Deflection-free Al2O3 membrane achieved by 2-step atomic layer deposition (ALD) technique

학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2017. 2. 윤의준.With increasing attention paid to energy and environmental issues,LEDs have been intriguing replacements for traditional incandescent orfluorescent lights. Since the emergence of III-nitride family, GaN-basedcompound semiconductor grown on a sapphire substrate has been dominant inmanufacturing a high-efficient LED device. However, obtaining a high qualityGaN crystalline is a continuing technical challenge, which occurs due to theinnate difference of material properties between sapphire substrate and GaN inhetero-epitaxy system. For example, there exists a large lattice mismatchbetween a sapphire substrate and GaN that results in reducing the light emissionefficiency. Also, a higher refractive index of GaN compared to air prevents lightfrom being extracted from the LED structure by provoking a total internalreflection and diminishes the light extraction efficiency. Furthermore, asubstantial difference in the thermal expansion coefficients between sapphireand GaN film induces a wafer bow during the cooling process. The problem of wafer bowing restricts the fabrication of the device and hence decreases its productivity. Therefore, solving the aforementioned technical issues is of prime importance in enhancing the efficiency of LED chips.Recently, our research group developed a groundbreaking growth scheme of GaN using cavity engineered sapphire substrate (CES) to achieve iihigh-efficiency GaN-based LEDs. In the CES scheme, GaN was grown on the crystalline a-Al2O3 membrane obtained by the phase transformations of amorphous-Al2O3. The amorphous-Al2O3 was deposited by atomic layer deposition (ALD) on a photo resist-patterned sapphire substrate and subsequently annealed at elevated temperature, forming the the rmodynamicallystable a-Al2O3. The annealed a-Al2O3, however, experienced a surface downward deflection during the phase transformation due to the volume contraction induced by a film densification, and this issue had a detrimental effect on the crystalline quality of GaN layer grown atop the annealed a-Al2O membrane. The LED structure manufactured on the GaN template with poor crystalline quality, therefore, has lower internal quantum efficiency due to the generation of defects such as threading and misfit dislocations.In this research, we investigated the density dependence of ALD Al2O3 film on its deposition temperature and addressed the effect of densifiedamorphous-Al2O3 on a degree of volume contraction after annealing. If thedensity difference between the amorphous-Al2O3 and a-Al2O3 during the phase transitions were minimized, the ensuing film was expected to have a reduced surface downward deflection accordingly. The ALD temperatures were varied ranging from 110 – 250 °C and the corresponding densities were measured byX-ray reflectivity (XRR). ALD deposition of amorphous-Al2O3 was carried outon a PR patterned sapphire substrate in a two-step process. Amorphous-Al2O3 was first deposited at 110°C for the thickness of 43nm to secure the pattern iiishape and further deposited at various temperatures of 140, 170, 200 and 250°C for the rest of target thickness, 57nm. During the latter process, the deposition occurred at a higher temperature range to maximize the density of amorphous Al2O3,aiming for the reduction in volume contraction as well as surface downward deflection upon thermal annealing. As a result, we observed the surface morphology of the annealed Al2O3 using atomic force microscopy (AFM)and found that the surface deflection was strongly dependent on the density of the ALD Al2O3 films. The specimen with amorphous-Al2O3 film deposited at200°C during the second-ALD step demonstrated a 50% reduction in a surface deflection compared to the reference sample fabricated by conventional 1-stepALD. XRD result also exhibited the substantial improvement in crystallinequality of GaN (002) for this specimen due to the minimized surface deflectionfrom volume reduction associated with the density increase.Chapter I. Introduction 1 1. Technical issues in GaN-based LEDs 2 1.1. Lattice mismatch and dislocations 2 1.2. Thermal expansion coefficient mismatch 5 1.3. Refractive index difference 7 2. Cavity-engineered sapphire substrate(CES) 8 2.1. Fabrication process of stripe-CES 8 2.2. Advantages and applications of stripe-CES 11 Chapter II. Experimental tools 13 1. Film deposition techniques 13 1.1. Atomic layer deposition (ALD) 13 1.2. Metal-organic chemical vapor deposition 13 2. Film characterization techniques 14 2.1. X-ray reflectivity (XRR) 14 2.2. Atomic force microscopy (AFM) 17 2.3. Scanning electron microscopy (FE-SEM) 17 2.4. Transmission electron microscopy (TEM) 17 Chapter III. Phase transformation of Al2O3 membrane 18 1. Mechanism of phase transformations 18 1.1. Solid-phase-epitaxy (SPE) of Al2O3 in CES 18 1.2. Volume reduction of Al2O3 membrane 21 2. Problems of surface deflection in Al2O3-membrane 23 2.1. Structural analysis of surface deflection 23 2.2. Observation of surface deflection 25 2.2.1. SEM image (3μm x 2μm) 25 2.2.2. AFM analysis (2x 2μm, 3 x 2μm) 27 2.2.3. TEM analysis (2 x 2μm) 29 Chapter IV. 2-step atomic layer deposition(ALD) 31 1. Reaction mechanism of ALD-Al2O3 31 2. Density of amorphous-Al2O3 vs. ALD deposition 34 2.1. Analysis of density change 34 2.2. X-ray reflectivity for density measurement 36 2.2.1. Density from critical angle 36 2.2.2. Fitting procedure for XRR 37 3. Deposition of amorphous-Al2O3 by two-step ALD 42 3.1. Motivation of two-step ALD 42 3.2. Fabrication process of two-step ALD 42 3.3. Experimental conditions 45 Chapter V. Effects of two-step ALD on reduction in surface deflection 47 1. Alpha-Al2O3 with reduced surface deflection 47 1.1. AFM analysis 47 1.2. TEM analysis 49 2. GaN on alpha-Al2O3 with reduced surface deflection 51 2.1. XRD measurement compared to reference 51 Chapter VI. Conclusion 53 Reference 54 국문초록 57Maste

