• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.1127-1132
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• 2010

Borosilicate glass was prepared in the composition of 81% $SiO_2$, 4% $Na_2O$, 2% $Al_2O_3$, 13% $B_2O_3$. The albite phase($NaAlSi_3O_8$) increased with the $ZrO_2$(0~10wt.%) addition. For measurement of glass transition temperature($T_g$), crystallization temperature($T_{c,max}$) measured by differential thermal analysis. The $T_g$ and $T_{c,max}$ were $510{\sim}530^{\circ}C$ $650{\sim}670^{\circ}C$, respectively. The crystallized glass was heated at various conditions(temperature, time). After nucleation at $550^{\circ}C$ for 2hours prior to crystal growth at $650^{\circ}C$ for 4hours, the resulting Vickers hardness, fracture toughness and bending strength were about $736H_v$, $1.0779MPa{\cdot}m^{1/2}$, and 493MPa, which were 17%, 45% and 149% higher than parent borosilicate glass, respectively. Crystal size and transmittance of crystallized borosilicate glass were analyzed by FE-SEM, EDX and UV-VIS-NIR spectrophotometer. Transmittance of crystallized borosilicate glass was decreased with increasing $ZrO_2$(wt%) at visible-range. The results prove that light-weight bulletproof can be fabricated by the crystallization of borosilicate glass.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.438-439
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• 2013

Microelectronic devices의 접촉저항의 향상을 위해 Metal silicides의 형성 mechanism과 전기적 특성에 대한 연구가 많이 이루어지고 있다. 지난 수십년에 걸쳐, Ti silicide, Co silicide, Ni silicide 등에 대한 개발이 이루어져 왔으나, 계속적인 저저항 접촉 소재에 대한 요구에 의해 최근에는 Rare earth silicide에 관한 연구가 시작되고 있다. Rare-earth silicide는 저온에서 silicides를 형성하고, n-type Si과 낮은 schottky barrier contact (~0.3 eV)를 이룬다. 또한, 비교적 낮은 resistivity와 hexagonal AlB2 crystal structure에 의해 Si과 좋은 lattice match를 가져 Si wafer에서 high quality silicide thin film을 성장시킬 수 있다. Rare earth silicides 중에서 ytterbium silicide는 가장 낮은 electric work function을 갖고 있어 낮은 schottky barrier 응용에서 쓰이고 있다. 이로 인해, n-channel schottky barrier MOSFETs의 source/drain으로써 주목받고 있다. 특히 ytterbium과 molybdenum co-deposition을 하여 증착할 경우 thin film 형성에 있어 안정적인 morphology를 나타낸다. 또한, ytterbium silicide와 마찬가지로 낮은 면저항과 electric work function을 갖는다. 그러나 ytterbium silicide에 molybdenum을 화합물로써 높은 농도로 포함할 경우 높은 schottky barrier를 형성하고 epitaxial growth를 방해하여 silicide film의 quality 저하를 야기할 수 있다. 본 연구에서는 ytterbium과 molybdenum의 co-deposition에 따른 silicide 형성과 전기적 특성 변화에 대한 자세한 분석을 TEM, 4-probe point 등의 다양한 분석 도구를 이용하여 진행하였다. Ytterbium과 molybdenum을 co-deposition하기 위하여 기판으로 $1{\sim}0{\Omega}{\cdot}cm$의 비저항을 갖는 low doped n-type Si (100) bulk wafer를 사용하였다. Native oxide layer를 제거하기 위해 1%의 hydrofluoric (HF) acid solution에 wafer를 세정하였다. 그리고 고진공에서 RF sputtering 법을 이용하여 Ytterbium과 molybdenum을 동시에 증착하였다. RE metal의 경우 oxygen과 높은 반응성을 가지므로 oxidation을 막기 위해 그 위에 capping layer로 100 nm 두께의 TiN을 증착하였다. 증착 후, 진공 분위기에서 rapid thermal anneal(RTA)을 이용하여 $300{\sim}700^{\circ}C$에서 각각 1분간 열처리하여 ytterbium silicides를 형성하였다. 전기적 특성 평가를 위한 sheet resistance 측정은 4-point probe를 사용하였고, Mo doped ytterbium silicide와 Si interface의 atomic scale의 미세 구조를 통한 Mo doped ytterbium silicide의 형성 mechanism 분석을 위하여 trasmission electron microscopy (JEM-2100F)를 이용하였다.

