The Surface-enhanced Raman Spectrum Of Mixed Metal Nanoparticles

Surface-enhanced Raman spectroscopy (SERS) is becoming a potential and widely used analytical technique, because it can provide extremely high detection sensitivity up to single molecule level and vibretional information spreading the whole molecular vibration spectrum.Having size effect, nanoparticle has unique optic and electric property, For example, ideal enhanced effect was observed on definite-size Au nanoparticles, and its enhancement factor can reach to 1014 on some"hot spot"between nanoparticles. Most previous studies have focused on the SERS effect from single metal nanoparticles, the report about the SERS behavior of two or more nanoparticles was less. Based on this, the paper studied the SERS effect from mixed nanoparticles.Electrostatically self-assembled two kinds of nanoparticles (gold nanoparticles and Au core Pt shell nanoparticles) on silicon surfaces which were silanization, the density of nanoparticles was controlled by changing the time of the substrate immersed in colloids. The substrate was characterized by scanning electron microscope (SEM), and the results indicates that Au and Au@Pt particles were dispersed on the substrate with mono/submonolayers. We use pyridine (Py) as a probing molecule, surface enhanced Raman spectroscopy (SERS) effect was investigated on pure Au and Au-Au@Pt mixed nanoparticle surfaces under the excitation line of 632.8 nm. The results revealed that there is on significant shift of the two characteristic peaks of Py, but the enhancement factors of Au dropped off precipitously with the introduction of the Au@Pt nanoparticles. We attributed this effect to the introduction of d-states from the metal, which would serve effectively to quench the surface plasmon excitation necessary for large (electromagnetic) enhancements in Raman spectroscopy. We get the same conclusion when use thiophenol (TP) as a probing molecular.In addition, this paper also investigate the SERS from the Ag-Au@Pt mixed system under different excitation line (514.5nm and 632.8nm). The same situation occurred on the mixed system: the enhancement factors of Ag dropped off precipitously with the introduction of the Au@Pt nanoparticles. The study indicated that the enhancement factors of high SERS active metal dropped off with the introduction of the less-SERS-active (Pt) metal. This results is very helpful to the study of SERS machanism.