• Proceedings of the Korean Vacuum Society Conference
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• 2006.08a
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• pp.203-203
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• 2006

• Journal of the Korean Ceramic Society
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• v.45 no.6
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• pp.331-335
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• 2008

The purpose of this study is to characterize the photo-catalytic efficiency of $TiO_2$ nanotube with respect to the distribution of anatase phase which can be changed by the annealing temperature of $TiO_2$ nanotube. $TiO_2$ nanotube was fabricated by the anodization method in the 0.5 wt% HF electrolyte. And then the $TiO_2$ nanotube was annealed at temperatures ranging from $380^{\circ}C$ to $780^{\circ}C$ in dry oxygen ambient for 2 h. For the photo-catalytic water-splitting tests, the photocurrent density was measured as a function of applied potential with a potentiostat using a Ag/AgCl reference, Pt counter electrode, and 1 M KOH electrolyte under illumination of UV by a Xe arc lamp of 1 KW. According to the UV photo-catalytic water-splitting tests, the nanotube annealed at $560^{\circ}C$ was found to show the highest photocurrent density.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.567-567
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• 2012

Since the carbon nanotubes (CNTs) have extraordinary material properties, many researchers are trying to make a practical application in various fields [1]. In particular, the high surface area of CNTs was fascinated for nano-template on the catalytic system. $RuO_2$ coated CNTs are useful functional nano-composites in many applications, including super capacitors, fuel cells, biosensors, and field emitters. However, the research of interaction between CNTs and $RuO_2$ was not satisfied with various fields [2]. In this study, we will introduce the change of chemical and electrical state of $RuO_2$/CNTs at different temperatures by synchrotron radiation photoemission spectroscopy (SRPES). The t-MWCNTs used in this experiment were grown on the Ni/TiN/Si substrates by chemical vapor deposition. $RuO_2$ of 4-20 nm in thickness was deposited on the t-MWNTs by sputter. The SRPES measurements were carried out at the 4B1 beamline of the Pohang Accelerator Laboratory in Korea. The result of XPS measurement indicates that the deposited $RuO_2$ on the CNTs was reduced into pure Ru at above $300^{\circ}C$. And we confirmed that the effective work function of $RuO_2$/CNTs was decreased with increasing temperature.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3730-3734
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• 2011

The degree of self-assembly and the size variation of nanotubular structures in anodic titanium oxide prepared by the anodization of titanium in ethylene glycol containing 0.25 wt % $NH_4F$ at 40 V were investigated as a function of anodization time. We found that the degree of self-assembly and the size of the nanotubes were strongly dependent on thickness deviation and thus indirectly on anodization time, as the thickness deviation was caused by the dissolution of the topmost tubular structures at local areas during long anodization. A large deviation in thickness led to a large deviation in the size and number of nanotubes per unit area. The dissolution primarily occurred at the bottoms of the nanotubes ($D_{bottom}$) in the initial stage of anodization (up to 6 h), which led to the growth of nanotubes. Dissolution at the tops ($D_{top}$) was accompanied by $D_{bottom}$ after the formed structures contacted the electrolyte after 12 h, generating the thickness deviation. After extremely long anodization (here, 70 h), $D_{top}$ was the dominant mode due to increase in pH, meaning that there was insufficient driving force to overcome the size distribution of nanotubes at the bottom. Thus, the nanotube array became disorder in this regime.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.881-885
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• 2004

We report a method for making a device on which semi-conducting single-walled carbon nanotubes are attached selectively between two metal electrodes. This method is divided two processes. First we can connect a rope of single-walled carbon nanotubes(SWNTs) between two electrodes using the electric field. But a SWNTs' rope obtained by the first process was composed of a few of metallic and semi-conducting SWNTs together. The second process is to burn the metallic and semi-conducting nanotubes through applying a voltage. As a result, we can obtain a semi-conducting SWNT device. To make the patterned electrodes, we deposited $SiO_2$(150nm) on a wafer. After then, we made a patterned samples with Ti(200 $\AA$)/Au(300$\AA$). We empirically obtained a electric condition 0.66 $V_{pp}$ /${\mu}{\textrm}{m}$@5MHz. From this result, we verified that most of current go through the metallic nanotubes in this device. When we apply DC voltage between two electrodes, the metallic carbon nanotubes are burnt. Finally, we can obtain a semi-conducting nanotube device which we desire to make. We got the I-V characteristic graph which has shown the semi-conducting property. We hope to apply to the various applications using this selective semi-conducting carbon nanotube deposition method.ethod.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.175-175
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• 1999

