Sulphate adsorption at chemically deposited silver thin film electrodes: time-dependent behaviour as studied by internal reflection step-scan infrared spectroscopy

Stable silver thin films were chemically deposited on a germanium substrate. Ex-situ STM images showed that these films are formed by grains with a diameter between 20 and 100 nm. The silver films have been used as the working electrode in infrared spectroelectrochemical experiments with an internal reflection (Kretschmann) configuration. The adsorption of sulphate anions in neutral or slightly acidic solutions has been studied. The high intensity of the S–O stretching bands in the absorption spectra allowed the monitoring of the time-dependent behaviour of the adsorption/desorption processes in time-domain step-scan experiments.     

ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes

The adsorption of acetate anions at silver thin film electrodes has been studied by in-situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. Stable silver thin films were chemically deposited on germanium substrates. Ex-situ STM images show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, respectively. The thickness of the silver film, measured by AFM, is typically around 10 nm for a deposition time of 10 min and increases up to 50 nm for a deposition time of 20 min. Roughness factors around 2.3 have been obtained for the silver films from the charge involved in lead underpotential deposition (UPD). A noticeable enhancement of the infrared absorption of adsorbed species (SEIRA effect) is observed when the silver films are used as electrodes under internal total reflection conditions. Maximum intensities of the adsorbate bands were observed for a deposition time of 10 min and an angle of incidence around 65 degrees . The potential-dependent infrared spectra of acetate and interfacial water are consistent with previously proposed models involving the existence of weakly hydrogen-bonded water molecules at potentials below the potential of zero charge and the reorientation of water molecules at potentials above the potential of zero charge. Results reported in this work suggest a weak interaction between acetate and water molecules adsorbed at the silver thin film electrodes.     

Photocapacitance spectroscopy of thin film cadmium selenide electrodes

Photocapacitance spectroscopic measurements were made on thin film CdSe that was prepared by electrodeposition from a solution of selenosulfite and cadmium ions. The spectra were very similar for five spots on three films that were prepared under identical conditions. In 0.5 M KOH solution, the film appeared stable for a number of measuremens at various applied potentials. At pH 10 the film was relatively stable for applied potentials negative of 0.0 V (SCE). At more positive potentials in this solution, surface oxidation appears to occur, resulting in the formation of a surface layer that alters the spectrum. In both solutions, the photocapacitance spectrum appears independent of applied potential over the range employed. The continuous rise without any abrupt steps in the spectrum as the photon energy is increased indicated that there are probably a series of bandgap states of comparable density. The energy levels range from E_c − 1.1 eV to E_c − 1.6 eV. In contrast with thin film CdSe prepared by vacuum coevaporation, the electrodeposited material did not require low frequency (7 to 70 Hz) for the measurement.     

Raman spectroscopy of C-, BN-, SiC-layers deposited on multifilament substrates

The analytic characterisation of various layers and layer systems on fibrous materials are presented. The layers, deposited by an isothermal CVD process, consisting mainly of pyrolytic carbon, hexagonal boron nitride and silicon carbide were characterised by different analytical methods, especially by Raman spectroscopy [1]. The surface enhanced Raman spectroscopy (SERS) was used first time for the investigation of boron nitride (BN) coatings on fibres.     

Wrinkles formed on a thin gold film deposited onto stretched elastic substrates

In this article the possibility of using various elastic polymer substrates for preparing wrinkled gold films was studied. The gold film was deposited on the substrate using an ion‐sputtering technique, while the substrate was stretched and fixed on a frame. The obtained gold film had wrinkles with a striped pattern. However, whether the pattern was well regulated or not depended on the substrate material. Polydimethylsiloxane (PDMS) was the preferable material when it did not contain fillers. Materials containing fillers are not suitable for this purpose. However, double layer substrates that consist of the PDMS without fillers (the upper layer) and the material containing fillers (the lower layer) could be used to obtain a relatively well‐ordered pattern. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface enhanced Raman spectroscopy study of the potential dependence of thymine on silver electrodes

The potential-induced changes in thymine coordination on polycrystalline silver electrodes are studied by surface enhanced Raman spectroscopy (SERS) for potentials positive to the potential of zero charge up to the end of the double layer range. Two distinct sets of spectra could be obtained in the range of potentials studied. Both states correspond to chemisorbed phases of thymine on silver, where a distinct heteroatom is deemed responsible for the bond with the surface. At less positive potentials, one of the ring oxygen atoms is responsible for the chemical bond and the molecule assumes a tilted position. At more positive potentials, one of the ring nitrogen atoms, possibly deprotonated, establishes a new bond with the surface, aligning the molecule's axis closer to the surface normal.This paper is dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday for his outstanding contributions to electrochemistry     

