• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.93-98
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• 2005

Rewritable optical disk is one of the essential data storage media in these days, which takes advantage of the different optical properties in the amorphous and crystalline states of phase change materials. As well known, data transfer rate is one of the most important parameter of the phase change optical disks, which is mostly limited by the crystallization speed of recording media. Therefore, we doped Sn/Bi to $Ge_2Sb_2Te_5$ alloy in order to improve the crystallization speed and investigated the dependence of phase change characteristics on Sn/Bi doping concentration. The Sn/Bi doped $Ge_2Sb_2Te_5$ thin film was deposited by RF magnetron co-sputtering system and phase change characteristics were investigated by X-ray diffraction (XRD), static tester, UV-visible spectrophotometer, electron probe microanalysis (EPMA), inductively coupled plasma mass spectrometer (ICP-MS) and atomic force microscopy (AFM). Optimum doping concentration of Bi and Sn were 5${\~}$6 at.$\%$ and the minimum time for crystallization was below than 20 ns. This improvement is correlated with the simple crystalline structure of Sn/Bi doped $Ge_2Sb_2Te_5$ and the reduced activation barrier arising from Sn/Bi doping. The results indicate that Sn/Bi might play an important role in the transformation kinetics of phase change materials..

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.4
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• pp.743-748
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• 2010

Boron nitride (BN) and carbon nitride (CN) films, which have relatively low work functions and commonly exhibit negative electron affinity behaviors, were coated on carbon nanotubes (CNTs) by magnetron sputtering. The CNTs were directly grown on metal-tip (tungsten, approximately 500nm in diameter at the summit part) substrates by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The variations in the morphology and microstructure of CNTs due to coating of the BN and CN films were analyzed by field-emission scanning electron microscopy (FE-SEM). The energy dispersive x-ray (EDX) spectroscopy and Raman spectroscopy were used to identify the existence of the coated layers (CN and BN) on CNTs. The electron-emission properties of the BN-coated and CN-coated CNT-emitters were characterized using a high-vacuum field emission measurement system, in terms of their maximum emission currents ($I_{max}$) at 1kV and turn-on voltage ($V_{on}$) for approaching $1{\mu}A$. The results showed that the $I_{max}$ current was significantly increased and the $V_{on}$ voltage were remarkably reduced by the coating of CN or BN films. The measured values of $I_{max}-V_{on}$ were as follows; $176{\mu}A$-500V for the 5nm CN-coated emitter and $289{\mu}A$-540V for the 2nm BN-coated emitter, respectively, while the $I_{max}-V_{on}$ of the as-grown (i.e., uncoated) emitter was $134{\mu}A$-620V. In addition, the CNT emitters coated with thin CN or BN films also showed much better long-term (up to 25h) stability behaviors in electron emission, as compared with the conventional CNT emitter.

• Journal of the Semiconductor & Display Technology
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• v.9 no.1
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• pp.41-47
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• 2010

The effects of thermal treatment on CNTs, which were coated with a-$CN_x$ thin film, were investigated and related to variations of chemical bonding and morphologies of CNTs and also properties of field emission induced by thermal treatment. CNTs were directly grown on nano-sized conical-type tungsten tips via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and a-$CN_x$ films were coated on the CNTs using an RF magnetron sputtering system. Thermal treatment on a-$CN_x$ coated CNT-emitters was performed using a rapid thermal annealing (RTA) system by varying temperature ($300-700^{\circ}C$). Morphologies and microstructures of a-$CN_x$/CNTs hetero-structured emitters were analyzed by FESEM and HRTEM. Chemical composition and atomic bonding structures were analyzed by EDX, Raman spectroscopy, and XPS. The field emission properties of the a-$CN_x$/CNTs hetero-structured emitters were measured using a high vacuum (below $10^{-7}$ Torr) field-emission measurement system. For characterization of emission stability, the fluctuation and degradation of the emission current were monitored in terms of operation time. The results were compared with a-$CN_x$ coated CNT-emitters that were not thermally heated as well as with the conventional non-coated CNT-emitters.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.275.2-275.2
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• 2014

