• Journal of Photoscience
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• 제4권1호
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• pp.11-16
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• 1997

We measured, using femtosecond pump-probe experiment, the time evolution of transient absorption in aqueous CdS colloids. The signal rises within the time resolution (= 0.5 ps) of the experiment and decays with two exponential time constants, 4.8 ps and 132 ps. The ultrafast rise of the transient absorption is considered to be for shallowly trapped conduction band electrons after photoexcitation. The amplitude ratio of the two decaying components varies with the pump intensity and the decay times increase in the presence of hole scavengers. Even though a biexponential function fits the decay well, we object hat two independent first order processes (geminate and nongeminate recombinations) are responsible for the decay. A function with an integrated rate equation for second order nongeminate recombination plus a long background fits the decay well. The long background is considered to be for deeply trapped charges at the CdS particle.

• 한국생물물리학회:학술대회논문집
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• 한국생물물리학회 2003년도 정기총회 및 학술발표회
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• pp.32-32
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• 2003

In the neuron, SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) assembly plays a central role in driving membrane fusion, a required process for neurotransmitter release. In the cytoplasm, vesicular SNARE VAMP2 (vesicle-associated membrane protein 2) engages with two plasma membrane SNAREs syntaxin 1A and SNAP-25 (synaptosome-associated protein of 25 kDa) to form the core complex that bridges two membranes. While various factors regulate SNARE assembly, the membrane also plays the regulatory role by trapping VAMP2 in the membrane. The fluorescence and EPR analyses revealed that the insertion of seven C-terminal core-forming residues into the membrane controls complex formation of the entire core region, even though preceding 54 core-forming residues are fully exposed and freely moving. When two interfacial Trp residues in this region were replaced with hydrophilic serine residues, the mutation supported rapid complex formation.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.254-260
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• 2014

Organic solar cells have attracted extensive attention as a promising approach for cost-effective photovoltaic devices. However, organic solar cell has disadvantage of low power conversion efficiency in comparison with other type of solar cell, due to the recombination ratio of hole and electron is too large in the active layer. Thus we have change the surface structure of PEDOT:PSS layers to improve the current density by colloidal lithography method using various-size of polystyrene sphere. The two types of coating method were applied to fabricate the different pattern shape and height, such as spin coating and drop casting. Using the organic solvent, we easily eliminate the PS sphere and could make the varied pattern shapes by controlling the wet etching time. Also we have measured the electrical properties of patterned PEDOT:PSS film to check whether it is suitable for organic photovoltaics.

• 한국정보통신학회논문지
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• 제18권5호
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• pp.1149-1154
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• 2014

본 연구는 산화물반도체트랜지스터의 터널링 현상을 살펴보기 위해서 게이트 절연막으로서 SiOC 박막을 사용하고 채널층으로 IGZO를 이용하여 트랜지스터를 제작 하였다. SiOC 박막은 분극이 작아질수록 비정질특성이 우수해지면서 절연특성이 좋아진다. SiOC 게이트 절연막과 채널 층 사이의 계면에 존재하는 접합특성은 SiOC의 분극특성에 따라서 달려졌다. 드레인소스 전류($I_{DS}$)와 게이트소스 전압($V_{GS}$)의 전달특성은 분극이 낮은 SiOC를 사용할 경우 양방향성 전달특성이 나타나고 분극이 높은 SiOC 게이트 절연막을 사용할 경우 단방향성 전달 특성이 나타났다. 터널링에 의한 양방향성 트랜지스터의 경우 바이어스 인가 전압이 낮은 ${\pm}1V$의 영역에서 쇼키접합을 나타냈었지만 트래핑효과에 의한 단방향성 트랜지스터의 경우 오믹접합 특성을 나타내었다. 특히 양방향성 트랜지스터의 경우 터널링 현상에 의하여 on/off 스위칭 특성이 개선되었다.

• 대한전자공학회논문지SD
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• 제41권11호
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• pp.7-13
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• 2004

두께가 약 3 nm 인 게이트 산화막을 갖는 P 및 NMOSFET를 제조하여 높은 압력 (5 atm.)의 중수소 및 수소 분위기에서 후속 열처리를 각각 행하여 중수소 효과(동위원소 효과)를 관찰하였다. 소자에 대한 스트레스는 -2.5V ≤ V/sub g/ ≤-4.0V 범위에서 100℃의 온도를 유지하며 진행되었다. 낮은 스트레스 전압에서는 실리콘 계면에 존재하는 정공에 의하여 게이트 산화막의 열화가 진행되었다. 그러나 스트레스 전압을 증가시킴으로써 높은 에너지를 갖는 전자에 의한 계면 결함 생성이 열화의 직접적인 원인이 됨을 알 수 있었다. 본 실험조건에서는 실리콘 계면에서 phonon 산란이 많이 발생하여 impact ionization에 의한 "hot" 정공의 생성은 무시할 수 있었다. 중수소 열처리를 행함으로써 수소 열처리에 비해 소자의 파라미터 변화가 적었으며, 게이트 산화막의 누설전류도 억제됨이 확인되었다. 이러한 결과로부터 impact ionization이 발생되지 않을 정도의 낮은 스트레스 전압동안 발생하는 게이트 산화막내 결함 생성은 수소 결합과 직접적인 관계가 있음을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.254.2-254.2
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• 2014

