Physical origin of non-linearity in Fowler–Nordheim plots of aligned large area multi-walled nitrogen-containing carbon nanotubes

Field electron emission properties of multi-walled nitrogen-containing carbon nanofibers were studied with particular interest in the mechanism responsible for their non-linearity of a Fowler–Nordheim (FN) plot. With vacuum gap d between anode and cathode varying in the range of 0.4–1.4 mm, the FN plots show distinct non-linearity and regular changes with the gap separation. Typically, two linear sections may approximately be defined in a FN plot, and thus two field enhancement factors may be derived rather than one. The variation of the field enhancement factors of the two sections with gap d show different behavior. The physical mechanisms responsible for the strong gap-dependent of I–V characteristics and their implication on technical applications are discussed.