Vicente Parra

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Recoleccion de germoplasma de semilla de hortalizas en las provincias de Pichincha, Cotopaxi, Tungurahua y Chimborazo

Recoleccion de germoplasma de semilla de hortalizas en las provincias de Pichincha, Cotopaxi, Tun... more

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An original all-organic sensor with integrated gas filtering layer for selective measurements of NO2

HAL (Le Centre pour la Communication Scientifique Directe), Jul 1, 2007

International audienceThe selective and real time monitoring of oxidising gases in atmosphere by ... more International audienceThe selective and real time monitoring of oxidising gases in atmosphere by semiconductor gas sensors remains a real challenge despite all improvements to reach analyzer performances. Thanks to its insensitivity to reducing species and its high reactivity with oxidising ones, even for low concentrations, copper phthalocyanine (CuPc) is one of the most attractive semiconductor for this application. In recent works, we have shown that selective detection of O3 can be obtained with CuPc based gas sensor, using an appropriate methodology of measurements exploiting the fastest kinetics of response to this gas [1-2]. For the selective detection of NO2 in air, ozone constitutes the most important interfering agent and leads to the irreversible degradation of phthalocyanine molecular units in long term which reduces the sensors lifetime [3]. Thus, to efficient monitoring of NO2 in atmosphere by phthalocyanine gas sensors, it appears necessary to eliminate O3 without altering NO2 concentration, by means of selective filter. Among all the material investigated as ozone filter (MnO2 powder or impregnated grids, charcoal, C60 powder, stainless steel cuttings, indigo powder...), only indigo can be considered as a real selective ozone filter. Moreover, indigo powder being easily sublimed to be deposited as thin layers, this material is really suitable for the realization of integrated selective ozone filter. The structure investigated in this work is constituted by a 300nm-CuPc thin film as sensitive layer and an additional indigo evaporated film as the filter layer. The range of thickness investigated for indigo layer is 10-100nm. The very low intrinsic conductivity of indigo films (Σ = 2.10-107-1.cm-1) makes them insulating, that's avoid bypassing the sensitive layer. Sensor responses measured for the same concentration of NO2 and O3 emphasize that response and recovery times remain high, gas/phthalocyanine interactions are reversible, the response under O3 is negligible and kinetics of response to NO2 is slower than device without indigo filter due probably to the slow diffusion of NO2 species through the filtering layer to reach the sensitive one. The last point is confirmed by experiments made on structures with different thicknesses of indigo: the thicker the layer is, the slower the kinetics of response is. The integrated indigo layer on phthalocyanine sensors makes them selective to NO2 and avoids the fast ageing effect due to the strong and irreversible interaction of O3 on the sensitive layer

Mono-crystalline silicon wafers manufactured by casting methods: Optoelectronic, structural and solar cell study

1) Introduction 2) The Quasi-mono, pseudo-mono, mono-like ERA. 3) Manufacturing mono-cast ingots:... more

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El principio de oportunidad en el nuevo sistema penal acusatorio

The principle of opportunity in the new penal system is the only exception to the obligation that... more The principle of opportunity in the new penal system is the only exception to the obligation that the General District Attorney of the Nation’s office has of advancing punitive action and carrying out the investigation of the facts that probe the characteristics of a crime. Its birth, in addition to having been prepared by a penal accusatory system, also has different classes of foundations, among which it is possible to emphasize the problem of the high rate of delinquency and the incapacity of the investigative sector and of the Judicial Branch in general, to investigate and judge the totality of conducts indicated as possible infractions to penal law.

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Daylight luminescence system for silicon solar panels based on a bias switching method

Energy Science & Engineering, 2020

Among the many characterization techniques for solar panel testing, two, electroluminescence (EL)... more Among the many characterization techniques for solar panel testing, two, electroluminescence (EL) and photoluminescence (PL), can provide useful visual information about the presence of different types of cell defects. EL is performed outdoors by night in commercial solar plants due to the very weak luminescence emission compared to sunlight. PL faces the added difficulty of needing to find a large‐area homogeneous light source to excite the modules. Since nighttime work poses many drawbacks and risks, a daylight outdoor EL/PL system would be useful for offering safe inspection of solar plants. We present daylight luminescence techniques based on a bias switching method, in which a pulsed luminescence signal is obtained by alternating the polarization state of the solar panels, synchronizing it with the luminescence image detection by an InGaAs camera. Fast switching and selecting an optimized exposure time are key to achieving high‐quality images. The daylight luminescence method d...

