Rodrigo Gonzalo Henríquez

Redox and solution chemistry of the SeSO32−–Zn–EDTA2− system and electrodeposition behavior of ZnSe from alkaline solutions

Abstract The specific redox and solution chemistry involved in the formulation of the plating solution for the electrodeposition of zinc selenide from the SeSO 3 2− /Zn 2+ /EDTA system was investigated. After a theoretical analysis which allowed the electrodeposition conditions to be fixed, based on potential–pH and solubility diagrams, an experimental study was conducted by varying the deposition parameters (composition, pH, potential). XRD, EDS, AFM and reflectance measurements were used to characterize the structure, morphology, composition, and optical properties of films deposited on conducting glasses. EDS analysis showed that the as grown films are almost stoichiometric in a wide potential interval and also that the film thicknesses are lower than the values estimated from the circulating charge. The possible reasons for the latter behavior are discussed.

ELECTRODEPOSITION AND CHARACTERIZATION OF ZnX (X=Se, Te) SEMICONDUCTOR THIN FILMS

El presente trabajo describe la sintesis y la caracterizacion de peliculas delgadas de ZnX (X = Se y Te) obtenidas por electrodeposicion a potencial constante en medio acido. Previamente, se realizo un estudio voltametrico y fotovoltametrico sobre diferentes substratos conductores los que permitieron determinar las mejores condiciones para la electro obtencion de estos compuestos. Las peliculas delgadas de ZnSe y de ZnTe fueron analizadas por diferentes tecnicas (SEM, EDS, XRD y medidas opticas). Las peliculas de ZnTe presentaron una composicion muy cercana a la estequiometrica, en tanto que las de ZnSe presentaron un exceso de Se el cual puede ser eliminado por un adecuado tratamiento termico. La caracterizacion optica de ambos semiconductores depositados sobre titanio arrojo valores de ancho de banda prohibida de transicion directa de 2,64 eV para ZnSe y 2,27 eV para ZnTe, muy cercanos a los aceptados en bibliografia.

A Novel Approach for the Electrodeposition of Epitaxial Films of ZnSe on (111) and (100) InP Using Dimethylsulfoxide as a Solvent

Results on the preparation and characterization of ZnSe epitaxial thin films obtained by electrodeposition on (111) and (100) n-type InP single-crystalline substrates, starting from elemental selenium dissolved in DMSO at423 K, are reported. Voltammetric studies have been performed on these substrates and compared to SnO 2 :F covered glass substrates. They show substrate dependent behavior and the presence of parasitic faradaic reactions attributed to the formation of di-selenide anions. However, composition analysis of the films by electron dispersive spectroscopy revealed that, independent on the substrate, nearly stoichiometric ZnSe films are obtained within the deposition potential range. Scanning electron microscopy images present a specific effect of chloride ion on the films morphology, whereas their optical characterization showed a direct band gap value of 2.64 eV. The epitaxial quality of the deposits has been confirmed by reflection of high energy electron diffraction and atomic force microscopy techniques.

The Oxygen Index on Soot Production in Propane Diffusion Flames

An experimental study of the effect of oxygen index (OI) on soot formation in laminar coflow propane diffusion flames is presented. The OI was defined as the oxygen volumetric concentration in the oxidizer flow, O2/(O2+N2), which was varied from 21% to 37%. The influence of the OI was quantified by means of three variables: the flame height, the soot volume fraction, and the vertical distribution of radiative heat flux. The flame height was based on CH* spontaneous emission and found to vary inversely with the OI, following the classical theory of Roper. As the OI increases, the rates of soot growth and soot oxidation are enhanced, and the maximum soot volume fraction and the peak of integrated soot volume fraction also increase. Moreover, the evolution of the peak of radiative heat flux and the maximum soot volume fraction are found to follow the same evolution with the OI.

Nucleation and growth mechanism of CdTe at polycrystalline gold surfaces analysed through Δm/t simulation transients

The nucleation and growth mechanisms of cadmium telluride have been investigated in aqueous H2SO4 solution using polycrystalline gold as substrate. Using cyclic voltammetry as a reference, a series of potential steps experiments were performed in order to simulate the corresponding j/t experimental transients that gave only a current decay proportional to t−1/2. Conducting the potential steps in an electrochemical quartz crystal microbalance (EQCM) allowed recording Δm/t transients that were potential dependent. Introducing some modifications in the classic equations of the nucleation and growth models, these transients gave information about the mechanism of CdTe electrocrystallization. It is proposed that the initial process is associated with the nucleation and growth of the Te islands followed by fast formation of Cd islands and that CdTe is formed through the slow diffusion of these islands. The slow rate of this process was evidenced through the time elapsed before observing a cathodic photocurrent when the electrode surface was illuminated. Gold surface has an influence on the nucleation mechanism favouring the instantaneous over the progressive, specially at more negative values of the final potential step. These results show that Δm/t transient simulations are a suitable tool for studying NGM when convolution of the classical j/t transients does not allow extraction of the appropriate information.

One-Step Electrodeposition of ZnO2–ZnS Thin-Film Mixtures onto n – InP ( 111 ) and n – InP ( 100 ) Substrates

Electrodeposition of ZnS-ZnO 2 film mixtures onto monocrystalline n-InP substrates through the simultaneous electroreduction of dioxygen and sulfur in the presence of zinc ions in dimethyl sulfoxide solution is reported. The films were thick, compact, transparent, and with a flat morphology. The mixture of phases was confirmed by the analysis of the reflection high-energy electron diffraction patterns. The optical absorption gave an Eg value of 3.47 eV, which agrees with the presence of ZnO in the mixture. The properties of the films suggest it might be a good alternative to replace the CdS window layer in Cu(In,Ga)Se 2 -based photovoltaic devices.

PHOTOELECTROCHEMICAL CHARACTERIZATION OF NATURAL COPPER SULPHIDE ELECTRODES IN ALKALINE MEDIA: EFFECT OF XANTHATE ADSORPTION

A photoelectrochemical approach is utilized for studying the processes that take place on copper sulfide mineral surfaces in alkaline solutions, either in absence or presence of potassium ethyl - xanthate. It is found that photoresponses are closely related to the mineral stoichiometric composition which also determines its semiconducting or metallic character. It appears that in the potential interval where xanthate anions can be adsorbed, surface composition and reactivity are closely linked