The field emission of individual multiwall carbon nanotubes grown by chemical vapor deposition was measured in a scanning electron microscope. By using a sharp anode, we were able to select one nanotube for measurements in carefully controlled conditions. Single nanotubes follow the Fowler-Nordheim law, and the dependence of the field enhancement with interelectrode distance and nanotube radius is in good agreement with the recent model of Edgcombe and Valdré. Our results suggest that only nanotubes with the highest field enhancement factors, i.e., at least 8x higher than those of the average nanotube population, contribute to the emitted current in usual large area measurements.
The influence of an applied electric field on carbon nanotubes protruding from a surface was investigated in situ using a high-resolution scanning electron microscopy. Under the applied electric field, the nanotubes flexed to orient themselves parallel to the electric field lines. For moderate field strengths below the electron field emission threshold, the flexed nanotubes relaxed back to their original shapes after the electric field was removed. However, when high electron field emission currents were extracted from the nanotubes, they were permanently deformed, leaving them aligned to the electric field direction after the electric field was removed. For high currents, the length of the carbon nanotubes were found to be shortened after field emission lasted for a period of time.
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