• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.380-380
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• 2011

ZnO nanorod (NR) arrays prepared via simple ammonia hydrothermal method exhibiting superhydrophilicity, high transmittance and antireflection. These properties result from the unique surface structure and material property of ZnO NR arrays. Highly rough surface due to ZnO NRs enhanced hydrophobicity/hydrophilicity of the films and short NRs (about 300 nm) made ZnO arrays transparent. ZnO NR films were chemically modified by dipping the sample into 5mM stearic acid/ethanol solution for 3 hours. Then the ZnO NRs became superhydrophobic surfaces, whose contact angle reached 159.2$^{\circ}$ maintaining their high transmittance. These biomimetic ZnO NR arrays can be used in diverse field, such as antifogging/self-cleaning surfaces and optical devices.

• Journal of Magnetics
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• v.18 no.3
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• pp.276-282
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• 2013

In this paper, magnetic flux distributions of several permanent magnet arrays, including Halbach array, are analyzed and compared. Also, braking force characteristics on a moving solid conductor in the eddy current brake systems with such magnet arrays are analyzed. Then, a new performance index taking into account the maximum braking force and the volume of the magnet is introduced for the comparison and case study of permanent magnet arrays. By changing the lengths, magnetization directions and the height of the permanent magnet arrays, a higher braking force per volume of the magnet can be achieved.

• Nuclear Engineering and Technology
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• v.53 no.12
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• pp.4080-4092
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• 2021

In this study, the performance of sequence tracking methods for multiple interaction events in specific CdZnTe Compton imagers was evaluated using Monte Carlo simulations. The Compton imager consisted of a 6 × 6 array of virtual Frisch-grid CZT crystals, where the dimensions of each crystal were 5 × 5 × 12 mm³. The sequence tracking methods for another Compton imager that consists of two identical CZT crystals arrays were also evaluated. When 662 keV radiation was incident on the detectors, the percentages of the correct sequences determined by the simple comparison and deterministic methods for two sequential interactions were identical (~80%), while those evaluated using the minimum squared difference method (55-59%) and Three Compton method (45-55%) for three sequential interactions, differed from each other. The reconstructed images of a 662 keV point source detected using single and double arrays were evaluated based on their angular resolution and signal-to-noise ratio, and the results showed that the double arrays outperformed single arrays.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.6
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• pp.994-1002
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• 2008

In this paper a novel tracking system is described, regarding the influence of shadow between array, aimed at improving the efficiency of PV tracking system. Comparing with a building site versus capacity power, domestic solar powers have a limited siting. Therefore, each array interferes with the shadow of other arrays. The loss by influence of those shadow can be compensated for by means of control algorithm of the tracking device. The paper suggests a method controlling an altitude for length which is received the shadow influence of PV array. By using an azimuth of current solar position and the length between arrays, the controller of tracking device is able to calculate the length between actual arrays and make a comparison of the shadow length at a specific time with the length between arrays. When the shadow length is longer than the length between arrays, the controller of tracking device can adjust a position by compensating error altitude of the length between arrays at an altitude of current solar position. In the paper, we develop the control algorithm able to minimize the loss caused by the influence of shadow on the PV tracking system, and compared this with conventional output system. The controller has been tested in the laboratory with proposed algorithm and shows excellent performance.

• Composites Research
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• v.29 no.4
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• pp.132-137
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• 2016

Based on mussel-inspired polydopamine (PDA), a novel technique to fabricate carbon nanowire (CNW) arrays is presented for a possible use of porous carbon electrode in electrochemical energy storage applications. PDA can give more porosity and nitrogen-doping effect to carbon electrodes, since it has high graphitic carbon yield characteristic and rich amine functionalities. Using such outstanding properties, the applicability of PDA for electrochemical energy storage devices was investigated. To achieve this, the decoration of the CNW arrays on carbon fiber surface was performed to increase the surface area for storage of electrical charge and the chemical active sites. Here, zinc oxide (ZnO) nanowire (NW) arrays were hydrothermally grown on the carbon fiber surface and then, PDA was coated on ZnO NWs. Finally, high temperature annealing was performed to carbonize PDA coating layers. For higher energy density, manganese oxide ($MnO_x$) nanoparticles (NPs), were deposited on the carbonized PDA NW arrays. The enlarged surface area induced by carbon nanowire arrays led to a 4.7-fold enhancement in areal capacitance compared to that of bare carbon fibers. The capacitance of nanowire-decorated electrodes reached up to $105.7mF/cm^2$, which is 59 times higher than that of pristine carbon fibers.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.357.1-357.1
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• 2014

