• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.2
• /
• pp.185-190
• /
• 1997

The 6H-SiC single crystals were grown using a self-designed crystal grower by the sublimation method. The grown crystals were typically 30 mm in diameter and 10 mm in length. Optimum growth conditions were established as follows : the temperature of the raw material was $2150~2250^{\circ}C$, the temperature of the substrate was $1950~2050^{\circ}C$, the temperature difference between the raw material and substrate was about $200^{\circ}C$, growth pressure was 50~200 torr and growth rate was 300~700 $\mu\textrm{m}$/hr. Optical microscopy was used for observing the surface of the 6H-SiC single crystal grown and the phenomenological approach was performed on the formation mechanism of the defects in the 6H-SiC crystal. Especially, the micropipes in the as-grown surface were examined to determine the formation mechanisms of the micropipes.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.9 no.4
• /
• pp.365-370
• /
• 1999

Computer simulations have played a central role in the development of our understanding of the atomic scale processes involved in crystal growth. The assumptions underlying computer modeling will be discussed and our recent work on modeling of the kinetic formation of thermodynamically unstable phases in alloys or mixtures will be reviewed. Our Monte Carlo computer simulations have reproduced the experimental results on the rapid recrystallization of laser-melted doped silicon. An analytical model for this phenomenon has been developed, and its applicability to other materials will be discussed.

• Journal of the Korean Ceramic Society
• /
• v.36 no.10
• /
• pp.1087-1093
• /
• 1999

Bioglass which is one of the surface active bionmaterials has a good biocompatibility but a poor mechanical strength, In the present work therefore two types of fluoride-containing bioglasses were coated on an alumina to improve mechanical strength. Crystallization of the coating layer and the hydroxyapatite formation on the bioactive glass coatings in tris-buffer solution were studied. When bioactive glass coated alumina was heat-treated Na2CaSi3O8 crystal was formed on the layer at lower temperature while wollastonite(CaSIO3) was obtained at higher temperature. Hydroxyapatite forming rate on the coating layer with Na2CaSi3O8 crystal was delayed with SiO2 contents in glass composition. However the hydroxyapatite was developed in 20minutes regardless SiO2 contents when the coating layer crystallized into wollastonite. More amount of P3+ ions were leached out of the coating layer with wollastonite than that with Na2CaSi3O8 crystal while Na+ and Ca2+ ions were leached out more easily from the Na2CaSi3O8 crystal containing coating layer.

• Journal of Magnetics
• /
• v.22 no.1
• /
• pp.29-33
• /
• 2017

We report a micromagnetic numerical study on different quasi-crystal formations of magnetic vortices in a rich variety of dynamic transient states in soft magnetic nano-disks. Only the application of spin-polarized dc currents to a single magnetic vortex leads to the formation of topological-soliton quasi-crystals composed of different configurations of skyrmions with positive and negative half-integer numbers (magnetic vortices and antivortices). Such topological object formations in soft magnets, not only in the absence of Dzyaloshinskii-Moriya interaction but also without magnetocrystalline anisotropy, are discussed in terms of two different topological charges, the winding number and the skyrmion number. This work offers an insight into the dynamic topological-spin-texture quasi-crystal formations in soft magnets.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.29 no.6
• /
• pp.294-297
• /
• 2019

New insights about macro-step formation has been investigated. The phenomena of surface instability caused by the interaction between step flow and fluid flow was describe in mechanical way. The rotation of the seed crystal in a clockwise direction was applied with a speed varied from 30 to 200 rpm during the TSSG process on the Si- and C-faces 4H-SiC. The macro-steps were formed along the two specific directions at different locations on the crystal for each, i.e., [10-10] or [01-10] directions or both. From the results, it is suggested that the macro-steps were generated from the micro-steps by interaction between step flow and fluid flow during the rotation of seed crystal. Furthermore, The fluid flow could be effective to control the micro- and/or macro-step behavior during solution growth.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06a
• /
• pp.528-528
• /
• 1996

• Bulletin of the Korean Chemical Society
• /
• v.16 no.6
• /
• pp.489-492
• /
• 1995

A new synthetic route to chiral liquid crystal dopant, 4-[2-(7S-methylnonanyl)oxy-5-pyrimidinyl]phenyl(2S,3S)-2-chloro-3-methylpentanoate (1), starting from 4-nitrophenylacetic acid is described. The key intermediate methylthiopyrimidine compound (8) has been synthesized from 4-nitrophenylacetic acid by Vilsmyer-Haack reaction followed by the formation of pyrimidine ring, and then converted to chiral ester (1) by the replacement of nitro group by (2S,3S)-2-chloro-3-methylpentanoic acid 2 through the formation of diazonium salt.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1999.06a
• /
• pp.69-80
• /
• 1999

Computer simulations have played a central role in the development of out understanding of the atomic scale processes involved in crystal growth. The assumptions underlying computer modeling will be discussed and out recent work on modeling of the kinetic formation of thermodynamically unstable phases in alloys or mixtures will be reviewed. Our Monte Carlo computer simulations have reproduced the experimental results on the rapid recrystallization of laser-melted doped silicon. An analytical model for this phenomenon has been developed, and its applicability to other materials will be discussed.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2002.08a
• /
• pp.191-192
• /
• 2002

We reported pushing of colloidal particles by a moving isotropic-nematic phase boundary. Here, we report tailoring the structure of 3-dimensional networks formed by these particles by adjusting the rate of phase transition and by application of an electric field. The resulting networks affect the electro-optic performance of liquid crystal devices.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.1
• /
• pp.13-16
• /
• 2000

Progress in Si crystal and wafer technologies is discussed on single crystal growth, wafer fabrication, epitaxial growth, gettering, 300 mm and SOI. As for bulk crystal growth, the mechanism of grown-in defects (voids) formation, the succes of grown-in defect free crystal growth technology and nitrogen doped crystal are shown. New wafer fabrication technologies such as both-side mirror polishing and etchingless process have been developed. The epitaxial growth of SiGe/Si heterostructure for high speed bipolar device is treated. Gettering technology under low temperature process such as RTP is important, and also it is shown that IG effect for Ni could be predicted using computer simulation of precipitate density and size. The development of 300 mm wafer and SOI has made progress steadily.