현재 자동차 분야에서 차량 경량화의 한 수단으로 자동차용 유리를 고강도 투명 플라스틱 소재인 Polycarbonate(PC)로 대체하고자 하는 연구가 이루어지고 있다. 하지만, PC의 낮은 내마모 특성과 자외선에 의한 열화 및 변색 현상은 해결하여야 할 문제점으로 지적되고 있으며, 에너지 소비 저감을 위하여 적외선 영역 반사율(reflectance)이 높은 저방사(low emissivity) 특성이 요구되고 있다. 본 연구에서는, ICP-assisted reactive magnetron sputtering 장비를 이용하여 투과율(transmittance)이 확보되고, 고경도 특성을 갖는 Al-Si-N와 300 nm 파장 이하의 자외선 차단 특성이 있는 SiN:H 그리고 저방사 특성을 위해 Al을 증착하였고, 박막의 증착 순서는 SiN:H 박막을 가장 아래에 증착하고 그 위에 Al/Al-Si-N 박막을 다층으로 형성하였다. 박막의 chemical state와 crystallinity를 확인하기 위하여 XPS(X-ray Photoelectron Spectroscopy), XRD (X-ray Diffraction)를 이용하여 분석하였다. Knoop ${\mu}$-hardness tester와 Taber tester를 이용하여 경도 및 내마모 특성을 분석하였다. 제작된 샘플의 Al-Si-N 박막 경도는 Si 비율에 따라 다른 경도 특성을 갖는데, 실제 Si/(Al+Si) 비율이 24%에서 최대 31 GPa의 경도 값을 갖는 것을 확인하였다. UV-Vis Spectrometer를 이용하여 250 nm~700 nm 파장의 투과율을 측정하였고, 자외선 영역의 경우 SiN:H 박막에 의해 300 nm 이하의 파장에서 2% 이하의 투과율을 확인하였다. 그리고 FT-IR(Fourier Transform Infrared Spectroscopy)를 이용하여 $2.5{\mu}m{\sim}15{\mu}m$ 파장의 반사율을 이용하여 방사율을 측정하였는데, 3*(Al/Al-Si-N) 구조의 다층 박막의 경우 방사율은 0.27로 측정되었다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.394-394
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• 2011

급속한 산업의 발달은 심각한 환경오염 및 에너지 문제를 가져왔다. 이를 해결하기 위하여 무한한 에너지원인 태양에너지를 원천으로 하는 친환경 정화소재로서의 광촉매(photocatalyst)를 통하여 인류의 에너지를 확보하는 것에 대한 관심이 급격하게 증가하고 있는 추세이다. 현재 광촉매로 가장 많이 사용되는 $TiO_2$의 경우 뛰어난 광활성과 저렴한 가격, 광 안정성, 화학적 안정성을 가짐에도 불구하고, 3.2 eV라는 상대적으로 넓은 band gap을 가지기 때문에 약 386 nm보다 짧은 파장을 갖는 자외선만 흡수할 수 있다. 이로 인한 가시광 응답성의 부재를 해결하기 위해 수십년간 많은 연구가 진행되어 왔다. 따라서 본 연구에서는 ICP assisted pulsed DC reactive magnetron sputtering을 이용하여 $TiO_2$를 기반으로 하면서 가시광영역의 빛을 흡수하여 높은 효율을 얻을 수 있도록 Nitrogen doping, Low band gap semi-conductor sensitization 등의 방법을 사용하여 광촉매를 제작하였다. 시료의 chemical state와 crystallinity를 확인하기 위하여 X-ray photoelectron spectroscopy와 X-ray diffraction method를 이용하여 분석을 수행하였으며, 이러한 공정을 통해 제작된 $TiO_2$기반 광촉매의 가시광 응답성을 확인하기 위하여 UV/Vis 스펙트럼을 측정하였다. 또한 물 분해 장치(water splitting device)를 제작하여 수소와 산소 생성시 흐르는 전류를 측정하여 광특성을 평가하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.187-191
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• 2006

Sputter deposition followed by surface treatment was studied using reactive RF plasma as a method for preparing titanium oxide $(TiO_2)$ films on the FTO $(SnO_2: F)$ substrate for dye-sensitized solar cells (DSCs). Anatase structure $TiO_2$ films deposited by reactive RF magnetron sputtering under the conditions of $Ar/O_2(5%)$ mixtures, RF power of 600W and substrate temperature of $400^{\circ}C$ were surface-treated by inductive coupled plasma (ICP) with $Ar/O_2$ mixtures at substrate temperature of $400^{\circ}C$, and thus the films were applied to the DSCs. We have chosen a solar cell width as a variable of a large-scaled DSCs and confirmed electric characteristics of an individual cell. As a result, the higher the internal resistance of DSC becomes, the wider the width gets. Internal resistance makes it difficult to collect photoelectron generated from dye. Ultimately up sizing DSC causes the increase of internal resistance and then has a bad effect on the cell characteristics.