• Korean Journal of Materials Research
• /
• v.23 no.6
• /
• pp.334-338
• /
• 2013

In this study, $BaTiO_3$ thin films were grown by RF-magnetron sputtering, and the effects of the thin film thickness on the structural characteristics of $BaTiO_3$ thin films were systematically investigated. Instead of the oxide substrates generally used for the growth of $BaTiO_3$ thin films, p-Si substrates which are widely used in the current semiconductor processing, were used in this study in order to pursue high efficiency in device integration processing. For the crystallization of the grown thin films, annealing was carried out in air, and the annealing temperature was varied from $700^{\circ}C$. The changed thickness was within 200 nm~1200 nm. The XRD results showed that the best crystal quality was obtained for ample thicknesses 700 nm~1200 nm. The SEM analysis revealed that Si/$BaTiO_3$ are good quality interface characteristics within 300 nm when observed thickness. And surface roughness observed of $BaTiO_3$ thin films from AFM measurement are good quality surface characteristics within 300 nm. Depth-profiling analysis through GDS (glow discharge spectrometer) showed that the stoichiometric composition could be maintained. The results obtained in this study clearly revealed $BaTiO_3$ thin films grown on a p-Si substrate such as thin film thickness. The optimum thickness was 300 nm, the thin film was found to have the characteristics of thin film with good electrical properties.

• Membrane Journal
• /
• v.27 no.5
• /
• pp.441-448
• /
• 2017

In this study, the effects of membrane characteristics on the power generation performance in reverse electrodialysis (RED) have been investigated with pore-filled ion-exchange membranes (PFIEMs) prepared by employing a porous polyethylene substrate and the mixtures of three cross-linking agents. As a result, it was confirmed through the correlation analyses that the cross-linking degree and free volume of the PFIEMs were effectively controlled by mixing the cross-linking agents having different molecular sizes, influencing complexly the electrochemical characteristics of the membranes and the power generation performance in RED. In particular, the pore-filled cation-exchange membranes at the optimum cross-linking conditions exhibited the power generation performance superior to that of the commercial membranes and the pore-filled anion-exchange membranes also showed the excellent performance close to that of the commercial membrane.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.10
• /
• pp.1855-1861
• /
• 2017

In this paper, the gain enhancement of an SDPA using a director and two parasitic patches is studied. The modified balun is used to increase the bandwidth, whereas the director and two parasitic patches are appended to the SDPA to enhance the gain in the middle and high frequency bands. The effects of the distance between the director and parasitic patches on the antenna performance are analyzed, and the SDPA with a gain over 7 dBi at 1.54-2.99 GHz band is designed. The proposed SDPA is fabricated on an FR4 substrate with a dimension of $90mm(L){\times}135mm(W)$ in order to validate its performance. The fabricated antenna shows a frequency band of 1.56-3.10 GHz for a VSWR < 2, and it is confirmed by measurement that gain maintains over 7 dBi in the frequency range of 1.54-3.00 GHz.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2012.10a
• /
• pp.583-585
• /
• 2012

In this paper, we introduce a design method for a broadband planar quasi-Yagi antenna (QYA) for terrestrial digital television (DTV) receiving. The coplanar strip line feeding the driver dipole is connected to a microstrip line and is terminated by short circuit. By appending a wide strip-type director at a location close to the driver dipole, a broadband impedance matching and a gain characteristics in a high frequency region are obtained. The gain characteristics in a low frequency region are improved by adding a reflector formed by a truncated ground plane. To reduce the antenna size, the strip-type dipole and reflector are modified to half bowtie (V)-shaped elements. The effects of various parameters on the antenna characteristics are examined. An antenna, as an design example for the proposed antenna, is designed for the operation in the frequency band of 470-806 MHz for terrestrial DTV. The optimized antenna is fabricated on an FR4 substrate and tested experimentally to verify the results of this study.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2013.05a
• /
• pp.56-58
• /
• 2013

In this paper, a design method to obtain a band rejection characteristic in the 2.4-2.484 GHz WLAN band is studied for a series-fed dipole pair (SDP) antenna operating in the band of 1.7-2.7 GHz for mobile communication base station applications. The band rejection characteristic is achieved by inserting U-shaped slots on the coplanar strip line connecting the two dipole elements of the SDP antenna. The effects of the location and dimension of the slots on the band rejection characteristics are examined. The optimized SDP antenna with WLAN band rejection is fabricated on an FR4 substrate and the experimental results show that the antenna has a desired band rejection performance with a frequency band of 1.65-2.78 GHz (51.0%) for a VSWR < 2, and a rejection band of 2.39-2.54 GHz.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.4
• /
• pp.1982-1987
• /
• 2013

In this paper, a design method to obtain a band rejection characteristic in the 2.4-2.484 GHz WLAN band is studied for a series-fed dipole pair (SDP) antenna operating in the band of 1.7-2.7 GHz for mobile communication base station applications. The band rejection characteristic is achieved by inserting U-shaped slots on the coplanar strip line connecting the two dipole elements of the SDP antenna. The effects of the location and dimension of the slots on the rejection band characteristics are examined. The optimized SDP antenna with WLAN band rejection is fabricated on an FR4 substrate and the experimental results show that the antenna has a desired band rejection performance with a frequency band of 1.65-2.78 GHz (51.0%) for a VSWR < 2, and a rejection band of 2.39-2.54 GHz.

