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) films of 8–14 layers were electrochemically reduced into Ag clusters, which made the observation of well-ordered scanning tunneling microscope (STM) images of the films with molecular resolution. A hexagonal packing of the hydrophobic chains was obtained. which was superimposed on the two-dimensional Ag clusters of 2–3 nm in diameter. Furthermore, a (2×1) structure of the hexagonal packing was observed. It was attributed to a self-assembled structure of the hydrophilic surface of the L-B films through hydrogen bonding. The strong surface enhanced Raman scattering (SERS) effect of Ag clusters made it possible to record Raman spectra of twoiayer stearic acid L-B films in the region of C—C stretching vibration frequencies. The appearance of the bands at 1 128.0 and 1 100. 7 cm−1, which correspond to the antisymmetric C—C stretching model of the acyl chains in theall-trans conformation and the C—C stretching model of the acyl chains in thegauche conformations, respectively, means that the methylene chains are mainly inall-trans conformation, but some of them become disordered.