Chapter 6 - Field Emission

Abstract

The theory of field emission was originally developed by Fowler and Nordheim, and has since been refined to include effects such as details of the tunneling potential and material-specific density of states. However, the basic aspects of the field emission can be captured from a simple theory of tunneling across a triangular potential barrier using the Wentzel, Kramers, Brillouin approximation. The unique band structure with van hove singularities in the density of states and localized/quasi-localized states at the tip may necessitate the need for a new model to describe field emission from nanotubes. While both the experiments and the theories have explored this topic, there is no clear conclusion. However, most experiments show that the total field emission current as a function of bias is quite consistent with the Fowler–Nordheim model in single wall nanotubes. The current–voltage characteristics are reasonably consistent with the Fowler–Nordheim model over a current window spanning more than two orders of magnitude. Deviations from the Fowler–Nordheim model for total current have been observed in specific samples because of adsorbates and possibly quantized energy levels in the tip.