  We report a combined valence band photoemission and Auger spectroscopy study
of single crystalline Ca(Fe,Co)2As2 and Ba(Fe,TM)2As2 with TM=Ni or Cu. The
valence band photoemission data show directly that the TM-states move to higher
binding energies with increasing atomic number, contributing less and less to
the states close to the Fermi level. Furthermore, the 3d8 final state of the
LVV Auger decay, which is observed for Ni and Cu, unambiguously reveals the
accumulation of charge at these impurities. We also show that the onsite
Coulomb interaction on the impurity strongly increases when moving from Co over
Ni to Cu. Our results quantify the impurity potentials and imply that the
superconducting state is robust against impurity scattering.
