Role of nanostructure on electron field emission from amorphous carbon thin films

Abstract

The mechanism of electron field emission from different forms of amorphous carbon (a-C) thin films is discussed. We show that it is possible to explain electron emission from a variety of amorphous carbon films by understanding the nature of electron states near the Fermi level. The films can be described as consisting of conductive sp2 C clusters lying within a more insulating sp3 C matrix. We show that the trend in the threshold field for emission can be explained in terms of improvements in the connectivity between these sp2 clusters and that cluster concentration and size can be in turn controlled by the choice of deposition conditions. The presence of the dielectric inhomogeneity between the two regions of sp2 clusters and sp3 C matrix is also shown to be very important in understanding the apparently low barrier heights that appear in the analysis of the current-voltage emission characteristics using the Fowler–Nordheim theory. This article attempts to set the framework for a unified model for electron emission from carbon films.