ABSTRACT
Early applications of High Resolution Electron Energy Loss Spectroscopy (HREELS) for the study of ultrathin polymer films and polymer-metal interfaces provided important information on bonding and electronic structure through analysis of sequentially-measured vibrational and electronic excitation spectra in the near-surface region. However, detailed analyses of vibrational spectra were limited by energy resolution >40 cm−1 which made it difficult to separate close-lying vibrational modes. Recent developments in HREEL spectrometers has made it possible to achieve <8 cm−1 energy resolution, and along with the ability to excite both optically-active and optically-forbidden transitions, virtually all the vibrational modes of complex polymer ultrathin films can be distinguished. Then the analysis of surface functionalities and interfacial bonding proceeds by comparison with reference infrared, Raman, and uv-vis spectra of molecular analogs. In this paper, we present brief highlights in the development of HREELS for the study of polymer systems and discuss our recent studies of polyaniline ultrathin films deposited on metal surfaces. These studies have (1) identified substrate-dependent effects in initial bonding and growth of vapor-deposited polyaniline oligomers, (2) shown evidence for polymerization at the surface, (3) found relatively high local conductivity in protonated films after ex-situ doping, and (4) provided new insights in the conductivity mechanisms themselves. Finally, prospects and limitations of HREELS as applied to polymer systems are noted.
