• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.1038-1041
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• 2003

In the paper, we investigated silicon surface microstructures formed by reactive ion etching in hollow cathode system. Wet anisotropic chemical etching technique use to form random pyramidal structure on <100> silicon wafers usually is not effective in texturing of low-cost multicrystalline silicon wafers because of random orientation nature, but High density hollow cathode plasma system illustrates high deposition rate, better film crystal structure, improved etching characteristics. The etched silicon surface is covered by columnar microstructures with diameters form 50 to 100nm and depth of about 500nm. We used $SF_{6}$ and $O_{2}$ gases in HCP dry etch process. This paper demonstrates very high plasma density of $2{\times}10^{12}$ $cm^{-3}$ at a discharge current of 20 mA. Silicon etch rate of 1.3 ${\mu}s/min$. was achieved with $SF_{6}/O_{2}$ plasma conditions of total gas pressure=50 mTorr, gas flow rate=40 sccm, and rf power=200 W. Our experimental results can be used in various display systems such as thin film growth and etching for TFT-LCDs, emitter tip formations for FEDs, and bright plasma discharge for PDP applications. In this paper we directed our study to the silicon etching properties such as high etching rate, large area uniformity, low power with the high density plasma.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.435-441
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• 2015

The ${\gamma}/{\gamma}^{\prime}$ two-phases, commonly known as a eutectic structure, are observed in the ${\gamma}$ interdendritic region of a Ni-base superalloy. However, the growth behavior of the ${\gamma}/{\gamma}^{\prime}$ two-phases, whether it is of eutectic or peritectic nature, has not been decidedly established. Directional solidifications were, thus, performed with the planar interface at a low growth rate of $0.5{\mu}m/s$ in order to promote macro segregation. Directional solidification started with the ${\gamma}$ planar interface and the ${\gamma}^{\prime}$ phase nucleated on the ${\gamma}$ planar interface at the solidification fraction of 0.75. The ${\gamma}/{\gamma}^{\prime}$ two-phases showed the ${\gamma}^{\prime}$ rod structure as major phase and the ${\gamma}$ minor phase between ${\gamma}^{\prime}$ rods, and the volume fraction of the ${\gamma}$ phase changed continuously with an increasing solidification fraction. The two-phase ${\gamma}/{\gamma}^{\prime}$ is seen as the coupled peritectic.

• Korean Journal of Materials Research
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• v.14 no.4
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• pp.235-238
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• 2004

The LT-MBE (low temperature molecular beam epitaxy) allows to dope GaAs with Mn over its solubility limit. A 75 urn thick GaMnAs layers are grown on a low temperature grown LT-GaAs buffer layer at a substrate temperature of $260^{\circ}C$ by varying Mn contents ranged from 0.03 to 0.05. The typical growth rate for GaMnAs layer is fixed at 0.97 $\mu\textrm{m}$/h and the V/III ratio is varied from 25 to 34. The electrical and magnetic properties are investigated by Hall effect and superconducting quantum interference device(SQUID) measurements, respectively. Double crystal X-ray diffraction(DCXRD) is also performed to investigate the crystallinity of GaMnAs layers. The $T_{c}$ of the $Ga_{l-x}$ /$Mn_{x}$ As films grown by LT-MBE are enhanced from 38 K to 65 K as x increases from 0.03 into 0.05 whereas the $T_{c}$ becomes lower to 45 K when the V/III ratio increases up to 34 at the same composition of x=0.05. This means that the ferromagnetic exchange coupling between Mn-ion and a hole is affected by the growth condition of the enhanced V/III ratio in which the excess-As and As-antisite defects may be easily incorporated into GaMnAs layer.

