Nature of group Ib metal films deposited on polymer surfaces photooxidized with far-ultraviolet (185 nm) radiation

Solid samples of three polymers (polymethyl methacrylate, polycarbonate, and polyimide), whose surfaces were photooxidized with far-ultraviolet (185 nm) radiation in air, were used as substrates for the deposition of gold, silver, and copper films in vacuo. The electrical conductivities of the films were studied in situ as a function of the film thickness (0–15 nm). At a thickness of 10 nm, silver films showed 10⁴ greater conductivities when deposited on the treated surfaces of all three polymers. Gold films showed no detectable differences between treated and untreated surfaces. Copper behaved similar to gold on PMMA but showed somewhat greater sensitivity (< 20 at 5.4 nm thickness) on photooxidized polyimide. Transmission electron microphotographs of silver films on treated and untreated surfaces showed that photooxidation of the polymer caused the metal to be deposited with better coverage of the surface, i.e., with fewer voids. A partial explanation for the observations would be that photooxidation increases the number of nucleating sites for the metal on the polymer surface. In some way, this must be specific to silver because the effect does not extend to either a more reactive element such as copper or a less reactive element such as gold.