Ag and Au nanoparticles were self-assembled on a silicon substrate simultaneously. The density of Ag and Au nanoparticles was controlled by changing the volume ratio of Au to Ag colloids. SEM images indicated that Ag and Au nanoparticles were dispersed on the substrate with mono/submono layers. By using pyridine (Py) as a probing molecule, surface enhanced Raman spectroscopy (SERS) effect was investigated on pure Au, pure Ag and Au-Ag mixed nanoparticle surfaces in the different excitation lines. By considering the difference in the enhancement effect between 632.8 and 514.5 nm excitation lines and the difference in the relative intensities of main SERS bands from Py, the SERS effect of Au nanoparticles in the mixture system was separated by a series of calibrations and subtractions of the spectra to eliminate the contribution from Ag nanoparticles. The results revealed that the SERS spectral features of Py from the mixture system and the separated spectrum of Au nanoparticles were similar with those from the pure Ag nanoparticles, indicating the coupling effect between the Ag and Au nanoparticles.

Key words: Ag/Au nanoparticle, self-assembly, surface enhanced Raman spectroscopy, pyridine