• 한국재료학회지
• /
• 제24권5호
• /
• pp.243-248
• /
• 2014

Silicon-carbon composite was prepared by the magnesiothermic reduction of mesoporous silica and subsequent impregnation with a carbon precursor. This was applied for use as an anode material for high-performance lithium-ion batteries. Well-ordered mesoporous silica(SBA-15) was employed as a starting material for the mesoporous silicon, and sucrose was used as a carbon source. It was found that complete removal of by-products ($Mg_2Si$ and $Mg_2SiO_4$) formed by side reactions of silica and magnesium during the magnesiothermic reduction, was a crucial factor for successful formation of mesoporous silicon. Successful formation of the silicon-carbon composite was well confirmed by appropriate characterization tools (e.g., $N_2$ adsorption-desorption, small-angle X-ray scattering, X-ray diffraction, and thermogravimetric analyses). A lithium-ion battery was fabricated using the prepared silicon-carbon composite as the anode, and lithium foil as the counter-electrode. Electrochemical analysis revealed that the silicon-carbon composite showed better cycling stability than graphite, when used as the anode in the lithium-ion battery. This improvement could be due to the fact that carbon efficiently suppressed the change in volume of the silicon material caused by the charge-discharge cycle. This indicates that silicon-carbon composite, prepared via the magnesiothermic reduction and impregnation methods, could be an efficient anode material for lithium ion batteries.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
• /
• pp.377-377
• /
• 2012

Microprocessor technology now relies on copper for most of its electrical interconnections. Because of the high diffusivity of copper, Atomic layer deposition (ALD) $TaN_x$ is used as a diffusion barrier to prevent copper diffusion into the Si or $SiO_2$. Another problem with copper is that it has weak adhesion to most materials. Strong adhesion to copper is an essential characteristic for the new barrier layer because copper films prepared by electroplating peel off easily in the damascene process. Thus adhesion-enhancing layer of cobalt is placed between the $TaN_x$ and the copper. Because, cobalt has strong adhesion to the copper layer and possible seedless electro-plating of copper. Until now, metal film has generally been deposited by physical vapor deposition. However, one draw-back of this method is poor step coverage in applications of ultralarge-scale integration metallization technology. Metal organic chemical vapor deposition (MOCVD) is a good approach to address this problem. In addition, the MOCVD method has several advantages, such as conformal coverage, uniform deposition over large substrate areas and less substrate damage. For this reasons, cobalt films have been studied using MOCVD and various metal-organic precursors. In this study, we used $C_{12}H_{10}O_6(Co)_2$ (dicobalt hexacarbonyl tert-butylacetylene, CCTBA) as a cobalt precursor because of its high vapor pressure and volatility, a liquid state and its excellent thermal stability under normal conditions. Furthermore, the cobalt film was also deposited at various $H_2/NH_3$ gas ratio(1, 1:1,2,6,8) producing pure cobalt thin films with excellent conformality. Compared to MOCVD cobalt using $H_2$ gas as a reactant, the cobalt thin film deposited by MOCVD using $H_2$ with $NH_3$ showed a low roughness, a low resistivity, and a low carbon impurity. It was found that Co/$TaN_x$ film can achieve a low resistivity of $90{\mu}{\Omega}-cm$, a low root-mean-square roughness of 0.97 nm at a growth temperature of $150^{\circ}C$ and a low carbon impurity of 4~6% carbon concentration.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.222-222
• /
• 2012

Metal oxide gas sensors based on semiconductor type have attracted a great deal of attention due to their low cost, flexible production and simple usability. However, most works have been focused on n-type oxides, while the characteristics of p-type oxide gas sensors have been barely studied. An investigation on p-type oxides is very important in that the use of them makes possible the novel sensors such as p-n diode and tandem devices. Monoclinic cupric oxide (CuO) is p-type semiconductor with narrow band gap (~1.2 eV). This is composed of abundant, nontoxic elements on earth, and thus low-cost, environment-friendly devices can be realized. However, gas sensing properties of neat CuO were rarely explored and the mechanism still remains unclear. In this work, the neat CuO layers with highly ordered mesoporous structures were prepared by a template-free, one-pot solution-based method using novel ink solutions, formulated with copper formate tetrahydrate, hexylamine and ethyl cellulose. The shear viscosity of the formulated solutions was 5.79 Pa s at a shear rate of 1 s-1. The solutions were coated on SiO2/Si substrates by spin-coating (ink) and calcined for 1 h at the temperature of $200{\sim}600^{\circ}C$ in air. The surface and cross-sectional morphologies of the formed CuO layers were observed by a focused ion beam scanning electron microscopy (FIB-SEM) and porosity was determined by image analysis using simple computer-programming. XRD analysis showed phase evolutions of the layers, depending on the calcination temperature, and thermal decompositions of the neat precursor and the formulated ink were investigated by TGA and DSC. As a result, the formation of the porous structures was attributed to the vaporization of ethyl cellulose contained in the solutions. Mesoporous CuO, formed with the ink solution, consisted of grains and pores with nano-meter size. All of them were strongly dependent on calcination temperature. Sensing properties toward H2 and C2H5OH gases were examined as a function of operating temperature. High and fast responses toward H2 and C2H5OH gases were discussed in terms of crystallinity, nonstoichiometry and morphological factors such as porosity, grain size and surface-to-volume ratio. To our knowledge, the responses toward H2 and C2H5OH gases of these CuO gas sensors are comparable to previously reported values.

