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Photoemission spectroscopy (PES) is a very useful tool for investigating the surface electronic structures of solid. There is increasing interest in nanostructured materials, especially in clusters grown on inert surfaces since they may have high catalytic activity. Thus, the question of how the PES of deposited nanoparticles reflects their electronic and geometric structures is quite important. A number of papers have published in which the core-level binding energy shifts are observed as a function of coverage when a metal is deposited on an insulating substrate. However, there is substantial disagreement over the assignment of the shifts to clusters formation or interfacial reaction at room temperature. In this work, different amounts of Ni were deposited to TiO2 substrate. We observed the shift of Ni 2p3/2 core-level binding energy to larger value than that of bulk Ni at smaller Ni coverage. It shifts back to Ni bulk binding energy value after annealing to 500 oC. The binding energy shifts to a larger value again with increasing annealing temperature to above 500 oC due to oxidation of Ni. But at room temperature, we attribute the larger binding energy value to small clusters formation at lower coverage, rather than interfacial reaction because it decreases with increasing temperature up to 500 oC (cluster size increases with increasing temperature). In this paper, we also study the 6 eV satellites of Ni 2p main line change with overlayers’ conditions and discuss the different many-electron behaviors during 2-dimensioanl (2-D) to 3-dimensioanl (3-D) transition. This will help us to understand the origin of cluster induced binding energy shifts, which is due to initial state contribution or final state screening effect. |