• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.98-98
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• 2013

완전화 박막이란 사용자가 원하는 용도에 맞게 최적의 성능을 구현하도록 제조된 박막을 의미하며 금속이나 화합물 박막을 제조하되 각종 구조 제어 Tool이나 증착 공정을 변화시켜 나노화와 다층화 또는 치밀화를 통해 구현될 수 있다. 최근 고성능의 증착 및 제어 Tool이 개발되고 빗각증착(Oblique Angle Deposition)이나 스침각 증착(Glancing Angle Deposition) 방법 등의 기술이 개발되면서 사용자 목적에 최적인 박막 소재를 제공하여 User-friendly한 응용을 위한 연구개발이 활발히 진행되고 있다. 완전화 박막 제조에 대한 시도는 1990년대에 일본에서 시작되었다. 일본에서는 산학연이 공동으로 참여하는 NEDO 프로그램을 통해 경질코팅을 이용한 Protective Layer를 제조하여 차단 방식에 의한 내식성 구현 연구를 수행하였다. 유럽에서는 제 7차 European Framework Program (7th FT)을 통해 2007년부터 CORRAL (Corrosion Protection with Perfect Atomic Layer) 프로젝트를 만들어 완전화 박막 연구를 진행하고 있다. 상기 프로젝트는 얇은 자연 산화막이 Bulk의 부식을 방지해주는 것에 착안하여 HIPIMS나 Filtered Arc 또는 ALD 공정을 이용하여 자연 산화막과 유사한 Defect-free 산화막을 제조하여 Barrier형 내식성 박막을 구현하는 것을 목표로 하고 있다. 본 연구에서는 완전화 박막 구현을 위한 연구동향을 파악하고 완전화 박막 제조를 위한 기술적 과제와 몇 가지의 시도에 대한 기초 연구 자료를 소개한다.

• Journal of Welding and Joining
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• v.27 no.6
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• pp.43-48
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• 2009

In this study, Cu-based bulk metallic glass (BMG) coatings were deposited by atmospheric plasma spraying (APS) process with different process conditions (with- and without hydrogen gas). As adding the hydrogen gas, thermal energy in the plasma flame increased and induced difference in the melting state of the Cu-based BMG particles. The microstructure and mechanical properties of the coatings were analyzed using a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) and nano-indentation tester in the light of phase analysis. It was elucidated by the nano-indentation tests that un-melted region was a mainly amorphous phase which showed discrete plasticity observed as the flow serrations on the load.displacement (P - h) curves, and the curves of solidified region showed lower flow serrations as amorphous phase mingled with crystalline phase. Oxides produced during the spraying process had the highest hardness value among the phases and were well mixed with other phases resulted from the increase in melting degree.

• Journal of the Korean institute of surface engineering
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• v.52 no.1
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• pp.6-15
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• 2019

Metal-halide perovskite (MHP) solar cell is a promising candidate for next-generation flexible devices and the BIPV (Building-integrated photovoltaics) because it can exhibit high power conversion efficiencies over 23%, good bendability and low processing cost. However, MHP solar cells are commonly fabricated by the spin coating that is not a reliable method to produce large-scale commercial solar cells. A shear coating can be one of the potential candidates for the large-scale deposition method of MHP films. In this work, the influences of the process parameters such as solvents of precursor solution, substrate temperature, concentrations of precursor solution, and annealing time on the thin film growth of MHP were investigated for the shear coating process. This study presents the possibility of the shear coating process for large-scaled perovskite film fabrication and reveals the role of process condition in the thin film growth of perovskites.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.447-452
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• 2018

Titanium nanotubes (TNT) of various lengths ranging from $0.34^{\circ}C$ to a maximum of $8.9^{\circ}C$ were prepared by anodizing a titanium metal sheet in an electrolyte containing fluorine ion ($F^-$) of HF, NaF and $NH_4F$. When TNT prepared by anodizing was calcined at $450^{\circ}C$, anatase crystals with photo activity were formed. The TNT-based dye-sensitized solar cell (DSSC) showed a maximum conversion efficiency of 4.71% when the TNT length was $2.5{\mu}m$. This value was about 18% higher than photo conversion efficiency of the FTO-based DSSC coated with titania paste. And the short circuit current density ($J_{sc}$) of the TNT-DSSC was $9.74mA/cm^2$, which was about 35% higher than the $7.19mA/cm^2$ of FTO-DSSC. The reason for the higher conversion efficiency of TNT-DSSC solar cells is that photoelectrons generated from dyes are rapidly transferred to the electrode surface through TNT, and the recombination of photoelectrons and dyes is suppressed.

