• Current Optics and Photonics
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• v.4 no.4
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• pp.380-390
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• 2020

In this study, the traditional electron-blocking layer (EBL) in (In,Ga)N/GaN light-emitting diodes is replaced by a circular EBL that is the same size as the n-pad. The three-dimensional (3D) nonlinear Poisson, drift-diffusion, and continuity equations are adopted to simulate current transport in the LED and its characteristics. The results indicate that the local carrier-density distribution obtained for the circular EBL design is more uniform than that for the traditional EBL design. This improves the uniformity of local radiative recombination and local internal quantum efficiency (IQE) at high injection levels, which leads to a higher lumped IQE and lower efficiency droop. With the circular EBL, the lumped IQE is higher in the outer active region and lower in the active region under the n-pad. Since most emissions from the active region under the n-pad are absorbed by the n-pad, obviously, an LED with a circular EBL will have a higher external quantum efficiency (EQE). The results also show that this LED works at lower applied voltages.

• Corrosion Science and Technology
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• v.13 no.5
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• pp.195-203
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• 2014

Modern industry has a wide variety of application areas such as ocean industry, construction and automobile industry. With the current circumstances, the need for anti-corrosion technology that can be used on materials to withstand in harsh environments, is increasing. In this study, we have sought to develop a metal coating technology with zinc and aluminum powders as a potential anti-corrosion material. To make a coating on metal products, a thermal diffusion coating method was used under the conditions of $350^{\circ}C$ for 30 minutes. Optical microscope, Field emission scanning electron microscope (FE-SEM&EDX) and X-ray diffraction analysis were used to analyze a coating layer. As a result, we have confirmed that the generated amount of rust on metal parts coated with thermal diffusion coating method decreased dramatically compared with non-coated metal parts. Furthermore, the anti-corrosion performance was evaluated according to the different ratio of zinc and aluminum. Finally, we confirmed the possibility of application and commercialization of our coating technique on metal parts used in harsh industrial based on the results of these performance.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.140-145
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• 2011

The aim of the present study is to derive optimized post heat treatment temperatures to get a proper formability for Ti/STS409L/Ti clad materials. These clad materials were fabricated by cold rolling followed by a post heat treatment process for 10 minutes at temperatures ranging from $500^{\circ}C$ to $850^{\circ}C$. The microstructure of the interface was observed using a Scanning Electron Microscope(SEM) and an Energy Dispersive X-ray Analyser(EDX) in order to investigate the effects of post heat treatment on the bonding properties of the Ti/STS409L/Ti clad materials. Diffusion bonding was observed at the interfaces with a diffusion layer thickness increasing with the post heat treatment temperature. The diffusion layer was composed of a type of(${\varepsilon}+{\zeta}$) intermetallic compound containing additional elements, namely, Fe, Ti and Ni. The micro Knoop hardness of the Ti/STS409L interfaces was found to increase with heat treatment up to $800^{\circ}C$ and then decrease for temperatures rising up to $850^{\circ}C$. The tensile strength was shown to decrease for heat treatment temperature increasing to $750^{\circ}C$ and then increase rapidly for temperature rising up to $850^{\circ}C$. A post heat treatment temperature range of $700{\sim}750^{\circ}C$ was found to optimize the formability of Ti/STS409L/Ti clad materials.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.11
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• pp.45-55
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• 1999

The small signal analyzer for the stationary drift-diffusion equation is developed. The slotboom variables of the potential, electron and hole concentrations for the response of applied small signal are defined and the stationary drift-diffusion equation is linearlized on DC operation point by $S^3A$ method. Frontal solver, which is used to solve the global matrix, progresses the accuracy of the solution in high frequency and minimizes the requirement of the memory. The simulations are executed on the structure of 3 dimensional N'P junction diode and 2 dimensional n-MOSFET to verify the proposed algorithm. The average relative errors of the conductance and the capacitance compared with MEDICI are about 26% and 0.67 for N'P junction diode and 7.75% and 2.24% for n-MOSFET. The simulation by the proposed algorithm can analyze the stationary drift-diffusion equation for applied small signal in high frequency region about 100GHz.

