  We investigate the field emission properties of nitrogenated and boronated
carbon nanotubes using time-dependent density functional theory, were the wave
function propagation is performed using the Crank-Nicholson algorithm. We
extract the current-voltage characteristics of the emitted electrons from
nanotubes with different doping configurations. We found that boron doping
either impedes, or slightly enhances, field emission. Nitrogen strongly
influences the emission current, and the current is sensitive to the location
of the nitrogen dopant in the nanotube. The emitted charge cloud from nitrogen
doped carbon nanotubes is, however, more diffuse than that from pristine ones,
our simulations show the emergence of a branching from the charge cloud, making
nitrogenated carbon nanotubes less convenient for use in narrow beam
applications.