• The Journal of Korean Physical Therapy
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• v.14 no.4
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• pp.119-130
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• 2002

The purpose of this study was to evaluate hemodynamics of intracranial blood flow for obtain clinically useful reference values and assess cerebral hemodynamics change with aging. 81 normal Korean subjects(age, 14$\thicksim\∼\thicksim$70 years) examined who han no history of neurologic disease and the subjects divided into group A(age, 14$\∼$39 years), group B(age, 40$\∼$59 years) and group C(age, 60$\∼$70 years). Transcranial doppler was use for measured the maximum velocity(Vmax), mean velocity(Vmean), pulsatility index(PI), resistive index(RI), stenosis index(SI) and depth of sample volume. Vmax was 99.1 1cm/s, Vmean was 63.57cm/s, PI was 0.85, RI was 0.56, SI was 31.94 and depth of sample volume was 52.35 in middle cerebral artery. Vmax was 85.54cm/s, Vmean was 52.52cm/s, PI was 0.82, RI was 0.55, SI was 34.48 and depth of sample volume was 73.62 in anterior cerebral artery. Vmax was 75.45cm/s, Vmean was 45.60cm/s, PI was 0.82, RI was 0.58, SI was 36.14 and depth of sample volume was 62.35 in posterior cerebral artery. Vmax was 70.44cm/s, Vmean was 47.07cm/s, PI was 0.87, RI was 0.58, SI was 29.83 and depth of sample volume was 75.23 in basilar artery Vmax was 63.92, Vmean was 42.42, PI was 0.89, RI was 0.58, SI was 29.89 and depth of sample volume was 66.65 in vertebral artery. Vmax and Vmean was significantly decreased with increasing age in middle cerebral artery, anterior cerebral artery, posterior cerebral artery, basilar artery and vertebral artery And PI and RI was significantly increased with increasing age in basilar artery and vertebral artery. And I suggest that transcranial doppler sonography can be used as one of useful clinical tool for detection of cerebral hemodynamics.

• Nuclear Engineering and Technology
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• v.45 no.7
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• pp.827-838
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• 2013

Interaction layer growth between U-Mo alloy fuel particles and Al in a dispersion fuel is a concern due to the volume expansion and other unfavorable irradiation behavior of the interaction product. To reduce interaction layer (IL) growth, a small amount of Si is added to the Al. As a result, IL growth is affected by the Si content in the Al matrix. In order to predict IL growth during fabrication and irradiation, empirical models were developed. For IL growth prediction during fabrication and any follow-on heating process before irradiation, out-of-pile heating test data were used to develop kinetic correlations. Two out-of-pile correlations, one for the pure Al matrix and the other for the Al matrix with Si addition, respectively, were developed, which are Arrhenius equations that include temperature and time. For IL growth predictions during irradiation, the out-of-pile correlations were modified to include a fission-rate term to consider fission enhanced diffusion, and multiplication factors to incorporate the Si addition effect and the effect of the Mo content. The in-pile correlation is applicable for a pure Al matrix and an Al matrix with the Si content up to 8 wt%, for fuel temperatures up to $200^{\circ}C$, and for Mo content in the range of 6 - 10wt%. In order to cover these ranges, in-pile data were included in modeling from various tests, such as the US RERTR-4, -5, -6, -7 and -9 tests and Korea's KOMO-4 test, that were designed to systematically examine the effects of the fission rate, temperature, Si content in Al matrix, and Mo content in U-Mo particles. A model converting the IL thickness to the IL volume fraction in the meat was also developed.

• Journal of Biomedical Engineering Research
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• v.21 no.3 s.61
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• pp.233-237
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• 2000

In general. fiber-optic medical endoscopes are made from glass step index (SI) fibers. These endoscopes have limitations in both image quality and mechanical properties. In particular. the image resolution of the SI endoscopes is limited to about 5$\mu$m. In this study the image resolution of plastic graded index (GRIN) super-resolution image guides with pixel sizes from 7 to 2.5 $\mu$m were measured and compared with those of 91ass SI image guides. There is an improvement in resolution of the plastic GRIN image guides as the microfiber diameter is reduced from 7 $\mu$m to 2.5 $\mu$m. The measured resolution of plastic GRIN image guide with 2.5 $\mu$m microfibers is more than a factor of two higher than that of g1ass SI image guide with 5$\mu$m microfibers. This new design of optical systems could have a major impact on a wide array of future optical systems used in defense. industrial, and medical applications.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.333-336
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• 1999

The relationship between the DC degradation characteristics of the $ZnO-Bi_2O_3$ varistor and post-annealing is investigated in this study. $ZnO-Bi_2O_3$ varistors containing $SiO_2$ range 0.3 mol% were fabricated by standard ceramic techniques. The post- annealing is performed at $550^{\circ}C$ for 0, 1.5 and 5h. A little phase transition is found according to the analysis of X-ray diffraction. DC degradation tests were conducted at $115\pm3^{\circ}C$ for periods up to 22h. Current-voltage analysis was used to determine nonlinear coefficients($\alpha$). Capacitance-voltage analysis enable the donor density($N_d$) and the barrier height($E_B$) to be determined. From above analysis, it is found that the past-annealing for 5h improved degradation characteristics in $ZnO-Bi_2O_3$ with Si additive.

