Effects of stress on electron emission from nanostructured carbon materials

Abstract

The electron field emission properties of highly graphite like (sp2 rich) amorphous carbon films have been investigated. These films were prepared by dual ion beam-assisted deposition technique, where the assisting energies were varied from 0 to 800 eV. Threshold fields as low as 8 V/μm is observed at an assisting energy of 400 eV, which is comparable to the best threshold fields observed in high sp3 carbon films. Surface nanostructures are found on these films during growth, but are thought not to be the primary reason for the observed low threshold fields. The combination of a highly graphite-like structure with a high intrinsic compressive stress and a high local (electronic) density, obtained from x-ray photoelectron spectroscopy, is identified as the source for the field enhancement. The controllable stress is thought to modify the band structures of the graphite-like sp2 rich component in the films, which results in high dielectric inhomogeneity. This analysis is in agreement with the concept of an internal or nongeometric field enhancement from sp2 nanostructures within the carbon thin films. The effect of stress induced band structure modification can also be extended to explain the field emission behavior of carbon nanotubes under stress.