A near-infrared FT-Raman (SERS) and electrochemical study of the synergistic effect of 1-[(1′,2′-dicarboxy)ethyl]-benzotriazole and KI on the dissolution of copper in aerated sulfuric acid

The adsorption on copper in aerated 0.5 m sulphuric acid (30°C) of 1-[(1,2-dicarboxy)ethyl]-benzotriazole (BTM) has been investigated by means of surface enhanced Raman scattering (SERS) techniques. The inhibition efficiency in aerated acid increased with increasing BTM concentration to a maximum (52%) at the 1 × 10–3 m level. Benzotriazole (BTAH) was found to be about 20% more efficient as an inhibitor for copper corrosion under the same conditions. BTM (1 × 10–3 m) showed increased inhibition with increasing pH reaching a maximum value of 78.3% at pH 8. Polarization studies showed that BTM suppressed both the cathodic and anodic corrosion reactions. The SERS studies suggest that, like BTAH, BTM inhibits copper corrosion by adsorption through the azole nitrogen. This study also showed that the performance of BTM can be significantly improved by adding KI. SERS indicates that the iodide ions displace the protonated BTM on the copper surface and this is followed by an overlayer of protonated BTM molecules.     

表面增强拉曼光谱研究稳定剂TAI在银上的吸附

用表面增强拉曼光谱的方法研究4－羟基－6－甲基－1，3，3a,7-四氮茚（TAI）在金属银上的吸附。实验表明TAI分子是通过分子上的N原子以化学吸附的方式吸附在银电极上。电极处理的氧化－还原循环次数并不影响振动频率，但在一定范围内对表面增强拉曼光谱的吸收强度有明显影响。     

An electrochemical and SERS study of benzyldimethylphenylammonium chloride at a polycrystalline gold electrode

The adsorption behaviour of benzyldimethylphenylammonium chloride (BDMPAC) on polycrystalline gold has been investigated by means of dc (cyclic voltammetry) and ac electrochemical techniques (differential capacitance (DC), electrochemical impedance spectroscopy) and in-situ vibrational spectroscopy (surface enhanced Raman spectroscopy (SERS)). The adsorption of this quaternary ammonium salt is found to be mediated by specifically adsorbed chloride ions in the potential domain positive to the pzc; when chloride ions are expelled from the compact layer out of electrostatic reasons, BDMPAC adsorbs interacting directly with the metal surface through one of its aromatic rings. In accordance with the DC results, SERS show a reorientation of the molecule around −200 mV versus Ag/AgCl.     

Shell-isolated nanoparticle-enhanced Raman spectroscopy of pyridine on smooth silver electrodes

The invention of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) extends the study of Raman spectroscopy into surface electrochemistry on the SERS-inactive smooth electrodes. This work aims to investigate the electrochemical system perturbation brought about by spreading Au–core silica–shell nanoparticles (Au@SiO₂ NPs) over the electrode surface for SHINERS. The differential capacitance measurements have shown SHINERS to cause the minimum of disturbance in the electrochemical system. The spectral features of SHINERS of pyridine adsorbed at smooth silver electrodes differs from that of SERS on the electrochemically roughened surface because pyridine interacts with silver much more strongly on the roughened electrode with many heterogeneous adsorption sites. Since most electrochemical data about surface adsorption are based on mechanically polished surface, the spectral information provided by the in situ SHINERS could be more reliable and better correlation.     

Determination of the Molecular Structure of Interphases Between Epoxy/4,4'-Diaminodiphenylsulfone Adhesives and Silver Substrates Using SERS and XPS

