• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.861-867
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• 2019

$Li_4Ti_5O_{12}$ is a promising next-generation anode material for lithium-ion batteries due to excellent cycle life, low irreversible capacity, and little volume expansion during charge-discharge process. However, it has poor charge capacity at high current density due to its low electrical conductivity. To improve this weakness, porous $Li_4Ti_5O_{12}$ was synthesized by sol-gel method with P123 as chelating agent. The physical characteristics of as-prepared sample was investigated by XRD, SEM, and BET analysis, and electrochemical properties were characterized by cycle performance test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS). $Li_4Ti_5O_{12}$ synthesized by 0.01mol ratio of P123/Ti showed most unified particle size, high specific surface area, and relatively high porosity. EIS analysis showed that depressed semicircle size was remarkably reduced, which suggested resistance value in electrode was decreased. Capacity in rate performance showed 178 mAh/g at 0.2C, 170 mAh/g at 0.5C, 110 mA/h at 5C, and 90 mAh/g at 10C. Capacity retention also showed 99% after rate performance.

• Membrane Journal
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• v.29 no.3
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• pp.173-182
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• 2019

Much research has been made for finding new and eco-friendly alternative sources of energy to solve the problems related with the pollution caused by emissions of greenhouse gases such as carbon dioxide as the use of fossil fuels increases worldwide. Among them, fuel cells draws particular interests as an eco-friendly energy generator because only water is obtained as a by-product. Anion exchange membrane-based alkaline fuel cell (AEMFC) that uses anion exchange membrane as an electrolyte is of increased interest recently because of its advantages in using low-cost metal catalyst unlike the PEMFC (potton exchange membrane fuel cell) due to the high-catalyst activity in alkaline conditions. The main properties required as an anion exchange membrane are high hydroxide conductivity and chemical stability at high pH. Recently we reported a chemically crosslinked poly(2-dimethyl-1,4-phenylene oxide) (PPO) by reacting PPO with N,N,N',N'-tetramethyl-1,6-hexanediamine as novel anion exchange membranes. In the current work, we further developed the same crosslinked polymer but having enhanced physicochemical properties, including higher conductivity, increased mechanical and dimensional stabilities by using the PPO with a higher molecular weight and also by increasing the crosslinking density. The obtained polymer membrane also showed a good cell performance.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.44 no.9
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• pp.25-33
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• 2007

In this paper, the high isolation and wideband 94 GHz MIMIC(Millimeter-wave Monolithic Integrated Circuit) single balanced cascode mixer was designed and fabricated. Also, we designed and fabricated a 3 dB tandem coupler which has a high isolation and wideband characteristic. The single balanced resistive mixer which does not require an external IF balun was designed using the 0.1 ${\mu}m$ InGaAs/InAlAs/GaAs metamorphic HEMT(High Electron Mobility Transistor). The DC characteristics of MHEMT's are 665 mA/mm of drain current density, 691 mS/mm of maximum transconductance. The current gain cut-off frequency($f_T$) is 189 GHz and the maximum oscillation frequency($f_{max}$) is 334 GHz. A 94 GHz single balanced cascode mixer was fabricated using our 0.1 ${\mu}m$ MHEMT MIMIC process. From the measurements, the fabricated couplers showed wideband characteristics. The conversion loss of single balanced cascode mixer was 9.8 dB at an LO power of 10.9 dBm. The LO to RF isolation of single balanced cascode mixer was 29.5 dB at 94 GHz. We obtained in this study a higher LO-RF isolation compared to some other single balanced mixers.

• Current Photovoltaic Research
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• v.7 no.4
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• pp.97-102
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• 2019

