SERS as a probe for adsorbate orientation on silver nanoclusters

Abstract

Surface-enhanced Raman scattering (SERS) spectroscopy has been used to characterize multilayers of three isomeric aromatic compounds adsorbed on silver nanoclusters. The three structural isomers, all of which adsorb in the carboxylate form onto the silver nanoclusters, bind in two different geometries to the silver surface. Different molecular configurations correlate to differences in bonding strength of these molecules to the silver surface, which can be probed by SERS. For ortho-hydroxybenzoic acid (salicylic acid), we observed red shifts of major SERS peaks in comparison to the normal Raman vibrations of nonadsorbed crystalline material. For this molecule the steric hindrance between the adjacent carboxylate and hydroxyl groups causes the carboxylate group to rotate from the common flat geometry of benzene substituents on surfaces and bond directly through one of the oxygen atoms to the surface. In this case, strong coordinative bonding between the carboxylate group and the metal surface causes the red shifts in the SERS peaks. For para-, and meta-hydroxybenzoic acid, the steric hindrance is less likely since the two functional groups are not at adjacent positions, and therefore these molecules adsorb on the silver surface in a totally flat geometry. For these molecules, in contrast to the ortho isomer, the CO 2 interacts with the surface through an extended π bond, and these molecules are physically adsorbed in the common flat position. Therefore, for the meta and para substituents, we do not observe significant red shifts in the SERS spectrum.

SERS study on surface chain geometry of atactic poly (methyl methacrylate) film and nanosphere

“…In order to analyze the orientation mechanism revealed by SERS, the EM component and chemical component must be considered, which occurs as a result of the excitation of surface plasmons in a metal nanocluster and the molecular interactions between the metal surface and the adsorbate, respectively. The chemical component may lead to wavenumber shifts of some molecular Raman vibrations . Such as the ρ(CH 3 ) expected at 970 cm −1 in normal spectrum, however, blue‐shifts to 1012 cm −1 (shown in Table and Fig.…”

“…The chemical component may lead to wavenumber shifts of some molecular Raman vibrations. [30] Such as the r(CH 3 ) expected at 970 cm À1 in normal spectrum, however, blue-shifts to 1012 cm À1 (shown in Table 1 and Fig. 4c) in the respective SERS spectra due to the physically adsorption.…”

Grafting of diazonium salts on oxides surface: formation of aryl-O bonds on iron oxide nanoparticles

“…All of them are based on a spectroscopic analysis of the organic species such as FTIR (PM-IRAS), (Risse et al 2003;Borasio et al 2005) Raman (SERS) (Nilsson et Pettersson 2004;Vericat et al 2006) and XPS. (S. Chen et Liu 2006;Fleger et al 2009) Surprisingly, tools based on the analysis of the substrate were seldom considered.…”

Tailoring gold and silver colloidal bimetallic nanoalloys towards SERS detection of rhodamine 6G

“…A series of FT-Raman experiments were carried out using rhodamine 6G (RhD6G, 80 mL, 1 Â 10 À4 M) as the molecular probe, which is a qualied analyte for SERS studies using Au, Ag and bimetallic NPs. [61][62][63][64][65][66][67] The mono and bimetallic colloids, as well as the physical mixture of Au and Ag (1 : 1) dispersions, were rstly tested for SERS detection by inducing the NPs aggregation using aqueous MgCl 2 solution and a non-resonant laser line of 632.8 nm, as seen in Fig. 5.…”