• Korean Journal of Materials Research
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• v.31 no.1
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• pp.43-53
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• 2021

Dynamic behavior of piezoelectric ZnO nanowires is investigated using finite element analyses (FEA) on FE models constructed based on previous experimental observations in which nanowires having aspect ratios of 1:2. 1:31, and 1:57 are obtained during a hydrothermal process. Modal analyses predict that nanowires will vibrate in lateral bending, uniaxial elongation/contraction, and twisting (torsion), respectively, for the three ratios. The natural frequency for each vibration mode varies depending on the aspect ratio, while the frequencies are in a range of 7.233 MHz to 3.393 GHz. Subsequent transient response analysis predicts that the nanowires will behave quasi-statically within the load frequency range below 10 MHz, implying that the ZnO nanowires have application potentials as structural members of electromechanical systems including nano piezoelectric generators and piezoelectric dynamic strain sensors. When an electric pulse signal is simulated, it is predicted that the nanowires will deform in accordance with the electric signal. Once the electric signal is removed, the nanowires exhibit a specific resonance-like vibration, with the frequency synchronized to the signal frequency. These predictions indicate that the nanowires have additional application potential as piezoelectric actuators and resonators.

• Transactions on Electrical and Electronic Materials
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• v.5 no.3
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• pp.93-97
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• 2004

Structural and optoelectronic properties of as-synthesized SnO$_2$ nanowires were examined in this study. The SnO$_2$ nanowires were first synthesized by thermal evaporation of ball-milled SnO$_2$ powders in argon atmosphere without the presence of any catalysts, arid their structural properties are then investigated by X-ray diffraction, Raman scattering, scanning electron microscopy, and transmission electron microscopy. This investigation revealed that the synthesized SnO$_2$ nanowires are single-crystalline and that their growth direction is parallel to the [100] direction. In addition, photoresponse of a single SnO$_2$ nanowire was performed with light with above-gap energy, and different characteristics of photoresponses were obtained for the nanowire at ambient atmosphere and in vacuum. The photoresponse mechanism is briefly discussed in this paper.

• Journal of the Korean Vacuum Society
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• v.22 no.4
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• pp.204-210
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• 2013

In order to improve osseointegration for biomedical implants, it is crucial to understand the interactions between nanostructured surfaces and cells. In this study, $TiO_2$ nanowires were prepared via Vapor-Liquid-Solid (VLS) process with Sn as a metal catalyst in the tube furnace. Nanowires were grown with $N_2$ heat treatment with their size controlled by the agglomeration of Sn layers in various thicknesses. MC3T3-E1 (pre-osteoblast) were cultured on the $TiO_2$ nanowires for a week. Preliminary results of the cell culture showed that the cells adhere well on the $TiO_2$ nanowires.

• Journal of Sensor Science and Technology
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• v.21 no.3
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• pp.180-185
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• 2012

${\gamma}$-ray radiolysis was used to functionalize networked ZnO nanowires with Au nanoparticles. The networked ZnO nanowires were prepared through a vapor phase selective growth method. The sensing performances of the Au-functionalized ZnO nanowires were investigated in terms of $NO_2$, CO and benzene gases. The Au-funtionalized ZnO nanowire sensors showed an applicable, reliable capability to detect the gases, indicating their potential in chemical gas sensors.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.430-430
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• 2013

Field effect transistor based on semiconductor nanowires has been attracting lots of concerns and studies of scientists because of its different characteristic comparing with other morphology like thin film. Nowadays, graphene is introducing a great promise as an active layer in field effect transistor due to its unique electronic and optoelectronic properties. Thus, a mix structure between etched graphene and semiconductor nanowires is believed to expose novel electrical characteristics. In this study, CuO nanowires (20~80 nm in diameter and $1{\sim}10{\mu}m$ length) were grown during oxidizing Cu foil at $450^{\circ}C$ for 24 h. Besides, 3-layersetched graphene was deposited on Cu foil at $1,000^{\circ}C$ using a feedstock of $CH_4$/$H_2$ mixed gas in CVD system. A structure of Ni/Au electrode + CuO nanowires + etched graphene was fabricated, afterward. Finally, field effect properties of the device was revealed and compared with individual devices of just nanowires and just graphene.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.203-203
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• 2015

