• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.10
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• pp.917-923
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• 2005

In this paper, effect of catalytic configuration on the sensing properties of $SnO_2$ nanoparticle gas sensitive thick film was investigated. Two types of catalytic configuration, mono and binary, were made on the $SnO_2$ nanoparticle. In case of mono catalytic system, $3 wt\%$ Pd or Pt catalyst was doped onto the $SnO_2$ nanoparticle, respectively. In case of binary catalytic system, Pd and Pt was doped simultaneously with concentration ratio of 1:2 to 2:1 onto the $SnO_2$ nanoparticle. After doping, gas sensitive thick film was printed on alumina substrate and heat-treated at 450 to $600^{\circ}C$. Gas sensing properties was evaluated using 500 to 10,000 ppm $CH_4$ gas. As a result, gas sensitive thick film with binary catalytic system showed unstable phenomena that the gas sensitivity was changed according to aging time. In contrary, the mono catalytic system showed relatively stable phenomena despite of aging time. Especially, gas sensitive thick film doped with $3 wt\%$ Pt catalyst and heat-treated at $500^{\circ}C$ showed good sensing properties such as 0.57 of $R_{3500}/R_{1000}$ and very small variation within $3.5\%$ after aging for 5 hours, and response time was very short less than 20 seconds.

• Proceedings of the Korean Magnestics Society Conference
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• 2000.09a
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• pp.287-296
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• 2000

We have developed a three-axis configurational in situ SMOKE apparatus by which three-dimensional vector magnetization reversal processes are studied for ultrathin Co films grown on a Pd (111) single crystal in the thickness range of spin-reorientation transition. This study provides a better understanding of magnetization reversal motions with the knowledge of 3 components of magnetization vector at the transition of an easy axis of magnetization from the film normal at 5 ML Co to in-plane at 6 ML Co (ML notes monolayer). For a 5.25 ML Co, it was observed that a slightly canted magnetization vector from the film normal rotated in the film plane under an applied field direction parallel to the film normal.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.141-141
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• 2000

In situ surface magneto-optic Kerr effect(SMOKE), X-ray photoelectron spectroscopy(XPS) and low energy electron diffraction(LEED) were used to study magnetic and structural properties of ultrathin Fe films grown on the Pd(111) surface. The SMOKE measurement showed strong enhancement of ferromagnetism after proper annealing process. Simultaneous changes in morphology was checked by LEED and XPS. After room temperature Fe deposition. longitudinal magnetization appeared above a critical thickness between 2.0 and 2.5 monolayers. When annealed at 450K, 2.0 monolayer Fe film exhibited boty longitudinal and polar magnetizations while 3.0 and 5.5 monolayer films showed little changes. After annealing at 600K, both magnetizations were totally destroyed in 2.0 monolayer film, but longitudinal magnetization was enhanced in 3.0 monolayer film. In the case of 5.5 monolayer film, it was only after 660K annealing that the enhancement of the longitudinal magnetization was observed. It was concluded that the surface flatness and the amount of intermixing were critical in the development of surface magnetism of this system.

• Journal of Magnetics
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• v.6 no.2
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• pp.53-56
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• 2001

We have developed a three-axis configurational in situ SMOKE apparatus by which three-dimensional vector magnetization reversal processes are studied for ultrathin Co films grown on a Pd (111) single crystal in the thickness range of spin reorientation transition. This study provides a better understanding of magnetization reversal motions with the knowledge of three components of the magnetization vector at the transition of an easy axis of magnetization from the film normal at 5 ML Co to in-plane at 6 ML Co (ML denotes monolayer). For a 5.25 ML Co, it was observed that a slightly canted magnetization vector from the film normal rotated in the film plane under an applied field direction parallel to the film normal.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.5
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• pp.435-440
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• 2002

In this study, we have investigated photo-induced changes of optical energy gap( $E_{OP)}$ and photoluminescence (PL) in amorphous ($\alpha$-) S $e_{100-x}$G $e_{x}$ (x=5, 25 and 33) thin films prepared by conventional thermal evaporation method. In the $\alpha$-S $e_{100-x}$G $e_{x}$ thin film, the $E_{OP}$ is obtained by a linear extrapolation of the ($\alpha$hν)$^{\frac{1}{2}}$ versus hν plot to the energy axis using the optical absorption coefficient ($\alpha$) calculated from the extinction coefficient k measured in the wavelength range of 290~900nm. Although the values of $\Delta$ $E_{OP}$ are very different, all films exhibit photo-induced photo-darkening (PD) effect that is a red shift of $E_{OP}$ . In particular, $\Delta$ $E_{OP}$ in $\alpha$-S $e_{75}$ G $e_{25}$ thin film exhibits the largest value (i, e., $\Delta$ $E^{OP}$ ~40meV for $\alpha$-S $e_{95}$ G $e_{5}$ , $\Delta$ $E_{OP}$ ~200meV for $\alpha$-S $e_{75}$ G $e_{25}$ , $\Delta$ $E_{OP}$ ~130meV for $\alpha$-S $e_{67}$ G $e_{33}$ ). PL spectra in $\alpha$-SeGe by hν$_{HeCd}$ have no-Stokes shift (SS) and show a tendency dependent on both composition and illumination time. We explain the energy-induced phenomena such as the PD and thermal bleaching, the native charged-defect generation and the no-SS PL, etc..the PD and thermal bleaching, the native charged-defect generation and the no-SS PL, etc..tc..

