  The Kondo temperature $T_K$ of single Co adatoms on monolayers of Ag on Cu
and Au(111) is determined using Scanning Tunneling Spectroscopy. $T_K$ of Co on
a single monolayer of Ag on either substrate is essentially the same as that of
Co on a homogenous Ag(111) crystal. This gives strong evidence that the
interaction of surface Kondo impurities with the substrate is very local in
nature. By comparing $T_K$ found for Co on Cu, Ag, and Au (111)-surfaces we
show that the energy scale of the many-electron Kondo state is insensitive to
the properties of surface states and to the energetic position of the projected
bulk band edges.
