Comparative XPS study of copper, nickel, and aluminum coatings on polymer surfaces

Two nitrogen-containing polymers, polyacrylonitrile and poly(styrene-co-acrylonitrile), and three oxygen-containing polymers, poly(vinyl methyl ether), poly(vinyl methyl ketone) and poly(methyl methacrylate), were coated with copper, nickel, and aluminum under ultrahigh vacuum, and their surfaces were analyzed by X-ray photoelectron spectroscopy. It was found that the morphology of the interface is mainly controlled by the properties of the metal, and, to a lesser extent, by the functionalities of the substrate and its physical state. Thus, aluminum condensed quickly on the polymer substrates and formed a uniform metal layer, whereas copper and nickel led to more diffuse interfaces. The mobility of copper inside oxygen-containing polymers was clearly identified, and its diffusion was enhanced by the rubbery substrates, promoting the regeneration of the polymer surface previously degraded by the metal condensation. In contrast to oxygen that did not move during the metallization (except when there was degradation), nitrogen diffused to the metal layer to form nitride species. In all cases (with Cu, Ni, and Al), metal oxide, metal nitride, and amorphous carbon were identified at the interfaces.