  Electronic properties of metal-finite semiconducting carbon nanotube
interfaces are studied as a function of the nanotube length using a
self-consistent tight-binding theory. We find that the shape of the potential
barrier depends on the long-range tail of the charge transfer, leading to an
injection barrier thickness comparable to half of the nanotube length until the
nanotube reaches the bulk limit. The conductance of the nanotube junction shows
a transition from tunneling to thermally-activated transport with increasing
nanotube length.
