디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2021. 2. 홍용택.일반적으로 제조 공정은 절삭 방식과 적층 방식으로 구분된다. 이 중에서 적층 방식 공정은 저비용 및 단시간으로 복잡한 형태의 구조를 만들 수 있어서 이에 대한 연구와 개발이 꾸준히 진행되어왔다. 특히 3D 프린팅은 적층 방식 공정 중에서 가장 대표적인 방법으로, 기계 부품 및 생체 기관 제조 등의 분야에서는 이미 상용화가 진행되고 있다. 하지만 전자 소자 및 광학 요소 분야에서의 3D 프린팅의 활용은 여전히 연구 개발 또는 시제품 제작 단계에 머무르고 있다. 특히 마이크로 렌즈, 컬러 필터 등이 3D 프린팅으로 응용할 수 있는 가장 가능성 있는 광학 요소로서 디스플레이 및 이미징 시스템에 널리 사용될 것으로 예상되지만 여전히 상용화를 위한 연구가 진행 중이다. 또한 3D 프린팅을 이용한 광학 요소의 제작은 소재, 길이 스케일, 형상 및 응용 방안 등에서도 제한이 많은 상황이다. 따라서 이러한 문제를 극복하기 위해서는 디스플레이 및 이미징 시스템에서의 3D 프린팅 된 광학 요소의 유용성을 확장해야 하며, 다음과 같이 세 가지 측면에서 향상된 성능을 달성해야 한다. 첫째, 다양한 방식의 3D 프린팅 방법을 통해 마이크로미터에서 센티미터까지 광범위의 길이 스케일을 가지는 구조물의 제작이 가능해야 한다. 둘째, 임의의 곡면, 계층적 구조 등 복잡한 형상의 구조물을 쉽게 제작할 수 있어야 한다. 셋째, 단단한 소재 대신 탄성체와 같은 소프트 소재를 이용하여 광학적인 기능을 용이하게 조절할 수 있어야 한다. 이와 같은 동기를 바탕으로 본 학위 논문에서는 디스플레이 및 이미징 시스템으로의 응용을 위한 3D 프린팅 기반 맞춤형 광학 요소의 개발에 대한 내용을 보고한다. 3D 프린팅 기반 광학 요소를 매크로 스케일, 마이크로 스케일 그리고 매크로 및 마이크로 스케일이 혼합된 계층적 구조 등 세 가지 유형으로 분류하고 각각에 대한 응용 분야를 제시한다. 매크로 스케일의 광학 요소로는 가장 기본적인 요소인 렌즈와 거울을 선택한다. 렌즈는 공압식 디스펜싱 방법을 이용하여 실린드리컬 쌍 형태로 제작되었으며, 심리스 모듈러 평판식 디스플레이의 구현을 위해 적용된다. 또한 용융 적층 방식의 3D 프린팅으로 만들어진 몰드를 이용하여 거울을 제작하고, 이를 이용하여 심리스 모듈러 커브드 엣지 디스플레이를 구현한다. 이와 같이 모듈러 디스플레이의 이음새 부분에 3D 프린팅으로 제작된 렌즈 또는 거울을 부착하는 방식으로 화면을 심리스로 확장하는 기술을 제시하고, 다양한 형태의 디스플레이에 적용할 수 있는 가능성을 보여준다. 마이크로 스케일의 광학 요소로는 발광 다이오드에서 색 변환과 광 추출 기능을 동시에 나타내는 색 변환 마이크로 렌즈를 선택한다. 양자 점/광 경화성 고분자 복합체의 전기수력학적 프린팅을 통해 양자 점이 내장된 다양한 형태의 색 변환 마이크로 렌즈를 제작하며, 이를 청색 마이크로 발광 다이오드 어레이의 발광부 상에 적용하여 풀 컬러 마이크로 발광 다이오드 디스플레이로의 응용 가능성을 제시한다. 마지막으로 매크로 및 마이크로 스케일이 혼합된 계층적 구조의 광학 요소로서 디스펜싱 및 건식 러빙 과정의 조합으로 제작된 겹눈 형태를 모사한 렌즈 구조를 제시한다. 반구 형태의 매크로 렌즈를 디스펜싱으로 형성하고, 매크로 렌즈의 곡면 상에 단층의 마이크로 입자의 배열을 얻기 위해 건식 러빙 공정을 진행한다. 이러한 방식으로 형성된 계층적 구조가 소프트한 소재로 복제되어서 신축성을 가지는 겹눈 형태 모사 구조가 완성된다. 마이크로 렌즈 어레이는 매크로 렌즈의 표면을 따라 형성되고 리지드 아일랜드로 역할을 하여, 전체 계층적 구조에 기계적 변형이 가해져 매크로 렌즈의 모양이 변형되어도 마이크로 렌즈는 형상과 해상도, 초점 거리 등의 광학적 특성을 유지할 수 있다. 본 학위 논문은 3D 프린팅을 이용하여 다양한 형태와 스케일의 광학 요소를 제작하고 디스플레이 및 이미징 시스템으로의 여러 응용을 보여줌으로서 앞으로의 새로운 연구 및 개발 방향성을 제시하는 것을 주요 목적으로 한다. 3D 프린팅 설비의 단가가 낮아지고 정밀도 및 해상도가 높아지는 추세에 따라, 광학 요소를 쉽게 만들고 응용할 수 있는 맞춤형 광학 또는 스스로 구현하는 광학 분야가 변형 가능하고 멀티 스케일의 광학계로 점차 확대될 것으로 예상된다. 궁극적으로는 차세대 디스플레이 및 이미징 시스템에 필요한 광학 요소를 위한 기술의 저변을 넓히고, 이를 산업 전반에 응용할 수 있는 기반을 마련하고자 한다.Generally, the manufacturing process is divided into the subtractive (top-down) type and additive type (bottom-up). Among them, the additive manufacturing process has attracted a lot of attention because it can manufacture products with complex shapes in a low-cost and short-time process. In particular, three-dimensional (3D) printing is a representative method, which has already been commercialized in the field of mechanical