4. Contact conductance

A particular feature of nanometric conductors is the phenomenon of contact resistance. This can be illustrated by the following simple reasoning.

The (13) formula describing particle diffusion is only valid if the variation in charge is relatively slow over a distance of the order of the mean free path. On the other hand, when two materials of dissimilar structure are brought into contact, a variation in potential V appears, which can be of the order of a volt over a distance of a few nanometers. Charges can be separated into two parts. For those whose kinetic energy is less than the Fermi energy, there is no diffusion current, and there are as many charges in one direction...