• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.50.2-50.2
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• 2009

ZnO 는 상온에서 3.37eV의 넓은 밴드갭과 60 meV의 엑시톤 결합에너지를 가지는 직접형 반도체로서 높은 투과성, 저가의 재료비, 비독성, 친환경적인 재료로서 발광다이오드, 디스플레이 응용분야 등 많은 부분에서 관심을 받고 있다. 유리 기판은무겁고 쉽게 깨지는 특성에도 불구하고 디스플레이 응용분야에서 폭넓게 사용되고 있으나 많은 연구자들은 이러한 문제점들을 해결하기 위해 플렉서블 기판위에서의 ZnO 성장 연구를 진행하고 있다 ZnO를 성장시키는 방법에는 molecular beam epitaxy (MEB), chemical vapordeposition (CVD), 그리고 atomic layer deposition (ALD)등많은 방법들이 있다. 이 연구에서 우리는 플렉서블기판의 플라즈마 전처리에 따른 ZnO의 구조적 그리고 광학적 특성에 대해 연구하였다. ZnO는 ALD 방법에 의해 성장되었고 반응물로는 temperature controlled bath 속에서 $10^{\circ}C$와 $30^{\circ}C$로 각각 온도를 유지시킨 diethylzinc (DEZn)과 distilled water ($H_2O$)를 사용하였다. 성장된 ZnO의 표면 morphology는atomic force microscope (AFM) 과 scanning electron microscope (SEM)으로 측정하였고, 광학적, 구조적특성은 Photoluminescence (PL)와 X-ray diffraction (XRD) 방법으로 각각으로 측정 되었다.

• Economic and Environmental Geology
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• v.26 no.1
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• pp.29-40
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• 1993

Several vermiculite deposits occur as the alteration product from phlogopite in ultramafic rock, in the Hongseong and Cheongyang area, South Korea. Some quarries show well-defined weathering profile. Samples collected from those quarries were examined by XRD and chemistry to define a vertical variations in mineralogy and chemistry of the weathering profile developed on ultramafic rocks. The analysis by X-ray diffractometry showed that mineral compositions changed continuously as depth of profile increasing, the vermiculite-the phlogopite/vermiculite interstratified-the phlogopite. Chemical analysis of bulk samples in altered zone revealed that regardless of composition and kinds of mineral in the rock, there are significant increase of MgO, CaO and $H_2O$, and decrease of K as depth of profile decrease reflecting the characteristics in vermiculitization. Also, there was a tendency that weathering indicies of each sample horizon change gradually with increasing depth. This tendency can be explained as variations of degree of vermiculitization. The regular changes of mineralogical and chemical composition in vertical profile suggest that weathering is the most important process in vermiculitization in this area.

• Bulletin of the Korean Chemical Society
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• v.10 no.2
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• pp.177-184
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• 1989

The structure of cholesteryl isobutyrate, $(CH_3)_2CHCOOC_{27}H_{45}$, was determined by single crystal X-ray diffraction methods. Cholesteryl isobutyrate crystallized monoclinic space group $P2_1$, with a = 15.115 (8)${\AA}$, b = 9.636 (5)${\AA}$, c = 20.224 (9)${\AA}$, ${\beta}$ = 93.15 (5)$^{\circ}$, z = 4, $D_c = 1.03 g/cm^3 $and Dm= 1.04 g/$cm^3$. The intensity data were measured for the 3417 reflections, within $sin{\theta}/{\lambda} = 0.59{\AA}^{-1}$, using an automatic four-circle diffractometer and graphite monochromated Mo-$K_{\alpha}$ radiation. The structure was solved by fragment search Patterson methods and direct methods and refined by full-matrix least-squares methods. The final R factor was 0.129 for 2984 observed reflections. The two symmetry-independent molecules (A) and (B) are almost fully extended. The molecules are in antiparallel array forming monolayers with thickness $d_{100}$ = 15.2${\AA}$, and molecular long axes are nearly parallel to the [$\bar{1}$01] directions. The two distinct molecules form separate stacks with almost the same orientations, but with differing degrees of steroid overlap. Thers is a close packing of cholesteryl groups within the monolayers. The packing type is similar to those of cholesteryl hexanoate and cholesteryl oleate.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.314-315
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• 2011

