zu schaffen, und ii) die optoelektronischen Eigenschaften ausgewählter MSC/ML-TMDCs-Grenzflächen. Darüber hinaus wird iii) der Einfluss des Substrats auf die elektronischen Eigenschaften einer MSC/ML-TMDC-Grenzfläche untersucht, um das Bauelementedesign zu steuern. Die Charakterisierung erfolgt hauptsächlich durch winkelaufgelöste Photoelektronenspektroskopie (ARPES), ergänzt durch Photolumineszenz (PL), Raman-Spektroskopie, UV-Vis-Absorption, Rastertransmissionselektronenmikroskopie (TEM) und Rasterkraftmikroskopie (AFM). Unsere Ergebnisse tragen zu einem besseren Verständnis der Auswirkungen von Defekten auf ML-TMDC und verwandte Grenzflächen mit MSCs bei, wobei auch die Auswirkungen der Substrate berücksichtigt werden, und sollten dazu beitragen, unser Verständnis des elektronischen Verhaltens in TMDC-verwandten Geräten zu verbessern.Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are amongst the most attractive emerging materials for next-generation optoelectronic devices. To realize the superior functionality of the TMDCs related devices, a comprehensive understanding of their electronic structure, including but not limited to the impact of defects on the electronic properties and energy level alignment (ELA) at TMDCs interfaces, is essential but presently not sufficient. In an attempt to get a deep insight into the electronic properties of TMDCs and the related interfaces combined with molecular semiconductors (MSCs), we investigate i) the fundamental band structure of monolayer (ML) TMDCs and band structure renormalization induced by sulfur vacancies (SVs), in order to provide a solid foundation for a better understanding the electronic properties of polycrystalline thin films and ii) the optoelectronic properties of selected MSC/ML-TMDC interface. In addition, iii) the impact of the substrate on the electronic properties of the MSC/ML-TMDC interface is investigated for guiding device design. The characterization is mainly performed by using angle-resolved photoelectron spectroscopy (ARPES), with complementary techniques including photoluminescence (PL), Raman spectroscopies, UV-vis absorption, scanning transmission electron microscopy (TEM), and atomic force microscopy (AFM) measurements. Our findings contribute to achieving a better understanding of the impact of defects on ML-TMDC and related interfaces with MSCs considering the substrates’ effect and should help refine our understanding of the electronic behavior in TMDC-related devices

이차원 전이금속 디칼코제나이드 박막물질의 성장거동과 미래전자소자로의 응용

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 재료공학부, 2021. 2. 오규환.Two-dimensional (2D) transition-metal dichalcogenides (TMDs) in the form of MX2 (M: transition metals, X: chalcogens) have drawn substantive scientific interests owing to their extraordinary structural and physical properties. Particularly, platinum (Pt)-based 2D chalcogenides present various appealing aspects absent in conventional 2D TMDs, including thickness-dependent semiconducting-to-metallic transition, superior air stability, and low synthesis temperature. Such properties of electrical property transition are known for related to the structure of the 2D