components and biomedical organ. However, it remains in the research and development step in the field of electronic devices and optical components. Especially, although 3D printed optical components including microlens and color filter are expected to be widely used in display and imaging systems, it is still under investigation for commercialized products, and there are limitations in terms of materials, length scale, shape, and practical applications of components. Therefore, to overcome these issues, it is required for investigating and expanding the potential usefulness for 3D printed optical components in display and imaging systems to achieve better performance, productivity, and usability in three aspects. First, it should be possible to manufacture structures with a wide range of length scales from micrometer to centimeter through various 3D printing methods. Second, complex shapes such as free-from curved surfaces and hierarchical structures should be easily fabricated. Third, it is necessary to add functionality by manufacturing structures in which tunable functions are introduced using soft materials like an elastomer. Based on the above motivations, 3D printing-based customized optical components for display and imaging system applications are introduced in this dissertation. 3D printed optical components are classified into three types and their applications are showed to verify the scalability of 3D printing: macro-scale, microscale, and hierarchical macro/micro-scale. As macro-scale printed optical components, lens and mirror which are the most basic optical components are selected. The lens is fabricated by a pneumatic-type dispensing method with the form of a cylindrical pair and adopted for demonstration of seamless modular flat panel display. Besides, a seamless modular curved-edge display is also demonstrated with a mirror, which is fabricated from fused deposition modeling (FDM)-type 3D printed mold. By simply attaching a printed lens or mirror onto the seam of the modular display, it is possible to secure seamless screen expansion technology with the various form factor of the display panel. In the case of micro-scale printed optical components, the color-convertible microlens is chosen, which act as a color converter and light extractor simultaneously in a light-emitting diode (LED). By electrohydrodynamic (EHD) printing of quantum dot (QD)/photocurable polymer composite, QD-embedded hemispherical lens shape structures with various sizes are fabricated by adjusting printing conditions. Furthermore, it is applied to a blue micro-LED array for full-color micro-LED display applications. Finally, a