Surface enhanced Raman spectra (SERS) of pyridine and dye-1555 adsorbed on silver bromide colloids

Substrates for Surface-Enhanced Raman Scattering Formed on Nanostructured Non-Metallic Materials: Preparation and Characterization

The efficiency of the generation of Raman spectra by molecules adsorbed on some substrates (or placed at a very close distance to some substrates) may be many orders of magnitude larger than the efficiency of the generation of Raman spectra by molecules that are not adsorbed. This effect is called surface-enhanced Raman scattering (SERS). In the first SERS experiments, nanostructured plasmonic metals have been used as SERS-active materials. Later, other types of SERS-active materials have also been developed. In this review article, various SERS substrates formed on nanostructured non-metallic materials, including non-metallic nanostructured thin films or non-metallic nanoparticles covered by plasmonic metals and SERS-active nanomaterials that do not contain plasmonic metals, are described. Significant advances for many important applications of SERS spectroscopy of substrates based on nanostructured non-metallic materials allow us to predict a large increase in the significance of such nanomaterials in the near future. Some future perspectives on the application of SERS substrates utilizing nanostructured non-metallic materials are also presented.

Surface enhanced Raman scattering (SERS) activity studies of Si, Fe, Ti, Al and Ag films' prepared by magnetron sputtering

By magnetron sputtering we can make different kinds of metal or semiconductor films to study SERS-active substrate surface. Changing the conditions of magnetron sputtering can give the films of different surface shapes that we want. In this paper we gained the transitional metal films of Fe and Ti, the general metal films of Ag and Al, and the semiconductor films of Si. Then we use the atomic force microscope (AFM) to get the top view pictures of the films. And we also study the SERS mechanism of different films by dropping p-hydroxybenzoic acid (PHBA) solution on them. By this method we find a kind of nearly unearthly SERS-active substrate.

Investigation of p-hydroxybenzoic acid from a new surface-enhanced Raman scattering system

In this paper, we developed a new kind of substrate, silver-coated indium tin oxide (ITO), to investigate the character of surface-enhanced Raman scattering (SERS) of p-hydroxybenzoic acid (PHBA). Homogeneous Ag-coated ITO substrate was obtained by decomposing AgNO(3) on the surface of ITO. A SERS spectrum of very good quality of "silver nanoparticles/PHBA/silver-coated ITO" was reported by adding PHBA aqueous solution and silver colloid onto the surface of silver-coated ITO repeatedly. PHBA molecules absorbed onto the surface of the silver nanoparticles through ionized carboxyl, and the PHBA molecules tended to tilt on the surface in this system. The rich information obtained from the silver nanoparticles/PHBA/silver-coated ITO system indicates that this is a highly SERS-active system. Not only was the number of the vibrational modes increased, but also were the frequencies of Raman bands shifted. The two SERS mechanisms, the "electromagnetic" and "chemical" mechanism, were mainly responsible for the experimental results. Furthermore, the silver nanoparticles modified on the silver-coated ITO surface play an important role in magnifying the surface local electric field near the silver film surface through resonant surface plasmon excitation.

Surface-enhanced Raman scattering system of sample molecules in silver-modified silver film

Surface-enhanced Raman scattering (SERS) spectrum of very good quality of "silver nano-particles/sample molecules/silver film" system was reported by nesting the sample molecules to the gap of silver nano-particles and silver film, indicating that "silver nano-particles/sample molecules/silver film" is a highly SERS-active system. Not only was the number of the vibrational modes increased, but also were the frequencies of Raman bands up and down shifted. It is difficult to separate the contributions of the electromagnetic and chemical mechanisms to the great enhancement of the Raman signal. The shift by 5-30cm(-1) of the SERS bands and the change in their relative intensity compared with the ordinary Raman spectrum indicate the chemisorption of the sample molecules on the silver-modified silver surface. Furthermore, the silver nano-particles modified on the rough silver film surface play an important role in magnifying the surface local electric field near the silver surface through resonant surface plasmon excitation. From the rich information, obtained from high-quality SERS of PHBA in ternary system, we inferred that PHBA molecules in ternary system adsorb onto the metal surfaces through carboxyl at a perpendicular orientation.

