• Membrane Journal
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• v.24 no.6
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• pp.423-430
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• 2014

PTMSP/LDH composite membranes were prepared by adding 0, 1, 3, and 5 wt% LDH contents to PTMSP. The gas permeability and selectivity for $H_2$, $N_2$, $CH_4$, $C_3H_8$, $n-C_4H_{10}$ were investigated as a function of LDH content. As LDH content of PTMSP/LDH composite membranes increased to 5 wt%, the gas permeability for $H_2$ and $N_2$ gradually decreased, while $n-C_4H_{10}$ permeability rapidly increased. The gas permeability for $CH_4$ and $C_3H_8$ was found to decrease for the membranes with LDH content range of 0~3 wt%, however increase in the range of 3~5 wt%. As LDH content of PTMSP/LDH composite membranes increased to 5 wt%, the selectivity of membranes gradually increased for $H_2$, $N_2$, $CH_4$, $C_3H_8$, $n-C_4H_{10}$ over $H_2$, $N_2$. However the selectivity for $C_3H_8$ and $n-C_4H_{10}$ over $CH_4$ increased in the range of LDH content 0~3 wt% but decreased in the range of 3~5 wt%. The $CH_4$ and $n-C_4H_{10}$ selectivity over $H_2$ and $N_2$ increased as $CH_4$ and $n-C_4H_{10}$ permeability increased. The $n-C_4H_{10}$ selectivity over $CH_4$ increased with increasing $n-C_4H_{10}$ permeability up to 182,000 barrer and decreased above 182,000 barrer of $n-C_4H_{10}$ permeability. The $C_3H_8$ selectivity over $H_2$ and $N_2$ was found to decrease as the $C_3H_8$ permeability increased from 46,000 to 50,000 barrer, but to increase with increasing permeability from 50,000 to 52,300 barrer and decrease again with increasing permeability from 52,300 to 60,000 barrer. The $C_3H_8$ selectivity over $CH_4$ was found to decrease with increasing $C_3H_8$ permeability up to 52,300 barrer but increase above 52,300 barrer.

• Membrane Journal
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• v.24 no.5
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• pp.358-366
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• 2014

Chitosan-HNT (halloysite nanotube) composite membranes were prepared by the addition of HNT 0, 3, 5, and 10 wt%. The structure of composite membranes were studied by FT-IR, XRD, TGA, and SEM. Gas permeation experiment were performed under condition of $30^{\circ}C$ and $4kgf/cm^2$. Gas permeability and selectivity were investigated by increasing the amount of HNT contents in the chitosan. Chitosan-HNT composite membrane for $CO_2$ and $CH_4$ showed the maximum value at 3 wt% of HNT content and decreased thereafter. The selectivity of ($CO_2/CH_4$) was increased due to its affinity with the OH groups on the HNT, was shown in the range of 1.3 to 3.8 at 0~10 wt%.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.4
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• pp.164-168
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• 2011

Etch selectivities of mask materials to ZnO and $SnO_2$ films were studied in $BCl_3$/Ar and $CF_4$/Ar inductively coupled plasmas for fabrication of nanostructure-based gas sensing layer with high aspect ratios. In $25BCl_3$/10Ar ICP discharges, selectivities of 5.1~6.1 were obtained for ZnO over Ni while no practical selectivity was obtained for ZnO over Al. High selectivities of 7 ~ 17 for ZnO over Ni were produced in $25CF_4$/10Ar mixtures. $SnO_2$ showed much higher etch rates than Ni and a maximum selectivity of 67 was observed for $SnO_2$ over Ni.

• Membrane Journal
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• v.24 no.3
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• pp.185-193
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• 2014

PDMS (polydimethylsiloxane)-HNT (halloysite nanotube) composite membranes were prepared with different amounts tendency of HNT 5, 10, 20 and 30 wt% and rubbery polymer PDMS. The characteristics of these membranes were studied by FT-IR, XRD, TGA, and SEM. Gas permeation experiment were performed under condition of $25^{\circ}C$ and $3kg/cm^2$. Gas permeability of $N_2$, $H_2$, $CH_4$, and $CO_2$ and selectivity were investigated by increasing the amount of HNT contents in the PDMS. In $H_2$, $N_2$, $CH_4$, and $CO_2$ gases, as increasing HNT contents from 0 to 30 wt%, decreasing value of the permeability were observed. The selectivity of ($CO_2/N_2$) was shown in the range of 14 to 44 and the range of selectivity of ($CO_2/CH_4$) was 3.0 to 7.0.