• Korean Chemical Engineering Research
• /
• 제55권1호
• /
• pp.121-129
• /
• 2017

$TiO_2$, $Al_2O_3$, $ZrO_2$, $SiO_2$와 같은 다양한 담체에 습식함침법을 이용하여 Pd 기반 촉매를 제조하여 일산화탄소 존재하에 수소의 선택적 산화반응에 적용하였다. 제조된 촉매는 물리화학적 특성을 알아보기 위하여 XRD, $N_2$ 흡착, CO-, (CO+$H_2O$)-TPD, CO-TPR, XPS등의 특성분석을 수행하였다. CO-TPD와 (CO+$H_2O$)-TPD를 통해 $CO_2$ 탈착에 대한 $H_2O$의 영향을 알아보았으며 이러한 TPD 결과는 $H_2/CO$ 전환율과 상관관계가 있음을 확인하였다. 사용된 촉매 중에서 $Pd/ZrO_2$가 $H_2$ 전환율 측면에서 가장 활성이 좋은 것으로 나타났다. $H_2O$가 첨가된 선택적 $H_2$ 산화반응에서는 $H_2O$, CO, $H_2$가 경쟁흡착을 하였으며, 첨가된 $H_2O$가 CO 및 $H_2$의 반응을 촉진시켰다.

• 한국결정성장학회지
• /
• 제7권3호
• /
• pp.428-436
• /
• 1997

0.8$\mu$의 평균입자크기와 63$m^2/g$의 비표면적을 갖는 소질성이 뛰어난 hexacelsian분말이 so;ution-polymerization 방법에 의해 제조되어졌다. polymerization 경정을 통한 분말합성을 위하여 PVA 용액이 사용되었다. 소결후 치밀화된 hexacelsian은 $\alpha$,$\beta$,$\gamma$ 간의 상전이 거동을 보였고, 상대밀도 98.5% 의 치밀화ㄱ된 celsian 소결체가 $1600^{\circ}C$에서 72시간의 서냉공정을 거쳐hexacelsian의 상전이에 의하여 얻어졌다.

• Journal of Microbiology and Biotechnology
• /
• 제15권5호
• /
• pp.1125-1129
• /
• 2005

Cloning of a 6.6-kb BamHI digested chromosomal DNA from S. griseus IFO13350 revealed the presence of an additional gene encoding a novel trypsin-like enzyme, named SprU. The SprU protein shows a high homology ($79\%$ identity, $88\%$ similarity) with the SGT protease, which has been reported as a bacterial trypsin in the same strain. The amino acid sequence deduced from the nucleotide sequence of the sprU gene suggests that SprU is produced as a precursor consisting of an amino-terminal presequence (29 amino acid residues), prosequence (4 residues), and mature trypsin consisting of 222 amino acids with a molecular weight of 22.94 kDa and a calculated pI of 4.13. The serine, histidine, and aspartic acid residues composing the catalytic triad of typical serine proteases are also well conserved. When the trypsin activity of the SprU was spectrophotometrically measured by the enzymatic hydrolysis of the artificial chromogenic substrate, N-${alpha}$-benzoyl-DL-arginine-p-nitroanilide, the S. lividans transformant with pWHM3-U gave 3 times higher activity than that of control. When the same recombinant plasmid was introduced into S. griseus, however, the gene dosage effect was not so significant, as in the cases of other genes encoding serine proteases, such as sprA, sprB, and sprD. Although two trypsins, SprU and SGT, have a high degree of homology, the pI values, the gene dosage effect in S. griseus, and the gene arrangement adjacent to the two genes are very different, suggesting that the biochemical and biological function of the SprU might be quite different from that of the SGT.

• Bulletin of the Korean Chemical Society
• /
• 제25권5호
• /
• pp.687-693
• /
• 2004

Composite membranes with a titania layer were prepared by soaking-rolling method with the titania sol of nanoparticles formed in the sol-gel process and investigated regarding the vapor permeation of various organic mixtures. The support modification was conducted by pressing $SiO_2$ xerogel of 500 nm in particle size under 10 MPa on the surface of a porous stainless steel (SUS) substrate and designed the multi-layered structure by coating the intermediate layer of ${\gamma}-Al_2O_3$. Microstructure of titania membrane was affected by heat-treatment and synthesis conditions of precursor sol, and titania formed at calcination temperature of 300$^{\circ}C$ with sol of [$H^+$]/[TIP]=0.3 possessed surface area of 210 $m^2$/g, average pore size of 1.25 nm. The titania composite membrane showed high $H_2/N_2$ selectivity and water/ethanol selectivity as 25-30 and 50-100, respectively. As a result of vapor permeation for water-alcohol and alcohol-alcohol mixture, titania composite membrane showed water-permselective and molecular-sieve permeation behavior. However, water/methanol selectivity of the membrane was very low because of chemical affinity of permeants for the membrane by similar physicochemical properties of water and methanol.

