Tuning the surface enhanced Raman scattering performance of anisotropic Au core−Ag shell hetero-nanostructure: The effect of core geometry

Noble metal nanostructures exhibit strong surface-enhanced Raman scattering (SERS) activity and attract much attention due to their enhancement of electromagnetic field that is induced by localized surface plasmon resonance (LSPR). It is well known that fabrication of gold nanoparticles with sharp corners or deposition of Ag on gold nanoparticles is the effective way to improve the SERS activity. In this paper, we investigated the SERS performance of gold nanorods (Au NRs) and gold nanobipyramids (Au NBs). Compared with Au NRs, Au NBs had two pentagonal pyramids of which the apexes were much sharper than those of Au NRs and hence possessed greater SERS activity due to the lightning-rod effect. In addition, Au NRs-Ag core-shell nanoparticles (Au [email protected] nanoparticles) and Au NBs-Ag core-shell nanoparticles (Au [email protected] nanoparticles) were successfully synthesized and their SERS activities were compared. It was observed that the Ag deposition processes were different between Au NRs and Au NBs. During the Ag deposition process, Au NRs gradually changed from nanorods to irregular morphologies (spherical, triangular pyramid, octahedron and so on); the shape of Au NBs changed from bipyramids to rice and adopted a final shape of cylindrical rod. Interestingly, the Au [email protected] nanoparticles had higher SERS activity than the corresponding Au [email protected] nanoparticles. The mechanism could be attributed to the Ag depositing-induced different shell shapes and alignment fashions of the nanoparticles.