Radiation-induced modification of reflection spectra beyond the ion path region in polyimide films

Modification of the surface layers of polyimide films under γ-radiation and implantation with 30–100 keV Ni, Mn, Ag, Co, Fe and B ions in the dose range of 10¹⁵–1.5 × 10¹⁷ cm^–2 are investigated by reflection spectra measurements. Ion implantation is shown to lead to the modification of reflection from the rear (unimplanted) polymer side. Depending on the kind of ion and implantation mode a strong increase in the integrated reflection coefficient in the polymer opacity range is observed, as well as growth of the reflection intensity of optical bands λ₁ = 254 and λ₂ = 311 nm and their shifts to the short-wavelength region. The change in the reflection coefficient far beyond the implanted region is caused by the radiation-induced transformation of the polymer supermolecular structure near the surface and the relaxation of mechanical stress formed during film production.