• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.226-229
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• 2004

A stoichiometric mixture of evaporating materials for $CuAlSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuAlSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $680^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuAlSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.24{\times}10^{16}\;cm^{-3}$ and $295\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuAlSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;2.8382\;eV\;-\;(8.68{\times}10^{-4}\;eV/K)T^2/(T+155K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CuAlSe_2$ have been estimated to be 0.2026 eV and 0.2165 eV at 10K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}so$ definitely exists in the ${\Gamma}_5$ states of the valence band of the $CuAlSe_2$. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• Journal of Welding and Joining
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• v.32 no.5
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• pp.32-43
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• 2014

Welding and joining technology has become a core field. Therefore it is more widely applied to nonferrous metals, inorganic and polymeric materials. That is because the high performance, high function and diversification trend of materials used as industrial technology develops. In the laser welding process, STS 304 and SCP1-S were used as the base materials, the output density was fixed $7MW/cm^2$, the protective gas was argon(Ar) and the transfer rate was fixed 5 mm/sec. and it was progressed while the magnetic field is gradually increasing by 100 mT ranging 0 to 400 mT. The tensile test showed in average about 6 % tensile strength improvement in the case of the laser welding process using the magnetic fields. In the shielded metal arc welding process using SPHC only or the combination of SPHC+STS304 as base materials. The electric current was set at 80 Amperes and the protective gas used argon(Ar) the same as the laser welding process and the strength of magnetic fields. In the shielded metal arc welding process using the magnetic fields, the tensile tests showed about 5 % tensile strength improvement in the case of using SPHC only, 3 % tensile strength improvement in the case of using the combination of SPHC+ STS304. In comparing the results of numerical analysis to the results of experimental tests, it was revealed that the temperature, thermal stress distribution and the behavior of molten pool were similar to those of real tests. Consequently, it may be considered that the numerical assumption and the analytical model used in this study were reasonable.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.799-801
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• 1988

This paper was studied on the effects of Ca-La-Nb substitution and Zr/Ti ratio variation to Pb(Zr, Ti)$O_3$ system on structural, electrical, optical and sound level characteristics in order to develope the piezoelectric and electrooptic ceramic devices. Also the specimens were prepared by the two stage sintering technique. The molecular formular was X($CaO{\cdot}1/4La_{2}O_{3}{\cdot}1/4Nb_{2}O_{5}){\cdot}(1-X)Pb(Zr_{Y}Ti_{1-Y})O_{3}$(x=100X, y=100Y), and the variation of x was $6{\sim}12$, y was 60${\sim}$49 and second stage sintering time was 20${\sim}$40 hours. The experimental results obtained from this study are as follows : 1. The density was decreased, the grain size was increased according to increase of Ca-La-Nb substitution. 2. The crystal structure was rhombohedral in composition 6/60/40, and the crystal structure was tetragonal and cubic according to increase of Ca-La-Nb substitution. 3. The Ca substitution of PZT system enhanced the sintering property. The Pb site vacancy resulting from the substitution of La-Nb increased the dielectrical constant, the piezoelectric charge constant, the dielectric loss and decreased the coercive field. 4. The resistivity of PZT system which has the P type conduction mechanism increased according to substitution of La-Nb because of the substituent acting as donor. 5. The PZT ceramics varied from ferroelectric substance according to increase of Ca-La-Nb substituent. The coercive field and saturation remanent polarization decreased, and at last straight line according to increase of La-Nb substitution. 6. The amount of Ca-La-Nb substitution to improve the light transmittance of speciment was 10 mol%, the Zr/Ti ratio was 49/51, and the second stage sintering time was 40 hours. 7. According to Ca-La-Nb substitution, the specimens was to be transparent. The 7.5/51/49 specimen was suitable for transparent sound vibrator because it had 58% light transmittance (thick 0.2[mm], wave length 700[mm]) and 48% electromechanical coupling factor.

