• 생명과학회지
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• 제10권2호
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• pp.210-217
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• 2000

A kinetic profile of the catalytic domain of stromelysin-1 (SCD) using the fluorescent peptide substrate has been determined by the stopped-flow technique. The pH profile has a pH optimum of about 5.5 with an extended shoulder above pH 7. Three pKa values, 5.0, 5.7, and 9.8 are found for the free enzyme state and two pH independent Kcat/Km values of 4.1$\times$104 M-1 s-1 and 1.4$\times$104 M-1 s-1 at low and high pH, respectively. The profile is quite different in shape with other MMP family which has been reported, having broad pH optimum with two pKa values. The substrate specificity of SCD towards fluorescent heptapeptide substrates has been also examined by thin layer chromatography. The cleavage sites of the substrates have been identified using reverse-phase HPLC method.SCD cleaves Dns-PLA↓L↓WAR and Dns-PLA↓L↓FAR at two positions. However, the Dns-PLA↓LRAR, Dns-PLE↓LFAR, adn Dns-PLSar↓LFAR are cleaved exclusively at one bond. The double cleavages of Dns-PLALWAR and Dns-PLALFAR by SCD are in marked contrast to the close structurally related matrilysin. A notable feature of SCD catalysis agrees with the structural data that the S1' pocket of SCD is deeper than that of matriysin. The differences observed between SCD and matrilysin may form the basis of understanding the structural relationships and substrate specificities of the MMP family in vivo.

• 한국재료학회지
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• 제27권2호
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• pp.107-112
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• 2017

The BCBJ (Back Contact and Back Junction) or back-lit solar cell design eliminates shading loss by placing the pn junction and metal electrode contacts all on one side that faces away from the sun. However, as the electron-hole generation sites now are located very far from the pn junction, loss by minority-carrier recombination can be a significant issue. Utilizing Medici, a 2-dimensional semiconductor device simulation tool, the interdependency between the substrate thickness and the minority-carrier recombination lifetime was studied in terms of how these factors affect the solar cell power output. Qualitatively speaking, the results indicate that a very high quality substrate with a long recombination lifetime is needed to maintain the maximum power generation. The quantitative value of the recombination lifetime of minority-carriers, i.e., electrons in p-type substrates, required in the BCBJ cell is about one order of magnitude longer than that in the front-lit cell, i.e., $5{\times}10^{-4}sec$ vs. $5{\times}10^{-5}sec$. Regardless of substrate thickness up to $150{\mu}m$, the power output in the BCBJ cell stays at nearly the maximum value of about $1.8{\times}10^{-2}W{\cdot}cm^{-2}$, or $18mW{\cdot}cm^{-2}$, as long as the recombination lifetime is $5{\times}10^{-4}s$ or longer. The output power, however, declines steeply to as low as $10mW{\cdot}cm^{-2}$ when the recombination lifetime becomes significantly shorter than $5{\times}10^{-4}sec$. Substrate thinning is found to be not as effective as in the front-lit case in stemming the decline in the output power. In view of these results, for BCBJ applications, the substrate needs to be only mono-crystalline Si of very high quality. This bars the use of poly-crystalline Si, which is gaining wider acceptance in standard front-lit solar cells.

• 공업화학
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• 제30권4호
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• pp.504-508
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• 2019

GaInP/AlGaInP 이종접합 구조를 제안하고 집광 조건에서 가장 높은 효율을 달성한 III-V 화합물 반도체 다중접합 태양전지의 맨 위 subcell에 주로 사용되는 GaInP 동종접합 구조를 대체해 이종접합 구조가 응용될 가능성에 대하여 조사하였다. $2^{\circ}$ off 된 웨이퍼와 $10^{\circ}$ off 된 서로 다른 off-cut 방향을 갖는 두 종류의 GaAs 기판 위에 성장된 태양전지의 특성을 집광 조건에서 측정하고 비교하였다. $10^{\circ}$ off 된 태양전지에서 더 높은 단락전류와 변환효율을 얻었다. 1 sun 조건에서 $10^{\circ}$ off 된 기판 위에 제작된 $2{\times}2mm^2$ 면적의 태양전지에서 $9.21mA/cm^2$의 단락전류밀도와 1.38 V의 개방 전압이 측정되었다. $10^{\circ}$ off 기판 위에 제작된 $5{\times}5mm^2$ 태양전지에서 집광도 증가에 따라 곡선인자(fiill factor)가 감소하여 변환효율은 6.03% (1 sun)에서 5.28% (20 sun)로 측정되었다.