• ETRI Journal
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• v.24 no.3
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• pp.211-220
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• 2002

This study characterizes an oxide etching process in a magnetically enhanced reactive ion etching (MERIE) reactor with a $CHF_3/CF_4$ gas chemistry. We use a statistical $2^{4-1}$ experimental design plus one center point to characterize the relationships between the process factors and etch responses. The factors that we varied in the design include RF power, pressure, and gas composition, and the modeled etch responses were the etch rate, etch selectivity to TiN, and uniformity. The developed models produced 3D response plots. Etching of $SiO_2$ mainly depends on F density and ion bombardment. $SiO_2$ etch selectivity to TiN sensitively depends on the F density in the plasma and the effects of ion bombardment. The process conditions for a high etch selectivity are a 0.3 to 0.5 $CF_4$ flow ratio and a -600 V to -650 V DC bias voltage according to the process pressure in our experiment. Etching uniformity was improved with an increase in the $CF_4$ flow ratio in the gas mixture, an increase in the source power, and a higher pressure. Our characterization of via etching in a $CHF_3/CF_4$ MERIE using neural networks was successful, economical, and effective. The results provide highly valuable information about etching mechanisms and optimum etching conditions.

• Membrane Journal
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• v.30 no.6
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• pp.420-432
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• 2020

Random copolymers made of both 'polymer of intrinsic microporosity (PIM-1)' and Ellagic acid were prepared for the first time by a facile one-step polycondensation reaction. By combining the highly porous and contorted structure of PIM (polymers with intrinsic microporosity) and flat-type hydrophilic ellagic acid, the membranes obtained from these random copolymers [(PIM-co-EA)-x] showed high CO2 permeability (> 4516 Barrer) with high CO2/N2 (> 23~26) and CO2/CH4 (> 18~19) selectivity, that surpassed the Robeson upper bound (2008) for both pairs of the gas mixture. Incorporation of flat-type ellagic acid into the PIM-1 not only enhances the gas permeability by disturbing the kinked structure of PIM-1 but also increases the selectivity of CO2 over N2 and CH4, due to an increase of rigidity and polarity in the resultant copolymer membranes.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.94-98
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• 2021

In this study, pure and Co3O4/CoFe2O4-loaded Indium oxide (In2O3) nanofibers were synthesized by the electrospinning of an Indium/Polyvinylpyrrolidone precursor solution containing cobalt and iron bimetallic zeolitic imidazolate frameworks and subsequent heat treatment. The ethanol, toluene, p-xylene, benzene, carbon monodxide, and hydrogen gas sensing characteristics of the solution were measured at 250-400 ℃. 0.5 at%-Co3O4/CoFe2O4-loaded In2O3 nanofibers exhibited extreme response (resistance ratio - 1) to 5 ppm of ethanol (210.5) at 250 ℃ and excellent selectivity over the interfering gases. In contrast, pure In2O3 nanofibers exhibited relatively low responses to all the analyte gases and low selectivity above 250-400 ℃. The superior response and selectivity toward ethanol is explained by the catalytic roles of Co3O4 and CoFe2O4 in gas sensing reaction and the electronic sensitization induced by the formation of p (Co3O4/CoFe2O4)-n (In2O3) junctions.

• Membrane Journal
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• v.31 no.6
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• pp.456-470
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• 2021

In this study, polyetherimide-based hollow fiber membranes were manufactured using the NIPS (nonsolvent induced phase separation) method. THF, Ethanol, and LiNO₃ were used as additives to control the morphology of the PEI-hollow fiber membranes. Furthermore, for the development of a high hydrogen separation membrane, the spinning conditions were optimized through the characterization of SEM and gas permeance. As a result, as the content of THF increased, the hydrogen/carbon dioxide selectivity increased. However, the permeance decreased due to the trade-off relationship. When ethanol was added, a finger-like structure was shown, and when LiNO₃ was added, a sponge structure was shown. In particular, in the case of a hollow fiber membrane with an optimized PDMS coating layer, the permeance was 40 GPU and the hydrogen/carbon dioxide selectivity was 5.6.

• Journal of Sensor Science and Technology
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• v.30 no.4
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• pp.191-195
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• 2021

Pure ZnFe₂O₄ and Fe₂O₃-ZnFe₂O₄ hetero-composite spheres were prepared by ultrasonic spray pyrolysis of a solution containing Zn- and Fe-nitrates. Additionally, the sensing characteristics of these spheres in the presence of 5 ppm ethanol, benzene, p-xylene, toluene, and CO (within the temperature range of 275-350 ℃) were investigated. The Fe₂O₃-ZnFe₂O₄ hetero-composite sensor with a cation ratio of [Zn]:[Fe]=1:3 exhibited a high response (resistance ratio = 140.2) and selectivity (response to p-xylene/response to ethanol = 3.4) to 5 ppm p-xylene at 300 ℃, whereas the pure ZnFe₂O₄ sensor showed a comparatively lower gas response and selectivity. The reasons for the superior response and selectivity to p-xylene in Fe₂O₃-ZnFe₂O₄ hetero-composite sensor were discussed in relation to the electronic sensitization due to charge transfer at Fe₂O₃-ZnFe₂O₄ interface and Fe₂O₃-induced catalytic promotion of gas sensing reaction. The sensor can be used to monitor harmful volatile organic compounds and indoor air pollutants.

• ETRI Journal
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• v.25 no.6
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• pp.503-509
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• 2003

Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high-density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas-phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E-beam patterns, we evaluated and controlled selectivity loss and non-uniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating.