Poly (2,2′-bithienyl-5,5′-diylvinylene) (PBTV) films formed by anodic oxidation of 2×10−3 M solutions of trans-1,2-di(2-thienyl)-ethylene (trans-DTE) in acetonitrile were studied by voltammetry and ellipsometry. For the doped and undoped films, refraction indices and absorption coefficients in the wavelength range of 400–800 nm were determined as functions of thickness. Differences in the structure were found depending on the height of the oxidation potential. A decrease in thickness by doping was observed and is discussed in terms of a possible cis-trans isomerization. The optical spectrum of the undoped polymer showed a high degree of π-electron delocalization (high “degree of conjugation”).

Ti and Nb electrodes were passivated galvanostatically in nitric acid solutions. The electrochemical and photoelectrochemical behaviour of these electrodes was studied and compared with the behaviour of similar electrodes passivated in sulphuric acid solutions under the same conditions. The flatband potential and donor concentration of the passive films were obtained from the corresponding Mott-Schottky plots. The photoelectrochemical investigations were carried out using a pulsed laser which rendered measurements with photon energies smaller than the band gap. The results showed that the behaviour of passivated titanium in nitric acid was differing from its behaviour in sulphuric acid. The behaviour of the passivated niobium was not much affected by the exchange of the two acids.

AbstractH2O2 shifts the flatband potential of p‐GaAs to more cathodic values in acidic solution and to more anodic values in alkaline medium, while it does not affect the flatband potential of n‐GaAs.

A polymer film formed by anodic oxidation of thiophene in acetonitrile on platinum at 2.08 V was examined by ellipsometry. The refraction index and absorption index were determined as a function of the wavelengths. The optical thickness was determined and compared with the electrical charge. Stoichiometric film growth by a two-electron reaction followed this comparison. The film properties studied were almost independent of the potential between −0.1 and +2.08 V. The time dependence of the ellipsometric parameter showed the film growth to be approximately linear with square root of time, typical for a diffusion controlled reaction.

In situ Raman spectra of electrochemically formed oxide films on Ti electrodes were measured. Below the formation potential of 10V, the spectra showed clear evidence for the formation of Rutile. At higher formation potentials new spectra, neither characteristic for rutile nor for anatase, were observed. Anatase spectra were found after emersion and drying of the oxide film and were also observed when the oxide film was formed in HNO 3 . In all examples, the film appeared to be of a crystalline nature.

A pulsed laser was used as a light source for photocurrent measurements of thin passive films on iron, nickel and iron-nickel alloys. The response of the oxide films on the laser illumination showed transition times characteristic for the relaxation of the charge distribution after illumination. The relaxation times differed for the two metals, in the order of 10 μs for iron and 100 μs for nickel. Further differences in the photocurrent behaviour of the two metals concern the sign of the photocurrent, iron giving anodic and nickel cathodic photocurrents, the photocurrent-potential dependence, and a saturation intensity only found for iron. The photocurrent behaviour of the iron-nickel alloys varied between iron and nickel depending on potential, prepolarization and time.

Poly(2,5-thiophenediyl) (PT) films formed by anodic oxidation of 0.4 M solutions of thiophene in acetonitrile were studied by voltammetry and ellipsometry. The film properties differed from films formed by anodic oxidation of less concentrated solutions (0.01 M) (J.O. Zerbino, W.J. Plieth and G. Kossmehl, J. Electroanal. Chem., 260 (1989) 361), with respect to the optical and oxidation-reduction properties. The refraction index and absorption coefficient were determined as a function of the wavelength (400–800 nm) and of the thickness for the oxidized (doped) and reduced (undoped) form of the film. Electrochemical oxidation (doping) increased the thickness by about 20%.

AbstractThe time dependence of photopotential and photocurrent decay occurring after the incidence of a laser pulse was measured at iron and titanium passive layers. The photopotential decay showed a second order reaction kinetic. The photopotential decay on titanium was found to be much slower than on iron. At the iron electrode the dependence of the photopotential transients on pH‐value, potential and light intensity was examined. The photocurrent transients were mainly determined by the electronic RC‐time constant of the cell and the measuring system.

Photoelectron emission from poly- and single-crystalline platinum and gold electrodes into an electrolyte was studied using a pulsed excimer laser, operating with KrF (λ = 248 nm = 5 eV). The 5/2 power law can be applied to the plot of the photocharge Q versus the electrode potential. The values for the threshold energy determined from these plots were higher (mean value 4.0 eV) than the values established in the literaure (3.15 eV). Anodic photocurrents were observed for gold in acid electrolytes above 0.5 V vs. SHE, but below the oxide layer formation, which also showed a linear dependence of the photocurrents to the power of 0.4 on the electrode potential. A threshold energy of 5.0 eV was determined.

