Substitutional Sites of Nitrogen Atoms in Carbon Nanotubes and their Influence on Field-Emission Characteristics

We studied the dependence of mutual position of substitutional nitrogen atoms on the diameter and helicity of carbon nanotubes by using a hybrid B3LYP method. It was found that nitrogen atoms prefer occupying the para-site of a hexagon in armchair nanotubes and to be far apart in zigzag and chiral nanotubes. Even more preferable position for both zigzag and armchair nanotubes is nitrogen location in pentagonal rings at the tube caps. These results are supported by experimental data indicating low concentration of nitrogen (similar to 1 at%) in single-wall carbon nanotubes. On the basis of the results of calculations, we plotted current-voltage dependences for initial and nitrogen-doped carbon (CNx) nanotubes for elucidating the effect of nitrogen atoms configuration on field-emission characteristics of nanotubes. Nitrogen doping of carbon armchair nanotubes was shown to reduce the voltage threshold and to increase the current density significantly. The improvement of field-emission property for carbon zigzag nanotubes is expected when nitrogen atoms are near the tube tip. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 2696-2704, 2011