• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.537-543
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• 2013

In this study, the push-pull structure polymer for organic photo voHaics (OPVs) was synthesized and characterized. The poly{4,8-didodecyloxybenzo[1,2-b;3,4-b]dithiophene-alt-5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (PDBDT-TBTD) was synthesized by Stille coupling reaction using the benzothiadiazole (BTD) derivative as an electron acceptor and benzodithiophene (BDT) derivative as an electron donor. The structure of monomers and polymers was identified by $^1H-NMR$ and GC-MS. The optical, physical and electrochemical properties of the conjugated polymer were identified by GPC, TGA, UV-Vis and cyclic voltammetry. The number average molecular weight ($M_n$) and initial decomposition temperature (5% weight loss temperature, $T_d$) of PDBDT-TBTD were 6200 and $323^{\circ}C$, respectively. The absorption maxima on the film was about 599 nm and the optical band gap was about 1.70 eV. The structure of device was ITO/PEDOT : PSS/PDBDT-TBTD : $PC_{71}BM/BaF_2/Ba/Al$. PDBDT-TBTD and $PC_{71}BM$ were blended with the weight ratio of 1:2 which were then used as an optical active layer. The power conversion efficiency (PCE) of fabricated device was measured by solar simulator and the best PCE was 2.1%.

• Journal of the Korean Chemical Society
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• v.28 no.4
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• pp.210-216
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• 1984

Solvatochromic comparison methods were applied to determine Taft's solvent parameters, ${\pi}^{\ast}$(solvent polarity-polarizability), ${\alpha}$(solvent hydrogen bond donor acidity) and ${\beta}$ (solvent hydrogen bond acceptor basicity) for MeOH-MeCN solvent mixtures. Swain's solvent parameters A(anion solvation scale) and B(cation solvation scale) were also determined by least square fitting of kinetic data in the same binary solvent mixtures. It was found that: (i)${\beta}$ depends on the basicity of the solvent and increases with the MeOH content owing to the increase in polymeric structure of methanol; (ii) ${\pi}^{\ast}$depends on the dipole moment of the solvent and increases with the MeCN content of the solvent; (iii) ${\alpha}$ increases rapidly with the MeOH content as the hydrogen bond donor acidity of the solvent mixtures increases. Taft's reaction constants a and s and Swain's reaction constants a and b were determined for the reactions reported from our laboratory previously using solvent parameters determined in this work. No meaningful inter-relationship was found between the two set of reaction parameters, but a good linear correlation was found between the ratios a/s and a/b. Solvent effect on the reaction mechanism, substituent effect and leaving group ability were examined in the light of these reaction constants ratios.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.7
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• pp.8-16
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• 2010

In this paper, we investigated the effects of $O_2$ fraction on the properties of Al-doped ZnO (AZO) thin films prepared by radio frequency (RF) magnetron sputtering. Hall, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) measurements revealed that the p-type conductivity was exhibited for AZO films with an $O_2$ fraction of 0.9 while the n-type conductivity was observed for films with $O_2$ fractions in range of 0 - 0.6. PL and XPS also showed that the acceptor-like defects, such as zinc vacancies and oxygen interstitials, increased in films prepared by an $O_2$ fraction of 0.9, resulting in the p-type conductivity in the films. Hall results indicated that AZO films prepared by $O_2$ fractions in range of 0 - 0.6 can be used for electrode layers in the applications of transparent thin film transistor. We concluded from the X-ray diffraction analysis that worse crystallinity with a smaller grain size as well as higher tensile stress was observed in the films prepared by a higher $O_2$ fraction, which is related to incorporation of more oxygen atoms into the films during deposition. The study of atomic force microscope suggested that the smoother surface morphology was observed in films prepared by using $O_2$ fraction, which causes the higher resistivity in those films, as evidenced by Hall measurements.