• Progress in Superconductivity
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• v.7 no.1
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• pp.58-63
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• 2005

We investigated the surface oxidation behavior of cube-textured polycrystalline nickel at various oxidation conditions. Cube-textured NiO film was formed on a cube-textured polycrystalline nickel regardless of oxidation conditions but different growth behavior of NiO crystals was observed depending on the oxidation conditions. The introduction of water vapor into $O_2$ did not affect the texture evolution, but rough and porous microstructure was developed. Microstructure of NiO film tends to be denser as the oxygen partial pressure increases. It is interesting that (111) peak of theta - two theta diffraction pattern started to get stronger in air atmosphere and (111) plane became the major texture in the substrate oxidized in high purity argon gas. Small amount of high index crystallographic plane NiO peak crystal was observed when $N_{2}O$ was used as an oxidant while only (200) plane crystal was formed in dry $O_2$ atmosphere. Flat and smooth surface was changed into rough faceted one when ramping rate to oxidation temperature was faster. The grain size of NiO was decreased when the oxygen partial pressure was low. It was also observed that the modification of nickel surface suppressed the development of (200) texture.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.189-193
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• 2012

ZnO nanorods were grown on the $Cd_xZn_{1-x}O$ seed layers with various Cd mole fractions by hydrothermal method. The effects of the Cd mole fraction for $Cd_xZn_{1-x}O$ seed layers on the structural and optical properties of the ZnO nanorods were investigated by scanning electron microscopy, X-ray diffraction, and photoluminescence. The narrowest full-width at half-maximum and largest grain size of the $Cd_xZn_{1-x}O$ seed layers, indicating improvement in crystal quality, were observed at the Cd mole fraction of 0.5. At the Cd mole fraction of 0.5, the largest enhancement in the density, the crystal quality, and the growth rate of the ZnO nanorods was observed while their appearance was not affected significantly by the incorporation of the Cd in the $Cd_xZn_{1-x}O$ seed layers. Consequently, the luminescent properties of the ZnO nanorods were enhanced. The largest improvement in the structural and optical properties of the ZnO nanorods was observed at the Cd mole fraction of 0.5.

• Journal of Korean Society of Forest Science
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• v.98 no.1
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• pp.115-124
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• 2009

New strain needs to maintain desirable characteristics for long term when it was bred, but in lapse of time it degenerates into a bad condition. Therefore the influence of temperature on the viability and survival rates of Lentinula edodes strains were examined after cryopreservation. Also, liquid nitrogen preservation for L. edodes has been proved to be one of the most reliable method. However, a mechanical damage of strain is inevitable during cryopreservation of the fungus because the fungus is very sensitive to stress of cooling rate in the freezing process. So we tried to find out state change of L. edodes with a programmable freezer. L. edodes strains were preserved at $-20^{\circ}C$, $-80^{\circ}C$ and $-196^{\circ}C$ for 50 days. At $-20^{\circ}C$, its mycelial growth became extinct. When thawed, the growth of mycelia which were preserved at $-80^{\circ}C$ was fastest. Attempts were made to investigate viability of L. edodes strains after freezing at $-80^{\circ}C$ and $-196^{\circ}C$, respectively. As the result, more than 90% showed high survival rate of strains tested at $-80^{\circ}C$ and $-196^{\circ}C$. Mycelial growth between apical and basal parts of colony after freezing preservation for 50 days was compared. At apical and basal parts, the survival rates showed 100% at $-80^{\circ}C$, but 98% and 94% at $-196^{\circ}C$, respectively. We confirmed that the ice crystal formation temperatures of L. edodes strains were $-6.0^{\circ}C$ for Sanlim 1, $-5.5^{\circ}C$ for the Sanlim 2, $-4.0^{\circ}C$ for the Sanlim 3 and $-15.5^{\circ}C$ for the Sanzo 302. These results indicated that L. edodes strains showed completely different responses to the ice crystal formation. We knew the fact that even the same species, especially L. edodes, they displayed completely different responses to the same freezing condition. Also, this has nothing to do with the connection between temperature type and freezing point. And a protocol was tried to minimize state change of L. edodes strains using programmable freezer when they are frozen, but it was not effective on them.

