Light Extraction Efficiency of Nanostructured III-Nitride Light-Emitting Diodes

III-nitride materials have been extensively employed in a wide variety of applications attributed to their compact sizes, lower operating voltage, higher energy efficiency and longer lifetime. Although tremendous progress has been reported for III-nitride light-emitting diodes (LEDs), further enhancement in the external quantum effciency (η_EQE), which depends upon internal quantum efficiency, injection efficiency and light extraction efficiency (η_extraction), is essential in realizing next generation high-efficiency ultraviolet (UV) and visible LEDs. Several challenges such as charge separation issue, large threading dislocation density, large refractive index contrast between GaN and air, and anisotropic emission at high Al-composition AlGaN quantum wells in the deep-UV regime have been identified to obstruct the realization of high-brightness LEDs. As a result, novel LED designs and growth methods are highly demanded to address those issues. The objective of this dissertation is to investigate the enhancement of η_extraction for various nanostructured III-nitride LEDs. In the first part, comprehensive studies on the polarization-dependent η_extraction for AlGaN-based flip-chip UV LEDs with microdome-shaped patterned sapphire substrates (PSS) and AlGaN-based nanowire UV LEDs are presented. Results show that the microdome-shaped PSS acts as an extractor for transverse-magnetic (TM)-polarized light where up to ~11.2-times and ~2.6-times improvement in TM-polarized η_extraction can be achieved for 230 nm and 280 nm flip-chip UV LEDs, while as a reflector that limits the extraction of transverse-electric (TE)-polarized light through the sapphire substrate. Analysis for 230 nm UV LEDs with nanowire structure shows up to ~48% TM-polarized η_extraction and ~41% TE-polarized η_extraction as compared to the conventional planar structure (~0.2% for TM-polarized η_extraction and ~2% for TE-polarized η_extraction). Plasmonic green LEDs with nanowire structure have also been investigated for enhancing the LED performance via surface plasmon polaritons. The analysis shows that both η_extraction and Purcell factor for the investigated plasmonic nanowire LEDs are independent of the Ag cladding layer thickness (H_Ag), where a Purcell factor of ~80 and η_extraction of ~65% can be achieved when H_Ag \u3e 60 nm. Nanosphere lithography and KOH-based wet etching process have been developed for the top-down fabrication of III-nitride nanowire LEDs. The second part of this dissertation focuses on alternative approaches to fabricate white LEDs. The integration of three-dimensional (3D) printing technology with LED fabrication is proposed as a straightforward and highly reproducible method to improve η_extraction at the same time to achieve stable white color emission. The use of optically transparent acrylate-based photopolymer with a refractive index of ~1.5 as 3D printed lens on blue LED has exhibited 9% enhancement in the output power at current injection of 4 mA as compared to blue LED without 3D printed lens. Stable white color emission can be achieved with chromaticity coordinates around (0.27, 0.32) and correlated color temperature ~8900 K at current injection of 10 mA by mixing phosphor powder in the 3D printed lens. Novel LED structures employing ternary InGaN substrates are then discussed for realizing high-efficiency monolithic tunable white LEDs. Results show that large output power (~170 mW), high η_EQE (~50%), chromaticity coordinates around (0.30, 0.28), and correlated color temperature ~8200 K can be achieved by engineering the band structures of the InGaN/InGaN LEDs on ternary InGaN substrates

Nanooptics with surface plasmons and resonant nanoparticles

[no abstract

Development of label-free colorimetric plasmonic sensor for biomedical applications