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.270-276
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• 2008

$N_2$ doped $TiO_2$ nano-sized powder was prepared using a DC arc plasma jet and investigated with XRD, BET, SEM, TEM, and photo-catalytic decomposition. Recently the research interest about the nano-sized $TiO_2$ powder has been increased to improve its photo-catalytic activity for the removal of environmental pollutants. Nitrogen gas, reacting gas, and titanium tetrachloride ($TiCl_4$) were used as the raw materials and injected into the plasma reactor to synthesize the $N_2$ doped $TiO_2$ power. The particle size and XRD peaks of the synthesized powder were analyzed as a function of the flow rate of the nitrogen gas. Also, the characteristics of the photo-catalytic decomposition using the prepared powder were studied. For comparing the photo-catalytic decomposition performance of $TiO_2$ powder with that of $TiO_2$ coating, $TiO_2$ thin films were prepared by the spin coating and the pulsed laser deposition. For the results of the acetaldehyde decomposition, the photo-catalytic activity of $TiO_{2-x}N_x$ powder was higher than that of the pure $TiO_2$ powder in the visible light region. For the methylene blue decomposition, the decomposition efficiency of $TiO_2$ powder was also higher than that of $TiO_2$ film.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.34.2-34.2
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• 2010

Cu(In,Ga)Se2 (CIGS) 화합물 반도체를 기반으로 한 태양전지는 박막태양전지 기술 중 세계최고효율을 기록하고 있다. CIGS를 합성하는 방법은 동시증발법, 스퍼터링/셀렌화 등의 진공방식과 나노분말법, 전착법, 용액법 등의 비진공방식이 있으나, 현재까지 진공방식이 양산기술로서 완성도가 높은 것으로 알려져 있다. 특히 스퍼터링에 의한 전구체 박막 증착과 셀렌 분위기에서의 열처리 공정을 결합시킨 2단계 공정은 동시증발법에 비해 대면적 모듈 제조에 유리한 것으로 알려져 있다. 셀렌화 공정은 통상 반응성이 매우 높은 H2Se 기체를 이용하고 있으나, 부식성 및 안전성 문제를 해결하기 위해 추가적인 설비가 요구되므로 제조비용을 높이는 단점을 갖는다. 한편, Se 증기를 이용하면 안전성은 담보되나 낮은 반응성으로 인해 고온에서 장시간 열처리를 해야하는 문제를 안고 있다. 본 연구에서는 새로운 Se 증기를 사용하되 반응효율을 높일 수 있는 새로운 셀렌화 열처리방법을 제시하고자 한다. 기존의 Se 증기가 별도의 증발원을 이용하여 공급된 것과는 달리, 금속전구체 직상부에 Se이 코팅된 별도의 커버글라스를 위치시켜 Se의 손실을 최대한 억제하였다. Se 커버글라스가 밀착된 금속프리커서를 $200{\sim}600^{\circ}C$ 온도범위에서 열저항가열로 내부에서 열처리하였으며, 추가로 Se을 공급하지는 않았다. 이와 같은 방법 제조된 CIGS 박막의 물성을 X선회절법, 주사전자현미경 등으로 관찰하였으며, 예비실험결과 비교적 낮은 온도에서 chalcopyrite 상이 형성됨을 확인하였다. 근접셀렌화에 의해 제조된 CIGS 박막이 적용된 태양전지를 제조하여 셀렌화 공정변수에 따른 소자특성변화를 제시하고자 한다.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.1
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• pp.15-26
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• 2017