• Journal of the Korean Chemical Society
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• v.47 no.3
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• pp.206-212
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• 2003

The reaction rates of substituted quinolines (6-Clqui., qui.) with p-substituted benzoylchlorides $(p-CH_3,\;p-H,\;p-NO_2)$ have been measured by conductometry in acetonitrile, and the rate constants are determined at various temperatures (10, 15, 20, $25^{\circ}C$) and pressures (1, 200, 500, 1000 bar). From the values of rate constants, the activation parameters $(Ea,\;{\Delta}V^{\neq},\;{\Delta}H^{\neq},\;{\Delta}S^{\neq}, \;{\Delta}G^{\neq})$and the pressure dependence of Hammett ρ values were determined. The rate constants increased with increasing temperatures and pressures, and are further increased to introduction to the electron acceptor substituents in substrate $(p-NO_2)$ with quinoline. The activation volume and the activation entropy are all negative. And the Hammett p values are negative for nucleophile ${\rho}_X$ and positive for the substrate ${\rho}_Y$ over the pressure range studied. The results of kinetic studies for pressure and substituent show that these reactions proceed through a typical $S_N2$ reaction mechanism and "associative $S_N2$" favoring bond formation with increasing pressures.

• Journal of the Korean Chemical Society
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• v.58 no.6
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• pp.535-542
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• 2014

A simple and efficient preconcentration method was developed using three-phase liquid phase microextraction prior to HPLC-UV for simultaneous extraction and determination of tetracycline antibiotics (tetracycline, oxytetracycline, and chlortetracycline). The tetracycline antibiotics were separated simultaneously on a column ($C_8$, $3.0{\times}150mm$, $3{\mu}m$) with high selectivity and sensitivity using gradient elution. Under optimized conditions (extraction solvent, heptanal; pH of donor, 9.0; pH of acceptor, 1.0; stirring speed, 700 rpm; NaCl salt, 0%; and extraction time, 60 min), enrichment factors (EF) were between 5.6 and 22.3. The limit of detection (LOD) and limit of quantitation (LOQ) in the spiked urine matrix were in the concentration range of $0.08{\sim}0.8{\mu}g/mL$ and $0.4{\sim}1.6{\mu}g/mL$, respectively. The calibration curves were linear within the range of $0.1{\sim}32{\mu}g/mL$ with the square of the correlation coefficient being more than 0.995. The precision (as a relative standard deviation, RSD) and accuracy (as a relative recovery) within working range were 1.3~9.1% and 84~118%, respectively.

• Korean Journal of Crystallography
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• v.12 no.3
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• pp.127-136
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• 2001

A stoichiometric mixture of evaporating materials for ZnGa₂Se₄single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, ZnGa₂Se₄mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 610℃ and 450℃, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of ZnGa₂Se₄single crystal thin films measured from Hall effect by von der Pauw method are 9.63×10/sup 17/㎤ and 296 ㎠/V·s at 293 K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the ZnGa₂Se₄single crystal thin film, we have found that the values of spin orbit splitting △so and the crystal field splitting Δcr were 251.9meV and 183.2 meV at 10 K, respectively. From the photoluminescence measurement on th ZnGa₂Se₄single crystal thin film, we observed free excition (Ex) existing only high quality crystal and neutral bound exiciton (A°, X) having very strong peak intensity. Then, the full-width-at-half-maximum (FWHM) and binding energy of neutral acceptor bound excition were 11 meV and 24.4 meV, respectivity. By Haynes rule, an activation energy of impurity was 122 meV.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.35 no.4
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• pp.271-276
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• 2009

The 3-dimensional quantitative structure-activity relationships (3D-QSARs) models between the substituents with changing groups ($R_1$ & $R_2$) of 4-($R_1$)-benzyl alcohol and 4-($R_2$)-phenol derivatives as substrate molecule and their inhibitory activities against tyrosinase were derived and discussed quantitatively. The optimized CoMSIA 2 model have best predictability and fitness ($r^2\;=\;0.858$ & $q^2\;=\;0.951$). The contour maps of optimized CoMSIA 2 model showed that, the inhibitory activities of the analogues against tyrosinase were expected to increase when hydrophobic favor, negative charge favor, steric disfavor and hydrogen bond donor disfavor groups were substituted at the $R^2$ position. When the positive charge and the hydrogen bond donor favor groups were substituted at the $R_1$ position, it is predicted that the substituents will be able to increase the inhibitory activity. However, hydrogen bond acceptor did not affect inhibitory activities of tyrosinase.

