Local field emission from individual vertical carbon nanofibers grown on tungsten filament

Individual high-aspect-ratio carbon nanofibers (CNFs) were grown on tungsten filament substrates by plasma-enhanced hot filament chemical vapor deposition. They are ∼100 nm in diameter and 6-30 μm in length with a density less than 106/cm2. The field emission property of single as-grown carbon nanofibers was measured in a scanning electron microscope equipped with a moveable nanoscale probe tip. The measurement results showed that the threshold field of single carbon nanofibers with different lengths was in the range of 4-5 V/μm with a corresponding emission current density of 20 μA/cm2, but an evident difference in the enhancement of emitted current between nanofibers of different lengths could be found when the applied field was increased continuously. This indicates that the field emission property of single carbon nanofibers depends mainly upon their length, which is essentially attributed to the change of field enhancement factor of single carbon nanofibers. In addition, field emission of the different positions on the wall of a single carbon nanofiber was studied.