• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.6.1-6.1
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• 2010

원자층 증착 기술 (Atomic Layer Deposition)은 기판 표면에서 한 원자층의 화학적 흡착 및 탈착을 이용한 nano-scale 박막 증착 기술이기 때문에, 표면 반응제어가 우수하며 박막의 물리적 성질의 재현성이 우수하고, 대면적에서도 균일한 두께의 박막 형성이 가능하며 우수한 계단 도포성을 확보 할 수 있다. 최근 ALD에 의한 박막증착 방법 중 플라즈마를 이용한 ALD 증착 방법에 대한 다양한 연구가 진행되고 있다. 플라즈마는 반응성이 좋은 이온과 라디컬을 생성하여 소스간 반응성을 좋게 하여, 소스 선택의 폭을 넓어지게 하고, 박막의 성질을 좋게 하며, 생산성을 높일 수 있는 장점이 있다. 그러나 플라즈마를 사용함으로써 플라즈마 내에 이온들이 가속되서 박막 증착 중에 기판 및 박막에 손상을 입혀 박막 특성을 열화 시킬 가능성이 있다. 따라서 플라즈마 발생 영역을 기판으로부터 멀리 떨어뜨린 원거리 플라즈마 원자층 공정이 개발 되었다. 이 기술은 플라즈마에서 생성된 ion이 기판이나 박막에 닫기 전에 전자와 재결합 되거나 공정 chamber에서 소멸하여 그 영향을 최소하고 반응성이 좋은 라디칼과의 반응만을 유도하여 향상된 막질을 얻을 수 있도록 하였다. 따라서 이 원거리 플라즈마 원자층 증착기술은 나노 테크놀러지 소자 개발하기 위한 나노 박막 기술에 있어서 그 활용이 점점 확대될 것이다. 그 적용으로써 리모트 플라즈마 원자층 증착 방법을 이용한 고유전 물질 개발이 있다. 반도체 소자의 고집적화 및 고속화가 요구됨에 따라 집적회로의 크기를 혁신적으로 축소하여 스위칭 속도(switching speed)를 증가시키고, 전력손실 (power dissipation)을 줄이려는 시도가 이루어지고 있다. 그 중 하나로 고유전율 절연막은 트렌지스터 소자의 스케일링 과정에 수반하여 커지는 게이트 누설 전류를 억제하기 위한 목적으로 도입되었다. 유전율이 크면 동일한 capacitance를 내는데 필요한 물리적인 두께를 늘릴 수 있어 전자의 tunneling을 억제할 수 있고 전력손실을 줄일 수 있기 때문이다. 이와 같은 고유전율 물질이 게이트 산화막으로 사용되기 위해서 높은 유전상수 열역학적 안정성, 낮은 계면 전하밀도, 낮은 EOT, 전극 물질과의 양립성 등의 특성이 요구되는데, 이에 따라 많은 유전물질에 대한 연구가 진행되었다. 기존 gata oxide를 대체하기 위한 가장 유력한 후보 재료로 주목 받고 있는 high-k 물질들로는 Al2O3, HfO2, ZrO2, La2O3 등이 있다. 본 발표에서는 ALD의 종류에 따른 기술을 소개하고 그 응용으로 고유전율 물질 개발 연구 (고유전율 산화물 박막의 증착, 고유전율 산화물의 열적 안정성 평가, Flatband 매카니즘 규명, 전기적 물리적 특성 분석)에 대해서 발표 하고자 한다.

• Korean Journal of Materials Research
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• v.11 no.1
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• pp.48-54
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• 2001

The effects of additives in the HCI etching solution on etching behaviors of aluminum foil as dielectric film for electrolytic capacitors were investigated. The etch pits formed in 1M hydrochloric acid containing ethylene glycol as an additive contain more fine and homogeneous etch tunnels compared to those in 1 M hydrochloric acid only, which led to the increase in the effective internal surface area of aluminum foil. After anodizing of aluminum foil etched in etching solutions, the LCR meter results have shown that the capacitance of dielectric film etched in hydrochloric acid with ethylene glycol was increased remarkably compared to that etched in hydrochloric acid only.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.152-152
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• 2017

Titanium and its alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element,such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}$-stabilizer and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Silicon (Si) and magnesium (Mg) has a beneficial effect on bone. Si in particular has been found to be essential for normal bone and cartilage growth and development. In vitro studies have shown that Mg plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Therefore, in this study, Si and Mg coatings on the hydroxyapatite film formed Ti-29Nb-xHf alloys by plasma electrolyte oxidation has been investigated using several experimental techniques. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. The electrolyte was Si and Mg ions containing calcium acetate monohydrate + calcium glycerophosphate at room temperature. The microstructure, phase and composition of Si and Mg coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.