TMDs layers. Despite much-devoted efforts, scalable and controllable synthesis of large-area 2D Pt-based 2D chalcogenides with well-defined layer orientation has not been established, leaving its projected structure−property relationship largely unclarified. The extremely small thickness coupled with extraordinary electrical and optical properties of 2D TMDs layer put it the best candidate of emerging stretchable and foldable electronics recently. Although intrinsically large strain limits are projected in them (i.e., several times greater than silicon), integrating 2D TMDs in their pristine forms does not realize superior mechanical tolerance greatly demanded in high-end stretchable and foldable devices of unconventional form factors. The work described in this thesis focuses on understanding the synthesis of large area 2D TMDs layer, especially 2D PtSe2 and PtTe2 layers of interest for growth behavior related to their structural and electrical properties. This dissertation also covers a versatile and rational strategy to convert 2D TMDs of limited mechanical tolerance to tailored three-dimensional (3D) structures with extremely large mechanical stretchability accompanying well-preserved electrical integrity and modulated transport properties, through the transfer/integration and kirigami/serpentine patterning techniques. In the first part, we investigate the structural evolution of large-area chemical vapor transition (CVT)-grown 2D PtSe2 and PtTe2 layers of tailored morphology and clarify its influence on resulting electrical properties. Specifically, we unveil the coupled transition of structural−electrical properties in 2D TMDs layers grown at a low temperature (i.e., 400 °C). The layer orientation of 2D PtSe2 and PtTe2 grown by the CVD selenization and tellurization of seed Pt films exhibits horizontal-to-vertical transition with increasing of Pt thickness. These growth transitions of PtSe2 and PtTe2 layers are a consequence of competing thermodynamic and kinetic factors dictated by accumulating internal strain. The exclusive role of the strain on dictating 2D layer orientation has been quantitatively verified by the transmission electron microscopy (TEM) strain mapping analysis. In the second part, we report two novel strategies to delaminate and integrate wafer-scale 2D TMDs layers of well-defined components and orientations using water. First, we report a generic and reliable strategy to achieve the layer-by-layer integration of large-area 2D TMDs and their heterostructure variations onto a variety of unconventional substrates. This new 2D layer integration method employs water only without involving any other chemicals, thus renders distinguishable advantages over conventional approaches in terms of material property preservation and integration size scalability. Second, we directly grew a variety of 2D TMDs layers on water-dissoluble single-crystalline salt wafers and precisely delaminated them inside water in a chemically benign manner. This manufacturing strategy enables the automated integration of vertically aligned 2D TMDs layers as well as 2D/2D hetero layers of arbitrary stacking orders on exotic substrates