Roughened Au Electrode Research Articles

In-Situ Electronic and Vibrational SERS Observation of Gold Electrodes Under Various pH Conditions

Surface-enhanced Raman scattering (SERS) is a vibrational scattering spectroscopy that enables selective and sensitive observation of chemical species existing near a metal surface. In particular, SERS is capable of detecting chemical information with high sensitivity at a buried interface such as an electrode/electrolyte interface. Compared to vibrational absorption spectroscopies, SERS can detect low-frequency vibrations in the THz region in addition to high-frequency vibrations in the so-called fingerprint region. Therefore, one can expect to obtain useful chemical information on electrode/electrolyte interfaces from extramolecular vibrations in such a low frequency region [1]. Moreover, we have recently reported that SERS background continuum is ascribed to surface-enhanced electronic Raman scattering, i.e., electronic SERS. This suggests that the background signals can provide electronic information on the metal electrode [2]. In this study, we measured both electronic and vibrational SERS spectra of electrode/electrolyte interfaces under electrochemical potential applications in various pH conditions.A gold electrode was roughened by applying oxidation and reduction cycles in 0.1 M KCl aqueous solution. In-situ SERS spectra for the gold electrode surface were measured in Ar-bubbled aqueous solutions with three different pH conditions under application of electrochemical potentials. A He-Ne laser radiation of 632.8 nm was used to measure SERS signals.Figure shows SERS spectra for the gold surface measured at -0.6, +0.2, and +0.6 V vs. Ag/AgCl in 0.1 M KOH solution. (The measured signal intensities were converted to the susceptibility [2].) In this pH condition, OH⁻ adsorption and surface oxidation occur at around -0.4 V and +0.3 V, respectively, during the positive-going potential scan. For vibrational peaks, the stretching modes of Au-OH⁻ and Au-O clearly showed the potential dependent behaviors, as expected; among these three potentials, νAu-OH- and νAu-O were observed only at +0.2 V and +0.6 V, respectively. Moreover, we found vibrational features in the THz region, which can be attributed to water cluster vibrations. These features decreased in intensity at +0.6 V. On the other hand, for the electronic background continuum, the signal intensity decreased at the potentials of OH⁻ adsorption and surface oxidation during the positive-going scan. This result suggests that surface adsorption-induced electronic change can be detected using electronic SERS. In the poster, we will present a detailed analysis of pH-dependence or anion-dependence of in-situ electronic and vibrational SERS spectra of gold surface.[1] M. Inagaki, K. Motobayashi, K. Ikeda, Electrochemical THz-SERS Observation of Thiol Monolayers on Au(111) and (100) Using Nanoparticle assisted Gap-Mode Plasmon Excitation. J. Phys. Chem. Lett. 8, 4236-4240 (2017)[2] M. Inagaki, T. Isogai, K. Motobayashi, K.-Q. Lin, B. Ren, K. Ikeda, submitted.Figure. SERS spectra of a roughened Au electrode in Ar-bubbled 0.1 M KOH solution under applied potentials of -0.6 V, +0.2 V, and +0.6 V vs Ag/AgCl. Figure 1

In Situ Raman Spectroscopic Studies of Dioxygen Reduction in Ionic Liquid Based Electrolytes for Non-Aqueous Alkali Metal-O2 Batteries

