• Proceedings of the KWS Conference
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• 2002.10a
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• pp.612-619
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• 2002

The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.

• Journal of the Korean Vacuum Society
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• v.14 no.2
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• pp.84-90
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• 2005

The influence of plasma parameters on the growth of $In_{0.2}Ga_{0.8}N/GaN$ heterostructures has been investigated using plasma-assisted molecular beam epitaxy. Since plasma ejects plenty of energetic particles with different energy levels and flux density at various rf power levels, plasma modulated both growth rate and optical properties significantly. For instance, surface roughness and the emission spectrum of photoluminescence were degraded at low and high rf power. According to sharp interfaces between epitaxial films and strong peaks observed from photoluminescence spectra, our experimental setup presented optimal operation range of rf powers at around 400W. The phenomena could be explained by the presence of energetic particles modulating the rate of plasma stimulated desorption and surface diffusion, and energetic particles exceeding critical value resulted in the incorporation of defects at subsurface. The optimal rf power regime increased by 100W for $In_{0.2}Ga_{0.8}N/GaN$ growth in comparison with GaN. The effects of rf power were discussed in conjunction with kinetic processes being stimulated by energetic particles.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.508-508
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• 1996

;The growth of films have considerable interest in the field of superlattice structured multi-layer epitaxy led to realization of new devices concepts. Molecular beam epitaxy (MBE) with in situ observation by reflection high-energy electron diffraction (RHEED) is a key technology for controlled layered growth on the atomic scale in oxide crystal thin films. Also, the combination of radical oxygen source and MBE will certainly accelerate the progress of applications of oxides. In this study, the growth process of single crystal films using by MBE method is discussed taking the oxide materials of Bi-Sr-Ca-Cu family. Oxidation was provided by a flux density of activated oxygen (oxygen radicals) from an rf-excited discharge. Generation of oxygen radicals is obtained in a specially designed radical sources with different types (coil and electrode types). Molecular oxygen was introduced into a quartz tube through a variable leak valve with mass flowmeter. Corresponding to the oxygen flow rate, the pressure of the system ranged from $1{\;}{\times}{\;}10^{-6}{\;}Torr{\;}to{\;}5{\;}{\times}{\;}10^{-5}$ Torr. The base pressure was $1{\;}{\times}{\;}10^{-10}$ Torr. The growth of Bi-oxides was achieved by coevaporation of metal elements and oxygen. In this way a Bi-oxide multilayer structure was prepared on a basal-plane MgO or $SrTiO_3$ substrate. The grown films compiled using RHEED patterns during and after the growth. Futher, the exact observation of oxygen radicals with MBE is an important technology for a approach of growth conditions on stoichiometry and perfection on the atomic scale in oxide. The oxidization degree, which is determined and controlled by the number of activated oxygen when using radical sources of two types, are utilized by voltage locked loop (VLL) method. Coil type is suitable for oxygen radical source than electrode type. The relationship between the flux of oxygen radical and the rf power or oxygen partial pressure estimated. The flux of radicals increases as the rf power increases, and indicates to the frequency change having the the value of about $2{\times}10^{14}{\;}atoms{\;}{\cdots}{\;}cm^{-2}{\;}{\cdots}{\;}S^{-I}$ when the oxygen flow rate of 2.0 seem and rf power 150 W.150 W.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.6
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• pp.34-40
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• 1985

Characteristics of GaAE epilayers grown on (100) CaAs wa(tors by molecular beam epitaxy (MBE) under various single crystal growing conditions were investigated. In fabrica-ting GaAs, epilayer by MBE, the most important factors are a substrate temperature(ts) and a flux density ratio (As/Ga). In this experiment, the substrate temperature was varied in the range of 48$0^{\circ}C$ to $650^{\circ}C$ and As and Ga cell temperatures were varied in the range of 218$^{\circ}C$ to 256$^{\circ}C$ and 876$^{\circ}C$ to 98$0^{\circ}C$, respectively. At the substrate temperature of 54$0^{\circ}C$, As cell temperature of 23$0^{\circ}C$, and Ga cell temperature of 91$0^{\circ}C$, the As/Ga ratio was 5"10, the surface morphology was most smooth . Investigation of As-stabilized surface by RHEED and of depth profile by SIM5 showed that As is less stable than Ga. Also, X-ray diffraction measurement revealed that single crystals of (400) and (200) were formed at the both sub-strate temperatures of 52$0^{\circ}C$ and 54$0^{\circ}C$.TEX>.