insensitive to their kind and shape. The original salt wafers can be recycled for additional growths, confirming high process sustainability and scalability. The generality and versatility of this approach have been demonstrated by developing proof-of-concept all 2D devices for diverse yet unconventional applications. These studies are believed to shed a light on leveraging opportunities of 2D TMDs layers toward achieving large-area mechanically reconfigurable devices of various form factors at the industrially demanded scale. Lastly, we report a versatile and rational strategy to convert 2D TMDs of limited mechanical tolerance to tailored 3D structures with extremely large mechanical stretchability accompanying well-preserved electrical integrity and modulated transport properties. We employed a concept of strain engineering inspired by paper-cutting arts, known as kirigami patterning and serpentine patterning, and developed 2D TMDs-based stretchable electronics. The vertically aligned metallic PtTe2 and PtSe2 layers were employed for the high-performance electronic heaters and high-stretchable (over 2000% stretch) conductors using our low-temperature direct growth method on polymeric substrates. The semiconducting PtSe2 and MoS2 layer were employed for large-area stretchable field-effect transistor (FET) electronic device and NO2 gas sensor showing high-performance of sensitivity. These multifunctional 2D materials in unconventional yet tailored 3D forms are believed to offer vast opportunities for emerging electronics and optoelectronics.MX2 (M: 전이 금속, X: 칼코겐) 형태를 나타내는 2 차원 (2D) 전이 금속 디칼코제나이드 (TMDs) 물질은 뛰어난 구조적, 물리적, 그리고 화학적 특성으로 인하여 전자기기장치 분야에서 많은 흥미를 받고 있다. 특히 백금 (Pt) 기반의 2D TMDs 물질은 두께에 따른 반도체에서 금속으로의 성질 변화, 높은 안정성, 그리고 낮은 합성온도 등의 기존 2D TMDs 물질에서는 나타나지 않는 다양한 이점을 가지고 있다. 이러한 반도체-금속의 전기적 물성 전이 특성은 2D TMDs 물질의 층상구조와 관련이 있는 것으로 알려져 있으나, 많은 연구에도 불구하고 아직까지 2D TMDs 물질의 구조적 특성과 전기적 특성 사시의 사이의 관계가 명확하게 밝혀지지 않고 있다. 또한 작은 두께로 기인되는 2D TMDs 물질은 그들의 뛰어난 전기적, 물리적, 광학적 특성으로 미래의 신축성 및 접이식 전자 장치의 우수한 후보로 여겨지고 있으며, 이러한 미래 전자장비로의 적용을 위하여 2D TMDs 물질을 유연한 기판으로의 박리 및 전사하는 기술이 요구되어 관련된 활발한 연구가 이루어지고 있다. 그러나 2D TMDs 물질의 큰 변형률의 한계를 갖는 뛰어난 물리적 특성에도 불구하고, 박리 및 전사를 통한 2D TMDs 물질의 높은 신축성, 접이식 전자 장치로의 응용을 위한 기계적 내구성의 확보는 아직까지 잘 실현되고 있지 않다. 본고에서는 대면적 2D TMDs 물질 중 PtSe2 층상구조 및 PtTe2 층상구조의 성장거동과 이와 관련된 구조적, 전기적 특성에 대해서 집중한다. 또한 2D TMDs 물질의 전송과 통합 방법과 3차원 (3D) 패터닝(patterning) 기술을 이용한 미래 전자 장치로의 2D TMDs 물질의 적용 가능성에 대한 연구를 다룬다. 첫 번째 장에서는 대면적 화학증기전이(CVT) 방법으로 성장한 PtSe2 와 PtTe2 층의 성장거동에 대하여 관찰 및 규명하였으며, 성장거동에 따른 전기적 특성의 변화에 대하여 관찰하여 그에 미치는 영향을 규명하였다. 저온 합성 공정(400℃)에서 성장한 PtSe2와 PtTe2층은 초기 플래티넘 (Platinum, Pt) 막의 두께가 증가함에 따라 수평에서 수직으로의 전이를 나타낸다. 이러한 PtSe2층과 PtTe2 층의 성장방향 전이는 성장 과정에서 생성된 내부 변형률에 따른 열역학적, 물리적 에너지에 따라 형성되며 투과전자현미경(TEM)을 통한 변형률 분산 분석을 통해 정량적으로 입증하였다. 두 번째 장에서는, 물을 사용한 대면적 2D TMDs 물질의 박리와 결합에 대한 새로운 방법에 대하여 탐구하였으며, 첫 번째로 물만을 사용한 2D TMDs 물질의 박리와 다양한 기판으로의 전사에 관한 손쉽고 신뢰할 수 있는 접근 방식을 보고하였다. 이 새로운 이차원 물질의 통합 방법은 다른 화학 물질을 사용하지 않고 물만 사용하므로 재료 속성 보존 및 통합 크기 대면적화 측면에서 기존 접근 방식에 비해 뚜렷한 이점을 제공한다. 두번째로는, 수용성 단결정 소금 기판 위에 다양한 2D TMDs 층상 물질을 직접 성장시키고 화학적으로 무해한 방식으로 물 속으로 넣어 기판을 물에 녹게 함으로써 2D TMDs 물질만을 정확하게 박리하는데 성공하였다. 