최근에 $Eu^{3+}$ 이온이 첨가된 적색 형광체에 대한 연구가 활발히 진행되고 있다. 현재 상업적으로 이용 가능한 적색 형광체와 비교하여 $GdVO_4$를 모체로 갖는 적색 형광체는 우수한 열적 안정성과 광학적 특성을 나타낸다. 본 연구에서는 고효율의 적색 형광체를 개발하기 위하여 고상 반응법을 사용하여 $Gd_{1-x}VO_4$ : $Eu_x^{3+}$ 형광체를 합성하였다. $Gd_{1-x}VO_4$ : $Eu_x^{3+}$ 형광체 분말 시료는 활성체인 $Eu^{3+}$의 함량을 0, 0.05, 0.10, 0.15, 0.20 mol로 변화시키며, 초기 물질 $Gd_2O_3$ (99.99%), $H_3BO_3$ (99.99%), $Eu_2O_3$ (99.9%)를 화학 적량으로 준비하였다. 분말은 볼밀과 건조 작업을 거친 후, 500$^{\circ}C$ 전기로에서 5시간 동안 하소 공정, 1,100$^{\circ}C$에서 6시간 동안 소성시켰다. 합성된 형광체 분말의 XRD 측정한 결과에 의하면, $Eu^{3+}$의 함량비에 관계없이 모든 분말 시료들에서 주 피크는 24.7$^{\circ}$와 33.2$^{\circ}$에 최대값을 갖는 (200)와 (112)면의 회절 신호들이 관측되었고, 상대적으로 약한 회절 세기를 갖는 (101), (211), (301), (103), (312)와 (420)면의 회절 신호들은 각각 18.6$^{\circ}$, 31.1$^{\circ}$, 40.1$^{\circ}$, 44.6$^{\circ}$, 49.2$^{\circ}$와 57.1$^{\circ}$에서 나타났다(Fig. 1). 이결과를 JCPDS(86-0996)와 비교함으로써, 합성된 형광체 분말의 결정 구조는 정방정계임을 확인할 수 있었다. $Eu^{3+}$의 함량비가 0.05 mol에서 0.15 mol로 증가함에 따라 주 피크인 (200)면의 회절 신호의 세기는 증가한 반면, 0.20 mol에서는 급격하게 감소하였으며, 이 경우에 반치폭의 크기는 0.16$^{\circ}$이었다. 결정 입자의 크기를 결정하기 위하여 (200)면의 회절 피크에 대한 정보를 잘 알려진 Scherrer의 식에 대입하여 계산한 결과, $Eu^{3+}$의 함량비가 0 mol인 경우에, 평균 크기는 48 nm이었다. $Eu^{3+}$ 함량비를 증가함에 따라 결정 입자의 크기도 비례하여 증가하였으며, 0.15 mol에서 최대값을 나타내었으나, 농도 억제 효과로 인하여 0.20 mol 에서는 현저히 감소하였다. 표면 형상의 변화를 관측한 SEM 측정 결과에 의하면, $Eu^{3+}$의 함량비가 0 mol에서 0.15 mol로 증가함에 따라 결정 입자의 모양은 사다리꼴 형태에서 모서리가 둥글게 깎인 구형으로 변형되는 것을 관측할 수 있었으며 평균 크기는 500 nm이었다(Fig. 2). $Eu^{3+}$의 함량이 0.20 mol인 경우에 결정 입자의 형상은 더욱 구형에 접근하였으나, 평균 크기는 최소값을 나타내었다. 실험 결과로부터, 적절한 함량비를 갖는 $Eu^{3+}$ 이온을 첨가함으로써 적색 형광체 $Gd_{1-x}VO_4$ : $Eu^{3+}$ 분말의 결정 크기와 발광 세기를 제어할 수 있음을 제안한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.281-281
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• 2011