• Journal of Surface Science and Engineering
• /
• v.38 no.5
• /
• pp.188-192
• /
• 2005

Indium zinc oxide (IZO) thin films were deposited on glass substrate by dc magnetron sputtering. The effects of oxygen flow rate and deposition temperature on electrical and optical properties of the films were investigated. With addition of small amount of oxygen gas, the characteristic properties of amorphous IZO films were improved and the specific resistivity was about $4.8{\times}10^{-4}\Omega{\cdot}cm$. Change of structural properties according to the deposition temperature was observed with XRD, SEM, and AFM. Films deposited above $300^{\circ}C$ were found to be polycrystalline. Surface roughness of the films was increased due to the formation of grains on the surface. Electrical conductivity became deteriorated for polycrystalline IZO films. Consequently, high quality IZO films could be prepared by do sputtering with $O_{2}/Ar{\simeq}0.03$ and deposition temperature in range of $150\~200^{\circ}C$; a specific resistivity of $3.4{\times}10^{-4}{\Omega}{\cdot}cm$, an optical transmission over $90\%$ at wavelength of 550 nm, and a rms value of surface roughness about $3{\AA}$.

• Journal of the Korean Electrochemical Society
• /
• v.14 no.3
• /
• pp.138-144
• /
• 2011

The transport phenomena of electron and ion around the electrode have been analyzed, herein the computational program to simulate the electrochemical signal of cyclic voltammetry has been implemented. For the dominant mass-transfer system, the governing equation and its boundary conditions are confined to the semi-infinite diffusion model and the reversible reaction at the electrode. In order to obtain the numerical solutions of cyclic voltammetry, MATLAB was used for the explicit finite difference method. Experimental results from the cyclic voltammetry of electrochemical system(10 mM $K_3Fe(CN)_6$ and 0.1M KCl) upon the ITO glass substrate were compared with the numerical solutions. Present program explains the experimental results fairly well, where they approached the simulated ones closely with deceasing the scan rate. Furthermore, the effects of electrode area, electrochemical reaction constants and transfering coefficients in the cyclic voltammetry were discussed quantitatively.

• Microbiology and Biotechnology Letters
• /
• v.43 no.1
• /
• pp.16-21
• /
• 2015

In this study, a facile two-step pretreatment method was investigated for producing fermentable sugars. Rice straw was pretreated using electron beam irradiation (EBI) and 4-methylmorpholine-N-oxide (NMMO) prior to enzymatic hydrolysis. In the first stage, the EBI on the rice straw was carried out at various doses (100, 300, 500 kGy) and then, irradiated rice straw was stirred with NMMO solution at 120°C for 1 h for the second stage. The pretreated rice straw was hydrolyzed by cellulase 1.5 L (70 FPU/ml) and Novozyme-188 (40 CbU/ml) at 50°C for 24, 48, and 72 h. A sugar yield of 83.8% was obtained from the pretreated rice straw after 72 h of enzymatic hydrolysis. Also, FTIR and XRD results indicate that the pretreatment of the rice straw was effective due to the synergic effects of the two-step pretreatment. In conclusion, rice straw might be a potential substrate for bioethanol production by yeast fermentation.

• Journal of Microbiology and Biotechnology
• /
• v.18 no.1
• /
• pp.145-152
• /
• 2008

A cell-based in vitro exposure system was developed to determine whether oxidative stress plays a role in the cytotoxic effects of volatile organic compounds (VOCs) such as benzene, toluene, xylene, and chlorobenzene, using human epithelial HeLa cells. Thin films based on cysteine-terminated synthetic oligopeptides were fabricated for immobilization of the HeLa cells on a gold (Au) substrate. In addition, an immobilized cell-based sensor was applied to the electrochemical detection of the VOCs. Layer formation and immobilization of the cells were investigated with surface plasmon resonance (SPR), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The adhered living cells were exposed to VOCs; this caused a change in the SPR angle and the VOC-specific electrochemical signal. In addition, VOC toxicity was found to correlate with the degree of nitric oxide (NO) generation and EIS. The primary reason for the marked increase in impedance was the change of aqueous electrolyte composition as a result of cell responses. The p53 and NF-${\kappa}B $ downregulation were closely related to the magnitude of growth inhibition associated with increasing concentrations of each VOC. Therefore, the proposed cell immobilization method, using a self-assembly technique and VOC-specific electrochemical signals, can be applied to construct a cell microarray for onsite VOC monitoring.