Amelioration of obesity-induced diabetes by a novel autophagy enhancer

Autophagy insufficiency due to aging, high-fat injury or genetic predisposition could be a factor in the progression of metabolic syndrome and diabetes. On the other hand, autophagy enhancement may have beneficial metabolic impact on in vivo metabolism of obese subjects. To identify novel, autophagy enhancer small molecules, we screened a chemical library using a Renilla-LC3-based luciferase assay [Lim et al. Nat Commun 9:1438]. Of the >7000 tested substances, one chemical compound, termed MSL (4-(4-fluorophenyl)sulfonyl-5-methylthio-2-phenyloxazole), (i) enhanced autophagic activity through Tfeb activation, (ii) expedited lipid clearance, probably through lipophagy, and (iii) reduced inflammasome activation through amelioration of mitochondrial dysfunction both in vitro and in vivo, leading to improved metabolic profile of mice with genetic or diet-induced obesity.ope

Lysosomal Ca 2+-mediated TFEB activation modulates mitophagy and functional adaptation of pancreatic β-cells to metabolic stress

Although autophagy is critical for pancreatic β-cell function, the role and mechanism of mitophagy in β-cells are unclear. We studied the role of lysosomal Ca2+ in TFEB activation by mitochondrial or metabolic stress and that of TFEB-mediated mitophagy in β-cell function. Mitochondrial or metabolic stress induced mitophagy through lysosomal Ca2+ release, increased cytosolic Ca2+ and TFEB activation. Lysosomal Ca2+ replenishment by ER- > lysosome Ca2+ refilling was essential for mitophagy. β-cell-specific Tfeb knockout (TfebΔβ-cell) abrogated high-fat diet (HFD)-induced mitophagy, accompanied by increased ROS and reduced mitochondrial cytochrome c oxidase activity or O2 consumption. TfebΔβ-cell mice showed aggravation of HFD-induced glucose intolerance and impaired insulin release. Metabolic or mitochondrial stress induced TFEB-dependent expression of mitophagy receptors including Ndp52 and Optn, contributing to the increased mitophagy. These results suggest crucial roles of lysosomal Ca2+ release coupled with ER- > lysosome Ca2+ refilling and TFEB activation in mitophagy and maintenance of pancreatic β-cell function during metabolic stress.ope

