• Journal of the Optical Society of Korea
• /
• v.20 no.1
• /
• pp.125-129
• /
• 2016

In this study, we have investigated a high-temperature AlN nucleation layer and AlGaN epilayers on c-plane sapphire substrate by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). High resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), scanning electron microscope (SEM) and Raman scattering measurements have been exploited to study the crystal quality, surface morphology, and residual strain of the HT-AlN nucleation layer. These analyses reveal that the insertion of an LT-AlN nucleation layer can improve the crystal quality, smooth the surface morphology of the HT-AlN nucleation layer and further reduce the threading dislocation density of AlGaN epifilms. The mechanism of inserting an LT-AlN nucleation layer to enhance the optical properties of HT-AlN nucleation layer and AlGaN epifilm are discussed from the viewpoint of driving force of reaction in this paper.

• Macromolecular Research
• /
• v.13 no.6
• /
• pp.499-505
• /
• 2005

Ordered mesoporous materials with a hydrothermally-stable, protozeolitic framework were prepared by exploring the direct conversion of inorganic species based on co-surfactant templating systems. To confer hydrothermal stability on the mesoporous aterials, the organic-inorganic hybrids were heat-treated in strongly basic media. Co-surfactant templating systems of cetyltrimethylammonium bromide [$C_{16}H_{13}(CH_{3})_{3}$NBr, CTAB] with 1,3,5-trim­ethylbenzene (TMB) or a nonionic block copolymer of poly(ethylene oxide )-b-poly(propylene oxide )-b-poly(ethyl­ene oxide) ($EO_{20}PO_{70}EO_{20}$) were employed to improve the hydrothermal stability of the organic-inorganic self-assembly during the solid rearrangement process of the inorganic species. The mesoscopic ordering of the pore structure and geometry was identified by X-ray diffraction, small angle neutron scattering and electron microscopy.

• Korean Journal of Optics and Photonics
• /
• v.9 no.1
• /
• pp.31-37
• /
• 1998

We fabricated acrylamie photopolymer holographic recording materials by photopolymerization of acrylamide, and described hologram formation process. Light absorption and phtobleaching process by MB(methylene blue) dye and radical polymerization process due to TEA(triethanolamind) are explained in detail. We adopted the Beer-lambert law in order to explain the photobleaching kinetics. Dependencies of diffraction efficiency of the hologram on monomer amout and the exposure are investigated. The scattering effect caused by grain of polymer crystal, and fixing method are also illustrated.

• Journal of Environmental Science International
• /
• v.18 no.8
• /
• pp.911-918
• /
• 2009

Electromagnetic interference (EMI) is defined as the interaction phenomena of electromagnetic waves scattered from a large structure or complex terrain. In this study, the propagation of linear wave is modeled with ray theory, direct simulation Monte Carlo (DSMC), and some classical theories on flat plates. The wave physics of reflection, refraction, and diffraction are simulated for the investigation of front and back scattering of the one-dimensional plane wave from a tower with ray theory and DSMC, respectively. The effect of rotating disk idealized from the real wind-turbine blades is modeled with a simplified version of the classical electromagnetic theory as well as DSMC based on the ray theory.

• Applied Science and Convergence Technology
• /
• v.24 no.6
• /
• pp.228-231
• /
• 2015

We investigated the adsorption structures and the initial growth mode of ultra-thin Al films on a W(110) surface at a high temperature. When Al atoms were adsorbed on the W(110) at the substrate temperature of 1100 K and with coverage of 0.5ML, Al atoms formed a p($2{\times}1$) double-domain structure. When the coverage was 1.0 ML, the double domain of a hexagonal structure (fcc(111) face) rotated ${\pm}5^{\circ}$ from the [100] direction of the W(110) surface and another distorted hexagonal structure were found. Low-energy electron diffraction results along with ion scattering spectroscopy results showed that the Al atoms followed the Volmer-Weber growth mode at a high temperature.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.33 no.3
• /
• pp.248-258
• /
• 1997

