High-Efficiency Electro-Optic Modulator with Low-Loss Waveguides Fabricated
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The researchers said that electrical contact was established the instant the nanotube was soldered to the second electrode. Metallic conduction was indicated by a linear current–voltage relationship. The researchers connected four nanotubes to microelectrode pairs and obtained reliable ohmic contacts with resistances in the range of 9–29 kΩ. The resistances show no clear correlation to the lengths of the bridges, were unaffected by the nanotube extensions, and were found to be constant in air for several days. The researchers verified the intrinsic conductivity of the soldering material by depositing gold–carbon bridges between microelectrode pairs and measuring the current–voltage characteristics. Ohmic resistances between 80 kΩ and 520 kΩ were observed. By using scanning electron microscopic images to estimate the bridge’s cross section and assuming a 60-Ω serial resistance, the researchers calculated resistivities of ~10-4 Ω cm. TEM analysis revealed that the soldering material is composed of a gold–carbon composite structure with a porous crust of 3–5 nanoparticles surrounding a dense core. “There are strong indications that this core is almost pure gold,” said Bøggild, “and we know now how to control the core diameter with respect to the crust to engineer the composition of the material. Attaching multiwalled CNTs to microelectrodes with a nonmetallic carbonaceous material resulted in devices with electrical conduction in the megohm range, which the researchers believe indicates that the metallic content of the soldering material is necessary for good electrical contact. The researchers found the soldering bonds to be mechanically strong compared to the multiwalled CNTs. Further quantitative investigation will involve integration of a piezoresistive force sensor into their setup. The researchers said that they “anticipate automated electron-beam nanosoldering to be useful for quickly connecting complex circuitry consisting of nanoscale components in a way similar to the soldering of electronic components on the macroscale.” Bøggild added, “The solder material is a metal-containing gas, the soldering iron is a beam of electrons, but apart from that, it’s basically the same thing.” STEVEN TROHALAKI
Electrochemical Technique Forms High Corrosion-Resistant Silicate Layer on Zn-Plated Steel Currently, Cr conversion coatings, which are deposited from toxic hexavalent baths, are used to protect steel, zinc, and other metals from corrosion, but silicate MRS BULLETIN/MARCH 2003
coatings are being considered as a substitute. The silica deposit yields better corrosion characteristics as compared to Cr conversion coatings, but the fabrication procedure is laborious, time-consuming, and not suitable for commercial application. As reported in the February issue of Electrochemical and Solid-State Letters, a group of researchers from the University of South Carolina and Elisha Technologies Co. have synthesized a stable deposit with uniform layers of SiO2 on a zinc surface by cathodic electrolysis of zinc-plated panels. B.N.
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