Field emission characteristics of carbon nanotube films fabricated on a metal mesh by filtration

Abstract

A novel-structured field emitter was fabricated by vacuum-filtrating in sequence an aqueous suspension of thin, highly crystalline multiwalled carbon nanotubes (MWCNTs) and an aqueous suspension of thick, defective MWCNTs through a metal mesh placed on a polymer membrane. We could form a mechanically strong CNT film by weaving carbon nanotubes (CNTs) through the metal mesh residing inside the film. On drying at 70°C, the polymer membrane was spontaneously separated from the CNT-mesh hybrid structure due to a large difference between their thermal expansion coefficients, producing vertically aligned bushes of thin CNTs on the CNT film. On top of the bushes, sharp CNT tips were well developed and worked excellently as field emitters. This structure was designed in such a way that the thin CNTs worked as field emitters while the thick CNTs supported the emitter CNTs. Our CNT emitters showed a high emission current density of 220mA/cm2 at 4.3V/μm, and its emission life span, measured at 40mA/cm2 in a DC bias mode, was ∼171h. We expect that the CNT emitters with a novel structure are promising for the applications to field emission sources requiring small area but high current, for example, X-ray generators, microwave amplifiers, etc.