Multiwall carbon nanotube inks as electron field emitters.

The work presented in this thesis is concerned with pure, water-soluble multiwall carbon nanotube inks, in particular their use in the fabrication of inexpensive field emission (FE) cathodes. This work is divided into three parts. Firstly, with the aim of fabricating a transparent FE cathode, nanotube inks are spin-coated onto transparent substrates, which subsequently are subject to laser treatment. An improvement in the FE properties with increasing laser fluency is observed, resulting in threshold fields of less than 6 V/mum (glass substrates) and less than 0.5 V/mum (plastic substrates). Secondly, with the aim of tailoring the geometric enhancement factor to improve the FE properties, nanotube inks are deposited onto paper substrates of varying surface morphology, via dip-coating. The FE properties are found to dramatically improve with increasing surface roughness of the paper, and a threshold field of less than 1 V/mum is achieved. Additionally, laser treatment is used to improve the threshold field. A 3-terminal device is fabricated with nanotube ink on paper substrates, operating with a gate voltage of 60 V and an anode voltage of 400 V. Finally, the effect that the work function has upon the FE properties of nanotube ink is investigated. An improvement in the threshold field from 0.42 to 0.25 V/mum is observed after lithium functionalisation was used to reduce the work function from 5.1 eV to 4.5 eV. Additionally, staircase-like current-field characteristics are observed for carboxylic-functionalised carbon fibres and these effects are discussed in terms of resonant tunnelling