J. Bukowska

SERS studies on the structure of thioglycolic acid monolayers on silver and gold

Chemisorption of thioglycolic acid (TGA) on silver and gold has been studied using surface-enhanced Raman scattering. We found that the strength of TGA strongly decreased after adsorption. Significantly more decreased strength was observed for TGA adsorbed on Au. The average conformation of adsorbed TGA molecules depends on the kind of the substrate and on degree of dissociation of TGA. The higher portion of TGA molecules adopts trans conformation when layers are formed on the Ag substrate and when more carboxylic acid groups are deprotonated. The ratio of gauche to trans conformers of TGA molecules significantly changed during the incubation on silver. In the first stage of incubation the relative amount of a gauche conformer increases, but after about 1 h the gauche conformer starts to disappear. The average conformation of TGA adsorbed on the gold substrate did not change during the incubation.

SERS of 1,8-diaminonaphthalene on gold, silver and copper electrodes polymerisation and complexes formed with the electrode material

Abstract Oxidation of 1,8-diaminonaphthalene (1,8DAN) on gold, silver and copper electrodes has been studied by SERS spectra. SERS results have been compared with Raman spectra of poly-1,8DAN thin film deposited on the platinum support. Oxidation of 1,8DAN on gold and silver electrodes leads to polymerisation. The pretreatment of the silver electrode influences the polymerisation: exposing the silver electrode to day light during the ORC procedure encourages growth of the polymer layer. In the case of a copper electrode the Cu 2+ -(1,8DAN) n complex is formed.

SURFACE-ENHANCED RAMAN SCATTERING (SERS) AT COPPER(I) OXIDE

Surface-enhanced Raman scattering spectra of pyridine at a copper(I) oxide hydrosol and at Cu2O-covered copper electrode produced by ‘oscillating reaction roughening’ are reported. It is shown that on such surfaces pyridine molecules adsorb as pyridinium cations. The ‘oscillating reaction’ pretreatment yields a passivated Cu surface which does not undergo any reduction during the cathodic scan, producing a SERS spectrum of pyridinium cations even after decreasing the electrode potential to strongly negative values.

Effect of anions on the electrosynthesis, electroactivity and molecular structure of poly(o-methoxyaniline)

Abstract The effect of different anions (Cl − , ClO 4 − ) on the electrooxidation of o -methoxyaniline ( o -MA), on the electroactivity of poly( o -methoxyaniline) (POMA) and on the molecular structure of the polymer has been studied. It has been found that the rate of o -MA oxidation is much higher in HCl than in HClO 4 solution. It was also found that the nucleation and growth mechanisms of POMA films depend on anions being diffusion-controlled progressive nucleation with three-dimensional growth in HCl solution and two-dimensional growth in HClO 4 . It was shown that the electroactivity of POMA depends on the composition of the polymerization bath and that the ability of POMA degradation increases in HCl solution.

ANION-INDUCED CHARGE-TRANSFER ENHANCEMENT IN SERS AND SERRS SPECTRA OF RHODAMINE 6G ON A SILVER ELECTRODE : HOW IMPORTANT IS IT ?

An additional anion-induced enhancement of surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) for Rhodamine 6G adsorbed on a silver electrode upon addition of chloride and citrate anions was determined as a function of the applied potential. The observed increase in intensities amounts to about 100- and 10-fold, for SERS and SERRS spectra, respectively. It was shown that the total increase in SERS intensity by added anions cannot be exclusively explained in terms of the potential-dependent charge-transfer effect and by the ‘active sites’ effect caused by thermodynamically unstable atomic-scale roughnesses. We suggest that this increase can be also ascribed to anion-induced reorientation of the dye molecule or to the potential-independent molecular resonance caused by the strong influence of coadsorbed chloride ions on the electronic levels of Rhodamine 6G.

In situ Raman studies of polypyrrole and polythiophene films on Pt electrodes

Abstract In situ Raman spectra of polypyrrole and polythiophene films were studied in order to describe the processes which occur during their electrochemical reduction and oxidation. It was shown that for both polymers these processes are influenced by the medium in contact with the film. The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in situ Raman spectra than by ex situ studies.

Electro-oxidation of o-aminophenol studied by cyclic voltammetry and surface enhanced Raman scattering (SERS)

Cyclic voltammetry and surface enhanced Raman scattering (SERS) spectra were used over a wide pH range to examine the products of o-aminophenol oxidation on a roughened silver electrode. The results of the study indicated that at least two oxidation products are formed at the stationary potential of the electrode. The major product in alkaline and neutral media was identified as 2,2′-dihydroxyazobenzene, a linear dimer formed by NN coupling of o-aminophenol cation radicals. In acidic solutions the cyclic dimer 3-aminophenoxazone formed by CN coupling of o-aminophenol cation radicals dominates on the silver electrode.

Characterization of the copper surface optimized for use as a substrate for surface-enhanced Raman scattering

Abstract A new electrochemical procedure of roughening of a copper surface was developed, producing a surface with a high surface-enhanced Raman scattering (SERS) activity. The surface morphology and composition was characterized by energy dispersive/wavelength dispersive/X-ray microprobe analysis and compared to the Cu electrodes roughened by the commonly used oxidation–reduction reactions. The morphology of such a surface was completely different from those produced by traditional electrochemical procedures. Moreover, X-ray microprobe analysis revealed that our new surface remained unoxidized in contrast to the other SERS active Cu surfaces. The potential profiles of SERS intensity of the ring breathing mode of pyridine adsorbed on these surfaces were discussed and interpreted in terms of charge-transfer (CT) effect.

Electrooxidation of O-methoxyaniline as studied by electrochemical and SERS methods

Abstract The electrooxidation of o -methoxyaniline ( o -MA) has been studied by electrochemical and surface-enhanced Raman scattering (SERS) methods. The electrochemical measurements showed that the early stages of o -MA electropolymerization were affected by both the monomer to acid concentration ratio and by the acid concentration. The SERS experiments demonstrated the C-N coupling mechanism of o -MA dimerization or oligomerization. The results of both methods indicate that the intermediate redox couple observed in electrochemical response of poly ( o -methoxyaniline) can be assigned to the incorporated dimer probably having the cyclic structure.

Spectroelectrochemical and EPR determination of the number of electrons transferred in redox processes in electroactive polymers. Polyindole films

Abstract The spectroelectrochemical (visible range—VIS) and in situ electron paramagnetic resonance (EPR) measurements were carried out for electroactive polyindole films. Both EPR and absorption VIS spectra were analyzed using the Nernst equation. The number of electrons transferred per monomer unit during the redox process in the polymer ( n ) as determined from both types of spectra is equal to 0.14 (VIS spectra) or 0.16 (EPR). The applicability of EPR data to determine the n value was verified by measurements for polypyrrole film. It seems that EPR spectra provide more credible values of the number of transferred electrons in redox reactions in the polymer matrix.