Biosensor technology is making strides due to its association with detection and quantification of a wide array of physiological profile makers, biomarkers, for the early detection of diseases. The newest technologies encompasses both qualitative as well as quantitative measurement of such markers. Colorimetric sensing, a method that enables the detection of target analytes via ‘color change’, lays the foundation of a user-friendly, economical and most of all, it’s accessibility to draw inference for the detection of notorious critical conditions such as, carcinomas, and other significant environmental monitoring. Therefore, the impact of colorimetric sensing on the clinical detection of diseases at earlier stages can be enormous, provided the gap between the accuracy of lab-equipment to point-of-care testing tools is approximated. This thesis discusses the design, fabrication and characterization of a label-free plasmonic-based colorimetric sensor on a flexible plastic substrate consisting of periodic nano cups, also referred a nano Lycurgus cups, in an array covered with metal nanoparticles on the side walls and have sub-wavelength openings to provide refractive index sensing. It is also anticipated that the colorimetric sensor can be applied to point-of-care diagnostics by utilizing proper surface functionalization techniques, which is one of the current limiting factors. Chapter 1, is an overview on the existing biosensor technologies with the requirement of the next generation label free biosensor based on nanohole arrays. Chapter 2, describes the recent development of nanoscale Lycurgus cup Array (nanoLCA) with design, fabrication and characterization of the nanoplasmonic device. Chapter 3 starts with the discussion on the influence of adhesion layer on the optical properties of the nanoLCA device followed by layer by layer deposition of polyelectrolyte layers to identify the decay length of the device. Furthermore, this chapter also describes the deposition of different polymers using micro contact printing and compares the spectral results with the colorimetric properties of the device. Chapter 4 gives a demonstration of detection of drug bindings with cytochrome P450-2J2 using the nanoLCA device. Cytochrome P450-2J2 is the most common enzyme found in human heart and it is involved in drug metabolism. All bio-molecular detections are done using nanoLCA based on the shift in resonance peak wavelength with respect to change in the refractive index on the surrounding medium of the device. However, there is a constraint in using nanoLCA device to detect the lower concentration of bio-marker. Therefore, in Chapter 5, we have introduced 3D plasmonic nano cavity structure of the device in which an optical resonant cavity is combined with the plasmonic resonance in one device. This device is a modification of the previously studied nanoLCA device with additional layers, referred as multilayer nanoscale Lycurgus cup array (ML-nanoLCA device). The ML-nanoLCA device is based on a semiconductor material such as cadmium sulfide (CdS) layer, which has a high refractive index and very low extinction coefficient, sandwiched between two gold (Au) layers. This method allows intensity based bio-sensing with the help of a simple bandpass filter to allow certain wavelengths to be transmitted in the visible region at normal incidence illumination. The multilayer plasmonic substrate results in further improvement in the refractive-index sensing, DNA hybridization detection, protein-protein interaction, and detection of lower concentration of cancer biomarker, carcinoembryonic antigen (CEA) with higher sensitivity, which is discussed in chapter 6. The summary of the thesis with future outlook of the nanoplasmonic biosensor is discussed in chapter 7

Development of novel series and parallel sensing system based on nanostructured surface enhanced Raman scattering substrate for biomedical application

