HIGHLY EFFICIENT QUANTUM DOT LIGHT-EMITTING DIODES BASED ON THE OPTIMIZATION OF QUANTUM DOT STRUCTURE AND DEVICE ARCHITECTURE

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2016. 2. 이창희.Semiconductor nanocrystals or colloidal quantum dots have many advantages because their superb optical and electrical properties can be tuned via shape- and size-control. To utilize these properties, substantial research has been devoted to enable semiconductor nanoparticles to be applied in next-generation optoelectronics (e.g., light-emitting diodes (LEDs), solar cells, and photo catalysts). For many years, the device fabrication processes and performances of quantum dot light-emitting diodes (QLEDs) have undergone substantial development because of efforts addressing material synthesis, electrophysical analysis and device design. Thus, the tailoring of the structure of semiconductor nanocrystals to control optical or electrical properties and their applications in optoelectronic devices must be discussed. In this thesis, high-performance colloidal QLEDs were studied from the perspective of device mechanism and device structure engineering. We developed and demonstrated highly efficient red, green, and blue (RGB) QLEDs with improved group II-VI QDs and environmentally benign Cd-free QDs. First, we investigated the influence of the shell thickness of group II-VI type-I heterostructure QDs on the QLED performance. We found that thick-shell QDs exhibited reduced Auger-type decay rates and suppressed energy transfer (ET) within QD films. In addition, we characterized the device performance and found high efficiency (peak EQE ~ 7.4 %) and record brightness (105,870 cd/m2). The operation stability of the devices is presented along with the improved device performance. Our suggestions for QLED design offer simple results and approaches but propose novel structural designs of core/shell heterostructure QDs to allow engineering of the optical properties of QD solids and the performances of corresponding devicesin addition, they provide rational guidelines for the practical use of QLEDs in high-power light sources. To improve the electron transport layers (ETLs), we demonstrate that the efficiency of inverted QLEDs is enhanced by using a double electron transport layer (ETL) consisting of ZnO nanoparticles and 1,3,5-tris(N-phenylbenzimidizol-2-yl)benzene (TPBI) as an organic electron transport material. TPBI, as a soluble organic electron transport material, fills the voids in the ZnO nanoparticle film and thereby reduces the leakage current path. As a result, the efficiency of blue QLEDs was considerably increased, reaching a maximum EQE of 3.4 %. For highly efficient InP QLEDs, the inverted device structure with a ZnO electron transporting layer (ETL) was adopted because of its numerous advantages in process and integration. However, the large difference in the conduction band (CB) between InP QDs and ZnO impedes efficient electron injection from ZnO to InP QDs. To solve the injection issue, a solution-processable poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-ioctylfluorene (PFN) layer was selected as an interfacial dipole layer. Because of differences in the solubility of ZnO, PFN, and QDs, stacking the three different layers substantially improved device performance in terms of maximum external quantum efficiency (EQE) of 3.46 % and a maximum luminance of 3900 cd/m2. In our forthcoming research, we believe that an in-depth investigation of nonradiative multicarrier decay during device operation and minute engineering of the core@shell heterostructure to minimize such processes will guide us one step further toward producing high–performance InP QLEDs. This thesis demonstrates a novel approach to increase the efficiency and carrier injection of inverted QLEDs. Furthermore, the physical properties of QDs were systematically studied to establish a method to maximize device performance. In addition, the novel InP QLED structure may be applied to a variety of optoelectronic devices, such as thin-film solar cells, LEDs and transistors.Chapter 1 1 1.1 Colloidal Quantum Dot Light-Emitting Diodes 1 1.2 Key Issues for Improving the Performances of QLEDs 8 1.3 Outline of Thesis 11 Chapter 2 13 2.1 Materials 13 2.1.1 Preparation of ZnO Nanoparticles 13 2.1.2 Synthesis of Red-color Emitting CdSe/Zn1-XCdXS Core/shell Heterostructured Quantum Dots 14 2.1.3 Synthesis of Cd-free Green Color Emitting InP/ZnSeS Core/shell Heterostructured Quantum Dots 15 2.1.4 Synthesis of Blue-color Emitting Cd1-xZnxS@ZnS Quantum Dots 16 2.1.5 Organic Materials 16 2.2 Device Fabrication and Characterization Methods 18 2.2.1 Device Fabrication 18 2.2.2 Current-voltage-luminance Measurement 19 2.2.3 Efficiency Calculation Methods 21 2.2.4 Other Characterization Methods 22 Chapter 3 25 3.1 Design of core/shell heterostructures QDs with different shell thicknesses. 28 3.2 Characteristics of electroluminescence devices made of a series of CdSe/Zn1-XCdXS QDs 33 3.3 Influence of QD shell thickness on the optical properties of QD films and the efficiencies of corresponding devices 37 3.4 Device characteristics plotted after consideration of absorption by individual QDs 46 3.5 Relationship between optical properties of QDs and the operational stability of corresponding devices 51 3.6 Summary 56 Chapter 4 57 4.1 Preparation of double electron transport layers 59 4.2 Characteristics of electroluminescence devices made of a series of double electron transport layers 61 Chapter 5 65 5.1 Preparation of InP QDs with multiple gradient shells 67 5.2 Adopting conjugated polyelectrolyte layer for InP QLEDs 72 5.3 Characteristics of green InP QLEDs using PFN layers 79 5.4 Effect of shell thickness on based on InP QLED performances. 83 5.5 Summary 90 Chapter 6 91 Bibilography 94 Publication 106 한글 초록 111Docto

