• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.7
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• pp.905-914
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• 1998

View factor determination is very important in thermal analysis problems with surface radiation but it is very difficult to determine view factors for complex geometries. Exact calculation of view factors for crystal growth furnace is essential due to not only its high surface temperature but the radiation shield, complicated heating system. In this study, view factor calculation algorithm is introduced and applied to cylindrical crystal growth furnace. This algorithm is based on the Hemi-Cube Algorithm and the results obtained with this algorithm show good agreements with those of analytical solution. As an application of this algorithm, temperature profiles and heating value distributions for various furnaces are calculated and the shape criteria for better furnace are suggested.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.5
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• pp.193-198
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• 2011

Recently sapphire crystals are used in LED applications. The Czochralski (CZ) growth process is one of the most important techniques for growing high quality sapphire single crystal. A successful growth of perfect single crystals requires the control of heat and mass transport phenomena in the CZ growth furnace. In this study, the growth processes of the sapphire crystal in an inductively heated CZ furnace have been analyzed numerically using finite element method. The results shown that the high temperature positions moved from the crucible surface to inside the melt and the crystal-melt interface changed to the flat shape when the rpm was increased. Also the crystal-melt interface shape has been influenced by the shoulder shape of the grown crystal during the initial stage.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.269-273
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• 2012

Ammonia decomposition over titanium carbides were investigated using eight different samples which have been synthesized by TPR (temperature-programmed reduction) method of titanium oxide ($TiO_2$) with pure $CH_4$. The resulting materials which were synthesized using wo different heating rates and space velocity exhibited the different surface areas. These results indicated that the structural properties of these materials have been related to heating rates and space velocity employed. The titanium carbides prepared in this study proved to be active for ammonia decomposition, and the activity changed with the particle size/surface area. These showed the relationship between ammonia decomposition activity and the different active species. Compared to molybdenum carbide, the titanium carbides were one order of magnitude less active, suggesting the correlation between the activity difference and the degree of electron transfer between metals and carbon in metal carbides.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.5
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• pp.218-223
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• 2001

The chemical-mechanical polishing process was carried out for 2"-dia. sapphire wafer grown by horizontalBridgman method on the urethane lapping pad with the silica sol. The polished wafer shows the full-width at halfmaximum of 200~400 arcsec in double-crystal X-ray diffraction, indicating that the slicing, grinding and lapping processes before the polishing process affected the crystalline structural property of the wafer surface by the mechanical residual stress. For the inclusion of surface treatments after chemical-mechanical polishing such as the thermal annealing at the temperature of $1,200^{\circ}C$for 4 hrs. and chemical etching, the crystalline quality was sigdicantly enhanced with the reduced full-width at half maximum up to 8.3 arcsec.arcsec.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.3
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• pp.327-333
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• 1999

Controlled Ca impurity implanted inner crack-like pore in the high purity alumina bi-crystal had been created by micro-fabrication technique, which includes ion implantation, photo-lithography, Ar ion milling, and hot press. The morphological change and the growth od crystals formed by heat treatment in Ca doped high purity single crystal alumina, were observed using optical microscopy. The dot was developed and hexagon like crystal appeared on inner surface of crack-like pore after heat treatment. Bar type crystals, probably CaO . $6Al_2O_3$, were observed on the inner surface of 100ppm Ca implanted specimen after 1 hour heat treatment at $1,500^{\circ}C$, but this bar type crystal disappeared after 1 hour heat treatment at $1,600^{\circ}C$. This disappearance means that there should be little increase of Ca solubility limit to alumina and/or changes of diffusion coefficient of Ca in alumina around this temperature.

• Transactions on Electrical and Electronic Materials
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• v.10 no.2
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• pp.40-43
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• 2009

The authors fabricated a nanopatterned surface on a GaN thin film deposited on a sapphire substrate and used that as an epitaxial wafer on which to grow an InGaN/GaN multi-quantum well structure with metal-organic chemical vapor deposition. The deposited GaN epitaxial surface has a two-dimensional photonic crystal structure with a hexagonal lattice of 230 nm. The grown structure on the nano-surface shows a Raman shift of the transverse optical phonon mode to $569.5\;cm^{-1}$, which implies a compressive stress of 0.5 GPa. However, the regrown thin film without the nano-surface shows a free standing mode of $567.6\;cm^{-1}$, implying no stress. The nanohole surface better preserves the strain energy for pseudo-morphic crystal growth than does a flat plane.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.459-462
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• 1999

Recent advances in NLO Borate Crystals for UV Generation are reviewed with the particular emphasis on the technique to improve the life time of UV optics. The laser-damage resistance of CLBO and fused silica surfaces was successfully improved after removing polishing compound by ion beam etching. The polishing compound embedded in the CLBO and fused silica surfaces were to a depth of less than 100nm. We were able to remove polishing compound without degrading the surface condition when the applied ion beam voltage was less than 200 V. The laser-induced surface damage threshold of CLBO was improved up to 15J/$\textrm{cm}^2$(wavelength: 355 nm, pulse width: 0.85 ns)as compared with that of the as-polished surface (11 J/$\textrm{cm}^2$). The laser-induced surface damage of fused silica also increased from 7.5J/$\textrm{cm}^2$ to 15J/$\textrm{cm}^2$. For the irradiation of a 266 nm high-intensity and high-repetition laser light, the surface lifetime of CLBO and fused silica could be more doubled compared with that of the as-polished surface.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.536-542
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• 1990

Single crystals of YBa2Cu3O7-x have been grown in BaCuO2 flux at temperature of 125$0^{\circ}C$ and examined using XRD, EDAX and light microscopy. The YBCO crystals were grown in a cavity which was formed by the reduction of CuO and became large by the directional solidification in the crucible. The observed crystal growth habit is square planar with the c-axis normal to the plane. The surface morphology of grown crystals were growth ledges and growth sprial paterns on a (001) face.

• Applied Microscopy
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• v.36 no.spc1
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• pp.19-24
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• 2006

The alumina-aluminum solid-liquid interfaces were directly observed at atomic scale by heating the alumina single crystal in high-voltage electron microscope (HVEM) owing to the electron beam damage processes, Atomic ordering in the first several layers of the liquid was clearly resolved adjacent to the alumina surface and its relevance to the single crystal growth was examined with the real-time observations.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.417-423
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• 1999

Detailed description of the crystal growth methods permitting one to obtain complicated shape crystals from the melt is given. The variable shaping technique provides the growth of crystals with a discrete altering cross-section configuration during crystallization. The dynamic local shaping technique enables one to grow items with a continuous alteration of the side surface profile by a preset program.