• Journal of IKEEE
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• v.21 no.3
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• pp.297-308
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• 2017

By using electron beam evaporation under appropriate conditions, we obtained graphene intercalated sheets on Si(111) with an average crystallite size less than 11nm. The formation of such nanocrystalline graphene was found as a time-dependent function of carbon deposition at a substrate temperature of $1000^{\circ}C$. The structural and electronic properties as well as the surface morphology of such produced materials have been confirmed by reflection high energy electron diffraction, Auger electron spectroscopy, X-ray photoemission spectroscopy, Raman spectroscopy, scanning electron microscopy, atomic force microscopy and scanning tunneling microscopy.

• Journal of Surface Science and Engineering
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• v.39 no.4
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• pp.166-172
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• 2006

Metallized Polyimide films are extensively used as base materials in microelectronics, optical and automotive applications. However it is difficult to deposit metals on those because of their structural stabilities. In this work, polyimide films are modified by a wet process with alkalinemetalhydroxide and additives to introduce functional groups. The surface molecular structures of polyimide are investigated using X-ray photoelectron spectroscopy(XPS), fourier transform infrared reflection spectroscopy(FTIR-ATR), atomic force micro-scopic(AFM). XPS spectra and FTIR spectra show that the surface structure of polyimide is converted into potassium polyamate. AFM image and AFM cross-sectional analyses reveal the increased roughness on the modified surface of polyimide films. As a result, it is shown that the adhesion strength between polyimide surface and electroless nickel layer is increased by the nano-anchoring effect.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.958-961
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• 1997

The compatibility and the surface structure of blends of poly(styrene-co-acrylonitrile) (SAN) with either poly(methyl methacrylate) (PMMA) or hydrolyzed PMMA (H-PMMA) were studied in terms of film thickness, interaction, and surface free energy difference on the basis of X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform IR spectroscopy and atomic force microscopy. The XPS measurement showed that the surface enrichment of (PMMA/SAN) blends with different AN contents of SAN and with different carboxyl acid contents of PMMA was dependent on the molecular interaction, the surface free energy difference between components and the sample preparation history. It was found that the compatibility of H-PMMA and SAN was reduced with increasing carboxyl acid content of PMMA.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.5
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• pp.327-334
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• 2013

The interaction of oblique incident waves with a surface-mounted horizontal porous plate is investigated using matched eigenfunction expansion method under the assumption of linear potential theory. The new boundary condition on the porous plate suggested by Zhao et al.(2010) when it is situated at the still water surface is used. The imaginary part of the first propagating-mode eigenvalue in the fluid region under a horizontal porous plate, is closely related to the energy dissipation across the porous plate. By changing the porosity, plate width, wave frequencies, and incidence angles, the reflection and transmission coefficients as well as the wave loads on the porous plate are obtained. It is found that the transmission coefficients can be significantly reduced by selecting optimal porous parameter b = 5.0, also increasing the plate width and incidence angle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1464-1471
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• 2003

In order to investigate the flows with shock wave in branch, 108$^{\circ}$ elbow and T-junction of the IRWST system of standard Korean nuclear reactor, detail time dependent behaviors of unsteady flow with shock wave, vortex and so on are obtained by numerical method using compressible three-dimensional Navier-Stokes equations. At first, the complex flow including the incident and reflected shock waves, vortex and expansion waves which are generated at the corner of T-junction is calculated by the commercial code of FLUENT6 and is compared with the experimental result to obtain the validation of numerical method. Then the flow fields in above mentioned units are analyzed by numerical method of [mite volume method. In numerical analysis, the distributions of flow properties with the moving of shock wave and the forces acting on the wall of each unit which can be used to calculate the size of supporting structure in future are calculated specially. It is found that the initial shock wave of normal type is re-established its type from an oblique one having the same strength of the initial shock wave at the 4 times hydraulic diameters of downstream from the branch point of each unit. Finally, it is turned out that the maximum force acting on the pipe wall becomes in order of the T-junction, 108$^{\circ}$ elbow and branch in magnitude, respectively.

• Journal of the Korean Society for Railway
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• v.10 no.6
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• pp.650-654
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• 2007

Induction motors are widely used as a source of driving force in electric vehicles and pulse width modulation (PWM) inverters are applied to their operation. The issue is that insulation of inverter-fed induction motors (IFMs) are more stressed than in line-powered motors by transient voltages. This paper dealt with experimental results on transient voltage produced by the PWM operation of an induction motor. The peak and the dv/dt of transient voltage depending on the length of power feeding cable and operating frequency were investigated. In the experiment, transient voltages up to 3.3PU of the rated-inverter voltage were recorded for the cable length of 50m. As the cable length is increased, the peak voltage appeared at the motor terminals increases. This phenomenon can be explained by the reflection and the transmission of travelling wave. Consequently, special care for the cable length between the motor and the inverter should be taken in the use of IFM to ensure the full life of insulation system.

