Electron-Induced Vibrational Spectroscopy. A New and Unique Tool To Unravel the Molecular Structure of Polymer Surfaces

Among the surface-sensitive spectroscopies used to characterize clean and surface-modified polymers, one technique has rather recently emerged as a very promising complementary tool. High-resolution electron energy loss spectroscopy, or electron-induced vibrational spectroscopy, has potentially all the attributes of the well-known optical (infrared and Raman) spectroscopies; it clearly adds to X-ray photoelectron spectroscopy the possibility to go beyond surface elemental and chemical analysis and to unravel the molecular structure of an extremely thin surface layer of a polymer. This ultrahigh vacuum spectroscopy is shown here to gather information from the last 25 angstrom or so of the polymer surface, as deduced from the analysis of sandwich layers of normal and perdeuterated PMMA Langmuir-Blodgett films. Four case studies of molecular-type information are presented, illustrating (1) the preferential surface segregation of CH3 chain ends on a crystalline polyethylene, (2) selective surface segregation and dynamics of deuterated material in mixtures of normal and deuterated polystyrenes, (3) tacticity induced molecular orientation of PMMA's and polystyrene, and (4) metalization induced molecular reorientation on the surface of polyimide films