Field focusing on carbon nanohorns

Abstract

Carbon nanohorns are a unique sharp conical nanostructure, with various potential applications including field emitters. Inspired by the recently measured negative real part of the dielectric constant of carbon nanotubes in the mid- and far-infrared regions, we numerically investigate the field focusing effect around carbon nanohorns. Our present study calculates the field enhancement factors at the tips of carbon nanohorns, quantitatively representing the degree of field focusing. Our calculations are based on the classical electromagnetic field theory in the quasistatic limit, for a model system consisting of a subwavelength-scale prolate hemispheroidal body protruding from a conducting plane. Field enhancement factors of about 300 and 100 in the air and H₂O, respectively, are observed around 0.1 eV (∼10 μm, ∼20 THz) for the incident electric field parallel to the carbon nanohorn. For the far-infrared region, the field enhancement factor ascends to 6 × 10⁶ at 3 meV (∼400 μm, ∼0.7 THz) and 7 × 10⁸ at 2 meV (∼600 μm, ∼0.5 THz) for the nanohorn aspect ratio of 100 and 1000, respectively. Our findings could lead to further improvement of carbon-based electrical and optical devices.