The role of oxygen at the interface between titanium and carbon nanotubes

We study the interface between carbon nanotubes (CNTs) and surface-deposited titanium using electron microscopy and photoemission spectroscopy, supported by density functional calculations. Charge transfer from the Ti atoms to the nano-tube and carbide formation is observed at the interface which indicates strong interaction. Nevertheless, the presence of oxygen between the Ti and the CNTs significantly weakens the Ti-CNT interaction. Ti atoms at the surface will preferentially bond to oxygenated sites. Potential sources of oxygen impurities are examined, namely oxygen from any residual atmosphere and pre-existing oxygen impurities on the nanotube surface, which we enhance through oxygen plasma surface pre-treatment. Variation in literature data concerning Ohmic contacts between Ti and carbon nanotubes is explained via sample pre-treatment and differing vacuum levels, and we suggest improved treatment routes for reliable Schottky barrier-free Ti-nanotube contact formation.