• Korean Journal of Crystallography
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• v.1 no.2
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• pp.99-104
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• 1990

The hetero-epitaxial growth of AmB v type onto-electronic material is attempted by means of the laser-induced chemical vapour deposition technique. The bimolecular gas phase reaction of trimethylgallium with ammonia on (001) alumina substrate for the epitaxy of gallium nitride is chosen as a model system. In this study, ArF exciter laser (193nm) is employed as a photon source. Marked difference is found in nucleation and in subsequent crystal incorporation between the doposits formed with and without the laser-irradiation. The surface coverage with isomorphically grown drystallites is pronounced upon "volume-excited" irradiation in comparison with the conventional thermal process. As to the crystal structure of the grown layers, the laser-induced deposits of GaN may be represented by either of the following two models: (001) plane of sapphire //y (001) plane of wurtzite-type GaN, OR (001) plane of sapphire//(001) plane of wurtzite-type-GaN (111) plane of twinned zinc blende-type GaN.

• Journal of electromagnetic engineering and science
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• v.15 no.4
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• pp.199-205
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• 2015

An electromagnetic band gap (EBG) metamaterial construction is presented. A construction of a multipath mitigating ground plane, based on the EBG metamaterial is described. A method of the ground plane application and installation, which provides the multipath mitigating without spoiling antenna element phase center stability, is suggested and explained. A designed construction of GNSS antenna module, which contains the multipath mitigating ground plane, made from the presented EBG metamaterial and installed in the described way is shown and parameters of the antenna module are provided.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1185-1188
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• 2002

The objective of this paper is to apply experimental methods to measure the in-plane vibration intensity of a semi-infinite beam. Two experimental methods have been implemented to measure the in-plane vibration intensity of the beam. The first method is the cross spectral intensity measurement method using two accelerometers. The second method is the frequency response method using the only one acrelerometer. It has the advantages of shortening measurement time and reducing accelerometer phase error. Experimental results showed that those experimental methods can be effectively used to measure the structural In-plane vibration intensity.

• Journal of the Semiconductor & Display Technology
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• v.2 no.4
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• pp.23-26
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• 2003

The general users find difficulties in using ellipsometers. Thus, the object of this study is to construct an ellipsometer with simple operation principle. We developed an ellipsometer which does not require alignment and calibration before measuring sample. A basis structure model after rotating a compensator spectroscopic ellipsometry, the fixed incidence angle at $70^{\circ}$. This ellipsometer does not demand calibration, because the plane of incidence is not changed due to the novel sample holder structure. The results for various standard samples were compared with those from conventional RCSE to test the performance of this instrument. Also repeated measurements were performed to test the precision of the calibration coefficient in a plane of incidence fixed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.924-929
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• 2000

This paper addresses a new technique of measuring the mean flow velocity over the cross sectional area of the pipe using sound field reconstruction. When fluid flows in the pipe and two plane waves propagate oppositely through the medium, the flow velocity causes the change of wave number of the plane waves. The wave number of the positive going plane wave decreases and that of negative going one increases in comparison to static medium in the pipe. Theoretical backgrounds of this method are introduced in detail and the measurement of mean flow velocity using the sound field reconstruction is not affected by velocity profile upstream of microphones.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.1
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• pp.1-5
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• 2007

The structural and morphological properties of planar, nonpolar (11-20) a-plane GaN layers grown by hydride vapor phase epitaxy on (1-102) r-plan sapphire substrates are characterized. We report on the effect of low temperature ($500/550/600/660^{\circ}C$) AIN buffer layers on the structural properties of HVPE grown a-GaN kayers. and for the comparison, low temperature GaN and InGaN buffer layers are also tried for the growth of a-plane GaN layers. The structural geometry of a-GaN layers is severely affected on the growth condition of low temperature buffer layers. The most planar a-GaN could be obtained with $GaCl_3$ pretreatment at the growth temperature of $820^{\circ}C$.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07a
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• pp.105-108
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• 2005

We demonstrate an electro-optical device based on the flexoelectric effect of a short-pitched cholesteric liquid crystal. By using a dual-frequency switchable nematic, a small amount of chiral dopant and a small amount of phase-separated polymer localized on the surface, we were able to create a device that operates in amplitude (flexoelectric) and phase(dielectric) modes. At high frequency the dual frequency liquid crystal suppresses the phase mode at higher voltage, which improves the switching speed, and thereby preserving the in-plane-switching mode.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.58-59
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• 2003

We propose the optical encryption system using two divided image to hide the original image and a joint transform correlator. The encryption procedure is performed by the Fourier transform of the product of each phase encoded image (divided phase images) and the same random phase image which is generated by computer processing. An autocorrelation term of joint transform correlator contributes to decrypt the original image. This system will be used in optical certification.

• Journal of Korean Association for Spatial Structures
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• v.10 no.1
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• pp.119-126
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• 2010

The some papers which deal with the dynamic instability for shell-like structures under the dynamic excitation have been published, but there are few papers which treat the essential phenomenon of the dynamic buckling using the phase plane for investigating occurrence of chaos. In nonlinear dynamic, examining the characteristics of attractor on the phase plane and investigating the dynamic buckling process are very important thing for understanding why unstable phenomena are sensitively originated by various initial conditions. In this study, the direct and indirect snapping of shallow EP shell considering geometrical nonlinearity are investigated by Galerkin method numerically. This finding out the characteristic of the dynamic instability through the phases curves and running response spectrum.

• Journal of the Korean Vacuum Society
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• v.18 no.1
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• pp.44-48
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• 2009

The effect of temperature gradient between the substrate and ambient gas on the structural characteristics of GaN nanorods grown on r-plane sapphire substrates by hydride vapor phase epitaxy was investigated. The density, diameter, and length strongly depended on the tempearture gradient. In addition, the cross-sectional shape of the nanorrods at the end of growth was found to be more dependedent on the temperature of a substrate itself than the temperature gradient.