  We have used low temperature scanning tunneling spectroscopy and atomic
manipulation to study the role of surface-state electrons in the Kondo effect
of an isolated cobalt atom adsorbed on Ag(111). We show that the observed Kondo
signature remains unchanged in close proximity of a monoatomic step, where the
local density of states of the surface-state electrons is strongly perturbed.
This result indicates a minor role for surface-state electrons in the Kondo
effect of cobalt, compared to bulk electrons. A possible explanation for our
findings is presented.
