Gerardo Vázquez

The Effect of the Cu2 + ∕ Cu + Step on Copper Electrocrystallization in Acid Noncomplexing Electrolytes

in all of the solutions employed. In cyclic voltammetry, a larger reduction peak was obtained in the nitrate electrolyte, in comparison with the other two media. This higher current has been associated with the catalytic reduction of nitrate ions on recently deposited metallic copper. This effect was confirmed in the potential-step analysis. Despite the fact that Cu + is not thermodynamically stable in these three solutions, the reduction step Cu 2+ /Cu + has been considered as an electron-transfer reaction. The anion type has a direct effect on this electron- transfer reaction and consequently, on the electrocrystallization process; sulfates provoke the most important current decrease associated with the Cu 2+ /Cu + step and also strongly influence the nuclei formation, while the nitrate ions accelerate the Cu 2+ /Cu +

Electrochemical Characterization of TiO2 Films Formed by Cathodic EPD in Aqueous Media

The present work studies the influence of applied electric field on the cathodic electrophoretic formation of TiO 2 films in an aqueous medium. The growth of the film was followed by measuring current density, deposited mass, and thickness under imposed electric field (ϕ). In scanning electronic microscopy images of the TiO 2 films formed under different electric fields, three regions can be seen: (i) formation of nuclei that are converted into agglomerates, (ii) uniform and one-sided growth, and (iii) growth by the formation of agglomerates on the TiO 2 surface. The characterization of semiconductor properties showed that increased ϕ for film growth leads to an increase in the density of donors and to a displacement of the flatband potential toward less negative values. The photoelectrochemical characterization of the oxide films revealed that the photoelectrochemical performance of the TiO 2 films decreases as a function of the electric field used to carry out the electrophoretic deposition (EPD) process. The electrochemical behavior observed for these films seems closely related to the content of Ti 3+ doping sites electrogenerated in situ during the EPD, which act as electron traps negatively affecting the electron transport toward the indium tin oxide collector, also making their photoelectrochemical activity inefficient.

Influence of Potentiostatic Aging on Nb and W Oxides Formed in 0.1 M HClO4

The evolution of the electrical properties of Nb 2 O 5 and WO 3 films, at different formation potentials (E f ), in 0.1 M HClO 4 , were followed by electrochemical impedance spectroscopy (EIS). During the growth of the oxide films, EIS spectra were acquired every hour, maintaining the potentiostatic pulse during 20 h. The Nb 2 O 5 and WO 3 impedance spectra show variations vs potentiostatic aging. However, the Mott-Schottky analysis showed that the density of donors (No) does not depend on the potentiostatic aging but depends on the E f , while, the flatband potential (E FB ) is almost constant with the potentiostatic aging and E f , for both oxides. The relationship between the invariability of the semiconductor properties (N D and E FB ) with the potentiostatic aging and the variation of the impedance spectra, in the case of the W, can be explained by the formation of an external layer of WO 3 ·(H 2 O) x , which must be very thin; the detachment of this layer causes a very small difference in the thickness, not modifying the semiconductor properties (N D and E FB ), but greatly changing the electric properties of the film, since WO 3 ·(H 2 O) x is more resistive. A similar hydration process may occur in the Nb 2 O 5 films to a lesser extent.

Generación de estados superficiales durante la formación electroforética catódica de películas de TiO2 sobre ito

In the present work TiO2 films were formed over Indium Tin Oxide (ITO) employing cathodic electrophoretic deposition (Cathodic-EPD) and Dr. Blade Technique. The films were characterized by electrochemical techniques in order to compare their electronic properties; as well as, their photoelectrochemical behavior. The electrochemical performance showed by the films, allowed to relate the modification occurring during the Cathodic-EPD, with the partial reduction of TiO2 nanoparticles, generating Ti3+ defects. These trapping states are modifying the electronic properties of the film, and diminishing the transport of the photoelectrogenerated electrons toward ITO.

A new approach to describe the passivity of nickel and titanium oxides

Abstract Nickel and titanium oxide films were grown by means of potentiostastic pulse in aqueous borate solution at different pH. The passive properties of these films were evaluated by EIS technique. These results were used to validate a new model, used in this work, to describe the conduction through the different semiconductors films. This model considers the initial assumptions of point defect model, and also, the presence of molecular hydrogen into the films.