The Transmission Fourier Transform Infrared spectroscopy (FTIR) of SiOx charge storage layer with the richest silicon content showed an assignment at peaks around 2000~2300 cm-1. It indicated that the existence of many silicon phases and defect sources in the matrix of the SiOx films. The total hysteresis width is the sum of the flat band voltage shift (${\Delta}VFB$) due to electron and hole charging. At the range voltage sweep of ${\pm}15V$, the ${\Delta}VFB$ values increase of 0.57 V, 1.71 V, and 13.56 V with 1/2, 2/1, and 6/1 samples, respectively. When we increase the gas ratio of SiH4/N2O, a lot of defects appeared in charge storage layer, more electrons and holes are charged and the memory window also increases. The best retention are obtained at sample with the ratio SiH4/N2O=6/1 with 82.31% (3.49V) after 103s and 70.75% after 10 years. The high charge storage in 6/1 device could arise from the large amount of silicon phases and defect sources in the storage material with SiOx material. Therefore, in the programming/erasing (P/E) process, the Si-rich SiOx charge-trapping layer with SiH4/N2O gas flow ratio=6/1 easily grasps electrons and holds them, and hence, increases the P/E speed and the memory window. This is very useful for a trapping layer, especially in the low-voltage operation of non-volatile memory devices.

• Bulletin of the Korean Chemical Society
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• 제23권9호
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• pp.1229-1258
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• 2002

This paper reports the photochemical reduction of benzil 1 to benzoin 2 and the reduction of 2 to hydrobenzoin 4 in deoxygenated solvents in the presence of triethylamine (TEA) and/or TiO2. Without TEA or TiO2, the photolysis of 1 resulted in very low yield of 2. The presence of TEA or TiO2 increased the rate of disappearance of 1 and the yield of 2, which were further increased considerably by the presence of water. The photoreduction of 1 to 2 proceeds through an electron transfer to 1 from TEA or hole-scavenged excited TiO2 followed by protonation. In the reaction medium of 88 : 7 : 2 : 3 CH3CN/CH3OH/H2O/TEA with 2.5 $㎎/m{\ell}$ of TiO2, the yield of 2 was as high as 85 % at 50 % conversion of 1. The photolysis of 2 in homogeneous media resulted in photo-cleavage to benzoyl and hydroxybenzyl radicals, which are mostly converted to benzaldehyde. The reduction product 4 is formed in low yield through the dimerization of hydroxybenzyl radicals. The addition of TEA increased the conversion rate of 2 and the yield of 4 significantly. This was attributed to the scavenging effect of TEA for benzoyl radical to produce N,N-diethylbenzamide and the photoreduction of benzaldehyde in the presence of TEA. The ratio of $(\pm)$ and meso isomers of 4 obtained from the photochemical reaction is about 1.1. This ratio is the same as that from the photochemical reduction of benzaldehyde in the presence of TEA. In the TiO2-sensitized photochemical reduction of 2, meso-4 was obtained in moderate yield. The reduction of 2 to 4 proceeds through two consecutive electron/proton transfer processes on the surface of the photocatalyst without involvement of ${\alpha}-cleavage$. The radical 11 initially formed from 2 by one electron/proton process can also combine with hydroxy methyl radical, which is generated after hole trapping of excited TiO2 by methanol, to produce 1,2-diphenylpropenone after dehydration reaction.

• 공업화학
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• 제22권1호
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• pp.26-30
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• 2011

염료 감응형 태양전지의 에너지 전환 효율을 향상시키고자 $TiO_2$에 $WO_3$을 첨가하여 광전극을 제조하고 그 전기화학적 특성 평가를 하였다. 또한 $WO_3$가 첨가된 $TiO_2$를 회쇄함으로써 회쇄 효과가 전지효율에 미치는 영향을 고찰하였다. I-V 곡선을 통하여 측정된 염료 감응형 태양전지의 효율은 $WO_3$ 첨가 및 회쇄 효과에 의하여 2.8에서 6.0%로 크게 증가하였다. 이와 같은 결과는 $TiO_2$의 전도대에서 전달되는 전자가 염료 및 전해질과 재결합되기 전에 $TiO_2$의 전도대보다 낮은 $WO_3$의 전도대를 통해 전달되기 때문에 전체 전류의 양이 증가되어 효율이 증가한 것으로 여겨진다. 또한, 임피던스 결과로부터 $TiO_2$/염료/전해질 계면의 저항 값이 감소하는 것을 확인하였다.

