Field emission and structure of aligned carbon nanofibers deposited by ECR-CVD plasma method

Aligned carbon nanofibers and hollow carbon nanofibers were grown by MW ECR-CVD method using methane and argon mixture gas at a temperature of 550°C. The carbon nanofibers and the hollow carbon nanofibers were deposited perpendicularly on Si substrates and on Si substrates coated with Ni catalyst, respectively. From TEM analysis the diameter and length of the nanofibers are approximately 60 nm and 15 μm, respectively. Raman spectra of these aligned carbon nanofibers showed new bands of 1340 and 1612 cm−1 of the first-order Raman scattering and 2660, 2940 and 3220 cm−1 of the second-order Raman scattering. The second-order Raman scattering bands were assigned to two overtone and one combination bands on the basis of a similar assignment of micro-crystal graphite by Nemanich and Solin. By the measurement of XPS C1s band energies of 284.6 eV for the carbon nanofiber and 284.7 eV for the hollow carbon nanofiber indicate mainly sp2 carbon component in the inclusion of a small amount (<5%) of oxygen in a high binding energy region (∼288 eV). Field emission characteristics of the well-aligned carbon nanofibers and hollow carbon nanofibers were investigated and the current densities were 7.25 and 0.69 mA/cm2 at 12.5 V/μm, respectively.