CORWIN COUPLED RECIPROCAL WINDOWS

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The quantum device aspects of the project are limited (for the moment) to the study of conductance of carbon nanotubes. The tubes are absorbed from an ethanol solution onto a glass substrate and then metal (either AuPd or Al) is evaporated atop the deposited tubes through an optical lithographic mask (feature size 5 micron) that defines gross features (pads and interconnects). After the evaporation, tubes are "visible" to the nanoManipulator because of the surface features they create as the metal "drapes" over them. Photoresist is spun onto the whole glass plate, and the nanoManipulator is used to carve lithographic images to form the sub-micron features for the electrical measurement of the nanotube. Three separate multiwall tubes have been set in such circuits and studied at room temperature. The combination of selective etchants for AuPd and multiwall tubes is a reliable process for making the metal contacts to the tubes. The resistivity (> 0.1 Ohm - cm) inferred from room-temperature measurements is consistent with theoretical expectations and other experiments. Since these measurements on multiwall tubes are more difficult to interpret tidily and since we have a reliable source of single-wall tubes in Zhou's lab, for now the multiwall tubes have ceased to be the focus of experiments. The more interesting case of single-wall nanotubes (SWNT) has yet to be produced by a reliable process. The HNO_3 used to etch AuPd appears to intercalate and disperse the SWNT bundles that have been exposed when the AuPd is etched away. We have therefore reverted to coating the tubes with Al and the selective etchant for Al appears to be more benign to the SWNT bundles: they remain upon removal of the Al overlayer. At present, room-temperature electrical measurements are proceeding on the exposed SWNT bundles.