• Korean Journal of Materials Research
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• v.24 no.1
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• pp.43-47
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• 2014

NiO-doped hibonite pigments were synthesized by the solid state method to get stabilized blue color pigment in both oxidation and reduction atmospheres. Optimum substitution condition with NiO for hibonite blue pigment was investigated. Experimental results were comparable to those of previous cobalt-minimization studies performed with other phosphate- or oxide-based cobalt-containing ceramic pigments (having olivine ($Co_2SiO_4$), spinel ($CoAl_2O_4$), or with co-doped willemite ($(Co,Zn)_2SiO_4$) structures). Composition was designed varying the NiO molar ratio increasing with $SnO_2$. The optimum substitution content is 0.93 mole NiO with 0.75mole $SnO_2$. The characteristics of the synthesized pigment were analyzed by XRD, Raman spectroscopy, SEM, and UV-vis. Synthesized pigment was applied to a lime-barium glaze with 10 wt% each and fired at an oxidation atmosphere of $1250^{\circ}C/1h$ and a reducing atmosphere $1240^{\circ}C/1h$. Blue color was obtained with $L^*a^*b^*$ values at 43.39, -6.78, -18.20 under a reducing atmosphere and 41.66, -6.36, -14.7 under and oxidation atmosphere, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.132-135
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• 1999

Recently, the ceramics of high permittivity are applied to DRAM and FRAM. In this study, (B $a_{x}$ S $r_{l-x}$)Ti $O_3$(BST) ceramics thin films were prepared by Sol-Gel method. BST solution was made and spin-coated on Pt/ $SiO_2$/Si substrate at 4000 [rpm] for 10 seconds. Coated specimens were dried at 150[$^{\circ}C$] for 5 minutes. Coating process was repeated 3 times and then sintered at 750[$^{\circ}C$] for 30 minutes. Each specimen was analyzed structure and electrical characteristics. Thickness of BST ceramics thin films are about 2000($\AA$). Dielectric constant and loss of thin films was little decreased at 1[KHz] ~1[KHz]. Dielectric constant and loss to frequency were 250 and 0.02 in $Ba_{0.7}$S $r_{0.3}$Ti $O_3$. The properly of leakage current as the realation between the current and the voltage was that change of the leakage current was stable when the applied voltage was 0~3[V].

• Electrical & Electronic Materials
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• v.9 no.7
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• pp.668-673
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• 1996

In this paper, (P $b_{1-x}$ L $a_{x}$)(Z $r_{0.52}$ $Ti_{0.48}$) $O_{3}$ (X=0-13[at%]) thin film were prepared by the Sol-Gel method, Multiple PLZT thin films were spin-coated on the Pt/Ti/ $SiO_{2}$Si substrate. The electrical properties of the films were investigated for varying the annealing temperature. In the PLZT(11/52/48) specimens, the dielectric ocnstant of 1236 and the polarization reversal time of 460[nm] were obtained and the breakdown of the film did not occur up to 1*10$^{10}$ cycles at the voltage of 7[V] by the bipolar acceleration. The remanent polarization and coercive field decreased with increasing the content of La in the range of 0-13[at%] and thin film of the PLZT(11/52/48) showed the value of 2.56[.mu.C/c $m^{2}$] and 21.1[kV/cm], respectively.ly.y.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.321-324
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• 2005

The main purpose of the present study has been placed on investigating the effects of controlled rolling and cooling on the microstructures and mechanical properties of C-Si-Mn-V steels for cold forming. The steels were manufactured in vacuum induction melting(VIM) furnace and casted to 1.1ton Ingots and the ingots were forged to $\Box150$ billet. The forged billets were reheated in walking beam furnace and rolled to coil, the stocks were rolled by Controlled Rolling and Cooling Technology (CRCT), so rolled at low temperature by water spraying applied in rolling stage and acceleratly cooled before coiling. Rolled coils were cold drawed to the degree of $27\%$ of area reduction without heat treatment. Microstructual observation, tensile test, compression test and charpy impact tests were conducted. The mechanical properties of the steels were changed by area reduction of cold drawing and it is founded that there are optimum level of cold drawing to minimize compression stress for these steels. From the result of this study, it is conformed that mechanical properties and microstructure of C-Si-Mn-V steels for cold forming were enhanced by accelerated cooling and founded optimum level of cold drawing.