  Core-level spectra of the Mn-doped Sr3Ru2O7 and Srn+1RunO3n+1 (n = 1, 2 and
3) crystals are investigated with X-ray photoelectron spectroscopy. Doping of
Mn to Sr3Ru2O7 considerably affects the distribution of core-level spectral
weight. The satellite of Ru 3d core levels exhibits a substantial change with
doping, indicating an enhanced electron localization across the doping- induced
metal-insulator transition. However, the Ru 3p core levels remain identical
with Mn-doping, thus showing no sign of doping-induced multiple Ru valences. In
the Srn+1RunO3n+1 (n = 1, 2 and 3), the Ru 3d core-level spectra are similar,
indicating that the chemical bonding environment around Ru ions remains the
same for different layered compounds. Meanwhile the Sr 3d shallow core levels
shift to higher binding energy with increasing n, suggesting their
participation in Sr-O bonding with structural evolution.
