New single element memory transistor with a phase transition thin film material as a gate insulator

Lee, Sang-Hyeon UMI Dissertation Services 2012 국내박사

Bioinspired composite cilia for active and passive droplet control

Sang-Hyeon Lee Ulsan National Institute of Science and Technology 2022 국내박사

Water droplets and wetting phenomena on various surfaces are ubiquitous in nature and pose significant challenges in various fields. Water droplets in contact with surfaces for a long period lead to the formation of biofilms and cause hygiene problems. They also cause surface icing and metal corrosion, which affect social infrastructure. In addition, water droplets on transparent surfaces degrade optical performance, such as light transmission. Various techniques have been used to address these problems, such as mechanical removal, chemical fluid release (de-icing, anti-corrosion, biocidal, etc.), and Joule heating. However, these techniques are ineffective, expensive, and environmentally harmful. Bioinspired droplet control technology has emerged as a fundamental solution to various problems caused by water droplets and the wetting phenomena. Inspired by living organisms, surfaces with nano/micro-scale cilia structures have been proposed as excellent candidates for droplet control. Multiscale cilia structure-based surfaces can solve the existing problems by maximizing the surface wettability to control the wetting / de-wetting behavior of droplets. A superhydrophobic surface, consisting of cilia array and hydrophobic material, removes the droplets from the surfaces and minimizes the contact between them, preventing freezing and corrosion. In contrast, a superhydrophilic surface, made of cilia array and hydrophilic material, spreads the droplets and forms a thin and continuous aqueous film on the surface, preventing settling of impurities and fogging caused by droplet condensation. However, single-strategy droplet control technologies based on such a simple structure still have several limitations. For example, if a typical superhydrophobic surface based on a cilia array is horizontally arranged, the droplets cannot be removed without additional external force. Moreover, superhydrophilic surfaces with cilia arrays are susceptible to fouling by airborne contaminants, such as dust, due to high surface energy of the hydrophilic materials. Recently, research has been conducted on active and passive droplet control technologies using functional materials to solve the problems caused by wetting phenomena and to address the limitations of the existing technology. First, active droplet control techniques based on stimuli-responsive materials can modulate the droplet manipulation and drop bouncing dynamics using various external stimuli. Among the stimuli-responsive materials, a magneto-responsive composite material was chosen as the primary functional material for active droplet control because it has a fast response speed and doesn’t require additional external power source for precise deformation control. The surface morphology of the magneto-responsive composite elastomer can be actively controlled using a magnet, which enables droplet manipulation and easy removal of droplets from the surface. Second, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution by the hydration barrier and weak adhesion. Second, owing to hydration barrier and weak adhesion, passive droplet control techniques based on anti-fouling materials can prevent a wide range of contamination such as airborne and waterborne pollution. An amphiphilic copolymer with both hydrophilic and hydrophobic segments is also being considered as a suitable material for passive droplet spreading. It was found that an amphiphilic copolymer has droplet spreading ability and exhibits “fouling-resistant” property in the hydrophilic segment and the “fouling-release” property in the hydrophobic segment. Therefore, based on their unique properties, amphiphilic material-based surfaces exhibit excellent anti-fogging and anti-biofouling properties. In addition, these surfaces can prevent external contaminants from firmly adhering to the surface and reduce surface contamination. However, single-strategy active and passive droplet control technologies based only on functional materials also have some limitations. Owing to the lack of de-wetting or wetting properties, planar surfaces composed of only functional materials without multiscale cilia structures do not exhibit a sufficiently high capability to remove or spread droplets on the surface. For example, droplets may adhere to a magneto-responsive composite planar surface because of insufficient hydrophobicity. In addition, it is not easy to spread droplets over a wide area on an amphiphilic planar surface because of its insufficient wetting performance. Many previous studies on droplet control focused on single-strategy techniques, such as typical superwetting surfaces based on multiscale structures or planar surfaces based on functional materials. However, such single-strategy approaches to droplet control have many limitations. Therefore, new strategies in multi-approaches, that integrate both strategies in approaches of multiscale architectures and functional composite materials, are needed to overcome the problems of existing technologies. We proposed a bioinspired magneto-responsive cilia array for active droplet control based on a superhydrophobic and hierarchical cilia array composed of a magneto-responsive composite elastomer. In this study, the dynamic cilia array showed robust droplet shedding performance by actively controllable multimodal drop bouncing dynamics and precise droplet manipulation. Furthermore, it exhibited remarkable anti-icing properties compared to conventional technologies. We also presented a bioinspired amphiphilic copolymer nanocilia array for passive droplet spreading. The hybrid of hydrophilic hydrogel, hydrophobic lubricant, and nanostructures showed significantly enhanced spreading ability due to the synergetic integration of the amphiphilic copolymer and nanoscale cilia array. The amphiphilic nanocilia hybrid exhibited a pronounced anti-fogging performance due to its water-spreading properties and retardation of droplet nucleation. It also exhibited notable anti-biofouling performance by integrating fouling-resistant, fouling-release, and foulant-killing mechanisms.