• Journal of Powder Materials
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• v.12 no.3
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• pp.186-191
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• 2005

A formation of aluminum hydroxide by hydrolysis of nano and micro aluminum powder has been studied. The nano aluminum powder of 80 to 100 nm in diameter was fabricated by a pulsed wire evaporation (PWE) method. The micro powder was commercial product with more than $10\;{\mu}m$ in diameter. The hydroxide type and morphology depending on size of the aluminum powder were examined by several analyses such as XRD, TEM, and BET. The hydrolysis procedure of micro aluminum powder was different from that of nano aluminum powder. The nano aluminum powder after immersing in the water was transformed rapidly to a nano fibrous boehmite, accompanying with a remarkable temperature increase, and then further transformed slowly to a stable bayerite. However, the micro powder was changed to the stable bayerite slowly and directly. The formation of fibrous aluminum hydroxide from nano aluminum powder might be due to the fine cracks which were formed by hydrogen gas pressure on the surface hydroxide layer during hydrolysis. The nano powder with large specific surface area and small size reacted more actively and faster than the micro powder, and transformed to meta-stable hydroxide in relatively short reaction time. Therefore, the formation of fibrous boehmite is special characteristic of hydrolysis of nano aluminum powder.

• Biomolecules & Therapeutics
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• v.14 no.2
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• pp.90-95
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• 2006

CKD-602 exerts its antitumor effect via inhibition of topoisomerase I in cancer cells. Multicellular spheroid (MCS) and Multicellular layers (MCLs) are known as in vitro 3-dimensional models which closely represent tumor conditions in vivo. In order to investigate the potential of CKD-602 against human colorectal tumors, we evaluated the anti-proliferative activity and penetration ability of CKD-602 in MCS and MCL cultures of DLD-l human colorectal cancer cells, respectively. The maximum effects($E_{max}$) induced by CKD-602 were significantly lower in MCS compared to monolayers (48% vs 92%). With prolonged drug exposure, the $IC_{50's}$ of CKD-602 decreased to $23.5{\pm}1.0nM$ in monolayers after 24 h exposure and $42.3{\pm}1.7nM$ in MCS after 6 days, respectively. However, no further increase in effect was observed for exposure time longer than growth doubling time (Td) in both cultures. Activity of CKD-602 was significantly reduced after penetration through MCL and also with cell-free insert membrane. In conclusion, CKD-602 showed significantly decreased anti-proliferative activity in 3D cultures (MCS) of human colorectal cancer cells. Tumor penetration of CKD-602 could not be determined due to loss of activity after penetration through cell free insert membrane, which warrants further evaluation using a modified model.

• Proceedings of the Korean Vacuum Society Conference
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• 1998.02a
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• pp.133-133
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• 1998

In the thin film alloy formation of the transition metals ion-beam-mixing technique forms a metastable structure which cannot be found in the arc-melted metal alloys. Sppecifically it is well known that the studies about the electronic structure of ion-beam-mixed alloys pprovide the useful information in understanding the metastable structures in the metal alloy. We studied the electronic change in the ion-beam-mixed ppt-Ct alloys by XppS and XANES. These analysis tools pprovide us information about the charge transfer in the valence band of intermetallic bonding. The multi-layered films were depposited on the SiO2 substrate by the sequential electron beam evapporation at a ppressure of less than 5$\times$10-7 Torr. These compprise of 4 ppairs of ppt and Cu layers where thicknesses of each layer were varied in order to change the alloy compposition. Ion-beam-mixing pprocess was carried out with 80 keV Ae+ ions with a dose of $1.5\times$ 1016 Ar+/cm2 at room tempperature. The core and valence level energy shift in these system were investigated by x-ray pphotoelectron sppectroscoppy(XppS) pphotoelectrons were excited by monochromatized Al K ａ(1486.6 eV) The ppass energy of the hemisppherical analyzer was 23.5 eV. Core-level binding energies were calibrated with the Fermi level edge. ppt L3-edge and Cu K-edge XANES sppectra were measured with the flourescence mode detector at the 3C1 beam line of the ppLS (ppohang light source). By using the change of White line(WL) area of the each metal sites and the core level shift we can obtain the information about the electrons pparticippating in the intermetallic bonding of the ion-beam-mixed alloys.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.316-316
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• 2010

