Human and Biological Skin-Inspired Electronic Skins for Advanced Sensory Functions and Multifunctionality

Department of Energy Engineering (Energy Engineering)The electronic skin (e-skin) technology is an exciting frontier to drive next generation of wearable electronics owing to its high level of wearability to curved human body, enabling high accuracy to harvest information of users and their surroundings. Altough various types of e-skins, based on several signal-transduction modes, including piezoresistive, capacitive, piezoelectric, triboelectric modes, have been developed, their performances (i.e. sensitivity, working range, linearity, multifunctionality, etc.) should be improved for the wearable applications. Recently, biomimicry of the human and biological skins has become a great inspiration for realizing novel wearable e-skin systems with exceptional multifunctionality as well as advanced sensory functions. As an ideal sensory organ, tactile sensing capabilities of human skin was emulated for the development of e-skins with enhanced sensor performances. In particular, the unique geometry and systematic sensory system of human skin have driven new opportunities in multifunctional and highly sensitive e-skin applications. In addition, extraordinary architectures for protection, locomotion, risk indication, and camouflage in biological systems provide great possibilities for second skin applications on user-interactive, skin-attachable, and ultrasensitive e-skins, as well as soft robots. Benefitting from their superior perceptive functions and multifunctionality, human and biological skins-inspired e-skins can be considered to be promising candidates for wearable device applications, such as body motion tracking, healthcare devices, acoustic sensor, and human machine interfaces (HMI). This thesis covers our recent studies about human and biological skin-inspired e-skins for advanced sensory functions and multifunctionality. First, chapter 1 highlights various types of e-skins and recent research trends in bioinspired e-skins mimicking perceptive features of human and biological skins. In chapter 2, we demonstrate highly sensitive and tactile-direction-sensitive e-skin based on human skin-inspired interlocked microdome structures. Owing to the stress concentration effect, the interlocked e-skin experiences significant change of contact area between the interlocked microdomes, resulting in high pressure sensitivity. In addition, because of the different deformation trends between microstructures in mutual contact, the interlocked e-skin can differentiate and decouple sensor signals under different directional forces, such as pressure, tensile strain, shear, and bending. In chapter 3, interlocked e-skins were designed with multilayered geometry. Although interlocked e-skin shows highly sensitive pressure sensing performances, their pressure sensing range is narrow and pressure sensitivity continuously decreases with increasing pressure level. The multilayer interlocked microdome geometry can enhance the pressure-sensing performances of e-skins, such as sensitivity, working range, and linearity. As another approach of e-skin with multilayered geometry, we demonstrate multilayered e-skin based on conductivity-gradient conductive materials in chapter 4. The conducive polymer composites with different conductivity were coated on the microdome pattern and designed as interlocked e-skin with coplanar electrode design, resulting in exceptionally high pressure-sensing performances compared with previous literatures. In chapter 5, inspired by responsive color change in biological skins, we developed mechanochromic e-skin with a hierarchical nanoparticle-in-micropore architecture. The novel design of hierarchical structure enables effective stress concentration at the interface between nanoparticle and porous structure, resulting in impressive color change under mechanical stimuli. In chapter 6, we emulate ultrahigh temperature sensitivity of human and snake skin for temperature-sensitive e-skin. The thermoresponsive composite based on semi-crystalline polymer, temperature sensor shows ultrahigh temperature sensitivity near the melting point of semi-crystalline polymer. In addition, integration of thermochromic composite, mimicking biological skins, enables dual-mode temperature sensors by electrical and colorimetric sensing capabilities. Finally, in chapter 7, we summarize this thesis along with future perspective that should be considered for next-generation e-skin electronics. Our e-skins, inspired by human and biological skin, can provide a new paradigm for realizing novel wearable electronic systems with exceptional multifunctionality as well as advanced sensory functions.clos

Theoretical analysis and simulations applied to rational design strategies of nanostructured materials