Superoxide (O2 -) is the key discharge intermediary driving many non-aqueous metal-oxygen battery cathode chemistries1–4. Fundamental investigations of the interphase at a roughened Au electrode in a variety of ionic liquid and solvent blended electrolytes have been performed to study electrolyte effects on the chemical nature of O2 - using in situ surface enhanced Raman spectroscopy (SERS). The observed (1095-1165cm-1) and (460-490cm-1) bond vibrations for O2 - at the electrode surface can vary greatly depending on the immediate coordinating environment5–7. Electrolytes that interact weakly with O2 - produce more radical oxide species that may be more likely to undergo parasitic side reactions and degrade alternatively, if stable, O2 - can diffuse away from the surface into the bulk electrolyte enabling a solution reaction pathway that has been linked with higher discharge capacities. Analysis of Raman peak positions, intensities and shifts in oxide spectral bands in different electrolytes and potentials allows for key information on O2 - radical character and its coordination environment to be elucidated. Overall four main parameters were shown to affect the radical character of O2 - at the interface in ionic liquid based electrolytes; (1) surface potential, (2) electrolyte cation, (3) electrolyte anion and (4) solvent electron acceptor/ donor numbers. Ionic liquids have gained significant attention due to a number of innate physical and electrochemical properties. The significantly large combinations of ions provide the opportunity for electrolytes to be tailored towards specific application, however a clear electrolyte tailoring methodology is remains under developed. Our study provides important information in the oxygen reduction reaction mechanism that can aid in the ionic liquid selection and tailoring process.

In situ SERS and SHINERS study of electrochemical hydrogenation of p-ethynylaniline in nonaqueous solvents

Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO2 nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems.

Triggering comprehensive enhancement in oxygen evolution reaction by using newly created solvent.

Theoretical calculations indicate that the properties of confined liquid water, or liquid water at surfaces, are dramatically different from those of liquid bulk water. Here we present an experimentally innovative strategy on comprehensively efficient oxygen evolution reaction (OER) utilizing plasmon-induced activated water, creating from hot electron decay at resonantly illuminated Au nanoparticles (NPs). Compared to conventional deionized (DI) water, the created water owns intrinsically reduced hydrogen-bonded structure and a higher chemical potential. The created water takes an advantage in OER because the corresponding activation energy can be effectively reduced by itself. Compared to DI water-based solutions, the OER efficiencies at Pt electrodes increased by 69.3%, 21.1% and 14.5% in created water-based acidic, neutral and alkaline electrolyte solutions, respectively. The created water was also effective for OERs in photoelectrochemically catalytic and in inert systems. In addition, the efficiency of OER increased by 47.5% in created water-based alkaline electrolyte solution prepared in situ on a roughened Au electrode. These results suggest that the created water has emerged as an innovative activator in comprehensively effective OERs.

Gold electrodes with rough surfaces. The Golden Hedgehog Project

A simple and technologically relevant way for Au surface roughening based on two physical processes is described: subjecting Au surface to mercury vapors and forming gold amalgamate followed by a thermal decomposition of the amalgamate under vacuum. All mercury is removed yielding the Au surface with numerous spine-like protrusions 2–4μm high and separated from each other by a few μm. A special tester is prepared with two working Au electrodes and two counter electrodes of which one pair of WE+CE underwent amalgamate roughening (the other pair remained unchanged). Electrochemical measurements show that the tester with the roughened Au electrode has a surface area larger than the tester with untreated Au electrode by 20–160% depending on the method. Advantages of this process in comparison to other methods for Au roughening are briefly discussed.

Surface sol–gel growth of ultrathin SiO2 films on roughened Au electrodes: Extending borrowed SERS to a SERS inactive material

We report the application of borrowed SERS to SERS-inactive SiO2, which is achieved by coating an ultrathin, pinhole-free SiO2 layer on a roughened Au electrode. The ultrathin SiO2 layer allows the transfer of the long-range electromagnetic fields created by the underlying Au to the SiO2 surface, achieving SERS therein (i.e., borrowed SERS). The pinhole-free nature of the SiO2 layer avoids spectral contamination from the underlying Au substrate. The roughened Au/SiO2 overlayered electrode thus enables acquiring vibrational spectra for molecules adsorbed at SERS-inactive SiO2, and such an overlayered strategy could be extended to enable borrowed SERS to be realized on more SERS-inactive materials.