• Journal of the Korean Ceramic Society
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• v.35 no.6
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• pp.640-646
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• 1998

Nucleation and crystallzation of a quaternary glass system for lead titanate glass-ceramics were in-vestigated using DTA(differential thermal analysis ) with variation of nucleation temperature and crystal growth time. Glass samples containing 60mol% of PbO-{{{{ { TiO}_{2 } }} were prepared from melts by the conventional normal cooling method in a cylindrical brass mould. The glass sample was nucleated between 40$0^{\circ}C$ and 50$0^{\circ}C$ for a given time and showed the maximum nucleation rate at 46$0^{\circ}C$ The DTA crystallization peak temperature decreased with increasing nucleating time and decreasing heating rate during DTA runs which indicated an increase of the number of nuclei produced in the system.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.5
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• pp.208-215
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• 2005

The 10mm diameter aggregates made of clay, carbon and $Fe_2O_3$ were prepared to investigate the mechanism of black core formation. The specific gravity, absorption rate, percent of black core area, fracture strength, total Fe analysis, and XRF were measured at various compositions, sintering temperatures, sintering times, sintering atmospheres, and sintering methods. Small addition of $Fe_2O_3$ did not affect physical properties of the aggregates; however, the percent of black core area increased with increasing carbon contents and increasing sintering temperature. Specific gravity of the aggregates decreased and the water absorption ratio increased with increasing percent of black core area. The aggregates sintered at oxidation atmosphere showed clear border between shell and black core area. Hence, the aggregates sintered at reduction atmosphere showed only black core area in the cross-section of the aggregates. The specific gravity of the aggregates sintered at reduction atmosphere increased with increasing carbon contents and that was the lowest of all comparing other aggregates sintered at different atmospheres. Adsorption rate increased with increasing carbon contents at all atmospheres. The fast sintered aggregates showed lower specific gravity, higher absorption rate, and more black core area than the normally sintered aggregates. It was turned out that the aggregates having more black core area showed higher fracture strength than that of aggregates with no black core area. From the total Fe analysis, the concentration of Fe and FeO was higher at black core area than at shell. Because the concentration of $Fe_2O_3$ in the shell was higher than other area, the color of the shell appeared red. It was also turned out from the XRF analysis that carbon was exist only at black core area.

• Journal of the Korean Ceramic Society
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• v.47 no.3
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• pp.256-261
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• 2010

Physical properties of Plasma electrolytic oxidized 8 different types of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was $Na_2SiO_3$ solutions with NaOH and some alkali earthen metal salts. Porous layer near the surface of PEO coating was not found, and surface roughness Ra50 was below 2.5 ${\mu}m$. Surface roughness was affected by growth rate of plasma electrolytic oxidized layer, not by Si content in Al alloy.

• Journal of Korea Foundry Society
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• v.3 no.1
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• pp.3-12
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• 1983

The influence of columnar dendirtes on the mechanical properties of Al-1% Cu alloys as unifirectionalloy solidified under the conditions of controlled crystal growth rate (R) and temperature gradient (G) was investigated. And the change of metallography and mechanical properties when unifirectionalloy solidified alloys and cast alloys were cold-rolled from 10% to 90% in reduction ratio was studied. The results are as follows: 1. The elongation and yield strength of unifirectionalloy solidified alloy are higher then those of cast alloy, but there is a little decrease in ultimate tensile strength. 2. The metallography and mechanical properties are changeable with the primary arm spacings when the unidirectionalloy solidified alloys were cold-rolled from 10% to 90% in reduction ratio. An alloy with larger primary arm spacings was easily changeable in metallography and mechanical properties when it was cold-rolled. 3. The tensile strength of transversely cold-rolled to 90% in reduction ratio was higher then that of longitudionalloy cold-rolled to 90% in reduction ratio. In the case, the fractorgraphs of fractured surface showed that the cast alloy and the unifirectionalloy solidified alloy was ductile-fractured, but the surface of transversely cold-rolled to 90% reduction of unidirection alloy solidified was slip plane qracture.