tunable bio-inspired compound (BIC) eyes structure with a combination of dispensing and a dry-phase rubbing process is suggested as a hierarchical macro/micro-scale printed optical components. A hemispherical macrolens is formed by the dispensing method, followed by a dry-phase rubbing process for arranging micro particles in monolayer onto the curved surface of the macrolens. This hierarchical structure is replicated in soft materials, which have intrinsic stretchability. Microlens array is formed on the surface of the macrolens and acts as a rigid island, thereby maintaining lens shape, resolution, and focal length even though the mechanical strain is applied to overall hierarchical structures and the shape of the macrolens is changed. The primary purposes of this dissertation are to introduce new concepts of the enabling technologies for 3D printed optical components and to shed new light on them. Optical components can be easily made as 3D printing equipment becomes cheaper and more precise, so the field of Consumer optics or Do it yourself (DIY) optics will be gradually expanded on deformable and multi-scale optics. It is expected that this dissertation can contribute to providing a guideline for utilizing and customizing 3D printed optical components in next-generation display and imaging system applications.Chapter 1. Introduction 1 1.1. Manufacturing Process 1 1.2. Additive Manufacturing 4 1.3. Printed Optical Components 8 1.4. Motivation and Organization of Dissertation 11 Chapter 2. Macro-scale Printed Optical Components 15 2.1. Introduction 15 2.2. Seamless Modular Flat Display with Printed Lens 20 2.2.1. Main Concept 20 2.2.2. Experimental Section 23 2.2.3. Results and Discussion 26 2.3. Seamless Modular Curved-edge Display with Printed Mirror 32 2.3.1. Main Concept 32 2.3.2. Experimental Section 33 2.3.3. Results and Discussion 36 2.4. Conclusion 46 Chapter 3. Micro-scale Printed Optical Components 47 3.1. Introduction 47 3.2. Full-color Micro-LED Array with Printed Color-convertible Microlens 52 3.2.1. Main Concept 52 3.2.2. Experimental Section 54 3.2.3. Results and Discussion 57 3.3. Conclusion 65 Chapter 4. Hierarchical Macro/Micro-scale Printed Optical Components 66 4.1. Introduction 66 4.2. Tunable Bio-inspired Compound Eye with Printing and Dry-phase Rubbing Process 69 4.2.1. Main Concept 69 4.2.2. Experimental Section 71 4.2.3. Results and Discussion 73 4.3. Conclusion 79 Chapter 5. Conclusion 80 5.1. Summary 80 5.2. Limitations and Suggestions for Future Researches 83 References 88 Abstract in Korean (국문 초록) 107Docto

Gallium Metal Nanoparticles for Plasmonics and Droplet Epitaxy: Formation and Properties.

