• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.416-420
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• 1995

An attempt has been made to investigate the mechanism of magnetic alignment in the magnets produced by upset forging the $Pr_{20}Fe_{74}B_{4}Cu_{2}$ cast bulk alloy. Upset forging of the cast alloy was carried out for 20 sec to an 80 % thickness reduction (strain rate : $4{$\times}10^{-2}s^{-1}$) in an open die configuration at varying temperatures in the range $600^{\circ}-900^{\circ}C$. It has been found that the upset forging process at temperatures above $800^{\circ}C$ can achieve a magnetic alignment to a great extent from copper-containing Pr-Fe- B-type cast ingot. The growth manner of the ferromagnetic $Pr_{2}Fe_{14}B$ matrix grain in Pr-Fe-B-type alloys was studied by examining the morphology change of the matrix grain in sintered body, and it was found that the matrix grains grew in anisotropic manner such that the grain grew more rapidly along the a- or b-axis than along the c-axis. This anisotropic grain growth led to the plate-like shape of the matrix grain. The magnetic alignment during the upset forging was attributed to grain boundary gliding of the plate-like grains, and the geometry of the grains in the cast ingot and the presence of a large amount of the praseodymium-rich grain boundary phase were thought to play a key role in the achievement of magnetic alignment.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.5-12
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• 2000

As a semiconductor material for electronic devices operated under extreme environmental conditions, silicon carbides (SiCs) have been intensively studied because of their excellent electrical, thermal and other physical properties. The growth characteristics of single- crystalline 6H-SiC homoepitaxial layers grown by a thermal chemical vapor deposition (CVD) were investigated. Especially, the successful growth condition of 6H-SiC homoepitaxial layers using a SiC-uncoated graphite susceptor that utilized Mo-plates was obtained. The CVD growth was performed in an RF-induction heated atmospheric pressure chamber and carried out using off-oriented ($3.5^{\circ}$tilt) substrates from the (0001) basal plane in the <110> direction with the Si-face side of the wafer. In order to investigate the crystallinity of grown epilayers, Nomarski optical microscopy, transmittance spectra, Raman spectroscopy, XRD, Photoluninescence (PL) and transmission electron microscopy (TEM) were utilized. The best quality of 6H-SiC homoepitaxial layers was observed in conditions of growth temperature $1500^{\circ}C$ and C/Si flow ratio 2.0 of $C_3H_8$ 0.2 sccm & $SiH_4$ 0.3 sccm.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.06a
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• pp.157-159
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• 1998

Sapphire crystals were grown by Horizontal Bridgman method. The effects of sliding rate (growth rate) of Molybdenum container, growth atmosphere, temperature gradient and orientation of see on crystal qualities were investigated. The size of the crystals grown was up to 150-200 mm in length, 90 mm in width and 25-35 mm in thickness. Crystals grown under the optimum conditions were colorless, transparent and could not be observed and macroscopic defects, such as bubbles, cracks, twins and mosaic structure. With the grown crystals, prototypes of sapphire substrate for blue wafers were characterized. As a result, we can get hight quality of sapphire wafers with c-axis, 1.5 inches in diameters and 0.33 mm in thickess.

• Proceedings of the Korea Contents Association Conference
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• 2009.05a
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• pp.807-809
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• 2009

Thin film deposition methods have been widely used and intensively investigated because high quality crystalline films enable to fabricate by sputtering. Especially rf magnetron sputtering deposition has advantages of being employ a relatively high deposition rate and also to achieve high crystalline films in low pressure because plasma density around target by magnetic is high. To apply ZnO thin film for SAW filter, it has highly flat surface, excellent c-axis preferred orientation and high resistivity value. As-deposited ZnO films showed the strong c-axis growth and excellent crystallinity. C-axis preferred orientation, resistivity and surface roughness highly depended on oxygen/argon gas ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.278-279
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• 2005

The crystallization of FePt/MgO(100) magnetic thin films of various thicknesses has been studied using synchrotron x-ray scattering, atomic force microscope, and vibrating sample magnetometer. In film with a 500-${\AA}$-thick, ordered (fct) FePt phase was dominantly crystallized into perpendicular (001) grains keeping the magnetically easy c-axis normal to the film plane during annealing. In film with a 812-${\AA}$-thick, however, longitudinal (110) grains keeping the c-axis parallel to the film plane were grown on top of the perpendicular (001) grains. The behavior of the magnetic properties was consistent with the thickness dependence of the crystallization. We attribute the thickness dependence of the crystallization to the substrate effect, which prefers the growth of the c-axis oriented perpendicular grains near the film/substrate interfacial area.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.185-188
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• 2009

