• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.165-165
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• 2012

비정질의 Tantalum-indium-zinc oxide (TIZO) 박막 트랜지스터는 RF-sputtering 방법으로 증착되었으며 소결된 단일 타겟을 사용하였다. 증착당시 반응 가스는 알곤과 산소를 95 : 5로 섞어 반응성 스퍼터링을 진행하였으며, 1 mtorr에서 5 mtorr까지 다양한 공정압력에서 증착한 이 후 Furnace system을 통하여 $350^{\circ}C$의 온도로 1시간 동안 후열처리 공정을 진행하였다. 비정질 TIZO 박막을 활성 층으로 사용하여 제작한 박막 트랜지스터는 공정압력이 낮아짐에 따라 높은 이동도와 낮은 subthrehsold gate swing 보였다. 이러한 현상의 원인을 규명하고자 물리적, 전기적, 광학적 분석을 통하여 공정압력의 변화가 박막 트랜지스터 구동에 미치는 영향을 해석하였다. 우선 공정압력에 따른 TIZO 박막의 Ta, In, Zn, O 각각의 조성을 분석하기 위하여 Rutherford back scattering (RBS) 분석을 실시하였다. 또한 X-선 회절(X-ray diffraction)분석을 통해 열처리된 TIZO 박막은 공정압력에 따라 물리적 구조의 변화를 일으키지 않으며 모든 박막은 비정질상을 보이는 것을 확인하였다. 3.3eV의 광학적 밴드 갭은 기존에 보고되었던 비정질 산화물 반도체(InGaZnO, HfInZnO 등)와도 유사한 밴드갭을 가지고 있음을 확인하였다. 또한, spectroscopic ellipsometry (SE)분석을 통하여 전도대 이하 밴드 갭 내에 존재하는 결함상태 및 전도대에서 결함상태까지의 에너지 준위 그리고 공정압력에 따라 결함의 양과 발생되는 에너지 준위가 변화하는 현상을 관측하였다. 박막을 제조 할 때의 공정압력은 박막 내의 결함의 양 및 발생되는 에너지 준위의 변화를 야기하고 변화된 결함의 양과 발생된 에너지 준위에 따라 박막트랜지스터의 전기적 특성을 변화시킨다는 결과를 도출하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제15권5호
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• pp.383-387
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• 2002

N-channel metal-ferroelectric-insulator-semiconductor field-effect-transistors (MFISFET's) by using $SrBi_2Ta_2O_9$/Silicon Nitride/Si (100) structure were fabricated. The fabricated devices exhibit comfortable memory windows, fast switching speeds, good fatigue resistances, and long retention times that are suitable for advanced ferroelectric memory applications. The estimated switching time and polarization ($2P_r$) of the fabricated FET measured at applied electric field of 376 kV/cm were less than 50 ns and about 1.5 uC/$\textrm{cm}^2$, respectively. The magnitude of on/off ratio indicating the stored information performance was maintained more than 3 orders until 3 days at room temperature. The $I_DV_G$ characteristics before and after being subjected to $10^11$ cycles of fatigue at a frequency of 1 MHz remained almost the same except a little distortion in off state.

• Proceedings of the Materials Research Society of Korea Conference
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• 한국재료학회 2011년도 춘계학술발표대회
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• pp.5-5
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• 2011

