• Journal of the Microelectronics and Packaging Society
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• v.16 no.4
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• pp.55-60
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• 2009

Porous silicon film is fabricated by electrochemical etching in a chemical mixture of HF and ethanol. Effects of Si type, Si resistivity, ultrasonic frequency, current density and etching time on surface morphology of PS film were studied. Electrochemical etching in ultrasonic bath promotes the uniformity of porous layer of Si. Frequency of ultrasonic was increased from 40 kHz to 130 kHz to obtain uniform pores on the Si surface. When current density was higher, the sizes of pores were larger. The new etching cell using back contact metal and current shield help to overcome nonhomogeneity and current crowding effect, and then leads to fabricate uniform pores on the Si surface. The distribution of pore size shows no notable tendency with etching time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.268-268
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• 2010

AC anodizing on aluminum foil was investigated by the variation of AC voltage and frequency. The voltage and frequency were applied in the range of approximately 40~200V, 0~400Hz. The porous alumina film was formed and the growth rate of oxide film is increased with frequency. The structural property was analyzed by SEM and XRD. SEM results show the approximate relation between frequency, voltage and growth rate. The AC voltage effect on the structural modulation of porous alumina indicates that AC anodizing is useful for the application to nanocapacitor material.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.10
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• pp.1019-1023
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• 2012

In this research, a novel direct-aluminum-heating-induced crystallization method was developed for the purpose of application to solar cells. By applying a constant current of 3 A to an aluminum thin film, a 200-nm-thick amorphous silicon (a-Si) thin film with a size of $1cm{\times}1cm$ can be crystallized into a polycrystalline silicon (poly-Si) thin film within a few tens of seconds. The Raman spectrum analysis shows a peak of 520 $cm^{-1}$, which verifies the presence of poly-Si. After removing the aluminum layer, the poly-Si thin film was found to be porous. SIMS analysis showed that the porous poly-Si thin film was heavily p-doped with a doping concentration of $10^{21}cm^{-3}$. Thermal imaging shows that the crystallization from a-Si to poly-Si occurred at a temperature of around 820 K.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.754-757
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• 2012

In this report, we fabricate the porous graphene films through embossing process and vacuum filtration method and demonstrate their superior electrochemical properties as supercapacitor electrode materials. Insertion/removal of polystyrene nanoparticles between the graphene sheets allows to provide pore structures, leading to the effective prevention of restacking in graphene films. As-prepared porous graphene films have a large surface area, a bicontinuous porous structures, high electrical conductivity, and excellent mechanical integrity. The electrochemical properties of the porous graphene films as electrode materials of supercapacitor are investigated by using aqueous $H_2SO_4$ and ionic liquid solution under three-electrode system. The porous graphene films exhibit a high specific capacitance (284.5 F/g), which is two-fold higher than that of packing graphene films (138.9 F/g). In addition, the rate capability (98.7% retention) and long-term cycling stability (97.2%) for the porous graphene films are significantly enhanced, due to the facilitated ion mobility between the graphene layers.

• Journal of the Korean institute of surface engineering
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• v.48 no.1
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• pp.11-22
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• 2015

Pd alloy hydrogen membranes for hydrogen purification and separation need thermal stability at high temperature for commercial applications. Intermetallic diffusion between the Pd alloy film and the porous metal support gives rise to serious problems in long-term stability of Pd alloy membranes. Ceramic barriers are widely used to prevent the intermetallic diffusion from the porous metal support. However, these layers result in poor adhesion at the interface between film and barrier because of the fundamentally poor chemical affinity and a large thermal stress. In this study, we developed Pd alloy membranes having a dense microstructure and saturated composition on modified metal supports by advanced DC magnetron sputtering and heat treatment for enhanced thermal stability. Experimental results showed that Pd-Cu and Pd-Ag alloy membranes had considerably enhanced long-term stability owing to stable, dense alloy film microstructure and saturated composition, effective diffusion barrier, and good adhesive interface layer.

