Synchrotron radiation ablative photodecomposition and production of crystalline fluoropolymer thin films

Abstract

Deposition of crystalline thin films of polytetrafluoroethylene (PTFE) was carried out on Si(100) substrates by synchrotron irradiation of a PTFE target in vacuo. In situ mass spectrometric analysis of gaseous species evolved during the irradiation shows that, different from the laser ablation of PTFE for the deposition, the SR-induced reactions should be ablative photochemical decomposition (APD) rather than photothermal unzipping decomposition, yielding saturated fluorocarbons rather than monomers as the main gaseous products. Detection of a trace of CF3 in the deposited films by XPS and FTIR was consistent with our APD mechanism. In our processing, an increase in the target temperature made great improvements including considerable enhancement of the deposition rates, reduction of the CF3 component, and achievement of the crystalline features closer to the PTFE target, whereas an increase in the substrate temperature made the film surface rough.