• Korean Journal of Materials Research
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• v.20 no.11
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• pp.623-627
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• 2010

Semiconducting metal oxides have been frequently used as gas sensing materials. While zinc oxide is a popular material for such applications, structures such as nanowires, nanorods and nanotubes, due to their large surface area, are natural candidates for use as gas sensors of higher sensitivity. The compound ZnO has been studied, due to its chemical and thermal stability, for use as an n-type semiconducting gas sensor. ZnO has a large exciton binding energy and a large bandgap energy at room temperature. Also, ZnO is sensitive to toxic and combustible gases. The NO gas properties of zinc oxide-single wall carbon nanotube (ZnO-SWCNT) composites were investigated. Fabrication includes the deposition of porous SWCNTs on thermally oxidized $SiO_2$ substrates followed by sputter deposition of Zn and thermal oxidation at $400^{\circ}C$ in oxygen. The Zn films were controlled to 50 nm thicknesses. The effects of microstructure and gas sensing properties were studied for process optimization through comparison of ZnO-SWCNT composites with ZnO film. The basic sensor response behavior to 10 ppm NO gas were checked at different operation temperatures in the range of $150-300^{\circ}C$. The highest sensor responses were observed at $300^{\circ}C$ in ZnO film and $250^{\circ}C$ in ZnO-SWCNT composites. The ZnO-SWCNT composite sensor showed a sensor response (~1300%) five times higher than that of pure ZnO thin film sensors at an operation temperature of $250^{\circ}C$.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.463-469
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• 2012

Solar thermochemical syngas and hydrogen production process bv redox system of metal oxide was performed under direct irradiation of the metal oxide on the SiC ceramic foam device using solar simulator. $CeO_2/ZrO_2$ nanotube has been synthesized by anodic oxidation method. Syngas and hydrogen production process is one of the promising chemical pathway for storage and transportation of solar heat by converting solar energy to chemical energy. The produced syngas had the $H_2/CO$ ratio of 2, which was suitable for methanol synthesis or Fischer-Tropsch synthesis process. After ten cycles of redox reaction, $CeO_2$ was analyzed using XRD pattern and SEM image in order to characterize the physical and chemical change of metal oxide at the high temperature.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.113-120
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• 2007

Chemical vapor deposition (CVD) is one of the various synthesis methods that have been employed for carbon nanotube (CNT) growth. In particular, Ren et al reported that large areas of vertically aligned multi-wall carbon nanotubes could be grown using a direct current (dc) PECVD system. The synthesis of CNT requires a metal catalyst layer, etchant gas, and a carbon source. In this work, the substrates consists of Si wafers with Ni-deposited film. Ammonia $NH_3$) and acetylene ($C_2H_2$) were used as the etchant gases and carbon source, respectively. Pretreated conditions had an influence on vertical growth and density of CNTs. And patterned growth of CNTs could be achieved by lithographical defining the Ni catalyst prior to growth. The length of single CNT was increased as niclel dot size increased, but the growth rate was reduced when nickel dot size was more than 200 nm due to the synthesis of several CNTs on single Ni dot. The morphology of the carbon nanotubes by TEM showed that vertical CNTs were multi-wall and tip-type growth mode structure in which a Ni cap was at the end of the CNT.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1839-1842
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• 1999

We have synthesized carbon nanotubes by thermal chemical vapor deposition of $C_2H_2$ on transition metal-coated silicon substrates. Carbon nanotubes are uniformly synthesized on a large area of the plain Si substrates, different from Previously reported porous Si substrates. It is observed that surface modification of transition metals deposited on substrates by either etching with dipping in a HF solution and/or $NH_3$ pretreatment is a crucial step for the nanotube growth prior to the reaction of $C_2H_2$ gas. We will demonstrate that the diameters of carbon naotubes can be controlled by applying the different transition metals.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.51 no.3
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• pp.121-124
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• 2002

CNTs(Carbon Nano Tube) were employed as an electron source in electron-gun of CRT(Cathode-Ray Tube). The CNTs were grown on the Si substrates and the electron gun by LP-CVD(Low Pressure-Chemical Vapor Deposition). Their physical and field emission property satisfied the requirements of the electron gun of CRT. The fabricated electron gun was inserted into 19 inch-sifted CRT and its operating properly was evaluated for practical usage.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.678-680
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• 2002

