Kr++ Ion Implantation-Induced Changes in Optical Properties of Polycarbonate

Transparent polycarbonate samples were implanted with 200 keV Kr++ ions to various doses ranging from 1 x 10(15) to 8.4 x 10(16) ions cm(-2) with a beam current density of 1 mu A cm(-2). Modification in the optical and chemical properties of polycarbonate as a function of the implantation fluence was investigated for UV-visible spectroscopy. UV-visible absorption analysis suggests the formation of a carbonaceous layer and a drastic decrease in optical band gap from 4.12 eV for unimplanted polycarbonate to 0.71 eV at an implanted dose of 8.4 x 10(16) ions cm(-2) has been observed. The width of the tail of localized states in the band gap was evaluated using the Urbach edge method and it increased from 0.10 eV for unimplanted polycarbonate to 2.46 eV for Kr++ implanted polycarbonate at the highest dose of 8.4 x 10(16) ions cm(-2), indicating an increase in disorder. The decrease in optical band gap points towards the formation of carbonaceous clusters and/or networks of conjugated unsaturated bonds. The number of carbon atoms, N, in a cluster can be calculated from absorption spectra and it increases from a value of 83 at a dose of 1 x 10(15) ions cm(-2) to 2333 at a dose of 8.4 x 10(16) ions cm(-2). The correlation between the decline in band gap and change in structure has been discussed.