Orientador: Douglas Soares GalvãoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb WataghinResumo: Esse documento apresenta uma coleção de trabalhos realizados dentro do amplo campo de materiais nanoestruturados, focando-se em descrições teóricas analíticas e simulações computacionais de diversos novos materias desse tipo. Uma nova fibra supereslástica e condutora é reportada. Essa fibra altamente esticável (até 1320%) é criada envolvendo-se um núcleo cilíndrico de borracha com uma camada de folha de nanotubos de carbono. O material resultante exibe uma interessante estrutura de enrugamentos hierárquicos na sua superfície, o que lhe garante propriedades elétricas úteis como conservar a sua resistencia constante enquanto esticada. Adicionando-se mais camadas de borracha ou nanotubos podemos obter aplicações como sensores de movimento ou deformação, atuadores/músculos artificiais ativados por corrente ou temperatura e operados reversivelmente por um mecanismo de acoplamento entre tensão e torção. Nós explicamos suas propriedades de condução elétrica e os fenômenos físicos envolvidos em cada uma dessas aplicações. Também desenvolvemos um novo método para o desenho racional de polímeros molecularmente impressos usando dinâmica molecular para simular o processo de impressão molecular e a análise subsequente utilizando experimentos de cromatografia simulada. Obtivemos com sucesso a primeira evidência teórica do mecanismo de impressão exibindo afinidade e seletividade para a substância alvo 17-beta-estradiol. Desenhamos e simulamos uma nova estrutura com formato de piramide em kirigami de grafeno, composta de uma folha de grafeno cortada em um padrão específico a fim de formar uma pirâmide quando sofre tensão na direção normal ao plano. Nós calculamos a resposta dessa estrutura a uma carga estática, quando ela age como uma mola de proporções nanométriacs. Também, utilizando simulações de dinâmica molecular de colisões balísticas, constatamos que a resistência desse material a impactos é ainda maior que de uma folha de grafeno puro, sendo ainda mais leve. Um novo método de reforçar fios de nanotubos de carbono, chamado ITAP, também é reportado. Esse método foi capaz de melhorar a resistencia mecanica do fio em até 1,5 vezes e torná-lo muito mais resistente ao ataque de ácido quando comparado com um fio não tratado. Utilizamos simulações de dinâmica molecular para testar a hipótese de que esse tratamento é suficiente para gerar ligações covalentes entre as paredes externas de nanotubos diferentes, o que seria responsável pelas propriedades do material. Aplicamos um algoritmo genético modificado ao problema do folding de proteínas em um modelo de rede 3D HP. Testamos o algoritmo utilizando um conjunto de sequencias de teste que têm estado em uso pelos últimos 20 anos na literatura. Fomos capazes de melhorar um dos resultados e demonstramos a aplicação e utilidade de operadores não canônicos que evitam a convergência prematura do algoritmo, sendo eles o operador de compartilhamento e efeito maternalAbstract: This document presents a colection of works done within the broad subject of nano-structured materials, focusing on analytical theoretical descriptions and computational simulations of new kinds of this class of materials. A new superelastic conducting fiber is reported, with improved properties and functionalities. They are highly stretchable (up to 1320%) conducting fibers created by wrapping carbon nanotube sheets on stretched rubber fiber cores. The resulting structure exhibited an interesting hierarchical buckled structure on its surface. By including more rubber and carbon nanotube layers, we created strain sensors, and electrically or thermally powered tensile and torsional muscles/actuators operating reversibly by a coupled tension-to-torsion actuation mechanism. We explain its electronic properties and quantitatively explain the compounded physical effects involved in each of these applications. We also developed a new method for the rational design of molecularly imprinted polymers using molecular dynamics to simulate the imprinting process and subsequent chromatography studies. We successfully obtained the first theoretical evidence of actual imprinting happening under unconstrained simulations showing affinity and selectivity to the target substance 17-beta estradiol. We designed and simulated a new graphene kirigami pyramid structure, composed of a cut graphene sheet in a specific pattern in order to form a pyramid when under stress perpendicular to the plane. We calculated the response to static loading of this structure that acts like a nano-sized spring. Also, with simulated ballistic collisions we obtained increased resistance to impact in comparison with a pure graphene sheet. A new method of strengthening carbon nanotube yarns, called ITAP, consisting of annealing at high temperature in vacuum is reported. This method is shown to increase the mechanical resistance of the wire up to 1.5 times and make it much more resistant to acid corrosion when compared to pristine non-treated wires. We applied a modified genetic algorithm to the protein folding problem using an 3D HP lattice model using known test sequences that have been in use for the last 20 years and obtained an improvement for the best solution found for one of these proteins. Also, the importance of new non-canonical operators that prevent rapid convergence of the algorithm was demonstrated, namely the Sharing and Maternal Effect operatorsDoutoradoFísicaDoutor em Ciências141198/2012-5CNP

