First information on metal diffusion in polymers resulted from surface
spectroscopies which mainly provided insight into chemical interactio
ns of metals at polymer surfaces and into their growth mode. Medium en
ergy ion scattering, electron microscopy, atomic force microscopy, and
second-harmonic generation revealed a strong tendency of metals of lo
w and intermediate reactivity to form clusters when deposited onto pol
ymers. The interplay of diffusion and aggregation was also studied by
Monte Carlo simulations. Metal diffusivities were obtained from radiot
racer and Rutherford backscattering measurements. The available result
s show that reactive metals do not have any long-range mobility and ar
e effective diffusion barriers. In contrast, isolated atoms of less re
active metals diffuse deep into polymers at elevated temperatures. How
ever, the very pronounced aggregation tendency of these metals effecti
vely impedes diffusion unless they are deposited at rates of the order
of monolayers per minute or lower. Nevertheless, traces of noble meta
ls always diffuse into polymers during the early stages of metal depos
ition, whereas no significant diffusion occurs from a continuous metal
film. Even noble metal diffusivities are many orders of magnitude sma
ller than diffusivities of non-reactive gas molecules and largely deco
upled from polymer dynamics. This is attributed to a pronounced reduct
ion in the local chain mobility near metal atoms, e.g., by temporary m
etal-atom-induced crosslinking. (C) 1998 Elsevier Science S.A.