Time- and space-resolved spectroscopic studies on various multichromophoric systems and semiconductor quantum dots

이상현 Graduate School, Yonsei University 2020 국내박사

Research on a variety of multichromophoric systems and quantum dots has attracted a lot of attention as a key technology that can provide new solutions for energy, electronics, display, and new material industry. To efficiently apply these various systems to photoelectronic devices, not only simple studies on structures or surface analysis but also in-depth studies on photophysical properties of various materials should be conducted. A lot of research has been studied to improve the efficiency and to increase their applicability of devices, however, most studies have been limited on the ensemble level. Studies on the ensemble level show averaged data, which is good to analyze the overall characterization of systems, however, that have limitations in identifying hidden minor effects or in studying the optoelectric properties of individual molecules. Single-molecule spectroscopy shows the properties of individual single molecules and gives detailed information on the difference of individual molecules in various local environments. It is important to study the photophysical properties of various systems by using single-molecule spectroscopy and to show the application on various optoelectronic devices. First, I studied the electronic interactions between porphyrin moieties in linear and star-shaped multi porphyrin systems (ZNE). Most single molecules of ZNE shows one-step photobleaching behaviors, which exhibit one quantum system with strong electronic interaction. Some ZNE molecules with weak interaction show multi-step photobleaching. Furthermore, by using excitation polarization fluorescence spectroscopy (ExPFS) and wide-field defocused imaging (WFDI) technique, we demonstrated the orientation of transition dipole moments and the structural information of absorbing and emitting units. The star-shaped structure Z5E shows both linear and star shape behaviors. Secondly, I investigated the conformational structures of long linear porphyrin systems (Zn) depending on their length by using ExPFS. It has been confirmed that the linear porphyrin system has coiled structures as the porphyrin units increases, and also that the coiled structures were stretched by solvent vapor annealing (SVA). From localization microscopy, emitting sites were identified more precisely and it confirmed the changes of structures by SVA. For the cyclic thiophene systems (C-5NTNV), I utilized the ExPFS to study the conformational heterogeneity of large cyclic thiophenes. As the thiophene unit increases 10 to 30, the larger cycles show significantly distorted structures and complete collapse of cyclic structures. The performance of devices with cyclic thiophenes systems is affected by how cyclic structures