Characterization of particulates accompanying laser ablation of pressed polytetrafluorethylene (PTFE) targets

We present observations of sub-micron- to micron-sized particles generated by high fluence (approximate to 2 J/cm(2)) 248-nm laser ablation of pressed polytetrafluorethylene (PTFE) targets in air at atmospheric pressure. The original target material was hydrostatically compressed approximate to 7 mu m PTFE powder, sintered at 275 degrees C. Collected ejecta due to laser irradiation consists of four basic particle morphologies ranging from small particles 50-200 nm in diameter to larger particles approximate to 10 mu m in diameter. Many particles formed in air carry electric charge. Using charged electrodes we are able to collect charged particles to determine relative numbers of +/- charge. We observe roughly equal numbers of positively and negatively charged particles except for the largest particles which were predominantly negative. For a range of particle sizes we are able to measure the sign and magnitude of this charge with a Millikan-oil-drop technique and determine surface charge densities. The implications of these observations with respect to pulsed laser deposition of PTFE thin films and coatings are discussed.