• Journal of Welding and Joining
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• v.20 no.4
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• pp.525-534
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• 2002

During laser spot welding of the braun tube electron gun, phenomena such as serious spattering and oxidative reaction, etc. were occurred. The spatter occurred from weld pool affects the braun tube, namely it blocks up a very small hole on the shadow mask and causes short circuit between two roles of the electron gun. We guessed that high power density and oxidative reaction are main sources of these problems. So, we studied to prevent and to reduce spatter occurring in spot welding of the braun tube electron gun using pulsed Nd:YAG laser. The characteristics of laser output power was estimated, and the loss of laser energy by optical parameter and spatter was measured by powermeter. The effects of welding parameters, laser defocused distance and incident angle, were investigated on the shape and penetration depth of the laser welded bead in flare and flange joints. From these results, the laser peak power was a major factor to control penetration depth and to occur spatter. It was found that the losses of laser energy by optic parameter and sticked spatter affect seriously laser weldability of thin sheets. The deepest penetration depth is gotten on focal position, and a "bead transition" occurred with a slight displacement of focal position relative to the workpiece surface and the absorption rate of the laser energy is affected by the shape factor of the workpiece. When we changed the incident angle of laser beam, the penetration depth was decreased a little with increasing of the incident angle, and the bead width was increased. The spattering was prevented by considering laser beam energy and incident angle.ent angle.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.162-162
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• 2000

We have studied magnetic properties of Co/Pt multilayered films which have attracted great interest as high-density magneto-optical (MO) recording media due to their good MO properties. For this study, [Pt(45 )/Co(35 )]$\times$8 films were deposited with a Pt buffer layer of 60 on Si(100) substrate by alternating electron-beam evaporation in a high vacuum and were ion beam mixed by using 80keV Ar+ at 25$0^{\circ}C$. Especially, an external magnetic field was added to help changing magnetic property during ion beam mixing (IBM). The intermixing of Co and Pt layers after IBM was confirmed with Rutherford Backscattering Spectroscopy (RBS) and Transmission Electron Microscopy (TEM). The MO property of the film was measured with magneto-optical Kerr spectrometer and the change of magnetic easy axis in the film plane was observed from Ker loop data. This anomalous result might be correlated with the change of atomic structure due to the intermixing effect.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.157-157
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• 2015

Recently, the growing interest in organic microelectronic devices including OLEDs has led to an increasing amount of research into their many potential applications in the area of flexible electronic devices based on plastic substrates. However, these organic devices require a gas barrier coating to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency OLEDs require an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}g/m^2day$. The Key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required ($1{\times}10^{-6}g/m^2day$) is the suppression of defect sites and gas diffusion pathways between grain boundaries. In this study NBAS process was introduced to deposit enhanced film density single gas barrier layer with a low WVTR. Fig. 1. shows a schematic illustration of the NBAS apparatus. The NBAS process was used for the $Al_2O_3$ nano-crystal structure films deposition, as shown in Fig. 1. The NBAS system is based on the conventional RF magnetron sputtering and it has the electron cyclotron resonance (ECR) plasma source and metal reflector. $Ar^+$ ion in the ECR plasma can be accelerated into the plasma sheath between the plasma and metal reflector, which are then neutralized mainly by Auger neutralization. The neutral beam energy is controlled by the metal reflector bias. The controllable neutral beam energy can continuously change crystalline structures from an amorphous phase to nanocrystal phase of various grain sizes. The $Al_2O_3$ films can be high film density by controllable Auger neutral beam energy. we developed $Al_2O_3$ high dense barrier layer using NBAS process. We can verified that NBAS process effect can lead to formation of high density nano-crystal structure barrier layer. As a result, Fig. 2. shows that the NBAS processed $Al_2O_3$ high dense barrier layer shows excellent WVTR property as a under $2{\times}10^{-5}g/m^2day$ in the single barrier layer of 100nm thickness. Therefore, the NBAS processed $Al_2O_3$ high dense barrier layer is very suitable in the high efficiency OLED application.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.11
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• pp.29-34
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• 2004

This paper reports the RF dispersion and linearity characteristics of unpassivated AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE). The devices with a 0.5 ${\mu}{\textrm}{m}$ gate-length exhibited relatively good DC characteristics with a maximum drain current of 730 mA/mm and a peak g$_{m}$ of 156 mS/mm. Highly linear characteristic was observed by relatively flat DC transconductance (g$_{m}$) and good inter-modulation distortion characteristics, which indicates tight channel carrier confinement of the InGaN channel. Little current collapse in pulse I-V and load-pull measurements was observed at elevated temperatures and a relatively high power density of 1.8 W/mm was obtained at 2 GHz. These results indicate that current collapse related with surface states will not be a power limiting factor for the AlGaN/InGaN HEMTs.

