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남기웅,김병구,임재영,Dong Yul Lee,김종수,김진수 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.9
The effect of an electron blocking layer (EBL) on the V − I curves for GaN/InGaN multiplequantum wells is investigated. For the first time, we found that the curves intersected at 3.012 V,and we investigated the reason for the intersection. The forward voltage in LEDs with a p-AlGaNEBL is larger than it is without the p-AlGaN EBL at low injection currents because the Mg-dopingefficiency for the p-GaN layer is higher than that for the p-AlGaN layer. However, the forwardvoltage in LEDs with a p-AlGaN EBL is smaller than it is without the p-AlGaN EBL at highinjection currents because the carriers overflow from the active layer when the injection currentincreases in LEDs without a p-AlGaN EBL, in case of LEDs with a p-AlGaN EBL, the carriers areblocked by the EBL.
남기웅,김성수,조의제,김경제,임재영,손정식,김성오 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.71 No.1
In this study, we fabricated high-quality ZnO films using hydrothermally grown ZnO nanorods and a spin-coated Al-doped ZnO film by using regrowth method. The phtoluminescence (PL) intensity ratios of the near-band-edge (NBE) to deep-level (DL) emission peaks (INBE/IDL) for ZnO nanorods (samples 1) and ZnO film (sample 2) were 2.13 and 24.3, respectively. The redshift from 3.288 (sample 2) to 3.278 eV (sample 1) and low INBE/IDL ratio in PL spectra were attributed to large mismatch between ZnO and Si substrate, resulting in a residual stress and the low optical properties. In case of sample 2, the photocurrent was sharply increased without the exponential rise because of enhanced optical properties of ZnO film by regrowth. The regrowth method is expected to represent a possible route for fast-response ultraviolet sensors.
급성 폐사 바지락 (Ruditapes philippinarum) 으로부터 Perkinsus olseni의 확산 기작
남기웅,정희도,송재희,최광식,박경일 한국패류학회 2015 The Korean Journal of Malacology Vol.31 No.4
This study was conducted in order to elucidate the dissemination mechanism of P. olseni using field and laboratory experiments. For this purpose, we quantified the level of P. olseni infection in buried (healthy) and surfaced (gapped) R. philippinarum from a clam bed on Wi-do Island on the west coast of Korea. In addition, the levels of internal and released P. olseni cells from artificially infected (and later dead) R. philippinarum were monitored for 8 days using the RFTM–2 M NaOH lysis method. Our results indicate that P. olseni cells in buried R. philippinarum was 2,655,625 ± 1,536,936 cells/clam; the level in gapped R. philippinarum was considerably lower, 28,203 ± 24,889 cells/clam (p < 0.05). In the laboratory experiment, the P. olseni cells remained in the host tissue 2 days after death was approximately 50% lower than the level of infection measured in living clams. The level dropped to 20% 4 days after death and to 1.5% 6 days after death; eight days after death, P. olseni cells were undetectable since the R. philippinarum flesh had completely decomposed. The level of released cells on the day of death was only 0.05% of the internal level in live R. philippinarum; however, the level increased to 2.3% 5 days after death then gradually decreased and no released cells were detected 8 days after death. Therefore, our laboratory experiment suggest that the low level of P. olseni infection observed in gapped R. philippinarum at Wi-do Island could be caused by lysis of the most of P. olseni cells during the decomposition of dead R. philippinarum tissues. Until the end of decomposition of R. philippinarum, 6.68% of the total amount of P. olseni was released within 8 days. Our study showed that the amount of P. olseni cells from dead host is a considerably higher level than naturally released from healthy R. philippinarum, suggesting that death of the host plays an important role in the dissemination of P. olseni.
남기웅,이상헌,소운섭,윤현식,김소람,김민수,정재학,이제원,김양수,임재영,김영구 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.1
The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons (D0X), two-electron satellite (TES), free-to-neutral-acceptors (e,A0), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes’ empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for D0X in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for D0X transitions.
Pear Skin Stain Caused by Mycosphaerella graminicola on Niitaka Pear (Pyrus pyrifolia Nakai)
남기웅,오소영,윤덕훈 한국식물병리학회 2014 Plant Pathology Journal Vol.30 No.3
Pear skin stains on ‘Niitaka’ pears, which occur from the growing stage to the cold storage stage, reportedly negatively influence the marketing of pears. These stains on fruit skin are likely due to a pathogenic fungusthat resides on the skin and is characterized by dark stains; however, the mycelium of this fungus does not penetrate into the sarcocarp and is only present on the cuticle layer of fruit skin. A pathogenic fungus was isolated from the skin lesions of infected fruits, and its pathogenicity was subsequently tested. According to the pathogenicity test, Mycosphaerella sp. was strongly pathogenic, while Penicillium spp. and Alternaria spp. showed modest pathogenicity. In this present study, we isolated the pathogenic fungus responsible for the symptoms of pears (i.e., dark brown-colored specks) and identified it as Mycosphaerella graminicola based on its morphological characteristics and the nucleotide sequence of the beta-tubulin gene. M. graminicola was pathogenic to the skin of ‘Niitaka’ pears, which are one of the most widely growing varieties of pears in South Korea.