Electron emission from films of carbon nanotubes and ta-C coated nanotubes

Abstract

The field emission properties of multiwall carbon nanotube films with and without a coating of tetrahedrally bonded amorphous carbon (ta-C) were investigated. Voltage thresholds of 2.4 V/μm for uncoated films and 1.5 V/μm for ta-C coated films were found. The results for the uncoated films are in good agreement with previous measurements of field emission from carbon nanotubes. The effect of the ta-C coating on the emission properties is discussed in light of current field emission models.

Approach curve method for large anode–cathode distances

“…4 are consistent with the emission measurements performed earlier for anode-cathode distances in the 400 µm range and for different kinds of samples, including CNTs (e.g. [6][7][8]), even though for CNTs the surface is evidently not flat in a microscopic sense. The results described in [6][7][8] are consistent with our idealized flat and uniform model cathode since the anode-cathode distance was substantially larger than the asperities of the nanotube sample.…”

“…However, good accuracy is only reached after a large amount of emission data is gathered since field emission is normally a very unstable process. This methodology assumes that the Vxd curves are straight lines, which has been confirmed experimentally for a number of systems [6][7][8][9]. Figure 2a is an example of IxV curves obtained from CNTs deposited on a metal plate and measured at three cathode-anode distances, demonstrating that the voltage required to yield a constant current decreases with decreasing the anode-cathode distance.…”

“…[6][7][8]), even though for CNTs the surface is evidently not flat in a microscopic sense. The results described in [6][7][8] are consistent with our idealized flat and uniform model cathode since the anode-cathode distance was substantially larger than the asperities of the nanotube sample. In this case the overall CNT cathode emission can be modeled as a flat surface with a very low "effective" work function.…”

“…A complete analysis of similar samples can be found in Refs. [6][7][8] where the linearity of the Vxd plot is demonstrated in more detail.…”

“…CNT samples prepared from powder, as the ones used in Refs. [6,12], are normally embedded in a resin (silver glue). The resulting mixture produces rough cathode surfaces, with mesoscopic bumps (tens to hundreds of microns in size) and non-uniform CNT concentration and distribution.…”