Improved surface-enhanced Raman scattering based on Ag-Au bimetals prepared by galvanic replacement reactions

In this work, the improved surface-enhanced Raman scattering (SERS) of Rhodamine 6G (R6G) adsorbed on Ag-Au bimetals synthesized via galvanic replacement of Ag with Au was first investigated. First, silver substrates were roughened by triangular-wave oxidation-reduction cycles (ORC) in aqueous solutions containing 0.1 M KCl. At the same time, Cl^- and Au-containing nanocomplexes in solutions were prepared by treating gold substrates with the similar electrochemically roughening procedures. Then the roughened Ag substrates were incubated in the Cl^- and Au-containing solutions for different couples of minutes to undergo the galvanic replacement reactions. Encouragingly, the SERS of R6G adsorbed on this roughened Ag substrate modified by the replacement of Ag with Au for 3 min exhibits a higher intensity by one order of magnitude and a better resolution, as compared with the SERS of R6G adsorbed on an unmodified roughened Ag substrate. The increased SERS effect can be ascribed to the compositions of complexes formed on the substrates. In this optimum condition, the atomic ratio of Ag to Au is ca. 6.6.