• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.141-141
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• 2010

The effect of thermal anneal on the characteristics of structural properties and the enhancement of luminescence and photovoltaic (PV) characteristics of silicon-rich silicon-nitride films were investigated. By using an ultra high vacuum ion beam sputtering deposition, B-doped silicon-rich silicon-nitride (SRSN) thin films, with excess silicon content of 15 at. %, on P-doped (n-type) Si substrate was fabricated, sputtering a highly B doped Si wafer with a BN chip by N plasma. In order to examine the influence of thermal anneal, films were then annealed at different temperature up to $1100^{\circ}C$ under $N_2$ environment. Raman, X-ray diffraction, and X-ray photoemission spectroscopy did not show any reliable evidence of amorphous or crystalline Si clusters allowing us concluding that nearly no Si nano-cluster could be formed through the precipitation of excess Si from SRSN matrix during thermal anneal. Instead, results of Fourier transform infrared and X-ray photoemission spectroscopy clearly indicated that defective, amorphous Si-N matrix of films was changed to be well-ordered thanks to high temperature anneal. The measurement of spectral ellipsometry in UV-visible range was carried out and we found that the optical absorption edge of film was shifted to higher energy as the anneal temperature increased as the results of thermal anneal induced formation of $Si_3N_4$-like matrix. These are consistent with the observation that higher visible photoluminescence, which is likely due to the presence of Si-N bonds, from anneals at higher temperature. Based on these films, PV cells were fabricated by the formation of front/back metal electrodes. For all cells, typical I-V characteristic of p-n diode junction was observed. We also tried to measure PV properties using a solar-simulator and confirmed successful operation of PV devices. Carrier transport mechanism depending on anneal temperature and the implication of PV cells based on SRSN films were also discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.264-264
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• 2012

As an environment-friendly alternative energy resource, ethanol may be used to obtain hydrogen, a clean energy source. Thus, studies on catalytic reactions involving ethanol have been studied to understand the underlying principles in the reaction mechanism using various oxide-supported catalysts. Among them, Au-based catalysts have shown a superior activity in producing hydrogen gas. In the present study, Au/$TiO_2$ catalysts were prepared by deposition-precipitation method to understand their catalytic activities toward ethanol and acetaldehyde with increasing gold loading, especially at the very low Au loading regime. A commercially available $TiO_2$ (Degussa P-25) was employed and the Au loading was varied to 0, 0.1, 0.5, and 1.0 wt% respectively. The catalysts showed characteristic x-ray diffraction (XRD) features at $2{\theta}=78.5^{\circ}$ that could be assigned to the presence of gold nanoparticles. Its reactivity measurements were performed under a constant flow of ethanol and acetaldehyde at a flow rate of ${\sim}0.6{\mu}mol/sec$ and the substrate temperature was slowly raised at a rate of 0.2 K/sec. We observed that the overall reactivity of the catalysts increased with increasing Au loading along with selectivity favoring dehydrogenation to product hydrogen gas. In addition, we disclosed various reaction channels involving competitive reaction paths such as dehydrogenation, dehydration, and condensation. In addition, subsequent reactions of acetaldehyde obtained from dehydrogenation of ethanol, were found to occur and produce butene, crotonaldehyde, furan, and benzene. Based on the results, we proposed overall reaction pathways of such reaction channels.

• 한국대기환경학회지
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• 제14권5호
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• pp.491-498
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• 1998

Fog water samples were collected at Chunchon, Korea, by using active fog sampler during foggy Period in fall of 1996 and 1997. The average annual foggy days at Chunchon increased from 37 days, for the yearn 1963 ∼ 1973, to 63 days , for the year 1974∼1993 that followed the construction of Lake Soyang. Volume weighted mean pH of fog water was 5.5 with a range of 4.8 to 7.0 in 1996, and 5.0 with a range of 4.1 to 6.6 in 1997. These pH values were higher than those of rain water sampled in corresponding years. However the concentration of ionic species in fog water were 26 times higher than those of rain water. The major anions in fog water were in order of SO42-, NO3- and Cl-, and their average concentrations were 1770.6meq/ml, 346.2 meq/ml, 216 meq/ml in 1996, and 901.8meq/ml, 269.6meq/ml, 141.0meq/ml in 1997, respectively. The major cations were Ca2+, NH4+, Mg2+ and K+, and their average concentrations frere 408.5meq/ml, 280.0meq/ml, 43.8meq/ml, 45.2meq/ml in 1996, and 400.4 meq/ml, 299.0meq/ml, 73.1meq/ml, 44.5meq/ml in 1997, respectively. The fraction acidity of fog water was 0.006 and that of rain water was 0.2, which means fog water was much more neutralized than rain water.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.181-181
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• 2012