A novel autophagy enhancer as a therapeutic agent against metabolic syndrome and diabetes

Autophagy is a critical regulator of cellular homeostasis, dysregulation of which is associated with diverse diseases. Here we show therapeutic effects of a novel autophagy enhancer identified by high-throughput screening of a chemical library against metabolic syndrome. An autophagy enhancer increases LC3-I to LC3-II conversion without mTOR inhibition. MSL, an autophagy enhancer, activates calcineurin, and induces dephosphorylation/nuclear translocation of transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy gene expression. MSL accelerates intracellular lipid clearance, which is reversed by lalistat 2 or Tfeb knockout. Its administration improves the metabolic profile of ob/ob mice and ameliorates inflammasome activation. A chemically modified MSL with increased microsomal stability improves the glucose profile not only of ob/ob mice but also of mice with diet-induced obesity. Our data indicate that our novel autophagy enhancer could be a new drug candidate for diabetes or metabolic syndrome with lipid overload.ope

The Paradoxical Characters of Constantin Brancusi's Sculptures

콘스탄틴 브랑쿠지는 아카데미의 조각 전통에서 벗어나 대상의 본질을 표상하는 감축된 형태를 창조해 낸 추상 조각의 원류로 규정되어 왔다. 단순한 기하 형태로 환원된 그의 조각은 형식주의 추상 조각의 전형으로서 순수한 형태를 추구한 결과물인 셈이다. 본 논문은 그의 조각에서 그러한 기존 모더니즘 추상 조각의 범주에서 양립하기 어려운 성격들을 발견하고 그것들을 살펴봄으로써 그의 조각의 성격을 새롭게 규명해보고자 하는 의도에서 출발하였다. 그의 작업에서 형식주의 추상 조각의 면모와는 배치되는 측면들이 보이기 때문이다. 그러나 기존의 형식주의적인 관점을 전면 부정하는 것이 아니라 그것을 포함하는 동시에 이질적인 성질을 드러내는 양면적인 형태로서 브랑쿠지의 조각을 바라보고자 한다. 루마니아 변방 지역 출신인 그는 프랑스의 파리에서 유럽 사회의 급속한 근대화 과정을 직접 경험한다. 당시 미술가들은 전통 미술의 주제와 형식을 탈피하여 새로운 미술을 향한 다양한 실험에 몰두하고 있었다. 이는 조각의 재료, 형태 그리고 공간과의 관계를 중심으로 조형적 시도에 민감한 경향과 그에 반하여 형식 자체에 침잠하는 미술을 부정하고 실제 삶과의 연관 속에서 의미를 찾으려는 경향과 같은 큰 흐름들로 다양하게 나타났는데, 브랑쿠지는 이러한 양분 상태에서 비교적 자유로운 작가로 존재했다. 그러나 그의 정제된 형태는 입체주의 미술을 잇는 미술의 추상화 경향과 무관하지 않으며 조각과 실용적 오브제를 혼용하며 받침대를 조각 요소로 사용하여 아상블라주하고 나아가 조각적 공간이 아닌 실제 공간을 작품에 도입하려는 의지는 다다와 같은 추상화에 반하는 경향과도 역시 무관하지 않다. 일찍이 가구와 가옥을 다루는 목공예 전통과 밀접하였던 그에게 실제 삶과 예술 사이의 경계선은 모호한 것이었다. 여기에 아방가르드 미술가들의 극단적인 작품들은 새로운 조각 형식의 창조는 물론 삶과 예술 간의 ‘경계 짓기’와 ‘허물기’에 대해 고민하게 했고 결국 그의 작업에 이들이 공존하는 것으로 반영되었다. 1910년대에 세부 묘사가 거의 없는 구, 원통, 입방체 등의 형태로 환원된 그의 추상 형태들은 유기적으로 조합되어 내적으로 완결된 구조를 보여주는 한편, 인체와 동물 그리고 신화적 모티브를 주제로 하는 재현의 영역에 머물러 있기도 하다. 또한 그의 ‘오브제-조각’은 의자와 테이블 같은 가구를 직접 조각 요소로 수용한 것으로 뒤샹의 레디메이드와 같은 미학적 지평을 공유하는 것이기도 하다. 또한 그의 작업에는 독창적 형태를 향한 변이와 형태를 참조하고 반복하는 복제의 논리가 공존하다. 작가의 자아가 그대로 전이되는 재료를 끊임없이 깎고 다듬는 노동과 같은 작업은 역설적으로 작가의 개성을 제거하였고 무한히 만들어진 동일한 형태는 대량 생산된 사물과 같은 복제물의 성격을 부각시킨다. 이상과 같은 브랑쿠지 조각에 내재된 모순적인 면모들은 기존의 형식주의적 시각에 한정된 그의 작품에 대한 접근의 폭을 넘나드는 것이다. 추상적 형식 실험과 레디메이드 미학과 같은 형식주의에 반하는 경향을 왕래하는 브랑쿠지의 작업은 20세기 전반기 미술의 양분된 양상을 드러내는 것으로 첨예한 두 경향 사이에서 순수 형식을 탐구하고 동시에 비예술을 아우르는 혼성성을 실험한 작업이라고 할 수 있다. 