Argon plasma-induced modifications at the surface of polycarbonate thin films

The chemical modification of the surfaces of polycarbonate films by microwave-induced argon plasma treatment has been followed by X-ray absorption spectroscopy (XAFS) and core level photoemission spectroscopy (XPS). Measurements have been made on thin films of both ex-situ spin-coated bis-phenol-A polycarbonate with phenol endgroups and the model compound bis-phenol-A polycarbonate (n = 1) with tert-butyl phenyl endgroups evaporated in-situ in UHV on single crystal surfaces. A preferential orientation of a monolayer of the model compound on a Ag{111} surface was determined from the angular dependence of the XAFS spectra. Spectral features were assigned to contributing transitions within different moieties. Relatively mild microwave Ar plasma activation of the surfaces of both types of films led to a decrease in intensity of carbonyl features in both XAFS and XPS. Combined with the observation of new spectral features in XPS the data can be interpreted in terms of a formation of ester and ether groups in the near-surface region with possible cross-linking after desorption of CO or CO2.