• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.18.2-18.2
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• 2011

We study and analyze here a novel and simple approach to produce copper oxide nanowires in a methanol as an alternative to chemical synthesis routs and VLS-growth method. First, copper oxide nanowires are grown from copper nanoparticles in methanol at $60^{\circ}C$. Nanoparticles are synthesized via inert gas condensation, one of the dry processes. Synthesized nanowires were confirmed via XRD, FESEM and TEM. As a result, all particles have grown to Cu2O nanowires (20~30 nm in diameter, 5~10 um in length; aspect ratio >160~500). Next, these synthesized oxide nanowires are reduced copper nanowires in the furnace under hydrogen flow at $200{\sim}450^{\circ}C$. The evolution of oxide nanowires and their transformation to copper nanowires is studied as a function of time.

• Korean Journal of Materials Research
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• v.24 no.7
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• pp.388-392
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• 2014

$Cu_2O$ nanowires were synthesized at large scale on copper plate by thermal oxidation in air. The effect of oxidation time and temperature on the morphology of the nanowires was examined. The oxidation time had no effect on the diameter of the nanowires, while it had a great effect on the density and the length of the nanowires. The density and the length of the nanowires increased, and then decreased, with increasing oxidation time. The oxidation temperature had a tremendous effect on the size-distribution as well as the density of the nanowires. When the oxidation temperature was $700^{\circ}C$, uniform size-distribution and high density of the nanowires was achieved. At lower and higher temperatures, the density of the nanowires was lower, and they displayed a broader size-distribution. It is suggested that the $Cu_2O$ nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the nanowires.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.27.1-27.1
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• 2009

In recent years, ZnO nanostructures have drawn considerable attentions for the development of futuristic electronic devices due to their superior structural and optical properties. As the growth of ZnO nanowires by MOCVD is a bottom-up technique, the nature of substrates has a vital role for the dimension and alignment of the nanowires. However, in the pursuit of next generation ZnO based nanodevices, it would be highly preferred if well-ordered ZnO nanowires could be obtained on various substrates like sapphire, silicon, glass etc. Vertically aligned nanowires were grown on A and C-plane sapphire substrates, where as nanopencils were obtained on R-plane sapphire substrates. In addition, C-axis oriented vertical nanowires were also found using an interfacial layer(aluminum nitride film) on silicon substrates. On the other hand, long nanowires were found on Ga-doped ZnO film on glass substrates. Structural and optical properties of the ZnO nanowires on various substrates were also investigated.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.43-49
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• 2002

Gray-colored materials were synthesized from ball-milled ZnO powders under a thermal annealing at 1380$^{\circ}C$ with an argon carrier gas for 3 hours. The synthesized materials were identified to be wurtzitic hexagonal structured ZnO nanowires by X-ray diffraction and scanning electron microscopy. The ZnO nanowires have the long cylinder-like shape of which cross-section is a circle, and these nanowires are in the range 15∼40 nm width and 10-70 $\mu\textrm{m}$ length, respectively. Transmission electron microscopy revealed that these nanowires are single-crystalline and grow along [110] direction. The optical properties of the ZnO nanowires were investigated with photoluminescence. The analytic results revealed that ZnO nanowires have the singly ionized oxygen vacancies in the surface lattices, as they emit strong green light in room temperature PL. In addition, the growth mechanism of the ZnO nanowires can be described by the vapor-solid procedures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.8
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• pp.651-657
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• 2002

Gray-colored materials were synthesized from ball-milled ZnO powders under a thermal annealing at $1380^{\circ}C$ with an argon carrier gas for 3 hours. The synthesized materials were identified to be wurtzitic hexagonal structured ZnO nanowires by X-ray diffraction and scanning electron microscopy. The ZnO nanowires have the long cylinder-like shape of which cross-section is a circle, and these nanowires are in the range 15~40nm width and 10~70 $\mu m$ length, respectively. Transmission electron microscopy revealed that these nanowires are single-crystalline and grow along ［110］ direction. The optical properties of the ZnO nanowires were investigated with photoluminescence. The analytic results revealed that ZnO nanowires have the singly ionized oxygen vacancies in the surface lattices, as they emit strong green light in room temperature PL. In addition, the growth mechanism of the ZnO nanowires can be described by the vapor-solid procedures.

• Korean Journal of Materials Research
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• v.25 no.10
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• pp.543-546
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• 2015

$TiO_2$ nanowires were grown by thermal oxidation of TiO powder in an oxygen and nitrogen gas environment at $1000^{\circ}C$. The ratio of $O_2$ to $N_2$ in an ambient gas was changed to investigate the effect of the gas ratio on the growth of $TiO_2$nanowires. The oxidation process was carried out at different $O_2$/$N_2$ ratios of 0/100, 25/75, 50/50 and 100/0. No nanowires were formed at $O_2$/$N_2$ ratios of less than 25/75. When the $O_2$/$N_2$ ratio was 50/50, nanowires started to form. As the gas ratio increased to 100/0, the diameter and length of the nanowires increased. The X-ray diffraction pattern showed that the nanowires were $TiO_2$ with a rutile crystallographic structure. In the XRD pattern, no peaks from the anatase and brookite structures of $TiO_2$were observed. The diameter of the nanowires decreased along the growth direction, and no catalytic particles were detected at the tips of the nanowires which suggests that the nanowires were grown with a vapor-solid growth mechanism.