Direct synthesis of graphene using a chemical vapor deposition (CVD) has been considered a facile way to produce large-area and uniform graphene film, which is an accessible method from an application standpoint. Hence, their fundamental understanding is highly required. Unfortunately, the CVD growth mechanism of graphene on Cu remains elusive and controversial. Here, we present the evidences for two different growth modes of graphene on Cu investigated by varying carbon feedstock (C2H2 and CH4) and working pressure. The number of uniform graphene layer grown by C2H2 increased with increasing its injection time. A combined secondary ion mass spectrometry (SIMS) and X-ray diffraction (XRD) study revealed a carbon-diffused Cu layer created below surface region of Cu substrate with the expansion of Cu lattice. The graphene on Cu was grown by the diffusion and precipitation mode not by the surface adsorption mode, because similar results were observed in graphene/Ni system. The carbon-diffused Cu layer was also observed after graphene growth under high CH4 pressure. Based on various previous results and ours, we have successfully found that there are two selective growth modes for graphene on Cu substrate, and a desired mode can be chosen by tuning working pressure corresponding to the kind of carbon feedstock. We believe that this finding will shed light on high quality graphene growth and its multifaceted applications.

• 한국기계가공학회지
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• 제17권2호
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• pp.83-88
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• 2018

Additive manufacturing (AM) technologies have attracted wide attention as key technologies for the next industrial revolution. Among AM technologies using various materials, powder bed fusion (PBF) processes and direct energy deposition (DED) are representative of the metal 3-D printing process. Both of these processes have a common feature that the laser is used as a heat source to fabricate the 3-D shape through melting of the metal powder and solidification. However, the material properties of the deposited metals differ when produced by different process conditions and methods. 17-4 precipitation-hardening stainless steel (17-4PH SS) is widely used in the field of aircraft, chemical, and nuclear industries because of its good mechanical properties and excellent corrosion resistance. In this study, we investigated the differences in microstructure and mechanical properties of deposited 17-4PH SS by PBF and DED processes, including the heat treatment effect.

• 대한치과기공학회지
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• 제27권1호
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• pp.79-88
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• 2005

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of $10\times10mm$ in dimension were polished sequentially from #600, #800, #1000 emery paper. The surface pure niobium specimens were anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was 10 $mA/cm^2$. The specimen was hydrothermal treated in high-pressure steam at 300$^{\circ}C$ for 2 hours using an autoclave. Then, specimens were immersed in the Hanks' solution with pH 7.4 at 37$^{\circ}C$ for 30 days. The surface of specimen was characterized by scanning electron microscope(SEM), energy dispersive X-ray microanalysis(EDX), potentiostat/galvanostat test, and cytotoxicity test. The results obtained was summarized as follows; According to the result of measuring corrosion behavior at 0.9% NaCl, corrosion resistance was improved more specimens treated with anodic oxide than in hydrothermal treated ones. The multi-porous oxide layer on surface treated through anodic oxidation showed a structure that fine pores overlap one another, and the early precipitation of apatite was observed on the surface of hydrothermal treated samples. According to the result of EDX after 30 days deposition in Hanks' solution, Ca/P was 1.69 in hydrothermal treated specimens. In MTT test, specimens treated through anodic oxidation and hydrothermal treated ones showed spectrophotometer similar to that of the control group. Thus no significant difference in cytotoxicity was observed (P>0.05).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.490-490
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• 2011

Graphene, hexagonal network of carbon atoms forming a one-atom thick planar sheet, has been emerged as a fascinating material for future nanoelectronics. Huge attention has been captured by its extraordinary electronic properties, such as bipolar conductance, half integer quantum Hall effect at room temperature, ballistic transport over ${\sim}0.4{\mu}m$ length and extremely high carrier mobility at room temperature. Several approaches have been developed to produce graphene, such as micromechanical cleavage of highly ordered pyrolytic graphite using adhesive tape, chemical reduction of exfoliated graphite oxide, epitaxial growth of graphene on SiC and single crystalline metal substrate, and chemical vapor deposition (CVD) synthesis. In particular, direct synthesis of graphene using metal catalytic substrate in CVD process provides a new way to large-scale production of graphene film for realization of graphene-based electronics. In this method, metal catalytic substrates including Ni and Cu have been used for CVD synthesis of graphene. There are two proposed mechanism of graphene synthesis: carbon diffusion and precipitation for graphene synthesized on Ni, and surface adsorption for graphene synthesized on Cu, namely, self-limiting growth mechanism, which can be divided by difference of carbon solubility of the metals. Here we present that large area, uniform, and layer controllable graphene synthesized on Cu catalytic substrate is achieved by acetylene-assisted CVD. The number of graphene layer can be simply controlled by adjusting acetylene injection time, verified by Raman spectroscopy. Structural features and full details of mechanism for the growth of layer controllable graphene on Cu were systematically explored by transmission electron microscopy, atomic force microscopy, and secondary ion mass spectroscopy.