• Journal of Sensor Science and Technology
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• v.16 no.6
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• pp.419-427
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• 2007

Single crystal $ZnIn_{2}S_{4}$ layers were grown on a thoroughly etched semi-insulating GaAs(100) substrate at $450^{\circ}C$ with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of $ZnIn_{2}S_{4}$ at $610^{\circ}C$ prepared from horizontal electric furnace. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $ZnIn_{2}S_{4}$ thin films measured with Hall effect by van der Pauw method are $8.51{\times}10^{17}\;electron/cm^{-3}$, $291{\;}cm^{2}/v-s$ at 293 K, respectively. The photocurrent and the absorption spectra of $ZnIn_{2}S_{4}$/SI(Semi-Insulated) GaAs(100) are measured ranging from 293 K to 10 K. The temperature dependence of the energy band gap of the $ZnIn_{2}S_{4}$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)$=2.9514 eV. ($7.24{\times}10^{-4}\;eV/K$)$T^{2}$/(T+489 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy(${\Delta}cr$) and the spin-orbit splitting energy(${\Delta}so$) for the valence band of the $ZnIn_{2}S_{4}$ have been estimated to be 167.8 meV and 14.8 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1}$-, $B_{1}$-, and $C_{41}$-exciton peaks.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1511-1517
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• 2008

The magneto-rheological fluid expresses different cohesiveness according to the strength of the external electric current. The magneto-rheological fluid damper, which uses such characteristics of the fluid, generates shear force due to the fluid's cohesiveness. The core can be said to determine the magneto-rheological fluid damper's performance. This study uses the finite element analysis to compare the performance of different electromagnetic forces, which are affected by the shapes of the coil, and thus to find the optimum design for the core. In addition, as a step to construct a high-efficient damper, we suggest a type of damper that can control multiple coils and compares the performance of this damper and that of the standard damper by comparing the performance of their electro-magnetic fields.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.234-238
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• 2004

A stoichiometric mixture of evaporating materials for $CuInSe_2$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $CuInSe_2$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were $620^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CuInSe_2$ single crystal thin films measured with Hall effect by van der Pauw method are $9.62{\times}10^{l6}\;cm^{-3}$ and $296\;cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuInSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)\;=\;1.1851\;eV\;-\;(8.99{\times}10^{-4}\;eV/K)T^2/(T+153K)$. The crystal field and the spin-orbit splitting energies for the valence band of the $CuInSe_2$ have been estimated to be 0.0087 eV and 0.2329 eV at 10K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the ${\Delta}_{so}$ definitely exists in the $\Gamma_6$ states of the valence band of the $CuInSe_2$. The three photocurrent peaks observed at 10K are ascribed to the $A_1-$, $B_1-$, and $C_1$-exciton peaks for n = 1.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.1
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• pp.36-42
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• 2005

This study examined the feasibility of producing sulfuric acid and ammonia water from ammonium sulfate solution using two-compartment electrodialysis with a bipolar membrane (EDBM). Electrodialysis experiments were carried out with 20 wt% ammonium sulfate at different current densities and sulfuric acid concentrations in a concentrate compartment. The current efficiency increased with the current density from 25 to $100\;mA/cm^2$. Nevertheless, the efficiency was relatively low compared with that of general desalting electrodialysis, owing to the diffusion of sulfuric acid from the concentrate compartment to the diluate. The diffusion rate through the anion exchange membrane increased with the sulfuric acid concentration in the concentrate compartment, which decreased the current efficiency. Conversely, the electrical resistance decreased with increasing current density owing to the Joulian heat generated during water dissociation in the transition region of the bipolar membrane under a high electric field. From the experimental results, we concluded that operating at a higher current density is effective from the perspective of current efficiency and electrical resistance when producing sulfuric acid and ammonia water from ammonium sulfate using a two-compartment EDBM process. Further studies on the effects of increasing the sulfuric acid concentration on current efficiency are required to apply the EDBM process practically.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.7
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• pp.4665-4674
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• 2014