The analytical solutions of the Fraunhofer Diffraction(FD) theory and the principle for measurement of the dispersion relation of plasma wave is presented. Especially, the method for measurement of low-frequency wave is discussed. The wavenumbers of the density fluctuations are obtained from the curve fitting between the expremental FD profile and theoretical one for each frequency component. In measurement of the wavenumber of the low -frequency region, the information of the wavenumber is easily obtained from the ratio of the intensity at = 0 to the intensity at =0.5. The millimeter wave FD apparatus was designed to measure low-frequency density fluctuations. The determined wavenumbers are in the range of =0.1~ 1.0cm. Thus, the millimeter wave FD method was shown to be useful for the measurement of low-frequency density fluctuations, which are impossible to be measured by using a convention. Thomson scattering. The obtained dispersion relations will be useful information for plasma waves.

• Journal of the Semiconductor & Display Technology
• /
• v.3 no.4
• /
• pp.5-11
• /
• 2004

Optical properties of PET(Polyethylene terephthalate), PC(Polycarbonate), Acrylic resin and PE(Polyethylene) sheets were studied as a function of heat treating temperature of $60^{\circ}C$ to $150^{\circ}C$. By the heat treatment, optical properties of transmittance, absorbance, and reflectance showed a considerable change with different ways according to the materials. To understand the reason of optical property change, X-ray diffraction and surface morphology were also investigated. It was observed that small crystallite and pore that can cause scattering largely affect the transmittance. It was suggested that change of surface chemical bond induce the reflectance variation.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.637-640
• /
• 2005

We propose a sound source localization method using the Head-Related-Transfer-Function (HRTF) to be implemented in a given platform. HRTFs contain not only the information regarding proper time delays but also phase and magnitude distortions due to diffraction and scattering by the shading object. Therefore, a set of HRTFs for any given platform provides a substantial amount of information as to the whereabouts of the source. In this study, we introduce new phase criterion in order to find the sound source location in accordance with the HRTF database empirically obtained in an anechoic chamber with the given platform. Using this criterion, we analyze the estimation performance of the proposed method in a household environment.

• Journal of the Semiconductor & Display Technology
• /
• v.16 no.2
• /
• pp.89-93
• /
• 2017

For various process pressures, aluminum doped zinc oxide(AZO) films were deposited by in-line pulsed-DC sputtering. The deposited AZO films were optically and electrically investigated and analyzed for the window layers of CIGS solar cell systems. As the pressure was increased from 9 mtorr to 15 mtorr, the thickness of AZO was decreased as a result of scattering and its sheet resistance was rapidly increased. The transmittance of AZO was slightly decreased as the pressure was increased and the calculation of figure of merit(F.O.M) was dependent on the sheet resistance. The structural characteristics of AZO thin films analyzed by X-ray diffraction(XRD) showed no significant dependency according to the pressure.

• Journal of the Korean Society of Radiology
• /
• v.7 no.1
• /
• pp.45-50
• /
• 2013

Non-invasive technique CT, called automated computed tomography, is used to detect lesion of a patient when diagnosing human body. Information obtained from CT plays an important role in assembling 3 dimensional images. Recently, new equipment, operated by CT, is required which can be appliable to physical and biological research. In accordance to this quest, micro-CT is invented that produce more detail and concrete information. Images supplied by CT are even more detailed and concrete, so it contributes much to the development of biology and polymer material engineering field. However, there has been little reliable reports regarding measuring information of space dose distribution about exposure dose limit of users operating micro-CT. In addition, little reports regarding space dose distribution of exposure has been known about unwanted diffraction light produced by usage of micro-CT. The exterior of micro-CT is covered by lead, which is for removing exposure of diffraction light. Thus, even if it is good enough to prevent exposure of diffraction light, consistent management of equipment will be required as time goes by and equipment are getting old as well. We measured space dose distribution regarding exposure of diffraction light of users operating micro-CT directly. Therefore, we suggest that proper management should be necessary for users operating micro-CT not to be exposed by unwanted diffraction light.