Field emission current from single walled carbon nanotubes with adsorbates and defects for several chiralities: A density functional study

摘要

Summary form only given. Field emission current from single walled carbon nanotubes (SWCNTs) is simulated via the OCTOPUS code implementation of time-dependent density functional theory (TD-DFT), a quantum many electron algorithm capable of solving problems with hundreds to thousands of electrons in the presence of time varying external potentials on massively parallel computer architecture. Simulations were performed in a finite computational domain such that imaginary absorbing potentials were necessary to allow charge migration out of volume boundaries and allow long time evolution. A real space grid of resolution 0.2 Å was found to properly converge all systems considered in this work. Adsorbed atoms, SWCNT defects as well as SWCNT chirality were investigated to determine the influence each has on work function and subsequent field emission current magnitude. Results indicate that Ag, Al adsorbates were especially useful for increasing field emission current over standard SWCNTs. Differences from the Fowler-Nordheim relation were observed for low field emission. Such results demonstrate the utility of CNT based cathodes for improving output power and efficiency in future high power microwave devices.