Application of 2D correlation methods to the analysis of XPS spectra of ion irradiated poly (ether ether ketone)

The effects of ion irradiation conditions on poly (ether ether ketone) (PEEK) was probed by X-ray photoelectron (XPS) and two-dimensional correlation (2D-COS) spectroscopies. XPS data were reorganized according to the absorbed dose and penetration of X-ray radiation into PEEK. Subsequently, generalized and hybrid 2D-COS techniques were used to explore the effects of ion irradiation energy, type, and beam current on the chemistry of PEEK. The carbon peak at 284.4 eV changed on opposite direction on irradiation with the two different ions, i.e. proton and helium, or by increasing the dose rate. The reduction in the peak at 286.3 eV on helium irradiation implied the formation of three-dimensional structures involving C-C bonding via the H-link mechanism. The carbon peaks shifted to higher binding energy on irradiation with low beam current, and the opposite was true using high beam current. The former indicated oxidation reactions, and the latter indicated cross-linking formation. Changing the ions used on irradiating polymer not only control cross-linking extent but also produced different cross-linking structures. XPS combined with 2D-COS techniques provides a powerful tool to investigate the mechanism of complicated reactions such those occurring in the ion irradiation of PEEK.