The research and development of hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV) and electric vehicle (EV) are intensified due to the energy crisis and environmental concerns. In order to meet the challenging requirements of powering HEV, PHEV and EV, the current lithium battery technology needs to be significantly improved in terms of the cost, safety, power and energy density, as well as the calendar and cycle life. One new technology being developed is the utilization of composite cathode by mixing two different types of insertion compounds [e.g., spinel $LiMn_2O_4$ and layered $LiMO_2$ (M=Ni, Co, and Mn)]. Recently, some studies on mixing two different types of cathode materials to make a composite cathode have been reported, which were aimed at reducing cost and improving self-discharge. Numata et al. reported that when stored in a sealed can together with electrolyte at $80^{\circ}C$ for 10 days, the concentrations of both HF and $Mn^{2+}$ were lower in the can containing $LiMn_2O_4$ blended with $LiNi_{0.8}Co_{0.2}O_2$ than that containing $LiMn_2O_4$ only. That reports clearly showed that this blending technique can prevent the decline in capacity caused by cycling or storage at elevated temperatures. However, not much work has been reported on the charge-discharge characteristics and related structural phase transitions for these composite cathodes. In this presentation, we will report our in situ x-ray diffraction studies on this mixed composite cathode material during charge-discharge cycling. The mixed cathodes were incorporated into in situ XRD cells with a Li foil anode, a Celgard separator, and a 1M $LiPF_6$ electrolyte in a 1 : 1 EC : DMC solvent (LP 30 from EM Industries, Inc.). For in situ XRD cell, Mylar windows were used as has been described in detail elsewhere. All of these in situ XRD spectra were collected on beam line X18A at National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory using two different detectors. One is a conventional scintillation detector with data collection at 0.02 degree in two theta angle for each step. The other is a wide angle position sensitive detector (PSD). The wavelengths used were 1.1950 ${\AA}$ for the scintillation detector and 0.9999 A for the PSD. The newly installed PSD at beam line X18A of NSLS can collect XRD patterns as short as a few minutes covering $90^{\circ}$ of two theta angles simultaneously with good signal to noise ratio. It significantly reduced the data collection time for each scan, giving us a great advantage in studying the phase transition in real time. The two theta angles of all the XRD spectra presented in this paper have been recalculated and converted to corresponding angles for ${\lambda}=1.54\;{\AA}$, which is the wavelength of conventional x-ray tube source with Cu-$k{\alpha}$ radiation, for easy comparison with data in other literatures. The structural changes of the composite cathode made by mixing spinel $LiMn_2O_4$ and layered $Li-Ni_{1/3}Co_{1/3}Mn_{1/3}O_2$ in 1 : 1 wt% in both Li-half and Li-ion cells during charge/discharge are studied by in situ XRD. During the first charge up to ~5.2 V vs. $Li/Li^+$, the in situ XRD spectra for the composite cathode in the Li-half cell track the structural changes of each component. At the early stage of charge, the lithium extraction takes place in the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component only. When the cell voltage reaches at ~4.0 V vs. $Li/Li^+$, lithium extraction from the spinel $LiMn_2O_4$ component starts and becomes the major contributor for the cell capacity due to the higher rate capability of $LiMn_2O_4$. When the voltage passed 4.3 V, the major structural changes are from the $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, while the $LiMn_2O_4$ component is almost unchanged. In the Li-ion cell using a MCMB anode and a composite cathode cycled between 2.5 V and 4.2 V, the structural changes are dominated by the spinel $LiMn_2O_4$ component, with much less changes in the layered $LiNi_{1/3}Co_{1/3}Mn_{1/3}O_2$ component, comparing with the Li-half cell results. These results give us valuable information about the structural changes relating to the contributions of each individual component to the cell capacity at certain charge/discharge state, which are helpful in designing and optimizing the composite cathode using spinel- and layered-type materials for Li-ion battery research. More detailed discussion will be presented at the meeting.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.304-304
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• 2012

III-V 화합물 태양전지는 실리콘 등 다른 태양전지에 비해 1sun상 30% 이상의 고효율을 갖고 있고 direct bandgap과 높은 이동도 등의 물질특성과 3족과 5족의 비율 조절로 같은 결정구조에서 에너지 bandgap이 다른 물질들을 만들기에 용이하여 태양전지 스펙트럼의 넓은 영역을 흡수할 수 있는 장점이 있다. 그러나 셀 자체의 물질이 실리콘에 비하여 고가여서 고성능이 요구되는 우주 인공위성 등에 적용이 되었지만, 2000년대 이후로 집광에 적용 가능한 태양전지의 연구를 거듭하여 2005년부터는 값싼 프레넬 렌즈를 이용하여 1 sun에 비해 500배 해당하는 빛을 셀에 집광하여 보다 효율을 증가시킴으로써 지상발전용에도 적용 가능한 셀을 형성하게 되었다. 더불어 태양전지의 효율을 증가시키기 위한 다양한 구조적 변화의 시도도 많이 이루어지고 있다. 최근 실리콘 태양전지의 표면에 texture 구조를 주어 높은 흡수율과 낮은 반사율을 갖게 함으로써 효율을 증가시키는 사례가 많아지고, III-V 화합물 태양전지도 texturing에 의해 증가된 효율을 발표한바 있다. 본 연구에서는 III-V 화합물 InGaP 태양전지의 window층으로 사용되는 InAlP 층에 Metal-assisted chemical etching (mac etching) 방법으로 texture 구조를 형성하여 etching 시간에 따른 InAlP층의 표면 변화와 반사율의 변화를 분석하였다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• 제49권8호
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• pp.445-450
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• 2000

