Institute Fisica and CINQUIFIMA

Montevideo, Uruguay

Institute Fisica and CINQUIFIMA

Montevideo, Uruguay
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Schrebler R.,Pontifical Catholic University of Valparaíso | Ballesteros L.A.,Pontifical Catholic University of Valparaíso | Gomez H.,Pontifical Catholic University of Valparaíso | Grez P.,Pontifical Catholic University of Valparaíso | And 4 more authors.
Journal of the Electrochemical Society | Year: 2014

Hematite nanostructures were electrochemically grown by ultrasound-assisted anodization of iron substrates in an ethylene glycol based medium. These hematite nano-architectures can be tuned from a 1-D nanoporous layer to a self-organized nanotube one if the grown is done onto a bare iron foil substrate or onto an electrochemical pretreated one, respectively. Depending upon the pre-treatment conditioning, the self-organized nanotube layer consists of nanotube arrays with a single tube inner diameter of approximately 40-50 nm and wall thickness of 20-30 nm. Their morphological, structural and optoelectronic properties are studied. The photoelectrochemical properties of the resulting hematite nanostructures are studied from the point of view of their application as photoanodes in splitting of water. Through the photocurrent transients for the three nanostructured hematite type electrodes under study, the rate constants ktr and krec corresponding to the rate constant of charge transfer and recombination processes have been determined. In all cases, the potential value where ktr > krec was attained at more negative values than the reversible potential of water oxidation, indicating a photocatalytic effect. All samples show a maximum IPCE value between 350 and 375 nm, being the samples pretreated at -1.0 V which shows the highest IPCE value: 45% at 375 nm. © The Author(s) 2014.

Guerguerian G.,Institute Fisica and CINQUIFIMA | Elhordoy F.,Institute Fisica and CINQUIFIMA | Pereyra C.J.,Institute Fisica and CINQUIFIMA | Marotti R.E.,Institute Fisica and CINQUIFIMA | And 4 more authors.
Journal of Physics D: Applied Physics | Year: 2012

Vertically aligned ZnO/Cu 2O heterostructure nanopillar arrays consisting of a ZnO core and a Cu 2O shell were fabricated by a two-step electrochemical deposition method. Morphological, structural and optical properties of the nanopillar heterojunctions were investigated. The surface of the single-crystalline ZnO nanopillars was coated uniformly, conformally and densely over the entire nanopillar length by numerous Cu 2O nanocrystals (2535nm mean diameter), constituting a conformal shell layer 90nm thick, integrating these two materials into an electronically intimate composite. The optical properties can be interpreted, by appropriate fittings of each feature, as being due to the properties of the bare ZnO nanopillar array plus the increased absorption of Cu 2O. This study demonstrates that electrodeposition is a suitable and accessible technique for large-scale fabrication of nanopillar heterostructures and to achieve conformal coverage of nanostructured samples. © 2012 IOP Publishing Ltd.

Gomez H.,Pontifical Catholic University of Valparaíso | Cantillana S.,Pontifical Catholic University of Valparaíso | Riveros G.,University of Valparaíso | Favre S.,Institute Fisica and CINQUIFIMA | And 4 more authors.
International Journal of Electrochemical Science | Year: 2013

Zinc oxide films have been electrochemically grown on gallium nitride substrates from an electrolytic bath composed of a zinc salt and oxygen dissolved in dimethylsulfoxide (DMSO). The XRD structural study showed the epitaxial growth of the films, specifically it was found that the c axis is perpendicular to the plane of the substrate, while a and b axes are aligned with the respective substrate lattice parameters. In spite the similarity of both crystal structures and the close values of their lattice parameters, for thinner films it was possible to detect acomponent under in-plane compression while thicker films presumably relax. The obtained Poisson's ratio for ZnO was in good agreement with tabulated values, indicating a real effect of elastic deformation and confirming the consistency of the performed analysis. The optical propertiesof the performed electrodeposited film showed that the transmittance spectra have a very similar general shape in comparison with the one of the substrate but with an increase in the totaloptical transmittance. Due to presence of ZnO, the diffused reflectance spectra showed also an increased absorption close to 400 nm. As a consequence of the difference in the defect density,the photoluminescence measurements recorded in stressed and relaxed samples also changes drastically. © 2013 by ESG.

Henriquez R.,Pontifical Catholic University of Valparaíso | Vasquez C.,Pontifical Catholic University of Valparaíso | Briones N.,Pontifical Catholic University of Valparaíso | Munoz E.,Pontifical Catholic University of Valparaíso | And 2 more authors.
International Journal of Electrochemical Science | Year: 2016

In current work the synthesis of single phase of FeS2 (pyrite) thin films from a combined electrochemical and hydrothermal techniques and without the need for a post sulfurization process is reported. Electrodeposition has been carried out in a non aqueous based electrolytic bath (diethylene glycol (DEG)). Voltamperometric measurements were conducted to study the electrochemical response of the precursors in this organic DEG solvent. These experiences allowed determining the best experimental conditions in DEG for obtaining the FeS/FeS2 mixture phases which were obtained applying a constant potential of -1.10V. The hydrothermal technique that was developed in a microwave oven improved stoichiometry and crystallinity of the deposits obtained by electrodeposition and led to obtaining a single pyrite phase. SEM micrographs exhibited complete substrate coverage whereas EDS analysis gave atomic ratio S/Fe very close to 2. XRD analysis of the final thin film shows that the deposit has a cubic structure without the presence of other undesired phases. However, Raman spectra indicate a later formation of amorphous superficial hematite. The optical measurements show an optical direct bandgap of 0.985 eV. Results open the possibility of applying the procedure to the formation of a thin film of FeS2 of good structural and optical characteristics that can be employed as an absorber material in solar cells. © 2016 The Authors.

Romero M.,Pontifical Catholic University of Valparaíso | Henriquez R.,Pontifical Catholic University of Valparaíso | Dalchiele E.A.,Institute Fisica and CINQUIFIMA
International Journal of Electrochemical Science | Year: 2016

The nucleation and growth mechanisms for the electrochemical synthesis of ZnO nanorod arrays on two different substrates (i.e., a naked FTO/glass substrate and a ZnO thin film seed layer/FTO/glass substrate) were investigated. This study was based on the analysis and deconvolution of the chronoamperometric transient curves that were obtained during the potentiostatic electrosynthesis of ZnO nanostructures. Using this potentiostatic method and existing theoretical formalism, the nucleation kinetic parameters were determined. Analysis of these results indicated that the presence of a seed layer did not change the nucleation or growth mechanisms and only affected the time constant of each contribution (i.e., 3D instantaneous nucleation with diffusion controlled growth and 3D instantaneous nucleation under charge-transfer control) as well as the associated Faradic charge. © 2016 The Authors.

Broitman E.,Linköping University | Bojorge C.,CONICET | Elhordoy F.,Institute Fisica and CINQUIFIMA | Kent V.R.,Institute Fisica and CINQUIFIMA | And 4 more authors.
Surface and Coatings Technology | Year: 2012

The microstructural, morphological, optical and water-adsorption properties of nanocrystalline ZnO thin films and ZnO nanowires were studied and compared. The ZnO thin films were obtained by a sol-gel process, while the ZnO nanowires were electrochemically grown onto a ZnO sol-gel spin-coated seed layer. Thin films and nanowire samples were deposited onto crystalline quartz substrates covered by an Au electrode, able to be used in a quartz crystal microbalance. X-ray diffraction measurements reveal in both cases a typical diffraction pattern of ZnO wurtzite structure. Scanning electron microscopic images of nanowire samples show the presence of nanowires with hexagonal sections, with diameters ranging from 30 to 90. nm. Optical characterization reveals a bandgap energy of 3.29. eV for the nanowires and 3.35. eV for the thin films. A quartz crystal microbalance placed in a vacuum chamber was used to quantify the amount and kinetics of water adsorption onto the samples. Nanowire samples, which have higher surface areas than the thin films, adsorb significantly more water. © 2012 Elsevier B.V.

Riveros G.,University of Valparaíso | Baez C.,University of Valparaíso | Baez C.,University of Santiago de Chile | Ramirez D.,University of Valparaíso | And 6 more authors.
Journal of Alloys and Compounds | Year: 2016

In this study, the electrodeposition of a composition-graded stacked CdSxSe(1-x) multilayer film is a matter which is reported for the first time. The electrodeposition was carried out using CdSO4, Na2S2O3 and SeO2 as precursors in an acid solution. Previously, an exhaustive electrochemical study was carried out in order to establish the best condition for the electrodeposition of this structure. In order to confirm the feasibility of the method proposed, CdSxSe(1-x) single-layer films of different composition were electrodeposited and characterized. The electrodeposition of the composition-graded stacked layer arrangement was potentiostatically performed through successive electrodeposition steps in a unique electrolytic solution in which its Se content is gradually increases. The characterization of both, single-layer films and multilayer structure was performed using different techniques, confirming the formation of an alloy between CdS and CdSe. Furthermore, the multilayer structure composition gradually changes from pure CdS to a rich selenium CdSxSe(1-x) compound as the electrolytic solution composition increases its SeO2, forming a depth bandgap graded material. © 2016 Elsevier B.V.

Catano F.A.,Pontifical Catholic University of Valparaíso | Gomez H.,Pontifical Catholic University of Valparaíso | Dalchiele E.A.,Institute Fisica and CINQUIFIMA | Marotti R.E.,Institute Fisica and CINQUIFIMA
International Journal of Electrochemical Science | Year: 2014

The electrochemical synthesis, the structural, morphological and optical characterization together with the photocatalytic activity of nanostructured ZnO films prepared from zinc nitrate aqueous solutions is reported. Changes in both, the precursor concentration and the electrodeposition time allows obtaining morphologies which evolve from nanoneedles and nanorods to thin films. The analysis of texture coefficients, particle sizes and SEM images give information regarding some aspects related to the crystalline growth of the films. The photocatalytic activity was tested following the degradation of methyl orange. Results show that the surface area, the crystalline planes exposed, the morphology and the band gap of the ZnO nanostructured thin films play an important role in this activity. © 2014 by ESG.

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