The aim of this study was to confirm the feasibility of the electro-coagulation process as a pre-treatment for the membrane separation of anaerobic digestion effluents to minimize membrane fouling. The reduction of membrane fouling was evaluated according to the number of electrodes (immersed surface area of electrodes), current density and contact time. In the case of the small surface area of electrodes, the increased electric field strength resulted in a soluble COD increase due to the destruction of the microbial flocs and/or cells, whereas large changes in the soluble COD were not observed in the case of the high surface area of electrodes. On the other hand, the T-P concentration decreased as a result of the precipitation of aluminum ions and phosphates. The membrane permeation flux increased and the fouling resistance (Rc+Rf) decreased with increasing electric current density. Although the particle size of the anaerobic digestion effluent increased slightly, it was not related directly to the reduced fouling phenomena. The main mechanism for the enhanced flux was attributed to the inorganic particulate produced during electrocoagulation, such as $AlPO_4$, which acted as a dynamic membrane deposited on the membrane surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.313-313
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• 2012

In recent years there have been many studies of InGaN/GaN based light emitting diodes (LEDs) in order to progress the performance of luminescence. Many previous literatures showed the performance of LEDs by changing the LED structures and substrates. However, the studies carried out by the researchers so far were very complicated and sometimes difficult to apply in practice. Therefore, we propose one simple method of changing the thickness and the numbers of multiple quantum wells (MQWs) in order to optimize their effects. In our research, we investigated electrical and optical properties by changing the well thickness and the number of quantum well (QW) pair in LED structures by growing the structure -inch Si (111) wafer. We defined the samples from LED_1 to LED_3 according to MQW structure. Samples LED_1, LED_2 and LED_3 consist of 5-pair InGaN/GaN (3.5 nm/ 4.5 nm), 5-pair InGaN/GaN (3 nm/4.5 nm) and 7-pair InGaN/GaN (3.5 nm/4.5 nm), respectively. We characterized electrical and optical properties by using electroluminescence (EL) measurement. Also, Efficiency droop was analyzed by calculating external quantum efficiency (EQE) with varying injection current. The EL spectra of three samples show different emission wavelength peaks, FWHM and the blueshift of wavelength caused by screening the internal electric field because of the effect of different MQW structure. The results of optical properties show that the LED_2 sample reduce the internal electric field in QW than LED_1 from EL spectra. the increase in the number of QW pairs reduces the strain and increase the In composition in MQW. And, the points of efficiency droop's peak show different trend from LED_1 to LED_3. It is related with the carrier density in active region. Thus, from the results of experiments, we are able to achieve high performance LEDs and a reduction of efficiency droop and emission wavelength blueshift by optimizing MQWs structure.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.3
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• pp.132-138
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• 2003

A stoichiometric mixture for $CdIn_2Te_4$ single crystal was prepared from horizontal electric furnace. The $CdIn_2Te_4$ single crystal was grown in the three-stage vertical electric furnace by using Bridgman method. The $CdIn_2Te_4$ single crystal was evaluated to be tetragonal by the power method. The (001) growth plane of oriented $CdIn_2Te_4$ single crystal was confirmed from back-reflection Laue patterns. The carrier density and mobility of $CdIn_2Te_4$ single crystal measured with Hall effect by van der Pauw method are $8.61\times 1016 \textrm {cm}^{-3}$ and 242 $\textrm{cm}^2$/V.s at 293 K, respectively. The temperature dependence of the energy band gap of the $CdIn_2Te_4$ single crystal obtained from the absorption spectra was well described by the Varshni's relation, $1.4750ev - (7.69\times10^{-3})\; ev/k)\;T^2$/(T + 2147k).The crystal field and the spin-orbit splitting energies for the valence band of the $CdIn_2Te_4$ single crystal have been estimated to be 0.2704 eV and 0.1465 eV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the $\Delta$so definitely exists in the $\Gamma_7$ states of the valence band of the $CdIn_2Te_4$ single crystal. The three photocurrent peaks observed at 10 K are ascribed to the $A_{1-} B_{1-}$ and Cl-exciton peaks for n = 1.