Surface-enhanced Raman spectroscopy study on the structure changes of 4-mercaptopyridine adsorbed on silver substrates and silver colloids

Surface-enhanced Raman scattering (SERS) of 4-mercaptopyridine (4-mpy) adsorbed on HNO3 etched silver foil, chemically deposited silver films (silver mirror) and silver colloids were measured. The SERS study has revealed that 4-mpy was adsorbed onto the three kinds of silver surfaces by a sulfur-silver bond with the plane of pyridine ring being normal to the silver substrates. The structure of 4-mpy adsorbed on the silver surfaces depends largely on the pH values of environment. When the pH values of the environment are changed, the structure of 4-mpy adsorbed on silver surfaces can easily be altered through a protonation or deprotonation reaction occurring on the N atom of the pyridine ring, and the modified structure shows unique characters on the SERS spectrum. Owing to the remarkable enhancement ability of SERS technique and characteristic spectrum of different species, a monolayer of 4-mpy assembled on a silver mirror holds potential as a H+ sensor for highly sensitive detection of the proton concentration in an aqueous solution.     

Raman spectroscopic investigation of silver electrodes

Raman spectroscopy has been applied to the study of the reduction of carbon dioxide and of formate and carbonate ions at a silver electrode. Raman spectra of adsorbed intermediate species, which are as yet only partially identified, have been detected and show marked variations with electrode potential. These spectral variations are clearly correlated with the voltammetric features for carbonate solutions and suggest that these reduction products complicate most measurements on silver electrodes in the cathodic region. The interpretation of the previously reported spectra due to adsorbed pyridine at silver electrodes has been reconsidered; interactions with surface carboxy species may be significant.     

Development of silver film via thermal decomposition of layered silver alkanecarboxylates for surface-enhanced Raman spectroscopy

This work demonstrates that optically tunable, SERS-active Ag films can be reproducibly fabricated on glass by the thermal decomposition of layered silver alkanecarboxylates.     

Fourier transform surface-enhanced Raman scattering of single-layer nucleolipid Langmuir-Blodgett films on silver island film substrates

Surface-enhanced Raman scattering (SERS) spectra of four amphiphilic nucleolipids in single-layer Langmuir-Blodgett (LB) films deposited on silver island film substrates from pure water and complementary nucleotide-containing subphase and corresponding powder normal Raman spectra were obtained. The analysis of these spectra indicates that the SERS effect is mainly caused by a charge-transfer mechanism, and only the nucleobase headgroup moieties and complementary bases combined with them through hydrogen bonds, which are directly in contact with the silver island film substrates, could be enhanced. For the amphiphilic nucleolipids with the identical nucleobase headgroups, the SERS spectra of the LB films are similar, implying that the orientations of these nucleobase moieties on the silver substrates are analogous. However, the nucleobase takes different orientations on the silver substrates before and after complementary binding. The nucleobases in the LB films deposited from pure water are nearly lying flat on the silver surface, while the complementary binding pairs transferred from the air/water interface tend to take an end-on orientation on the metal surface.     

Raman spectroscopy of silver pertechnetate

The title compound, AgTcO₄, contains close Ag—O contacts, and Raman spectroscopy shows a reduction in the Tc—O stretching frequencies on changing the pertechnetate counter‐cation from K⁺ to Ag⁺.     

Effect of argon plasma treatment on surface-enhanced Raman spectroscopy of polypyrrole deposited on electrochemically roughened gold substrates

In this work, polypyrrole (PPy) films were electrodeposited on electrochemically roughened gold substrates modified by argon plasma treatment. First, a gold substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N HCl. Then the roughened gold substrate was further treated by argon plasma. Encouragingly, the surface-enhanced Raman scattering (SERS) spectroscopy of polypyrrole electrodeposited on this roughened gold substrate modified by argon plasma treatment exhibits a higher intensity by 8-fold, as compared with the SERS of PPy electrodeposited on an unmodified roughened gold substrate. Meanwhile, the electropolymerization for pyrrole monomers occurring on the modified roughened gold substrate is easier. Also, the nucleation and growth of electropolymerization of pyrrole monomers on the modified and unmodified gold substrates are different.     

