• Korean Journal of Plant Resources
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• v.33 no.6
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• pp.675-681
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• 2020

This study describes an efficient and stable droplet vitrification following cryopreservation of strawberry shoot tip (Fragaria × ananassa Duch.) accessions 'Massey' and 'MDUS3816'. The shoot tips were precultured in Murashige and Skoog (MS) liquid medium supplemented with sucrose (0.3-0.7M). Precultured explants were osmoprotected with loading solution (LS, C4) containing 17.5% glycerol and 17.5% sucrose for 40 min and exposed to dehydration solution (B1) containing 50% glycerol and 50% sucrose for 40 min at 25oC. Subsequently, the explants were transferred onto droplets containing 2.5 µL PVS3 on sterilized aluminum foils (4 cm× 0.5 cm) prior to direct immersion in liquid nitrogen (LN) for 1 h. The highest regrowth rate (%) in both the cultivars was obtained when the shoot tips were precultured with 0.3M sucrose for 30 h + 0.5M sucrose for 16 h at 25oC. The cryopreserved shoots tips exhibited 57.8 % recovery rate by culturing in NH₄NO₃-free MS medium supplemented with 3% sucrose, 1.0 g/L casein, 1.0mg/L GA₃, and 0.5 mg/L BA for 5 weeks and in MS medium supplemented with 0.5 mg/L GA₃ for 8 weeks. Variation was not observed in both of ploidy analysis and morphological investigation on plantlets of two accessions cryopreserved under variable preculture conditions.

• 한국항공운항학회:학술대회논문집
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• 2016.05a
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• pp.14-18
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• 2016

본 연구에서는 하이브리드로켓 모터와 고체로켓 모터를 이용하여 목표 고도 1km인 2단 로켓 설계를 수행하였다. 비행 시나리오는 총 비행시간 51.59초, 1단부 로켓 연소시간은 3초이며 연소 종료 후 3초 뒤 단 분리를 수행하여 2단부 로켓 점화가 이루어져 총 3초간 연소가 진행된다. 1단부 모터는 하이브리드로켓으로써 5port의 HDPE를 연료 그레인으로 사용하였고 $LN_2O$를 산화제로 사용하였다. 2단부 모터는 고체로켓으로 KNSB(Sorbitol/$KNO_3$)추진제를 사용하였다. 단 분리는 영전자석을 이용하여 분리하며 2단부 모터의 점화는 광학 센서와 니크롬선 점화방식을 이용하여 점화하도록 설계하였다. 비행하는 동안 AVR를 이용해 압력, 가속도, GPS 등의 자료를 수집할 수 있도록 설계하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.256-256
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• 2016