The molecular structure of interphases formed by curing an epoxy/4,4'-diaminodiphenylsulfone (DADPS) adhesive against rough silver substrates was determined using surface-enhanced Raman scattering (SERS) and x-ray photoelectron spectroscopy (XPS). SERS spectra obtained from the adhesive deposited onto silver island films were very similar to SERS spectra obtained from the DADPS curing agent spun onto silver island films, indicating that DADPS in the adhesive system segregated to the interphase and was preferentially adsorbed onto the silver substrate. Differences in the relative intensity of several bands in the normal Raman and SERS spectra of DADPS were observed. For example, the band near 1603 cm^-1 was stronger in SERS spectra of DADPS than in normal Raman spectra. The band near 1150 cm^-1 was weaker in SERS spectra of DADPS than in normal Raman spectra. These results implied that DADPS was adsorbed through one of the NH groups with an end-on conformation. Consistent results were also obtained from XPS spectra. C(ls) spectra of the adhesive and silver fracture surfaces of specimens prepared by curing the adhesive against silver substrates were more similar to the C(ls) spectra of DADPS than to those of the bulk adhesive. These results confirmed the preferential adsorption of DADPS onto the silver substrate from the adhesive system. The similarity of the C(ls) spectra obtained from adhesive and silver fracture surfaces indicated that a thin DADPS-rich interphase was formed between the bulk adhesive and the silver substrate and that the locus of failure was partially within this layer. However, less nitrogen and sulfur were detected on the silver fracture surface than on the adhesive fracture surface. A large amount of silver was observed on the substrate fracture surface and a trace was found on the adhesive fracture surface. These results indicated that failure of the adhesive joints was within the interphase but near the silver substrate. No evidence of chemisorption of DADPS onto the substrate was observed.     

Excitation wavelength dependent surface enhanced Raman scattering of 4-aminothiophenol on gold nanorings

Detailed understanding of the underlying mechanisms of surface enhanced Raman scattering (SERS) remains challenging for different experimental conditions. We report on an excitation wavelength dependent SERS of 4-aminothiophenol molecules on gold nanorings. SERS and normal Raman spectra, combined with well-characterized surface morphology, optical spectroscopy and electromagnetic (EM) field simulations of gold nanoring substrates indicate that the EM enhancement occurs at all three excitation wavelengths (532, 633 and 785 nm) employed but at short wavelengths (532 and 633 nm) charge transfer (CT) results in additional strong enhancements of particular Raman transitions. These results pave the way to further understanding the origin of the SERS mechanism.     

Two-dimensional ultrathin gold film composed of steadily linked dense nanoparticle with surface plasmon resonance

Background

Noble metallic nanoparticles have prominent optical local-field enhancement and light trapping properties in the visible light region resulting from surface plasmon resonances.

Results

We investigate the optical spectral properties and the surface-enhanced Raman spectroscopy of two-dimensional distinctive continuous ultrathin gold nanofilms. Experimental results show that the one- or two-layer nanofilm obviously increases absorbance in PEDOT:PSS and P3HT:PCBM layers and the gold nanofilm acquires high Raman-enhancing capability.

Conclusions

The fabricated novel structure of the continuous ultrathin gold nanofilms possesses high surface plasmon resonance properties and boasts a high surface-enhanced Raman scattering (SERS) enhancement factor, which can be a robust and cost-efficient SERS substrate. Interestingly, owing to the distinctive morphology and high light transmittance, the peculiar nanofilm can be used in multilayer photovoltaic devices to trap light without affecting the physical thickness of solar photovoltaic absorber layers and yielding new options for solar cell design.     

表面增强拉曼散射基底的研究进展

表面增强拉曼光谱(SERS)由于其高的灵敏度、抗干扰能力强等优点,被广泛应用在表面科学、分析化学、物理学等领域,是研究表面和界面过程的重要工具,是定性鉴定化学组成相近化合物的有力手段.因此,高品质、高活性的SERS基底一直是科研工作者们追求和研究的重点.本文对SERS活性基底的发展进行了介绍,从金、银金属纳米粒子作为基底的拉曼效应的科学研究,又进一步总结了非金属纳米粒子ZnO、TiO₂、ZnS、Cu₂O、CdTe、CdS等SERS基底.今后,将贵金属与半导体纳米材料复合将是SERS基底的研究热点.SERS光谱目前可以在液相色谱分析的检测器、医学检测仪器、刑侦分析检测等众多领域得到应用.     