Cobalt ferrocyanide (CoFC) or nickel ferrocyanide (NiFC) magnetic nanoparticles (MNPs) were fabricated for efficient removal of radioactive cesium, followed by rapid magnetic separation of the absorbent from contaminated water. The $Fe_3O_4$ nanoparticles, synthesized using a co-precipitation method, were coated with succinic acid (SA) to immobilize the Co or Ni ions through metal coordination to carboxyl groups in the SA. CoFC or NiFC was subsequently formed on the surfaces of the MNPs as Co or Ni ions coordinated with the hexacyanoferrate ions. The CoFC-MNPs and NiFC-MNPs possess good saturation magnetization values ($43.2emu{\cdot}g^{-1}$ for the CoFC-MNPs, and $47.7emu{\cdot}g^{-1}$ for the NiFC-MNPs). The fabricated CoFC-MNPs and NiFC-MNPs were characterized by XRD, FT-IR, TEM, and DLS. The adsorption capability of the CoFC-MNPs and NiFC-MNPs in removing cesium ions from water was also investigated. Batch experiments revealed that the maximum adsorption capacity values were $15.63mg{\cdot}g^{-1}$ (CoFC-MNPs) and $12.11mg{\cdot}g^{-1}$ (NiFC-MNPs). Langmuir/Freundlich adsorption isotherm equations were used to fit the experimental data and evaluate the adsorption process. The CoFC-MNPs and NiFC-MNPs exhibited a removal efficiency exceeding 99.09% for radioactive cesium from $^{137}Cs$ solution ($18-21Bq{\cdot}g^{-1}$). The adsorbent selectively adsorbed $^{137}Cs$, even in the presence of competing cations.

• Korean Journal of Optics and Photonics
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• v.21 no.1
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• pp.33-37
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• 2010

We performed time-domain terahertz (THz) spectroscopy to determine optical constants of highly conductive carbon nanotube (CNT) films. The CNT films have been fabricated on a flexible plastic substrate by using spin-coating or vacuum filtration. We found that the transmission of THz waves can be controlled by manipulating the thickness of the films and by post-treatments. From amplitude and phase information of the transmitted THz waves, we obtain optical constants such as refractive indices and dielectric constants of the CNT films. The frequency dependent dielectric constants show good metallic behaviors, relevant to the Drude free electron models with high plasma frequencies. It is also found that the dielectric constants are higher for the acid-treated films. Finally, the frequency dependent dielectric constants which are free from substrate effects have been demonstrated by using CNT films deposited on cellulose membranes.

• Journal of the Korean GEO-environmental Society
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• v.17 no.1
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• pp.13-19
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• 2016

Soft ground stabilization is needed to construct large civil facilities on the soft clay ground. Pre-loading method, which is accelerating consolidation method, is generally used to stabilize the soft ground. However, pre-loading method is required long construction period and quantities of fill material. Therefore, electro-osmosis method is used to replace pre-loading method for stabilizing the soft ground. Electro-osmosis method is disadvantageous in constructive and economic aspects because it is needed a metallic electrode. So, in order to solve the those disadvantages, plastic electrode was developed to replace metallic electrode. Plastic electrode, which is made by using nano-technology on existing Plastic Drain Board (PDB), was used to supply the electric power. In this study, therefore, the model test was conducted to confirm the effect of improvement and electrical characteristics of soft ground by spacing of plastic electrode. The result shows that the effect of improvement of soft ground was decreased up to 45% by increasing electrode spacing and electrical characteristics on the soft ground were influenced by consolidation settlement with electrode spacing.

• Korean Journal of Materials Research
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• v.14 no.9
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• pp.634-641
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• 2004

The photocatalytic performance of $TiO_2$ thin films coated on porous alumina balls using various aqueous $TiOCl_2$ solutions as starting precursors, to which 1.0 $mol\%$ transition metal ($Ni^{2+},\;Cr^{3+},\;Fe^{3+},\;Nb^{3+},\;and\;V^{5+}$) chlorides had been already added, has been investigated, together with characterizations for $TiO_2$ sols synthesized simultaneously in the same autoclave through hydrothermal method. The synthesized $TiO_2$ sols were all formed with an anatase phase, and their particle size was between several nm and 30 nm showing ${\zeta}-potential$ of $-25{\sim}-35$ mV, being maintained stable for over 6 months. However, the $TiO_2$ sol added with Cr had a much lower value of -potential and larger particle sizes. The coated $TiO_2$ thin films had almost the same shape and size as those of the sol. The pure $TiO_2$ sol showed the highest optical absorption in the ultraviolet light region, and other $TiO_2$ sols containing $Cr^{3+},\;Fe^{3+}\;and\;Ni^{2+}$ showed higher optical absorption than pure sol in the visible light region. According to the experiments for removal of a gas-phase benzene, the pure $TiO_2$ film showed the highest photo dissociation rate in the ultraviolet light region, but in artificial sunlight the photo dissociation rate of $TiO_2$ coated films containing $Cr^{3+},\;Fe^{3+}\;and\;Ni^{2+}$ was measured higher together with the increase of optical absorption by doping.