Understanding the Y chromosome variation by haplogroup and haplotype analyses in a Korean population

Dept. of Medical Science/박사Genetic variation on the non-recombining portion of the Y-chromosome contains information about the ancestral and geographical origin of biological samples as well as differentiation between male lineages. A molecular characterization of the Y-chromosome genetic structure was performed using a combination of Y-chromosomal single nucleotide polymorphisms (Y-SNPs) and Y-chromosomal short tandem repeats (Y-STRs) in a Korean population. Six multiplex PCRs followed by SBE reaction and two multiplex allele-specific PCR assays were developed for the identification of haplogroups in Koreans as well as haplogroups frequent in East Asians. Validation experiments demonstrated that the multiplex PCR systems followed by SBE reaction were optimized for analyzing low template and highly degraded DNA whereas a multiplex allele-specific PCR assay would be useful for simple and reliable determination of haplogroups in a large number of samples. In a test using DNA samples from Korean males, a total of 21 different haplogroups were identified by 33 Y-SNPs including the newly redefined markers (PK4, KL2 and P164) in haplogroup O. When genotyping the SNPs, phylogenetic nonequivalence was found between SNPs M117 and M133, which define haplogroup O3a2c1a, suggesting that the position of the M133 marker should be changed. This study has shown that the haplotypes consisting of DYS392, DYS393, DYS437, DYS438, DYS448 and DYS388 loci can preserve phylogenetic information by their relatively low mutation rates, and hence can be used to roughly distinguish Y-chromosome haplogroups, whereas more rapidly mutating Y-STRs such as DYS449 and DYS458 are useful for differentiating male lineages. At the relatively rapidly mutating DYS447, DYS449, DYS458 and DYS464 loci, unusually short alleles and intermediate alleles with common sequence structures are informative for elucidating the substructure within the context of a particular haplogroup. In addition, some deletion mutations in the DYS385 flanking region and the null allele at DYS448 were associated with a single haplogroup background. These variants support the hypothesis that the variant originated from a single mutational event like binary markers. The high-resolution haplogroup and haplotype data will improve our understanding of the Korean population substructure and will also help to infer haplogroup background or common ancestry.ope

Web-based Y-STR Database for Haplotype Frequency Estimation and Kinship Index Calculation

ope

A modified mini-primer set for analyzing mitochondrial DNA control region sequences from highly degraded forensic samples

To facilitate the analysis of mitochondrial DNA (mtDNA) control region sequences from highly degraded skeletal remains, a modified mini-primer set was designed to overcome the limitations of the Armed Forces DNA Identification Laboratory (AFDIL) mini-primer set. This modified mini-primer set is less affected by nucleotide variability and PCR amplification conditions than the AFDIL mini-primer set, and was able to amplify the mtDNA sequences of 55-year-old skeletal remains with high efficiency, indicating that it is a useful tool for analyzing mtDNA control region sequences from highly degraded forensic samples.ope

Genetic characteristics of 23 Y-STR loci in Koreans

To construct a Korean Y-chromosomal STR database for 22 Y-STRs (DYS19, DYS385, DYS388, DYS389I/II, DYS390, DYS391, DYS392, DYS393, DYS437, DYS438, DYS439, DYS446, DYS447, DYS448, DYS449, DYS456, DYS458, DYS464, DYS635, and GATA H4.1), 708 DNA samples from unrelated Korean males were analyzed using three multiplex PCR systems. During analysis, thirty two microvariant alleles were observed at DYS449, DYS458, and DYS464, and duplicated alleles were occurred once each for DYS19, DYS390, and DYS447. In haplotype analysis for the 22 Y-STRs, a total of 693 different haplotypes were observed with overall haplotype diversity of 0.9999, and of these, 680 haplotypes were unique. By combining each marker for the extended SWGDAM haplotype, DYS458 was the most informative marker. In addition, the diversity of combined haplotypes of DYS447, DYS458, DYS635, GATA H4.1, and the SWGDAM Y-STR loci was comparable to haplotypes of 17 loci in the AmpFlSTR(R) Yfiler(TM) kit.ope

