Seongjae Boo

Fabrication and optical characteristics of a novel optical fiber doped with the Au nanoparticles.

Optical fibers containing gold metal nanoparticles were developed by modified chemical vapor deposition, in which Au(OH)3 and tetraethyl-orthosilicate (TEOS) was used via sol-gel process to incorporate gold metals by providing the reduction atmosphere. The absorption peak appeared near 490 nm was found to be due to the surface plasmon resonance of the gold nanoparticles incorporated in the fiber core.

Luminescence enhancement by Au nanoparticles in Er(3+)-doped germano-silicate optical fiber.

We report on the fabrication of the Au nanoparticles/Er(3+) codoped germano-silicate fibers by modified chemical vapor deposition and solution doping processes. Absorption and luminescence characteristics of the Er(3+)-doped germano-silicate fibers incorporated with Au nanoparticles in the core of the fibers were investigated. The Au nanoparticles were found to be effective absorbents for hydroxyl groups to enhance the luminescence of Er(3+) ions upon pumping with the 980nm laser diode.

Mesoporous manganese dioxide cathode prepared by an ambient temperature synthesis for Na-ion batteries

A manganese dioxide (γ-MnO2) cathode was prepared by a simple ambient temperature redox reaction method for Na-ion batteries. The X-ray diffraction (XRD) pattern of the as-prepared sample annealed to low-temperatures (∼200 °C) revealed diffraction peaks confined to the orthorhombic phase of γ-MnO2. The particle morphology of the sample, as revealed by the electron microscopy studies, was comprised of aggregated nanowire crystallites with diameters and lengths in the range of 2–3 and 25–40 nm, respectively. From the N2 adsorption and Brunauer Emmett Teller (BET) studies, the average pore diameter and the surface area of the annealed γ-MnO2 was determined to be 3.77 nm and 148 m2 g−1 respectively and thereby the mesoporous sample characteristics were confirmed. When employed in a Na/MnO2 cell, the mesoporous γ-MnO2 cathode registered initial discharge and charge capacities of 234 and 233 mA h g−1 with almost 100% Coulombic efficiency. Although gradual capacity fading was observed on successive electrochemical cycling, the present study confirms the use of mesoporous electrodes as suitable Na-intercalation/de-intercalation hosts for emerging sodium battery applications.

Structural and Electrical Properties of Polysilicon Films Prepared by AIC Process for a Polycrystalline Silicon Solar Cell Seed Layer

Polycrystalline silicon (pc-Si) films are produced by aluminum-induced crystallization (AIC) process for a polycrystalline silicon solar cell seed layer, and the structural and electrical properties of the films are analyzed. The used structure is glass/Al/ Al2O3/a-Si, and the thickness of Al2O3 layer was varied from 2 nm to 20 nm to investigate the influence of the Al2O3 layer thickness on the formation of the polycrystalline silicon. The annealing temperature and annealing time were fixed to 400∘C and 5 hours, respectively, for the AIC process conditions. As a result, it is observed that the average grain size of the pc-Si films is rapidly smaller with increasing the thickness of Al2O3 layer, whereas the film quality, as defects and Hall mobility, was gradually degraded with only small difference. We obtained the maximum average grain size of 15 μm for the pc-Si film with the thickness of Al2O3 layer of 4 nm. The best resistivity and the Hall mobility was 6.1×10−2 Ω⋅cm and 90.91 cm2/Vs, respectively, in the case of 8 nm thick Al oxide layer.

Investigation of aluminum-induced crystallization of amorphous silicon and crystal properties of the silicon film for polycrystalline silicon solar cell fabrication

Polycrystalline silicon (pc-Si) films are fabricated and characterized for application to pc-Si thin film solar cells as a seed layer. The amorphous silicon films are crystallized by the aluminum-induced layer exchange (ALILE) process with a structure of glass/Al//a-Si using various thicknesses of layers. In order to investigate the effects of the oxide layer on the crystallization of the amorphous silicon films, such as the crystalline film detects and the crystal grain size, the layer thickness arc varied from native oxide to 50 nm. As the results, the defects of the poly crystalline films are increased with the increase of layer thickness, whereas the grain size and crystallinity are decreased. In this experiments, obtained the average pc-Si sub-grain size was about at relatively thin layer thickness ( 16 nm). The preferential orientation of pc-Si sub-grain was .

UV Photoluminescence of Alumino-Germano-Silicate Glass Optical Fiber Incorporated with Gd2O3 Nano-Particles Upon Illumination of Xenon-Lamp

Alumino-germano-silicate glass optical fiber incorporated with Gd2O3 nano-particles (NPs) was developed by using the modified chemical vapor deposition and the drawing process. The formation of spherical Gd2O3 NPs in the fiber core with average diameter of 10.8 nm was confirmed by the TEM. The distinct absorption peaks in the fiber preform appearing in the UV region at 205, 247, 253, 274, and 312 nm were due to the incorporated Gd2O3 NPs via reorganization of the seven 4f electrons into various multiplets of Gd ions. In the case of the optical fiber obtained by drawing of the preform at high temperature about 2150 °C, absorption peaks due to Gd2O3 NPs were found to appear at 383 and 455 nm, which were red-shifted from 274 and 312 nm of the preform, respectively, and it may be due to increase in the size of Gd2O3 NPs after the drawing process. To investigate the photoluminescence (PL) property for UV sensor applications, the PL of the fiber was obtained by illumination of the Xenon-lamp. A PL band appeared in the wavelength band from 370 nm to 450 nm, centering at about 400 nm, which can be attributed to the presence of Gd2O3 NPs embedded in the fiber core. It was also found that the PL intensity at 400 nm showed linear dependence with the excitation power from 0 to 400 W.

