Workfunction of purified and oxidised carbon nanotubes

We report for the first time the ultraviolet photoelectron spectroscopy (UPS) of purified multi-wall carbon nanotubes. Purification was carried out by successive sonication, centrifuge, sedimentation, and filtration processes of nanotubes-water solution dispersed by the non-ionic surfactant. Purified nanotubes showed the workfunction of 4.3 eV, very close to that of graphite (4.4 eV). It was found that purified nanotubes possess a finite density of states (DOS) at Fermi energy (EF), suggesting the existence of metallic nanotubes as predicted theoretically. The oxygen-plasma treatment which opens the end-cap and generates defects in the outer layers increased the workfunction dramatically up to 4.8 eV and removed the DOS at EF, indicating a new way to modify the electronic properties of nanotubes.