• Composites Research
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• v.16 no.1
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• pp.19-25
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• 2003

In this paper, electrical properties of nanostructured carbon blacks (CB)-filled high density polyethylene (HDPE) composites were investigated as a function of temperature, which were prepared by the conventional melt-mixing method. The composites were irradiated with electron beam in a dosage of 30∼150 kGy to enhance an electronical reproducibility and to reduce a negative temperature coefficient (NTC) phenomenon. And, gel contents (%) of irradiated CB/HDPE composites were estimated by solvent extraction method. From the experimental results. the positive temperature coefficient (PTC) intensity of the composites was strongly depended on the CB content and particle size. And, the increase of gel contents (%) and disappearance of NTC behavior of the composites were identified at a dosage of 60 kGy. It was also found that the electron beam irradiation made an improvement of electrical reproducibility of the composites. This result was probably due to the reduction of the freedom of CB movement at above the melting temperature of the polymer crystalline, resulting in increasing the crosslinking structure of the composites.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.57-77
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• 1998

Heteroepitaxial $Y_2O_3$ films were grown on a Si(111) substrate by ionized cluster beam deposition(ICBD) in ultra high vacuum, and its qualities such as crystllitnity, film stress, and morphological characteristics were investigated using the various measurement methods. The crystallinity was investigated by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). Interface crystallinity was also examined by Rutherford backscattering spectroscopy(RBS) channeling, transmission electron microscopy(TEM). The stress of the films was measured by RBS channeling and XRD. Surface and interface morphological characteristics were investigated by atomic force microscopy (AFM) and x-ray scattering method. Comparing the interface with the surface characteristics, we can conclude that many defects at the interface region were generated by interface reaction between the yttrium metal and SiO2 layer and by ion beam characteristic such as shallow implantation, so that they influenced the film qualities. The film quality was dominantly depended on the characteristic temperature range. In the temperature range from $500^{\circ}C$ to $600^{\circ}C$, the crystallinity was mainly improved and the surface roughness was drastically decreased. On the other hand, in the temperature range from $600^{\circ}C$ to $700^{\circ}C$, the compressive stress and film density were dominantly increased, and the island size was more decreased. Also the surface morphological shape was transformed from elliptical shape to triangular. The film stress existed dominantly at the interface region due to the defects generation.

• Journal of the Korean Vacuum Society
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• v.6 no.4
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• pp.354-358
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• 1997

Crystal properties of wurtzite GaN films grown on $Al_2O_3$(0001) substrates under various nitrogen pressure and plasma power by electron cyclotron resonance molecular beam epitaxy were investigated by full width at half maximum of X-ray diffraction peak and scanning electron microscope. It was found that the nitrogen pressure has a large effect on the FWHM value of XRD, and the GaN film grown under the optimum nitrogen pressure contains high density of dislocations. These results suggest that the crystal quality is sensitive to the plasma source conditions and that the relaxation of stress depends of V/III ratio. However, substrate-surface nitridation has little effect on the relaxation of misfit stress.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.4
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• pp.143-148
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• 2019

We have successfully fabricated high aspect-ratio GaN-based nanowires on Si substrates using molecular beam epitaxy (MBE) system for high-efficiency hydrogen generation of photoelectrochemical water splitting. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) demonstrated that p-GaN:Mg and p-InGaN nanowires were grown vertically on the substrate with high density. Furthermore, it was also confirmed that the emission wavelength of p-InGaN nanowire can be adjusted from 552 nm to 590 nm. Such high-aspect ratio p-InGaN nanowire structure will be a solid foundation for the realization of ultrahigh-efficiency photoelectrochemical water splitting through sunlight.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.3
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• pp.83-88
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• 2015

Coating materials used in the electron beam (EB) deposition method, which is being studied as one of the fabrication methods of thermal barrier coating, are exposed to high power electron beam at focused area during the EB deposition. Therefore the coating source for EB process is needed to form as ingot with appropriate density and microstructure to sustain their shape and stable melts status during EB deposition. In this study, we tried to find the optimum powder condition for fabrication of ingot of 8 wt% yttria stabilized zirconia which can be used for EB irradiation. It seems that the ingot, which is fabricated through bi-modal type initial powder mixture which consists of tens of micro and nano size particles, was shown better performance than the ingot which is fabricated using monolithic nanoscale powder when exposed to high power EB.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.1
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• pp.44-53
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• 2006

In this study, the non-destructive computed tomography was adopted to observe the density profile of the needle-punched Carbon/Carbon(C/C) composites nozzle throat. The density profile of C/C was evaluated within ${\pm}0.01g/cm^3$ with 98.74% confidence when the correction of the image and high signal-to-noise ratio were achieved by the optimization of the beam hardening, the electrical noise and the scattered X-ray. The density variation of C/C with the computed tomography was in good agreement with the results obtained by the water immersion method and the observation with scanning electron microscope.