Vertically Aligned Carbon Nanotubes for Field Emission Cathodes

Systematic field emission (FE) studies of cathodes made from arrays of individual vertically-aligned carbon nanotubes (va-CNTs) and arrays of isolated tufts of va-CNTs were performed in order to assess the most advantageous spatial configuration for FE stability and lifetime in a poor vacuum working environment (~10^-7 torr), which is specific for industrial applications. We conclude that under large FE currents the back-ion sputtering, due to the ionization of the residual gas under the e-beam, destroyed the individual CNTs. This led to a gradual destruction of the CNTs in the arrays then to the failure of the cathode when most of them have disappeared. In the case of arrays of tufts of CNTs, results indicate that the consequence of the e-beam induced ion sputtering only pruned out the tuft. A tuft is still a FE site as long as one CNT exists. Under ion sputtering, the collective behavior of the tufts is the main reason for the observed extension of the FE lifetime by a factor in the range of 5 to 10 compared to isolated individual va-CNTs