Photon-stimulated field emission from semiconducting (10,0) and metallic (5,5) carbon nanotubes

We present three-dimensional simulations of field emission through an oscillating barrier from ideally open (10,0) and (5,5) carbon nanotubes without adsorption, by using a transfer-matrix methodology. By introducing pseudopotentials for the representation of carbon atoms and by repeating periodically a basic unit of the nanotube, band-structure effects are manifested in the energy distributions. The total-energy distributions also exhibit oscillations, which are related to stationary waves in the structure. The current enhancement due to the photon-stimulation process reaches a saturation plateau for photon energies larger than 5 eV and decreases when the photon energy exceeds 9 eV. The results indicate a maximal current enhancement at a photon energy of 8.4 eV. This maximum may correspond to the best compromise between increasing width of the energy distribution and decreasing efficiency of the photon stimulation. In addition, a resonant photon-stimulation process seems associated with the maximum. For a power flux density of 5.96×1012W/m2 and a local field of 2.5 V/nm, a relative current enhancement up to 109 is achieved with the semiconducting (10,0) nanotube while it is only of 140% for the metallic (5,5), this large difference being explained by the semiconducting (10,0) nanotube having an intrinsic emission (without photonic stimulation) 5×108 times lower than that of the metallic (5,5). These results indicate that photon-stimulated field emission from semiconducting carbon nanotubes may lead to important technological applications, like THz amplifiers (if a femtosecond modulation of the radiation can be achieved).