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Growth and properties of Si–N–C–O nanocones and graphitic



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Growth and properties of Si N C O nanocones and graphitic nanofibers synthesized using three nanometer diameter iron platinum nanoparticle catalyst H Cuia Oak Ridge National Laboratory Oak Ridge Tennessee 37831 X Yang Department of Materials Science and Engineering University of Tennessee Knoxville Tennessee 37996 H M Meyer and L R Baylor Oak Ridge National Laboratory Oak Ridge Tennessee 37831 M L Simpson Department of Materials Science and Engineering University of Tennessee Knoxville Tennessee 37996 and Oak Ridge National Laboratory Oak Ridge Tennessee 37831 W L Gardner and D H Lowndes Oak Ridge National Laboratory Oak Ridge Tennessee 37831 L An and J Liu Department of Chemistry Duke University Durham North Carolina 27708 Received 23 July 2004 accepted 3 January 2005 Cone shaped nanostructures of mixed composition nanocones and largely graphitic nanofibers were synthesized on silicon substrates using iron platinum alloy nanoparticles as the catalyst in a direct current plasma enhanced chemical vapor deposition reactor The catalyst nanoparticles were monodisperse in size with an average diameter of 3 1 nm The nanocones were produced on laterally widely dispersed catalyst particles and were oriented perpendicular to the substrate surface with an amorphous internal structure The nanocones were produced by gas phase mixing and deposition of plasma sputtered silicon nitrogen carbon and oxygen species on a central backbone nucleated by the Fe Pt catalyst particle Field emission measurements showed that a very high turn on electric field was required for electron emission from the nanocones In contrast the graphitic nanofibers that were produced when silicon sputtering and redeposition were minimized had the stacked cup structure and well defined voids could be observed within nanofibers nucleated from larger catalyst particles I INTRODUCTION Growth of isolated and vertically aligned carbon nanofibers VACNFs is interesting for fundamental understanding of nanomaterial growth mechanisms and for potential practical applications that include field emission cathodes for vacuum nanoelectronic devices1 highly parallel e beam lithography 2 cellular membrane mimics 3 electrochemical probes of viable cells 4 and scanning probe tips 5 Extensive studies using a plasma enhanced chemical vapor deposition PECVD process have demonstrated that VACNF growth is highly deterministic in a Address all correspondence to this author e mail cui ornl gov DOI 10 1557 JMR 2005 0106 850 J Mater Res Vol 20 No 4 Apr 2005 that a single VACNF can be grown wherever an appropriately sized catalyst particle is formed generally by using e beam lithography EBL for patterning small evaporated catalyst metal dots 6 8 and complete VACNF arrays can be grown at temperatures 700 C 7 9 The wall structure of VACNFs is quite imperfect compared to concentric hollow carbon nanotubes consisting of disordered layers of sp2 bonded graphitic carbon with a bamboo like or stacked cup cross section 7 10



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