Anomalous diffusion of Pb atoms into polyethylene implanted with F⁺and As⁺ ions to different doses

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 different doses was studied at room and boiling temperatures. The standard Rutherford backscattering (RBS) technique was used for the determination of concentration depth profiles of incorporated atoms. Pb diffusion in the pristine polymer proceeds according to the common Fickian law with diffusion coefficients of 1.5 × 10^-16 cm²s^-1 and D = 5.3 × 10^-14 cm² s^-1 at room and boiling temperatures, respectively. Anomalous diffusion of Pb atoms was observed into the PE implanted to ion doses below 5 × 10¹⁴ cm^-2. In these cases a pronounced diffusion-capturing mechanism takes place with the Pb atoms being captured on trapping centres produced by electronic energy losses of implanted ions. For implanted doses above 5 × 10¹⁴cm^-2, nearly Fickian diffusion is again observed with diffusion coefficients close to those of pristine material. Strongly reduced Pb incorporation in specimens implanted to higher doses is explained by structural changes of the polymer surface layer.