• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.34 no.1
• /
• pp.8-15
• /
• 2024

The CaF₂ single crystal has notable characteristics such as a large band gap (12 eV), excellent transparency over a wide wavelength range, low refractive index and dispersion. Due to these outstanding properties, CaF₂ single crystal has considered as a promising material for short-wavelength light sources in recent lithography processes. However, there is an inherent birefringence of the material at 157 nm and the resulting aberration can be compensated for through the combination of the (100) plane and the (111) plane. Therefore, it is necessary to investigate the characteristics according to the plane. In this study, we analyzed crystallinity, optical properties of commercial CaF₂ single crystal wafers grown by the Czochralski method. In particular, through chemical etching under various conditions, it was confirmed that the shape of etch pits appears differently depending on the plane and the shape and array of specific etch pits affected by dislocations and defects were examined.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.1 no.2
• /
• pp.14-19
• /
• 2010

Theories for advanced composite structures are too difficult for such design engineers for construction and some simple but accurate enough methods are necessary. The senior author has reported that some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. For such plates, the fiber orientations given above behave as specially orthotropic plates and simple formulas developed by the senior author. Most of the bridge and building slabs on girders have large aspect ratios. For such cases further simplification is possible by neglecting the effect of the longitudinal moment terms(Mx) on the relevant partial differential equations of equilibrium. In this paper. the influence of the aspect ratio on the natural frequency of the composite laminated plates is studied and it is concluded that the method used is sufficiently accurate for engineering purposes.

• The Journal of the Petrological Society of Korea
• /
• v.20 no.4
• /
• pp.219-230
• /
• 2011

Jurassic granite from Hapcheon was analysed with respect to the characteristics of the rock cleavage. The phases of distribution of microcracks were well evidenced from the enlarged photomicrographs(${\times}6.7$) of the thin section. The planes of principal set of microcracks are parallel to the rift plane and those of secondary set are parallel to the grain plane. These rift and grain microcracks are mutually near-perpendicular on the hardway planes. Consequently the rock cleavage of Jurassic granite from the studied quarry can be related to the preferred orientation of microcracks. Microcrack parameters such as number, length and density show an order of rift > grain > hardway. These results indicate a relative magnitude of the rock cleavage. Meanwhile, brazilian tensile strengths were measured with respect to the six directions. The results revealed a strong correlation between mechanical property with microcrack parameters.

• Polymer(Korea)
• /
• v.28 no.4
• /
• pp.298-304
• /
• 2004

We fabricated a polymer dispersed liquid crystal (PDLC) cell using LC with negative dielectric anisotropy and UV curable monomer exhibiting transparent state initially (called normally transparent (NT)) and studied the electro-optic characteristics. The NT PDLC cell made with the ratio of LC : monomer = 70/30 wt%, curing temperature of 20 $^{\circ}C$ and strong UV intensity of 198 ㎽/$\textrm{cm}^2$ had high contrast ratio and showed good electro-optic characteristics. In this condition, LC is aligned vertically on the substrate due to the vertical alignment layer and the polymer made with the UV exposure does not influence the alignment of the LC much. Therefore, the transmittance at the zero voltage is very high and the scattering state of the cell is good after applying the voltage because LC with negative dielectric anisotropy tries to align perpendicular to the field. And also, the NT PDLC cell showed better viewing angle characteristics than that in the normally scattering (NS) PDLC.

• Journal of the Korean Vacuum Society
• /
• v.14 no.4
• /
• pp.201-206
• /
• 2005

In this work, we tried to improve the fabrication process in HVPE (Hydride Vapor Phase Epitaxy) system by using Si(111) substrate with pre-deposited Al layer. PL measurements was done for samples with and without pre-deposited Al on Si and it was also examined the dependence of the optical characteristic properties on AlN buffer thickness for GaN/AIN/Al/Si. A sample with thin Al nucleation layer on Si substrate reveals a better optical property than the other. And it suggests that the thickness for AlN buffer layer with thin Al nucleation layer on Si(111) substrate is most proper about $260{\AA}$ to grow GaN in HVPE system. The surface morphology of GaN clearly shows the hexagonal crystallization. The XRD pattern showed strong peak at GaN{0001} direction.

• Korean Journal of Materials Research
• /
• v.6 no.8
• /
• pp.825-832
• /
• 1996

적외선 센서의 재료로 활용되고 있는 PLT박막 (두께:8000$\AA$-9000$\AA$)을 Pt/Ti/SiO2/Si와 Pt/M\ulcorner의 하부 구조상에 50$0^{\circ}C$, 55$0^{\circ}C$ 및 $600^{\circ}C$에서 스퍼터링 증착하여 결정성 및 전기적 특성을 조사하였다. $600^{\circ}C$로 in-situ 성장된 PLT박막은 Si기판을 이용한 경우 randomly oriented perovskite 결정구조를 나타내었으며, Pt/MgO 구조위에서는 c-축(00ι)방향으로 배향 성장되었다. $600^{\circ}C$에서 in-situ 성장된 PLT박막의 비유전상수($\varepsilon$r)와 유전정접(tan $\delta$)을 10kHz-100kHz의 주파수에서 측정한 결과 Pt/Ti/SiO2/Si 구조상에 증착된 박막은$\varepsilon$r=90과 tan $\delta$=0.02의 값을 Pt/MgO 구조상에 증착된 박막은 $\varepsilon$e=35와 tan$\delta$=0.01의 값을 나타내었다. 잔류분극량(2Pr)과 초전계수(${\gamma}$)는 상온부근에서 Si 기판을 이용한 경우 각각 0.6$\mu$C/$\textrm{cm}^2$.。C과 0.5x10-8C/$\textrm{cm}^2$.。C정도로 매우 작게 나타났으나 PLT/Pt/MgO 구조에서는 2Pr=5$\mu$C/$\textrm{cm}^2$, r=4x10-8C/$\textrm{cm}^2$.。C로 비교적 양호한 초전박막의 전기적 특성을 나타내었다.