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

Transparent Conductive Films Based on Polymer-Encapsulated Graphene Oxide Sheets

Transparent conductive films (TCFs) play a key role in number of devices, including solar panels, LCD/OLED displays and touchscreens. Graphene has emerged as a promising material in this area due to its unique mechanical and electrical properties. Despite noteworthy progress in the fabrication of large-area graphene sheet-like nanomaterials, the vapor-based processing still requires sophisticated equipment and a multistage handling of the material. An alternative approach to manufacturing functional graphene-based films includes the employment of graphene oxide (GO) micron-scale sheets as precursors. However, search for a scalable manufacturing technique for the production of high-quality GO nanoscale films with high uniformity and high electrical conductivity is still continuing. The study presented in this dissertation is dedicated to the fabrication and characterization of electrically conductive films made of reduced graphene oxide sheets (rGO) deposited on both rigid and flexible substrates. Here we show that conventional dip-coating technique can offer fabrication of high quality mono- and bilayered films made of GO sheets. The method is based on our recent discovery that encapsulating individual GO sheets in a nanometer-thick copolymer layer poly(Oligo Ethylene Glycol methyl ether Methacrylate [OEGMA]- Glycidyl Methacrylate [GMA]) allows for the nearly perfect formation of the GO layers on hydrophilic substrates. By thermal reduction at 1000 ⁰C the bilayers (cemented by a carbon-forming polymer linker) are converted into highly conductive and transparent reduced GO films with a high conductivity up to 10000 S/cm and optical transparency on the level of 90%. The value is the highest electrical conductivity reported for thermally reduced nanoscale GO films and is close to the conductivity of indium tin oxide (ITO) currently in use for transparent electronic devices, thus making these layers intriguing candidates for replacement of ITO films. To facilitate the deposition of GO sheets on rigid and flexible hydrophobic substrates, the amphiphilic copolymer poly(Oligo Ethylene Glycol methyl ether Methacrylate [OEGMA]- Glycidyl Methacrylate [GMA]- Lauryl Methacrylate [LMA]) with additional hydrophobic block was used. The results show that the obtained GO layers had well-defined and uniform structure. Thus, it leads to enhanced hydrophobic-hydrophobic (van der Waals) interaction between the hydrophobic substrate and GO. To this end, the morphology, opto-electrical properties and electro-mechanical stability of chemically reduced GO layers are also investigated. Finally, we demonstrate the excellent stability of rGO on polymeric substrates with no delamination or significant loss in conductivity even after 50000 bending cycle