are maintained with planar structures. This information gives a good indicator of the application for optoelectronic devices using cyclic thiophenes. In addition to these organic materials, semiconductor InP quantum dots were also studied by single-dot spectroscopy. The difference of photophysical properties of InP QDs between two InP QDs, gradient alloy shell and discrete mid shell, were investigated. In the previous studies, the gradient shell contributes the increases of efficiency by reducing Auger recombination, however, the InP/ZnSe/ZnS QDs with discrete shell show higher quantum efficiency than InP/ZnSeS/ZnS with gradient mid-shell. Single-dot studies on these two InP QDs also showed that InP QDs with discrete shell exhibited the decreases of Auger recombination and spectral diffusion. These findings are expected to give understanding for photophysical properties of various structures and to be a good indicator for the development of optoelectronic devices with high efficiency, stability, and performance. 다양한 다중 발색단 시스템 및 반도체 양자점에 대한 연구는 에너지, 전자, 디스플레이, 신소재 산업 등에 새로운 해결책을 제시할 수 있는 핵심 과학기술로써 높은 관심을 받고 있다. 이러한 다양한 시스템들을 광전기적 소자로 효율적으로 응용하기 위해서는, 단순한 구조나 표면 분석 등의 기초적인 연구에서 더 나아가 여러 물질의 광물리적 특성을 관찰하는 심도있는 연구가 진행되어야 한다. 이에 많은 연구들에서 소자의 효율과 응용성을 높이기 위해 위해 다양한 연구를 진행하고 있지만, 대부분의 연구들이 앙상블 수준에서 진행되어왔다. 이러한 앙상블 수준에서의 연구들은 평균화된 데이터를 볼 수 있어, 전체적인 특성을 확인하기에는 좋지만, 일부의 효과를 저해하는 특성을 찾거나, 개개의 분자들의 특성들을 연구하기에는 한계점이 있다. 단분자 분광학은 개개의 단분자에서의 광물리적 특성을 확인하여, 물질의 미세한 특성들을 확인하고, 다양한 세부 환경에서 나타나는 물질의 특성 차이들을 세밀하게 연구할 수 있다. 이에, 단분자 분광학을 이용하여 다양한 시스템들에서의 광물리적 특성들을 연구하여, 광전기적 소자로 응용하는 것이 중요하다. 포피린의 선형 및 십자가 형태의 다중 발색단 시스템 (ZNE) 에서 포피린간의 전자적 상호작용이 어떻게 일어나는지에 대해 연구하였다. ZNE에서 대부분의 단분자들이 한 단계의 형광소광이 나타나는 것을 통해 강한 전자적 결합으로 하나의 양자 시스템을 이루는 것을 확인하였다. 또한 일부의 약하게 결합된 분자들에서는 여러 단계 형광소광이 나타나는 것을 확인하였다. 여기 편광 형광 실험과 넓은장 허초점 이미징 기술을 바탕으로 구조에 따른 쌍극자 모멘트의 방향을 확인하여, 흡수나 발광하는 단위체의 구조를 확인하였다. 십자가 모양의 Z5E 에서는 선형과 십자가 형태 모두의 현상을 나타내는 것을 확인하였다. 또한 여기 편광 형광 실험을 통해 긴 선형 포피린 시스템 (Zn) 에서 길이에 따라 포피린 다중 발색단에서의 입체 구조가 어떻게 나타나는지에 대해 연구하였다. 선형 다중 포피린 시스템이 길어짐에 따라 꼬인 구조를 갖는 것을 확인하였고, 또한 용매 증기 어닐링 방법을 통해 꼬인 구조가 풀릴 수 있다는 것도 확인하였다. 이러한 변화를 국지화 현미경법을 통해 좀더 정밀하게 관찰하였다. 그리고 이러한 연구를 고리형 싸이오펜 분자 시스템 (C-5NTNV) 에서도 진행하여 고리형 구조의 크기가 싸이오펜 단위체 10개에서 30개까지 커짐에 따라, 구조가 급격히 꼬인 구조를 가지며, 고리형 구조를 갖지 못하는 것을 확인하였다. 고리형 싸이오펜 구조는 고리형을 얼마나 잘 유지하는지에 따라 응용성이 높아지므로, 그에 대한 지표를 확인할 수 있었다. 이러한 유기 물질뿐 만 아니라, 반도체 InP 양자점에서도 연구를 진행하였다. InP/ZnSe/ZnS 핵/껍질/껍질 구조를 갖는 양자점에서 중간 껍질에서 ZnSe 와 ZnS 가 연속적인 밀도 구배를 갖는지 불연속적인 구조를 갖는지에 따라 나타나는 광학적 차이점을 연구하였다. 기존 연구들에서는 연속적인 밀도 구배를 갖는 껍질이 오제 재결합을 줄여서 높은 효율에 기여할 수 있다고 하였지만, 본 연구에서는 연속적인 밀도 구배를 갖는 중간껍질을 가질 때 더 높은 효율 및 성능을 보일 수 있음을 밝혔다. X-선 회절과 라만 분광학 실험을 통해 연속적 밀도 구배를 갖는 양자점에서 더 큰 격자 불일치를 확인하였다. 또한, 단일 양자점 연구를 통해 불연속적인 껍질 구조를 갖는 양자점에서 오제 재결합이 줄어들고, 스펙트럼 확산현상이 줄어드는 것을 확인하였다. 이러한 연구 결과들은 다양한 광 전기적 소자를 개발함에 있어서, 다양한 구조의 시스템들이 갖는 특성들을 이해할 수 있게 해주고 높은 효율, 안정성 및 성능을 갖는 소자를 개발하는데 좋은 지표가 될것으로 기대된다.

