SERRS and absorption spectra of pyridine on Au m Ag n (m + n = 6) bimetallic nanoclusters: substrate composition and applied electric field effects.

Surface-enhanced Raman scattering (SERS) and absorption spectra of the pyridine molecule adsorbed on Au m Ag n (m + n = 6) bimetallic clusters are theoretically investigated by time-dependent density functional theory. The contributions of static chemical enhancement to the ground-state system are analyzed, and the static Raman intensity of Py-Au m Ag n complexes are enhanced by an order of 10. A method of visualization on charge transfer is used to distinguish the contributions of charge-transfer enhancement and electromagnetic enhancement. The intensity of surface-enhanced resonance Raman scattering (SERRS) spectroscopy of Py-Au m Ag n is strongly enhanced by an order of 103 -105 , compared to the static Raman intensity of pyridine. The influence of the static external electric field on SERS is investigated by calculating the optical properties of the Py-Au3 Ag3 complex. The intensity of SERRS spectra and normal Raman spectra can be significantly enhanced by the positive electric fields, and the intensities of specific Raman vibrational modes could be selectively enhanced or weakened by tuning the direction and strength of the static electric field applied on Py-Au3 Ag3 .