Investigation of surface and non-local screening effects in the Ni 2p core level photoemission spectra of NiO

► Origin of the shoulder in the Ni 2p XPS spectra of NiO. ► Surface peak comes from the NiO5 clusters of the surface. ► Surface plus non-local explain the Ni 2p XPS peak in all cases. ► Surface contribution is controlled by the Inelastic Mean Free Path.