본 논문은 그러한 양면적인 브랑쿠지 조각의 속성들을 밝혀내어 역설적인 관계로 설명함으로써 새롭게 그의 작품을 조망하고, 모더니즘 미술계에서 그의 작가적 지점을 재고하였다는 점에서 의의를 찾을 수 있을 것이다.;Contantin Brancusi has been established as the source of a abstract sculpture because he created reduced forms which represented the essence of things against the Academic tradition. His sculptures were likely to be results to pursue a pure form as type of Modernism sculpture. This study started from intention of revealing the other features of his works which are difficult to coexist with in the category of Modernism and looking into his ones by examining them as they have aspects of contrariety to it. However, it is not wholly against the viewpoint of the existing formalism but including that. I suppose I intend to look at his sculptures as forms with both sides. Brancusi from s fringe area in Rumania had experienced directly the process of swift modernization of European societies in Paris. Then Artists were absorbing in various experiments for new art out of traditional subject and formality. It was cut in many tendencies such as pure formal trials stressing a material, form and the relation of the space and denying it radical movements trying to find out the meaning in the connections to real lives. Brancusi was relatively free from both tendencies, but his refined forms are not related to abstract movements after Cubism and his use of supports as sculptural elements and his will to make assemblages and further more to induce real space are also not related to anti-Formalism of Dada. To him the boundary between life and art was vague as earlier he was familiar to wood work, Moreover many Avangarde artist's extreame works made him think not only about making new sculptural form but about drawing and destroying a border between life and art, in the end these were reflected on his works together. In 1910s, his each forms were reduced into simple forms like a sphere, a cylinder and a cube and showed internally completed structures combined organically. Meanwhile they remained in the field of representation to present a human body, animals and mythical stories as a theme. His 'objet-sculptures' are works introducing furniture like a stool, a chair, a table and so on into a sculpture. At the same time those share the esthetics of Marcel Duchamp's Ready-made. Besides, a variation for a creative art form and a duplicative logic referencing and repeating his own form coexist in his works. The process when he had carved and smoothed materials consistently transferred sculptor's ego to his works and got rid of his individuality as it is paradoxically. Similar forms made infinitely emphasis things like aspects of the mass produced things. As is stated above, paradoxical characters in Brancusi's sculptures are getting out of limited analysis under Formalism. His works come and go between Formalism and the tendency against it. That is, that reveals both sides in early 20 century of modernism art and is experimental work to examine a pure form and to put other artistic circles together in it.목차 Ⅰ. 서론 = 1 Ⅱ. 브랑쿠지의 작업과 20세기 초기 아방가르드 미술계 = 9 Ⅲ. 브랑쿠지 조각에 나타난 양면적 요소들의 역설적 관계 = 18 1. 순수 추상 형식과 구상적 주제의 공존 = 18 2. 조각 작품으로 놓인 실용적 오브제 = 26 3. 형태 변이에서 드러나는 복제의 양상 = 36 4. 개별 형태이자 실제 공간 속의 설치된 조합물 = 49 Ⅳ. 결론 = 58 참고문헌 = 62 도판목록 = 69 영문초록(Abstract) = 7

