  We have investigated the effects of the interfacial bond arrangement on the
electronic transport features of metal-nanotube-metal systems. The transport
properties of finite, defect-free armchair and zigzag single-walled carbon
nanotubes attached to Au(111) metallic contacts have been calculated by means
of the non-equilibrium Green functional formalism with the Tight-Binding and
the Extended Huckel Hamiltonians. Our calculations show that the electrode
material is not the only factor which rules contact transparency. Indeed, for
the same electrode, but changing nanotube helicities, we have observed an
overall complex behaviour of the transmission spectra due to band mixing and
interference. The comparison of the two models shows that the Tight Binding
approach fails to give a satisfactory representation of the transmission
function when a more accurate description of the C-C and Au-C chemical bonds
has to be considered. We have furthermore examined the effect of interface
geometry variance on conduction and found that contact-nanotube distance has a
significant impact, while contact-nanotube symmetry plays a marginal, yet
evident role.
