A simple method to fabricate high-performance carbon nanotube field emitters

A simple new method to fabricate carbon nanotube field emitters was developed. Single wall carbon nanotubes with high graphitization were attached on Sn or Ni layered glass substrate in-situ in arc-discharge chamber. Post heat treatments below the deformation temperature of soda-lime glass guaranteed a good mechanical adhesion and electrical contact of the nanotubes. The morphology of the metal electrode layers was examined with the heat treatment temperatures to optimize the heat treatments. The emitters formed on Sn layers showed lower turn-on voltage and higher current density than those formed on Ni layers. A good field emission performance was realized in an emitter where nanotubes were deposited on Sn layer of the thickness 100 nm and annealed at 300^∘C. The current density was 2.5 mA/cm² at 3.5 V/μm. The emitter structure was maintained stable for 8 h.     

Fabrication of MgO-coated TiO2 nanotubes and application to dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) are more spotlighted than conventional photovoltaic devices due to their relatively low cost, easy fabrication and high efficiency. However, there are limitations to increase the conversion efficiency of DSCs. The limiting factors are the quantity of dye adsorption and charge recombination between TiO₂ electrode and electrolyte. Coating other materials such as high energy band gap insulators or semiconductors on the TiO₂ electrode enhances dye adsorption and reduces charge recombination. We fabricated DSCs based on bare TiO₂ nanotube arrays and 0.02 and 0.04 M MgO coated TiO₂ nanotube arrays. MgO layer increased the photovoltage and photocurrent. The overall conversion efficiency of DSCs using 0.02 M MgO coated TiO₂ nanotubes was 1.61%. MgO formed insulating layers between TiO₂ nanotube array electrode and electrolyte. Charge recombination was inhibited at the interfaces of TiO₂ nanotube array electrode and electrolyte by MgO insulating layers. MgO coating also improved dye adsorption because iso-electric point (IEP) of MgO was larger than TiO₂. When the IEP of coating material is larger than TiO₂, the chemical attraction between the electrode surface and Ru-based dye molecule is increased.     

A study on the characteristics of hydrated La2O3 thin films with different oxidation gases on the various annealing temperature

In order to investigate the structural and electrical properties of La₂O₃ films deposited by O₂ and O₃, films were hydrated in DI-water and annealed at 600 and 900 °C. La₂O₃ films deposited by O₃ showed better hydration resistance than those deposited by O₂. The thickness of both hydrated films decreased after annealing at 600 °C and increased after annealing at 900 °C. The dielectric constants of the La₂O₃ films deposited by O₃ were greater than films deposited by O₂ after annealing at 600 °C and slightly less after annealing at 900 °C. The leakage current density of the La₂O₃ films deposited by O₃ was lower than those by O₂ after annealing at 900 °C. To this end, La₂O₃ films deposited by O₃ showed better dissolution resistance than O₂ for hydration experiment as a function of dipping time.     

Magnetic properties of insulating RTiO3 thin films

The magnetic properties of epitaxial RTiO₃ (R?=?Y, Eu) thin films are reported. The films were grown on various substrates with different lattice mismatches using the pulsed laser deposition technique. Ferromagnetic YTiO₃ thin films could only be grown on LaAlO₃ (110) substrates, while EuTiO₃ films could be grown on various substrates. The magnetic properties of the grown films are discussed in light of the structural characterization.     

Efficient and ripple-mitigating dc–dc converter for residential fuel cell system

Proton exchange membrane fuel cell (PEMFC) systems for residential application require efficient and ripple-mitigating power conditioning system (PCS). The key point to reach it, is the design and control of the dc–dc converter. Based on the theoretical and experimental analysis of the traditional converter, this paper proposes a novel parallel-series full bridge (P-SFB) dc–dc converter, and improves its phase shifting scheme. This paper also proposes a novel controller for low frequency ripple current suppressing applied on the converter. The experimental results verify that, the dc–dc converter achieves a peak efficiency of 95.5%. Therefore PCS’s maximum efficiency reaches 92.9%. And the input current ripple is reduced significantly with the new controller.     

Applications of Highly-Nonlinear Chalcogenide Glass Devices Tailored for High-Speed All-Optical Signal Processing

Ultrahigh nonlinear tapered fiber and planar rib Chalcogenide waveguides have been developed to enable highspeed all-optical signal processing in compact, low-loss optical devices through the use of four-wave mixing (FWM) and cross-phase modulation (XPM) via the ultra fast Kerr effect. Tapering a commercial As₂Se₃ fiber is shown to reduce its effective core area and enhance the Kerr nonlinearity thereby enabling XPM wavelength conversion of a 40 Gb/s signal in a shorter 16-cm length device that allows a broader wavelength tuning range due to its smaller net chromatic dispersion. Progress toward photonic chip-scale devices is shown by fabricating As₂S₃ planar rib waveguides exhibiting nonlinearity up to 2080 W^-1ldr km^-1 and losses as low as 0.05 dB/cm. The material's high refractive index, ensuring more robust confinement of the optical mode, permits a more compact serpentine-shaped rib waveguide of 22.5 cm length on a 7-cm- size chip, which is successfully applied to broadband wavelength conversion of 40-80 Gb/s signals by XPM. A shorter 5-cm length planar waveguide proves most effective for all-optical time-division demultiplexing of a 160 Gb/s signal by FWM and analysis shows its length is near optimum for maximizing FWM in consideration of its dispersion and loss.     

