Study of optical band gap and carbonaceous clusters in swift heavy ion irradiated polymers with UV-Vis spectroscopy

The formation of carbonaccous clusters in swift heavy ion irradiated polymer films has been investigated extensively. The information about these clusters may be obtained from Ultraviolet-Visible (UV-Vis) spectroscopic studies. The optical band gap (E-g), calculated from the absorption edge of the UV spectra of these polymers can be correlated to the number of carbon atoms (N) in a cluster with the Tauc equation. Films of 50 mu m, 80 mu m, 125 mu m, 250 gin thicknesses of PET, PTFE, PMMA and PES polymers, respectively, were irradiated with Si8+ ions of energy 100 MeV to different fluences from 10(10) to 10(13) ions/cm(2) at Pelletron accelerator, Inter University Accelerator Centre, New Delhi, India. UV-Vis absorption studies show that optical energy gap decreases with transferred energy density of the ion beams. The energy band gap (E-g) values were computed from the absorption edge in the 200-800 nm region with the Tauc relation. The values vary from 3.86 to 1.61 eV for the pristine and various irradiated polymer samples. Maximum change of 40% is observed in PES irradiated to 10(13) ions/cm(2). The cluster size shows a variation in the range of 79-454 carbon atoms per cluster for the polymers studied here. (c) 2008 Elsevier B.V. All rights reserved.