The development of new materials in nanophotonics, defined as the use of multiscale materials to control light-matter interactions, has proven to be the foundation for revolutionary advances in both science and technology. In this thesis, we utilize Ga droplets as a plasmonic metal nanoparticle (NP) as well as a seed for droplet epitaxy of ZB GaN nanostructures, and examine the formation of embedded GaAs:Ga nanocomposites and ZB GaN nanostructures, and their structural and optical properties. Metallic nanostructures generate surface plasmons an incident electromagnetic wave, leading to enhancements in absorption and emission. However, materials research and device fabrication have focused nearly exclusively on 2-dimensional dispersions of Ag and Au formed on surfaces, with plasmon resonances limited to visible wavelengths. Thus, it is necessary to explore a new plasmonic materials, which cover wide wavelength ranges. Here, we examined the formation of embedded Ga NP arrays and their influence on GaAs NBE PL efficiency using ion beams and molecular beam epitaxy. Using a combined computational-experimental approach, we revealed new insight into the influence of the embedded NPs on the PL of GaAs. This approach provides an opportunity to enhance the PL efficiency from a variety of semiconductor heterostructures, using a seamless approach to embed non-noble metals during epitaxy. GaN is of interest for optoelectronic applications. However, GaN typically crystallizes in a WZ structure, exhibiting piezoelectric properties leading to a reduced probability for recombination of electrons and holes and consequently limit the performance of devices. Thus, interest in polarization-free ZB GaN nanostructures is rapidly increasing. In this thesis, we first demonstrate the growths of ZB GaN nanostructures via DE. By varying the surface conditions of substrates and nitridation processes, GaN QDs were grown polycrystalline, WZ, and ZB. Furthermore, we examined the growth of ZB-WZ mixed NW growth via controlling SiNx interlayer formation, using a two-step MBE growth method of Ga pre-deposition followed by GaN growth on Si (001). We demonstrate, for the first time, a growth process consisting of pre-deposition at high Ga flux, followed by GaN growth at low Ga flux, thereby resulting in GaN NW ensembles with a significant ZB content.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120759/1/syjeon_1.pd

Earth Resources: A continuing bibliography with indexes, issue 29, April 1981

This bibliography lists 308 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1981 and March 31, 1981. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

셀룰로오스 나노섬유 매트릭스 지지 3차원 프린팅

학위논문(박사)--서울대학교 대학원 :농업생명과학대학 바이오시스템·소재학부(바이오소재공학전공),2020. 2. 현진호.Cellulose nanofibers (CNFs) are attracting material for a three-dimensional (3D) printing matrix due to excellent rheological characteristics. In 3D printing with CNFs, a nozzle moves through the viscoelastic CNF matrix and makes patterns with ink materials. Rheological properties of CNFs are related to various factors including fiber dimension and concentration of CNFs in the aqueous dispersion, and influence on the printing fidelity. The different morphology of CNFs was prepared by varying the degree of carboxymethylation with CNFs. The printing fidelity was evaluated by observing the shape of ink features that were printed directly inside the CNF matrix. The relationship between the rheological properties of the CNF matrix and the printing fidelity was investigated on the printing speed, strain fields, and yielded regions. The cell-containing bio-ink and hydrophobic silicon-based inks were printed in the CNF matrix in a complex structure with high printing fidelity. Amazingly, the structure printed freely in the CNF hydrogels was able to retain its highly resolved 3D features in an ultrathin two-dimensional (2D) paper using a simple drying process. The dimensional change in the CNF hydrogels from 3D to 2D resulted from simple dehydration of the CNFs and provided transparent, stackable paper-based 3D channel devices. The CNF devices exhibited selective diffusion of molecules from the channel wall, indicating the applicability for the sensor and the cell culture platforms.