Raman spectra of carbon monoxide adsorbed on silver electrodes

Weak Raman spectra of carbon monoxide on silver electrode surfaces exhibit frequency and intensity variations with changing potential. The frequency-potential dependence is rationalized in terms of electron-transfer to the antibonding π^* state of electrosorbed CO.     

Surface-enhanced Raman scattering of water adsorbed on silver electrodes

Temporal evolution of the Raman spectra of H₂O, D₂O and HDO during an oxidation-reduction cycle of a Ag electrode in aqueous 1 M KCl or KBr has been recorded with an optical multichannel analyzer. Surface enhanced Raman spectra of the adsorbed water are readily observable and are different from the Raman spectra of bulk water.     

Sub-wavelength Raman spectroscopy on isolated silver islands

Surface Enhanced Raman Spectroscopy (SERS) is a valuable analytical tool for the investigation of molecules adsorbed on roughened noble metal surfaces. The shape, size, and surrounding of the metal protrusions play an important role in the Raman scattering enhancement. By combining scanning near-field optical microscopy (SNOM) with Raman spectroscopy the spatial resolution suffices for investigating isolated silver islands on SERS active substrates. We demonstrate an optical resolution below 70 nm for recording spectra on specifically prepared and fully characterized SERS substrates. For a quantitative evaluation of the SERS signal the spatial distribution of Rhodamine 6G (R6G) deposited on the SERS substrate was determined by friction force measurements. By comparing the Raman intensities of the SERS substrates with those of unmetallized support plates absolute SERS enhancement factors at specific locations on top and in the vicinity of the silver islands were determined directly.     

Ultrasmooth silver thin film electrodes with high polar liquid wettability for OLED microcavity application

For a lab-on-chip application, we fabricate a blue bottom emitting strong microcavity organic light emitting diode (OLED), using very smooth and optically thin (25 nm) silver film as anode on a glass substrate. To improve the hole injection in the OLED device, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid)) has been used, so the silver anode must present not only a very smooth surface but also a strong adherence on the glass and a high wettability to allow a good PEDOT-PSS spin coating deposition. To obtain these physical properties, different 5 nm thick nucleation layers (germanium, chromium, and hydrogenated amorphous carbon) have been used to grow the silver thin films by e-beam deposition. The Ge/Ag bilayer presents all the desired properties: this bilayer, investigated by ellipsometry, optical profilometry, contact angle measurements, and XPS analysis, highlights an ultrasmooth surface correlated with the film growth mode and a high wettability related to its surface chemical composition.     

Impedance spectroscopy of lithium-tin film electrodes

A method of electrochemical impedance spectroscopy was used to study the reversible lithium intercalation from nonaqueous electrolyte into tin films with the thickness of 0.1–1 μm. The impedance spectra of lithium-tin (Li _x Sn) electrodes have a complicated shape depending on the electrode state and prehistory; they reflect the occurrence of several consecutive and parallel processes, including the lithium migration, diffusion, and accumulation. The formation of a solid-electrolyte layer on the surface at Li intercalation into Sn is observed. Equivalent circuits are proposed that adequately model the experimental data on the Li _x Sn electrodes both freshly prepared and after prolonged cycling. Problems associated with the choice of equivalent circuits and determination of their parameters, the accuracy of the diffusion coefficient determination, the trends in the parameters’ variation with electrode potential (composition) are discussed.     

Surface-enhanced Raman spectrometry with silver particles on stochastic-post substrates

A special type of substrate for surface-enhanced Raman scattering (s.e.r.s.) is evaluated. The substrates consist of silver particles deposited on stochastically arranged SiO₂ posts produced by plasma etching of a quartz surface using a silver island film as an etch mask. The optimization of various experimental parameters such as silver layer thickness, silver evaporation angle, and excitation energy are discussed in detail. Comparative studies with p-nitrobenzoic acid as the model compound indicate that this present substrate is at least one order of magnitude more effective than other common s.e.r.s. substrates, such as the silver island film and the crossed-grating surface, which were previously found to induce the strongest s.e.r.s. signals. The preparation of these silver-particle-post substrates avoids the elaborate lithographic procedures required for crossed-grating structures. The quantitation of species in a three-component mixture illustrates the selectivity of the s.e.r.s. technique.