기존의 디스플레이 기슬은 마스크를 통해 특정 부분에만 유기재료를 증착시키는 방법을 사용하였으나, 기판의 크기가 커짐에 따라 공정조건에 제약이 발생하였다. 이를 해결하기 위해 최근 용액 공정에 대한 연구가 활발히 진행되고 있다. 용액 공정은 기존 진공 증착 방식과 비교하였을 때 상온, 대기압에서 증착이 가능하며 경제적이고, 대면적 균일 증착에 유리하다는 장점이 있다. 반면, 용액 공정으로 제작한 소자는 시간이 지남에 따라 점차 전기적 특성이 변하는 aging effect를 보인다. Aging effect는 용액에 포함된 C기와 OH기 기반의 불순물의 영향으로 시간의 경과에 따라서 문턱전압, subthreshold swing 및 mobility 등의 전기적 특성이 변하는 현상으로 고품질의 박막을 형성하기 위해서는 고온의 열처리가 필요하다. 지금까지 고품질 박막 형성을 위한 열처리는 퍼니스 (furnace) 장비에서 주로 이루어졌는데, 시간이 오래 걸리고, 상대적으로 고온 공정이기 때문에 유리, 종이, 플라스틱과 같은 다양한 기판에 적용하기 어렵다는 단점이 있다. 따라서, 본 연구에서는 $100^{\circ}C$ 이하의 저온에서도 열처리가 가능한 microwave irradiation (MWI) 방법을 이용하여 solution-processed InGaZnO TFT를 제작하였고, 기존의 열처리 방식인 furnace로 열처리한 TFT 소자와 aging effect를 비교하였다. 먼저, solution-processed IGZO TFT를 제작하기 위해 p type Si 기판을 열산화시켜서 100 nm의 SiO2 게이트 산화막을 성장시켰고, 스핀코팅 방법으로 a-IGZO 채널층을 형성하였다. 증착후 열처리를 위하여 1000 W의 마이크로웨이브 출력으로 15분간 MWI를 실시하여 a-IGZO TFT를 제작하였고, 비교를 위하여 furnace N2 gas 분위기에서 $600^{\circ}C$로 30분간 열처리한 TFT를 준비하였다. 제작된 직후의 TFT 특성을 평가한 결과, MWI 열처리한 소자가 퍼니스 열처리한 소자보다 높은 이동도, 낮은 subthreshold swing (SS)과 히스테리시스 전압을 가지는 것을 확인하였다. 한편, aging effect를 평가하기 위하여 제작 후에 30일 동안의 특성변화를 측정한 결과, MWI 열처리 소자는 30일 동안 문턱치 전압(VTH)의 변화량 ${\Delta}VTH=3.18[V]$ 변화되었지만, furnace 열처리 소자는 ${\Delta}VTH=8.56[V]$로 큰 변화가 있었다. 다음으로 SS의 변화량은 MWI 열처리 소자가 ${\Delta}SS=106.85[mV/dec]$인 반면에 퍼니스 열처리 소자는 ${\Delta}SS=299.2[mV/dec]$이었다. 그리고 전하 트래핑에 의해서 발생하는 게이트 히스테리시스 전압의 변화량은 MWI 열처리 소자에서 ${\Delta}V=0.5[V]$이었지만, 퍼니스 열처리 소자에서 ${\Delta}V=5.8[V]$의 큰 수치를 보였다. 결과적으로 MWI 열처리 방식이 퍼니스 열처리 방식보다 소자의 성능이 우수할 뿐만 아니라 aging effect가 개선된 것을 확인할 수 있었고 차세대 디스플레이 공정에 있어서 전기적, 화학적 특성을 개선하는데 기여할 것으로 기대된다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.166-166
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• 2007

ZnO는 육방정계(wurtzite) 결정구조를 지니며 상온에서 3.37eV의 wide band gap을 갖는다. ZnO의 엑시톤 결합 에너지는 GaN에 비해 2.5배 높은 60meV로서 고효율의 광소자 적용 가능성이 높다. 또한 고품위의 박막합성이 가능하다. 이러한 특성 때문에 display소자의 투명전극, 광전소자, 바리스터, 압전소자, 가스센서 등에 폭 넓게 응용되고 있다. ZnO박막의 제조는 스퍼터링, CVD, 진공증착법, 열분해법 등이 있다. 본 논문에서는 RF 마그네트론 스퍼터에 의해 제작된 ZnO 박막에 CMP공정을 수행하여 연마율과 비균일도 특성 및 광투과 특성을 연구하였다. ZnO박막은 $2{\times}2Cm$의 Corning glass위에 증착되었다. 로터리 펌프와 유확산 펌프를 이용하여 초기진공을 $2{\times}10^{-6}$ Torr까지 도달시킨 후 Ar과 $O_2$를 주입하였다. 증착은 상온에서 이루어졌으며 공정압력은 $6{\times}10^{-2}$Torr이였다. 초기의 불안정한 상태의 풀라즈마를 안정시키기 위해 셔터를 이용하여 pre-sputtering을 하였다. CMP 공정조건은 플레이튼 속도, 슬러리 유속, 압력은 칵각 60rpm, 90ml/min, $300g/cm^2$으로 일정하게 유지하였으며 헤드속도는 20rpm에서 100rpm까지 증가시키면서 연마특성을 조사하였다. 실리카슬러리의 적합성을 알아보기 위해 DIW와 병행하여 CMP공정을 수행하고 비교 분석하였다. CMP공정 결과 광투과도는 굉탄화된 표면의 확보로 인해 향상된 특성을 보였다. 실리카 슬러리를 사용하여 CMP를 할 경우는 헤드속도는 저속으로 하여야 양호한 연마특성을 얻을 수 있었다.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.339-346
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• 2008