그래핀 양자점과 반양자점의 합성

학위논문 (박사)-- 서울대학교 대학원 : 화학부 물리화학 전공, 2016. 2. 홍병희.Graphene is a zero-gap semiconductor since the conduction and valence bands meet at the Dirac points and exhibit a linear dispersion. The electronic density of states is zero at the Dirac points. This topology of the bands gives rise to unique and exotic electronic transport properties. The charge carriers are massless, which affects an extreme intrinsic carrier mobility. This makes graphene a promising candidate for applications in high-frequency electronics as a being more suitable than logic-based transistors. While it is clear that outstanding properties of graphene with fascinating electronic structure that received the most attention, this intrinsic character is seen as one of the most challenging in terms of the opening the band gap. Recently, the constricting of graphene into a finite structure has attracted the most intensive research. A great mount of theoretical work demonstrated that the influence of band structure can be varied by edge structure and width. The first experimental results, known as a graphene nanoribbon (GNR), were patterned by electron beam lithography. The measured energy gaps were found to be inversely proportional to GNR width. However, lithographic and graphene etching resolution is limited within the sub-10nm regime. In an attempt to solve these problems, solution processing with chemical reagents was employed to exfoliate the graphite sheets down into a narrower size, which yield GNR with a variety of shapes and repeatable uniformity. Furthermore, graphene nanomesh as a closely related structure to GNRs has been reporteda periodic array of holes in a graphene sheet, with the necks between adjacent holes narrowing to 5nm, which provides the confinement to easily open a band gap. The objective of this dissertation is to mainly introduce the optical properties and their applications of nanostructured graphenegraphene quantum dot (GQD) as a closely related with GNR material, and pseudo-nanomesh fabricated from catalytic etching of metal nanoparticle. The book starts with a broad description of the graphene, which contains the atomic structure of graphene, synthetic methods, characterization using optical tool, and patterning, since these will help a general understanding of the graphene. Once an understanding of the graphene is obtained, we move towards describing each of experiments in Chapter 2 and 3.Chapter Ⅰ. Introduction 1 1. The Atomic structure of Graphene 1 2. Band structure of Graphene 4 3. Synthesis Methods 5 4. Raman spectroscopy of graphene 9 5. Nanostructured graphene 17 6. Reference 21 Chapter Ⅱ. Synthesis of Graphene quantum dot and its application 34 1. Introduction 34 2. Experiment 36 3. Result and Discussion 37 4. Conclusion 41 5. Reference 42 Chapter Ⅲ. Synthesis of Graphene Antidots 56 1. Introduction 56 2. Experiment 58 3. Result and Discussion 61 4. Conclusion 70 5. Reference 71 Appendix 92 A. List of publication 93 B. List of presentation 94 Abstract in Korean 95Docto

Pleasure, Resistence, Ideology

어떤 학자의 지적처럼, 80년대 서구의 대중문화 텍스트 연구에서는 "이데올로기가 결정 (Determinate)하는데 실패하고, 주체 (Sutject)를 호명 (Interpellate)하는데 실패하고 해독(Reading)이 선호(Prefer)되는데 실패하는" 방식에 관심이 집중되고 있는 것을 볼 수 있다(Turner, 1990:216). 바꾸어 말하면 구조주의·문화론적 연구 전통의 주요 관심사였던, 지배 이데올로기의 생산 및 재생산의 문제, 주체 구성에 의한 지배 이데올로기의 이념작용, 미디아 문화 텍스트의 선호된 해독(Preferred Reading)의 이론 같은, 미디아 문화를 지배 이데올로기의 강력한 헤게모니 구축의 수단으로 보고 그 메카니즘을 설명하고자 했던 이론들이 갖고 있었던 설명력이 약화되어 가고 있음을 의미한다. 그러한 이유는 항시 하나의 이론이나 방법론이 일정기 간 풍미한 뒤에는 반드시 드러나게 되는 그 이론의 약점, 문제점들에 대한 주목 때문이기도 하지만, 새로이 속속 등장하고 있는 대중문화들이 (포스트 모던문화라고 분류되는 문화를 포함해서) 그러한 기존의 틀만으로는 설명이 쉽지 않는다는데서 보다 더 큰 이유를 찾을 수 있을 것 같

廣告端緖가 브랜드 資産(brand equity)形成에 影響을 미치는 過程에 關한 硏究

학위논문(석사)--서울大學校 大學院 :經營學科 經營學專攻,1996.Maste

Research on multiple real options valuation : an application on the research and development of fuel cells

학위논문 (석사)-- 서울대학교 대학원 : 산업·조선공학부, 2011.2. 오형식.Maste