Yo-Min Choi

Thermochemical hydrogen sensor based on chalcogenide nanowire arrays.

The hydrogen gas-sensing properties have been investigated of two types of thermochemical hydrogen (TCH) sensors composed of thermoelectric layers based on chalcogenide nanowire arrays and anodic aluminum oxide (AAO) templates. The monomorphic-type TCH sensor, which had only Bi2Te3 nanowire arrays, showed an output signal of 23.7 μV in response to 5 vol% hydrogen gas at room temperature, whereas an output signal of 215 μV was obtained from an n-p junction-type TCH sensor made of connected Bi2Te3 and Sb2Te3 nanowire arrays in an AAO template. Despite its small deposition area, the output signal of the n-p sensor was more than nine times that of the monomorphic sensor. This observation can be explained by the difference in electrical connections (parallel and serial conversions) in the TCH sensor between each type of nanowire array. Also, our n-p sensor had a wide detection range for hydrogen gas (from 400 ppm to 45 vol%) and a fast response time of 1.3 s at room temperature without requiring external power.

A Novel Method for Fine Patterning by Piezoelectrically Induced Pressure Adjustment of Inkjet Printing

In this paper, a method is proposed for fine line pattern formation on polyimide films by drop-on-demand inkjet printing without the need to reduce the nozzle size. The rapid change in the shape of a piezoelectric actuator caused by a pressure wave causes the fluid to be ejected as droplets. By shortening the duration of the chamber compression period, smaller droplets can be ejected from the nozzle orifice. The pressure wave is a key factor in determination of the line width. A 20-µm-wide line pattern pulsed at 0.5 µs intervals was successfully fabricated using a Cu complex ion ink and a cartridge with volume of 1 pl. This method is expected to be widely used in various applications that demand high-resolution patterning. The 20-µm line width of the conducting track is a particularly useful size for fabrication of transparent electrodes.

Synthesis of macro-mesoporous Pt/alumina catalyst to enhance catalytic activity of hydrogen oxidation

Macro-mesoporous Pt/alumina catalysts were synthesized by the sol-gel process with the assistance of a PS colloidal crystal template to improve the catalytic activity of hydrogen oxidation. Macropores in catalysts improve hydrogen gas diffusion and enhance the accessibility of hydrogen gas to the center of the catalyst. The diffusion coefficients of hydrogen gas in macro- and mesopores were theoretically calculated. The effect of macropores on exothermic properties induced by hydrogen oxidation was investigated using various concentrations of H2/air gas mixture. The temperature increase of macro-mesoporous Pt/alumina was dramatically higher than that of mesoporous Pt/alumina without macropores. The results clearly show that macropores effectively improve the catalytic reaction of hydrogen oxidation.

A noble gas sensor platform: linear dense assemblies of single-walled carbon nanotubes (LACNTs) in a multi-layered ceramic/metal electrode system (MLES)

Monodispersed Pt nanocatalyst-doped and undoped assemblies of single-walled carbon nanotubes (SWCNTs) were aligned with high anisotropy on a multi-layered ceramic/metal electrode system (MLES), which was used as a cheap and cost-effective electrode system, by dielectrophoretic orientation to form linear dense assemblies of SWCNTs (LACNTs). It is envisaged that they can be used as a potentially inexpensive platform for multi-gas sensing nano-devices. To form homogeneously dispersed Pt nanocatalysts (NCs), an aqueous chloroplatinic acid solution (H2PtCl6) was deposited on the surface of acid-treated SWCNTs. This was followed by alignment under the application of alternative currents ranging from 5 kHz to 50 MHz to create electrically conducting LACNT bundles on the MLES platform and reduction under hydrogen plasma. The analysis showed that the Pt nanocatalysts (2 nmav, deviation: ±1 nm) are monodispersed on the SWCNTs, which contributed to a noticeable enhancement in the gas sensing properties towards H2, NO2, H2S and NH3 gases. In addition, the principal component analysis results showed fairly good discrimination of the gases by employing a sensor array composed of Pt/LACNTs and SWCNTs, and the hydrogen sensing performance was high in terms of sensitivity compared to other literature studies. This gas sensing device based on an MLES may pave the way for extended applications of new multi-gas sensing devices as a low-cost and life-long gas sensing platform.

Post-Tensioned Interior Precast Wide Beam—Column Connections Subjected to Lateral Loading

The post-tensioned precast concrete system (PPS) developed in this study consists of U-shaped precast wide beams and concrete columns, where the continuity of wide beam-column joint is provided with the cast-in-place concrete on the U-shaped precast wide beam and the post-tensioning to the beam after casting of slab. The PPS structure can overcome the defect of discontinuity in the connections of precast members using cast-in-place concrete on precast members, and complement the low sectional efficiency of wide beam by applying the post-tensioning. In this study, an experimental investigation was performed with three half-scale specimens of interior connection fabricated employing PPS structure. Specifically, this paper presents the response of PPS interior beam-column joint subjected to cyclic lateral loading and evaluates the relevance of the beam-to-column width ratio criteria specified in ACI 318–05. The test results indicate that the PPS specimens can resist properly seismic loads maintaining overall structural integrity.

Fabrication and Characterization of Hydrogen Getter Based on Palladium Oxide Doped Nanoporous SiO 2 /Si Substrate

The existing metal getters are invariably covered with thin oxide layers in air and the native oxide layer must be dissolved into the getter materials for activation. However, high temperature is needed for the activation, which leads to unavoidable deleterious effects on the devices. Therefore, to improve the device efficiency and gas-adsorption properties of the device, it is essential to synthesize the getter with a method that does not require a thermal activation temperature. In this study, getter material was synthesized using palladium oxide (PdOx) which can adsorb H2 gas. To enhance the efficiency of the hydrogen and moisture absorption, a porous layer with a large specific area was fabricated by an etching process and used as supporting substrates. It was confirmed that the moisture-absorption performance of the SiO2/Si was characterized by water vapor volume with relative humidity. The gas-adsorption properties occurred in the absence of the activation process.