Key Engineering Materials Vol. 566

Abstract: Films of hexagonal BN (h-BN) codoped with Mg and O atoms were grown on n-type Si and quartz substrates heated at 500 °C by sputtering targets consisting of h-BN and MgO powders. An absorption is seen at a wavelength < 400 nm for h-BN films prepared in an Ar atmosphere. In contrast, films prepared from the target containing 0.25 mol% MgO in an atmosphere of Ar + 1% O₂ shows an absorption at a wavelength < 260 nm and an electron field emission at a lower electric field of 3.6 V/μm.

Abstract: Thin films of a composite of molybdenum disilicide (MoSi₂) and silicon (Si) were fabricated by radio frequency magnetron sputtering using a target made of a powder mixture of MoSi₂ and Si with a Si-to-Mo molar ratio of 1:X (2.0 X 2.5). The Hall coefficients were measured to identify the conduction mechanisms in the thin films. The sign and magnitude of the Hall coefficients revealed that thin films with X = 2.02.2 having a hexagonal crystal structure showed p-type conduction, while the mechanism for the n-type film with X = 2.33 was unknown and that for a composite of hexagonal and an unknown structure with X = 2.3, 2.4 and 2.5 showed mixed conduction.

Abstract: Thin films of (La,Sr)MnO₃ (LSMO) were fabricated by industrial-versatile chemical solution deposition (CSD) technique. Well [100]-oriented LSMO films were fabricated at 650-750 °C by use of buffer layers of LaNiO₃ buffer layer on a silicon substrate. The product of lower electrical resistivity is promising as an electrode of fatigue-free ferroelectric capacitor.

Abstract: Films containing ZnO quantum dots (ZnO QDs) with ca.5 nm in size were grown at 125°C by chemical vapor deposition. An emission is seen at a wavelength of 367 nm in photoluminescence spectra of the ZnO QDs, and its intensity is enhanced after the deposition of a Ga₂ZnO₄ film on the ZnO QDs. Using the films of ZnO QDs, we fabricated PIN devices constructed from In_1.8Zn_0.2O₃ / InGaZnO₄ / ZnO QDs / Ga₂ZnO₄ / Ni_0.7Zn_0.3O / Ni. The PIN devices exhibit good rectification characteristics.

Abstract: Films of titanium dioxide (TiO₂) were deposited by aerosol deposition at room temperature. Anatase TiO₂ powders were used. The crystal structure of these films was a mixture of the anatase and brookite TiO₂ phases, while the rutile TiO₂ phase was observed at high carrier gas flow rates. The TiO₂ film thickness increased in proportion with the scan time and the carrier gas flow rate. Film thickness was constant at constant total deposition times. Flake-like and mesh-like surface morphologies were observed on the films. The direct-current resistivity was estimated from the dielectric constant and the loss tangent; it was found to be much smaller than that of bulk TiO₂. We speculate that this low resistivity is due to reduction of TiO₂ particles during room-temperature impact consolidation in a N₂ atmosphere.

Abstract: The absence of cracks and a high optical transparency are critical factors for obtaining high performance when TiO₂ thin films are used as cathodes in dye-sensitized solar cells (DSSCs). Synthesized and classified TiO₂ nanoparticles were deposited by constant-current electrophoresis in ethanol. The optical transparency of thin films and the DSSC efficiency increased rapidly with decreasing particle size and increasing film homogeneity. This increase in the DSSC efficiency suggests that the electron conduction path in a thin film consists of connections in the crystal lattice formed between TiO₂ nanoparticles. This formation of connections increases the electron diffusion length.

Abstract: Titanium dioxide nanotubes (TNTs) were grown by anodic oxidation of a titanium thin film deposited on an indium tin oxide (ITO) glass substrate. The TNTs were arranged densely and formed a thin film on the ITO substrate. Anodic oxidation was carried out at 550oC in an electrolyte. The inner diameter and tube length of a grown TNT were approximately 15 nm and 0.5 μm, respectively. Several of the TNT tube openings were closed by lids. These lids could be removed by sputter etching for a short time. The crystal structure was non-crystalline. The power conversion efficiency of a dye sensitized solar cell fabricated using the TNT thin film as a negative electrode is much smaller than that fabricated using conventional TiO₂ nanoparticle thin films, at present.

Abstract: Polycrystalline sample of the reduced barium titanate Ba₄Ti₁₂O₂₇ was prepared by solid state reaction in Ar atmosphere. The magnetic susceptibility was nearly temperature independent in the range of 75-300 K, suggesting the Van Vleck Paramagnetism. The temperature dependence of the electric conductivity does not obey any Arrhenius type behavior.

Abstract: A low-cost composite electromagnetic wave absorber made of sendust dispersed in resin was developed that does not contain any rare metals. In this study, spherical sendust particles with average particle sizes of approximately 5 and 20 μm were dispersed in polystyrene resin at volume ratios in the range 2040 vol% to broaden the absorption frequency bandwidth at frequencies above 10 GHz. The optimal volume ratios of sendust with average particle sizes of approximately 5 and 20 μm were found to be approximately 30 and 35 vol%, respectively. Electromagnetic wave absorbers can be flexibly designed by controlling the volume ratio of spherical sendust particles in resin.

Abstract: With the goal of fabricating varistors with low varistor voltages, we investigated the effects of adding Ba and Si to BiCoMn-added ZnO varistors on the varistor voltage and the resistance to electrical degradation. Ba₂Mn₃O₈, which reduces the resistance to electrical degradation, was not formed at the grain boundary when Si was added. The resistance to electrical degradation was considerably improved by adding 0.10.15 mol% Si relative to samples to which small amounts of Sb had been added. The varistor voltage increased monotonically with increasing amount of added Si; it was approximately 36 V/mm for 0.1 mol% Si.