An x-ray photoemission spectroscopy study of chemical interactions at silver/plasma modified polyethylene interfaces: Correlations with adhesion

Plasma treatment is a convenient way to modify the surface (∼25–50 Å) of a polymer for improved adhesion of vacuum deposited metals. X-ray photoemission analysis of plasma modified polyethylene (PE) indicates no detectable chemical effects for argon plasmas, whereas oxygen and nitrogen plasmas create new chemical species which alter the chemical reactivity of the PE surface for vacuum deposited Ag. The adhesion strength of vacuum deposited Ag on PE is shown to increase in the following order: untreated<argon plasma<oxygen plasma<nitrogen plasma treated PE. Changes in chemical bonding and nucleation of submonolayer vacuum deposited Ag on plasma treated PE correlate with Ag/PE adhesion. Changes in the PE core levels after submonolayer deposition of Ag are interpreted as due to the formation of Ag–O–C and Ag–N–C species on oxygen and nitrogen plasma treated PE, respectively. In contrast, no chemical bonding effects are observed on untreated or argon plasma treated PE. The Ag valence-band structure suggests that the plasma induced species act as nucleation and chemical bonding sites resulting in a much smaller average cluster size for vacuum deposited Ag. Interfacial analysis of peeled thin films of vacuum deposited Ag on PE suggests the locus of failure changes from interfacial adhesive failure for untreated and argon plasma treated PE to cohesive failure of the PE for oxygen and nitrogen plasma treated PE.