Surface characteristics of Ag‐doped Au nanoparticles probed by Raman scattering spectroscopy

Abstract

We have examined the surface characteristics of Ag-doped Au nanoparticles (below 5 mol% of Ag) by means of the surfaceenhanced Raman scattering (SERS) of 2,6-dimethylphenylisocyanide (2,6-DMPI) and 4-nitrobenzenethiol (4-NBT). When Ag was added to Au to form ∼35-nm-sized alloy nanoparticles, the surface plasmon resonance band was blue-shifted linearly from 523 to 517 nm in proportion to the content of Ag up to 5%. In the SERS spectra of 2,6-DMPI, the N-C stretching peak also shifted almost linearly from 2184 to 2174 cm −1 when the Ag content was 5 mol% or less; the peak then remained the same as that of the pure Ag film. The potential variation of the SERS spectrum of 2,6-DMPI in an electrochemical environment, as well as the effect of organic vapor, also showed a similar tendency. From the SERS of 4-NBT, we confirmed the occurrence of a surfaceinduced photoreaction converting 4-NBT to 4-aminobenzenethiol, when Ag was added to Au to form alloy nanoparticles. The photoreaction induction ability also increased linearly with the Ag content, reaching a plateau level at 5 mol% of Ag. All these observations suggest that the surface content of Ag should increase almost linearly as a function of the overall mole fraction of Ag and, once the Au/Ag nanoparticles reach 5 mol% of Ag, their surfaces are fully covered with Ag, showing the same surface characteristics of pure Ag nanoparticles.

Recent advances in linear and nonlinear Raman spectroscopy. Part VII

“…Kim and co‐workers studied the surface characteristics of Ag‐doped Au nanoparticles with Raman scattering. Their observations suggest that the surface content of Ag should increase almost linearly as a function of the overall mole fraction of Ag and, once the Au/Ag nanoparticles reach 5 mole% of Ag, their surfaces are fully covered with Ag, showing the same surface characteristics of pure Ag nanoparticles . In a related paper, these same investigators studied surface potential variation of gold nanoparticles by organic vapors as revealed by Raman scattering of 1,4‐phenylenediisocyanide.…”