Annealing effect: Controlled modification of the structure, composition and plasmon resonance of hybrid Au-Ag/C nanostructures

Here we present a novel approach to the synthesis of hybrid Au-Ag/C nanoparticles (NPs) which were found to be carbon nanospheres containing dispersed Au-Ag bimetallic nanoparticles (1-5 nm). The Au-Ag/C NPs were obtained by laser-induced liquid phase deposition from solutions of supramolecular complex. It was revealed that subsequent annealing procedure of Au-Ag/C NPs at various temperatures over the range 100-600 °C allows variation and directed control of NPs' morphology and composition (relative contents of principal components). For nanoscale carbon material the critical evaporation temperature was found to be about 300 °C, while for Ag and Au components - 500 °C and 600 °C accordingly. The morphology and composition variation makes possible tuning of the surface plasmon resonance characteristics that opens an efficient way of the NPs' functional properties control, like for example Surface-Enhanced Raman Scattering (SERS). It was found that the obtained hybrid Au-Ag/C NPs display pronounced SERS activity with the enhancement factor (EF) ca. 105.