• The Journal of the Convergence on Culture Technology
• /
• v.9 no.1
• /
• pp.539-544
• /
• 2023

The subject of this study is the Maae Buddha statue in granodiorite of the Mesozoic Cretaceous period, which is concerned about stability as a standing stone cultural property located in ◯◯-dong, Gyeongsangbuk-do. For stability analysis, three-dimensional face mapping, geological properties of joints, three-dimensional scanning, ultrasonic velocity, polarization microscopy, electron microscopy analysis and XRD analysis were performed. In addition, the safety factor of the Maaebul was calculated by analyzing the damage status investigation, stereographic projection analysis, rock classification, and limit equilibrium analysis. The types and scales of damage and possible collapse by section depend on the degree of weathering of the rock and the orientation and characteristics of the joints, but wedge-failure and toppling-failure are expected to be small-scale. The safety factor of Maaebul in dry and wet conditions is less than 1.2, so stability is concerned. The types of damage were mainly observed, such as exfoliation, cracking, granular decomposition, and vegetation growth. The Maaebul rock is granodiorite, and the surface discoloration materials are K, Fe, and Mg. The 4 sets of joints are developed, J1 is tensile joint and the others are shear joint. The uniaxial compressive strength estimated by ultrasonic exploration is 514kgf/cm2, which corresponds to most soft rocks and some weathered rocks. Rock classification(RMR) is estimated to be grade 5, very poor rock mass. These technique along with the existing methods of safety diagnosis of cultural properties are expected to be a reasonable tool for objective interpretation and stability review of stone cultural properties.

• Journal of the Korean Electrochemical Society
• /
• v.2 no.2
• /
• pp.81-87
• /
• 1999

Poly-acrylonitrile (PAN) based carbon fibers were stabilized under various tensions in the presence of air at about $200^{\circ}C$ and sequentially carbonized under some different gas environments in the range of 700 to $1500^{\circ}C$. The prepared carbon fibers were used for rechargeable lithium ion battery anode to investigate preparation parameters effects on electrochemical characteristics. It was found that the tension during stabilization, carbonization temperature and gas atmospheres affect the carbon fiber properties such as conductivity, mechanical strength, surface morphology and diffusion coefficient of lithium ion, which are closely related to the on electrolchemical properties as well as the charge/discharge characteristics.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.20 no.6
• /
• pp.254-261
• /
• 2010

Polycrystalline silicon (pc-Si) films are fabricated and characterized for application to pc-Si thin film solar cells as a seed layer. The amorphous silicon films are crystallized by the aluminum-induced layer exchange (ALILE) process with a structure of glass/Al/$Al_2O_3$/a-Si using various thicknesses of $Al_2O_3$ layers. In order to investigate the effects of the oxide layer on the crystallization of the amorphous silicon films, such as the crystalline film detects and the crystal grain size, the $Al_2O_3$ layer thickness arc varied from native oxide to 50 nm. As the results, the defects of the poly crystalline films are increased with the increase of $Al_2O_3$ layer thickness, whereas the grain size and crystallinity are decreased. In this experiments, obtained the average pc-Si sub-grain size was about $10\;{\mu}m$ at relatively thin $Al_2O_3$ layer thickness (${\leq}$ 16 nm). The preferential orientation of pc-Si sub-grain was <111>.

• The Journal of the Petrological Society of Korea
• /
• v.16 no.3
• /
• pp.144-161
• /
• 2007

The studied Nangsan area is widely covered by the Jurassic biotite granodiorite, which is mainly light grey in color and medium-grained in texture. Results of the regional fracture pattern analysis for the granodiorite body are as follows. Strike directions of fractures show three dominant sets in terms of frequency order. The sets are in an order of a (1) $N80^{\circ}{\sim}90^{\circ}E$ (1st-order)>(2) $N70^{\circ}{\sim}80^{\circ}E$ (2nd-order)>(3) $NS{\sim}N10^{\circ}E$ (3rd-order). Spacings of the fractures are mostly predominant in less than 200 cm. Therefore, the granodiorite of the area has more potential for non-dimensional stones than dimension ones. And orientations of vertical quarrying planes can be also divided into two groups in terms of frequency $N14^{\circ}W{\sim}N16^{\circ}E$ (1st-order) and (2) $N78^{\circ}E{\sim}N88^{\circ}E$ (2nd-order). The orientations of the two groups are more or less different from those of the regional fracture patterns. These can be mainly attributed to the preferred orientations of microcrack developed in the quarries. Of physical properties, specific gravity, absorption ratio, porosity, compressive strength, tensile strength and abrasive hardness are 2.65, 0.28%, 0.73%, $1,628kg/cm^2,\;100kg/cm^2$ and 31, respectively. Contrary to the porosity, both granites of the Nangsan and Sogrisan areas show almost similar values of the abrasive hardness. These can be explained by the differences of Qz+Af modes, which can be regarded as an index for abrasive resistance. Meanwhile, it is anticipated that comprehensive understanding of the orientations of vertical quarrying planes and characteristics of various physical properties will be utilized as an important information for stone resources.