and m* is the effective mass of the conduction electron. The mean
free path of the conduction electrons in the bulk (l∞ ∼ 42 nm for
gold) is simply the product of τs and the Fermi velocity (vF). In
small particles the mean free path is reduced due to collisions of
electrons with the particle surface, which is represented by an
additional contribution τc to the collision time, where τc ) R/vF,
19
and hence the dependence of the mean free path on R for a small
spherical particle is given by