• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.7
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• pp.354-358
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• 2006

In this paper, we investigated the selective etching rate of amorphous As-Ge-Se-S thin film due to the photoexpansion effect and fabricated the 2-dimensional embossing type diffraction grating hologram. We measured the thickness change with the etching time among NaOH solution after forming 1-dimension diffraction grating. As a results, we found that the selective etching rate were $2.5\AA/s,\;3.3\AA/s,\;3.9\AA/s$ where NaOH solution concentration were 0.26N, 0.33N, 0.36N, respectively. Also after the formation of 2-dimensional diffraction grating by the $90^{\circ}$ degree of circulation on the formed 1-dimensional diffraction grating, we etched selectively during 60sec, among 0.26N NaOH solution and obtained 2-dimensional embossing diffraction grating. As the results of AFM (Atomic Force Microscopy), we confirmed the formation of distinct embossing type 2-dimensional diffraction grating hologram, successfully.

• Transactions on Electrical and Electronic Materials
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• v.5 no.1
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• pp.34-37
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• 2004

Amorphous chalcogenide thin films, especially a-(Se, S) based films, exhibit a number of photo-induced phenomena. In this study, we make the As$\_$40/Ge$\_$10/Se$\_$15/S$\_$35//Ag thin film and then we measure the holographic diffraction efficiency according to thickness of Ag. And we form the two-dimensional holographic grating. At first, we formed one-dimensional grating and then we form two-dimensional grating by rotate the sample. We found out the most suitable thickness of Ag and in case of As$\_$40/Ge$\_$10/Se$\_$15/S$\_$35//Ag(600${\AA}$), the diffraction efficiency was more higher than other samples. The holographic grating was formed by He-Ne laser(λ=632.8nm). The intensity of incident beam was 2.5mW and incident angle was 20$^{\circ}$. We confirm. the two-dimensional holographic grating by the pattern of diffracted beam and AFM(Atomic Force Microscope) image. We perform the etching process using by 0.26N NaOH in order to confirm clearly two-dimensional grating.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.976-979
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• 2003

In this study, we formed the 2-dimensional holographic grating in order to mamufactured 2-dimensional photonic crystal in amorphous $As_{40}Ge_{10}Se_{15}S_{35}$ and $Ag/As_{40}Ge_{10}Se_{15}S_{35}$ thin film which have the excellent optical sensetivity using by He-Ne laser(632.8nm). The intensity of incident beam was 2.5mW and incident angle that $2{\theta}$ is $20^{\circ}$. We formed the holographic grating after had formed the 1-dimansional holographic grating and then rotate the sample. We confirmed that 2-dimensional holographic grating result of the figure of diffracted beam and AFM(Atomic Forced Microcopy) image.

• Tribology and Lubricants
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• v.24 no.4
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• pp.196-204
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• 2008

In this study, the pressure distributions on the oil film of piston pin bearings are found by two-dimensional lubrication analysis in order to help the optimum design of the bearings of piston pin. The lubrication analysis is carried out together with an equation related with the oil pressure-viscosity index. The oil film pressure distribution is used as an input data for pressure boundary conditions at the piston pin-boss surface. Finally, the piston pin-boss stress distribution coupled with the thermal stress is calculated, and then compared with the results of the stress analysis which is not counted with the oil film pressure boundary condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.161-164
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• 2006

A design program has been developed to predict film cooling performance in a liquid rocket engine combustion chamber. A thermal protecting effect of low mixture ratio gas has been analysed by CFD. A one-dimensional film cooling model based on the CFD results has been implemented in the previously developed design program of regenerative cooling. The predicted heat flux at the nozzle throat ranges from -16% to +28% when it is compared to the published measured data. The throat heat flux reduces by 36% when film cooling of 10% of fuel mass flow rate is applied.