본 논문에서는 셀룰로오스 나노섬유 하이드로겔을 3D 프린팅 매트릭스로 활용하기 위한 전략과 프린팅 충실도를 평가하기 위한 기준을 제시하였고, 건조 시 얇고 투명한 필름을 제조할 수 있다는 특성을 바탕으로 마이크로유체칩을 제조하였다. 셀룰로오스 나노섬유는 3차원 인쇄에 적합한 유변학적 특성으로 인해 최근 3D 프린팅 분야에서 주목을 받아왔으며, 3D 프린팅 잉크로의 활용 가능성이 높은 재료이다. 그러나 하이드로겔 잉크는 변형에 취약하여 기존의 프린팅 기술로는 3차원 구조물을 제조하는데 한계가 있어, 구조물을 지지해줄 수 있는 매트릭스 재료를 활용한 매트릭스 지원 3D 프린팅 기술이 제안되었다. 현재까지 셀룰로오스 나노섬유를 3D 프린팅 매트릭스로 활용하고자 하는 연구는 보고된 바가 없으며 본 연구에서는 셀룰로오스 나노섬유가 3D 프린팅 매트릭스로 활용되기 위한 최적의 조건을 탐색하였다. 셀룰로오스 나노섬유의 유변학적 특성은 섬유의 크기 및 농도에 의해 결정된다. 본 연구에서는 섬유의 크기를 카르복시메틸화를 통해 조절하였으며, 다양한 농도 조건에서의 프린팅 충실도를 평가하기 위한 기준을 제시하였다. 프린팅 충실도는 셀룰로오스 나노섬유 매트릭스와 혼화성의 차이를 보이는 친수성, 소수성 모델 잉크를 프린팅 하고 잉크의 형상을 관찰하여 평가하는 방식으로 진행하였다. 각이진 선을 프린팅 하고 각도의 날카로운 정도와 잉크의 단면 비율, 그리고 잉크 표면 거칠기를 분석하여 매트릭스의 유변학적 특성과 프린팅 충실도 간의 관계를 분석하였다. 이를 활용하여 셀룰로오스 나노섬유 매트릭스 내부에 바이오 잉크를 프린팅 할 수 있었으며 소수성 실리콘 기반 잉크로 복잡한 3차원 구조체를 제조할 수 있었다. 셀룰로오스 나노섬유는 프린팅 매트릭스로 활용될 수 있을 뿐만 아니라 간단한 건조과정을 통해 얇고 투명한 디바이스를 제조하기 최적화 되어있는 재료이다. 이러한 장점을 활용하여 셀룰로오스 나노섬유 기반의 마이크로유체칩을 제조할 수 있었다. 셀룰로오스 나노섬유의 투명도와 물질확산특성은 화학 센서뿐만 아니라 세포를 배양하고 세포의 거동을 분석할 수 있는 세포 배양 플랫폼으로도 활용될 수 있었다.Ⅰ. Introduction 1 Ⅱ. Literature Survey 4 2.1. Various 3D printing technologies 4 2.2. Matrix-assisted 3D printing (MAP) 8 2.2.1. Rheological requirements for MAP 10 2.2.2. Various matrix systems for MAP 11 2.3. Cellulose 16 2.3.1. Cellulose nanofiber (CNF) 17 2.3.2. Extraction methods of CNF 18 2.3.3. Rheological properties of CNF 21 2.4. CNF as a 3D printing material 23 2.4.1. CNF as a rheology modifier 23 2.4.2. CNF as a reinforcement 24 2.5. CNF based devices 27 2.5.1. Transparent and thin device through dehydration 27 2.5.2. Electronic devices 28 2.5.3. Biological and chemical sensing devices 29 2.5.4. Cell culture devices 30 Ⅲ. Materials and Methods 32 3.1. Preparation and characterization of the CNF matrix 32 3.2. Preparation of various types of ink 33 3.2.1. Cross-linked polyacrylic acid-based model ink 33 3.2.2. CNF based bio-ink 34 3.2.3. Petroleum-jelly based removable ink 34 3.2.4. Silicone ink-based curable ink 34 3.3. Rheological properties of CNF matrices and inks 35 3.4. Matrix-assisted 3D printing of a single line 35 3.4.1. Matrix-assisted 3D printing of straight line 35 3.4.2. Matrix-assisted 3D printing of angled line 36 3.5. Matrix-assisted 3D printing of multi-lines 36 3.5.1. Matrix-assisted 3D printing of multi-lines 36 3.5.2. Particle Image Velocimetry (PIV) test 36 3.6. Living cell embedded bio-ink printing 37 3.7. Silicone actuator printing 37 3.8. Fabrication of CNF based open-channel microfluidic devices 38 3.8.1. Fabrication process of CNF microfluidic devices 38 3.8.2. CNF based pH sensor 39 3.8.3. CNF based heavy metal sensor 39 3.9. Fabrication of CNF based open cell culture platform 40 3.9.1. Hydrophobic treatment of CNF 40 3.9.2. Mass transfer test at the CNF layers 41 3.9.3. Cell culture on CNF microfluidic devices 41 3.10. Imaging 42 Ⅳ. Results and Discussion 43 4.1. Properties of carboxymethylated CNF matrix 43 4.2. Rheological properties of CNF matrix 52 4.2.1. Shear-thinning property of CNF matrix 52 4.2.2. Yielding property of CNF matrix 55 4.2.3. Creep and recovery properties of CNF matrix 58 4.3. Evaluation of printing fidelity in a single printing line feature 60 4.3.1. Evaluation of printing fidelity by sharpness