• Journal of the Korean institute of surface engineering
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• v.49 no.3
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• pp.286-300
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• 2016

Pd-Ag alloy membranes have attracted a great deal of attention for their use in hydrogen purification and separation due to their high theoretical permeability, infinite selectivity and chemical compatibility with hydro-carbon containing gas streams. For commercial application, Pd-based membranes for hydrogen purification and separation need not only a high perm-selectivity but also a stable long-term durability. However, it has been difficult to fabricate thin, dense Pd-Ag alloy membranes on a porous stainless steel metal support with surface pores free and a stable diffusion barrier for preventing metallic diffusion from the porous stainless steel support. In this study, thin Pd-Ag alloy membranes were prepared by advanced Pd/Ag/Pd/Ag/Pd multi-layer sputter deposition on the modified porous stainless steel support using rough polishing/$ZrO_2$ powder filling and micro-polishing surface treatment, and following Ag up-filling heat treatment. Because the modified Pd-Ag alloy membranes using rough polishing/$ZrO_2$ powder filling method demonstrate high hydrogen permeability as well as diffusion barrier efficiency, it leads to the performance improvement in hydrogen perm-selectivity. Our membranes, therefore, are expected to be applicable to industrial fields for hydrogen purification and separation owing to enhanced functionality, durability and metal support/Pd alloy film integration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05a
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• pp.13-16
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• 2003

Magnetic and magneto-optical properties of Fe/Pt/Fe, Co/Pd/Co trilayers and also the sandwiches with wedge-shaped magnetic (Fe, Co) and nonmagnetic (Pt, Pd) layers were investigated. The oscillatory behavior of the saturation field $H_{s}$ of the studied trilayers with changing the thickness of the nonmagnetic layer (NML) $t_{NML}$ was revealed. That was explained by the exchange coupling between ferromagnetic layers (FML) through the nonmagnetic spacer. For the first time, oscillations of the transverse Kerr effect (TKE) with changing the Pt- and Pd-wedge thickness were discovered. Period of these oscillations was found to depend on the FML thickness and the photon energy of the incident light. TKE spectra of the examined samples were discovered to modify very strongly with increasing $t_{NML}$. The discovered peculiarities of magneto-optical properties of thin-film systems were explained by a concept of the spin-polarized quantum well states in the pt and Pd layers.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.3
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• pp.160-164
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• 2018

We have proposed a hydrogen detection sensor based on a Pd (palladium)-coated, single-mode, optical fiber. The experimental results demonstrated that the sensor could detect hydrogen in air as well as in insulation oil. The influence of Pd film thickness and environmental temperature on response time and sensitivity was analyzed. The reflected optical power at the optical-fiber/Pd interface decreased as the concentration of hydrogen increased, in both air and the insulation oil. The sensor showed 0.75 dB of optical power variation when the concentration of dissolved hydrogen was saturated in the insulation oil.

• Transactions of the Korean hydrogen and new energy society
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• v.7 no.2
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• pp.173-180
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• 1996

4-probe resistivity measurement technique was used to study kinetics of hydrogen absorption-desorption on Pd film($520{\AA}$ thick) at room temperature upto 1 bar. Kinetics data are fitted well to 1st order kinetics equation in ${\alpha}$ and ${\alpha}^{\prime}$ phases. In ${\alpha}+{\alpha}^{\prime}$ phase, absorption kinetics was very complicated, but it could be explained partially with nucleation and growth process. Ln(dR/dt) vs. time plot gives rate constant k value(R is resistance of sample, t is time). k value for absorption is $4^{-6}{\times}10^{-4}/sec$ in ${\alpha}$ phase. k is increasing upto $4^{\times}10^{-2}/sec$ as hydrogen pressure increasing in ${\alpha}^{\prime}$ phase. k is proportional to ln(Pop/Peq), where Peq is equilibrium plateau pressure and Pop is the opposing pressure. In contrast to bulk sample k value was decreasing with increasing number of A-D cycling in ${\alpha}^{\prime}$ phase absorption.

• Korean Journal of Materials Research
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• v.19 no.4
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• pp.192-197
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• 2009

Carbon nanotubes (CNT) were used as a catalyst support where catalytically active Pd and Pt metal particles decorated the outside of the external CNT walls. In this study, Pd and Pt nanoparticles supported on $HNO_3$-treated CNT were prepared by microwave-assisted heating of the polyol process using $PdCl_2$ and $H_2PtCl_6{\codt}6H_2O$ precursors, respectively, and were then characterized by SEM, TEM, and Raman. Raman spectroscopy showed that the acid treated CNT had a higher intensity ratio of $I_D/I_G$ compared to that of non-treated CNT, indicating the formation of defects or functional groups on CNT after chemical oxidation. Microwave irradiation for total two minutes resulted in the formation of Pd and Pt nanoparticles on the acid treated CNT. The sizes of Pd and Pt nanoparticles were found to be less than 10 nm and 3 nm, respectively. Furthermore, the $SnO_2$ films doped with CNT decorated by Pd and Pt nanoparticles were prepared, and then the $NO_2$ gas response of these sensor films was evaluated under $1{\sim}5\;ppm$ $NO_2$ concentration at $200^{\circ}C$. It was found that the sensing property of the $SnO_2$ film sensor on $NO_2$ gas was greatly improved by the addition of CNT-supported Pd and Pt nanoparticles.