• 공업화학
• /
• 제25권5호
• /
• pp.455-462
• /
• 2014

유러퓸-활성화 스트론튬 오쏘실리케이트($Sr_2SiO_4:Eu^{2+}$) 황색 형광체 분말의 소수성 코팅을 위하여 상압 유전체배리어 방전 플라즈마가 사용되었다. 전구물질은 헥사메틸다이실록세인(HMDSO), 톨루엔 및 n-헥세인이었으며, 운반기체는 아르곤이었다. 엑스선 회절분석 결과 플라즈마 코팅 처리 후에도 오쏘실리케이트의 격자구조는 변화가 없는 것으로 나타났다. 플라즈마 코팅된 형광체 분말의 특성은 주사전자현미경, 형광분광광도계, 접촉각 분석을 통해 조사되었다. HMDSO를 사용한 형광체 분말의 소수성 코팅시 물 접촉각은 $21.3^{\circ}$ (코팅 전)에서 $139.5^{\circ}$ (최대 $148.7^{\circ}$)로 증가되었고, 글리세롤 접촉각은 $55^{\circ}$ (코팅 전)에서 $143.5^{\circ}$ (최대 $145.3^{\circ}$)로 증가되었는데, 이 결과는 형광체 분말 표면에 소수성 박막 층이 잘 형성되었음을 나타낸다. 퓨리에변환적외선분광기 및 엑스선광전자분광기를 이용한 표면분석을 통해서도 형광체 분말에 소수성 박막 층이 잘 형성되어 있음을 알 수 있었다. HMDSO를 사용한 소수성 코팅 후 형광체의 광발광 효율이 증가하는 것으로 나타났으나, 톨루엔과 n-헥세인을 전구물질로 사용했을 때는 광발광 효율이 다소 저하되었다. 본 연구의 결과는 유전체배리어방전 플라즈마가 분말 형태인 형광체의 코팅에 이용될 수 있는 실용적인 방법임을 나타낸다.

• 한국재료학회지
• /
• 제17권1호
• /
• pp.31-36
• /
• 2007

Nanoimprint lithography (NIL) is a new lithographic method that offers a sub-10nm feature size, high throughput, and low cost. One of the most serious problems of NIL is the stiction between mold and resist. The antistiction layer coating is very effective to prevent this stiction and ensure the successful NIL results. In this paper, an antistiction layer was deposited by VSAM (vapor self assembly monolayer) method on silicon samples with FOTS (perfluoroctyltrichlorosilane) as a precursor for making an antistiction layer. A specially designed LPCVD (low pressure chemical vapor deposition) was used for this experiment. All experiments were achieved after removing the humidity. First, the evaporation test of FOTS was performed for checking the evaporation temperature at low pressure. FOTS was evaporated at 5 Tow and $110^{\circ}C$. In order to evaluate the temperature effect on antistiction layer, chamber temperature was changed from 50 to $170^{\circ}C$ with 0.1ml of FOTS for 1 minute. Good hydrophobicity of all samples was shown at about $110^{\circ}$ of contact angle and under $20^{\circ}$ of hysteresis. The surface energies of all samples calculated by Lewis acid/base theory was shown to be about 15mN/m. The deposited thicknesses of all samples measured by ellipsometry were almost 1nm that was similar value of the calculated molecular length. The surface roughness of all samples was not changed after deposition but the friction force showed relatively high values and deviations deposited at under $110^{\circ}$. Also the white circles were founded in LFM images under $110^{\circ}$. High friction forces were guessed based on this irregular deposition. The optimized VSAM process for FOTS was achieved at $170^{\circ}C$, 5 Torr for 1 hour. The hot embossing process with 4 inch Si mold was successfully achieved after VSAM deposition.

• Korean Chemical Engineering Research
• /
• 제54권3호
• /
• pp.299-304
• /
• 2016

Nitrate-citrate 혼합 전구체로부터 ZnO 입자 합성을 위한 자체진행 반응(Self-propagating reaction)의 특성을 고찰하였다. 질화물과 Citrate 그룹간의 자체진행 반응을 위해 탄소/질소 성분의 비는 0.7~0.8 수준으로 유지하였으며, 출발물질의 시료를 TGA방법에 의해 열분해하였다. 반응의 후반부인 반응 전환율이 0.5 이상에서 자체진행 반응의 특성을 나타내었으며 시료는 매우 짧은 시간에 많은 열을 방출하며 분해되었다. 반응의 전반부(X<0.5)가 전체반응의 율속단계로 나타났으며, 이 율속단계에서 반응의 특성을 Friedman, Ozawa-Flynn-Wall 그리고 Vyazovkin의 방법들을 사용하여 해석하였다. 율속단계에서 활성화 에너지는 46~130 (kJ/mol)의 범위로 반응 전환율이 증가함에 따라 증가하였으며, 반응차수는 2.9~0.9, 그리고 반응속도의 빈도인자(Frequency factor)는 85~278 ($min^{-1}$)의 범위에서 승온속도가 증가함에 따라 각각 전자는 감소하고 후자는 증가하였다.