Thin films spin-coated from solvent solutions are characterized by solution parameters and spin-coating process. In this study, performance characteristics of polymer solar cells were investigated with changing solution parameters such as solvent and additives. The phase-separation between polymer and fullerene is needed to make the percolation pathway for better transportation of hole and electron in polymer solar cells. For this reason, cooperative effects of solvent mixtures adding additives with distinct solubility have been studied recently. In this study, chlorobezene, 1, 2-dichlorbenzene, and chloroform were used as solvent. 1, 8-diiodoctaned and 1, 8-octanedithiol were used as additives and were added into poly(3-hexylthiophene-2, 5-diyl)/[6, 6]-phenyl C61 butyric acid methyl ester (P3HT/PCBM) blends. Pre-patterned ITO glass was cleaned using ultrasonication in mixed solvent with ethyl alcohol, isopropyl alcohol and acetone. PEDOT:PSS was spin-coated on to the ITO substrate at 3000rpm and was baked at $120^{\circ}C$ for 10min on the hotplate. The prepared solution was spin-coated at 1000rpm and the spin-coated thin film was dried in the Petri dishes. Al electrode was deposited on the thin film by thermal evaporation. The devices were annealed at $120^{\circ}C$ for 30min. By adding 2.5 volume percent of additives into the chlorobenzene from that bulk heterojunction films consisting of P3HT/PCBM, the power efficiency (AM 1.5G conditions) was increased from 2.16% to 2.69% and 3.12% respectively. We have investigated the effect of additives in P3HT/PCBM blends and the film characteristics and the film characteristics including J-V characteristics, absorption, photoluminescence, X-ray diffraction, and atomic force microscopy to mainly depict the morphology control by doping additives.

• Journal of Korean Society on Water Environment
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• v.33 no.3
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• pp.326-333
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• 2017

The lakes and reservoirs have been reported as important sources of carbon emissions to the atmosphere in many countries. Although field experiments and theoretical investigations based on the fundamental gas exchange theory have proposed the quantitative amounts of Net Atmospheric Flux (NAF) in various climate regions, there are still large uncertainties at the global scale estimation. Mechanistic models can be used for understanding and estimating the temporal and spatial variations of the NAFs considering complicated hydrodynamic and biogeochemical processes in a reservoir, but these models require extensive and expensive datasets and model parameters. On the other hand, data driven machine learning (ML) algorithms are likely to be alternative tools to estimate the NAFs in responding to independent environmental variables. The objective of this study was to develop random forest (RF) and multi-layer artificial neural network (ANN) models for the estimation of the daily $CO_2$ NAFs in Daecheong Reservoir located in Geum River of Korea, and compare the models performance against the multiple linear regression (MLR) model that proposed in the previous study (Chung et al., 2016). As a result, the RF and ANN models showed much enhanced performance in the estimation of the high NAF values, while MLR model significantly under estimated them. Across validation with 10-fold random samplings was applied to evaluate the performance of three models, and indicated that the ANN model is best, and followed by RF and MLR models.

• International Journal of Highway Engineering
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• v.10 no.4
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• pp.213-224
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• 2008

Flexible pavement responses to vehicular loading, such as critical stresses and strains, in each pavement layer, could be predicted by the multilayered elastic analysis. However, multilayered elastic theory suffers from major drawbacks including spatial dimension of a numerical model, material properties considered in the analysis, boundary conditions, and ill-presentation of tire-pavement contact shape and stresses. To overcome these shortcomings, three-dimensional finite element (3D FE) models are developed and numerical analyses are conducted to calculate pavement responses to moving load in this study. This paper introduces a methodology for an effective 3D FE to simulate flexible pavement structure. It also discusses the mesh development and boundary condition analysis. Sensitivity analyses of flexible pavement response to loading are conducted. The infinite boundary conditions and time-dependent history of calculated pavement responses are considered in the analysis. This study found that the outcome of 3D FE implicit dynamic analysis of flexible pavement that utilizes appropriate boundary conditions, continuous moving load, viscoelastic hot-mix asphalt model is comparable to field measurements.

• Progress in Superconductivity
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• v.9 no.2
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• pp.177-182
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• 2008

[ $MgB_2$ ] thin films were fabricated using hybrid physical-chemical vapor deposition (HPCVD) method on silicon substrates with buffers of alumina grown by using atomic layer deposition method. The growth war in a range of temperatures $500\;{\sim}\;600^{\circ}C$ and under the reactor pressures of $25\;{\sim}\;50\;Torr$. There are some interfacial reactions in the as-grown films with impurities of mostly $Mg_2Si$, $MgAl_2O_4$, and other phases. The $T_c$'s of $MgB_2$ films were observed to be as high as 39 K, but the transition widths were increased with growth temperatures. The magnetization was measured as a function of temperature down to the temperature of 5 K, but the complete Meissner effect was not observed, which shows that the granular nature of weak links is prevailing. The formation of mostly $Mg_2Si$ impurity in HPCVD process is discussed, considering the diffusion and reaction of Mg vapor with silicon substrates.