• Carbon letters
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• v.12 no.3
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• pp.171-176
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• 2011

Polyacrylonitrile-based carbon nanofibers (CNFs) containing Ti and Mn were prepared by electrospinning. The effect of metal content on the hydrogen storage capacity of the nanofibers was evaluated. The nanofibers containing Ti and Mn exhibited maximum hydrogen adsorption capacities of 1.6 and 1.1 wt%, respectively, at 303 K and 9 MPa. Toward the development of an improved hydrogen storage system, the optimum conditions for the production of metalized CNFs were investigated by characterizing the specific surface areas, pore volumes, sizes, and shapes of the fibers. According to the results of Brunauer-Emmett-Teller analysis, the activation of the CNFs using potassium hydroxide resulted in a large pore volume and specific surface area in the samples. This is attributable to the optimized pore structure of the metal-containing polyacrylonitrile-based electrospun CNFs, which may provide better sites for hydrogen adsorption than do current adsorbates.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.151-156
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• 2006

A method for fabrication of nano-scale GaN structure by inductively coupled plasma etching is proposed, exploiting a thermal dewetting of Pt thin film as an etch mask. The nano-scale Pt metal islands were formed by the dewetting of 2-dimensional film on $SiO_2$ dielectric materials during rapid thermal annealing process. For the case of 30 nm thick Pt films, pattern formation and dewetting was initiated at temperatures greater $600^{\circ}C$. Controlling the annealing temperature and time as well as the thickness of the Pt metal film affected the size and density of Pt islands. The activation energy for the formation of Pt metal island was calculated to be 23.2 KJ/mole. The islands show good resistance to dry etching by a $CF_4$ based plasma for dielectric etching indicating that the metal islands produced by dewetting are suitable for use as an etch mask in the fabrication of nano-scale structures.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.166.2-166.2
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• 2014

In this work, we demonstrated a facile and effective method for deposition of metal tetraphenylporphyrin (MTPP) thin film by a combined a thermal evaporation (TE) and atomic layer deposition (ALD). For the deposition of Zn-TPP thin film, Tetraphenylporphyrin (TPP) and diethyl zinc (DEZ) were used as organic and inorganic materials, respectively. Optimum conditions for the deposition of Zn-TPP thin film were established systematically: (1) the exposure time of DEZ as inorganic precursor and (2) the substrate temperature were adjusted, respectively. As a result, we verified that the surface reaction between organic semiconductor (TPP) and metal atom (Zn) was ALD process. In addition, we calculated activation energy by using Arrhenius equation for the substrate temperature versus area change rate of pyrrolic nitrogen. The surface and interface reactions between TPP with Zn were investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, UV-vis spectroscopy, and scanning electron microscopy. These results show a facile and well-controllable fabrication technique for the metal-organic thin film for future electronic applications.

• Korean Journal of Materials Research
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• v.9 no.5
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• pp.441-445
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• 1999

Alkaline earth metal oxides were added to the conventional MgO films as a protective layer for dielectric materials to have lower firing voltage(Vf) of the plasma display panel(PDP). Panels with various protective layers of MgO-alkaline earth metal oxides were prepared on glass by using e-beam evaporation and its effect on firing voltage characteristics were investigated. (Ba-Mg)O films had poor voltage characteristics because of higher activation energy of BaO. But, (Sr-Mg)O, (Ca-Mg)O and (Ca-Sr-Mg) O had better voltage characteristics than the conventional MgO. A mixture film of (Mg-Ca-Sr)O show the lowest firing voltage which is less than that of MgO by 20V. The chemical composition to have lowest firing voltage is MgO:SrO:CaO ratio of 6:2:2. The mixture of MgO-Alkaline earth metal oxides films showed good transmittance properties within the visual range.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.97.2-97.2
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• 2011

Pt-Ru and Pt-Ni bimetallic catalysts were prepared and tested for heavy hydrocarbon reforming. Metals were supported on CGO($Ce_{0.8}Gd_{0.2}O_{2.0-x}$) by incipient wetness method. The prepared catalysts were characterized by Temperature programmed reduction(TPR). Oxidative steam reforming of n-dodecane was conducted to compare the activity of the catalysts. The reforming temperature was varied from $500^{\circ}C$ to $800^{\circ}C$ at fixed $O_2$/C of 0.3, $H_2O$/C of 3.0 and GHSV of 5,000/h.Reduction peaks of metal oxide, surface CGO and bulk CGO were detected. Reduction temperature of metal oxide decreased over the bi-metallic catalysts. It is considered that interaction between metals leads to decrease interaction between metal and oxygen. On the other hands, reduction temperatures of surface CGO were dectected in the order of Pt-Ru > Pt-Ni > Pt. low reduction temperatures of surface CGO indicates the low activation energy for oxygen ion conduction to metal. Oxygen ion conduction is known as de-coking mechanism of ionic conducting supports such as CGO. In activity test, fuel conversion was in the same order of Pt-Ru > Pt-Ni > Pt. Especially, 100% of fuel conversion was obtained over Pt-Ru catalysts at $500^{\circ}C$.

