SURFACE-ANALYSIS OF POLYCARBONATE THIN-FILMS BY HIGH-RESOLUTION ELECTRON-ENERGY LOSS SPECTROSCOPY - NEGATIVE-ION RESONANCES AND SURFACE VIBRATIONS

High-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy are used to examine thin polycarbonate films. While the HREEL vibrational spectra for thin films exhibit bands that correlate well with known infrared vibrational modes of bulk bisphenol-A-polycarbonate, there are significant intensity differences that are attributed to different vibrational excitation mechanisms, surface sensitivity, and temporary negative-ion resonance effects. Several vibrational modes show significant intensity variations with primary beam energy. Enhancement of carbonate vibrational features at approximately 3.5 eV and CH stretching (aromatic and aliphatic) related vibrational modes at approximately 4.5 and approximately 5.0 eV, respectively, indicate electron interaction with the polymer surface via temporary negative-ion resonances. Annealing of the polymer thin film at the glass transition temperature enhances the intensity of the aromatic CH stretching mode with respect to the intensity of the aliphatic CH stretching mode. This enhancement is a reflection of increasing aromaticity at the polycarbonate surface. No evidence of radiation damage from the electron beam or decomposition due to annealing in ultrahigh vacuum is detected.