Raman spectroscopic study of poly(N-methylaniline) as a thin layer deposited at a electrode was performed in an electrochemical system. A broad range of Raman excitation wavelengths from UV (325 nm) through blue (442 nm) and red (633 nm) to NIR (785 nm) were used. Two limiting redox forms, a reduced (leucoemeraldine) and a fully oxidized one, were considered as obtained at controlled electrochemical potential conditions, and two solution pH of 2.0 and 8.0 were selected to ensure the existence of protonated and deprotonated forms. The Raman spectra obtained and discussed show a strong enhancement for the reduced form at UV and blue laser line excitations, whereas the Raman enhancement for an oxidized form was observed for red and NIR laser line excitations. The main Raman features for the combinations of the reduced and oxidized, and protonated or deprotonated states of poly(N-methylaniline) were analyzed and compared.

A detailed study on Raman spectroelectrochemistry of poly(N-methylaniline) (PNMA) layer deposited at a gold electrode was performed. Raman spectra were excited by four different laser wavelengths: UV line at 325 nm, a blue line at 442 nm, a red line at 633 nm, and a NIR line at 785 nm in solutions of different pH ranging from 1 to 9, and at different electrode potentials ranging from-0.5 V to 0.8 V. UV excitation reveals features characteristic for the reduced form of PNMA, even within the electrochemical potential range where oxidized forms of this polymer prevail. At a blue laser excitation, again, features of the reduced form are revealed, along with indications on the appearance of some kind of intermediate redox state within a definite potential window. Both red and NIR laser line excitations result in rich Raman features, disclosing all major redox forms as well as their interconversions by changing of electrode potential. The presence of polaronic form of PNMA even in pH-neutral and alkaline solutions has been disclosed. A detailed analysis of Raman vibrational bands is presented for different excitation wavelengths, different electrode potentials, and different solution acidities.(c) 2022 Elsevier B.V. All rights reserved.

A comparative study of polyaniline (PANI) and poly(N-methylaniline) (PNMA) has been performed by means of Raman spectroelectrochemical technique at 633 nm and 785 nm laser line excitations. The exci-tation wavelengths used fall into a resonance with the blue colored semi-and full-oxidized forms of these conducting polymers. The dependence of Raman features on electrode potential and solution acidity was studied, and relative content of polaronic and bipolaronic states was evaluated. In an acidic solution, the semioxidized emeraldine form of either PANI or PNMA exists in equilibrium between their polaronic and bipolaronic states. In a neutral or even slightly alkaline solution, this equilibrium for PANI shifts to bipo-laron state, resulting in loss of its conductance. For PNMA, however, the relative content of polaron state appears high enough even in pH-neutral soulions, thus determining a higher conductivity of PNMA in pH -neutral environment as compared to that of PANI. A mechanistic interpretation for this, based on differ-ences in the chemical structures of these polymers, is also presented. (c) 2021 Elsevier B.V. All rights reserved.

Polyaniline layer has been deposited at a gold electrode and subjected to differential multiwavelength Raman spectroelectrochemical study. A broad set of laser line excitation wavelengths was used, including UV (325 nm), blue (442 nm), green (532 nm), red (633 nm), and far red (785 nm). From measurements performed, potential-difference Raman spectra, related to small-step changes of electrode potential were derived, and specific spectral and structural features were obtained and analysed. Similarly, pH-difference spectra for solution pH changes were obtained. A strong resonance enhancement of Raman spectra for reduced form of polyaniline at UV and blue line excitations, and for oxidized forms at red and far red excitations was observed and analysed. The 442-nm excited potential-difference resonance Raman spectra revealed presence of intermediate oxidation state compound formed during the electrooxidation of leucoemeraldine with characteristic vibrational bands at 1622, 1187, 881, and 817 cm(-1). (C) 2019 Elsevier B.V. All rights reserved.

A detailed Raman spectroelectrochemical study on polyaniline has been performed with the use of different laser lines ranging from UV (325 nm) through blue (442 nm) and green (532 nm) up to the red (633 nm) for spectra excitation, and within a broad range of solution pH from 1 to 9. From the data obtained, differential Raman spectra showing spectral changes occurring by a partial electrooxidation of polyaniline from its reduced to semioxidized, and by full oxidation to the fully oxidized states, were derived and analyzed. Different spectral features, appearing in electrochemical processes, were related to structural changes occurring during a partial or full electrooxidation of this polymer, to changes in its protonation state, and to resonance enhancement at different excitation wavelengths for different redox forms.