Application of Ag–ceramic composite electrodes to low firing piezoelectric multilayer ceramic actuators

Ag–ceramic composite materials were investigated as low-cost internal electrodes for low firing piezoelectric multilayer ceramic actuators (MLCA). Ag–ceramic pastes were prepared by adding Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr_0.475,Ti_0.525)O₃ (PMNZT) ceramic powders to a commercial Ag paste in the range of 0 to 50 wt.%. PMNZT/Ag–PMNZT multilayered laminates were fabricated using tape casting and subsequently cofired at 925°C for 10 h. The addition of PMNZT into Ag electrode decreased the thermal shrinkage mismatch between the composite layers, which led to improve mass producibility of MLCA through reducing delamination probability during cofiring process.     

Electrical conductivity of the Al-stabilized La<Subscript>2/3</Subscript>TiO<Subscript>3</Subscript>

A-site deficient lanthanum titanate (La_2/3TiO₃) materials with perovskite structure are attractive due to their electrical applications such as ion conductors and dielectrics. However, its stability at room temperature in air is obtained only if Na or Li etc. is incorporated into La site or Al into Ti site. In this study, the electrical conductivities of La_0.683(Ti_0.95Al_0.05)O₃ have been measured in oxygen partial pressure (Po₂) between 1 and 10⁻¹⁸ atm at 1000~1400°C. The electrical conductivity exhibited −1/4, −1/6 and −1/5 dependence (log σ ∝ log , n = −1/4, −1/6, −1/5) depending upon temperature and Po₂. The defect model explaining the observation was proposed and discussed. The chemical diffusion coefficient was estimated from the electrical conductivity relaxation.     

Selective CO Gas Detection of Zn2SnO4 Gas Sensor

The ability of semiconductor gas sensors to differentiate between gases is essential but difficult to obtain. In this study, Zn₂SnO₄ was made to be CO selective and the possible mechanism for the selectivity was studied.The electrical and the gas-sensing properties of uncoated and CuO-coated Zn₂SnO₄ were investigated. In order to obtain an ohmic contact to Zn₂SnO₄, a ZnO layer was stacked on top of Zn₂SnO₄ and co-fired. CuO was coated by immersing the sintered sample in Cu-containing solution. Both uncoated and CuO-coated samples showed the higher sensitivity to 200 ppm CO gas than to 200 ppm H₂ gas. However, the CuO-coated Zn₂SnO₄ showed much enhanced sensitivity and thus good selectivity for CO gas (S _CO/S _{H 2} 6) compared to the uncoated sample. The excellent selectivity of Zn₂SnO₄-based materials for CO gas was explained by the difference in the mechanisms of CO and H₂ oxidation.     

Electromechanical properties of ternary BiFeO<Subscript>3</Subscript>−0.35BaTiO<Subscript>3</Subscript>–BiGaO<Subscript>3</Subscript> piezoelectric ceramics

In the present work, composition dependent crystal structure, ferroelectric, piezoelectric, and temperature dependent dielectric properties of the BiGaO₃-modified (1–x)(0.65Bi_1.05FeO₃–0.35BaTiO₃) (BFBT35–xBG, where x?=?0.00–0.03) lead-free ceramics were systematically investigated by solid-state reaction method, followed by water quenching process. The substitution of BG successfully diffuses into the lattice of the BFBT ceramics, without changing the pseudo-cubic structure of the samples. The scanning electron microscopy (SEM) results revealed that the average grain size was increased with BG-content in BFBT system. The BFBT–xBG ceramics showed a maximum in permittivity (?_max) at temperatures (T_max) above 500 °C in the compositional range of 0.00?≤?x?≤?0.03. The electro-strain is measured to be 0.125% (d^*₃₃ ~ 250 pm/V) under unipolar fields (5 kV/mm) for BFBT–0.01BG ceramics. The same composition (x?=?0.01), large static piezoelectric constant (d₃₃ ~ 165 pC/N) and electromechanical coupling factor (k_p ~ 25%) were obtained. The above investigated characterizations suggests that BFBT–BG material is favorable for piezoelectric and high temperature applications.