Bifacial and semitransparent hydrogenated amorphous silicon (a-Si:H) thin-film solar cells in p-i-n configuration were prepared with front and rear transparent conducting oxide (TCO) electrodes using plasma-enhanced chemical vapor deposition method. Fluorine-doped tin oxide and tin-doped indium oxide films were used as front and rear TCO contacts, respectively. Film thickness of intrinsic a-Si:H absorber layers were controlled from 150 nm to 450 nm by changing deposition time. The dependence of performance characteristics of solar cells on the front and rear illumination direction were investigated. For front illumination, gradual increase in the short-circuit current density (J_SC) from 10.59 mA/㎠ to 14.19 mA/㎠ was obtained, whereas slight decreases from 0.83 V to 0.81 V for the open-circuit voltage (V_OC) and from 68.43% to 65.75% for fill factor (FF) were observed. The average optical transmittance in the wavelength region of 380 ~ 780 nm of the solar cells decreased gradually from 22.76% to 15.67% as the absorber thickness was changed from 150 nm to 450 nm. In case of the solar cells under rear illumination condition, the J_SC increased from 10.81 to 12.64 mA/㎠ and the FF deceased from 66.63% to 61.85%, while the V_OC values were maintained at 0.80 V with increasing the absorber thickness from 150 nm to 450 nm. By optimizing the deposition parameters, a high-quality bifacial and semitransparent a-Si:H solar cell with 350 nm-thick i-a-Si:H absorber layer exhibited the conversion efficiencies of 7.69% for front illumination and 6.40% for rear illumination, and average visible optical transmittance of 17.20%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.441-441
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• 2009

Dye-sensitized solar cells (DSSCs) have been widely investigated as a next-generation solar cell because of their simple fabrication process and low coats. The cells use a porous nanocrystalline TiO2 matrix coated with a sensitizer dye that acts as the light-harvesting element. The photo-exited dye injects electrons into the $TiO_2$ particles, and the oxide dye reacts with I- in the electrolyte in regenerative cycle that is completed by the reduction of $I_3^-$ at a platinum-coated counter electrode. Since $TiO_2$ porous film plays a key role in the enhancement of photoelectric conversion efficiency of DSSC, many scientists focus their researches on it. Especially, a high light-to-electricity conversion efficiency results from particle size and crystallographic phase, film porosity, surface structure, charge and surface area to volume ratio of porous $TiO_2$ electrodes, on which the dye can be sufficiently adsorbed. Effective treatment of the photoanode is important to improve DSSC performance. In this paper, to obtain properties of surface and dispersion as nitric acid treated $TiO_2$ photoelectrode was investigate. The photovoltaic characteristics of DSSCs based the electrode fabricated by nitric acid pre-treatment $TiO_2$ materials gave better performances on both of short circuit current density and open circuit voltage. We compare dispersion of $TiO_2$ nanoparticles before and after nitric acid treatment and measured Ti oxidized state from XPS. Low charge transfer resistance was obtained in nitric acid treated sample than that of untreated sample. The dye-sensitized solar cell based on the nitric acid treatment had open-circuit voltage of 0.71 V, a short-circuit current of 15.2 mAcm-2 and an energy conversion efficiency of 6.6 % under light intensity of $100\;mWcm^{-2}$. About 14 % increases in efficiency obtained when the $TiO_2$ electrode was treated by nitric acid.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.5 s.335
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• pp.61-68
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• 2005

In this paper, low conversion loss 94 GHz MIMIC resistive mixer was designed and fabricated. The $0.1{\mu}m$ InGaAs/InAlAs/GaAs Metamorphic HEMT, which is applicable to MIMIC's, was fabricated. The DC characteristics of MHEMT are 665 mA/mm of drain current density, 691 mS/mm of maximum transconductance. The current gain cut-off frequency(fT) is 189 GHz and the maximum oscillation frequency(fmax) is 334 GHz. A 94 GHz resistive mixer was fabricated using $0.1{\mu}m$ MHEMT MIMIC process. From the measurement, the conversion loss of the 94 GHz resistive mixer was 8.2 dB at an LO power of 10 dBm. P1 dB(1 dB compression point) of input and output were 9 dBm and 0 dBm, respectively. LO-RF isolations of resistive mixer was obtained 15.6 dB at 94.03 GHz. We obtained in this study a lower conversion loss compared to some other resistive mixers in W-band frequencies.

