Pulsed laser deposition of compact high adhesion polytetrafluoroethylene thin films

Polytetrafluoroethylene (PTFE) thin films were prepared from pressed powder pellets via pulsed laser deposition by using ArF (193 nm) excimer laser. The applied laser fluences were in the 1.6-10 J cm-2 range, the substrate temperature was varied between 27 deg. C and 250 deg. C and post-annealing of the films was carried out in air at temperatures between 320 deg. C and 500 deg. C. Films deposited at 250 deg. C substrate temperature were found to be stoichiometric while those prepared at lower temperatures were fluorine deficient. Morphological analyses proved that the film thickness did not significantly depend on the substrate temperature and the post annealing at 500 deg. C resulted in a thickness reduction of approximately 50%. It was demonstrated that the films prepared at 8.2 J cm-2 fluence and annealed at 500 deg. C followed by cooling at 1 deg. C min-1 rate were compact, pinhole-free layers. The adherence of films to the substrates was determined by tensile strength measurements. Tensile strength values up to 2.4 MPa were obtained. These properties are of great significance when PTFE films are fabricated for the purpose of protecting coatings. (author)