• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.202-206
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• 2010

Single crystals of $ZnWO_4$ were grown successfully in the [100], [010] and [001] directions using the Czochralski method. The growth parameters and the formation of slip plane in $ZnWO_4$ crystals were studied. $ZnWO_4$ crystals had a cleavage plane of (010). The dislocation density on the (010) plane at the center of the crystal was lower than that of the edge region. It was inferred that the high density at the edge of the crystals was caused by the thermal gradient during crystal growth. The etch pit arrangement revealed the (100) slip plane to be most active during crystal growth.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.42-47
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• 2000

The surface structure and the crystalline features in the near surface region have been investigated for CZ(Czochralski) grown Si wafers. Si wafers were annealed by RTA (Rapid Thermal Annealing) method in H$_2$ambient after mirror polished process. The densities of COPs (Crystal Originated Particles) after RTA process were remarkably decreased at the surface and in the region of 5um depth from the surface as well. terrace type surface structure which was formed by etching and re-arrangement of Si atoms during $H_2$annealing process also has been observed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.9
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• pp.795-800
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• 2008

A sublimation method using the SiC seed crystal and SiC powder as the source material is commonly adopted to grow SiC bulk single crystal. However, it has proved to be difficult to achieve the high quality crystal and the process reliability because SiC single crystal should be grown at very high temperature in closed system. The present research was focused to improve SiC crystal quality grown by PVT method through using the new inner guide tube. The new inner guide tube was designed to prevent the enlargement of polycrystalline region into single crystalline region and to enlarge the diameter of SiC single crystal. The 6H-SiC crystals were grown by conventional PVT process. The seed adhered on seed holder and the high purity SiC source materials are placed on opposite side in sealed graphite crucible surrounded by graphite insulation. The SiC bulk growth was conducted around 2300 $^{\circ}C$ of growth temperature and 50 mbar in an argon atmosphere of growth pressure. The axial thermal gradient across the SiC crystal during the growth was estimated in the range of 15${\sim}$20 $^{\circ}C$/cm.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.966-970
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• 2011

The thermo-mechanical interaction between brake block and wheel tread during braking has been found to cause thermal crack on the wheel tread. Due to thermal expansion of the rim material, the thermal cracks will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The wheel rim is in residual compression stress when is new. After service running, the region in the tread has reversed to tension. This condition can lead to the formation and growth of thermal cracks in the rim which can ultimately lead to premature failure of wheel. In the present paper, the thermal cracks of railway wheel, one of severe damages on the wheel tread, were evaluated to understand the safety of railway wheel in running condition. The residual stresses for damaged wheel which are applied to tread brake are investigated. Mainly X-ray diffusion method is used. Under the condition of concurrent loading of continuous rolling contact with rails and cyclic frictional heat from brake blocks, the reduction of residual stress is found to correlate well with the thermal crack initiation.

• Journal of the Korean Ceramic Society
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• v.38 no.10
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• pp.871-875
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• 2001

Cobalt silicidation at sidewall spacer edge of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with post annealing treatment for capacitor forming process has been investigated as a function of dopant species. Cobalt silicidation of nMOSFET with n-type Lightly Doped Drain (LDD) and pMOSFET with p-type LDD produces a well-developed cobalt silicide with its lateral growth underneath the sidewall spacer. In case of pMOSFET with n-type LDD, however, a void is formed at the sidewall spacer edge with no lateral growth of cobalt silicide. The void formation seems to be due to a retarded silicidation process at the LDD region during the first Rapid Thermal Annealing (RTA) for the reaction of Co with Si, resulting in cobalt mono silicide at the LDD region. The subsequent second RTA converts the cobalt monosilicide into cobalt disilicide with the consumption of Si atoms from the Si substrate, producing the void at the sidewall spacer edge in the Si region. The void formed at the sidewall spacer edge serves as a resistance in the current-voltage characteristics of the pMOSFET device.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.675-678
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• 2004

Ozone is usually generated from oxygen gas using a silent discharge apparatus and its concentration is less then 10 mol%. An ozone condensation system is constructed for metal oxide thin film fabrication. Ozone is condensed by the adsorption method, which is widely used for the growth of oxidation thin films such as superconductor. Highly condensed ozone is analyzed by three methods; ultraviolet absorption, thermal decomposition and Q-mass analyzing methods. Thermal decomposition method is most effective in the highly condensed ozone region and its method is superior to Q-mass analyzer for determining ozone concentration because of the simplicity of the method.

