• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.9
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• pp.397-402
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• 2005

The ($Sr_{1-x}Ca_x)TiO_3(SCT)$ thin films are deposited on Pt-coated electrode (Pt/TiN/SiO$_{2}$Si) using RF sputtering method with substitutional contents of Ca. The optimum conditions of RF power and Ar/O$_{2}$ ratio were 140(W) and 80/20, respectively. Deposition rate of SCT thin film was about $18.75{\AA}$/min. The dielectric constant was increased with increasing the substitutional contents of Ca, while it was decreased if the substitutional contents of Ca exceeded over $15[mol\%]$. The capacitance characteristics had a stable value within $\pm4[\%]$ in temperature ranges of $-80\~+90[^{\circ}C]$. All SCT thin films used in this study show the phenomena of dielectric relaxation with the increase of frequency, and the relaxation frequency is observed above 200[kHz].

• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.31-34
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• 1999

In the present study, we fabricated stoichiometric $(Ba_{1-x}Sr_x)TiO_3$ thin films at various substrate temperature and contents using of magnetron sputtering method on optimized Pt-based electrodes (Pt/TiN/$SiO_2$/Si). The substate temperature deposited at 200[ $^{\circ}C$], 400[$^{\circ}C$] and 600[$^{\circ}C$] and crystalline BST thin films show above 400[$^{\circ}C$]. Also, the composition of $(Ba_{1-x}Sr_x)TiO_3$ thin films deposited on Si wafer substrate at 400[$^{\circ}C$] were closed to stoichiometry($1.015{\sim}1.093$ in A/B ratio), but compositional deviation from a stoichiometry is larger as $SrCO_3$ is added. The drastic decrease of dielectric constant and increase of dielectric loss in $(Ba_{1-x}Sr_x)TiO_3$thin films is observed above 100[kHz]. V-I characteristics of $(Ba_{1-x}Sr_x)TiO_3$ thin films show the decrease of leakage current with the increase of $SrCO_3$ contents.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.2
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• pp.115-118
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• 2017

Highly photosensitive and wide bandgap amorphous silicon oxide (a-$SiO_x$:H) films were developed at low temperature ranges ($100{\sim}150^{\circ}C$) with employing plasma-enhanced chemical vapor deposition by optimizing $H_2/SiH_4$ gas ratio and $CO_2$ flow. Photosensitivity more than $10^5$ and wide bandgap (1.81~1.85 eV) properties were used for making the a-$SiO_x$:H thin film solar cells, which exhibited a high open circuit voltage of 0.987 V at the substrate temperature of $100^{\circ}C$. In addition, a power conversion efficiency of 6.87% for the cell could be improved up to 7.77% by employing a new n-type nc-$SiO_x$:H/ZnO:Al/Ag triple back-reflector that offers better short circuit currents in the thin film photovoltaic devices.

• New & Renewable Energy
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• v.4 no.4
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• pp.80-87
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• 2008

Steam reforming of LPG was investigated over spc-Ni/MgAl catalyst in a temperature range of $600{\sim}850^{\circ}C$, feed molar ratio of $H_2O/C=1.0{\sim}3.0$, space velocity of $10,000{\sim}90,000h^{-1}$ and at atmospheric pressure. spc-Ni/MgAl catalyst was prepared by a co-precipitation method, whereas Ni/MgO and $Ni/Al_2O_3$ catalysts were prepared by an incipient wetness method. The characteristics of catalysts were analyzed by N2 Physisorption, CO chemisorption, XRD, TOF-SIMS, SEM and TEM techniques. The Ni/MgO and $Ni/Al_2O_3$ catalysts were deactivated by the formation of carbon. However, the spc-Ni/MgAl catalyst showed higher conversion and $H_2$ selectivity than the other catalysts, even though carbon was formed on the surface of the catalyst during the reaction under the tested reaction conditions.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1397-1400
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• 2013

The influence of electron beam irradiation on photocatalytic activity of $TiO_2$ thin films was investigated. $TiO_2$ thin films were prepared by anodization of Ti foil, and they were then subjected to an 1 MeV electron beam. Changes in physical properties and photocatalytic activity of $TiO_2$ before and after e-beam irradiation were investigated. The crystallinity of the synthesized materials was investigated by X-ray diffraction, and the oxidation states of both titanium and oxygen were determined by X-ray photoelectron spectroscopy (XPS). The density of donor ($N_d$) and flat band potential ($E_{fb}$) were investigated by Mott-Schottky analysis, and photocurrent was measured under a 1kW Xenon lamp illumination. After e-beam irradiation, significant change of Ti oxidation state was observed. $Ti^{3+}/Ti^{4+}$ ratio increased mainly due to the surface reduction by electron, and photocurrent was observed to increase with e-beam irradiation.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.276-276
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• 2007

As a candidate for lead-free piezoelectric materials, dense $(Na_xK_{0.94-x}Li_{0.06})NbO_3$ ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding 1 mol% $Li_2O$ as a sintering aid. The electrical properties of $(Na_xK_{0.94-x}Li_{0.06})NbO_3$ ceramics were investigated as a function of Na/K ratio. When the sample sintered at $950^{\circ}C$ for 4 h with the compositions of morphotropic phase boundary, 0.47 < x < 0.51, electro-mechanical coupling factor ($k_p$) and piezoelectric coefficient ($d_{33}$) were found to reach the highest values of 0.42 and 190 pC/N, respectively. These excellent piezoelectric and electro-mechanical properties indicate that this system is potentially good candidate for lead-free material for a wide range of electro-mechanical transducer applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.1
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• pp.29-33
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• 2018