The redox dye Nile blue has been adsorbed and electrochemically polymerised at a roughened gold electrode. The resulting modified electrodes were subjected to Raman spectroelectrochemical study with 785 nm laser line excitation. For both types of electrodes, well-expressed and rich in features Raman spectra were obtained. The spectra are closely related to those of another oxazine type redox dye Meldola blue. At solution pH 7.0, the overall intensity of the Raman spectra for both types of modified electrodes appears higher than in a pH 1.0 solution. Probably, this is caused by different light absorbance properties of this dye in two solutions. In a pH-neutral solution, the dye possess light absorbance in the red range of the visible spectrum, thus, resonance enhancement is possible. The intensity of the Raman spectra also increases by the shift of the electrode potential to higher positive values. This effect could be understood taking into account an intensifying colouration of the dye at a stepwise increase of the electrode potential due to a continuous growth of the content of oxidised forms within the electrode-bound layer.

Polyaniline has been electrodeposited at a gold electrode, and subjected to Raman spectroelectrochemical study at a red (633 nm) and NIR (785 nm) laser line excitations at electrode potentials varying from - 0.5 V to 0.8 V, and different solution pH values ranging from 1 to 9. The results obtained are compared with 532 nm excitation spectra. Some new phenomena have been observed and discussed. The 1620 cm(-1) Raman band diminishes in its intensity with a positive potential shift at a green excitation, whereas a maximum of intensity for this band around 0.6 V was observed for the red excitation. Adversely, a positive potential shift causes an increase of intensity for 1585 cm(-1) band for both these excitation wavelengths. For NIR excitation, both these bands grow in intensity by positive potential shift. This behavior, as well as increase of spectral intensity with a progressive oxidation of polyaniline layer, were interpreted based on the differences of optical absorption and its changes with changing electrode potential. For the most Raman bands, the shift of the onset potential for their intensity growth to less positive values has been observed by increasing of solution pH.

A layer of polyaniline has been deposited at a gold electrode and studied by differential multiwavelength Raman spectroelectrochemistry. A set of laser line excitation wavelengths was used, including blue (442 nm), green (532 nm), red (633 nm) and far red (785 nm). From the results obtained, the difference spectra between deprotonated (pH 9.0) and protonated (pH 1.0) forms of oxidized and reduced polyaniline were derived and analysed. The characteristic features for different forms of polyaniline were identified, and their dependence on the excitation wavelength was shown. In addition to the usual Raman spectroscopy, the differential spectroscopy enables one to analyse the increase or decrease of intensity for selected Raman bands upon a reversible deprotonation of this polymer.

A comparative Raman spectroelectrochemical study on polyaniline electrodeposited at a gold electrode was performed within the broad range of spectra excitation wavelengths from UV (325 nm) through blue (442 nm), green (532 nm), red (633 nm) to NIR (785 nm) laser lines. Two solutions of pH 2.0 and 8.0 were selected for protonated and deprotonated forms of polyaniline, and two limiting redox forms, a reduced (leucoemeraldine), and a fully oxidized one were taken into account. Raman spectra obtained and discussed reveal a strong enhancement of spectra for reduced form at a short wavelength excitation, and for oxidized form at red and NIR excitations. Raman features for all four polyaniline forms differing in protonation degree and redox state were analyzed and compared; excitation wavelength-dependent characteristic marker bands were suggested.

Electrooxidation of hydroquinone (HQ) to benzoquinone (BQ) has been studied by Raman spectroelectrochemistry at a gold electrode modified with adsorbed or electropolymerized layer of the redox dye Nile blue. Raman spectra were excited with 785 nm laser line. Reversible electrochemical oxidation of HQ proceeded at a midpoint potential of 0.43–0.45 V vs. Ag/AgCl in pH 1.0 solution. The formation of a reaction product BQ has been observed at a controlled electrode potential of 0.6 V by Raman scattering from the modified electrode. The formation of BQ appears to occur faster at a higher concentration of HQ. By comparing the data with our previous studies done with electrodes modified by the variety of azine class redox dyes Meldola blue, Neutral red, and Toluidine blue, it was concluded that the formation of a reaction product BQ could be observed by Raman spectroelectrochemistry only in absence of resonance Raman enhancement of surface attached dye, viz. at a sufficient long distance on the wavelength scale between the dye optical absorbance and laser line used for spectra excitation.