• BMB Reports
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• v.31 no.6
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• pp.590-594
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• 1998

X-ray crystallographic studies of the deoxy form of human adult hemoglobin (Hb A) have shown that ${\beta}99Asp$ is hydrogen bonded to both ${\alpha}42Tyr$ and ${\alpha}97Asn$ in the ${\alpha}_1{\beta}_2$ subunit interface, suggesting that the essential role of ${\beta}99Asp$ is to stabilize the deoxy-Hb by creating the intersubunit hydrogen bond. In particular, for Hb Kempsey (${\beta}99Asp{\rightarrow}Asn$), molecular dynamics simulation indicated that a new hydrogen bond involving ${\beta}99Asn$ can be induced by replacing ${\alpha}42Tyr$ with a strong hydrogen-bond acceptor such as Asp. Designed mutant recombinant (r) Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$) have been produced in the Escherichia coli expression system and have shown that functional defects of Hb Kempsey could be compensated by the ${\alpha}42Tyr{\rightarrow}Asp$ substitution. However, as the ${\alpha}42 Tyr{\rightarrow}Asp$ mutation has never been reported before, it is still possible that the functional properties of r Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$) may be due to the mutation itself. Thus, it is required to produce r Hb (${\alpha}42Tyr{\rightarrow}Asp$) and r Hb Kempsey (${\beta}99Asp{\rightarrow}AsnX$( as controls, and to compare their properties with those of r Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$). r Hb (${\alpha}42Tyr{\rightarrow}Asp$) could not be purified because it is an unstable hemoglobin which forms Heinz bodies. r Hb Kempsey (${\beta}99Asp{\rightarrow}Asn$) exhibits very high oxygen affinity and greatly reduced cooperativity. Thus, r Hb (${\beta}99Asp{\rightarrow}Asn$) and r Hb (${\alpha}42Tyr{\rightarrow}Asp)$ compensate each other.

• Asian-Australasian Journal of Animal Sciences
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• v.25 no.6
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• pp.812-817
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• 2012

Nitrate can serve as a terminal electron acceptor in place of carbon dioxide and inhibit methane emission in the rumen and nitrate reducing bacteria might help enhance the reduction of nitrate/nitrite, which depends on the type of feed offered to animals. In this study the effects of three levels of sodium nitrate (0, 5, 10 mM) on fermentation of three diets varying in their wheat straw to concentrate ratio (700:300, low concentrate, LC; 500:500, medium concentrate, MC and 300:700, high concentrate, HC diet) were investigated in vitro using buffalo rumen liquor as inoculum. Nitrate reducing bacteria, isolated from the rumen of buffalo were tested as a probiotic to study if it could help in enhancing methane inhibition in vitro. Inclusion of sodium nitrate at 5 or 10 mM reduced (p<0.01) methane production (9.56, 7.93 vs. 21.76 ml/g DM; 12.20, 10.42 vs. 25.76 ml/g DM; 15.49, 12.33 vs. 26.86 ml/g DM) in LC, MC and HC diets, respectively. Inclusion of nitrate at both 5 and 10 mM also reduced (p<0.01) gas production in all the diets, but in vitro true digestibility (IVTD) of feed reduced (p<0.05) only in LC and MC diets. In the medium at 10 mM sodium nitrate level, there was 0.76 to 1.18 mM of residual nitrate and nitrite (p<0.01) also accumulated. In an attempt to eliminate residual nitrate and nitrite in the medium, the nitrate reducing bacteria were isolated from buffalo adapted to nitrate feeding and introduced individually (3 ml containing 1.2 to $2.3{\times}10^6$ cfu/ml) into in vitro incubations containing the MC diet with 10 mM sodium nitrate. Addition of live culture of NRBB 57 resulted in complete removal of nitrate and nitrite from the medium with a further reduction in methane and no effect on IVTD compared to the control treatments containing nitrate with autoclaved cultures or nitrate without any culture. The data revealed that nitrate reducing bacteria can be used as probiotic to prevent the accumulation of nitrite when sodium nitrate is used to reduce in vitro methane emissions.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.143-144
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• 2010