Vertically aligned carbon nanotubes(CNTs) have been grown on Ni-coated TiN/Si substrate by microwave plasma chemical vapor deposition using $H_2/CH_4$ mixture gas. We have investigated the Effect of process parameters on the growth of CNT. During the growth, microwave power, pressure, and growth temperature were varied from 300 W to 700 W, 10 Torr to 30 Torr, and 300 $^{\circ}C$ to 700 $^{\circ}C$. respectively. Then we controlled the size of CNTs. The structure of CNT was sensitively dependent on the process parameters.

• Journal of Electrochemical Science and Technology
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• v.3 no.3
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• pp.116-122
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• 2012

As an effort to address the chronic capacity fading of Si anodes and thus achieve their robust cycling performance, herein, we develop a unique electrode in which silicon nanoparticles are embedded in the carbon nanotubes network. Utilizing robust contacts between silicon nanoparticles and carbon nanotubes, the composite electrodes exhibit excellent electrochemical performance : 95.5% capacity retention after 140 cycles as well as rate capability such that at the C-rate increase from 0.1C to 1C to 10C, the specific capacities of 850, 698, and 312 mAh/g are obtained, respectively. The present investigation suggests a useful design principle for silicon as well as other high capacity alloying electrodes that undergo large volume expansions during battery operations.

• Korean Chemical Engineering Research
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• v.43 no.2
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• pp.215-221
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• 2005

A Fe-containing mesoporous silica (Fe-MCM-41) in which part of Si in the framework was replaced by Fe(Si-O-Fe) has been successfully prepared using $Fe^{3+}$ salt by a direct synthesis route. Physical properties of the material were characterized by XRD, $N_2$ adsorption, SEM/TEM, UV-vis and FT-IR spectroscopies. Fe-MCM-41 exhibited high catalytic activity in phenol hydroxylation using $H_2O_2$ as oxidant, giving phenol conversion of ca. 60% at $50^{\circ}C$ [phenol : $H_2O_2$ = 1:1, water solvent]. Fe-MCM-41 was also applied to the growth of CNTs, utilizing a thermal-CVD reactor using acetylene gas, which demonstrated that multi-wall CNTs could be prepared efficiently using the Fe-MCM-41 catalyst.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.418-418
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• 2009

Vertically aligned arrays of multi-walled carbon nanotube (MWCNT) on layered Si substrates have been synthesized by water-assisted thermal chemical vapor deposition (CVD). We studied changes in growth by parameters of growth temperature, growth time, rates of gas and annealing time of catalyst. Also, We grew CNTs by adding a little amount of water vapor to enhance the growth of CNTs. $H_2$, Ar, and $C_2H_2$ were used as carrier gas and feedstock, respectively. Before growth, Fe served as catalyst, underneath which AI were coated as an underlayer and a diffusion barrier, respectively, on the Si substrate. The water vapor had a greater effect on the growth of CNTs on a smaller thickness of catalyst. When the water vapor was introduced, the growth of CNTs was enhanced than without water. CNTs grew 1.29 mm for 10 min long by adding the water vapor, while CNTs were 0.73 mm long without water vapor for the same period of time. CNTs grew up to 1.97 mm for 30 min prior to growth termination under adding water vapor. As-grown CNTs were characterized by using scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy.

• Journal of Sensor Science and Technology
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• v.23 no.5
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• pp.305-309
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• 2014

Well-ordered $TiO_2$ nanotubes with Au nanoparticles are a desirable configuration to enhance the gas sensing properties such as response and selectivity due to their high surface area to volume ratio and catalytic effect of Au nanoparticles. We have synthesized the well-ordered $TiO_2$ nanotubes directly on a Pt IDEs patterned $SiO_2/Si$ substrate and then decorated Au nanoparticles on inner and outer surface of $TiO_2$ nanotubes using electrodeposition method. The Au-decorated $TiO_2$ nanotubes shows ultrahigh response to $C2_H_5OH$ and the highest increasing ratio to $H_2$ compared with other gases.