• Journal of the Korean Magnetics Society
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• v.24 no.6
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• pp.186-190
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• 2014

To establish the coating conditions for $^{57}Co$, non-radioactive Co ions are dissolved in an acid solution and electroplated on to a copper plate. Then, the thermal diffusion of electroplated Co into a copper matrix was studied to apply a $^{57}Co$ $M{\ddot{o}}ssbauer$ source. Nanocrystalline Co particles were coated on a Cu substrate using DC electro-deposition at a pH of 1.89 to 5 and $20{\sim}30mA/cm^2$. The average grain size was up to 54 nm as the pH increased to 5. The second phase of Co-oxide was formatted as the pH was increased above 4. The diffusion degree was evaluated by mapping using scanning electron microscopy (SEM). The influence of different annealing conditions was investigated. The diffusion depth of Co depends on the annealing temperature and time. The results obtained confirm that the deposited Co diffused almost completely into a copper matrix without substantial loss at an annealing temperature of $900^{\circ}C$ for 2 hours.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.549-556
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• 2011

This study aimed to evaluate the performance of diffusion barriers in order to prevent fuel-cladding chemical interaction (FCCI) between the metallic fuels and the cladding materials, a potential hazard for nuclear fuel in sodium-cooled fast reactors. In order to prevent FCCI, Zr or V metal is deposited on the ferritic-martensitic stainless steel surface by physical vapor deposition with a thickness up to $5{\mu}m$. The diffusion couple tests using uranium alloy (U-10Zr) and a rare earth metal such as Ce-La alloy and Nd were performed at temperatures between 660~800$^{\circ}C$. Microstructural analysis using SEM was carried out over the coupled specimen. The results show that significant interdiffusion and an associated eutectic reaction ocurred in the specimen without a diffusion barrier. However, with the exception of the local dissolution of the Zr layer in the Ce-La alloy, the specimens deposited with Zr and V exhibited superior eutectic resistance to the uranium alloy and rare earth metal.

• Journal of IKEEE
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• v.11 no.4
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• pp.272-278
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• 2007

In this paper, we report on the 2D (two-dimensional) simulation result of the DC (direct current) electrical and thermal characteristics of AlGaN/GaN HEMTs (high electron mobility transistors) grown on Si substrate, in comparison with those grown on sapphire and SiC (silicon carbide) substrate, respectively. In general, the electrical properties of HEMT are affected by electron mobility and thermal conductivity, which depend on substrate material. For this reason, the substrates of GaN-based HEMT have been widely studied today. The simulation results are compared and studied by applying general Drift-Diffusion and thermal model altering temperature as 300, 400 and 500 K, respectively. With setting T=300 K and $V_{GS}$=1 V, the $I_{D,max}$ (drain saturation current) were 189 mA/mm for sapphire, 293 mA/mm for SiC, and 258 mA/mm for Si, respectively. In addition, $G_{m,max}$ (maximum transfer conductance) of sapphire, SiC, Si was 38, 50, 31 mS/mm, respectively, at T=500 K.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.218-218
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• 2012

