Raman spectroscopy of phenylcarbyne polymer films under pulsed green laser irradiation

The polycarbyne polymer films were coated on silicon substrates and then irradiated by a pulsed Nd:yttrium-aluminum-garnet laser (λ=532 nm) with various fluences in argon gas atmosphere. Significant changes in microstructures and chemical bonding (sp³/sp²) during laser treatment were investigated by Raman spectroscopy. At a laser fluence below 50 mJ/cm², the Raman spectrum of the film was similar to that of the original polymer film. In a fluence range from 100 to 650 mJ/cm², the thermal decomposition of the polymer occurred, resulting in upshift of G peak and downshift of the D peak both with narrower peak width. With increasing laser fluence from 650 to 950 mJ/cm², both the G and D peaks downshifted simultaneously due to the thermal decomposition. The simultaneous downshift of both peaks indicated the increased sp³/sp² ratio in the carbon film converted from the polymer. With increasing laser fluence in this range, the thermal decomposition also induced the narrowing of both peaks. The narrowing of both peaks indicated the increased ordering of sp³ and sp² bonding components in the converted carbon film. The scanning electron microscopy studies provided the further evidence. The carbon films converted from the polymer films may contain the highest sp³ carbon bonding at laser fluences in the range from 850 to 1000 mJ/cm².