Cold Spray Deposition of Copper Electrodes on Silicon and Glass Substrates

Copper lines with widths varying from 150 to 1500 μm were deposited onto crystalline silicon wafers and soda-lime glass plates by cold spraying copper particles with 1 μm average diameter through a mask. This direct deposition method yielded high-aspect-ratio electrodes with minimum shadowing effects and maximum electrode-to-silicon contact area. The copper lines had triangular cross sections with aspect ratios (height/width) ranging from 0.1 to 1.1, depending on the number of spray gun passes. Copper particles were densely packed with increasing the width of the masking slit. This study presents the potential use of the cold spray technology in printing lines as front electrodes in solar cell applications.     

Enhanced signal-to-noise ratios in frog hearing can be achieved through amplitude death

In the ear, hair cells transform mechanical stimuli into neuronal signals with great sensitivity, relying on certain active processes. Individual hair cell bundles of non-mammals such as frogs and turtles are known to show spontaneous oscillation. However, hair bundles in vivo must be quiet in the absence of stimuli, otherwise the signal is drowned in intrinsic noise. Thus, a certain mechanism is required in order to suppress intrinsic noise. Here, through a model study of elastically coupled hair bundles of bullfrog sacculi, we show that a low stimulus threshold and a high signal-to-noise ratio (SNR) can be achieved through the amplitude death phenomenon (the cessation of spontaneous oscillations by coupling). This phenomenon occurs only when the coupled hair bundles have inhomogeneous distribution, which is likely to be the case in biological systems. We show that the SNR has non-monotonic dependence on the mass of the overlying membrane, and find out that the SNR has maximum value in the region of amplitude death. The low threshold of stimulus through amplitude death may account for the experimentally observed high sensitivity of frog sacculi in detecting vibration. The hair bundles'' amplitude death mechanism provides a smart engineering design for low-noise amplification.     

Conducting polymer-doped polyprrrole as an effective cathode catalyst for Li-O2 batteries

Polypyrrole conducting polymers with different dopants have been synthesized and applied as the cathode catalyst in Li-O₂ batteries. Polypyrrole polymers exhibited an effective catalytic activity towards oxygen reduction in lithium oxygen batteries. It was discovered that dopant significantly influenced the electrochemical performance of polypyrrole. The polypyrrole doped with Cl⁻ demonstrated higher capacity and more stable cyclability than that doped with ClO₄⁻. Polypyrrole conducting polymers also exhibited higher capacity and better cycling performance than that of carbon black catalysts.     

Characteristics of Nylon 6 nanofilter for removing ultra fine particles

Electrospinning is a fabrication process that uses an electric field to make polymer nanofibers. Nanofibers have a large specific surface area and a small pore size; these are good properties for filtration applications. In this paper, the filtration characteristics of a Nylon 6 nanofilter made by electrospun nanofibers are tested as a function of the fiber diameter. Nanofilter media with diameters in the range of 100–730 nm can be produced in optimized conditions. The pressure drop of a Nylon 6 nanofilter linearly increases with the increasing face velocity. An electrospun Nylon 6 filter (mean fiber diameter: 100 nm) shows a much lower pressure drop performance relative to the commercial HEPA filter media when the filtration efficiency of the Nylon 6 nanofilter and the HEPA filter are over 99.98% with test particles of 0.02–1.0 μm in diameter. The pressure drop at 5 cm/s of the face velocity is measured as 27 mmAq for the Nylon 6 nanofilter media, and 37.1 mmAq for the HEPA filter media. The particle size with minimum efficiency decreases with the decreasing fiber diameter. And the minimum efficiency becomes greater as the fiber diameter is decreased.     

Effects of Co3(PO4)2 coatings on LiNi0.8Co0.16Al0.04O2 cathodes during application of high current

The electrochemical properties of bare and Co₃(PO₄)₂-coated LiNi_0.8Co_0.16Al_0.04O₂ electrodes after high current damage testing were characterized. Damage was induced by cycling with a high current density of 600 m Ag⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.16Al_0.04O₂ electrodes exhibit lower capacity loss and better charge retention than bare LiNi_0.8Co_0.16Al_0.04O₂ electrodes after damage testing. The discharge capacity reduction of bare and Co₃(PO₄)₂-coated electrodes after damage testing were ∼27 and 15%, respectively. The impedance of cells containing bare electrodes remarkably increased after high current cycling, which may be induced by damage to the electrode surface. However, damage was successfully suppressed by the Co₃(PO₄)₂ coating. Bare LiNi_0.8Co_0.16Al_0.04O₂ electrodes developed large amounts of cracks and other extended defects after high current cycling. In contrast, Co₃(PO₄)₂-coated electrodes maintained stable features after high current cycling, indicating the coating layer effectively protected the surface of the LiNi_0.8Co_0.16Al_0.04O₂ powder.     

Numerical analysis of 3-D flow through LNG marine control valves for their advanced design

A numerical analysis of three dimensional incompressible turbulent flows through high pressure drop control valves was carried out by using a CFD-ACE code to develop anti-cavitation control valve used in LNG marine system. For this, numerical simulation was performed on several models of control valve that have different orifice diameters of anti-trim and the size of valve discharge. In this study, flow characteristics of control valves with complex flow fields including pressure drop, cavitation effect and variation of flow coefficient as well as correlation of discharge coefficient were investigated and analyzed. Comparing with conventional control valves, newly designed valves by using the CFD analysis showed an improved flow pattern with reduced cavitation and an anticipated performance characteristic. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Electroless coating of tungsten oxide on the surface of copper powder

Tungsten oxide was successfully deposited on the surface of copper powder and the thickness of coating layer was dependent on deposition time. Because a spontaneous reaction occurred on the interface between copper and tungsten-peroxo electrolyte, there was a maximum thickness that could be obtained, as confirmed from XRD and EDX results. Mesoporous tungsten oxide was also deposited using SDS as a structure directing agent. As-synthesized tungsten oxide was amorphous and, after calcination at 450 °C, crystallized tungsten oxide was produced. Compared to pure tungsten oxide, the tungsten oxide coated copper oxide showed enhanced absorption in the visible region.     

Synthesis and characterization of CuO nanowires by a simple wet chemical method

We report a successful synthesis of copper oxide nanowires with an average diameter of 90 nm and lengths of several micrometers by using a simple and inexpensive wet chemical method. The CuO nanowires prepared via this method are advantageous for industrial applications which require mass production and low thermal budget technique. It is found that the concentration and the quantity of precursors are the critical factors for obtaining the desired one-dimensional morphology. Field emission scanning electron microscopy images indicate the influence of thioglycerol on the dispersity of the prepared CuO nanowires possibly due to the stabilization effect of the surface caused by the organic molecule thioglycerol. The Fourier transform infrared spectrum analysis, energy dispersive X-ray analysis, X-ray diffraction analysis, and X-ray photoemission spectrum analysis confirm clearly the formation of a pure phase high-quality CuO with monoclinic crystal structure.