이러한 방법은 전사 기판의 종류와 모양에 구애받지 않으며, 다양한 종류의 2D TMDs 물질뿐 아니라 수직으로 정렬된 물질의 박리와 전사도 가능하게 한다. 또한 추가 성장을 위해 원래 소금 기판을 재활용할 수 있으므로 높은 공정 지속 가능성과 확장성을 확인할 수 있다. 이러한 연구를 통하여 산업적으로 요구되는 대규모에서의 다양한 구조의로의 장치를 개발하기 위한 2D TMDs 구조 물질의 적용 가능성을 확인할 수 있다. 세 번째 장에서는, 제한된 기계적 물성의 특징을 나타내는 2D TMDs 물질을 전기적, 구조적, 광학적 성질을 유지하면서 매우 큰 기계적 신축성을 나타내게 하는 3차원 구조로의 변환에 대한 연구를 보고한다. 우리는 키리가미 패터닝과 뱀 모양 패터닝의 종이 절단 예술에서 영감을 얻은 변형 기술을 사용하여 2D TMDs 물질 기반의 신축성 전자 장치를 개발하였다. 수직으로 정렬된 금속 PtTe2 및 PtSe2 물질은 고분자 기판에서 저온 직접 성장 방법을 사용하여 고성능 전자 히터 및 2000% 가 넘는 고신축성 전도체에 사용되었으며, 반도체 물성을 나타내는 PtSe2 및 MoS2 물질은 대면적 신축성 전계 효과 트랜지스터(FET) 전자 장치 및 고성능 감도를 나타내는 이산화 질소(NO2) 가스 센서에 사용되었다. 3D 형태를 나타내는 이러한 다기능 2D 재료의 변환은 새로운 전자 및 광전자 기술에 2D TMDs 물질의 적용 가능성에 대한 기회를 제공한다.Abstract I Table of Contents V List of Figures XIII Chapter 1. Introduction 1 1.1. Introduce of 2D TMDs Materials 1 1.2. Structure of 2D TMDs Layers 4 1.2.1. Atomic Structure of 2D TMDs Layers 4 1.2.2. Growth Orientation of 2D TMDs Layers 8 1.3. Transfer and Integration of 2D TMDs Layer 9 1.4. Engineering the Structure of 2D TMDs to be Mechanically Reconfigurable 10 1.4.1. 3D texturing based on pre-structured polymeric templates. 11 1.4.2. Strain engineering of large-area 2D TMDs by origami and kirigami patterning. 12 1.5. Reference 14 Chapter 2. Growth Behavior and its Properties of 2D TMDs Layers 20 2.1. Growth Behavior and Properties of 2D PtSe2 Layers 20 2.1.1. Introduction 20 2.1.2. Experimental Section 22 2.1.2.1. 2D PtSe2 Layer Growth 22 2.1.2.2. TEM/STEM Characterization 23 2.1.2.3. Raman Characterization 23 2.1.2.4. Device Fabrication and Electrical Measurement 23 2.1.2.5. DFT Calculation 24 2.1.2.6. XPS Characterization 24 2.1.3. Results and Discussion 25 2.1.3.1. Orientation Controlled Growth of PtSe2 Layers 25 2.1.3.2. Atomic-scale Structural Analysis of Orientation Transition 29 2.1.3.3. Chemical and Electronic Structures of 2D PtSe2 Layers 32 2.1.3.4. DFT calculation of various morphology and orientation 2D PtSe2 38 2.1.3.5. The Growth Mechanism of Horizontal-to-vertical 2D Layer Transition in PtSe2 Layer 41 2.1.4. Conclusion 44 2.1.5. Reference 44 2.2. Growth Behavior and Properties of 2D PtTe2 Layers 50 2.2.1. Introduction 50 2.2.2. Experimental Method 52 2.2.2.1. Synthesis of 2D PtTe2 Layers 52 2.2.2.2. TEM Characterization and Analysis 53 2.2.2.3. XRD Characterization 53 2.2.2.4. Electrical Characterization 54 2.2.2.5. AFM Characterization 54 2.2.2.6. Computational Details 54 2.2.3. Results and Discussion 55 2.2.3.1. Growth and Structural Analysis of PtTe2 Layers 55 2.2.3.2. Orientation Controlled Growth and the Mechanism of Orientation Transition of PtTe2 Layers 58 2.2.3.3. DFT calculation for various morphology and orientation of 2D PtTe2 Layers 71 2.2.3.4. Electronic Structures of 2D PtTe2 Layers 74 2.2.4. Conclusion 79 2.2.5. Reference 79 Chapter 3. Transfer and Integration of 2D TMDs Layers 85 3.1. Water-assisted Transfer method for 2D TMDs Layers 85 3.1.1. Introduction 85 3.1.2. Experimental Method 87 3.1.2.1. Synthesis of 2D TMDs Films 87 3.1.2.2. Structural Characterization 87 3.1.3. Results and Discussion 88 3.1.3.1. Procedure of Water-assisted 2D TMDs Layer Integration 88 3.1.3.2. Demonstration of Water-assisted 2D TMDs Layer