• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.6
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• pp.234-238
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• 2005

Effects of plasma composition, ion flux and ion energy on the etch rate, surface morphology and near surface stoichiometry of a single crystalline $La_3Ga_5SiO_{14}$ wafer have been examined in $Cl_2/Ar$ inductively coupled plasma (ICP) discharges. Maximum etch rate ${\sim}1600{\AA}/min$ was achieved either at relatively high source power $({\sim}1000W)$ or high $Cl_2$ content conditions in $Cl_2/Ar$ discharges. The etched surfaces showed similar or better RMS roughness values than those of the unetched control sample and the near surface stoichiometry was found not to be affected by ICP etching.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.1
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• pp.10-15
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• 2005

Effects of CH₄/H₂ flow rate ratio, chuck bias and microwave power on the structural properties and particle densities of diamond thin films deposited on Ti substrates in microwave plasma CVD were examined. High quality diamond thin films were deposited on Ti substrates in 2∼3 CH₄ Vol.% conditions due to the preferential formation of sp³-bonus ana selective removal of sp²-bonus in the CH₄/H₂ mixtures, and the mechanism for the formation of diamond particles on Ti was analysed. Diamond particle density increased with increasing negative chuck bias to Ti substrate due to bias-enhanced nucleation of diamond and the threshold voltage was found at ∼-50 V. With increasing microwave power the evolution from micro-crystalline graphite layer to diamond layer was observed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.60-63
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• 1999

Application of reactive ion etching (RIE) technique to Ta-Al alloy thin film with a thickness of $1000{\AA}$ was studied. $CF_{4}$ gas could be used effectively to etch the Ta-Al alloy thin film. The etching rate in the thin film with Ta content of 50 mol% was about $67{\AA}/min$. NO selectivity between the Ta-Al alloy film and $SiO_{2}$ film was observed during the etching using the $CF_{4}$ gas. The etching rate of the $SiO_{2}$ layer was 12 times faster than that of the Ta-Al alloy thin film. It was also observed that photoresist of AZ5214 was more useful than Shiepley 1400-27 in RIE with the $CF_{4}$ gas.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.2
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• pp.71-75
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• 2006

The aggregates made of clay, carbon and $Fe_2O_3$ were prepared to investigate the mechanism of black core formation and the property differences at various sintering atmospheres. The aggregates were sintered at oxidized, neutralized and reduced atmospheres. The specific gravity, absorption rate, percent of black core area were measured at various compositions and sintering atmospheres. The aggregates sintered at oxidized atmosphere showed clear border between shell and black core area. Hence, the aggregates sintered at reduced and neutralized atmospheres showed only black core area in the cross-section of the aggregates. The specific gravity of the aggregates sintered at reduced atmosphere increased with increasing carbon contents and that was the lowest of all aggregates sintered at various atmospheres. Adsorption rate increased with increasing carbon contents at all atmospheres.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.655-659
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• 1998

The effect of quenching speed of melt-spinning on intrinsic coercivity ($_iH_c$$) of annealed ribbons and the crystallization behavior from amorphous $Nd_{14.73}Fe_{78.67}B_{6.60}$ alloy have been studied. We have found that the intrinsic coecivity for annealed melt-spun ribbon is reduced with increasing of quenching rate. $\alpha$-Fe and $Fe_3B$ were formed as intermediate phases prior to the formation of $Nd_2Fe_{14}B$ phase during crystallization. The $Fe_3B$ is disappeared with crystallization of $Nd_2Fe_{14}B$ phase. But the $\alpha$-Fe phase is retained in fully crystallized ribbon by annealing. The intrinsic coercivity loss of annealed ribbon with increasing of quenching speed is believed to be due to existence of soft magnetic phase $\alpha$-Fe in annealed ribbons.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.5
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• pp.217-221
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• 2003