The effects of the growth temperature on the properties of ZnO thin films were investigated by using X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectrophotometry, and Hall measurements. The ZnO films were deposited by rf magnetron sputtering at various growth temperatures in the range of 100-$400{^{\circ}C}$. A strong c-axis preferred orientation is observed for all of the samples. As the growth temperature increases, the crystalline orientation of the ZnO (002) plane is not changed, but the full width at half maximum gets smaller. The dependence of the electron concentration, mobility, and resistivity on the growth temperature exhibits that the ZnO films have a higher electron concentration at higher temperatures, thus giving them a low resistivity. The optical transmittance and band gap energy, calculated from the spectra of optical absorbance, show a significant dependence on the growth temperature. As for the sample grown at $100{^{\circ}C}$, the average transmittance is about 90% in the visible wavelength range and the band gap is estimated to be 3.13 eV.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.279-285
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• 2000

High quality crystals of $YMnO_3$, which is interested in non-volatile memory device application, were grown by the floating zone method. Optimum condition for powder synthesis was established to be $1200^{\circ}C$ for 10 hrs and optimum condition for sintering of $YMnO_3$feed-rod was established to be $1500^{\circ}C$ for 10hrs respectively. It was found from non-seeded growth experiment that $YMnO_3$crystal was grown preferentially to the [1010] orientation. The $YMnO_3$single crystal, which was grown to the direction of perpendicular to C-axis, was typically 5mm in diameter, 50 mm in length and showed dark-blue color.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.4
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• pp.141-144
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• 2005

[ $(Y_{0.5}Sm_{0.25}Nd_{0.25})Ba_2Cu_3O_y$ ] [(YSN)-123] high $T_c$ composite superconductors with $CeO_2$ addition were systematically investigated by top seeded melt growth (TSMG) process in air atmosphere. A melt textured $NdBa_2Cu_3O_y$ (Nd-123) single crystal was used as a seed for achieving the c-axis alignment large grains perpendicular to the surface of (YSN)-123 composite oxides. The size of $(Y_{0.5}Sm_{0.25}Nd_{0.25})_2BaCuO_5$ [(YSN)211] nonsuperconducting inclusions of the melt textured (YSN)-123 samples with $CeO_2$ addition were remarkably reduced and uniformly distributed within the (YSN)123 superconducting matrix except in the region very close to the Nd-123 seed crystal. The sample showed a sharp superconducting transition of 91 K.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.6 s.177
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• pp.1584-1592
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• 2000

Reversed plane bending fatigue tests were conducted on SiC whisker reinforced aluminum composite which were consolidated by squeeze casting process. Initiation and growth of small surface fatigue c racks were investigated by means of a plastic replica technique. The fatigue crack initiated in the vicinity of SiC whisker/matrix interface. It was found that a fatigue crack deflected along SiC whisker and grew in a zig-zag manner microscopically, although the crack propagated along the direction normal to the loading axis macroscopically. The coalescence of micro-cracks was observed in the tests conducted at high stress levels, but were not evident in tests in which lower levels of stress were applied. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn -ΔK realtionship.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.50-53
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• 2002

YMnO$_3$ thin films were spun-coated on the Pt/Ti/SiO$_2$/Si substrates by sol-gel process using alkoxides, and then dried on hot plates from 300 to 450 $^{\circ}C$. The prepared YMnO$_3$ thin films were annealed at 850 $^{\circ}C$ in O$_2$ atmosphere for 1 h. The crystallization of YMnO$_3$ thin films were improved to preferred c-axis orientation and the dielectric characteristics were progressed by increasing the drying temperature. The range of dielectric constant of thin film dried at 450 $^{\circ}C$ is 12.9-22.3 and close to that of YMnO$_3$ single crystal. The ferroelecrtic property of YMnO$_3$ thin film was observed on the YMnO$_3$ films. The maximum remnant polarization (2Pr) of YMnO$_3$ thin films dried at 450 $^{\circ}C$ was about 2.91 ${\mu}$ C/cm2. It was suggested that the drying temperature affect to the initial stage of thin film growth of preferred c-axis orientation.