The electronic states of cobalt nano-islands on a nitrogen-saturated Cu(001) surface have been studied by soft X-ray emission spectroscopy and soft X-ray absorption spectroscopy. The L3 resonant X-ray emission spectrum was decomposed into two components; emission from nitrogen-adsorbed single-layer Co islands and that from more than double-layer islands. A narrower width and a lower binding energy of the former agrees with the 3d density of states calculated by a first-principles method for a nitrogen-adsorbed single-layer Co film on Cu(001). When the surface is covered with small nitrogen-adsorbed Co islands, a shoulder structure in L-edge absorption spectrum was observed at an energy ∼3 eV higher than the absorption edge. By considering the calculated unoccupied 3d states and X-ray photoelectron spectra, the shoulder was attributed to the correlation among 3d electrons. The perimeter Co atoms of the islands are assigned as the origins of the correlation satellite considering the surface morphology observed by scanning tunneling microscopy. The 3d band narrowing and enhanced correlation in the Co nano-islands are clearly demonstrated.
