• 공업화학
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• 제24권2호
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• pp.132-137
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• 2013

포스파티딜콜린이 다량 함유된 수첨레시틴을 이용한 실험에서 액정구조가 잘 형성됨을 알 수 있었다. 액정구조를 형성하는 물질로는 포스포리피드, 에탄올, 물로 이루어짐을 알 수 있었고 로즈마린산을 지표물질로 캡슐화하였다. 액정의 평균입자크기는 480 nm ~ $3{\mu}m$로 이는 액의 구성물질과 물리적인 힘에 따라 다양한 크기의 형태로 존재하였다. 리포좀과 비교했을 때 액정구조는 매우 높은 캡슐화 효율을 보였다. 수첨레시틴의 함량이 증가하면 많은 액정을 형성하였고, 수첨레시틴의 함량이 적으면 액정의 양도 적게 나타났다. 로즈마린산을 함유한 액정구조의 방출실험결과 리포좀으로 형성된 베지클보다 훨씬 적은 양이 방출됨을 알 수 있었다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.265-267
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• 1997

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.171-174
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• 1997

• 한국대기환경학회지
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• 제25권5호
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• pp.392-401
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• 2009

Ice-crystal clouds observation was conducted using a GIST/ADEMRC Multi-wavelength Raman lidar system in order to measure vertical profile and optical depth at Gwangju ($35^{\circ}$10'N, $126^{\circ}$53'E), Korea in December 2002, and March and April 2003. Ice-crystal clouds at high altitude can be distinguished from atmospheric aerosols by high depolarization ratio and high altitude. Ice-crystal clouds were observed at 5~12 km altitudes with a high depolarization ratio from 0.2 to 0.5. Optical depth of ice-crystal clouds had varied from 0.14 to 1.81. The radiative effect of observed ice-crystal cloud on climate system was estimated to be negative net flux in short wavelength (0.25~$4.0{\mu}m$) and positive net flux in short+long wavelength (0.25~$100{\mu}m$) at top of the atmosphere. Net flux by ice-crys tal cloud per unit optical depth was comparable to that of Asian dust.

• 한국전기전자재료학회논문지
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• 제32권6호
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• pp.516-521
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• 2019

The top seeded solution growth (TSSG) method is an alternative technique to grow high-quality SiC crystals that has been actively studied for the last two decades. However, the TSSG method has different issues that need to be resolved when compared to the commercial SiC crystal growing method, i.e., physical vapor transport (PVT). A particular issue of the TSSG method of results from the presence of liquid droplets on the grown crystal that can remain even after crystal growth; this induces residual stress on the crystal surface. Hence, the residual droplet causes several unwanted effects on the crystal such as the initiation of micro-cracks, micro-pipes, and polytype inclusions. Therefore, this study investigated the formation of the residual droplet through multiphysics simulations and lead to the development of a liquid droplet removal method. As a result, we found that although residual liquid droplets significantly apply residual stress on the grown crystal, these could be vaporized by adopting thermal annealing processes after the relevant crystal growing steps.

• 한국결정성장학회지
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• 제12권6호
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• pp.272-282
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• 2002

Mercurous bromide ($Hg_{2}0Br_{2}$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region, the buoyancy-driven convection may occur. The effects of thermal convection on the crystal growth rate was investigated in this study in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. The results showed that the growth rate increases linearly with Grashof number, and for 0.2 $\leq$ Ar (transport length-to-height, L/H)$\leq$1.0 sharply for Ar=5 and $\Delta$T=30 K. We have also shown that the magnitude of convection decreases with the Ar. For gravity levels of less than $10^{-2}$g the non-uniformity of interfacial distribution is negligible.

• Journal of Magnetics
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• 제19권4호
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• pp.333-339
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• 2014

Single crystal growth of $BaFe_{12}O_{19}$ by the solid state crystal growth method was attempted. Seed crystals of ${\alpha}-Fe_2O_3$ were pressed into pellets of $BaFe_{12}O_{19}$ + 2 wt% $BaCO_3$ and heat-treated at temperatures between $1150^{\circ}C$ and $1250^{\circ}C$ for up to 100 hours. Instead of single crystal growth taking place on the seed crystal, BaO diffused into the seed crystal and reacted with it to form a polycrystalline reaction layer of $BaFe_{12}O_{19}$. The microstructure, chemical composition and structure of the reaction layer were studied using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), x-ray Diffraction (XRD) and micro-Raman scattering and confirmed to be that of $BaFe_{12}O_{19}$. XRD showed that the reaction layer shows a strong degree of orientation in the (h00)/(hk0) planes in the sample sintered at $1200^{\circ}C$. $BaFe_{12}O_{19}$ layers with a degree of orientation in the (hk0) planes could also be grown by heat-treating an ${\alpha}-Fe_2O_3$ seed crystal buried in $BaCO_3$ powder.

• 한국결정성장학회지
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• 제5권2호
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• pp.87-93
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• 1995

Floating zone법으로 strontium titanate 단결정을 육성하였다. 성장조건은 공기 분위기하에서 성장속도 3mm/hr, 상부축 회전속도 20~25rpm, 하부축 회전속도 15~20rpm이었으며 육성한 단결정은 옅은 갈색을 띄고 있었으며 투명하였고 annealing 후 색깔이 옅어짐을 확인할 수 있었다. 성장방위는 [112] 방향이었으며 XRD, EDS로 화학양론적인 조성은 $SrTiO_3$단일 결정상임을 알 수 있었다. $350^{\circ}C$, KOH용액에서 5분동안 chemical etching하여 etch pit pattern을 조사하였으며 상온하에서$350^{\circ}C$의 온도 범위에서 유전상수 값을 조사하였다.

• Coupled systems mechanics
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• 제5권4호
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• pp.341-353
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• 2016

Manufactures of multi-crystalline silicon ingots by means of the directional solidification system (DSS) is important to the solar photovoltaic (PV) cell industry. The quality of the ingots, including the grain size and morphology, is highly related to the shape of the crystal-melt interface during the crystal growth process. We performed numerical simulations to analyze the thermo-fluid field and the shape of the crystal-melt interface both for steady conditions and transient processes. The steady simulations are first validated and then applied to improve the hot zone design in the furnace. The numerical results reveal that, an additional guiding plate weakens the strength of vortex and improves the desired profile of the crystal-melt interface. Based on the steady solutions at an early stage, detailed transient processes of crystal growth can be simulated. Accuracy of the results is supported by comparing the evolutions of crystal heights with the experimental measurements. The excellent agreements demonstrate the applicability of the present numerical methods in simulating a practical and complex system of directional solidification system.

• 한국결정성장학회지
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• 제30권5호
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• pp.163-167
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• 2020

본 연구에서는 PVT(Physical Vapor Transport) 방법을 이용하여 반도체 식각 공정용 소재로 사용되는 링 모양의 SiC(Silicon carbide) 다결정을 제조하였다. 흑연 도가니 내부에 원기둥 모양의 흑연 구조물을 배치하여 PVT법에 의한 링 모양의 SiC 다결정을 성장시켰다. 성장된 결정은 Raman 및 UVF(Ultra Violet Fluorescence) 분석을 이용하여 결정의 상분석을 하였고, SEM(Scanning Electron Microscope), EDS(Energy Dispersive Spectroscopy) 분석을 통해 미세조직 및 성분을 확인하였다. PVT 성장 초기의 온도변화를 통하여 SiC 다결정의 결정립 크기와 성장 속도를 조절할 수 있었다.