• Journal of the Korean Mathematical Society
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• v.47 no.5
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• pp.967-983
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• 2010

Let M be an n-dimensional complete simply connected Riemannian manifold with sectional curvature bounded above by a nonpositive constant $-{\kappa}^2$. Using the cone total curvature TC($\Gamma$) of a graph $\Gamma$ which was introduced by Gulliver and Yamada [8], we prove that the density at any point of a soap film-like surface $\Sigma$ spanning a graph $\Gamma\;\subset\;M$ is less than or equal to $\frac{1}{2\pi}\{TC(\Gamma)-{\kappa}^2Area(p{\times}\Gamma)\}$. From this density estimate we obtain the regularity theorems for soap film-like surfaces spanning graphs with small total curvature. In particular, when n = 3, this density estimate implies that if $TC(\Gamma)$ < $3.649{\pi}\;+\;{\kappa}^2\inf\limits_{p{\in}F}Area(p{\times}{\Gamma})$, then the only possible singularities of a piecewise smooth (M, 0, $\delta$)-minimizing set $\Sigma$ are the Y-singularity cone. In a manifold with sectional curvature bounded above by $b^2$ and diameter bounded by $\pi$/b, we obtain similar results for any soap film-like surfaces spanning a graph with the corresponding bound on cone total curvature.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.164.2-164.2
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• 2014

In order to combine advantages of ZnO thin film transistors (TFTs) with a high on-off ratio and graphene TFTs with extremely high carrier mobility, we present a facile methodology for fabricating ZnO thin film/graphene hybrid two-dimensional TFTs. Hybrid TFTs exhibited ambipolar behavior, an outstanding electron mobility of $329.7{\pm}16.9cm^2/V{\cdot}s$, and a high on-off ratio of $10^5$. The ambipolar behavior of the ZnO/graphene hybrid TFT with high electron mobility could be due to the superimposed density of states involving the donor states in the bandgap of ZnO thin films and the linear dispersion of monolayer graphene. We further established an applicable circuit model for understanding the improvement in carrier mobility of ZnO/graphene hybrid TFTs.

• Journal of the Korean Applied Science and Technology
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• v.12 no.2
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• pp.29-39
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• 1995

The phase separated structure and the electro-optical properties of the (polymer/liquid) crystal : LC) composite film strongly depended on the weight fraction of LC in it. The continuous LC phase was formed in a three-dimensional polymer network when the LC weight fraction was above 40wt%. The aggregation structure of the composite film could be controlled by controlling the solvent evaporation velocity during the film preparation process. The smaller LC domains or channels were formed in the case of the faster solvent evaporation velocity. The composite film exhibited reversible light scattering-light transmission switching upon electric field -OFF and -ON states, respectiverly. The light scattering properties of the composite film strongly depended on the spatial distortion of the nematic directors as well as the mismatch in refractive indices between matrix polymer and LC.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.15-22
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• 2003

Computational study using the 2-dimensional, compressible, Navier-Stokes equations is performed to predict the discharge coefficient of air flow through a film-cooling hole. In order to investigate the effect of internal/external flows on discharge coefficient, the present computational results which are obtained for three flow cases, only external flow, only internal flow, and no flow, are compared with experimental ones. It is found that the computational results predict the discharge coefficient of the film-cooling hole in a reasonable accuracy and the external crossflow reduces the discharge coefficient, while the internal crossflow increases the discharge coefficient in a range of momentum flux ratio $I_{c-jet}$ > 1 due to the total pressure loss and boundary layer effect.

• Applied Chemistry for Engineering
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• v.16 no.1
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• pp.112-116
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• 2005

We investigated the surface modification method for the preparation of organic-inorganic hybrid composite thin film. Gelatin obtained from the decomposition of collagen was allowed to adsorb in a polystyrene tissue culture dish for 2 h to from layers of gelatin. Supersaturated ionic solution of calcium and phosphorus was injected on the gelatin adsorbed layer to form calcium phosphate thin film. During the initial period of incubation, nucleates were formed. With increase of the incubation time, CaP (calcium phosphate) thin film grew on the surface of the culture dish. The gelatin/CaP thin film displayed the highly porous three-dimensional surface structure. Attenuated, total reflectance Fourier transform, infra-red spectroscopy (ATR-FTIR) was used to analyze the chemical properties of CaP film. The analysis demonstrated that the CaP film formed at initial period of treatment appeared to be amorphous. With increase of incubation time, the crystallinity of the film was slightly increased, but the presence of the peaks for the low crystalline CaP confirmed that the CaP thin film prepared in this study was poorly crystallized.