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Honolulu, Hawaii, United States, 2006/09/28 - A research group in Spain now reports that sulfur may be used as a highly efficient additive in chemical vapor deposition (CVD) processes, allowing enhanced selectivity in the synthesis of helical and Y-shaped CNTs.
Individual carbon nanotubes (CNTs) of different structural and thus electronic characteristics can be joined to build up three-terminal logic devices. However, today this can only be achieved using highly sophisticated nanomanipulation processes. The direct growth of intrinsic functional CNT elements such as Y-shaped CNTS (YCNTs) and helical CNTs (HCNTs) can be considered as an important alternative. YCNTs already have proven to show rapid and nonlinear transistor action without the need for external gating, while HCNTs could be used as inductive elements offering rapid signal processing. Additionally, HCNTs have shown operational functionality as high sensitivity force and mass sensors and are of great interest for nanoelectromechanical systems (NEMS). A research group in Spain now reports that sulfur may be used as a highly efficient additive in chemical vapor deposition (CVD) processes, allowing enhanced selectivity in the synthesis of helical and Y-shaped CNTs.
CVD techniques are widely used to fabricate these functional CNT elements. It has been reported previously that sulfur can be used to produce HCNTs, YCNTs or even double-wall carbon nanotubes. However, the situation seemed to be quite controversial under which conditions a specific type of these above mentioned tubes could grow. To research the possible effects of sulfur on the growth of CNTs, the Spanish group carried out two approaches: (a) for the first time sulfur is added to the sol–gel catalysts directly at the stage of their fabrication (sulfonated catalysts), and (b) sulfur is introduced in the form of thiophene vapor into the reaction system containing the original non-sulfonated sol–gel catalysts.
Dr. Ana Benito, a member of the Group of Carbon Nanostructures and Nanotechnology at Instituto de Carboquimica in Zaragoza, Spain, explained the scientific core of her group's findings to Nanowerk: "Our results underline the general importance of the nature of the sol-gel matrix itself for the formation of HCNTs as well of the local fluctuations in the gas phase for the growth of YCNTs. We show that additives efficiently can be used to control the catalyst system during preparation with respect to its composition and catalyst-support interaction, as well as to control the processes in the gas phase with respect to local fluctuations."
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By Michael Berger, Copyright 2006 Nanowerk, LLC