Morphology and temperature-dependent electron field emission from vertically aligned carbon nanofibers

Effects of temperature and the aspect ratio on the electron field emission properties of vertically aligned carbon nanofibers in thin-film form were studied in detail. Vertically aligned carbon nanofibers have been synthesized on silicon substrates via a direct current plasma enhanced chemical vapor deposition technique. Surface morphologies of the films were studied by an atomic force microscope. It was found that the length of the nanofibers increased and the diameter decreased as the thickness of the Ni catalyst film decreased. The threshold field for the electron field emission was found to be in the range from 4.3 to 5.4 V/mu m for carbon nanofibers having different aspect ratios. The threshold field for carbon nanofibers having diameter similar to 200 nm and aspect ratio similar to 7.5 was found to decrease from 4.8 to 2.1 V/mu m when the temperature was raised from 27 to 350 degrees C. This dependence was due to the change in work function of the nanofibers with temperature. The field enhancement factor, the current density and the effective work function were calculated and used to explain the emission mechanism.