High sensitivity surface enhanced Raman spectroscopy of R6G on in situ fabricated Au nanoparticle/graphene plasmonic substrates

Plasmonic gold nanoparticles (AuNP) with controllable dimensions have been fabricated in situ on graphene at moderately elevated temperature for high sensitivity surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Significantly enhanced Raman signature of R6G dyes were observed on AuNP/graphene substrates as compared to the case without graphene with an improvement factor of 400%, which is remarkably greater than previous results obtained in ex situ fabricated SERS substrate. Simulation of localized electromagnetic field around AuNPs with and without the underneath graphene layer reveals an enhanced local electromagnetic field due to the plasmonic effect of AuNPs, while additional Ohmic loss occurs when graphene is present. The enhanced local electromagnetic field by plasmonic AuNPs is unlikely the dominant factor contributing to the observed high SERS sensitivity on R6G/AuNP/graphene substrate. Instead, the p-doped graphene, which is supported by the large positive Dirac point shift away from “zero” observed in AuNP/graphene field effect transistors, promotes SERS signals through enhanced molecule adsorption and non-resonance molecular–substrate chemical interaction.     

The influence of a mixed radiation environment on the properties of the passive film on tungsten

The properties of the passive film formed on the tungsten (W) in H₂SO₄ (pH 1.6) during proton irradiation (spallation) were characterized with electrochemical impedance spectroscopy (EIS), surface enhanced Raman spectroscopy (SERS), and the Mott-Schottky (MS) method. EIS data were associated with an adsorption pseudocapacitance. Observed changes in the adsorption pseudocapacitance were consistent with thinning of the outer layer of the passive film. SERS experiments found that the spallation environment had no affect on the molecular state of the oxide. Results from MS experiments found that the oxygen vacancy concentration in films formed during proton irradiation were lower than those films formed in the absence of irradiation. In accordance with the point defect model (PDM) for oxide films, a decrease in the oxygen vacancy concentration indicates proton irradiation alters the passive film by either decreasing the oxygen vacancy flux or increasing oxygen vacancy diffusion. Calculations using the LAHET and MCNP transport codes have demonstrated that spallation reactions are capable of generating numerous energetic particles such as, electrons, neutrons, protons, and photons. Each of these species is capable of generating a wide variety of defects in the oxide film altering its electronic and transport properties and, thus, explaining the observed electrochemical phenomena.     

Electrochemical synthesis of silver oxide nanowires,microplatelets and application as SERS substrate precursors

We describe the electrochemical synthesis of silver oxide nanowires and nanowire bundles, filled platelets and hollow microplatelets in either basic or acidic N,N-dimethylformamide solution. We propose that these nanostructures are formed at the electrode surface via two competing reactions namely, silver dissolution off the electrode in the presence of NH₃ or HF during the anodization of silver, and silver oxide precipitation. Results show that the precipitated silver oxide nanoparticles aggregate into nanowires as well as into filled and hollow microscale platelets, depending upon the nuclei concentration and the anodization current density. X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and Raman scattering spectroscopy show that the nanowires and microplatelets are mainly composed of Ag₂O. Nanowire bundles are used as substrates for surface-enhanced Raman scattering (SERS) where single molecule detection is achieved and evidenced using a bianalyte Raman technique.     

A spectroelectrochemical investigation of the influence of sodium diisobutyldithiophosphinate on silver dissolution in aqueous cyanide

Polarization studies have been carried out to determine the influence of diisobutyldithiophosphinate (DIBDTPI) on the dissolution of silver in cyanide solutions at pH 11. DIBDTPI was found to inhibit dissolution at concentrations similar to those used when this compound is applied as a flotation collector. The inhibition efficiency in 10^–2 mol dm^–3 CN^– was found to increase with increase in DIBDTPI concentration in the range 10^–6–10^–4 mol dm^–3, and with increase in time of exposure of the silver to the DIBDTPI solution. The inhibition efficiency found for 10^–4 mol dm^–3 DIBDTPI in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 64.6% and 95.0% for exposure times of 10 min and 2 h, respectively. These values are significantly less than those found previously for 2-mercaptobenzothiazole under the same conditions. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of DIBDTPI displacing cyanide from the silver surface. Voltammetry at 0.5 mV s^–1 indicated that adsorption of DIBDTPI involves charge transfer.     

