Metal-polymer interfaces: Adhesion and x-ray photoemission studies

Abstract

The interfaces formed by evaporating copper, nickel, and chromium layers on polystyrene, polyvinyl alcohol, polyethylene oxide, polyvinyl methyl ether, polyvinyl acetate, and polymethyl methacrylate have been studied with x-ray photoemission spectroscopy (XPS). The adhesion strengths of the metal films to the polymers were measured by a tensile-pull test. At submonolayer coverages of the metals, the peak positions and widths of the metallic electron core levels measured with XPS vary significantly from one polymer substrate to another. Most of these variations can be accounted for in terms of changes in the atomic and extra-atomic relaxation energies during the photoemission process. Much of this change is brought about when the metal atom deposited on an oxygen-containing polymer interacts with the substrate oxygen and forms a metal-oxygen-polymer complex. The presence of this complex is verified by changes in the photoemission lineshapes of the substrate carbon and oxygen atoms. The XPS signatures of these various complexes are quite similar and suggest that they are chelate-like complexes. The adhesion strength of any metal on an oxygen-containing polymer is greater than on the oxygen-free polystyrene. In general, the increased adhesion strength correlates with the presence of the metal-oxygen chelate complexes.