Subsurface growth of ultrathin Ni films on Cu(001) surfaces: Photoemission singularity index study

Using photoemission singularity index, we show that interface growth mode can be explored at atomic level for the epitaxial interface. The initial growth of Ni on Cu(001) surface has been demonstrated to be a segregated subsurface Ni layer growth below one Cu capping layer which behaves as a promoter. The observations are interpreted as evidence for interface exchange processes between Cu and Ni atoms. Based on the change of singularity index which is sensitive to the atomic environment, the interfacial density of states (DOS) at the Fermi level responsible for the screening is decreasing with increasing the Ni coverage. The Cu 4s/Ni 3d interfacial hybridization is enhanced on the disordered surface which is attributed to the increased step edge. The interfacial electronic structure change is also explained within the subsurface growth mode.