Modifications Induced by Swift Heavy Ion Beam of 60 MeV Si^{5 +} in Poly(3-octylthiophene)

The spin coated thin films of poly(3-octylthiophene) (p3ot) on glass and Si substrates were irradiated with 60 MeV Si⁵⁺ swift heavy ions (SHI). On-line quadrupole mass analysis was performed to monitor the evolved gases during SHI irradiation in order to understand the chemistry involved. Mass spectra shows the evolution of various gaseous species i.e., C₂H₄, C₂H₂, C₃H₃ etc., which reveals the chain scissoring and thus chemical changes in the polymer. Pre and post irradiation spectroscopic investigations [Fourier transform infra-red (FTIR) and UV-visible absorption spectroscopy] reveal the chemical changes and changes in optical properties of the films due to irradiation. FTIR spectra reveal the bond scissoring in the localized region of polymer chains. Optical band gap decreases with increasing ion fluence. The crystallinity of pre and post irradiation samples was analyzed by X-ray diffraction (XRD) and decreases with increasing ion fluence. An effort was made to understand the mechanisms of evolution of gases within ion track and correlate the changes with FTIR, XRD and UV-Vis absorption results.