AN IN-SITU XPS STUDY OF THE FORMATION OF NICKEL POLYETHYLENE AND NICKEL POLYPROPYLENE INTERFACES

The initial stages of formation of nickel-polyethylene and nickel-poly propylene interfaces have been investigated by X-ray photoelectron spe ctroscopy (XPS). Nickel was sputter-deposited on the polymer surfaces in the UHV chamber attached to the spectrometer, and the Ni 2p3/2 and C1s regions were analysed in situ as a function of deposition time, un til the completion of a metallic overlayer of approximately 30 angstro m. The examination of the measured XPS spectra shows that there is no additional signal in the C1s region which would be associated with the formation of a strong chemical bond with charge transfer, in contrast with previous findings for aluminium sputter-deposited on the same po lymers. Accordingly, the Ni 2p3/2 region does not show any additional signal, but it exhibits a marked shift in the binding energy for the s mall amounts of deposited nickel (0.7 eV for the shortest deposition t ime). This shift in binding energy decreases with increasing amount of deposited metal. This observation gives evidence of the presence of s mall clusters on the surface, which finally form a continuous metallic layer with a thickness of approximately 8 angstrom.