3-5족 화합물 반도체를 이용한 집광형 삼중 접합 태양전지는 40% 이상의 광변환 효율로 많은 주목을 받고 있다[1]. 삼중 접합 태양전지의 하부 셀은 기계적 강도가 높고 장파장을 흡수할 수 있는 Ge이 사용된다. Ge위에 성장될 III-V족 단결정막으로서 Ge과 격자상수가 일치하는 GaInP나 GaAs가 적합하고, 성장 중 V족 원소의 열확산으로 인해 Ge과 pn접합을 형성하게 된다. 이때 GaInP의 P의 경우 GaAs의 As보다 확산계수가 낮아 태양전지 변환효율향상에 유리한 얇은 접합 형성이 가능하고, 표면 에칭효과가 적기 때문에 GaInP를 단결정막으로 선택하여 p-type Ge기판 위 성장으로 단일접합 Ge구조 제작이 가능하다. 하지만 이종접합 구조 성장으로 인해 발생한 계면사이의 전위나 미세결함들이 결정막내부에 존재하게 되며 이러한 결함들은 광학소자 응용 시 비발광 센터로 작용할 뿐 아니라 소자의 누설전류를 증가시키는 원인으로 작용하여 태양전지 변환효율을 감소시키게 된다. 이에 결함감소를 통해 소자의 전기적 특성을 향상시키고자 수소 열처리나 플라즈마 공정을 통해 수소 원자를 박막내부로 확산시키고, 계면이나 박막 내 결함들과 결합시킴으로서 결함들의 비활성화를 유도하는 연구가 많이 진행되어 왔다 [2][3]. 하지만, 격자불일치를 갖는 GaInP/Ge 구조에 대한 수소 열처리 및 불순물 준위의 거동에 대한 연구는 많이 진행되어 있지 않다. 따라서 본 연구에서는 Ga0.45In0.55P/Ge구조에 수소 열처리 공정을 적용을 통하여 단결정막 내부 및 계면에서의 결함밀도를 제어하고 이를 통해 태양 전지의 변환효율을 향상시키고자 한다. <111> 방향으로 $6^{\circ}C$기울어진 p-type Ge(100) 기판 위에 유기금속화학증착법 (MOCVD)을 통해 Si이 도핑된 200 nm의 n-type GaInP층을 성장하여 Ge과 단일접합 n-p 구조를 제작하였다. 제작된 GaInP/Ge구조를 furnace에서 250도에서 90~150분간 시간변화를 주어 수소열처리 공정을 진행하였다. 저온 photoluminescence를 통해 GaInP층의 광학적 특성 변화를 관찰한 결과, 1.872 eV에서 free-exciton peak과 1.761 eV에서 Si 도펀트 saturation에 의해 발생된 D-A (Donor to Acceptor)천이로 판단되는 peak을 검출할 수 있었다. 수소 열처리 시간이 증가함에 따라 free-exciton peak 세기 증가와 반가폭 감소를 확인하였고, D-A peak이 사라지는 것을 관찰할 수 있었다. 이러한 결과는 수소 열처리에 따른 단결정막 내부의 수소원자들이 얕은 불순물(shallow impurity) 들로 작용하는 도펀트들이나, 깊은 준위결함(deep level defect)으로 작용하는 계면근처의 전위, 미세결함들과의 결합으로 결함 비활성화를 야기해 발광세기와 결정질 향상효과를 보인 것으로 판단된다. 본 발표에서는 상술한 결과를 바탕으로 한 수소 열처리를 통한 박막 및 계면에서의 결함준위의 거동에 대한 광분석 결과가 논의될 것이다.