  In metallic nanoparticles, shifts in the ionization energy of surface atoms
with respect to bulk atoms can lead to surface bands. Within a simple Tight
Binding model we find that the projection of the electronic density of states
on these sites presents two overlapping structures. One of them is
characterized by the level spacing coming from bulk states and the other arises
from the surface states. In very small particles, this contributes to an
over-broadening of the NMR absorption spectra, determined by the Knight shift
distribution of magnetic nuclei. We compare our calculated Knight shifts with
experiments on aluminum nanoparticles, and show that the deviation of the
scaling law as a function of temperature and particle size can be explained in
terms of surface states.
