Polythiophene Nanowires Written onto Si Wafers
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stopping the light exposure, thus giving the researchers control over the shape and size of the nanoparticles. “When you go from a sphere to a prism you get new properties—new optical properties, electrical properties, chemical properties, and catalytic properties,” said Mirkin, who is the George B. Rathmann Professor of Chemistry at Northwestern. “It’s the same material, but a different shape and size. And that makes all the difference.”
Polythiophene Nanowires Written onto Si Wafers Chemists at Duke University have prepared polythiophene nanowires on semiconducting and insulating Si wafers using an atomic force microscope-based direct-writing technique: electrochemical dip-pen nanolithography. Faculty members J. Liu and M.W. Grinstaff and graduate students B.W. Maynor and S. Filocamo report in the January 30 issue of the Journal of the American Chemical Society that 3,4-ethylenedioxythiophene (EDOT) can be electrochemically polymerized at an AFM tip/Si surface interface to afford well-defined sub-100-nm wires of polyEDOT. To pattern these nanostructures, an EDOT-coated AFM tip is translated across the Si wafer while a negative bias voltage is applied to electrochemically polymerize the monomer. Nanowire morphology is controlled by applied voltage and tip translation speed. According to Grinstaff and Liu, the capability to pattern poly-EDOT on insulating surfaces provides a means to use this polymer in future nanodevices. When combined with other micro- and nanofabrication techniques, this approach provides opportunities for designing and developing devices for a wide range of applications in the electronics, pharmaceutical, and biotechnological industries, they said.
Supercritical-Fluid-Extraction Method Cleans RadioactiveContaminated Soil By applying a ligand-assisted supercriticalfluid-extraction method, chemists at the Idaho National Engineering and Environmental Laboratory have decontaminated a sample of soil spiked with 239 Pu and 241Am. They used pressurized, heated carbon dioxide and an added metal-binding chemical compound to clean the soil, removing >69% of the plutonium and americium. As reported in the October 2001 issue of Radiochemica Acta, a chemical agent
added to the carbon dioxide flowed through the soil and grabbed the plutonium and americium, whisking the compound back into the fluid-like carbon dioxide. The carbon dioxide was then shunted out of the soil and depressurized, dropping the compound into a vial on its way back into the atmosphere. The researchers added ethanol and said they could add different chemical agents to improve the efficiency of the extraction. The chemists reported that the supercritical-fluid-extraction method leaves the soil intact. Chemist Robert Fox said that other methods used, such as nitric-acid extraction, dissolved 25% of the soil mass. He said, “Dissolving soil in nitric acid creates a radioactive sludge that must still be disposed of.” The chemists said that the effectiveness of the supercritical-fluid-extraction method in removing radioactive elements from
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