Produção de substratos sers eficientes através da deposição de ouro sobre um molde de microesferas de poliestireno

This work reports on the SERS activity of a nanostructured substrate that was obtained by electrodepositing gold over a template consisting of polystyrene microspheres. This substrate displayed superior SERS performance for the detection of 4-merctaptopyridine as compared to a conventional roughened Au electrode. In order to investigate the substrate capability for the detection at low concentration limits, a series of Rhodamine 6G (1 nM) spectra were registered. Our spectral dynamics data is in agreement with single-molecule behavior, showing that the control over the substrate morphology is crucial to enable the production of highly reproducible and sensitive SERS substrates.

Potential-Dependent Characterization of Bombesin Adsorbed States on Roughened Ag, Au, and Cu Electrode Surfaces at Physiological pH

This paper reports the direct surface-enhanced Raman spectroscopic (SERS) and generalized two-dimensional correlation analysis observations of the different orientations of the neurotransmitter bombesin (BN) chemisorbed on electrochemically roughened Ag, Au, and Cu electrode surfaces at different applied electrode potentials and at physiological pH. The presence of the indole ring of Trp(8) and the amide bond between Gln(7) and Trp(8) of BN on these surfaces generates a specific SERS profile of BN adsorbed on the roughened Ag and Au electrodes that is affected by the electrode potential. Furthermore, for BN on Au, slight changes are observed in the band enhancement in comparison to what is observed for this neurotransmitter immobilized on Ag. In addition, there are larger changes in the spectra triggered by the substitution of Ag with Au electrodes and Ag with Cu electrodes than by substitution of Au with Cu electrodes.

Elimination of oxidation and decomposition by SnCl2 in the SERS study of pyridoxine on a roughened Au electrode

AbstractSevere interference from the oxidation and laser carbonization was encountered in the measurements of surface‐enhanced Raman scattering (SERS) spectra of pyridoxine (PN) on the roughened gold electrode. However, we found that high‐quality SERS spectra of PN could be obtained by the introduction of SnCl2, which only has few Raman peaks at low wavenumbers. SnCl2, as a good reductive, is capable of removing the oxidative species on the gold substrate and the dissolved oxygen in solution, and as a result lowering the open circuit potential (OCP). Sn(II) can also strongly chemically adsorb on the gold surface and interact with PN through coordination/chelation, such that not only to prevent PN from damage by the giant electromagnetic field for the ‘first‐layer’ effect, but also to give rise to very strong Raman scattering signals of PN where chemical enhancement plays an important role. Those are the main reasons for the elimination of the oxidation and decomposition of PN and for the high‐quality SERS spectra of PN. The way the SnCl2 confines PN within the enhanced electromagnetic field by its ability of adsorption and coordination/chelation can be utilized to improve the routine SERS analysis of analogous type of reactive organic/biomolecules. In addition, this method has been successfully extended to the SERS measurements of PN on the substrates of roughened silver and copper. Copyright © 2008 John Wiley & Sons, Ltd.

Reflectance and SERS from an ordered array of gold nanorods

The optical properties of arrays of Au nanorods were studied by specular reflectance spectroscopy. The spectra were dominated by the surface plasmon modes of the Au nanoarrays superimposed on the effects of interference through the films. The longitudinal plasmon resonance moved to longer wavelength as the aspect ratio of the nanorods increased. The reflectance spectra were modelled by applying the Maxwell-Garnett approximation to a uniaxial thin film (composite Au/alumina) and this yielded a good match to the experimental data. SERS spectra on the Au nanorod arrays were recorded at different externally applied potentials and significant differences with respect to an electrochemically roughened Au electrode were revealed. These have been attributed to the nature of the composite nanoarrays, both their nanostructuring into rods and the regular arrangement of these rods.

Ultraviolet Raman study of thymine on the Au electrode

We record the potential-dependent Raman spectra of thymine adsorbed on the roughened Au electrode by ultraviolet (UV) excitation at 325 nm, and we find that the surface-enhanced Raman spectra of thymine changed intensely with the negative shift of the applied potential. When the vibrational mode changes, the resonance potential (potential of maximum intensity) varies accordingly, indicating that the thymine molecules were chemisorbed on the roughened Au surface. The charge transfer (CT) mechanism could probably explain the experiment results in the present work.

