Vacuum gap dependence of field electron emission properties of large area multi-walled carbon nanotube films

Field electron emission properties of aligned multi-walled carbon nanotube films were studied with variation of the vacuum gap d between anode and cat hode. With d varying in the range of 0.4-2 mm, the emission current-gap vol tage characteristics and the corresponding Fowler-Nordheim (FN) plots show distinct nonlinearity and regular changes with electrode separation. Three field enhancement factors may be derived from the three linear sections of a FN plot. Their variation with gap d results in different behaviours; sign ificantly a drop of five times in the field enhancement factor is observed. The physical process responsible for our findings is suggested to be the s pace charge effect and both theoretical and experimental evidence is provid ed to support our arguments. The implication of our findings in technical a pplications is also discussed.