Conducting polymers and hybrid materials for technological applications

Depletion of natural resources and non-renewable energy sources has recently accelerated due to the development of globalized economy and industrialization. During the last years, the scientific community has devoted much of its efforts to developing and improving renewable energy sources. In this context, electrochemical capacitors, or supercapacitors, have received great interest owing to their properties and potential applications. Supercapacitors and their different components constitute the main line of work of the present thesis. More specifically the thesis investigates the use of hydrogels in various distinct functions. The work done in the thesis has been developed both experimentally and corroborated by theoretical studies based on quantum mechanics and molecular dynamics. The main body of the thesis is divided into three parts. The first one includes the synthesis and characterization of a hydrogel derived from an unsaturated polyesteramide as a solid electrolyte in a supercapacitor. This part consists of the electrochemical characterization of the hydrogel obtained, evaluating the performance of the hydrogel when acting as a solid electrolyte, as well as a study of ion diffusion through the hydrogel carried out with molecular dynamics. These studies allow to obtain the optimal conditions for the synthesis and use of this hydrogel. The second part is based on the preparation and characterization of a multilayer system as an electrode in a supercapacitor. More specifically, it covers the preparation of a multilayer system consisting of PVA and the conductive polymer PEDOT, prepared by a layer-by-layer process. The chapter also consists of a theoretical study of quantum mechanics in which the movement and changes of a PEDOT monolayer are studied, and allows to elucidate the mechanisms and electronic properties that had not been fully understood at the experimental level. Finally, the third and last part incorporates the preparation of a multifunctional system consisting entirely of hydrogels. The chapter begins by detailing the preparation of an electrode of a supercapacitor based on a PEDOT hydrogel and alginate. After its characterization as an electrode, other functionalities that can be given to this system are explored. Among them, a reusable and recyclable pressure sensor is prepared to detect pressure changes linearly and with great sensitivity, as well as a controlled drug release system, in particular a controlled release by electrical stimulation of curcumin.Degut al desenvolupament de l'economia globalitzada i la industrialització, s'ha accelerat l'esgotament de recursos naturals i fonts d'energia no renovables. En els últims anys, la comunitat científica ha dedicat una gran part dels seus esforços a desenvolupar i millorar les fonts d'energia renovable. En aquest context, els capacitors electroquímics, o supercapacitors, han rebut un gran interès degut a les seves propietats i potencials aplicacions. El principal camp de treball d'aquesta tesis són els supercapacitors i les diferents parts que els constitueixen, més concretament la tesis estudia l'ús d'hidrogels en diverses funcions diferents. El treball fet a la tesis s'ha desenvolupat tant a nivell experimental com corroborat mitjançant estudis teòrics basats en la mecànica quàntica i la dinàmica molecular. El cos principal de la tesis està dividit en 3 parts. La primera part inclou la síntesis i caracterització d'un hidrogel derivat d'una poliesteramida insaturada com a electròlit sòlid en un supercapacitor. Aquesta part consta de la caracterització electroquímica de l'hidrogel obtingut, avaluant el rendiment de l'hidrogel a l'hora d'actuar com un electròlic sòlid, així com també consta d'un estudi de difusió dels ions a través d¿aquest dut a terme amb dinàmica molecular. Aquests estudis permeten obtenir les condicions òptimes per la síntesis i ús d'aquest hidrogel. La segona part està dedicada a la preparació i caracterització d'un sistema multicapa com a elèctrode en un supercapacitor. Més concretament, es basa en la preparació d'un sistema multicapa format per PVA i el polímer conductor PEDOT, preparat mitjançant un procés capa per capa. El capítol consta també d'un estudi teòric de mecànica quàntica en el que s'estudia el moviment i canvis d'una monocapa de PEDOT, i permet elucidar els mecanismes i propietats electròniques que no s'havien entès completament a nivell experimental. Finalment, l'última part es tracta de la preparació d'un sistema multifuncional format completament per hidrogels. El capítol comença detallant la preparació d'un elèctrode d'un supercapacitor basat en un hidrogel de PEDOT i alginat. Després de la seva caracterització com a elèctrode, s'exploren les altres funcionalitats que se li poden donar a aquest sistema. Es prepara un sensor de pressió reutilitzable i reciclable que permet detectar canvis de pressió linealment i amb una gran sensibilitat, i també es prepara un sistema d'alliberament controlat de fàrmacs, concretament l'alliberament controlat mitjançant estímul elèctric de curcuminaPostprint (published version

Flexible and Stretchable Lithium-Ion Batteries Based on Solid Polymer Nanocomposite Electrolyte

The prevalence of flexible electronics including the ubiquitous touch-screens, roll-up displays, implantable medical devices and wearable sensors has motivated the development of high performance flexible energy storage devices. High energy density lithium-ion batteries (LIBs) are the leading candidates to convert into flexible and stretchable batteries to integrate with the flexible and stretchable applications. The ultimate challenge is to obtain mechanical flexibility while conserving the high electrochemical performance of conventional LIBs including high capacity and cycling stability. In this study, two types of polymer nanocomposite electrolytes are investigated for battery and fuel cell applications. The first polymer studied is based on Nafion, and a key problem in PEMFCs is the dehydration of Nafion and the subsequent low performance especially at higher temperatures. We introduced a bio-friendly coconut shell activated carbon (AC) nanoparticles into the Nafion membranes. We showed that a small amount (i.e., 0.7%) of AC nanofillers could dramatically enhance proton conductivity without significantly compromising the mechanical properties. The second type of polymer for lithium-ion battery application is based on the polyethylene oxide (PEO)|Li salt system. It offers enhanced safety, stability and thin-film manufacturability compared to the traditional organic liquid electrolytes. The electrochemical properties of the pure polymer are improved by adding 1% graphene oxide (GO) nanosheets. We developed a high performance flexible Li ion battery based on the solid polymer nanocomposite electrolyte. The flexible battery exhibits a capacity higher than 0.1 mAh cm-2 at 1 mA current and excellent cycling stability over 100 charge/discharge cycles. PEO/GO electrolyte was also incorporated in a novel design of spiral stretchable battery capable of large out-of-plane deformation. The spiral Li-ion battery displays robust mechanical stretchability and an energy density of 4.862 mWh/cm3 at 650% out-of-plane deformation and provides an average capacity above 0.1 mAh/cm2 in different stretching configurations. We also investigated the temperature effects on solid polymer electrolyte based batteries. A 1-D LIB model that predicts the discharge behavior of coin cell batteries at different temperatures was developed. The modeling simulations based on electrochemical-thermal coupling show good agreement with experimental results and provide fundamental insights on the battery operation at different conditions.Mechanical Engineering, Department o