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We report on the characteristics of indium-oxide-doped ZnO (IZO) ohmic contact to p-GaN. The IZO ohmic contact layer was deposited on p-GaN by a Roll-to-Roll (RTR) sputter method. IZO contact film with a thickness of 360, 230 and 100 nm yielded an ohmic contact resistance of 4.70×10.4, 5.95×10.2, 4.85× 10.1 Ωcm2 on p-GaN when annealed at 600℃ for 1 min under a nitrogen ambient, respectively. While the transmittance of IZO film with a thickness of 360 nm slightly increased in the wavelength range of 380-800 nm after annealing, the transmittance rapidly increased up to 80% after annealing at 600℃ in the wavelength range of 380~430 nm because the crystallization of IZO film and created Ga vacancies near the p-GaN surface region were affected by the annealing. These results indicate that ohmic contact resistance and transmittance of the IZO films improved.

keyword : electrical/electronic materials, sputtering, electrical properties, electrical conductivity/resistivity, transmittance

Silver conducting films were formed from nano-sized silver powders and glass frits prepared by flame spray pyrolysis. The mean sizes of the silver powders and glass frits were 73 and 63 nm, respectively. Nano-sized glass frits improved the adhesion strength of the silver conducting film to the glass substrate. The densities of the silver conducting films increased by increasing the glass contents of the films at firing temperatures of 400 and 500℃. The specific resistances of the silver conducting films with 5 wt.% glass of silver component were 7.8, 4.2 and 2.4 cm at firing temperatures of 400, 450 and 500℃.

keyword : conductors, chemical synthesis, electrical properties, conductivity/resistivity, flame spray pyrolysis

Effects of the surface modification on the deposition behaviors of apatite crystals in Zr-1Nb plates were studied. Zr-1Nb alloy plates were polished with abrasive papers to have different roughness and some of them were treated in NaOH or coated with collagen before deposition of apatites in the simulated body fluid (SBF). The weight gain due to the deposition of apatite crystals increased as the surface roughness increased in Zr-1Nb. The size of granular apatite crystals were found to be smaller in Zr-1Nb roughened by 162 μm abrasive paper than in Zr-1Nb roughened by 8.4 μm paper, suggesting the nucleation rate increased with increase of surface roughness. After, 10 days immersion in a SBF, NaOH-treated Zr-1Nb was completely coated with apatite with the deposited apatite weight comparable to that in Ti-6Al-4V. The deposition rate of Zr-1Nb was not appreciably influenced by NaOH treatment unlike the significant influence of NaOHtreatment on the deposition rate of apatite in Ti-6Al-4V. One significant observation in this study is an appreciable increase of the apatite deposition rate after collagen coating both on Zr-1Nb and Ti-6Al-4V plate, which may be caused by the interaction between collagen and Ca+2 ions.

keyword : biomaterials, deposition, microstructure, scanning electron microscopy, apatite

Two-dimensional computer simulations were conducted on a percolation structure in which the second phases of various aspect ratios were arranged in a lattice (matrix). The second phases were randomly arranged in an array with two different computational programs, one prohibiting an overlap among the second phases and the other allowing the overlap. From the simulation prohibiting the overlap, we predicted that a complete path was formed at smaller amounts of thesecond phase with higher aspect ratios. In the simulation allowing the overlap, a complete path throughout the array was formed by arranging the second phase of an aspect ratio of 1, 5, 20, 100 with less than 59%, 43%, 19%, 4% in the array, respectively. These results agreed with the completion path formation in filament-winded CP-GFRP composites consisting of an insulator matrix (vinyl ester) and electrically conductive graphite additives.

keyword : composites, powder processing, electrical properties, computer simulation, percolation structure