• 한국지반공학회논문집
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• 제19권6호
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• pp.161-168
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• 2003

대부분의 자연상태의 사질토는 어느 정도 경화되어 있다. 경화의 정도는 흙의 체적변형 거동이나 강도에 중요한 영향을 준다. 경화된 사질토 지반의 중요한 특징은 사질토임에도 불구하고 굉장히 높이 서 있을 수 있다는 것이다. 많은 현장 관측이나 경화모래로 된 사면의 파괴 해석들은 기존의 사면해석방법이 적절하지 않다는 것을 보여준다. 이것은 단지 파괴면이 원호가 아니라는 점뿐만 아니라 파괴면에서의 전단응력이 실험으로부터 얻어진 전단강도보다 훨씬 작기 때문일 것이다. 이러한 사실은 파괴양상이 Mohr-Coulomb 전단파괴와 다르다는 것을 말한다. 이런 파괴는 파괴역학 개념과 이론으로 설명될지도 모른다. 이 논문에서는 파괴 역학 개념을 이용해서 경화모래로 이루어진 급경사 사면의 해석을 수행하였다. FEM 해석 결과는 파괴역학의 개념을 이용한 해석방법이 경화사질토로 이루어진 지반구조물의 설계나 안정해석에 훌륭한 대안임을 보여주고 있다.

• 열처리공학회지
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• 제24권5호
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• pp.243-250
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• 2011

When alloys are vacuum-deposited on cooled substrates, super-rapidly cooled alloy films in the unequilibrium state can be obtained. As an application of this method, Ag-Cu, Ag-Ni and Ag-C alloys were successfully produced, and their mechanical properties with tempering temperature were investigated. The following results were obtained : (1) In case of Ag-Cu alloys, the solid solution was hardened by tempering at $150^{\circ}C$. The hardening is considered to occur when the solid solution begins to decompose into ${\alpha}$ and ${\beta}$ phases. The Knoop hardness number of a 40 at.%Ag-Cu alloy film deposited on a cooled glass substrate was 390 $kg/mm^2$. The as-deposited films were generally very hard but fractured under stresses below their elastic limits. (2) In case of Ag-Ni and Ag-C alloys, after the tempering of 4 at.%Ni-Ag alloy at $400^{\circ}C$ and of 1 and 2 at.%C-Ag alloys at $200^{\circ}C$, they were hardened by the precipitation of fine nickel and carbon particles. The linear relationship between proof stress vs. $(grain\;diameter)^{-l/2}$ for bulk silver polycrystals can be applied to vacuum-deposited films up to about 0.1 ${\mu}m$ grain diameter, but the proof stress of ultra-fine grained silver with grain diameters of less than 0.1 ${\mu}m$ was smaller than the value expected from the Petch's relation.

• 공업화학
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• 제26권2호
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• pp.121-127
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• 2015

전기화학적 양극산화 기법으로 제조한 타이타늄 나노튜브는 타이타늄 특유의 강한 화학내구성 및 나노튜브의 높은 종횡비로 인하여 넓은 범위에 응용된 소재이다. 전해질의 구성 성분과 종류, pH, 전압, 온도 그리고 양극산화 시간이 타이타늄 나노튜브의 성상을 결정짓는 요소들이며 도핑을 통해 촉매능을 부여할 수 있다. 비금속 및 금속 원소 모두 도핑 가능하며 도핑 방법 역시 다양하다. 도핑 방법에는 합금 양극산화, 열처리법, 함침법, 전기도금법 등 다양한 방법들이 이용되며 점차 간단하고 빠른 도핑 방법을 찾는 방향으로 연구가 진행되고 있다. 본 총설에서는 타이타늄 나노튜브의 생성 원리와 상용된 제법들에 관하여 기술하고 도핑과 그 응용 및 최근의 도핑 연구 동향을 다루도록 하겠다.