Transfer and Integration 91 3.1.3.3. Principle of Water-assisted 2D TMDs Layer Separation 94 3.1.4. Conclusion 99 3.1.5. Reference 99 3.2. Water Dissoluble Salt Substrates for 2D TMDs Layer 103 3.2.1. Introduction 103 3.2.2. Experimental Section 104 3.2.2.1. Growth of 2D TMD Layers 104 3.2.2.2. Delamination and Integration of 2D TMD Layers 105 3.2.2.3. Structural and Chemical Characterization 106 3.2.3. Results and Discussion 106 3.2.3.1. The Manufacturing Process of the Water-assisted 106 3.2.3.2. Structural and Chemical Analysis of 2D TMDs Layer grown on Salt Substrates 110 3.2.3.3. The Diversity of Salt Substrates for 2D TMDs Growth and Delamination 113 3.2.3.4. The Heterogeneous Integration of Multiple 2D TMDs Layers 116 3.2.4. Conclusion 119 3.2.5. Reference 119 Chapter 4. Application to Stretchable Future Electronics 125 4.1. High Stretchable Electronic Device 125 4.1.1. Introduction 125 4.1.2. Experimental Method 127 4.1.2.1. Preparation of a Kirigami-Patterned PI Substrate 127 4.1.2.2. Two-Dimensional PtSe2 Layer Growth 128 4.1.2.3. Electrical and Optoelectrical Characterization 128 4.1.2.4. XPS and TEM/STEM Characterization 129 4.1.3. Results and Discussion 129 4.1.3.1. The Manufacturing Process of High Stretchable 2D PtSe2/PI Kirigami Device 129 4.1.3.2. Structural and Chemical Analysis of 2D PtSe2 Layers 132 4.1.3.3. The Mechanical Properties of 2D PtSe2/PI Device 135 4.1.3.4. FEM Simulation for the Optimization of Device Design 140 4.1.3.5. Stretchable FET Device of 2D PtSe2/PI Layer 144 4.1.4. Conclusion 147 4.1.5. Reference 147 4.2. Stretchable Electronic Heater of 2D PtTe2 Layers 152 4.2.1. Introduction 152 4.2.2. Experimental Method 154 4.2.2.1. 2D PtTe2 Synthesis 154 4.2.2.2. Crystal Structure Characterization 155 4.2.2.3. Raman and Electrical Characterization 155 4.2.2.4. Heating performance Test 156 4.2.2.5. Kirigami-pattern Fabrication and Finite Element Method 156 4.2.3. Results and Discussion 157 4.2.3.1. 2D PtTe2 Layer Growth 157 4.2.3.2. Electrical and electrothermal properties of 2D PtTe2 layer 160 4.2.3.3. Flexibility of 2D PtTe2 Layer on PI Substrate 167 4.2.3.4. Kirigami-patterned stretchable heater based on 2D PtTe2 170 4.2.4. Conclusion 175 4.2.5. Reference 175 4.3. Stretchable High-Performance Gas Sensor 179 4.3.1. Introduction 179 4.3.2. Experimental Method 181 4.3.2.1. CVD Growth of VA-2D MoS2 Layers 181 4.3.2.2. VA-2D MoS2 Layer Transfer and Integration Process 181 4.3.2.3. AFM, UVVis, Raman, XPS, and TEM Characterizations 182 4.3.2.4. Device Fabrication and Electrical/Optical Characterization 182 4.3.2.5. Gas Sensing Characterization 182 4.3.2.6. FEM Simulation and DFT Calculation 183 4.3.3. Results and Discussion 184 4.3.3.1. The Sequential Growth, Integration, and Patterning Process of the VA-2D MoS2 Layers 184 4.3.3.2. Structural and Chemical Analysis of 2D VA-MoS2 Layers 188 4.3.3.3. Gas Sensing Performance of Serpentine VA-MoS2 Layers 192 4.3.3.4. FEM Simulation for Mechanical Stretching 198 4.3.3.5. DFT Calculations for the Superiority of VA-2D MoS2 Layers for NO2 Gas Sensing 201 4.3.4. Conclusion 205 4.3.5. Reference 205 Chapter 5. Total Conclusion 212 Abstract in Korean 215Docto