• Archives of Pharmacal Research
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• 제19권4호
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• pp.280-285
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• 1996

The sustained release dosage form which delivers melatonin (MT) in a circadian fashion over 8 h is of clinical value for those who have disordered circadian rhythms because of its short halflife. The purpose of this study was to evaluate the gelling properties and release characteristics of alginate beads varying multivalent cationic species $(Al^{+++}, \; Ba^{++}, \; Ca^{++}, \; Mg^{++}, \; Fe^{+++}, \; Zn^{++})$. The surface morphologies of Ca- and Ba-alginate beads were also studied using scanning electron microscope (SEM). MT, an indole amide pineal hormone was used as a model drug. The $Ca^{++}, \; Ba^{++}, \; Zn^{++}, \; Al^{++}\; and\; Fe^{+++}\; ions\; except\; Mg^{++}$ induced gelling of sodium alginate. The strength of multivalent cationic alginate beads was as follows: $Al^{+++}\llFe^{+++} the induced hydrogel beads were very fragile and less spherical. Fe-alginate beads were also fragile but stronger compared to Al-alginate beads. Ba-alginate beads had a similar gelling strength but was less spherical when compared to Ca-alginate beads. Zn-alginate beads were weaker than Ca- and Ba-alginate beads. Very crude and rough crystals of Ba- and Ca-alginate beads at higher magnifications were observed. However, the type and shape of rough crystals of Ba- and Ca-alginate beads were quite different. No significant differences in release profiles from MT-loaded multivalent cationic alginate beads were observed in the gastric fluid. Most drugs were continuously released upto 80% for 5 h, mainly governed by the passive diffusion without swelling and disintegrating the alginate beads. In the intestinal fluid, there was a significant difference iq the release profiles of MT-loaded multivalent cationic alginate beads. The release rate of Ca-alginate beads was faster when compared to other multivalent cationic alginate beads and was completed for 3 h. Ba-alginate beads had a very long lag time (7 h) and then rapidly released thereafter. MT was continuously released from Feand Zn-alginate beads with initial burstout release. It is assumed that the different release rofiles of multivalent cationic alginate beads resulted from forces of swelling and disintegration of alginate beads in addition to passive diffusion, depending on types of multivalent ions, gelling strength and drug solubility. It was estimated that 0.2M $CaCl_2$ concentration was optimal in terms of trapping efficiency of MT and gelling strength of Ca-alginate beads. In the gastric fluid, Ca-alginate beads gelled at 0.2 M $CaCl_2$ concentration had higher bead strength, resulting in the most retarded release when compared to other concentrations. In the intestinal fluid, the decreased release of Ca-alginate beads prepared at 0.2 M $CaCl_2$ concentration was also observed. However, release profiles of Ca-alginate beads were quite similar regardless of $CaCl_2$ concentration. Either too low or high $CaCl_2$ concentrations may not be useful for gelling and curing of alginate beads. Optimal $CaCl_2$ concentrations must be decided in terms of trapping efficiency and release and profiles of drug followed by curing time and gelling strength of alginate beads.

• 한국재료학회지
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• 제20권7호
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• pp.345-350
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• 2010

For the present paper, we prepared MgO/MWCNT/$TiO_2$ photocatalyst by using multi-walled carbon nanotubes (MWCNTs) pre-oxidized by m-chlorperbenzoic acid (MCPBA) with magnesium acetate tetrahydrate $(Mg(CH_2COO)_2\cdot4H_2O)$ and titanium n-butoxide $(Ti\{OC(CH_3)_3\}_4)$ as magnesium and titanium precursors. The prepared photocatalyst was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The decomposition of methylene blue (MB) solution was determined under irradiation of ultraviolet (UV) light. The XRD results show that the MgO/MWCNT/$TiO_2$ photocatalyst have cubic MgO structure and anatase $TiO_2$ structure. The porous structure and the $TiO_2$ agglomerate coated on the MgO/MWCNT composite can be observed in SEM images. The Mg, O, Ti and C elements can be also observed in MgO/MWCNT/$TiO_2$ photocatalyst from EDX results. The results of photodegradation of MB solution under UV light show that the concentration of MB solution decreased with an increase of UV irradiation time for all of the samples. Also, the MgO/MWCNT/$TiO_2$ photocatalyst has the best photocatalytic activity among these samples. It can be considered that the MgO/MWCNT/$TiO_2$ photocatalyst had a combined effect, the effect of MWCNT, which could absorb UV light to create photoinduced electrons $(e^-)$, and the electron trapping effect of MgO, which resulted in an increase of the photocatalytic activity of $TiO_2$.