SERS and EQCM studies on the effect of allyl thiourea on copper dissolution and deposition in aqueous sulfuric acid

We investigated the effect of allyl thiourea (ATU) on both the electrodeposition and electrodissolution of copper in aqueous sulfuric acid by combining cyclic voltammetry (CV) with electrochemical quartz crystal microbalance (EQCM) studies and surface enhanced Raman spectroscopy (SERS). The results demonstrated that the two-electron transfer reaction is the predominant process for the copper dissolution–deposition process in 1.0 M H₂SO₄ solution not containing ATU in the potential range −0.65 to 0.05 V versus SCE. In comparison, the copper dissolution–deposition process in 1.0 M H₂SO₄ solution containing ATU corresponds to a one-electron transfer reaction. The spectral features observed from the SERS studies showed at molecular level that ATU can be adsorbed tilted to the copper electrode surface and that coordination occurs via the sulfur atom. The secondary amino group is nearer to the surface than the primary amino group. SO₄²⁻ and HSO₄⁻ can be coadsorbed on the protonated −NH (CH₂CHCH₂) groups.     

Controlled Layer-by-Layer Formation of Ultrathin Oxide Films on Silver Island Films for Surface-Enhanced Raman Scattering Measurement

Methods for the controlled deposition of ultrathin metal oxide layers onto silver island films for surface-enhanced Raman scattering (SERS) measurements are reported. Two related deposition techniques are explored for thin film growth: a surface sol-gel method and atomic layer deposition. Both methods exhibit excellent control of the deposited film thickness to atomic level precision while conformally coating the complex structures found in silver island films. Coating of metal oxide films onto silver substrates provides a method for monitoring the distance dependence of SERS enhancements and offers a platform for exploring adsorption and interaction of analytes on dielectric surfaces. Analysis of the distance dependence of the Raman signal with increasing film thickness yields estimated silver particle sizes that are in agreement with microscopy, which is consistent with the layer-by-layer growth mechanism of uniform metal oxide films on the silver substrate. These methods can be easily extended to grow a variety of laminar or mixed metal oxide films for the exploration of interfacial phenomena.     

An electrochemical investigation of the suppression of silver dissolution in aqueous cyanide by 2-mercaptobenzothiazole

Triangular potential sweep voltammetry, potentiokinetic generation of polarization curves, and coupon corrosion tests have been carried out to determine the influence of 2-mercaptobenzothiazole (MBT) on the dissolution of silver in cyanide solutions at pH 11. MBT has been shown to be an effective inhibitor for silver dissolution at concentrations similar to those used when MBT is applied as a flotation collector. The inhibition efficiency (i.e., [1 – the ratio of the corrosion rates in the presence and absence of MBT], expressed as a percentage) in 10^–2 and 10^–3 mol dm^–3 CN was found to increase with increase in MBT concentration in the range 10^–6 to 10^–4 mol dm^–3, and with increase in time of exposure of the silver to the MBT solution. The inhibition efficiency found for 10^–4 mol dm^–3 MBT in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 98.9%, 99.4% and 99.99% for exposure times of 10 min, 2 h and 5 days, respectively. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of MBT displacing cyanide from the silver surface.     

Fourier-transform surface enhanced Raman scattering studies of molecular self-assembly of disulfides on metals and the application in adhesion promotion

The adsorption and molecular orientation of phenyl disulfide and 4-aminophenyl disulfide on silver surface has been investigated by the use of Fourier transform (FT) surface enhanced Raman scattering (SERS). There is a concentration dependence of the molecular orientation of adsorbed disulfides on silver surface. Disulfides could be adsorbed on Ag surface as self-assembled, well oriented monolayers from a very dilute solution. The amino group exposed outwards on the 4-aminophenyl disulfide adsorbed on metal can take part in chemical reactions with epoxy group. Modification at the interface has been achieved for polymer/metal systems by using 4-aminophenyl disulfide as a coupling agent, resulting in adhesion promotion.     