Single-crystal $ZnIn_2S_4$ layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at $450^{\circ}C$ with a hot wall epitaxy (HWE) system by evaporating a $ZnIn_2S_4$ source at $610^{\circ}C$. The crystalline structures of the single-crystal thin films were investigated via the photoluminescence (PL) and Double-crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the $ZnIn_2S_4$ obtained from the absorption spectra was well described by Varshni's relationship, $E_g(T)=2.9514\;eV-(7.24{\times}10^{-4}\;eV/K)T2/(T＋489K)$. After the as-grown $ZnIn_2S_4$ single-crystal thin films was annealed in Zn-, S-, and In-atmospheres, the origin-of-point defects of the $ZnIn_2S_4$ single-crystal thin films were investigated via the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_S$, $Zn_{int}$, and $S_{int}$ obtained from the PL measurements were classified as donor or acceptor types. Additionally, it was concluded that a heat treatment in an S-atmosphere converted $ZnIn_2S_4$ single crystal thin films into optical p-type films. Moreover, it was confirmed that In in $ZnIn_2S_4$/GaAs did not form a native defects, as In in $ZnIn_2S_4$ single-crystal thin films existed in the form of stable bonds.

• Nuclear Engineering and Technology
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• v.44 no.3
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• pp.273-282
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• 2012

A new effective methodology for optimizing the enrichment of low-enriched zones as well as gadolinia fuel ($UO_2/Gd_2O_3$) rod designs in PLUS7 fuel assemblies was developed to minimize the maximum peak power in the core and to maximize the cycle lifetime. An automated link code was developed to integrate the genetic algorithm (GA) and the core design code package of ALPHA/PHOENIX-P/ANC and to generate and evaluate the candidates to be optimized efficiently through the integrated code package. This study introduces an optimization technique for the optimization of gadolinia fuel rod designs in order to effectively reduce the peak powers for a few hot assemblies simultaneously during the cycle. Coupled with the gadolinia optimization, the optimum enrichments were determined using the same automated code package. Applying this technique to the reference core of Ulchin Unit 4 Cycle 11, the gadolinia fuel rods in each hot assembly were optimized to different numbers and positions from their original designs, and the maximum peak power was decreased by 2.5%, while the independent optimization technique showed a decrease of 1.6% for the same fuel assembly. The lower enrichments at the fuel rods adjacent to the corner gap (CG), guide tube (GT), and instrumentation tube (IT) were optimized from the current 4.1, 4.1, 4.1 w/o to 4.65, 4.2, 4.2 w/o. The increase in the cycle lifetime achieved through this methodology was 5 effective full-power days (EFPD) on an ideal equilibrium cycle basis while keeping the peak power as low as 2.3% compared with the original design.

• Microbiology and Biotechnology Letters
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• v.18 no.6
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• pp.591-598
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• 1990

Six species under the basidiomycetes were screened for extracellular tannase (tannin acyl hydrolase EC 3.1. 1.20) production in submerged culture and Lenzites betulina was found to be most effective for the production of tannase. The optimum cultural conditions for tannase production were $25^{\circ}C$, pH 6.0 and 21 days of culture period, The efficient composition of culture medium for the production of tannase was performed in synthetic medium containing tannic acid, 2g; sucrose, 5g; bacto-peptone, 2g; ,$ KH_2PO_4, \;2g,\; MgSO_4.7H_2O \;0.5g,\; CuS0_4.5H_2O$, 2 mg; thiamine HCl, 100 ug and distilled water 100 ml, The tannase produced from Lenzites bdulin*r was 223.3 unit (umole of gaUic acidiml of brothlmin). The tannase had an optimal reaction conditions ofpH 6.0 and temperature of $40^{\circ}C$. The enzyme was stable at temperature below $40^{\circ}C$ and lost its activity by 50% above $60^{\circ}C$. And the stable pH range was 5.5 to 6.0.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.265.2-265.2
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• 2016