Gallium Oxide (Ga2O3) has been widely investigated for the optoelectronic applications due to its wide bandgap and the optical transparency. Recently, with the development of fabrication techniques in nanometer scale semiconductor materials, there have been an increasing number of extensive reports on the synthesis and characterization of Ga2O3 nano-structures such as nano-wires, nano-belts, and nano-dots. In contrast to typical vapor-liquid-solid growth mode with metal catalysts to synthesis 1-dimensional nano-wires, there are several difficulties in fabricating the nano-structures by using sputtering techniques. This is attributed to the fact that relatively low growth temperatures and higher growth rate compared with chemical vapor deposition method. In this study, Ga2O3 nanowires (NWs) were synthesized by using radio-frequency magnetron sputtering method. The NWs were then coated by Au thin films and annealed under Ar or N2 gas enviroment with no supply of Gallium and Oxygen source. Several samples were prepared with varying the post annealing parameters such as gas environment annealing time, annealing temperature. Samples were characterized by using XRD, SEM, and PL measurements. In this presentation, the details of fabrication process and physical properties of branched Ga2O3 NWs will be reported.

• Korean Journal of Materials Research
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• v.24 no.8
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• pp.423-428
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• 2014

We synthesized Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell nanowires(NWs) by means of a co-electrospinning method and demonstrated their magnetic properties. To investigate the structural, morphological, chemical, and magnetic properties of the samples, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy were used, as was a vibrating sample magnetometer. The morphology of the nanostructures obtained after calcination at $500^{\circ}C$ exhibited core/shell NWs consisting of $TiO_2$ in the core region and ${\alpha}-Fe_2O_3$ in the shell region. In addition, the XPS results confirmed the formation of Fe-doped $TiO_2$ by the doping effect of $Fe^{3+}$ ions into the $TiO_2$ lattice, which can affect the ferromagnetic properties in the core region. For comparison, pure ${\alpha}-Fe_2O_3$ NWs were also fabricated using an electrospinning method. With regard to the magnetic properties, the Fe-doped $TiO_2/{\alpha}-Fe_2O_3$ core-shell NWs exhibited improved saturation magnetization(Ms) of approximately ~2.96 emu/g, which is approximately 6.1 times larger than that of pure ${\alpha}-Fe_2O_3$ NWs. The performance enhancement can be explained by three main mechanisms: the doping effect of Fe ions into the $TiO_2$ lattice, the size effect of the $Fe_2O3_$ nanoparticles, and the structural effect of the core-shell nanostructures.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.34.1-34.1
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• 2009

A great deal of attention has been focused on ZnO nanowires for various electronics and optoelectronics applications. in the pursuit of next generation nanodevices, it would be highly preferred if well-ordered ZnO nanowires of lower dimension could be fabricated on silicon. Before the growth of nanowires, silicon substrates were selectively etched using silicon nitride as masking layer. Vertical aligned ZnO nanowires were grown by metal organic chemical vapor deposition on patterned silicon substrate. The shape of nanostructures was greatly influenced by the micropatterned surface of the substrate. The aspect ratio, packing fraction and the number density of nanowires on top surface are around 10, 0.8 and $10^7\;per\;mm^2$, respectively, whereas the values are 20, 0.3 and $5\times10^7\;per\;mm^2$, respectively, towards the bottom of the cavity. XRD patterns suggest that the nanostructures have good crystallinity. High-resolution transmission electron microscopy confirmed the single crystalline growth of the ZnO nanowires along [0001] direction.

• Journal of Sensor Science and Technology
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• v.17 no.1
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• pp.69-74
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• 2008

VOCs (Volatile Organic Compound) sensors were fabricated using $SnO_2$nanowires-based thin films and its gas sensing behaviors were studied. The $SnO_2$ nanowires synthesized from a thermal evaporation process were dispersed in a solution and the sensor film was prepared by dropping the slurry on the substrate with the electrodes and an embedded heater. The gas response (Ra/Rg, Ra: resistance in air, Rg: resistance in gas) to $30{\sim}40$ ppm Benzene, Ethyl Benzene, o-xylene were in the range of $39{\sim}42$, which were significantly higher than those to 50 ppm of CO, $CH_4$ and $C_3H_8$ ($12{\sim}19$).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.245-250
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• 2019

We investigated the post-annealing effect of Sn-incorporated β-Ga₂O₃ (β-Ga₂O₃ : Sn) nanowires (NWs) grown on sapphire (0001) substrates using radio-frequency powder sputtering. The β-Ga₂O₃ : Sn NWs were converted to a porous structure during the vacuum annealing process at 800℃. Host non-stoichiometric Ga₂O_3-x, is transformed into stoichiometric Ga₂O₃, where Sn atoms separate and form Sn nano-clusters that gradually evaporate in a vacuum atmosphere. As a result, the amount of Sn atoms was reduced from 1.31 to 0.27 at%. Pores formed on the sides of β-Ga₂O₃ : Sn NWs were observed. This increases the ratio of the surface to the volume of β-Ga₂O₃ : Sn NWs.