Using a vanadium dioxide ($VO_2$) source, highly pure and amorphous vanadium oxide (VO) thin films were deposited using an e-beam evaporator at room temperature and high vacuum (<$10^{-7}$ Torr). Then, by controlling the post-annealing conditions such as $N_2:O_2$ pressure ratio and annealing time, we could easily synthesize a homogeneous $VO_2$ thin film and also mixed-phase VO thin films, including $VO_2$, $V_2O_5$, $V_3O_7$, $V_5O_9$, and $V_6O_{13}$. The crystallinity and phase of these were characterized by X-ray diffraction, and the surface morphology by FE-SEM. Moreover, the electrical properties and ethanol sensing measurements of the VO thin films were analyzed as a function of temperature. In general, mixed-phases as a self-doping effect have enhanced electrical properties, with a high carrier density and an enhanced response to ethanol. In summary, we developed an easy, scalable, and reproducible fabrication process for VO thin films that is a promising candidate for many potential electrical and optical applications.

• Journal of the Korean institute of surface engineering
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• v.57 no.4
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• pp.285-295
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• 2024

PVDC-resin transforms into porous carbon through the removal of heteroatoms during heat treatment. When PVDC-resin mixed with chemical agent undergoes heat treatment, it transforms into porous carbon with a significant surface area. In this study, we aim to produce porous carbon using PVDC-resin as a precursor by mixing it with an inexpensive CuO agent in various ratios (1:1, 1:2) and varying the process temperatures (750℃, 950℃). To utilize the developed porous carbon as electrode for supercapacitors, this study explored the formation of micropores and mesopores during the activation process. The porous characteristics and specific surface area of the synthesized porous carbon were estimated using N₂ isotherm. The specific capacitance and rate capability required for supercapacitor electrodes were evaluated through cyclic voltammetry. Experimental results demonstrated that when the precursor and agent were mixed in a 1:2 ratio, a high surface areal carbon with numerous micropores and mesopores was obtained. When the activation was performed at 950℃, no impurities remained from the agent, resulting in high rate performance. The porous carbon synthesized using PVDC-resin and CuO demonstrated high specific surface area and excellent rate capability, indicating its potential as an electrode material for supercapacitors.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.51 no.4
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• pp.282-286
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• 2006

The effect of biofertilizer (compound of microbial inoculants or groups of micro-organisms) on growth and yield of rice was investigated. The experiment was carried out in a randomized complete block design with 3 replications and 7 treatments namely: $RF=N-P_2O_{5-}K_2O$ (11-5.5-4.8 kg $10a^{-1}$); half of the recommended fertilizer rate, $HRF=N-P_2O_5-K_2O$ (5.5-2.75-2.4 kg $10a^{-1}$); HRF+Bio 250=HRF combined with 250 kg biofertilizer $10a^{-1}$; HRF+Bio 500=HRF combined with 500 kg biofertilizer $10a^{-1}$; Bio 250=250 kg biofertilizer $10a^{-1}$; Bio 500=500 kg biofertilizer $10a^{-1}$; and NF = No Fertilizer. Results showed that the recorded values of plant height, tiller number and chlorophyll content at 40 to 60 days after transplanting (DAT) in HRF+Bio 500 were significantly higher than those recorded in the RF treatment. Similar observations between these two treatments were only recorded from 60 DAT onwards. Yield components were also superior in HRF+Bio 500 treatment and comparable to that of RF. The highest grain yield obtained in HRF+Bio 500 treatment (785.8 kg $10a^{-1}$) was statistically similar to that of RF (739.8 kg $10a^{-1}$) but significantly higher than that of NF (506.7 kg $10a^{-1}$). Finally, head grain recovery (90.9) was low while chalkiness (0.03) was high at HRF+Bio 500 treatment as compared with RF, which were (96.1) and (0.3), respectively. Results showed that combined treatment of HRF and 500 kg biofertilizer $10a^{-1}$ has similar effects on the growth and yield of rice with that of RF.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1555-1562
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• 2015

Metal oxide semiconductors have been applied in several areas, such as solar cells, sensor, optical elements and displays, due to the high surface area, unique electrical and optical characteristics. Zinc oxide among the metal oxide has excellent physicochemical properties. Zinc oxide is a n-type semiconductor with a wide direct transition band gap of 3.37 eV at room temperature and large exciton binding energy of 60 meV. Cation-doped zinc oxide studies were conducted to complement the electrical and optical characteristics. In this paper, Al-doped ZnO was synthesized by hydrothermal synthesis using microwaves. ZnO was synthesized by adjusting the precursor ratio and using different dopants. The optimal ZnO synthesis conditions for crystal shape and optical properties were determined. The optical properties of aluminum doped zinc oxide were then examined by SEM, XRD, PL, UV-vis absorbance spectrum, and EDS.