In this work, chemical-solution derived silicate fibers were prepared by mixing tetraethyl orthosilicate, ethanol, distilled water, and hydrochloric acid in order to investigate surface roughness of fiber. Silicate fibers were drawn by using a viscous solution after evaporation at $80^{\circ}C$. The dried gel fibers were finally annealed at $1000^{\circ}C$, $1100^{\circ}C$, $1200^{\circ}C$ and $^1300{\circ}C$ for 60 min in dried air (flow rate = ∼200 ml/min). The crystallinity of the heat-treated silica fiber was analyzed by the X-ray diffraction $\theta$-2$\theta$ scan. A field emission-scanning electron microscope and an atomic force microscope were used to evaluate surface properties. The silicate fiber annealed at $1300^{\circ}C$ showed high value of root mean square roughness and had a relatively inhomogeneous surface structure.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.5
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• pp.197-202
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• 2001

The influence of thermal treatment and cold drawing was investigated for poly(ethy1ene terephthalate) films fabricated with various experimental conditions. Samples were elongated at room temperature under stepwise-drawing condition with the cross-head speed kom 0.5 to 500 mrdmin in an universal tester. Stress oscillation was observed in the stress-stnin curve of the samples heat-treatd at 50, 72 and $129^{\circ}C$ for 30 min, but it was not observed in the samples heat-treatd at $83^{\circ}C$ for 30 min. Thermal analyses of the samples were carried out in differential scanning calorimeter at the heating rate df $10^{\circ}C$/min/min, and the glass transition temperature, crystallization peak, enthalpy of fusion and degree of crystallinity were measured. The dynamic mechanical analyses of the samples were also carried out in a multiplefimction internal kiction pendulum at 1 Hz with the heating rate of $1.5^{\circ}C$/min, and it was found that the elastic modulus increases in the order of non-treated, heat-treated, and elongated samples.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.4
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• pp.395-404
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• 1994

Ni-graphite composite powders were prepared by reduction of $Ni^{++}$ from ammoniacal nickel sulfate solution on graphite core by hydrogen gas. Effect of reaction factors on the reduction rate and the properties of nickel layer were investigated by SEM, Optical Microscopy, size and chemical analysis. Induction period, a time lag between the injection of hydrogen gas and the start of the reduction, was 20~110 mins and affected by the reaction temperature and stirring speed. The reduction rate of $Ni^{++}$ was $4.5g/{\ell}/min$ at optimum condition and increased with increasing reaction temperature and stirring speed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.2
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• pp.249-254
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• 1998

The etching experiments for n-GaN were done using the wet chemical, photo-enhanced-chemical and electro-chemical etching methods. The experimental results show that n-GaN is etched is diluted NaOH solution at room temperature and the removed thickness of n-GaN is linearly increased with etching times. The etching rate of the photo-enhanced-chemical and electro-chemical etching methods are several times higher than that of the wet chemical method. The maximum etching rate of n-GaN with $n{\fallingdotseq}1{\times}10^{19}cm^{-3}$ was 164 $\AA$/min under the experimental condition of the Photo-enhanced-chemical etching. The etching rates of n-GaN are very much dependant on the electron concentrations of the samples. The pattern is $100{\mu}m{\times}100{\mu}m$ rectangulars covered with $SiO_2$film. It is shown that the etched side-wall charactistics of the pattern is vertical without dependance of the n-GaN orientations, and the smoothness of etched n-GaN surface is fairly flat.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.6
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• pp.304-308
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• 2003

By controlling the internal pressure in the cyclone separator, we investigated the separation charateristics of $Al_2O_3$, $Fe_2O_3$ particles with the internal pressure variation. 3-dimensional Langrangian approach was applied for the analysis of the particles separation, and then the minimum cut diameter of the separated particles and the separation rate were calculated through tracking the particle trajectories. The density of the argon gas for transporting particles was decreased corresponding the pressure decrease, consequently, caused the internal pressure drop in the cyclone separator. For that reason the finer particles were separated as the pressure was changed from an atmospheric pressure to an low pressure. Specifically, at 50 torr pressure, $Al_2O_3$ particles of the size of about 4 $\mu\textrm{m}$ and $Fe_2O_3$particles of about 3 $\mu\textrm{m}$ could be separated.