Synchrotron X-ray induced damage in polymer (PS) thin films

Abstract: Thin polystyrene (PS) films (M w =234,000) are spin coated on silicon substrates with a Chromium (Cr) layer as a sandwiched metallic layer that produces photoelectrons (by synchrotron X-rays). Earlier studies on synchrotron radiation damage in PS films, without metallic layer, have shown a decrease in interfacial roughness and a slight increase in thickness, at temperatures below T g [A.G. Richter, R. Guico, K. Shull, J. Wang, Macromolecules 39 (2006) 1545]. Similar trend is observed in the presence of a thin layer of Cr film (∼2.5nm). For the sample with a thick Cr layer the opposite effect was observed for X-ray radiation damage. For the 50nm thick Cr film system thickness of the polystyrene film decreased by ≈4.4% which amount to a loss of about 0.021nm3 per incident photon in the fluence range studied (6.8×109 photonsmm−2 to 1×1014 photonsmm−2). Interfacial roughness also increased from about 1.0nm to 2.1nm in the process. These effects are explained by invoking the presence of more number of X-ray induced photoelectrons and secondary electrons for 50nm thick Cr film case compared to 2.5nm thin film case. [Copyright &y& Elsevier]