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Semiconductor Tranducer and Its Use in a Sensor for Detecting Electron-Donor or Electron-Acceptor Species

Visualización 3D de Deformación y Corte de Objetos Virtuales basada en Descomposición Ortogonal

Polibits, 2008

Resumen-Se muestra la implementación gráfica de un nuevo modelo para la renderización de fuerzas ... more Resumen-Se muestra la implementación gráfica de un nuevo modelo para la renderización de fuerzas de contacto durante la interacción háptica dentro de ambientes virtuales 3D para deformación y corte de objetos virtuales con propiedades dinámicas y superficiales complejas. Se define un algoritmo simple para la triangulación de un objeto virtual, empleando algoritmos clásicos para la detección de colisiones. Se desarrolló un algoritmo para la visualización del corte de la malla triangular así como para el cálculo de las dinámicas de la malla durante el corte. Se presentan imágenes de la plataforma utilizando OpenGL y Visual C++, para la parte gráfica y el dispositivo Falcon para la retroalimentación háptica. Palabras clave-Dispositivo háptico, renderización 3D, deformación y corte.

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Electronic panel test used to monitor the ageing of a red wine carried out in oak barrels and by alternative methods

An on-line experiment: Solar Cell IV Characterization

ABSTRACT

Molecular organization of discotic mesogenic cis-dichlorobis(3,4,5-trialkoxyphenylisonitrile)platinum (II) complexes on Langmuir and Langmuir-Blodgett films

Langmuir and Langmuir-Blodgett films of a new class of square planar metallomesogens, the cis-dic... more Langmuir and Langmuir-Blodgett films of a new class of square planar metallomesogens, the cis-dichlorobis(3,4,5trialkoxyphenylisonitrile)platinum (II) complexes (PtC n ), have been prepared. The structure and the stability of the floating monolayers of these discotic complexes have been investigated by means of compression isotherms, surface potential measurements and Brewster angle microscopy (BAM). A certain influence of the peripheral substituents on the properties of the Langmuir films are observed. It is shown that the hexoxy derivative (PtC 6 ), which shows mesogenic behavior at room temperature, has a more marked tendency to self-organization in ordered multilayers than the butoxy complex (PtC 4 ) which is not liquid crystalline at room temperature. The structural properties of films, transferred at different pressures, have been studied by AFM and UV-VIS, FT-IR transmission and reflection-absorption infrared spectroscopy (RAIRS). The transfer of the monolayers onto solid substrates leads to Langmuir-Blodgett films in which face-on orientation is found for the molecule cores. The organization of the aliphatic chains depends on the pressure at which the monolayers are transferred.

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Photophysics, electrochemistry and structure of a pyrazolino[60]fullerene dendrimer in solid molecular films

Synthetic Metals, 2005

A novel pyrazolino [60]fullerene dendrimer is studied in solid molecular films. Orientated monola... more A novel pyrazolino [60]fullerene dendrimer is studied in solid molecular films. Orientated monolayers of this donor-acceptor system are formed by means of the Langmuir-Blodgett (LB) technique. The fullerodendrimer exhibits high collapse pressures but a tendency to aggregate at the air-water interface. Nonetheless, the subsequent LB deposition process shows a good transfer behaviour onto a variety of substrates. Concurrently, cast dropped films are prepared to compare particular properties respect to those of the LB films. Steady-state absorption spectra imply J-aggregation through solution-LB-cast films. The photoinduced outcomes suggest an enhanced charge transfer between donor-acceptor in thin films via intermolecular effects, although an energy transfer process may coexists. Therefore, square wave voltammetry (SWV) is applied to study the electronic behaviour of the C 60 -dyad. The results are qualitatively correlated with the photophysics. Further, reflection-absorption infrared spectroscopy (RAIRS) and atomic force microscopy (AFM) are applied to analyse the structure of the films, which is the main responsible of their properties. In this regard, it can be distinguished the preferential intermolecular arrangement in LB films with respect to cast film, and an aggregation growing with increasing number of transferred monolayers in case of LB films, but upholding homogeneity all along the surface's coating, contrary to the cast heterogeneousness.

