• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 유기절연재료 방전 플라즈마연구회
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• pp.61-64
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• 2003

In the response to an increasing demand for electrical energy, much effort aimed to develop and commercialise HTS power equipments is going on around the world. For the development, it is necessary to establish the dielectric technology in $LN_2$. Hence many types of dielectric tests should be carried out to understand the dielectric phenomena at cryogenic temperature and to gather various dielectric data. Among the many types dielectric tests, the barrier effect were conducted with the simulated electrode after analysing the insulating configuration of the pancake coil type HTS transformer. The influence of a barrier on the dielectric strength was measured according to the size and the position of the barrier. It was shown that the effectiveness, the ratio of the breakdown voltage in presence of barrier to the voltage without barrier, is highest when the barrier is placed at the needle electrode side. And the barrier effect was not depend on the electrode array. The life time to breakdown with decreasing the applied voltage was increased remarkably having wide error band but the shape parameter in Weibull distribution was almost constant.

• 전기학회논문지
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• 제60권6호
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• pp.1169-1174
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• 2011

CdTe thin-film solar cell technology is well known that it can theoretically improve its conversion efficiency and manufacturing costs compared to the conventional silicon solar cell technology, due to its optical band gap energy (about 1.45eV) for solar energy absorption, high light absorption capability and low cost requirements for producing solar cells. Although the prior studies obtained the high light absorption, CdTe thin film solar cell has not been come up to the sufficient efficiency yet. So, doping method was selected for the improvement of the electrical characteristics in CdTe solar cells. Some elements including Cu, Ag, Cd and Te were generally used for the p-dopant as substitutional acceptors in CdTe thin film. In this study, the sputtering-deposited CdTe thin film was immersed in $AgNO_3$ solution for ion exchange method to dope Ag ions. The effects of immersion temperature and Ag-concentration were investigated on the optical properties and electrical characteristics of CdTe thin film by using Auger electron spectroscopy depth-profile, UV-visible spectrophotometer, and a Hall effect measurement system. The best optical and electrical characteristics were sucessfully obtained by Ag doping at high temperature and concentration. The larger and more uniform diffusion of Ag ions made increase of the Ag ion density in CdTe thin film to decrease the series resistance as well as mede the faster diffusion of light by the metal ions to enhance the light absorption.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.317-318
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• 2013

Terahertz (THz) wave는 광학 영역과 방송파 영역 사이에 광대역 주파수 스펙트럼을 차지하고 있다. X선과는 달리 비이온화 광원으로 직진성, 투과성, 낮은 에너지 (meV)를 가지고 있어 비파괴적이고 무해한 장점을 지니고 있다. 본 연구에서는 In0.53Ga0.47As:Be/In0.52Al0.48As의 multi quantum well (MQW)을 Semi-insulting InP:Fe substrate 위에 active layer의 두께와 적층을 변화주어서 성장하였고Au (200 nm)/Ti (30 nm)의 금속전극으로 공정을 하였다. Ti:Sapphire femtosecond pulse laser를 조사하여 THz time-domain spectrometer 시스템을 이용하여 광전도검출법으로 THz 검출 특성을 연구하였다. THz 검출은 짧은 전하수명과 높은 저항을 요구한다. LTInGaAs의 경우 AsGa antisite로 인하여 짧은 전하수명을 얻게 되면 n-type의 높은 전하밀도를 가지게 되어서 저항이 낮아지게 된다. 높은 저항을 만들기 위하여 Be doping을 이용하여 과잉의 전자들을 보상하고 InAlAs layer를 삽입시켜 보다 높은 저항을 얻었다. LT-InGaAs:Be는 LT-GaAs보다 1/70 정도의 amplitude를 보이는데 LT-InGaAs/InAlAs MQW의 경우 LT-GaAs 대비 약 3/4 정도의 큰 amplitude를 얻었다. 또 active layer의 두께가 얇고 적층이 많을수록 신호가 커지는 것을 알 수 있었다. 이는 상대적으로 band gap이 큰 InAlAs층이 더 높은 저항을 만든 것으로 사료된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.226-226
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• 2013