The protonation/deprotonation of methyl orange adsorbed on a smooth platinum electrode has been investigated by modulated reflectance spectroscopy in the visible spectral region. The modulated reflectance spectra are mainly governed by the potential modulation of the protonation equilibria of methyl orange and the buffer (acetate/acetic acid), respectively. The p K values of the protonation equilibria within the adsorption layer change with the electrode potential E in the following way: dp K /d E = 0.8 V −1 and —1.0 V −1 for methyl orange and acetic acid, respectively.

Modulated reflectance spectra of p-nitroaniline adsorbed on a smooth Pt electrode have been measured. Spectra were obtained only with light polarized parallel with respect to the plane of incidence. The spectra depend on p-nitroaniline concentration, modulation amplitude, electrode potential, and pH of the supporting electrolyte. The form and the properties of the spectra are explained by the electrochromic (Stark) effect of the adsorption layer caused by the double-layer field. Experimental results allow a determination of the ad-molecular orientation within the adsorption layer and some other properties of the adsorbed molecules.

The irradiation of an electrode–electrolyte interface with light pulses of an excimer laser causes photocurrent pulses. On metal–electrolyte interfaces in the double-layer region, cathodic photocurrents were found to be caused by photoelectron emission into the electrolyte. If a thin oxide layer covers the electrode surface, anodic photocurrents occur because of electron–hole pair excitation in the semiconducting oxide and a charge separation in the gradient of the electric field across the oxide. The dependence of the anodic photocurrents on the light intensity shows that a threshold intensity and a saturation region can both be used for a characterization of the properties of the oxide layers.

Surface-enhanced Raman spectra of p-dimethylaminobenzonitrile were measured on polycrystalline silver electrodes. The height of the Raman lines depended on the potential. A hysteresis of the Raman signal was observed in the cyclic voltammogram. The frequency of most Raman lines was independent of the potential, except the frequency of the CN vibration at 2210 cmt–. The intensity depended on the type and the concentration of the supporting electrolyte. The results suggest a perpendicular orientation of the molecules with respect to the metal surface. Raman enhancement is explained by surface complexes of metal clusters of potential-dependent activity.

A thermodynamic relation between the difference of the reversible metal/metal ion potentials and the difference of the potentials zero charge of a metal in different modifications has been derived. The difference is given by the difference of the partial molar Gibbs energies of the metal ions in the metal lattice and by the difference of the surface dipole potentials in both modifications. The equation quantifies the correlation between both quantities postulated in a recent publication. Two examples are discussed: (i) bulk metal and colloidal metal; (ii) bulk metal and an underpotential deposition layer of this metal.

The electrostatic interaction of the double layer field with optically absorbing admolecules can cause modulation reflectance spectra owing to the Stark effect and the dissociation field effect, respectively. The spectra depend on the state of polarization of incident light, the stationary electrode potential, the pH value and other parameters. From the results it could be concluded to the admolecular orientation, the field strength in the double layer and interfacial protonation. This is illustrated for some organic substances.

The kinetic, thermodynamic and optical properties of the adsorption layers of bromide ions on polycrystalline gold electrodes were investigated by potentiostatic, potendiodynamic and optical measurements. The kinetics of adsorption are controlled by diffusion up to bromide concentrations of 10−2 M. The adsorption follows the Temkin isotherm; the interaction parameter was determined to be 56 kJ/mol; the electrosorption valency γ is equal to 0.8. The change of the reflection of the electrode surface with bromide adsorption was measured as a function of the potential and as a function of the wavelength of light polarized perpendicular and parallel to the plane of incidence. The reflection spectra showed an overall dependence on the potential similar to the electroreflection spectrum of a gold electrode without specific adsorption. Transitions at 2.55, 2.85 and 3.6 eV were observed in the spectra for perpendicular polarization and at 2.6 and 3.25 eV for parallel polarization, increasing with the potential, similar to the overall spectrum. A different behaviour was observed for a peak at 3.0 eV for light polarized in the plane of incidence. This peak decreased with increasing bromide coverage.

AbstractPotentiostatische und ‐dynamische Messungen in Lösungen mit 0.5 M B2804 zeigten, daß für BF‐Konzentrationen bis zu l0′: Mdie Adsorption diffusionsbestimmt ist (Temkin‐Isotherme).