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Light Beam Induced Current Mapping of mc-Si Solar Cells: Influence of Grain Boundaries and Intragrain Defects

MRS Proceedings, 2010

The photovoltaic market is currently dominated by multicrystalline silicon. However, this materia... more The photovoltaic market is currently dominated by multicrystalline silicon. However, this material is characterized by intrinsic structural heterogeneity due to point defects, dislocations and grain boundaries. In order to improve the cell performance the control of the electrical properties of the grain boundaries and dislocations is required. The laser beam induced current technique allows the estimation of the variations of the charge capture rates due to the different trapping centers, and is a powerful tool for the characterization of multicrystalline silicon solar cells. Nevertheless, one has to control the reflected light in order to obtain a reliable estimation of the electrical parameters.

A Chemical Microsystem for selective detection of polluting gases in vehicle compartments

This paper deals with the design of an original microsystem devoted to the real time monitoring o... more This paper deals with the design of an original microsystem devoted to the real time monitoring of air polluting gases in vehicle compartments. The selective detection is focused on two species, ozone and nitrogen dioxide, because of their specific toxicity. The gas sensing element is made of thin layers of an organic semiconductor provided with a specific chemical filter. A particular methodology of measurement is implemented, witch allows a selective sensing behaviour. On-board tests are presented.

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On the effect of ammonia and wet atmospheres on the conducting properties of different lutetium bisphthalocyanine thin films

Thin Solid Films, 2008

In this article, we present new experimental data regarding the influence of ammonia (NH 3 ) and ... more In this article, we present new experimental data regarding the influence of ammonia (NH 3 ) and water (from wet atmospheres) in the conducting properties of lutetium bisphthalocyanine (LuPc 2 )-based films in two very different structural features, namely Langmuir-Blodgett (LB) and vacuum evaporated (VE) films, deposited onto interdigitated electrodes. We pay particular attention to the effect of the mass flow rate ratios of the active gases, which certainly influence the mechanism of conduction of the chemiresistors. The particular trends observed are discussed on the basis of two main contributions: the electronic effects and the competition between gases in the adsorption process.

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Electronic tongue based on chemically modified electrodes and voltammetry for the detection of adulterations in wines

Sensors and Actuators B: Chemical, 2006

An electronic tongue based on chemically modified voltammetric electrodes is able to detect succe... more An electronic tongue based on chemically modified voltammetric electrodes is able to detect successfully model fraudulent red wines obtained by adding a range of forbidden adulterants (frequently used in wine industry to improve the organoleptic characteristics of wines) to a given wine sample. The sensor array consists in two families of sensors, one based on phthalocyanine-based carbon paste electrodes (CPEs) and a second one based on electrodes covered with conducting polypyrrole doped with a range of counterions. The electrochemical response of both families of electrodes is related to the ions and to the electroactive molecules present in the solution, being particularly sensitive to pH and antioxidants. The use of sensitive materials with different chemical properties allows obtaining complementary information that enhances the capability of discrimination of the system. Prediction models have been successfully used to estimate chemical parameters, such as alcoholic degree and acidity by means of partial least squares (PLS). The sensor array coupled with pattern recognition techniques is able to distinguish the adulterations on account of their chemical nature.