• 한국세라믹학회지
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• 제39권10호
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• pp.928-934
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• 2002

Ga을 치환 고용시킨 ZnO(GZO) 박막을 GZO 세라믹 타켓을 사용하여 직류 마그네트론 스퍼터법에 의해 기판온도(RT, 400${\circ}C$), 잔류 $H_2O$ 분압(PH2O; 1.61${\times}10^{-4}∼2.2{\times}10^{-3}$ Pa), $H_2$ 가스 첨가(8.5%), 캐소드의 자장강도(250, 1000G)등의 다양한 조건하에서 제작했다. 기판 가열 없이 100% Ar를 사용한 경우, $P_{H_2O}$가 1.61${\times}10^{-4}$ Pa에서 2.2${\times}10^{-3}$ Pa로 증가 했을 때, 박막의 결정립 크기는 24 nm에서 3 nm로 감소했으며, 비저항은 3.0${\times}10^{-3}$에서 3.1${\times}10^{-2}{\Omega}㎝$ 로 크게 증가함을 보였다. 그러나, 8.5% $H_2$를 Ar 가스에 혼합하여 제막한 결과, GZO 박막의 전기적 특성은 $P_{H_2O}$의 증가에도 불구하고 변화 없이 나타났다. 또한 캐소드의 자장강도를 250G에서 1000G로 증가시킨 경우, GZO 박막의 결정성 및 전기적 특성은 $P_{H_2O}$와 상관없이 크게 향상되었으며, 이것은 플라즈마 임피던스의 감소에 따른 박막 손상의 감소에 기인한다고 생각된다.

• 반도체디스플레이기술학회지
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• 제8권3호
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• pp.57-60
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• 2009

Transparent electrode ZnO:Al(AZO)films were deposited on a PES (polyethersulfone) polymer substrate for thin film solar cells applications. A PES substrate with a thickness of 0.2mm and transmittance > 90% in the visible range was used because it is light weight and can deform easily. AZO thin films were prepared at a fixed DC power, $PO_2\;=\;P(O_2)/[P(O_2)\;+\;P(Ar)]$, and various substrate temperatures. The properties of AZO thin films were examined by X-ray diffraction, UV/VIS spectroscopy, four-point probe, Hall measurements, and field emission scanning electron microscopy. The lowest resistivity of all the films was $4.493\;{\times}\;10^{-4}\;[\Omega-cm]$ and the transmittance was > 80% in the visible range.

• 한국전기전자재료학회논문지
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• 제22권2호
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• pp.128-131
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• 2009

Silicon carbide (SiC) has attracted significant attention for high frequency, high temperature and high power devices due to its superior properties such as the large band gap, high breakdown electric field, high saturation velocity and high thermal conductivity. We performed Al ion implantation processes on n-type 4H-SiC substrate using a SILVACO ATHENA numerical simulator. The ion implantation model used Monte-Carlo method. We simulated the effect of channeling by Al implantation in both 0 off-axis and 8 off-axis n-type 4H-SiC substrate. We have investigated the effect of varying the implantation energies and the corresponding doses on the distribution of Al in 4H-SiC. The controlled implantation energies were 40, 60, 80, 100 and 120 keV and the implantation doses varied from $2{\times}10^{14}$ to $1{\times}10^{15}\;cm^{-2}$. The Al ion distribution was deeper with increasing implantation energy, whereas the doping level increased with increasing dose. The effect of post-implantation annealing on the electrical properties of Al-implanted p-n junction diode were also investigated.

• Journal of Electrochemical Science and Technology
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• 제3권4호
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• pp.178-184
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• 2012

A porous nickel (P-Ni) substrate was prepared by selective leaching of zinc from pressed pellets containing powders of Ni & Zn in 4 M NaOH solution. Anodic deposition of manganese oxide onto the porous Ni substrate ($MnO_x$/P-Ni) formed nano-flakes of manganese oxide layers as revealed in SEM studies. Pseudocapacitance of this oxide electrode was evaluated by cyclic voltammetry (CV) and chronopotentiometry (CHP) in 2 M NaOH solution. The specific capacitance of the Mn oxide electrode was as high as 1515 F $g^{-1}$, which was ten times higher than Mn oxide deposited on a flat Ni-ribbon. 80% of capacity was retained after 200 charge/discharge cycles. The system showed no loss of activity in dry form over period of days. The impedance studies indicated highly conducting $MnO_x$/P-Ni substance and the obtained specific capacitance from impedance data showed good agreement with the charge/discharge measurements.