Many successful developments and microscopic studies have been made on the high quality insulating materials. However, a little attention have given to the macroscopic interface in HV(High Voltage) insulating systems. In this study, AC interfacial breakdown strength and V-t characteristic of the interface between Epoxy/EPDM(ethylene propylene diene terpolymer) are investigated. Electrode system is designed to reduce the charges from electrodes and to have the tangential potentials along the interface between Epoxy/EPDM by FEM(finite elements method). The AC breakdown strength is observed when HV is given to the interface. It is shown that AC interfacial breakdown strength is improved by increasing interfacial pressure and oiling. In particular, it was saturated at certain interfacial pressure level. V-t characteristic is able to extend to the life time of the interface between Epoxy/EPDM. Oiling also plays a good roll in prolongation of the life time.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.427-427
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• 2013

잉크젯 프린팅 방법은 전도성 고분자 물질을 잉크 재료로 사용하여 전자 소자의 전극 패턴을 형성할 수 있으며 비접촉, drop-on-demand 공정으로 현재 많은 관심을 받고 있는 연구 분야이다. Ag는 $1.59{\mu}m{\cdot}cm$의 저항을 나타내는 가장 낮은 저항을 가지고 있는 물질 중의 하나이며, Ag 전도성 잉크는 고전도 패턴의 형성을 위해 현재 많이 사용되고 있는 물질이다. 본 연구에서는 a-IGZO 박막을 채널층으로 사용하여 Ag S/D 전극을 잉크젯 프린팅 방법으로 형성하여 산화물 트랜지스터를 제작하였다. a-IGZO 채널층은 $SiO_2$가 증착된 Si 기판위에 스퍼터링 방식으로 80 nm의 두께로 형성하였다. Ag S/D 전극은 10 pl의 카트리지가 장착된 Fujifilm Dimatix DMP 2800 장비를 사용하여 형성하였으며, 프린팅 후 $130^{\circ}C$로 20분간 열처리를 하였다. Fig. 1은 잉크젯 프린팅된 Ag S/D을 가진 a-IGZO의 트랜지스터 특성을 보여준다. 채널 W/L가 90/$50{\mu}m$ 구간에서 드레인 전압이 50 V 일때, 전계효과이동도 $0.27cm^2$/Vs, 문턱전압 6.03 V, 문턱전압 아래의 기울기 값은 2.06 V/dec를 얻었다. 이와 같은 특성은 잉크젯 프린팅 방법으로 Ag S/D 전극을 형성함으로써 산화물 TFT에서 잉크젯 프린팅 방식의 다양한 응용 가능성을 확인할 수 있었다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.141-141
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• 2018

Copper is one of the most abundant metals on earth. Its oxide (CuO) is an intrinsically p-type metal-oxide semiconductor with a bandgap ($E_g$) of 1.2-2.0 eV 1. Copper oxide nanomaterials are considered as promising materials for a wide range of applications e.g., lithium ion batteries, dye-sensitized solar cells, photocatalytic hydrogen production, photodetectors, and biogas sensors 2-7. Recently, high-density and uniform CuO nanostructures have been grown on Cu foils in alkaline solutions 3. In 2011, T. Soejima et al. proposed a facile process for the oxidation synthesis of CuO nanobelt arrays using $NH_3-H_2O_2$ aqueous solution 8. In 2017, G. Kaur et al. synthesized CuO nanostructures by treating Cu foils in $NH_4OH$ at room temperature for different treatment times 9. The surface treatment of Cu in alkaline aqueous solutions is a potential method for the mass fabrication of CuO nanostructures with high uniformity and density. It is interesting to compare the gas sensing properties among CuO nanomaterials synthesized by this approach and by others. Nevertheless, none of above studies investigated the gas sensing properties of as-synthesized CuO nanomaterials. In this study, CuO nanowalls versus nanoparticles were synthesized via the oxidation process of Cu foil in NH4OH solution at $50-70^{\circ}C$. The gas sensing properties of the as-prepared CuO nanoplates were examined with $C_2H_5OH$, $CH_3COCH_3$, and $NH_3$ at $200-360^{\circ}C$.

• Journal of The Korea Institute of Healthcare Architecture
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• 제19권4호
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• pp.7-18
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• 2013