With the advance of nanofabrication, the capability of nanoscale metallic structure fabrication opens a whole new study in nanoplasmonics, which is defined as the investigation of photon-electron interaction in the vicinity of nanoscale metallic structures. The strong oscillation of free electrons at the interface between metal and surrounding dielectric material caused by propagating surface plasmon resonance (SPR) or localized surface plasmon resonance (LSPR) enables a variety of new applications in different areas, especially biological sensing techniques. One of the promising biological sensing applications by surface resonance polariton is surface enhanced Raman spectroscopy (SERS), which significantly reinforces the feeble signal of traditional Raman scattering by at least 104 times. It enables highly sensitive and precise molecule identification with the assistance of a SERS substrate. Until now, the design of new SERS substrate fabrication process is still thriving since no dominant design has emerged yet. The ideal process should be able to achieve both a high sensitivity and low cost device in a simple and reliable way. In this thesis two promising approaches for fabricating nanostructured SERS substrate are proposed: thermal dewetting technique and nanoimprint replica technique. These two techniques are demonstrated to show the capability of fabricating high performance SERS substrate in a reliable and cost efficient fashion. In addition, these two techniques have their own unique characteristics and can be integrated with other sensing techniques to build a serial or parallel sensing system. The breakthrough of a combination system with different sensing techniques overcomes the inherent limitations of SERS detection and leverages it to a whole new level of systematic sensing. The development of a sensing platform based on thermal dewetting technique is covered as the first half of this thesis. The process optimization, selection of substrate material, and improved deposition technique are discussed in detail. Interesting phenomena have been found including the influence of Raman enhancement on substrate material selection and hot-spot rich bimetallic nanostructures by physical vapor deposition on metallic seed array, which are barely discussed in past literature but significantly affect the performance of SERS substrate. The optimized bimetallic backplane assisted resonating nanoantenna (BARNA) SERS substrate is demonstrated with the enhancement factor (EF) of 5.8 × 108 with 4.7 % relative standard deviation. By serial combination with optical focusing from nanojet effect, the nanojet and surface enhanced Raman scattering (NASERS) are proved to provide more than three orders of enhancement and enable us to perform stable, nearly single molecule detection. The second part of this thesis includes the development of a parallel dual functional nano Lycurgus cup array (nanoLCA) plasmonic device fabricated by nanoimprint replica technique. The unique configuration of the periodic nanoscale cup-shaped substrate enables a novel hybrid resonance coupling between SPR from extraordinary (EOT) and LSPR from dense sidewall metal nanoparticles with only single deposition process. The sub-50nm dense sidewall metal nanoparticles lead to high SERS performance in solution based detection, by which most biological and chemical analyses are typically performed. The SERS EF was calculated as 2.8 × 107 in a solution based environment with 10.2 % RSD, which is so far the highest reported SERS enhancement achieved with similar periodic EOT devices. In addition, plasmonic colorimetric sensing can be achieved in the very same device and the sensitivity was calculated as 796 nm/RIU with the FOM of 12.7. It creates a unique complementary sensing platform with both rapid on-site colorimetric screening and follow-up precise Raman analysis for point of care and resource limited environment applications. The implementations of bifunctional sensing on opto-microfluidic and smartphone platforms are proposed and examined here as well

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

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

Nanofabrication

We face many challenges in the 21st century, such as sustainably meeting the world's growing demand for energy and consumer goods. I believe that new developments in science and technology will help solve many of these problems. Nanofabrication is one of the keys to the development of novel materials, devices and systems. Precise control of nanomaterials, nanostructures, nanodevices and their performances is essential for future innovations in technology. The book "Nanofabrication" provides the latest research developments in nanofabrication of organic and inorganic materials, biomaterials and hybrid materials. I hope that "Nanofabrication" will contribute to creating a brighter future for the next generation

Writing 3D nanomagnets using focused electron beams

Focused electron beam induced deposition (FEBID) is a direct-write nanofabrication technique able to pattern three-dimensional magnetic nanostructures at resolutions comparable to the characteristic magnetic length scales. FEBID is thus a powerful tool for 3D nanomagnetism which enables unique fundamental studies involving complex 3D geometries, as well as nano-prototyping and specialized applications compatible with low throughputs. In this focused review, we discuss recent developments of this technique for applications in 3D nanomagnetism, namely the substantial progress on FEBID computational methods, and new routes followed to tune the magnetic properties of ferromagnetic FEBID materials. We also review a selection of recent works involving FEBID 3D nanostructures in areas such as scanning probe microscopy sensing, magnetic frustration phenomena, curvilinear magnetism, magnonics and fluxonics, offering a wide perspective of the important role FEBID is likely to have in the coming years in the study of new phenomena involving 3D magnetic nanostructures

Optically Induced Nanostructures

Nanostructuring of materials is a task at the heart of many modern disciplines in mechanical engineering, as well as optics, electronics, and the life sciences. This book includes an introduction to the relevant nonlinear optical processes associated with very short laser pulses for the generation of structures far below the classical optical diffraction limit of about 200 nanometers as well as coverage of state-of-the-art technical and biomedical applications. These applications include silicon and glass wafer processing, production of nanowires, laser transfection and cell reprogramming, optical cleaning, surface treatments of implants, nanowires, 3D nanoprinting, STED lithography, friction modification, and integrated optics. The book highlights also the use of modern femtosecond laser microscopes and nanoscopes as novel nanoprocessing tools