Investigation of pulsed laser deposited crystalline PTFE thin layer with pulsed force mode AFM

Teflon thin films were prepared via pulsed laser deposition using an ArF excimer laser (λ=193 nm, FWHM=20 ns) from pressed powder pellets. The applied fluence was 6.25±0.23 J/cm2, the number of pulses was 10 000, the pressure in the vacuum chamber was 2x10-5 Torr and the substrate temperature was 250 deg. C. The layers were post-annealed at temperature within the range 320-500 deg. C. The atomic force microscopy and pulsed force mode atomic force microscopy (PFM) investigations demonstrated that the effective surface reaches its maximum at 320 deg. C. At higher temperatures (360-500 deg. C) it decreased significantly to an approximately constant value. Measuring the local adhesion the difference between the adhesion forces at 320 and 360 deg. C was kept within the error range. Increasing the annealing temperatures, the adhesion force decreased over the investigated range. Post-annealing of the samples at 360 deg. C resulted in highly crystalline spherulites with lateral dimensions of several hundred micrometers. By optimizing the heating and cooling rate during the annealing the average dimension of spherulites increased and ringed structures were obtained. The PFM measurements showed that the adhesion force increased significantly compared to the similar samples without ringed structures