We prepared Au/Ag core-shell nanoparticles by growing Ag shell onto 12 nm Au core, using silver nitrate and sodium citrate as the reactants. By changing the molar ratio of Ag to Au, the shell thickness and thus the size of bimetallic particles could be controlled in convenient way. The formation of core-shell structure was proved by UV-Vis spectra, transmission electron microscopy(TEM), etc.. The core-shell particles showed a more narrow size distribution than Ag colloid prepared without Au core. The SERS activity of the core-shell particles was investigated by using 2,4-dimethylpyridine as the probe, which strongly indicated their potential application in SERS substrate materials.
We present our work on direct assembly of Ag nanoparticulate film onto mica substrates without coupling agent, and investigate the potential application of this kind of assembly to SERS. Colloidal Ag is assembled onto mica substrates treated with MnCl 2 solution by electrostatic interaction, which forms a two-dimensional submonolayer. As shown by AFM study, the assembled process is size-selective, e.g., Ag particles assembled onto mica are more uniform than the mother colloid. The as-prepared Ag nanoparticulate films were shown to be active for surface-enhanced Raman scattering(SERS), as evidenced by the strongly enhanced Raman scattering from the self-assembled films(SAMs) of p-mercaptoaniline(p-MA).
