AG CLUSTERS ELECTROCHEMICALLY REDUCED IN STEARIC-ACID LANGMUIR-BLODGETT-FILMS AND THEIR STRUCTURAL CHARACTERIZATIONS

Silver ions confined in the silver stearate Langmuir-Blodgett (L-B) fi lms of 8-14 layers were electrochemically reduced into Ag clusters, wh ich made the observation of well-ordered scanning tunneling microscope (STM) images of the films with molecular resolution. A hexagonal pack ing of the hydrophobic chains was obtained, which was superimposed on the two-dimensional Ag clusters of 2-3 nm in diameter. Furthermore, a (2 X 1) structure of the hexagonal packing was observed. It was attrib uted to a self-assembled structure of the hydrophilic surface of the L -B films through hydrogen bonding. The strong surface enhanced Raman s cattering (SERS) effect of Ag clusters made it possible to record Rama n spectra of two-layer stearic acid L-B films in the region of C-C str etching vibration frequencies. The appearance of the bands at 1 128.0 and 1 100.7 cm(-1), which correspond to the antisymmetric C-C stretchi ng model of the acyl chains in the all-trans conformation and the C-C stretching model of the acyl chains in the gauche conformations, respe ctively, means that the methylene chains are mainly in all-trans confo rmation, but some of them become disordered.