사간에서 분리한 텍토리딘과 텍토리게닌의 신경세포 보호효과

학위논문(석사) --서울대학교 대학원 :제약학과,2007.Maste

아밀로수크레이즈 처리 전분을 첨가한 쌀과 감자 전분의 구조적 및 유변학적 특성

학위논문 (석사)-- 서울대학교 대학원 : 농생명공학부(식품생명공학전공), 2013. 2. 문태화.Rice and potato starches with low digestibility were prepared using amylosucrase(AS) from Neisseria polysaccharea and mixed with raw starches in different ratios (0%, 25%, 50%, 75%, and 100%). These mixtures were compeletely gelatinized and retrograded for 14 days at 4℃. The blending of unmodified raw starch and modified starch caused the changes of structural characteristics such as branch chain length distribution, X-ray diffraction and thermal properties, leading to the changes in digestibility and texture properties. The increase in the chains of DP ≥ 13 was observed in the AS-treated starches and starch mixtures, while the short chains of DP ≤ 12 decreased compared with raw starches. Differential scanning calorimetry showed that the onset, peak and conclusion temperatures increased with an increase in the proportion of AS-treated starches. Especially, the enthalpy of starch mixtures was lower than that of native starch and laid between those of the respective raw and AS-treated starches, suggesting that the starch mixtures had a low tendency towards retrogradation compared with individual raw and AS-treated starches. After AS treatment, X-ray diffraction pattern of rice starch changed from A to B-type, whereas potato starch maintained the original B-type pattern. All starch mixtures exhibited B-type pattern, and their relative crystallinity increased with an increase in the proportion of AS-treated starch. The contents of SDS and RS were proportional to the amount of AS-treated starch. In texture analysis, the starch mixtures showed lower or similar gel hardness compared with the respective individual starches, unmodified starch and modified starch. The chewiness exhibited a similar tendency to by hardness and cohesiveness. Especially, chewiness and cohesiveness were related to microstructure of starch mixture gels. The samples with low values of cohesiveness and chewiness exhibited more loose structures and contained some empty spaces. In summary, the starch mixtures showed different structural and rheological characteristics according to the amount of AS-treated starch added. These mixtures maintained low digestibility and reduced the rheological disadvantages of AS-treated starches.Abstract Ι Abbreviations III Contents IV List of figures VI List of tables VII Introduction 1 Materials and Methods 5 1. Materials 5 2. Methods 6 2-1. Assay of amylosucrase activity 6 2-2. Preparation of AS-treated starches 6 2-3. Determination of amylopecin branch chain distribution by high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) 7 2-4. Starch digestibility 8 2-5. Preparation of starch mixtures 9 2-6. X-ray diffraction patterns and relative crystallinity 10 2-7. Thermal properties determined by differential scanning calorimetry (DSC) 10 2-8. Texture analysis 11 2-9. Energy-filtering transmission electron microscopy (EFTEM) 12 2-10. Statistical analysis 13 Results and Discussion 14 1. In vitro starch digestility of AS-treated starches affected by storage time 14 2. Branch chain length distributions of raw and AS-treated starches 18 3. Thermal properties 25 4. X-ray diffraction patterns and relative crystallinity 32 5. Determination of digestibility of starch mixtures 40 6. Gel textural properties 44 7. Microstructures of starch mixture gels 50 Conclusion 54 References 56 국문초록 64Maste

Conceptual Ecology of Lifelong Learning: Expansion, Interconnection and Evolution