Purpose: The aim of this paper is to reduce the stress and the disturbance occur in selective action of patient. This article will also help us to control spreading and reduce the order and bacteria produced by leprosy disease among the lepers. This will be achieved with the help of several variables and these variables help us on health benefits is 5S (Sort, Straighten, Shine, Standardize, Sustain) i.e. ratio of sectional morphology, lessor 90 degree angles, day light, universal design building and maximum ventilation. The replies from the questionnaire were collected based on varying levels of satisfaction and gloominess on the scale of 1-10. Methods: The multi-layer methodological framework for maximising the healing environment obtained from the observation of schemes and parameters of ANOVA: (Analysis Of Variance between five deciding factors) are. Firstly applied for the calculation of the patient's satisfaction for U.V light from sun on ECOTECT simulation, secondly the number of $90^{\circ}$ angle, along the corridors. Thirdly understanding the ways to represent people's perceptual structures and way finding with Space Syntax software. Fourthly the ratio of depth to height of the building typology and finally interviewing the subjects describing their special experiences based on scale value. The focus of this testing of human subjects was to receive data for the existence of image scheme in way-finding and to identify the mechanisms by which sun light impacts human (lepers) health. Results: AMPVA studies concluded that there is similarity between I and O plan as well as L and H plan whereas U plan was difference among the five selected architectural shapes. Implications: The purpose of this research is to show the effects of the I-type, L-type, C-type, U-type and O-type plan design, and to analyse the morphology for EBD (Evidence-Based Design) healing environment which is a universal design for Munghopir Karachi, in Pakistan.

• Food Science and Preservation
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• 제12권1호
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• pp.80-85
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• 2005

The effect of 12 edible mushroom species on the antioxidant and cytotoxicity on cancer cells were studied Methanol extract of Lyophyllum ulmarium, Cordyceps militaris and Sarcodon aspratus showed $30\~60\%$ DPPH radical scavenging activity and $39\~53\%$ protective effects against the cytotoxicity of $B_2O_2$. Methanol extracts of Sarcodon aspratus, Lyophyllum ulmarium, Cordyceps militaris, Agaricus blazei and Ganoderma lucidum revealed high inhibitive activities in cytotoxicity on human leukemia tells such as promyelocytic leukemia cell (HL60) and histiocytic lymphoma cell (U937). Highest toxicity was observed against HL60 cells in Sarcodon aspratus methanol extract showing $70.5\%$ inhibition at 1mg/mL whereas Cordyceps militaris methanol extract showed $81.5\%$ inhibition against U937 cells. Most water extracts of edible mushrooms exhibited the lowest effect against HL60 and U937 cells compared to methanol extract. These extract did not show cytotoxic effects against human lymphocyte. Results revealed 5 kinds of edible murshroom (Cordyceps militaris, Agaricus blaxei, Lyophyllum ulmarium, Ganoderma lucidum and Sarcodon aspratus) have strong antioxidative and in vitro anticancer efforts.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.475-475
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• 2013

Cuprous oxide ($Cu_2O$)는 밴드갭이 2.17 eV p-type 산화물 반도체로써 태양에너지 변환기, photocatalysis (광촉매작용), 센서, 스위칭 메모리 등 응용이 다양한 재료이다. 산화물 반도체의 기본 특성은 나노/마이크로 범위 안에서 재료의 표면형태, 크기, 구조와 형상 공간방향등에 크게 영향을 받는다. 그렇기 때문에 원하는 $Cu_2O$ 특성을 얻기 위해서 성장 거동을 아는 것은 매우 중요하다. RF 마그네트론 스퍼터법으로 rod 성장 사례는 잘 알려지지 않았다. 그래서 RF 마그네트론 스퍼터법 $Cu_2O$ rod 형성 실험을 통하여 $Cu_2O$ 형성과 성장 거동을 알아보았다. RF 마그네트론 스퍼터법으로 $Cu_2O$ rod를 glass 기판 위에 Cu metal target을 이용하여 형성시켰다. $Cu_2O$ rod 합성을 위해 기판온도 및 산소분압 O2/(Ar+O2)=3%, 5%, 7% 증착시간 등을 변화시켜 실험하였다. 성장된 rod의 분석은 XRD, SEM으로 확인하였다. 성장 거동은 증착온도와 증착시간에 차이를 보였다. 증착온도 $550^{\circ}C$에서 rod가 생성되는 것을 관찰하였다. 증착시간이 길어질수록 rod 길이가 길어지고 일정 시간이 지나면 rod의 길이 성장보다는 두께(폭)가 성장하는 것을 확인하였다. 증착온도 $550^{\circ}C$ 그리고 산소분압 3%, 5%, 7% 조건에서 rod 합성 실험을 하였을 때 3%, 5% 조건에서 rod의 성장을 확인하였다. 이때 3%, 5% 산소분압에 따라 rod의 모양이 변화하였다. 하지만 7% 조건에서는 rod가 성장하지 않았다. 이유는 3%, 5%에서는 Cu metal peak을 확인하였지만, 7% 조건에서는 Cu metal peak이 없었다. 이로부터 Cu metal이 $Cu_2O$ rod 생성에 영향을 미치는 중요한 요소임을 예상할 수 있었다.