EVIDENCE FOR UNZIPPING REACTIONS IN THE LASER-ABLATION OF POLYTETRAFLUOROETHYLENE (PTFE)

We have characterized the neutral and charged species emitted by pulsed-laser irradiation of polytetrafluoroethylene (PTFE) in vacuum at 248 nm in fluence regimes appropriate for the pulsed-laser deposition of PTFE thin films. The time-of-flight behavior of the major neutral species is consistent with-thermal emission at temperatures where PTFE is known to decompose thermally. The laser fluence dependence of the intensity of the most intense neutral component (the C2F4 monomer) is analyzed in terms of a thermally activated decomposition process. Under isothermal conditions, thermal decomposition is believed to be rate limited by radical formation, with an activation energy of a few eV. In contrast, the fluence dependence of the monomer intensity indicates an activation energy of about 0.9 eV - appropriate to an unzipping reaction rate limited by radical transport along the polymer chain.