Circumventing problems lying in the conventional lithographic techniques, we devised a new method for the fabrication of nanometer scale metal wires inspired by the unique characteristics of carbon nanotubes (CNTs). Since carbon nanotubes could act as masks when CNT-coated thin Au/Ti layer on a SiO2 surface was physically etched by low energy argon ion bombardment 9ion milling), Au/Ti nano-wires were successfully formed just below the CNTs exactly duplicating their lateral shapes. Cross-sectional analysis by transmission electron microscopy revealed that the edge of the metal wire was very sharply developed indicating the great difference in the milling rates between the CNTs and the metal layer as well as the good directionality of the ion milling. We could easily find a few nanometer-wide Au/Ti wires among the wires of various width. After the formation of nano-wires, the CNTs could be pushed away from the metal nano-wire by atomic force microscopy, The lateral force for the removal of the CNTs are dependent upon the width and shape of the wires. Resistance of the metal nano-wires without the CNTs was also measured through the micro-contacts definted by electron beam lithography. since this CNT-based lithographic technique is, in principle, applicable to any kinds of materials, it can be very useful in exploring the fields of nano-science and technology, especially when it is combines with the CNT manipulation techniques.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.615-616
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• 2005

Carbon Nanotubes (CNT) on flexible indium tin oxide (ITO) PET films were prepared for dye-sensitized solar cell (DSSC). These CNTs were prepared by spray coating method for various amount of light transparency. Also, Pt counter electrode was prepared by electro deposition method. All $TiO_2$ electrodes were deposited on ITO-PET films by spray coating method. Micro structural images show that CNT counter electrodes prepared by spray-coating have more dense structure with increasing spraying time (0 to 60 seconds). DSSC consisting of $TiO_2$ electrode and CNT counter electrode was fabricated with various amount of light absorption. DSSC have higher light energy conversion efficiency with increasing the thickness of CNT counter electrode. CNT counter electrode is at least compatible to that of CNT counter electrode.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.5
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• pp.501-509
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• 2016

In this study, a flat-type photocatalytic reactor is applied under solar irradiation for simultaneous treatment of target pollutants: reduction of Cr(VI) to Cr(III) and oxidation of EDCs (BPA, EE2, E2). An immobilized type of photocatalyst was fabricated to have self-grown nanotubes on its surface in order to overcome limitations of powdery photocatalyst. Moreover, Ti mesh form was chosen as substrate and modified to have both larger surface area and photocatalyst content. Ti mesh was anodized at 50V and $25^{\circ}C$ for 30min in the mixed electrolytes ($NH_4F-H_2O-C_2H_6O_2$) and annealed at $450^{\circ}C$ for 2 hours in ambient oxygen to have anatase structure. Surface characterization was done with SEM and XRD methodologies. Fabricated NTT was applied to water treatment, and coexisting Cr(VI) and organics (EDCs) enhanced each other's reactions by scavenging holes and electrons and thus impeding recombination. Also, several experiments were conducted outdoor under direct sunlight and it was observed that both solar-tracking and applying modified photocatalyst were proven to enhance reaction efficiency.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.466.2-466.2
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• 2014

The Quantum dot (QD) solar cells have been under active research due to their high light harvesting efficiencies and low fabrication cost. In spite of these advantages, there have been some problems on the charge collection due to the limitation of the diffusion length. The modification of advanced nanostructure is capable of solving the charge collection problem by increasing diffusion length of electron. One dimensional nanomaterials such as nanorods, nanowires, and nanotubes may enhance charge collection efficiency in QD solar cells. In this study, we synthesized $TiO_2$ anatase nanorod arrays with length of 200 nm by two-step sol-gel method. The morphology and crystal structure for the nanorod were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The anatase nanorods are single-crystalline and possess preferred orientation along with (001) direction. The photovoltaic properties for the heterojunction structure QD solar cells based on the anatase nanorod were also characterized. Compared with conventional $TiO_2$ nanoparticle based QD solar cells, these nanostructure solar cells exhibited better charge collection properties due to long life time measured by transient open circuit studies. Our findings demonstrate that the single crystalline anatase nanorod arrays are promising charge transport semiconductors for heterojunction QD solar cells.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.306-306
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• 2007

The surface was transformed to porous titanium oxide by the anodization of pure titanium. Titanium was anodized in non-aqueous and aqueous electrolytes at different potentials between 5 V and 150 V. Various electrolytes were compose of ethylene glycerol, $H_2SO_4,\;NH_4F\;and\;H_2O$. We obtained titania nanotube arrays on the micro pore of titanium. Micro pores and nano tubes were obtained by anodization at high potentials and low potentials, respectively. Morphologies of nanotubes and micro pore were characterized by FE-SEM. The unique surface structure is very attractive to electrical and medical applications such as gas sensor, biosensor, dental implant and stent.