• Proceedings of the Materials Research Society of Korea Conference
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• 2007.11a
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• pp.149.2-149.2
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• 2007

• Journal of Electrochemical Science and Technology
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• v.7 no.2
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• pp.161-169
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• 2016

Porous tungsten oxide thin films were prepared by electrodeposition and tested as anodes of lithium secondary batteries. The synthesized films were composed of nanoparticles of 60-140 nm size, with porosities of 30-40 %. Increasing the temperature turned out to be a more effective approach to introduce porosity in the structure than increasing the electrolyte viscosity. The assessment of the synthesized films as anodes of lithium secondary batteries revealed a much higher initial discharge capacity for the porous than the dense samples. The discharge capacity retention significantly increased with increasing porosity and was further enhanced by heat treatment. In particular, a thin film composed of particles of about 140 nm in size and with a porosity of 40 % exhibited an initial discharge capacity higher than 600 mAh/g and a remaining capacity above 300 mAh/g after 30 cycles. Following heat treatment, the remaining capacity of this sample after 30 cycles increased to about 500 mA h/g.

• Journal of the Korean Ceramic Society
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• v.43 no.5 s.288
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• pp.265-269
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• 2006

We have deposited NiO films by RF sputtering on $Al_2O_3/SiO_2/Si$ and 100 nm-thick Gd doped $CeO_2$ covered $Al_2O_3/SiO_2/Si$ substrates at various $Ar/O_2$ ratios. The deposited films were reduced to form porous Ni thin fllms in 4% $H_2\;at\;400^{\circ}C$. For the films deposited in pure Ar, the reduction was retarded due to the thickness and the orientation of the NiO films. On the other hand, the films deposited in oxygen mixed ambient were reduced and formed porous Ni films after 20 min of reduction. We also investigated the possibility of using the films for the single chamber operation by studying the electrical property of the films in the fuel/air mixed environment. It is shown that the resistance of the Ni film increases quickly in the mixed gas environment and thus further improvements of Ni-base anodes are required for using them in the single chamber operation.

• Macromolecular Research
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• v.12 no.5
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• pp.443-450
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• 2004

We have studied the effects that inorganic zeolite powder have on structurally different copolymer [poly(propylene-co-ethylene)] and terpolymer [poly(propylene-co-ethylene-co-l-butene)] systems and the possibility of preparing suitable porous composite films. The impact strength and yield stress of the composites did not improve upon any further loading of zeolite, but the modulus increased gradually with respect to the filler loading. The experimental modulus of each of the two systems was compared with theoretical models. We performed a morphological study of the filler mixing efficiency and image analysis. The number-, weight-, and z-average air hole diameters were compared with respect to the draw ratio as well as the zeolite loading. The experimental results suggest that these two matrices can provide a new choice for preparing future multiphase polymeric porous films by stretching them unidirectionally. In particular, we suggest that a 40 wt% zeolite loading at a draw ratio of 4 is useful for porous film applications.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.3950-3956
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• 2012

In order to improve the bioactivity and mechanical properties of hydroxyapatite (HAp), chitosan (Chi) was in situ combined into HAp to fabricate a composite scaffold by a sublimation-assisted compression method. A highly porous film with sufficient mechanical strength was prepared and the bioactivity was investigated by examining the apatite formed on the scaffolds incubated in simulated body fluid. In addition, the cytotoxicity of the HAp/Chi composite was studied by evaluating the viability of murine fibroblasts (L-929 cells) exposed to diluted extracts of the composite films. The apatite layer was assessed using scanning electronic microscopy, inductively coupled plasma-optical emission spectrometry and weight measurement. Composite analysis showed that a layer of micro-sized, needle-like crystals was formed on the surface of the composite film. Additionally, the WST-8 assay after L-929 cells were exposed to diluted extracts of the composite indicated that the HAp/Chi scaffold has good in vitro cytocompatibility. The results indicated that HAp/Chi composites with porous structure are promising scaffolding materials for bone-patch engineering because their porous morphology can provide an environment conductive to attachment and growth of osteoblasts and osteogenic cells.