산업 환경에서 친환경 및 에너지효율성을 중요한 조건이 되면서 고효율성 및 다기능을 가진 재료에 대한 연구가 활발히 진행 되고 있다. 특히 Al-Ti-N 코팅은 이미 경도 측면에서 우수 하여 고속 공구 부품에 널리 사용되고 있고 최근에 Al-TiN에서 Si 첨가는 40GPa이상의 고경도와 1000도 이상의 산화온도를 지닌 나노 혼합물 코팅을 형성 시키는 것으로 알려져 있다. 본 연구에서 Al-Ti에 Si, Cu, Cr 을 첨가하였을 때 코팅을 형성하였을 때 바뀌는 물성 변화을 확인하였다. 이러한 연구를 위해 Al-Ti 합금 조성 중 가장 우수한 것으로 알려진 60:40으로 타겟을 만들어 스퍼터 장비를 이용해 코팅을 형성하여 기초 실험을 진행하였다. 그 근거로 하여 3원계인 Si, Cu, Cr 을 첨가하여 각각의 단일 타겟으로 만들고 코팅을 형성하였다. 타겟과 코팅의 성분이 동일한지 확인하기 위해 EPMA분석을 하였고 그 결과 오차 범위 내에 동일한 것으로 확인하였다. 또 내산화성 테스트를 위해 400도에서 1000도로 가열된 대기 중에 코팅 층을 1시간씩 노출시키는 공정을 통해 확인하였고 내식성 테스트는 SUS 304계열 위에 코팅을 하여 Potentiodynamic polarization scan 장비로 비교해 보았다. 표면경도는 3원계 코팅인 경우 질소비율이 증가할수록 30GPa ~ 35GPa까지 증가하였고 XRD 분석 결과와 비교 시 (111), (200) peak가 명확할수록 경도 값이 높은 것으로 확인하였다. 마모테스트 결과 3원계인 코팅 층이 dry상태에서 감소하는 경향을 보였다. 특히 0,26까지 감소한 Si 을 첨가한 코팅 층은 H/E지수도 좋아 마모트랙의 길이도 짧아 우수한 것으로 알 수 있었다. 이런 결과에서 보듯 3원소 이상 첨가 시 특성변화가 차이가 있다는 것을 알 수 있었다.

• Journal of Biomedical Engineering Research
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• v.18 no.3
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• pp.307-313
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• 1997

he photoconductive gain mechanism in amorphus silicon devices was investigated in connection with applications to radiation detection. Various device types such as p-i-n, n-i-n and i-i-p-i-n structures were fabricated and tested. Photoconductive gain was measured in two time scales : one for short pulses of visible light(<$1{\mu}sec$) which simulate the transit of energetic charged particles or ${\gamma}$-rays, and the other for rather long pulses of light(1msec) which simulate x-ray exposure in medical imaging, We used two definitions of phtoconductive gain : current gain and charge gain which is an integration of the current gain. We obtained typical charge gains of 3~9 for short pulses and a few hundreds for long pulses at a dark current density level of 10mA/$cm^2$. Various gain results are discussed in terms of the device structure, applied bias and dark current density.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.698-702
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• 2000

The characteristics of optical absorption in $Al_{0.24}Ga_{0.76}As/GaAs$ multi-quantum wells(MQWs) structure were investigated by using the surface photovoltage(SPV). The Spy features near 1.42 eV showed two overlapping signals. By chemical etching, we found associated with the GaAs substrate and the GaAs cap layer. The Al composition(x=24 %) was determined by Kuech's composition formula. In order to identify the transition energies. the experimentally observed energies were compared with results of the envelope function approximation for a rectangular quantum wells An amplitude variation of the relative Spy intensity from the GaAs substrate, llH, and llL was observed at different light intensities. A variation in the SPY line shape of the transition energies were observed with decreasing tempera­t ture.