이 연구는 평생학습(lifelong learning) 개념이 평생교육·인적자원개발 영역의 경계를 넘어 범학문적으로 확장되어가는 한편, 이 연구분야를 중심으로 각 학문분과간 초연결성을 형성해가는 양상을 분석한다. 또한 이 과정에서 기존의 평생교육 연구분야에서는 나타나지 않던 새로운 개념층위적 창발성이 진화되어 나오는 모습을 드러낸다. 연구자들은 이것을 평생학습 개념생태계의 성장과 진화라는 차원에서 이해하려고 한다. 이를 위하여 연구자들은 지난 20년 동안 국내 및 국외의 학술연구 데이터베이스에서 '평생학습' 혹은 'lifelong learning'을 키워드로 설정한 학술논문들을 추출하여 그 주제영역과 연구문제들을 분석하였다. 연구 결과 국외에서의 평생학습은 (1) 교육학 일반 영역으로 확장되는 한편 사회과학, 생명과학, 공학과 의학, 인문학과 교양학 등 거의 모든 분야로 그 적용범위를 넓혀가고 있었으며, (2) 핵심 연구주제들, 예컨대 노인발달과 학습, MOOCs, 전문가계속교육(의사, 공학자, 건축가 등) 등 주제와 관련된 융합학문적 연구로 발전하고 있었고, (3) 다른 한편에서 기존의 학교학습으로 표현하기 어려웠던 새로운 학습의 세계를 표상하는 플랫폼 개념으로 자리매김하고 있었다. 특히 인공지능 등의 기계학습 분야에서 평생학습 개념이 활용되는 모습을 관찰하였다. (4) 반면, 국내의 경우 평생학습 연구는 전통적 평생교육/HRD영역 안에 갇혀있는 양상을 보였으며 다학문간 활발한 융합연구를 찾아보기 어려웠다. 이제 평생학습 개념은 더 이상 50년 전의 그 개념이 머물 수 없으며, 학술개념의 리더십도 더 이상 평생교육연구자집단(혹은 성인교육연구자집단) 안에 한정되어서는 안 된다. 평생학습 개념은 조만간 혁신적 업그레이드를 통하여 새로운 역할을 부여받는 개념으로 거듭날 필요가 있으며, 주요 융합주제들을 통해서 보다 적극적으로 초학문간(transdisciplinary) 협력연구를 촉진할 수 있어야 한다. This research aims to investigate the way in which the notion of lifelong learning has expanded beyond the territory of educational researches, created new interconnectivities with other major areas of academic researches, and eventually evolved into a new platform of conceptual emergence. The researchers adopted a complexity perspective to understand this whole process as a part of dynamic conceptual ecologies in evolution. Within this framework, an academic concept, being developed as part of practical reality in the related field, came to existence to obtain a discursive power, or governmentality, adopting Foucaults terminology, which authorizes collective legitimacy to the piecemeal of the fragmented practices, and to provide them justification and social values. To reveal the characteristics, we used two major scholarly databases to select articles whose researches have mainly focused on the notion of 'lifelong learning.' One is SCOPUS scholarly database, the other is Korean research database of RISS. From the two databases, we compared the distribution of the articles whose main theme is related with lifelong learning, both in Korea and overseas. Upon the data collected, we found out that (1) the expansivity and interconnectivity of lifelong learning discourses between various academic fields is far restricted in Korea than overseas; (2) lifelong learning in Korea is more strictly bound within the territory of educational researches, while in overseas more articles were found in the areas such as medicine, engineering, social science, humanities, and others; (3) newly emerging research themes were created especially in the areas of artificial intelligence and machine learning that were standing over the platform of Industry 4.0 or post-humanism. Overall, the notion of lifelong learning today came to be a general and transdisciplinary concept that shares more connectivity and alliances in collective researches to shed new lights on the old phenomena of human learning in a new epoch. Nevertheless, the conceptual sophistication and major upgrade have not been supported enough by the original adult education research group; rather, the clock of the concept stopped at the point when it was first invented. All kinds of cliche and old implications are repeated without further evolution. Adult educators are no longer standing at the center of the academic leadership in this phenomenon.N