Si is a dominant solar material, which is the second most abundant element in the earth giving a benefit in the aspect in cost with low toxicity. However, the inherent limit of Si has an indirect band gap of 1.1 eV resulting in the limited optical absorption. Therefore, a critical issue has been raised to increase the utilization of the incident light into the Si absorber. The enhancement of light absorption is a crucial to improve the performances and thus relieves the cost burden of Si photovoltaics. For the optical aspect, an efficient design of a front surface, where the incident light comes in, has been intensively investigated to improve the performance of photon absorption. Lambertian light trapping can be attained when the light active surface is ideally rough to increase the optical length by about 50 compared to a planar substrate. This suggests that an efficient design may reduce thickness of the Si absorber from the conventional 100~300 ${\mu}m$ to less than 3 ${\mu}m$. Theoretically, a hole-array structure satisfies an equivalent efficiency of c-Si with only one-twelfth mass and one-sixth thickness. Various approaches have been applied to improve the incident light utilization in a Si absorber using textured structures, periodic gratings, photonic crystals, and nanorod arrays. We have designed hole and pillar structured Si absorbers. Four-different Si absorbers have been simultaneously fabricated on an identical Si wafer with hole arrays or pillar arrays at a fixed depth of 2 ${\mu}m$. We have found that the significant enhanced solar cell performances both for the hole arrayed and pillar arrayed Si absorbers compared to that of a planar Si wafer resulting from the effective improvement in the quantum efficiencies.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.619-619
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• 2013

The interfacial state between $Ta_2O_5$ and a Si substrate during the growth of $Ta_2O_5$ films by atomic layer deposition (ALD) was investigated using in-situ synchrotron radiation photoemission spectroscopy (SRPES). A newly synthesized liquid precursor Ta($N^tBu$) $(dmamp)_2Me$ was used as the metal precursor, with Ar as a purging gas and $H_2O$ as the oxidant source. After each half reaction cycle, samples were analyzed using in-situ SRPES under ultrahigh vacuum at room temperature. SRPES analysis revealed that Ta suboxide and Si dioxide were formed at the initial stages of $Ta_2O_5$ growth. However, the Ta suboxide states almostdisappeared as the ALD cycles progressed. Consequently, the $Ta^{5+}$ state, which corresponds with the stoichiometric $Ta_2O_5$, only appeared after 4.0 cycles. Additionally, tantalum silicate was not detected at the interfacial states between $Ta_2O_5$ and Si. The measured valence band offset between $Ta_2O_5$ and the Si substrate was 3.22 eV after 3.0 cycles.

• 한국미생물·생명공학회지
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• 제47권4호
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• pp.522-529
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• 2019

A Bacillus strain, SJ4, exhibiting strong fibrinolytic activity was isolated from saeu (shrimp, Acetes chinensis) jeotgal, a Korean traditional fermented food and was identified as B. subtilis. The B. subtilis SJ4 strain can grow at a NaCl concentration of up to 15% (w/v). The fibrinolytic activity of B. subtilis SJ4 (152.0 U/ml) cultured in Luria-Bertani (LB) broth for 48 h at 37℃ with aeration was higher than that of B. subtilis SJ4 cultured in TSB (124.5 U/ml) under same culture conditions. The major proteins in the LB culture supernatant of B. subtilis SJ4 were analyzed by SDS-PAGE, which revealed three major bands (23, 25, and 28 kDa). The band (23 kDa) with strong fibrinolytic activity, analyzed on fibrin zymogram, was observed at 60-96 h of cultivation. The aprESJ4 gene encoding the major fibrinolytic enzyme, AprESJ4, was cloned by PCR. The aprESJ4 gene sequence exhibited high similarities with the fibrinolytic gene sequences of other Bacillus species. The amino acid sequence of AprESJ4 exhibited 98.9 and 98.4% similarity with subtilisin NAT and AprE2 of B. subtilis, respectively. Hence, B. subtilis SJ4 can be a potential starter culture for jeotgal products.

