  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
nanotube 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 pretreatment. 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.