Surface-enhanced Raman scattering studies on the adsorption of p-nitrobenzoic acid at Au electrode under different potential with ultraviolet excitation

The potential-dependent surface-enhanced Raman spectrum of adsorbed p-nitrobenzoic acid (PNBA) on the roughened Au electrode has been obtained by using ultraviolet (UV) excitation at 325 nm. The surface-enhanced Raman spectra of PNBA intensely changed when the voltage was in the rang of negative value, and the electrode potential at which the resonance (potential of maximum intensity) occurs varied when the vibrational mode changes, indicating that the PNBA molecules were chemisorbed on the roughened Au surface. The charge transfer (CT) mechanism could probably explain the experiment results in the present work.

Surface-Enhanced Raman Scattering Studies of 1,10-Phenanthroline Adsorption and Its Surface Complexes on a Gold Electrode

This paper reports on the interface processes of 1,10-phenanthroline (phen) at a roughened Au electrode by surface-enhanced Raman scattering (SERS) for the first time. Both the adsorption and coordination of phen on the roughened gold electrode have been studied. In comparison to the normal Raman spectrum of phen monohydrate, the frequency and relative intensity change significantly in the SERS spectra. As evidenced by cyclic voltammetry, the electrochemical behavior of the Au electrode is strongly modified by the adsorbed phen. It was found that a new pair of redox peaks appeared in the cyclic voltammogram only when both phen and X (X = Cl-, Br-) were present. Information on coordination bonds of Au-N and Au-X as well as on adsorbed bonds of Au-N(ad) and Au-X(ad), was obtained by the SERS spectra. In situ SERS investigations together with electrochemical measurements convincingly prove the formation of surface complexes 1,10-phenAu2X6 or [1,10-phenAuX2]AuX4 during the electro-oxidation process of Au while phen and X coadsorbed on the surface.

Surface Raman scattering studies on the adsorption of p-hydroxybenzoic acid at Au electrodes with ultraviolet excitation

The potential-dependent surface Raman spectrum of adsorbed p-hydroxybenzoic acid (PHBA) on a roughened Au electrode has been obtained with ultraviolet excitation at 325 nm. The surface Raman spectra of PHBA are sensitive to the negative shift of potential and the electrode potential at which the resonance (potential of maximum intensity) occurs varies with the vibrational mode, indicating that the PHBA molecules are chemisorbed on the Au surface. A non-radiative charge transfer mechanism could probably explain the experiment results in the present work. The probable reasons are given.

Ultraviolet laser excited surface enhanced Raman scattering of thiocyanate ion on the Au electrode

We demonstrated for the first time the observation of surface enhanced Raman scattering of thiocyanate ion on the roughened Au electrode under ultraviolet laser excitation. Its fruitful information was obtained by an algorithm which enables the elucidation of the bond polarizability (derivative) from the Raman intensity. Together with EHMO calculation, the charge transfer pathway between the adsorbed SCN and Au electrode is also proposed.

Potential Dependence of the Conformations of Nicotinamide Adenine Dinucleotide on Gold Electrode Determined by FT−Near-IR−SERS

High-quality Fourier transform surface-enhanced Raman scattering (FT−SERS) of a dilute solution of nicotinamide adenine dinucleotide (NAD) was recorded on a roughened Au electrode. It was found that the detection limit could be lower as much as 3 orders of magnitude by using a near-infrared laser as the exciting source and an in-situ roughening technique. The SERS of NAD shows a strong potential dependence in the non-Faradaic regions. In regions of positive electrode potential, only the bands responsible for the adenine and nicotinamide moieties can be observed. In contrast, with a negative shift of the potential, several additional strong bands representing the ribose and phosphate moieties are also evident. Based upon the SERS behaviors of NAD in the regions of different potential, an adsorption mechanism for dilute NAD on the gold electrode was proposed. With this mechanism, the stacked NAD molecule is considered to be opened to some extent on an electric charged electrode. Specifically, under sufficie...