Oxide thin film transistors (TFTs) have attracted considerable interest for gate diver and pixel switching devices of the active matrix (AM) liquid crystal display (LCD) and organic light emitting diode (OLED) display because of their high field effect mobility, transparency in visible light region, and low temperature processing below $300^{\circ}C$. Recently, oxide TFTs with polycrystalline In-Ga-O(IGO) channel layer reported by Ebata. et. al. showed a amazing field effect mobility of $39.1cm^2/Vs$. The reason having high field effect mobility of IGO TFTs is because $In_2O_3$ has a bixbyite structure in which linear chains of edge sharing InO6 octahedral are isotropic. In this work, we investigated the characteristics and the effects of oxygen partial pressure significantly changed the IGO thin-films and IGO TFTs transfer characteristics. IGO thin-film were fabricated by rf-magnetron sputtering with different oxygen partial pressure ($O_2/(Ar+O_2)$, $Po_2$)ratios. IGO thin film Varies depending on the oxygen partial pressure of 0.1%, 1%, 3%, 5%, 10% have been some significant changes in the electrical characteristics. Also the IGO TFTs VTH value conspicuously shifted in the positive direction, from -8 to 11V as the $Po_2$ increased from 1% to 10%. At $Po_2$ was 5%, IGO TFTs showed a high drain current on/off ratio of ${\sim}10^8$, a field-effect mobility of $84cm^2/Vs$, a threshold voltage of 1.5V, and a subthreshold slpe(SS) of 0.2V/decade from log(IDS) vs VGS.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.222-224
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• 2006

A non-vacuum process for $Cu(In,Ga)Se_2$ (CIGS) thin film solar cells from nanoparticle precursors was described in this work CIGS nanoparticle precursors was prepared by a low temperature colloidal route by reacting the starting materials $(CuI,\;InI_3,\;GaI_3\;and\;Na_2Se)$ in organic solvents, by which fine CIGS nanoparticles of about 20nm in diameter were obtained. The nanoparticle precursors were mixed with organic binder material for the rheology of the mixture to be adjusted for the doctor blade method. After depositing the mixture of CIGS with binder on Mo/glass substrate, the samples were preheated on the hot plate in air to evaporate remaining solvents ud to burn the organic binder material. Subsequently, the resultant (porous) CIGS/Mo/glass simple was selenized in a two-zone Rapid Thermal Process (RTP) furnace in order to get a solar ceil applicable dense CIGS absorber layer. Complete solar cell structure was obtained by depositing. The other layers including CdS buffer layer, ZnO window layer and Al electrodes by conventional methods. The resultant solar cell showed a conversion efficiency of 0.5%.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.5
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• pp.797-802
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• 2023

We prepared GZO (Ga₂O₃ : 5 wt %, ZnO : 95 wt %) thin film on glass substrate according to the substrate temperature using the pulsed laser deposition method and investigated electrical and optical properties of the thin film. Through the XRD measurements, their were confirmed that all GZO thin films grew preferentially in c-axis and the GZO thin film deposited at 300℃ showed the best crystallinity with a FWHM of 0.38°. As the substrate temperature increased from 150 to 300℃, the resistivity of GZO thin film tend to decrease, while the average transmittance in the visible light region was not significantly affected. The figure of merit of the GZO thin film deposited at 300℃ was 2.05×10⁴ Ω^-1·cm^-1, which was the best value, the resistivity and the average transmittance in the visible light region were 3.72 × 10^-4 Ω·cm and 87.71 %, respectively. In this study, it was found that GZO thin film is very promising material for transparent conducting thin film.