Enhanced Raman Scattering in Gaps Formed by Planar Au and Au/Ag Alloy Nanoparticles

Abstract

In this study, the Raman spectral characteristics of 1,4-phenylenediisocyanide (1,4-PDI) and 4-aminobenzenethiol (4-ABT) positioned at the nanogap formed by Au/Ag alloy nanoparticles and a flat Au substrate were examined, and three-dimensional finite-difference time-domain (3-D FDTD) calculations were carried out. A more intense Raman signal was measured, regardless of the excitation wavelength, when Ag-rich Au/Ag alloy nanoparticles were used to form the nanogaps. Regarding the excitation wavelength, 568 nm of light was the most effective in inducing a Raman signal, particularly when Ag nanoparticles were adsorbed on 1,4-PDI or 4-ABT, whereas 632.8 nm of light was slightly more effective than 568 nm of light when Au nanoparticles were adsorbed onto them. The Raman spectra of 1,4-PDI could be attributed to the electromagnetic enhancement mechanism. The dependencies of the Raman spectra of 1,4-PDI on the excitation wavelength and the type of Au/Ag alloy nanoparticle were comparable to those predicted by the 3-D FDTD calculations. From the measured NC stretching frequencies, the surface of 35 nm sized Au/Ag alloy nanoparticles containing more than 5 mol % of Ag atoms was concluded to be covered fully with Ag atoms. The Raman spectra of 4-ABT were interpreted to be a product of electromagnetic and chemical enhancement mechanisms. Assuming that the Raman intensity ratios of the b 2 -and a 1 -type bands were indicative of the extent of chemical enhancement, the Ag-to-4-ABT electron transfer appeared more facile than the Au-to-4-ABT transfer did and more favorable by excitation with a 514.5 nm laser than a 568 nm or 632.8 nm laser.

Trace-Level Detection of Secondary Explosives Using Hybrid Silver–Gold Nanoparticles and Nanostructures Achieved with Femtosecond Laser Ablation

“…31−33 Some of them are a mixture of chemical and physical processes such as ablating a bulk plasmonic metal target in solutions such as HAuO 4 or AgNO 3 . 34,35 However, in the present study, we tried to prepare bulk Ag−Au targets by mixing through melting the gold and silver at different proportions (1 g of Ag + 0.5 g of Au, 0.5 g of Ag + 0.5 g of Au, 0.5 g of Ag + 1 g of Au) and were successful. The alloys were prepared by mixing the melts of Ag and Au thoroughly and subsequent to cooling the targets were immediately (within The Journal of Physical Chemistry C Article 2−3 h) used for ablation to avoid any undesirable surface effects.…”

Ultrahigh Enhancement of Electromagnetic Fields by Exciting Localized with Extended Surface Plasmons

“…25,[35][36] All these advantages make the MNOMF a good platform for SERS, SEF, plasmon-enhanced photoluminescence, and other techniques. 22,[37][38][39][40] Generally, the metal NP and the metal film can sustain LSPRs and ESPs, respectively. For periodic NP array on metallic film, the NP array can excite the ESPs of the metal film by acting as a 2D grating to provide additional momentum.…”

Au–Ag alloy nanoparticle-incorporated AgBr plasmonic photocatalyst

“…2b) can be explained in terms of the LEFE effect of the Au-Ag alloy NPs. However, the origin for the increase in Q-factor with a slight dose of Au into Ag NP remains unclear since simulations for Au x -Ag 1−x alloy NPs at 0 ≤ x ≤ 1 by finite-difference time-domain method indicated that the increase in x decreases the LEFE factor with the LSPR peak wavelength redshifted [26][27][28][29][30] . Based on these results, we discuss the action mechanism of Au-Ag@AgBr in the photocatalytic degradation of 2-naphthol (Scheme 2).…”