Nanocrystalline $SnO_2$ colloids are synthesized by hydrolysis of $SnCl_4{\cdot}5H_2O$ in aqueous ammonia solution. The synthesized $SnO_2$ nanoparticles with ca. 15 nm in diameter are coated on a fluorinedoped thin oxide (FTO) conductive substrate and heated at $550^{\circ}C$. The annealed $SnO_2$ film is treated with aqueous $TiCl_4$ solution, which is sensitzied with MK-2 dye (2-cyano-3-[5'''-(9-ethyl- 9H-carbazol-3-yl)-3',3'',3''',4-tetra-n-hexyl-[2,2',5',2'',5'',2''']-quater thiophen-5-yl]). Compared to bare $SnO_2$ film, the conversion efficiency is significantly improved from 0.22% to 3.13% after surface treatment of $SnO_2$ with $TiCl_4$, which is mainly due to the large increases in both photocurrent density from 1.33 to $9.46mA/cm^2$ and voltage from 315 to 634 mV. It is noted that little change in the amount of the adsorbed dye is detected from 1.21 for the bare $SnO_2$ to $1.28{\mu}mol/cm^2$ for the $TiCl_{4-}$ treated $SnO_2$. This indicates that the photocurrent density increased by more than 6 times is not closely related to the dye loading concentration. From the photocurrent and voltage transient spectroscopic studies, electron life time increases by about 13 order of magnitude, whereas electron diffusion coefficient decreases by about 3.6 times after $TiCl_4$ treatment. Slow electron diffusion rate offers sufficient time for regeneration kinetics. As a result, charge collection efficiency of about 40% before $TiCl_4$ treatment is improved to 95% after $TiCl_4$ treatment. The large increase in voltage is due to the significant increase in electron life time, associated with upward shift of fermi energy.

• Journal of Environmental Health Sciences
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• v.44 no.3
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• pp.293-300
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• 2018

Objectives: We investigated the antioxidant and antibacterial activities of Pinus densiflora ethanol extracts (PDEE) treated with trypsine as a protease. Methods: Various antioxidant activities were evaluated by measuring total contents of polyphenol and flavonoid, DPPH electron-donating ability and $ABTS^+$ radical scavenging activity of test material. To compare the antibacterial activity, paper disc diffusion assay was performed against two resident bacteria in human skin (Staphylococcus aureus and Staphylococcus epidermidis). Results: As for the total contents of polyphenol and flavonoid, and the electron-donating ability and ABTS+ radical scavenging activity, both PDEE and trypsin-treated Pinus densiflora ethanol extract (T-PDEE) showed high antioxidant activity in dose-dependent manner. And the T-PDEE showed slightly higher activity than PDEE, which indicated protease treatment seemed to affect in antioxidant activity. In the result of paper disc diffusion assay, antibacterial activity was confirmed in all two types of skin resident bacteria. T-PDEE was more active than PDEE and it seems that treatment of protease may increase the antibacterial activity of PDEE. Conclusion: All of these results, we confirmed that treatment of protease to PDEE can increase the antioxidant and antibacterial activities, and it can be explained thought that this would be applicable as a cosmeceutical material in the future.

• Journal of the Korean Chemical Society
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• v.31 no.3
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• pp.250-257
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• 1987

The electrical conductances for the thorium (IV) complexes with crown ethers have been measured in DMSO, and water solvents, and the oxidation-reduction reaction mechanisms, electron number and diffusion coefficients in the reversible reduction process have been examined by polarography and cyclic voltammography. The dissociation mole ratio of $Th^{4+}$ and nitrate ion are 1:1 and in aprotic solvent, and 1:4 in protic solvent like as water. The limiting molar conductances of all complexes in aprotic solvent have been found to be in the range of $92.2{\times}159$ $ohm^{-1}cm^2mol^{-1}$. In aprotic solvent, DMSO, the reduction of each complex is reversible by one electron reduction of one step, and the range of diffusion coefficients is obserbed to be $5.83\;10^{-6}{\sim}6.90{\times}10^{-6}$. The complexes which have reduction step were hydrolyzed above at 1.8volt with reference saturated calomel electrode, generating the hydrogen gas. The reaction mechanisms of thorium (IV)-crown ether complexes appear as follows. ${Th_m(IV)L_n(H_2O)_x(NO_3)_{4y}}_=^{DMSO} {\overline{{Th_m(IV)L_n(H_2O)_x(NO_3)_{4y-1}}}^+ + NO_3-$