Evolution of the 2p satellite of Ni nano-clusters onTiO2(001) surfaces

Abstract

Correlation enhancement of electrons in Ni nano-clusters due to confinementin reduced dimensions has been observed. Both the size and shape of thenano-clusters have a strong influence on the Ni 2p satellite structures. For smallNi clusters, apart from the 6 eV satellite, a 3 eV satellite structure emerges inNi 2p3/2 photoemission spectra due to the existence of the3F atomic state. However, the intensity of the 3 eV satellite decreases with increasing cluster sizebecause the Ni 3d level becomes increasingly occupied in large clusters. The increased electronpopulation in the 3d level is achieved through electron transfer from the free-electron-like4sp states to the unhybridized pure 3d spin down states; the latter is lower in energy thanthe 3d–4sp hybridized states. The correlation-induced 6 eV satellite energy is enhanced byAr+ bombardment. These observations make it feasible to gauge the Ni 3d electron populationby probing the 2p photoemission spectra and to modify the supported Ni nano-clustersthrough thermal treatment and/or ion bombardment.