• Journal of the HCI Society of Korea
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• v.1 no.1
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• pp.37-44
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• 2006

Specular reflections provide the visual feedback that describes the material type of an object, its local shape, and lighting environment. In photorealistic rendering, there have been a number of research available to render specular reflections effectively based on a local reflection model. In traditional cel animations and cartoons, specular reflections plays important role in representing artistic intentions for an object and its related environment reflections, so the shapes of highlights are quite stylistic. In this paper, we present a method to render and control stylized specular reflections using projective textures based on principal curvature analysis. Specifying a texture as a pattern of a highlight and projecting the texture on the specular region of a given 3D model, we can obtain a stylized representation of specular reflections. For a given polygonal model, a view point, and a light source, we first find the maximum specular intensity point, and then locate the texture projector along the line parallel to the normal vector and passing through the point. The orientation of the projector is determined by the principal directions at the point. Finally, the size of the projection frustum is determined by the principal curvatures corresponding to the principal directions. The proposed method can control the position, orientation, and size of the specular reflection efficiently by translating the projector along the principal directions, rotating the projector about the normal vector, and scaling the principal curvatures, respectively. The method is be applicable to real-time applications such as cartoon style 3D games. We implement the method by Microsoft DirectX 9.0c SDK and programmable vertex/pixel shaders on Nvidia GeForce FX 7800 graphics subsystems. According to our experimental results, we can render and control the stylized specular reflections for a 3D model of several ten thousands of triangles in real-time.

• Journal of the Korean Vacuum Society
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• v.19 no.5
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• pp.371-376
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• 2010

The GaAs epitaxial layers were grown on Si(100) substrates by molecular beam epitaxy (MBE) using the two-step method. The Si(100) substrates were cleaned with three different surface cleaning methods of vacuum heating, As-beam exposure, and Ga-beam deposition at the substrate temperature of $800^{\circ}C$ in the MBE growth chamber. Growth temperature and thickness of the GaAs epitaxial layer were $800^{\circ}C$ and $1{\mu}m$, respectively. The surface structure and properties were investigated by reflection high-energy electron diffraction (RHEED), AFM (Atomic force microscope), DXRD (Double crystal x-ray diffraction), PL (Photoluminescence), and PR (Photoreflectance). From RHEED, the surface structure of GaAs epitaxial layer grown on Si(100) substrate with Ga-beam deposition is ($2{\times}4$). The GaAs epitaxial layer grown on Si(100) substrate with Ga-beam deposition has a high quality.

• Journal of the Korean Vacuum Society
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• v.18 no.5
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• pp.352-357
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• 2009

The InAs multi-quantum dots (MQDs) solar cell and InGaAs multi-quantum wells (MQWs) solar cell to cover 1.1 eV and 1.3 eV were designed by 1D poisson, respectively. The MQDs and MQWs of 5, 10, 15 layers were grown by molecular beam epitaxy. The photo luminescence results showed that the 5 period stacked MQDs have the highest intensity at around 1.1 eV with 57.6 meV full width at half maximum (FWHM). Also we can observe 10 period stacked MQWs peak position which has highest intensity at 1.31 eV with 12.37 meV FWHM. The density and size of QDs were observed by reflection high energy electron diffraction pattern and atomic force microscope. Futhermore, AlGaAs/GaAs sandwiched tunnel junctions were modified according to the width of GaAs layer on p-type GaAs substrates. The structures with GaAs width of 30 nm and 50 nm have backward diode characteristics. In contrast, tunnel diode characteristics were observed in the 20 nm of that of sample.

• Korean Journal of Materials Research
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• v.6 no.8
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• pp.817-824
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• 1996

Removal of Cu impurities on Si substrates using remote H-plasma was investigated. Si substrates were intentionally contaminated by 1ppm ${CuCI}_{2}$, standard chemical solution. To determine the optimal process condition, remote H-plasma cleaning was conducted varying the parameters of rf power, cleaning time and remoteness(the distance between the center of plasma and the surface of Si substrate). After remote H-plasma cleaning was conducted, Si surfaces were analysed by TXRF(total x-ray reflection fluorescence) and AFM(atomic force microscope). The concentration of Cu impurity was reduced by more than a factor of 10 and its RMS roughness was improved by more than 30% after remote H-plasma cleaning. TXRF analysis results show that remote H-plasma cleaning is effective in eliminating Cu impurity on Si surface when it is performed under the optimal process condition. AFM analysis results also verifies that remote H-plasma cleaning makes no damage to the Si surface. The deposition mechanism of Cu impurity may be explained by the redox potential(oxidation-reduction reaction potential) theory. Based on the XPS analysis results we could draw a conclusion that Cu impurities on the Si substrate are removed together with the oxide by a "lift-off" mechanism when the chemical oxide( which forms when Cu ions are adsorbed on the Si surface) is etched off by reactive hydrogen atoms.gen atoms.