Complex Assemble Of Different Metal Nanoparticles And Surface-enhanced Raman Spectrum Studies

Having size effect, nanoparticle has unique optic and electric property, For example, ideal enhanced effect was observed on definite-size Au or Ag nanoparticles, and its enhancement factor can reach to 1014 on some"hot spot"between nanoparticles, which attracted extensive attention of scientists and can fulfill its high sensitve in detection of monomolecule.In this paper, 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 submonolayers. By using pyridine (Py) as a probing molecule, surface enhanced Raman spectrum (SERS) effect was investigated on pure Au, pure Ag and Au-Ag mixed nanoparticle surfaces in the different excitation lines. By using the difference in the enhancement effect between 632.8 nm and 514.5nm excitation lines and the difference in the relative intensities of main SERS bands from Py, we investigated the change of Py SERS from the substrate on which Au and Ag existed together. 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 as well. 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.We also investigated the SERS from the Au&Pt mixed system. The results show that the intensity of SERS spectrum from the Au-Pt mixed system is weaker than that from Au.