N. John DiNardo

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. Early applications of High Resolution Electron Energy Loss Spectroscopy 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. Thin film polymers are used in a host of applications ranging from protective coatings to insulating layers in microelectronics devices. Ultrathin films deposited on conducting substrates can usually conduct well so that charging effects are minimized. Vapor-deposited ultrathin poly aniline films grown on silver(110) and gold can be compared with those grown on copper(110). No oligomer-substrate losses are observed on the silver and gold surfaces suggesting that the amino groups react only weakly with these surfaces. Significantly, similar trends in the transfer of intensity of the CH out-of-plane modes from monosubstituted rings to paradisubstituted rings are observed indicating the occurrence of a polymerization reaction.

To ultimately understand macroscopic adhesion in metallized plastics, fundamental metal-organic bonding chemistry at metal-polymer interfaces must be probed. Experimental surface spectroscopies have generally produced information for well-defined systems in surface chemistry. New applications of surface techniques to complex systems such as metal-polymer interfaces have recently produced exciting new developments in studies related to adhesion technology. Recent studies of electronic and vibrational structure and the morphology of metal-polymer interfaces are reviewed. Due to the high degree of interest in the particular system, we concentrate upon the metal-polyimide interface as a means to describe the scientific approach. The general applicability of these techniques and future directions are discussed.