• 미생물학회지
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• 제14권3호
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• pp.117-127
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• 1976

A cellulase fraction (F IV-1) purified to about 8-folds was obtained from crude cellulase prepared from the wheat bran culture of S.atra. The partial purification of the enzyme was made by DEAE Sephadex and Sephdex cloumn chromatography in conjuction with ammonium sulfate precipitation. After stading at various pH's for 22 hours at $20^{\circ}C$, F IV-1 was most stable at pH 5.0 but when the enzyme fraction was stood for 74 hours, the point of pH stability was raised to around pH 6.0-7.0. After heating at various temperatures for 1 hour, F IV-1 was most stable at $20^{\circ}C$. The optimal enzyme activities of F IV-1 were seen at pH 6.0 and $50^{\circ}C$. The optimal concentrations of $Zn^{++}\;and\;Ca^{++}$ for the activities of crude cellulase were 6 and 4 mM respectively, but $Ca^{++}$ inhibited the enzyme activity at concentrations below 2 mM and above 6mM. Both $Cu^{++}\;and\;Mn^{++}$ ions inhibited cellulase activities and a ocmplete inactivation of crude cellulase was achieved at concentratioins of 5 and 2 mM of ions respectively. When Na-CMC was used as substrate, the Km values of crude cellulase and F IV-1 were calculated to be $5{\times}10^{-4}\;and\;2{\times}10^{-5}mM$, and V values 32 and 1.35 mmoles/hour, respectively. The Ki values of $Mn^{++}$ for crude cellulase and F IV-1 were found to be $8{\times}10^{-2}\;and\;3{\times}10^{-2}\;mM\;while\;those\;of\;Cu^{++}\;were\;at\;2{\times}10^{-1}\;and\;1{\times}10^{-1}\;mM\;respectively.\;Both\;Mn^{++}\;and\;Cu^{++}$ showed competitive inhibition with substrate.

• 한국세라믹학회지
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• 제37권7호
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• pp.665-672
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• 2000

The ferroelectric YMnO3 thin films were prepared by MOD(metal-organic decomposition) method with Y- and Mn-acetylacetonate as starting materials. Thin films were grown on various substrates by spin-coating technique. The crystalline phases of the thin films were identified by X-ray diffractometer as a function of heat-treatment temperature, pH of coating solution and substrate. In addition, the effect of Mn/Y molar ratio(0.8~1.2) on the formation of hexagonal-YMnO3 phase was investigated. In forming highly c-axisoriented hexagonal-YMnO3 single phase, the Pt coated Si substrate was more effective than the bare Si substrate, and the optimum heat-treatment condition was at 82$0^{\circ}C$ for 30 min. Higher Mn/Y molar ratio within 0.8~1.2 and pH of YMnO3 precursor solution within 0.5~2.5 favored formation of ferroelectric hexagonal phase rather than orthorhombic phase. Leakage current density of the hexagonal-YMnO3 thin film formed on Pt(111)/TiO2/SiO2/Si substrate was low enough as 0.4~4.0$\times$10-8(A/$\textrm{cm}^2$) at 5 V and its remanent polarization(Pr), calculated from the P-E hysteresis loop, was 3 nC/$\textrm{cm}^2$.

• 한국세라믹학회지
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• 제35권4호
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• pp.364-370
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• 1998

광집적회로용 평면도파로를 구현하기 위한 $B_2O_3-P_2O_5-SiO_2$ 실리카 광도파막을 실리콘 기판위에 FDH(Flame Hydrolysis Depositon)법으로 제조하여 미립자의 미세구조, 실리카막의 굴절률과 조성을 고찰하였다. FHD법에서 도펀트(dopant)물질로, $B_1\;P_1\;Ge$ 등의 산화물이 사용되며, $B_1$ Ge 산화물의 경우 $SiO_2$와의 결합특성이 우수하여 비교적 도핑(doping)이 용이하지만 P의 경우 $P_2O_5$의 낮은 융점에 의한 증발 등으로 효과적인 도핑이 어렵다. 수직형 FHD 토치를 사용하고 화염온도, 기판온도, 토치와 기판간의 거리를 최적화하여 P 농도가 3.3 Wt%이상이고 고밀화 온도가 $1180^{\circ}C$ 이하인 양질의 실리카막을 얻었다. 실리카막의 굴절률은 $1.55\;\mu\textrm{m}$ 파장에서 $1.4480{\pm}1{\times}10^{-1}$로 측정되었으며, $22{\pm}1\;\mu\textrm{m}$의 두께를 보였다.