Estimation of survival probabilities based on pseudo-value observations : Pseudo-Value Observations을 이용한 생존 확률의 추정

이상현 경북대학교 대학원 2011 국내석사

생존 분석은 생존시간을 분석하여 생존 확률 혹은 생존 곡선을 추정하는 통계적 방법이다. 생존 분석의 특징은 자료 수집 과정이나 연구 조사 과정에서 데이터가 중도 절단 되거나 탈락 되는 등으로 인해서 완전한 데이터를 얻기 힘들다는 것이다. 이 논문에서는 위와 같이 자료가 중도 절단 되어 완전한 데이터를 얻을 수 없을 때 생존 확률을 추정하는 방법 중 대표적인 방법인 Kaplan-Meier 방법, 그리고 Jackknife 방법을 생존 분석에 도입한 Pseudo-Value Observations을 이용하여 추정하는 방법 두 가지를 비교하여 볼 것이다. 각 방법을 100회 반복하여 추정되는 생존 확률을 추정하여 실제 확률에 얼마나 잘 근사되는 지를 알아보고 그 때의 두 방법들 간의 상대효율을 분석하여 어느 방법이 더 효율적인 가를 알아보고자 한다.

Mass Chip Test & Outer Barrel Hybrid Integrated Circuit Assembly for ALICE ITS Upgrade and Study of Monolithic Active Pixel Sensor

이상현 부산대학교 대학원 2019 국내석사

A Large Ion Collider Experiment (ALICE) team has planned the upgrade of the Inner Tracking System (ITS) during Long Shutdown2 (LS2) of a Large Hadron Collider (LHC) for following the increased beam luminosity. The new ITS will be improved as follows. First, a distance between the first layer and the interaction point will get close from 39 mm to 23mm, the material budget (X/X0) will be smaller from 1.14% to 0.3%, and the pixel size of the detector will be smaller from 50 μm x 425 μm to 26.88 μm x 29.24 μm. These allow the improvement of impact parameter. Second, only a silicon pixel detector will be used, and the detector layers will be increased from 6 to 7. These allow the improvement of tracking efficiency (position resolution ~5 μm) and momentum resolution at low transverse momentum(pT). Third, data read-out rate will be improved to 100 kHz (in p-p collision), 400 kHz (in Pb-Pb collision) from 1 kHz. Monolithic Active Pixel Sensor is a new sensor which integrates the read-out circuitry and the sensor, and it has high granularity, low material budget, and fast read-out rate. In the new ITS, ALICE Pixel Detector (ALPIDE) which is made by MAPS technology will be used. In the ITS upgrade project, around 60k ALPIDE chips were tested. Tested ALPIDE chips will be assembled for Outer Barrel Hybrid Integrated Circuit (OB HIC), and around 2000 HICs will be assembled. Pusan National University and Inha University co-worked together for the chip test and the OB HIC assembly. The chip test and the OB HIC assembly is done by ALICE Integrated Circuit Inspection and Assembly (ALICIA) machine. Around 11k chips were tested from 2017, and around 300 OB HICs will be assembled until May 2019. The investigator chip which is researched in this thesis is MAPS. It has 134 mini-matrices which has various pixel design. 64 pixels can output analog signal in parallel with 65 MHz sampling rate. The investigator chip was measured with the DAQ board and a 55Fe source for the research. From the experimental results with various reverse bias voltages, pixel pitches, diameters of the collection n-well diode, and spacings, relative depletion regions were estimated and the Charge Collection Efficiency (CCE) and the Charge Collection Time (CCT) were researched.