Experimental (SERS) and theoretical (DFT) studies on the adsorption of p-, m-, and o-nitroaniline on gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of p-, m-, and o-nitroaniline (PNA, MNA, and ONA) adsorbed on gold nanoparticles were studied, respectively, in a gold colloidal solution and on dried gold-coated filter paper. Significant changes were found in the SERS spectra of p-, m-, and o-nitroaniline molecules adsorbed on the two substrates, indicating that the behavior of p-, m-, and o-nitroaniline adsorbed on gold nanoparticles coated on filter paper was different from that in gold aqueous colloids. Moreover, on the filter paper it was found that the SERS spectra of the PNA molecules changed with the coverage density of the gold nanoparticles, while the MNA and ONA did not evidently change. The analyses showed that the origins of these changes were the different adsorption behavior of molecules adsorbed on the gold nanoparticles and that the adsorption behavior of molecules was greatly affected by the surface characteristic of the substrate and the surface configuration of the adsorbate. In addition, the vibrational frequencies and Raman scattering intensities of the three nitroanilines were calculated by use of the density functional theory (DFT-B3LYP/6-31G(d)) method. The combination of SERS spectroscopy and DFT calculation is quite useful for studies of adsorption orientation of a molecule on a metal nanoparticle.

Surface-enhanced Raman scattering and the adsorption behavior of (RS)-phenylsuccinic acid

The surface geometry of (RS)-phenylsuccinic acid molecule was studied by analysis of the SERS spectra of aromatic dicarboxylic acid adsorbed on silver colloid surfaces. For a reliable analysis of the SERS spectrum, we also performed density functional theoretical calculations. The SERS spectral features indicated that the RSPSA molecules should bound to the silver as dicarboxylate, with a strongly tilted orientation with respect to the normal to the surface. Such a tilted orientation was presumed to occur by the simultaneous sigma and pi-type coordination of carboxylate groups to silver surface caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups, and thereby RSPSA on silver was easily displaced with aromatic carboxylic acids. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for aromatic carboxylic acid derivatives to assemble on a silver surface. The large enhancement of in-plane bending, out of plane bending and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a 'at least vertical' configuration, with the ring perpendicular to the silver surface.

Probing of porphyrin surface chemistry in systems with laser-ablated Ag nanoparticle hydrosol: role of thiosulfate anions

The influence of sodium thiosulfate (THS) concentration in Ag colloid/THS/H(2)TMPyP and Ag colloid/H2TMPyP/THS systems (H2TMPyP = 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin) was investigated by a combination of surface-enhanced resonance Raman scattering (SERRS) spectroscopy, surface plasmon extinction (SPE) measurements, and transmission electron microscopy (TEM). THS was found to have a strong impact on Ag nanoparticle surface structure and aggregation state and on interaction with H2TMPyP probe molecules, as evidenced by variations of the SERRS spectrum. In the Ag colloid/THS/H2TMPyP system, when laser-ablated Ag colloid was THS pretreated prior to the porphyrin addition, a critical threshold THS concentration (4 x 10(-5) M) was discovered. At concentrations below the threshold, THS mainly reduces the number of Ag+ adsorption sites. This leads to increased Ag nanoparticle aggregation prior to the porphyrin addition and significant weakening of the overall SERRS signal. Dominant contributions in the SERRS spectrum correspond to free base H2TMPyP and Ag+ containing the AgTMPyP form. At concentrations above the threshold, THS mediates also the formation and stabilization of new adsorption sites, probably Ag(0) sites. This induces a turn in the aggregation state of the pretreated Ag-c/THS system, an increase of the overall SERRS signal, and the appearance of a new spectral form of Ag metalated porphyrin.

The adsorption behavior of p-hydroxybenzoic acid on a silver-coated filter paper by surface enhanced Raman scattering

On dried filter paper coated with silver nanoparticles, surface-enhanced Raman scattering (SERS) spectra of p-hydroxybenzoic acid (PHBA) were studied, and high-quality SERS spectra were obtained, indicating that the silver-coated filter paper is a highly SERS-active substrate. The analysis showed that the adsorption behavior of PHBA molecules on silver nanoparticles coated on filter paper was different from that in silver aqueous colloids. On the filter paper, it was found that the SERS spectra of PHBA changed with the proportion of PHBA molecules and silver nanoparticles, indicating that the adsorption behavior of PHBA molecules changed with the proportion. The probable reasons are given.