V. Hnatowicz et al., ANOMALOUS DIFFUSION OF PB ATOMS IN POLYETHYLENE IMPLANTED WITH F+ ANDAS+ IONS TO DIFFERENT DOSES, Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms, 93(3), 1994, pp. 282-287
The diffusion of Pb atoms from a 0.5M aqueous solution of lead acetate
into polyethylene (PE) implanted with 150 keV F+ and As+ ions to diff
erent doses was studied at room and boiling temperatures. The standard
Rutherford backscattering (RBS) technique was used for the determinat
ion of concentration depth profiles of incorporated atoms. Pb diffusio
n in the pristine polymer proceeds according to the common Fickian law
with diffusion coefficients of 1.5 x 10(-16) cm2 s-1 and D = 5.3 x 10
(-14) cm2 s-1 at room and boiling temperatures, respectively. Anomalou
s diffusion of Pb atoms was observed into the PE implanted to ion dose
s below 5 X 10(14) cm-2. In these cases a pronounced diffusion-capturi
ng mechanism takes place with the Pb atoms being captured on trapping
centres produced by electronic energy losses of implanted ions. For im
planted doses above 5 x 10(14) cm-2, nearly Fickian diffusion is again
observed with diffusion coefficients close to those of pristine mater
ial. Strongly reduced Pb incorporation in specimens implanted to highe
r doses is explained by structural changes of the polymer surface laye
r.