Analysis of the Gold/Polymer Electrolyte Membrane Interface by Polarization-Modulated ATR-FTIR Spectroscopy

We developed a new FTIR system with two polarizers in its optics in order to conduct polarization-modulated measurements. Polarization characteristics were examined for the Kretschmann polarization-modulated attenuated total reflectance (ATR) configuration by the use of gold-sputtered films of 10-100 nm thickness on Ge and ZnSe prisms. The marked increase of the polarization characteristics for Au film thicknesses below 30-40 nm is closely associated with a large reflectivity decrease of the p-polarized radiation. A cast film of sulfonated block poly(arylene ether sulfone ketone) membrane was formed on the Au film, and the interfacial spectra were acquired by the use of the ATR FTIR system. The interfacial spectra resemble those of the ATR spectra of the bulk membrane but exhibited strong dependence of the intensity and line shape of the vibrational modes on the Au thickness. The dependence is closely associated with a change of the polarization characteristics of the interface. Electromagnetic as well as chemical effects were concluded to be responsible for the band anomalies and enhancement.