• Journal of the Korean Vacuum Society
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• v.16 no.2
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• pp.79-90
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• 2007

Prototype of $800{\ell}$ vacuum web coater (Vic Mama) consisting of ion source with low energy less than 250 eV for high speed surface modification and 4 magnetron sputter cathodes was designed and constructed. Its performance was evaluated through fabricating the adhesiveless flexible copper clad laminate (FCCL). Pumping speed was monitored in both upper noncoating zone pumped down by 2 turbo pumps with 2000 l/sec pumping speed and lower surface modification and sputter zone vacuumed by turbo pumps with 450 1/sec and 1300 1/sec pumping speed respectively. Ion current density, plasma density, and uniformity of ion beam current were measured using Faraday cup and the distribution of magnetic field and erosion efficiency of sputter target were also investigated. With the irradiation of ion beams on polyimide (Kapton-E, $38{\mu}m$) at different fluences, the change of wetting angle of the deionized water to polyimide surface and those of surface chemical bonding were analyzed by wetting anglometer and x-ray photoelectron spectroscopy. After investigating the deposition rate of Ni-Cr tie layer and Cu layer was investigated with the variations of roll speed and input power to sputter cathode. FCCL fabricated by sputter and electrodeposition method and characterized in terms of the peel strength, thermal and chemical stability.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.351-359
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• 1996

We have investigated the effect of hydrogen plasma on the formation of InAs QDs (quantum dots) structure by using a CBE (chemical beam epitaxy)system equipped with ECR (electron cyclotron resonance) plasma source. It is confirmed that the formation of self-organized InAs-QDs on GaAs is started after the growth of InAs layer up to 2.6 ML (monolayer) with the irradiation of hydrogen plasma while it is started after 1.9 ML without hydrogen gas and hydrogen plasma through the observation of RHEED patterns. Density and size of the QDs formed at $T_{sub}=370^{\circ}C$ are $1.9{\times}10^{11}cm^{-2}$ and 17.7 nm without hydrogen plasma, and $1.3{\times}10^{11}cm^{-2}$ and 19.4 nm with hydrogen plasma, respectively. It is also observed from the PL(photoluminescence) measurement on InAs-QDs that red shift in PL peak energy and broadening in FWHM (full width at half maximum)of PL peak caused by the effects of hydrogen plasma on the increment of size and its distribution. These effects of hydrogen plasma are considered as a act of atomic hydrogen which enhances the layer-growth of InAs on GaAs resulted from the relief of misfit strain between GaAs substrate and InAs.

• Journal of the Korea Computer Industry Society
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• v.8 no.2
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• pp.97-102
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• 2007

[ $CO_2$ ] laser sees that is most suitable to get this effect through minimum formation damage and advantage that is root enemy of effect that happen in minimum cellular tissue depth of 0.1mm is stable living body organization or internal organs institution. Formation damage by ten can be related in formation's kind or energy density, length of evaporation time. If shorten evaporation time, surroundings cellular thermal damage 200 - because happen within 400um laser beam in rain focus sacred ground surroundings cellular tissue without vitiation me by evaporation Poe of very small floor as is clean steam can . Application is possible to vulva cuticle cousins by a paternal aunt quantity, uterine cancer, cuticle tumor by laser system that $CO_2$ laser gets into standard in obstetrics and gynecology application. Because effect that super pulse output is ten enemies of laser if uniformity one pulse durations are short almost is decreased, most of all pulse module special quality of Pulse style $CO_2$ laser for obstetrics and gynecology mode stabilization by weight very, in this research to get into short pulse duration and higher frequency density, do switching by high frequency in DC-DC Converter output DC's ripple high frequency to be changed, high frequency done current ripple amount of condenser for output filter greatly reduce can . Ripple of output approximately to Zero realization applying possible inductor realization through a special quality experiment do.

• Nuclear Engineering and Technology
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• v.2 no.3
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• pp.149-161
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• 1970

This paper describes a detailed investigational performance on the gamma radiation shield effect of heavy concretes that were manufactured by the use of mineral ores produced domestically and which may be possibly applied for the biological shield design. Ten different kinds of mineral ores were collected for use as the aggregates, physical test and chemical analysis for them were carried out to select the aggregate with a better property. Through the experimental investigation on the shielding effect of various concretes with different combination of concrete components such as water-cement and fine-coarse aggregate ratios, it was possible to derive some criteria for the best condition being capable of obtaining the concretes with high density and good uniformity. Data on the shielding-effectiveness of the different concretes were obtained by performing collimated beam experiment using 60Co gamma-ray. Analyzing the shielding-efficiency, shielding-concrete specific gravity and biological shield cost, the optimum condition of yielding the best economic shielding design, with low cost and good spatial distribution to some extent was determined.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.98-98
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• 1999

Highly transparent and conducting tin-doped indium oxide (ITO) films were deposited on polycarbonate substrate by ion-assited deposition. Low substrate temperature (<10$0^{\circ}C$) was maintained during deposition to prevent the polycarbonate substrate from be deformed. The influence of ion beam energy, ion current density, and tin doping, on the structural, electrical and optical properties of deposited films was investigated. Indium oxide and tin-doped indium oxide (9 wt% SnO2) sources were evaporated with assisting ionized oxygen in high vacuum chamber at a pressure of 2$\times$10-5 torr and deposition temperature was varied from room temperature to 10$0^{\circ}C$. Oxygen gas was ionized and accelerated by cold hallow-cathode type ion gun at oxygen flow rate of 1 sccm(ml/min). Ion bea potential and ion current of oxygen ions was changed from 0 to 700 V and from 0.54 to 1.62 $\mu$A. The change of microstructure of deposited films was examined by XRD and SEM. The electrical resistivity and optical transmittance were measured by four-point porbe and conventional spectrophotometer. From the results of spectrophotometer, both the refractive index and the extinction coefficient were derived.

• 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.