• Korean Journal of Materials Research
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• v.24 no.6
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• pp.301-304
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• 2014

The effect of oxygen pressure on the synthesis of ZnO nanowires by means of melt-oxidation of an Al-Zn mixture was investigated. The samples were prepared in oxygen ambient for 1 h at $1,000^{\circ}C$ under oxygen pressure ranging from 0.5 to 100 Torr. ZnO nanowires were formed at oxygen pressures lower than 10 Torr. As the oxygen pressure increased from 0.5 to 10 Torr, the width of the nanowires increased, but their length decreased. The ZnO nanowires had a needle shape, which became gradually thinner toward the tip. X-ray diffraction patterns showed that the nanowires had a hexagonal wurtzite structure. However, ZnO nanowires were not observed when the oxygen pressure increased from 10 Torr to 100 Torr. In roomtemperature cathodeluminescence spectra of the ZnO nanowires, the intensity of ultra-violet emission at 380 nm increased with decreasing oxygen pressure, which indicated that the lower the oxygen pressure, the better the crystallinity of the ZnO nanowires.

• Bulletin of the Korean Chemical Society
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• v.32 no.9
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• pp.3405-3410
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• 2011

We have investigated the cytotoxic potential of tellurium (Te) nanowires in BALB/3T3 fibroblast cells. Te nanowires were synthesized through an aqueous phase surfactant assisted method. Toxicological experiments, such as analysis of morphological changes, MTT assay, DAPI staining, and estimation of intracellular reactive oxygen species, were carried out to reveal the cytotoxic effects of Te nanowires. Te nanowires were found to be cytotoxic at all concentrations tested, in a dose-dependent manner. The UV/Vis spectra of Te nanowires suspended in a culture medium showed drastic changes and disappearance of two broad absorption peaks. The physicochemical properties such as, surface charge, size, and shape of Te nanowires were found to be altered during exposure of cells, due to the instability and agglomeration of nanowires in the culture medium. These results suggest that the chemical components of the DMEM medium significantly affect the stability of Te nanowires. In addition, TEM images revealed that necrosis was the basic pattern of cell death, which might stem from the formation of toxic moieties of tellurium, released from nanowire structures, in the bioenvironment. These observations thus suggest that Te nanomaterials may pose potential risks to environmental and human health.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.27.2-27.2
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• 2010

In recent years, there is a strong requirement of low cost, stable microelectro mechanical systems (MEMS) for resonators, microswitches and sensors. Most of these devices consist of freely suspended microcantilevers, which are usually made by the etching of some sacrificial materials. Herein, we have attempted to use Si nanowires, inherited from the parent Si wafer, as a sacrificial material due to its porosity, low cost and ease of fabrication. Prior to the fabrication of the Si nanowires silver nanoparticles were continuously formed on the surface of Si wafer. Vertically aligned Si nanowires were fabricated from the parent Si wafers by aqueous chemical route at $50^{\circ}C$. Afterwards, the morphological and structural characteristics of the Si nanowires were investigated. The morphology of nanowires was strongly modulated by the resistivity of the parent wafer. The 3-step etching of nanowires in diluted KOH solution was carried out at room temperature in order to control the fast etching. A layer of $Si_3N_4$ (300 nm) was used for the selective fabrication of nanowires. Finally, a freely suspended bridge of zinc oxide (ZnO) was fabricated after the removal of nanowires from the parent wafer. At present, we believe that this technique may provide a platform for the inexpensive fabrication of futuristic MEMS.

• Korean Journal of Materials Research
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• v.22 no.8
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• pp.421-425
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• 2012

Two types of Pt nanoparticle electrocatalysts were composited on Pt nanowires by a combination of an electrospinning method and an impregnation method with NaBH4 as a reducing agent. The structural properties and electrocatalytic activities for methanol electro-oxidation in direct methanol fuel cells were investigated by means of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry. In particular, SEM, HRTEM, XRD, and XPS results indicate that the metallic Pt nanoparticles with polycrystalline property are uniformly decorated on the electro-spun Pt nanowires. In order to investigate the catalytic activity of the Pt nanoparticles decorated on the electro-spun Pt nanowires, two types of 20 wt% Pt nanoparticles and 40 wt% Pt nanoparticles decorated on the electro-spun Pt nanowires were fabricated. In addition, for comparison, single Pt nanowires were fabricated via an electrospinning method without an impregnation method. As a result, the cyclic voltammetry and chronoamperometry results demonstrate that the electrode containing 40 wt% Pt nanoparticles exhibits the best catalytic activity for methanol electro-oxidation and the highest electrochemical stability among the single Pt nanowires, the 20 wt% Pt nanoparticles decorated with Pt nanowires, and the 40 wt% Pt nanoparticles decorated with Pt nanowires studied for use in direct methanol fuel cells.