Condensation Coefficients of Ag on Polymers

Using a novel very sensitive radiotracer technique, we have measured the condensation coefficient $C$ of Ag on several polymers. $C$ shows an extreme variation ranging from close to unity for polyimide to values as low as 0.002 for Teflon ${\mathrm{AF}}^{\mathrm{TM}}$ at room temperature. $C$ decreases strongly at elevated temperatures and exhibits a drop somewhere below the bulk glass transition temperature. The observed angular distribution of reemitted atoms does not depend on the angle of incidence and has a $\cos \theta$ form. This, among other arguments, suggests them to be adsorbed at the surface prior to reemission. Nucleation, studied on a polycarbonate, turned out to take place at preferred sites.