Properties of Single Walled Carbon Nanotube Films
The preparation and physical properties of transparent, single-walled carbon nanotube (SWNT) networks fabricated from a novel, organic dispersion are described here for the first time. Characterisation of SWNT dispersions uncovered shifts in the radial breathing modes as a function of aggregation. These modes were redshifted in centrifuged butylamine dispersions by ~3cm -1. SWNT films cast using a simple, drop-deposition technique were annealed at 300'C after fabrication to remove solvent and surfactant residue. Annealed films with a sheet resistance of magnitude ~10 4 kOhms/square and transparency of ~85 % were fabricated in this study. The optoelectronic properties showed some inconsistency due to varying levels of oxygen doping and film thickness. Thin films annealed at 500'C were found to be preferentially depleted of nanotubes with high chiral angle and small diameter. Oxidative effects were also observed upon annealing at temperatures as low as 300'C. However, the reasons for this premature combustion are as yet uncertain. Temperature-dependent conduction studies revealed that the removal of adsorbed surfactant considerably reduced tunnelling barriers in annealed films. The dominant conduction mechanism in both unannealed and annealed films was found to be 3D variable range hopping. In the annealed films, a high temperature activation regime (with activation energy of 220 meV) was observed above 225 K. This regime is due to thermal activation over Schottky barriers within the nanotube network or electron activation over the pseudogap in armchair tubes.