Structural and chemical surface modification of polymers by low-energy ions and influence on nucleation, growth and adhesion of noble metals

Changes in physical and chemical properties of a polymer film can be induced by exposing it to a variety of surface modification techniques, one of which is low-energy ion-beam treatment, which allows to induce changes on the polymer surface without affecting the bulk. Using XPS and TEM, polystyrene (PS) and polypropylene (PP) surfaces were examined after 1 keV energy ion-beam treatments in the ion fluence range from 10¹² to 10¹⁶ cm^-2 in order to clarify the following points: identification of adsorption-relevant species for metal atoms, formation of crosslinks in the outermost polymer layer, effect of post-treatment reaction after exposure to atmosphere and the influence of Ar⁺ and O₂⁺ ion bombardments on the condensation coefficient of metals, as well as on the enhancement of adhesion strength. The ion bombardment altered the polymer surface chemical structure by introducing new functional groups which influenced metal/polymer interaction. The increase in the PS surface glass transition temperature is explained in terms of an enhanced degree of crosslinking in the outermost polymer surface layer, which is also the reason for the etch rate reduction. The ion bombardment created a defined concentration of defects which acted as new adsorption sites on polymer surfaces, leading to an increase in the cluster density of metals with ion fluence and the enhancement in the condensation coefficient, which approached unity at an ion fluence of 10¹⁵ cm^-2. The surface treatments improved the adhesion between the metal and the polymer by two orders of magnitude compared to the untreated polymer. The locus of failure changed from interfacial failure for untreated polymer surfaces to cohesive failure in the polymer for modified surfaces.