Superhydrophobic WOx nanowire (NW) arrays were fabricated using a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting WOx NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic WOx NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of WOx NWs arrays was conducted by changing hydrostatic pressure and surface energy of WOx NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of WOx NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1457-1462
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• 2007

A simple and facile sonochemical route was described for the fabrication of diameter-controlled ZnO nanorod arrays on Si wafers. The diameter of ZnO nanorods was controlled by the concentration of zinc cations and hydroxyl anions in aqueous precursor solution. At high concentration of the precursor solution, thick ZnO nanorod arrays were formed. On the contrary, thin ZnO nanorod arrays were formed at low concentration of the precursor solution. The average diameter of ZnO nanorods varies from 40 to 200 nm. ZnO nanorod arrays with sharp tip were also fabricated by the step-by-step decrease in precursor solution concentration. The crystal structure and optical characteristics of ZnO nanorods were investigated by transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. Growth mechanism of ZnO nanorod arrays was also proposed.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.601-601
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• 2013

Superhydrophobic W18O49 nanowire (NW) arrays were synthesizedusing a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting W18O49 NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic W18O49 NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of W18O49 NWs arrays was conducted by changing hydrostatic pressure and surface energy of W18O49 NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of W18O49 NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.1165-1168
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• 2014

We prepared dye-sensitized solar cells (DSSCs) with enhanced energy conversion efficiency using open-ended $TiO_2$ nanotube arrays with a $TiO_2$ scattering layer. As compared to closed-ended $TiO_2$ nanotube arrays, the energy conversion efficiency of the open-ended $TiO_2$ nanotube arrays was increased from 5.63% to 5.92%, which is an enhancement of 5.15%. With the $TiO_2$ scattering layer, the energy conversion efficiency was increased from 5.92% to 6.53%, which is an enhancement of 10.30%. After treating the open-ended $TiO_2$ nanotube arrays with $TiCl_4$, the energy conversion efficiency was increased from 6.53% to 6.89%, a 5.51% enhancement, which is attributed to improved light harvesting and increased dye adsorption.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.525-531
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• 2011

Two dimensional (2D) arrays of noble metal nanoparticles are widely used in the sensing of nanoscale biological and chemical events. Research in this area has sparked considerable interest in many fields owing to the novel optical properties, e.g., the localized surface plasmon resonance, of these metallic nanoarrays. In this paper, we report successes in fabricating 2D arrays of gold nano-islands using nanosphere lithography. The reproducibility and the effectiveness of the nano-patterning method are tested by means of spin coating and capillary force deposition. We found that the capillary force deposition method was more effective for nanospheres with diameters greater than 600 nm, whereas the spin coating method works better for nanospheres with diameters less than 600 nm. The optimal deposition parameters for both methods were reported, showing about 80% reproducibility. In addition, we characterize gold nano-island arrays both geometrically with AFM as well as optically with UV-VIS spectrometry. The AFM images revealed that the obtained nano-arrays formed a hexagonal pattern of truncated tetrahedron nano-islands. The experimental and theoretical values of the geometric parameters were compared. The 2D gold nano-arrays showed strong LSPR in the absorption spectra. As the nano-islands increased in size, the LSPR absorption bands became red-shifted. Linear dependence of the plasmon absorption maximum on the size of the gold nano-islands was identified through the increment in the plasmon absorption maximum rate for a one nanometer increase in the characteristic length of the nano-islands. We found that the 2D gold nano-arrays showed nearly seven-fold higher sensitivity of the absorption spectrum to the size of the nano-islands as compared to colloidal gold nano-particles.