Cluster core-level binding-energy shifts: the role of lattice strain.

Our combined experimental and theoretical analysis of the shifts, with particle size, of core-level binding energies (BE's) of metal nanoparticles on insulating supports, shows that these shifts have an important initial state contribution arising, in large part, because of lattice strain. This contribution of BE shifts has not been recognized previously. Lattice strain changes the chemical bonding between the metal atoms and this change induces BE shifts.