  We study the Metal-Insulator transition in one-dimensional Hubbard
superlattices (SL's), modelled by a repeated pattern of repulsive (i.e.,
positive on-site coupling) and free sites. The evolution of the local moment
and of the charge gap (calculated from Lanczos diagonalization of chains up to
18 sites), together with a strong coupling analysis, show that the electron
density at which the system is insulating increases with the size of the free
layer, relative to the repulsive one. In the insulating state, the mechanism of
interaction between fermions separated by a free layer is the analog of
superexchange, and the charge gap display universal features.
