Influence of particulate size on the formation of polytetrafluoroethylene thin films during pulsed laser deposition

The lowest thickness of contiguous polytetrafluoroethylene (PTFE) thin films prepared by pulsed laser deposition is influenced by the size of the particulates emitted from the target. Since the particulates reach the substrate at random, by the time a contiguous layer is formed its average thickness can be several times as much as the mean size of the particulates. During our experiments the size distribution of the particulates emitted during ArF excimer laser deposition from pressed PTFE pellets was studied as the function of the applied ablating fluence in the range of 1.1 - 6.2 J/cm². The size distribution of the particulates could be described with a first order exponential decay function. The value of the decay constant varied between 3.94 and 6.15 depending on the laser fluence. With the knowledge of the size distribution of the depositing particulates a theoretical model was used for simulating the growth of the thin film. The minimum number of the pulses required to obtain a contiguous layer and its thickness could be estimated. The thinnest layer could be obtained at the lowest investigated fluence.