• Korean Journal of Poultry Science
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• v.37 no.3
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• pp.207-213
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• 2010

The current study was conducted to estimate the effect of dietary pyroligneous acid (PA) on performance, noxious gas emission in excreta, blood parameter and fatty acid composition of breast meat in Korean native chicken. A total of 240 one-day-old chicks were allocated to three treatments (PA; 0, 0.1, 0.2%) with five replicate of 16 each per treatment for 10 weeks. Although there was no effect on the performance, ammonia gas concentration was significantly decreased in the PA treatments compared to the control (p<0.05). Birds fed PA had higher serum total protein and high density lipoprotein-cholesterol (HDL-cholesterol) concentration but lower triglyceride content in the PA 0.2% treatment than control (p<0.05). In fatty acids composition of breast meat, myristic and stearic acid were significantly decreased, whereas oleic and linolenic acid were significantly increased in the group fed PA compared to those of the control group (p<0.05). The result of the current study indicates that dietary PA may reduce the noxious gas emission and improve lipid levels as well as increase of monounsaturated fatty acids composition of breast meat in Korean native chickens.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.4
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• pp.405-418
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• 2019

Based on spent fuels characteristics from domestic nuclear power plants and a disposal scenario from the current basic plan for high-level radioactive waste management, an improved disposal system has been proposed that enhances disposal efficiency and economic effectiveness compared to the existing disposal system. For this purpose, two disposal canisters concepts were derived from the length of the spent fuel generated from the nuclear power plants. In the disposal scenario, the acceptable amount of decay heat for each disposal container was determined, taking into account the discharge and disposal times of spent fuels in accordance with the current basic plan. Based on the determined decay heat of the two types of disposal canisters and the associated disposal system, thermal stability analyses were performed to confirm their suitability to the proposed disposal system design requirement and disposal efficiency assessment. The results of this study confirm 20% reduction in the disposal area and 20% increase in disposal density for the proposed disposal system compared to the existing system. These results can be used to establish a spent fuel management policy and to design a viable commercial disposal system.

• Macromolecular Research
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• v.17 no.12
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• pp.963-968
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• 2009

Liquid crystal (LC; E7 and/or ML-0249)-embedded, poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-co-HFP)-based, polymer electrolytes were prepared for use in dye-sensitized solar cells (DSSCs). The electrolytes contained 1-methyl-3-propylimidazolium iodide (PMII), tetrabutylammonium iodide (TBAI), and iodine ($I_2$), which participate in the $I_3^-/I^-$ redox couple. The incorporation of photochemically stable PVdF-co-HFP in the DSSCs created a stable polymer electrolyte that resisted leakage and volatilization. DSSCs, with liquid crystal(LC)-embedded PVdF-co-HFP-based polymer electrolytes between the amphiphilic ruthenium dye N719 absorbed to the nanocrystalline $TiO_2$ photoanode and the Pt counter electrode, were fabricated. These DSSCs displayed enhanced redox couple reduction and reduced charge recombination in comparison to that fabricated from the conventional PVdF-co-HFP-based polymer electrolyte. The behavior of the polymer electrolyte was improved by the addition of optimized amounts of plasticizers, such as ethylene carbonate (EC) and propylene carbonate (PC). The significantly increased short-circuit current density ($J_{sc}$, $14.60\;mA/cm^2$) and open-circuit voltage ($V_{oc}$, 0.68 V) of these DSSCs led to a high power conversion efficiency (PCE) of 6.42% and a fill factor of 0.65 under a standard light intensity of $100\;mW/cm^2$ irradiation of AM 1.5 sunlight. A DSSC fabricated by using E7-embedded PVdF-co-HFP-based polymer electrolyte exhibited a maximum incident photon-to-current conversion efficiency (IPCE) of 50%.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.1
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• pp.18-24
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• 2002

n this paper, we have fabricated pseudomorphic high electron mobility transistors (PHEMT) with a 0.2 ${\mu}{\textrm}{m}$ wide-head T-shaped gate using electron beam lithography by a dose split method. To make the T-shape gate with gate length of 0.2 ${\mu}{\textrm}{m}$ and gate head size of 1.3 ${\mu}{\textrm}{m}$ we have used triple layer resist structure of PMMA/P(MMA-MAA)/PMMA. The DC characteristics of PHEMT, which has 0.2 ${\mu}{\textrm}{m}$ of gate length, 80 ${\mu}{\textrm}{m}$ of unit gate width and 4 gate fingers, are drain current density of 323 ㎃/mm and maximum transconductance 232 mS/mm at $V_{gs}$ = -1.2V and $V_{ds}$ = 3V. The RF characteristics of the same device are 2.91㏈ of S21 gain and 11.42㏈ of MAG at 40GHz. The current gain cut-off frequency is 63GHz and maximum oscillation frequency is 150GHz, respectively.ively.