Energy distribution of field emitted electrons from carbon nanotubes

Field emission properties of single-walled carbon nanotubes (SWNTs), deposi ted on n-type Si substrates, were investigated by a combination of classica l I-V characterization and field emission energy distribution (FEED) measur ements. I-V characterization showed that current densities on the order of 1 mA/cm(2) could be obtained at nominal electric fields as low as 3 V/mu m. A current density of up to 25 mA/cm(2) was observed, and long-term current stability and reproducibility were excellent. FEED measurements revealed t hat at low current densities, the field emitted electrons originated from e nergy levels close to the Fermi level of the Si substrate. At larger applie d voltages and larger current densities, I-V characterization of the field emitters showed primarily an ohmic behavior; FEED data taken under the same experimental conditions showed a shift of the main spectral peak toward lo wer kinetic energies with increasing applied voltages. This energy shift wa s found to be linear with the applied voltage and emission current over a w ide range. Both FEED and I-V data thus indicated that the field emission cu rrent was primarily limited by the ohmic resistance of the nanotubes and/or the contact resistance between the nanotubes and the Si substrate; typical measured values for the cathode surface resistances were 100 k Omega cm(2) . (C) 2000 Elsevier Science S.A. All rights reserved.