Properties of poly silicon films deposited on silicon seed-layers prepared by AIC process

A polycrystalline silicon (pc-Si) film is produced by low-temperature LPCVD process on a poly silicon seed layer. The properties of such film are characterized and compared with the films on a glass substrate and a silicon wafer. The poly crystalline silicon seed layers are fabricated by aluminum-induced crystallization (AIC) process with a glass/Al/Al2O3/a-Si structure, in which the Al layer was deposited on the glass substrate by a DC magnetron sputter, and a-Si film by PECVD method, respectively. After the AIC process with 400°C for 150min, the poly silicon film has the average grain size of about 10μm. The poly silicon seed layer is thickened (i.e. the poly silicon film is deposited on the seed layer) by LPCVD process with 600°C for 60min. As results, it is observed that the quality of the poly silicon film on the seed layer is better than that on the glass and worse than that on the silicon wafer. But the deposited poly silicon absorber layer could not reflect the property of the poly silicon seed layer, due to the relatively low temperature process.

Temperature and Vibration Dependence of the Faraday Effect of Gd2O3 NPs-Doped Alumino-Silicate Glass Optical Fiber

All-optical fiber magnetic field sensor based on the Gd2O3 nano-particles (NPs)-doped alumino-silicate glass optical fiber was developed, and its temperature and vibration dependence on the Faraday Effect were investigated. Uniformly embedded Gd2O3 NPs were identified to form in the core of the fiber, and the measured absorption peaks of the fiber appearing at 377 nm, 443 nm, and 551 nm were attributed to the Gd2O3 NPs incorporated in the fiber core. The Faraday rotation angle (FRA) of the linearly polarized light was measured at 650 nm with the induced magnetic field by the solenoid. The Faraday rotation angle was found to increase linearly with the magnetic field, and it was about 18.16° ± 0.048° at 0.142 Tesla (T) at temperatures of 25 °C–120 °C, by which the estimated Verdet constant was 3.19 rad/(T∙m) ± 0.01 rad/(T∙m). The variation of the FRA with time at 0.142 T and 120 °C was negligibly small (−9.78 × 10−4 °/min). The variation of the FRA under the mechanical vibration with the acceleration below 10 g and the frequency above 50 Hz was within 0.5°.

Characterization of polycrystalline silicon films produced by aluminum-induced layer exchange for the various thicknesses of an aluminum oxide layer

We characterized polycrystalline silicon films produced by aluminum-induced layer exchange (ALILE) for the various thicknesses of an aluminum oxide layer. The pc-Si film is fabricated by the ALILE process with a structure of glass/Al/Al<inf>2</inf>O<inf>3</inf>/a-Si for application to a seed layer of polycrystalline silicon (pc-Si) solar cells using dc and RF sputtering, and PECVD methods, respectively. For investigation of the effects of oxide film thickness on the crystallinity in the ALILE process, the thickness of Al<inf>2</inf>O<inf>3</inf> was varied from 4 to 50 nm including native oxidation in the ambient atmosphere. For characterization OM, SEM, Raman spectroscopy analyses are carried out. As results, the crystallinity was exponentially decayed with increase of Al<inf>2</inf>O<inf>3</inf> thickness. Also, the grain size is decreased with increase of Al<inf>2</inf>O<inf>3</inf> layer thickness. The maximum pc-Si grain size of about 60 µm is obtained at the relatively thin oxide layer. The preferential crystal orientation was (111) and more dominant for the thinner Al<inf>2</inf>O<inf>3</inf> layers. In this work the effects of Al<inf>2</inf>O<inf>3</inf> film thickness on the crystallization properties of a-Si by ALILE process are closely demonstrated such as grain size, preferential crystal orientation, and crystallinity.

Electrochemical Hydrogenation Behavior of Surface-Treated Mg-based Alloys for Hydrogen Storage of Fuel Cell

The effects of surface treatment on the hydrogen storage properties of a alloy particle were investigated by the microvoltammetric technique, in which a carbon-filament microelectrode was manipulated to make electrical contact with the particle in a KOH aqueous solution. It was found that the hydrogen storage properties of at room temperature were improved by the surface treatment with a nickel plating solution. The sodium salts(sodium phosphate and sodium dihydrogen citrate) contained in the nickel plating solution made the alloy form an amorphous-like state, resulting in an improved hydrogen charge/discharge capacity at room temperature as high as about 150[mAh/g] from the original value of 17[mAh/g]. Potential-step experiment was carried out to determine the apparent chemical diffusion coefficient of hydrogen atom() in the alloy. Since the alloy particle we used here was a dense, conductive sphere, the spherical diffusion model was employed for data analysis. was found to vary the order between over the course of hydrogenation and dehydrogenation process.