of angled-line 60 4.3.2. Evaluation of printing fidelity by cross-sectional ratio 66 4.3.3. Evaluation of printing fidelity by straightness of line surface 69 4.3.4. Evaluation of printing fidelity with hydrophobic ink 74 4.4. Evaluation of printing fidelity in multi printing lines feature 82 4.4.1. Particle image velocimetry (PIV) test 82 4.4.2. Velocity magnitude around nozzle 86 4.4.3. Matrix composition and printing path effects on fidelity 88 4.5. Printing of various ink materials 90 4.5.1. Rheological properties of various ink materials 90 4.5.2. Living cell embedded 3D bio-printing 92 4.5.3. Feasibility test of printed silicone actuator 92 4.6. Fabrication of CNF based open-channel microfluidic devices 95 4.6.1. Feasibility test of microfluidic channel devices 97 4.6.2. Control of channel diameters 99 4.6.3. Dimension control of the microfluidic device 101 4.6.4. Feasibility of pH sensor 103 4.6.5. Colorimetric analysis of heavy metal ions 105 4.7. Fabrication of CNF based open cell culture platform 107 4.7.1. Evaluation of hydrophobicity of MTMS treated CNF 111 4.7.2. Diffusion of FITC-Dex to CNF channel layers 114 4.7.3. Cell viability of the CNF-based platform 117 4.7.4. Effect of cisplatin at the CNF-based platform 118 Ⅴ. Conclusion 121 Ⅵ. References 123Docto

Sustainable Molecular Gelators: Beta-D-Glucoside Derived Structuring Agents and Their Material Application

Though molecular gelators may by synthesized and formulated into gels following a variety of methods, it should serve that the most valued methods may utilize renewable and waste resources and follow sustainable procedures. Molecular gelators are systems capable of structuring liquids into solid-like materials and they represent a class of surfactant and amphiphilic materials which posses the capability to be not only useful in their ability to form gels, but multifunctional in the ability to respond smartly to a variety of stimuli. Thus there is an interest in the development of sustainable molecular gelators capable of being applied to applications, which may have been previously linked to gels, or more interestingly those with which gels have not yet been applied. The use of naturally occurring starting materials in the form of renewable resources serves to inspire biomimetic species which allow for the simultaneous development of materials for applied research, while affording researchers the opportunity to study the importance of non-covalent intermolecular interaction and their roles in natural molecules. Deriving these gelators from the basic primary metabolites may help unveil the nature of these forces in their assembly, and most excitingly their function. In an effort to explore the functionality and utility of biobased gelled supramolecular systems, two gelators, one primarily structuring organic solvents, and the other a hydrogelator are discussed from a synthetic point of view and characterized for their non-covalent interactions. Enzymatic catalysis is performed to afford these species in high yields, allowing for the eventual potential commercialization of these gelators through benign means. In addition to the gelator characterization, the resultant composite gels are studied for their mechanical properties, but of most interest their ability to be defined as smart materials in their response to shear, heat and light. Lastly these materials are examined for their application to three different areas of current interest: healthful edible oil structuring, next-generation gelled fuels, and radiation sensing gels. This study should serve as a rigorous investigation not only in the sustainable development of functional value-added chemicals, but their formulation and processing into value-added materials