• Journal of Korean Vacuum Science & Technology
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• v.3 no.2
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• pp.139-144
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• 1999

Hydrogen concentration depth profiles in homoepitaxial Si(001) films grown from hyper-thermal Si beams generated by ultrahigh vacuum (UHV) ion-beam sputtering have been measured by nuclear reaction analyses as a function of film growth temperature and deposition rate. Bulk H concentrations CH in the crystalline Si layers were found tio be below detection limits, 1${\times}$1019cm-3, with no indication of significant H surface segregation at the crystalline/amorphous interface region. This is quite different than the case for growth by molecular-beam epitaxy (MBE) where strong surface segregation was observed for similar deposition conditions with average CH values of 1${\times}$1020cm-3 in the amorphous overlayer. The markedly decreased H concentrations in the present experiments are due primarily to hydrogen desorption by incident hyperthermal Si atoms. Reduced H surface coverages during growth combined with collisionally-induced filling of interisland trenches and enhanced interlayer mass transport provide an increase in critical epitaxial thicknesses by up to an order of magnitude over previous MBE results.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.383-387
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• 1998

The vacuum-Bridgman equipment for large size diameter (4 inch more over) crystal growth was organized simply and the $CaF_2$ single crystal which was grown in the conditions of growth rate of 2mm/hr, freezing temperature gradient of $12^{\circ}C$/cm, have analyzed to keep excellent properties. Using Mo thermal reflector of umbrella shape, it could be eliminated the formation of polycrystalline. The preferential growth direction was (111) and the calculated lattice parameter was $5.460 \AA$ by XRD peaks. The secondary phases, also, was not formed by means of powder-XRD analysis. The value of EPD is $1.4{\times}10^4 \textrm{cm}^{-2}$ and the optical quality, which is the transmittance is 91% up in UV region, is suitable for optical components of UV applications.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.6
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• pp.272-282
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• 2002

Mercurous bromide ($Hg_{2}0Br_{2}$) crystals hold promise for many acousto-optic and opto-electronic applications. This material is prepared in closed ampoules by the physical vapor transport (PVT) growth method. Due to the temperature gradient between the source and the growing crystal region, the buoyancy-driven convection may occur. The effects of thermal convection on the crystal growth rate was investigated in this study in a horizontal configuration for conditions ranging from typical laboratory conditions to conditions achievable only in a low gravity environment. The results showed that the growth rate increases linearly with Grashof number, and for 0.2 $\leq$ Ar (transport length-to-height, L/H)$\leq$1.0 sharply for Ar=5 and $\Delta$T=30 K. We have also shown that the magnitude of convection decreases with the Ar. For gravity levels of less than $10^{-2}$g the non-uniformity of interfacial distribution is negligible.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.6
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• pp.609-620
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• 2002

It is well known that during tensile testing, a part of the mechanical work done on the specimen is transformed into heat energy. However, the ultimate temperature rise and the rate of temperature rise is related to the nature of the material, conditions of the test and also to the deformation behaviour of the material during loading. The recent advances in infrared sensors and image/data processing techniques enable observation and quantitative analysis of the heat energy dissipated during such tensile tests. In this study, infrared imaging technique has been used to characterise the tensile deformation in AISI type 316 nuclear grade stainless steel. Apart from identifying the different stages during tensile deformation, the technique provided an accurate full-field temperature image by which the point and time of strain localization could be identified. The technique makes it possible to visualise the region of deformation and failure and also predict the exact region of fracture in advance. The effect of thermal gradients on plastic flow in the case of interrupted straining revealed that the interruption of strain and restraining at a lower strain rate not only delays the growth of the temperature gradient, but the temperature rise per unit strain decreases. The technique is a potential NDE tool that can be used for on-line detection of thermal gradients developed during extrusion and metal forming process which can be used for ensuring uniform distribution of plastic strain.