A comparative in situ time-resolved Raman spectroelectrochemical study on aniline polymerization at platinum, smooth gold, and roughened gold electrodes was performed with 785 nm laser excitation. Under the constant anodic current density electrolysis performed at the platinum electrode, the intensity of Raman bands grows continuously reaching a steady state within 8–10 min. At the smooth gold electrode, the maximum intensity is observed in a few or few tens of seconds, and appears to be ca. 1.5 orders of magnitude higher than for the platinum one. At the roughened gold electrode, again, a fast growth of intensity is observed, being ca. 3 orders higher than for the platinum one. After a prolonged electrolysis of ca. 150–200 mC/cm2, the intensities for all three electrodes appear to be of a similar intensity. The results obtained show a strong surface enhancement of Raman spectra at the gold electrode, a very strong at the roughened gold one, and no enhancement at the platinum electrode at the beginning of electrooxidation, turning into a regular Raman scattering at a prolonged electrolysis, sufficient for the formation of a stable layer of polyaniline at the electrode surface.

Electrochemical redox processes taking place within a hybrid polyaniline (PANI) and copper hexacyanoferrate (CuHCF) modified electrode, as well as of solution species at the surface of a modified electrode, have been investigated by near-infrared laser (785 nm) induced Raman spectroscopy. It has been shown that the composite CuHCF-PANI layers can be obtained at electrode surface by first covering the electrode by CuHCF layer using potential cycling procedure, followed by electropolymerization of aniline onto this layer at a controlled electrode potential. A reverse in this order does not result in a composite layer. Raman bands observed within a broad spectral range, as well as their dependence on electrode potential, have been analyzed. Electrochemically driven changes in spectral features related to redox transformations both of PANI and CuHCF have been observed and discussed. Slow redox transformations have been noted, most probably related to slow charge transfer within these hybrid layers. Electrochemical reduction of hydrogen peroxide at a hybrid modified electrode occurs through the redox mediation of CuHCF, whereas PANI remains not involved in this process.

Chemical oxidative polymerization of aniline and N-methylaniline was studied with in situ time-resolved near-infrared (785 nm excitation wavelength) Raman spectroscopy. As an oxidant, dichromate anion at a molar ratio of 1:4.7 (oxidant to monomer) has been used. The results obtained have been analysed both in terms of kinetics, and changes in molecular structure. It has been shown that different features of reaction products possess different kinetic behavior. For aniline as a monomer, the relative content of reduced molecular fragments of the reaction product increases somewhat faster than that of oxidized products. For N-methylaniline, no remarkable differences have been found. (C) 2017 Elsevier B.V. All rights reserved.

Electrochemical redox processes taking place at copper hexacyanoferrate (CuHCF) modified electrode have been investigated by near-infrared laser (785 nm) induced surface-enhanced Raman spectroscopy (SERS). Raman bands observed within the spectral ranges of 2200–2000 cm− 1 and 500–100 cm− 1, as well as their dependence on electrode potential, have been analysed. The most characteristic Raman bands, related to triple CN bond vibrations and centered at 2187 and 2127 cm− 1 were assigned to the oxidised and the reduced forms of CuHCF, respectively. Time-resolved Raman spectroelectrochemical study shows that the electrochemical redox interconversions between these two forms proceed relatively slow, thus resembling the behaviour of structurally related cobalt hexacyanoferrate, and differing essentially from that of Prussian blue layer studied previously. It has been shown by the time-resolved Raman spectroelectrochemistry that the rate of some redox processes of solute species like the anodic oxidation of ascorbate or cathodic reduction of hydrogen peroxide at CuHCF modified electrode appears to be limited by the slow electrochemical redox transformations within the modifier layer itself rather than by the redox interactions of a modifier with the solute species.

Prussian blue (PB) has been electrodeposited at a smooth and at an electrochemically roughened gold electrodes as a thin layer of a few tens of nmol/cm(2) coverage (or a few tens of nanometers thick), and studied by Raman spectroelectrochemical technique using 785-nm laser excitation. It has been shown that the spectra obtained from a roughened electrode are by one order of magnitude more intense than those obtained from a smooth electrode. This shows that even at a relative thick layer of a modifier PB the surface enhancement of Raman spectra plays an important role in obtaining well- defined spectra from modified electrodes.

