Electronic linear energy transfer dependent molecular structural growth in polyethylene terephthalate

Thin films (13 mum) of polyethelene terephthalate (PET) are irradiated by different swift metallic heavy ions (180 MeV Ag14+ and 200 MeV Au15+) with the projectile linear energy transfer (LET) (similar to10-14 keV/nm), respectively. LET dependence on the molecular structural changes in PFT irradiated at different ion fluences has been studied by the Fourier transform infrared spectroscopy. The study has revealed that beyond a critical LET entirely different pathways of amorphization beginning with partial recrystallization at lower ion fluence impact occurs in PET, contrary to the earlier established results. At considerably higher LET (similar to14 keV/nm), the most characteristic crystalline stretching and bending vibration bands such as at 850 cm(-1) (CH2 rocking), 972 cm(-1) (Cdouble bondO stretching), 1341 and 1471 cm(-1) (CH2 bending) in PET have shown a significant rise in the respective infrared absorbance intensities upon lower ion fluence (similar to10(11) ions/cm(2)) impact. The absence of previously reported unsaturations such as alkynes at both the LET beam used are also observed. Interestingly, the aromatic system also appears to be unstable and participating in the modification process, particularly at the higher LET (similar to14 KeV/nm). Possible interpretations are discussed. (C) 2002 American Institute of Physics.