• Journal of Bio-Environment Control
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• v.11 no.1
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• pp.5-11
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• 2002

In this study, new development of natural ventilation window was accomplished to control environment of greenhouse with no use of farced ventilation during hot season. The ventilation effect of developed ventilation window was investigated in experimental greenhouse which was designed using side wall panel and folding type panel fur natural ventilation. Folding panel type ventilation window was designed to open upper part of the side wall and top of the roof using two hinges which are located bottom of the side wall and the roof panel to grab one side of each panels and guide the other side along with the guidance rail. Developed ventilation window has top ventilation part with maximum moving distance X=ι (1-cos$\theta$)=848.5 mm and side ventilation part with maximum moving distance Y=ι/2 $\times$sin$\theta$=1,184.4 mm at 45$^{\circ}$ of theoretical opening angle. It took 4.5 minutes to open roof vent fully and temperature at 1.2 and 0.8 m height decreased after 1 minute from starting opening and became equilibrium state maintaining 3-4$^{\circ}C$ difference after 2 minutes from complete opening. Air exchange rate was 15.2~39.3 h$^{-1}$ which was more than 10~15 h$^{-1}$ of continuous type and Venlo type greenhouse. The descent effect of temperature by ventilation windows was two times higher than Venlo type greenhouse.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.4
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• pp.164-167
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• 2010

Bulk GaN single crystal with 1.5 mm thickness was successfully grown by hydride vapor phase epitaxy (HVPE) technique. Free-standing GaN substrates of $10{\times}10,\;15{\times}15$ mm size were fabricate after lift-off of sapphire substrate and their optical properties were characterized properties for device applications. X-ray diffraction patterns showed (002) and (004) peak, and the FWHM of the X-ray rocking curve (XRC) measurement in (002) was 98 arcsec. A sharp photoluminescence spectrum at 363 nm was observed and defect spectrum at visible range was not detected. The hexagonal-shaped etch-pits are formed on the GaN surface in $200^{\circ}C\;H_3PO_4$ at 5 minutes. The defect density calculated from observed etch-pits on surface was around $5{\times}10^6/cm^2$. This indicates that the fabricated GaN substrates can be used for applications in the field of optodevice, and high power electronics.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.469-472
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• 2002

Solid state fermentation was performed for the production of entomopathogenic fungus Metarhizium anisopliae HY-2 using wheat bran media containing rice bran. Fungal growth in a solid state fermentation system was estimated by viable cell count, spore count, and mycelial biomass. It was used chemical method measuring N-acetyl-glucosamine (chitin) content for estimating of mycelial biomass. In static flask culture, viable cell reached 2.40 ${\times}$ $10^8$ cfu/g at 23 days of culture at $27^{\circ}C$ and then mycelial biomass was 41.59 mg/g. Specific growth rate(${\mu}$ max) was 0.0418 $h^{-1}$ between 3 and 9 days when estimated by viable cell count and was 0.00976 $h^{-1}$ between 9 and 17 days when N-acetylglucosamine content was measured. Viable cells reached 1.12 ${\times}$ $10^8$ cfu/g in polypropylene-bag at 28 days of culture at $27^{\circ}C$. Formulated microbial pesticide containing M. anisopliae HY-2 were tested their bio-activity against Chestnut Brown Chafer (Adoretus tenuimaculatus). The protection rate of the liquid culture showed 13 ${\sim}$ 26 % with 1st to 3rd instar, and spore suspension of M. anisopliae HY-2 showed 56 ${\sim}$ 64%. Conidia produced by large scale solid-state fermentation showed 20 ${\sim}$ 27 % activity 60 ${\sim}$ 64 % with M. anisopliae HY-2.