  The modeling of carbon nanotube-metal contacts is important from both basic
and applied view points. For many applications, it is important to design
contacts such that the transmission is dictated by intrinsic properties of the
nanotube rather than by details of the contact. In this paper, we calculate the
electron transmission probability from a nanotube to a free electron metal,
which is side-contacted. If the metal-nanotube interface is sufficiently
ordered, we find that k-vector conservation plays an important role in
determining the coupling, with the physics depending on the area of contact,
tube diameter and chirality. The main results of this paper are: (i)
conductance scales with contact length, a phenomena that has been observed in
experiments and (ii) in the case of uniform coupling between metal and
nanotube, the threshold value of the metal Fermi wave vector (below which
coupling is insignificant) depends on chirality. Disorder and small phase
coherence length relax the need for k-vector conservation, thereby making the
coupling stronger.
