Advances in Cn x Nanotube Growth
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ADVANCES IN CNX NANOTUBE GROWTH J. Liu, R. Czerw, S. Webster, D.L. Carroll, Center for Nanotechnology and Department of Physics, Wake Forest University, Winston-Salem NC, U.S.A. J. H. Park and Y. W. Park, School of Physics and Condensed Matter Research Institute, Seoul National University, Seoul 151-747, Korea M. Terrones, Advanced Materials Department, IPICyT, Av. Venustiano Carranza 2425-A Colonia Bellas Lomas, 78210 San Luis Potosi, SLP, Mexico
ABSTRACT Carbon nanotubes containing substitutionally “doped” nitrogen were synthesized using injection chemical vapor deposition methods. X-ray photoelectron spectroscopy comparisons between materials grown with different nitrogen sources suggest that the nitrogen content of the nanotubes has little correlation with the total nitrogen content of the “dopant” gas. Tunneling microscopy and spectroscopy do, however, confirm that drastic distortions occur within the graphene lattice as the nitrogen is substituted. Further, donor states are clearly identifiable within the density of electronic states.
INTRODUCTION Since their discovery [1], carbon nanotubes and related materials have attracted much interest due to their many exceptional properties. Recently, nitrogen doping of carbon nanotubes has gained increasing attention because of the possibility it presents in altering, or tailoring, properties in comparison with pure carbon nanotubes [2,3]. Since the first report on the formation of aligned arrays of N-doped carbon nanotubes by the pyrolysis of aminodichlorotriazine over laser-etched Co thin films at 1050 o C [4], a few different nitrogen containing precursors have been explored in synthesizing nitrogen doped carbon nanotubes, such as benzylamine [5], Ni phthalocyanine [6], melamine [7-10] and by the pyrolysis of pyridine [11-13]. However, the ability to synthesize high yield (in grams) high quality (low defect) nitrogen doped carbon nanotubes is still illusive. Further, it is still unclear how the local bonding and atomic percentage of nitrogen within the growth gas might affect the overall nitrogen content of the nanotubes. In this paper, we report a scale-able synthesis method for highly aligned CNx nanotubes by injection CVD methods. We further compare two different nitrogen sources, pyridine and melamine under different growth conditions. X-ray photoelectron spectroscopy (XPS) shows the nitrogen concentration of these materials is between 1%
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and 2%. Tunneling spectroscopy clearly suggests that the nitrogen is incorporated into the carbon nanotube lattice as a substitutional dopant. EXPERIMENTAL The experimental set up used to synthesize our CNx nanotube materials consists of a two stage tube furnace, with the first zone a preheater used to crack carrier gasses, and the second zone for tube growth. T
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