X-ray photoelectron spectroscopy (XPS) has been used to examine the nature of the interactions between Pt and Ti nitride formed in situ by Ti deposition in a nitrogen atmosphere on Si (111) surfaces in ultrahigh vacuum (UHV). The 4f 7/2 electron binding energy of the initially deposited Pt corresponded to that of the intermetallic compound PtTi. Increasing the amount of deposited Pt shifted the binding energy toward that of metallic Pt. Complementary angleresolved XPS revealed that Pt remains on the outer surface region of the resulting multicomponent film. The results show that TiN layers with a thickness of only ca. 1 nm already form an effective barrier to Pt diffusion at room temperature.