Surface-enhanced Raman spectroscopy and electrochemistry of 2,2′-bipyridine adsorbed at copper electrode

The adsorption of 2,2′-bipyridine (22BPY) on the surface of polycrystalline copper electrode was studied by means of surface-enhanced Raman spectroscopy (SERS) and cyclic voltammetry in a wide range of electrode potential. Experiments were carried out in both acidic and neutral solutions, as well as in presence of two kinds of supporting electrolyte (KCl and LiClO₄) in order to examine the influence of molecule protonation and specifically adsorbed anions. It was found that a molecule orientation with respect to the surface changes from perpendicular to more tilted in the neutral perchlorate solution followed by the conformation change from cis to trans in strongly negative potentials. This conformational transition occurs gradually, probably through a series of intermediate states. The SERS features due to trans conformers are uniquely observed in presence of perchlorate anions. In the presence of chloride the molecular plane is at least slightly inclined towards the surface in the whole potential range. In acidic solutions the SERS results indicate that 22BPY adsorbs in non-protonated form independent on the present anion with the molecular plane tilted although it becomes more perpendicular with respect to the surface at negative potentials. The cyclic voltammetry measurements revealed that the hydrogen evolution is inhibited in presence of 22BPY in both neutral and acidic solutions. It suggests strong adsorption of this molecule in a wide range of electrode potentials.     

Surface-enhanced Raman scattering of suspended monolayer graphene

Abstract

The interactions between phonons and electrons induced by the dopants or the substrate of graphene in spectroscopic investigation reveal a rich source of interesting physics. Raman spectra and surface-enhanced Raman spectra of supported and suspended monolayer graphenes were measured and analyzed systemically with different approaches. The weak Raman signals are greatly enhanced by the ability of surface-enhanced Raman spectroscopy which has attracted considerable interests. The technique is regarded as wonderful and useful tool, but the dopants that are produced by depositing metallic nanoparticles may affect the electron scattering processes of graphene. Therefore, the doping and substrate influences on graphene are also important issues to be investigated. In this work, the peak positions of G peak and 2D peak, the I_2D/I_G ratios, and enhancements of G and 2D bands with suspended and supported graphene flakes were measured and analyzed. The peak shifts of G and 2D bands between the Raman and SERS signals demonstrate the doping effect induced by silver nanoparticles by n-doping. The I_2D/I_G ratio can provide a more sensitive method to carry out the doping effect on the graphene surface than the peak shifts of G and 2D bands. The enhancements of 2D band of suspended and supported graphenes reached 138, and those of G band reached at least 169. Their good enhancements are helpful to measure the optical properties of graphene. The different substrates that covered the graphene surface with doping effect are more sensitive to the enhancements of G band with respect to 2D band. It provides us a new method to distinguish the substrate and doping effect on graphene.

PACS

78.67.Wj (optical properties of graphene); 74.25.nd (Raman and optical spectroscopy); 63.22.Rc (phonons in graphene)     

纳米银的制备及其在SERS上的研究

纳米银制备的方法繁多,综述了用液相法、固相法制备纳米银,给出了这些方法得到的纳米银的表面增强拉曼散射（SERS）结果,并提出了分子吸附状态的一些影响因素。对生物技术、理论分析（如密度泛函理论）应用于纳米银的制备以及表面增强拉曼散射（SERS）的研究等提出了展望。     

In situ Raman spectroelectrochemical study of redox processes at poly(Toluidine blue) modified electrode

Electrooxidation of hydroquinone and ascorbic acid at a gold electrode modified with electropolymerized layer of phenothiazine dye Toluidine blue (PTB) has been studied with the use of in situ Raman spectroelectrochemical technique, surface enhanced resonance Raman spectroscopy (SERRS). It was shown that the redox state of PTB at any electrode potential can be determined in pH 1.0 and 4.0 solutions following specific changes in Raman spectra of these modifier layers. Electrooxidation of hydroquinone at PTB modified electrode in pH 1.0 solution, and of ascorbic acid in pH 4.0 solution, proceed without any detectable changes in a net redox state of modifier layers. It has been concluded that, under the conditions studied, both anodic oxidation processes occur most probably at the modifier/electrolyte interface rather than within the modifier film, as opposed to electrooxidation of same species at polyaniline modified electrodes studied earlier.