Silicon solar cell technology is dominating in the photovoltaic industry, however, a further increase in cost-effectiveness is needed. This can be achieved by increasing the light coupling in the active layer of the cell. Passivation layer of the commercial polycrystalline silicon solar cells was textured using the laser beam interference patterning technique to obtain enhanced optical properties due to the formation of periodic refractive index grating. As a consequence of laser irradiation, passivation layer of silicon nitride was partially oxidized at the intensity peaks of the interference distribution. Periodic distribution of oxidized areas was found by EDS. Investigation of optical and electrical properties of the laser treated solar cells shows increased light coupling and better photo-electrical performance. Simulations were carried out to evaluate the influence of refractive index grating formed in silicon oxy-nitride to optical properties of the patterned solar cells. Periodic oxide grating was found to be more efficient for light coupling in thinner film structures. The results of this work may find applications in other fields as it allows alteration of material composition in the well-defined periodic pattern. (C) 2015 Optical Society of America

Commercial polycrystalline silicon solar cells were textured by the Laser Beam Interference Ablation technique to produce periodical grating in the antireflective and passivation layer. Modeling of periodical hole arrays and refractive index gratings in the antireflective coating on silicon substrate was used to select the fabrication regime and explain alterations in optical properties of the laser treated samples. Visual and elemental analysis of the laser treated areas was performed as well as measurement of photo-electrical characteristics before and after the laser treatment. Two modification regimes were established: ablation and oxidation of the antireflective layer. Changes in surface structure and composition as well as optical and electrical properties of patterned solar cells are discussed.

Cobalt hexacyanoferrate (CoHCF) modified electrode has been prepared by electrodeposition, and studied by cyclic voltammetry and Raman spectroscopy using near-infrared laser excitation (785 nm). Raman features observed within the spectral range of 2200-2000 cm(-1), related to tripple C-N bond vibrations, have been analysed. Based on in situ spectroelectrochemical study performed in potassium or sodium chloride or nitrate electrolytes, Raman bands located around 2130 and 2080 cm(-1) have been assigned to reduced, and the band around 2185 cm(-1) -to oxidised form of CoHCF. With the use of time-resolved Raman spectroelectrochemistry, it has been shown that the electrochemically driven redox interconversion between the two redox forms of CoHCF proceeds relatively slow, in contrast to fast transformations occuring within Prussian blue layers studied previously. It was also shown that the efficiency of some electrode processes taking place at CoHCF modified electrode, like the cathodic reduction of hydrogen peroxide, appears to be limited by slow redox transformations within the modifier layer. (C) 2014 Elsevier B.V. All rights reserved.

For the first time, chemical oxidation of aniline and N-methylaniline with dichromate as oxidant has been studied by Raman spectroscopy with 785 nm laser beam excitation, and the suitability of this technique for kinetic study of this process was demonstrated. For both monomers used, a sigmoidal growth of the intensities for most prominent Raman bands was observed, showing a self-accelerating character of this reaction. Self-acceleration appears most clearly expressed for aniline, and for the low oxidant-to-monomer molar ratio used. After reaching their maximum values, the intensities of Raman bands drop almost to zero, most probably due to increase in opacity and optical absorbance of reaction mixture. The kinetics of an increase, and the next following decrease of band intensities depend on the monomer used, and oxidant-to-monomer molar ratio.

Gold electrodes modified with adsorbed or electropolymerized layers of the redox dye Meldola blue have been prepared and studied by Surface enhanced Raman spectroscopy (SERS) at 785 nm laser excitation. The intensity of SEAS spectra obtained differ essentially for electrochemically oxidized and reduced layers of MB, both in pH 1.0 and pH 7.0 solutions studied. Electrooxidation of ascorbate at MB modified electrodes in pH 7.0 solution was studied, and it has been shown with in situ SERS spectroscopy that the relative content of oxidized and reduced forms of MB within adsorbed or electropolymerized layer depends on electrode potential and ascorbate concentration. Also, electrooxidation of hydroquinone at MB modified electrodes in pH 1.0 solution has been studied, and the formation of reaction product benzoquinone has been demonstrated with SERS spectroscopy. This process occurs faster at electrode modified with electropolymerized MB, and at higher concentration of hydroquinone. (C) 2013 Elsevier B.V. All rights reserved.