Investigation on electrical charging/discharging properties of thin ps/pmma polymeric films by dynamic x-ray photoelectron spectroscopy
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Electrical charging/discharging properties of thin layers of spin coated pure PS polystyrene (PS), and pure poly(methyl methacrylate), (PMMA) and an immiscible PS/PMMA blend are studied with externally applied DC and dynamic(squarewave stress) X-Ray Photoelectron Spectroscopy (XPS). PS and PMMA exhibit quite different charging properties under DC stress. Due to the different charging properties of PS and PMMA domains within an immiscible PS/PMMA blend film, charge contrast or phase separation is clearly observed between domains. Electrical parameters of PS and PMMA thin films while employing a squarewave pulse stress in a 10-3 - 103 Hz range of frequency are probed by dynamic XPS. A model, which can simulate the dynamical XPS measurements, is shown to lead to obtain effective resistance and capacitance values for each polymer. RC time constants and inflection points(frequency) are also determined. Moreover, thickness also affects the charging/discharging properties and other electrical parameters of polymeric thin films. Furthermore, to mimic certain dielectric properties of thin polymeric films and to validate our model, we have included an externally RC circuit to a conducting graphite sample under both DC and squarewave pulse stresses.