Polymer–nanotube composites: Burying nanotubes improves their field emission properties

Composite structures of single walled carbon nanotubes (SWNTs) and poly(3-octylthiophene) polymer were tested as field emitters. The structures studied were formed on n+-Si by mixing the two materials after they had been dissolved in chloroform. Three different structures were tested: (a) a SWNT mat, (b) a SWNT mat on a SWNT (30 wt %)–polymer composite and (c) a SWNT mat on pure polymer. Although the conductivity of the composite is very much lower than that of the nanotube mat, experiments show that the field emission threshold is lower and the emission current higher from structure (b) compared to the pure SWNT mat on n+-Si. A comparison between the field enhancement factors and the expected aspect ratios shows that enhancement due to an additional field enhancement mechanism other than that due to the geometrical shape of the SWNTs must exist. We propose that the field due to the surface potential modification at the triple junction between SWNTs, polymer and vacuum is adequate to create additional field emission from such sites. This mechanism can also be used to explain previously reported field emission characteristics of CNx nanocomposite films.