• Korean Journal of Materials Research
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• v.18 no.6
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• pp.302-306
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• 2008

Polycrystalline germanium (Ge) thin films were grown by metal organic chemical vapor deposition (MOCVD) using tetra-allyl germanium [$Ge(allyl)_4$], and germane ($GeH_4$) as precursors. Ge thin films were grown on a $TiN(50nm)/SiO_2/Si$ substrate by varying the growth conditions of the reactive gas ($H_2$), temperature ($300-700^{\circ}C$) and pressure (1-760Torr). $H_2$ gas helps to remove carbon from Ge film for a $Ge(allyl)_4$ precursor but not for a $GeH_4$ precursor. $Ge(allyl)_4$ exhibits island growth (VW mode) characteristics under conditions of 760Torr at $400-700^{\circ}C$, whereas $GeH_4$ shows a layer growth pattern (FM mode) under conditions of 5Torr at $400-700^{\circ}C$. The activation energies of the two precursors under optimized deposition conditions were 13.4 KJ/mol and 31.0 KJ/mol, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.145-145
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• 2000

M-CeO2 (M : noble metal) catalysts have been widely studied as three-way catalysts and methanol synthesis catalysts. Ceria is thought to play a number of roles in these catalysts. The Ce(IV)/Ce(III) redox pair may store/release gases under oxidizing/reducing conditions, extending the operational window. Additionally, metal-ceria interactions lead to several effects, including the dispersion of the active components and promoting the activation of molecules such as CO or NO. Pd is a promising component to current TWC formulations and behaves particularly well when compared with Pt and Rh-based catalysts for low-temperature oxidation of Co and hydrocarbon. However the effect of Pd-ceria interactions on the physicochemical properties of Pd and the redox properties of Ce is not elucidated yet. In order to know exactly about the metal-ceria interactions, the model study are expecting to give a better environment, resulting in the wide use of the surface science tools. The substrate was Si(100) wafer, on which Ta metal was sputtered as a thickness of 100nm. The CeO2 thin film of 30nm was deposited by using the magnetron sputtering. Spin coating and magnetron sputtering methods were used to make the Pd thin film layer. The prepared sample was investigated by in-situ XPS, AES, SEM and AFM analysis.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.381-383
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• 2021

Light-activated metal oxide gas sensors have been investigated in recent decades. Light illumination enhances the sensing attributes, including the operational temperature, sensitivity, and selectivity. Unfortunately, high operating temperature is a major problem for gas sensors because of the huge energy consumption. Therefore, the importance of light-activated room-temperature sensing has increased. This paper reviews recent light-activated sensors and their sensing mechanisms with a specific focus on metal oxide gas sensors. Studies use the outstanding ZnO and SnO₂ sensors to research photoactivation when illuminated by various sources such as ultraviolet (UV), halogen lamp, or monochromatic light. Photon induction generates electron-hole pairs that increase the number of adsorption sites of gas molecules and ions improving the sensor's sensing properties.

• Journal of Hydrogen and New Energy
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• v.17 no.3
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• pp.248-254
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• 2006

The promotion effects of noble metals upon the activity and reducibility in steam methane reforming over $Ni/MgAl_2O_4$ catalysts were investigated. While $Ni/MgAl_2O_4$ catalysts require the pre-reduction by $H_2$, the noble metal-added catalysts show high catalytic activities without pre-treatment. According to $CH_4$-TPR, the addition of noble metal makes the $Ni/MgAl_2O_4$ catalyst easily reducible. The reduction degree of NiO in the noble metal-added catalysts after using at $650^{\circ}C$ without pre-reduction was $15{\sim}20%$, and was lower than that in the $H_2$-reduced $Ni/MgAl_2O_4$ catalyst(reduction degree=27%). The enhancement of the catalytic activity over noble metal-added catalysts results from easier reducibility by addition of noble metal and the synergy effect between noble metal and Ni.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.217-217
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• 2011

Recently, demand for thermally stable metal nanoparticles suitable for chemical reactions at high temperatures has increased to the point to require a solution to nanoparticle coalescence. Thermal stability of metal nanoparticles can be achieved by adopting core-shell models and encapsulating supported metal nanoparticles with mesoporous oxides [1,2]. However, to understand the role of metal-support interactions on catalytic activity and for surface analysis of complex structures, we developed a novel catalyst design by coating an ultra-thin layer of titania on Pt supported silica ($SiO_2/Pt@TiO_2$). This structure provides higher metal dispersion (~52% Pt/silica), high thermal stability (~600$^{\circ}C$) and maximization of the interaction between Pt and titania. The high thermal stability of $SiO_2/Pt@TiO_2$ enabled the investigation of CO oxidation studies at high temperatures, including ignition behavior, which is otherwise not possible on bare Pt nanoparticles due to sintering [3]. It was found that this hybrid catalyst exhibited a lower activation energy for CO oxidation because of the metal-support interaction. The concept of an ultra-thin active metal oxide coating on supported nanoparticles opens-up new avenues for synthesis of various hybrid nanocatalysts with combinations of different metals and oxides to investigate important model reactions at high-temperatures and in industrial reactions.