• Current Photovoltaic Research
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• 제3권2호
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• pp.39-44
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• 2015

$Cu(In,Ga)_3Se_5$ (${\beta}-CIGS$) has a band gap of 1.35 eV which is an optimum value for high solar-energy conversion efficiency. However, ${\beta}-CIGS$ film was not well characterized yet due to lower efficiency compared to $Cu(In,Ga)Se_2$ (${\alpha}-CIGS$). In this work, ${\beta}-CIGS$ films were fabricated by a three-stage co-evaporation of elemental sources with various Se fluxes. As the Se flux increased, the crystallinity of ${\beta}-CIGS$ phase was improved from the analysis of Raman spectroscopy and a deep-level defect was reduced from the analysis of photoluminescence spectroscopy. A Se treatment of the ${\beta}-CIGS$ film at $200^{\circ}C$ increased Ga content and decreased Cu content at the surface of the film. With the Se treatment at $200^{\circ}C$, the cell efficiency was greatly improved for the CIGS films prepared with low Se flux due to the increase of short-circuit current and fill factor. It was found that the main reason of performance improvement was lower Cu content at the surface instead of higher Ga content.

• Current Photovoltaic Research
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• 제5권1호
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• pp.15-19
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• 2017

The fossil fuel power consumption generates $CO_2$, which causes the problems such as global warming. Also, the increase in energy consumption has accelerated the depletion of the fossil fuels, and renewable energy is attracting attention. Among the renewable energies, the solar energy gets a lot of attention as the infinite clean energy source. But, the supply level of solar cell is insignificant due to high cost of generation of electric power in comparison with fossil fuels. Thus several researchers are recently doing the research on ultra-low-cost solar cells. Also, $Cu_2O$ is one of the applied materials as an absorption layer in ultra-low-cost solar cells. Cuprous oxide ($Cu_2O$) is highly desirable semiconductor oxide for use in solar energy conversion due to its direct band gap ($E_g={\sim}2.1eV$) and a high absorption coefficient that absorbs visible light of wavelengths up to 650 nm. In addition, $Cu_2O$ has several advantages such as non-toxicity, low cost and can be prepared with simple and cheap methods on large scale. In this work, we fabricated the $Cu_2O$ thin films by reactive sputtering method. The films were deposited with a Cu target with variable parameters such as substrate temperature, rf-power, and annealing condition. Finally, we confirmed the structural properties of thin films by XRD and SEM.

• Journal of Microbiology and Biotechnology
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• 제12권6호
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• pp.972-978
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• 2002

Streptomyces sp. AD001 is a Gram-positive soil actinomycetes secreting an uncharacterized 2,4-dichlorophenol (DCP) oxidizing enzyme, whose activity is similar to the previously known Actinomycetes lignin-peroxidase (ALiP). This extracellular peroxidase was purified from Streptomyces sp. AD001 as a single protein band on an SDS-PACE by ammonium sulfate fractionation, Q-sepharose, concanavalin A, and Bio-Gel HTP column chromatographies. The molecular mass of the purified peroxidase was determined by SDS-PAGE to be 45.2 kDa, and 49.7 kDa with MALDI-TOF-MS, respectively. The highest level of peroxidase activity was observed at pH 7.5 and $30^{\circ}C$. The amino terminal sequence of the purified peroxidase (G-E-P-E-E-G-N-V-D-G-T-L) showed no significant homologies to my known proteins, suggesting that Streptomyces sp. AD001 may secrete a novel kind of bacterial peroxidase Initial rate kinetic data of the 2,4-DCP oxidation were best modeled with a random-binding bireactant system.