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E-tongue based on a hybrid array of voltammetric sensors based on phthalocyanines, perylene derivatives and conducting polymers: Discrimination capability towards red wines elaborated with different varieties of grapes

Sensors and Actuators B: Chemical, 2006

An innovative hybrid sensor array formed by voltammetric electrodes chemically modified with thre... more

Array of voltammetric sensors for the discrimination of bitter solutions

Sensors and Actuators B: Chemical, 2004

ABSTRACT Novel voltammetric sensors based on electrodes chemically modified with electroactive su... more ABSTRACT Novel voltammetric sensors based on electrodes chemically modified with electroactive substances (conducting polymers and on phthalocyanine complexes), with improved cross-selectivity have been developed. Polymeric sensors have been obtained by electrodeposition of the corresponding monomer (pyrrole) in the presence of different doping agents. Phthalocyanine electrodes have been prepared using the carbon paste electrode technique. The performance and the capability of discrimination of the sensors has been evaluated by testing model solutions of bitterness including MgCl2, quinine, and four phenolic compounds (monoaldehydic and dialdehydic forms of the oleuropein and of ligstroside), which are the main responsible of the bitterness detected in some foods and beverages such as olive oils. The features observed in the voltammograms reflect the redox processes related both to the electroactive material itself and to the studied solutions. In consequence, each sensor shows a rich and characteristic electrochemical response when exposed to the model solutions of bitterness improving the cross-selectivity. A multichannel taste sensor has been constructed using those sensors with the best stabilities, and cross-selectivities. The principal component analysis (PCA) of the obtained signals has allowed the clear discrimination of the bitter solutions.

A Novel Gas Sensor Transducer Based on Phthalocyanine Heterojunction Devices

Sensors, 2007

Experimental data concerning the changes in the current-voltage (I-V) performances of a molecular... more Experimental data concerning the changes in the current-voltage (I-V) performances of a molecular material-based heterojunction consisting of hexadecafluorinated nickel phthalocyanine (Ni(F 16 Pc)) and nickel phthalocyanine (NiPc), (Au|Ni(F 16 Pc)|NiPc|Al) are introduced as an unprecedented principle of transduction for gas sensing performances. The respective n-and p-type doped-insulator behaviors of the respective materials are supported, owing to the observed changes in surface potential (using the Kelvin probe method) after submission to electron donor (ammonia) and electron acceptor gases (ozone). On the other hand, the bilayer device exhibits strong variations in the built-in potential of the junction and in its rectification ratio. Moreover, large increases occur in forward and reverse currents in presence of ammonia vapors. These make possible a multimodal principle of detection controlled by a combined effect between the heterojunction and the NiPc|Al contact. Indeed, this metal/organic junction plays a critical role regarding the steady asymmetry of the I-V profiles during the device's doping even using high ammonia concentrations. This approach offers a more sophisticated alternative to the classically studied, but at times rather operation-limited, resistive gas sensors.

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About the origin of low wafer performance and crystal defect generation on seed-cast growth of industrial mono-like silicon ingots

Progress in Photovoltaics: Research and Applications, 2012

The era of the seed-cast grown monocrystalline-based silicon ingots is coming. Mono-like, pseudom... more The era of the seed-cast grown monocrystalline-based silicon ingots is coming. Mono-like, pseudomono or quasimono wafers are product labels that can be nowadays found in the market, as a critical innovation for the photovoltaic industry. They integrate some of the most favorable features of the conventional silicon substrates for solar cells, so far, such as the high solar cell efficiency offered by the monocrystalline Czochralski-Si (Cz-Si) wafers and the lower cost, high productivity and full square-shape that characterize the well-known multicrystalline casting growth method. Nevertheless, this innovative crystal growth approach still faces a number of mass scale problems that need to be resolved, in order to gain a deep, 100% reliable and worldwide market: (i) extended defects formation during the growth process; (ii) optimization of the seed recycling; and (iii) parts of the ingots giving low solar cells performance, which directly affect the production costs and yield of this approach. Therefore, this paper presents a series of casting crystal growth experiments and characterization studies from ingots, wafers and cells manufactured in an industrial approach, showing the main sources of crystal defect formation, impurity enrichment and potential consequences at solar cell level. The previously mentioned technological drawbacks are directly addressed, proposing industrial actions to pave the way of this new wafer technology to high efficiency solar cells.

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Electroactivity of a starburst hole-transport material in Langmuir?Blodgett films. Solid state effects and intervalence charge transfer

Physical Chemistry Chemical Physics, 2007

Here we report on the electroactivity properties of Langmuir-Blodgett (LB) films of the hole-tran... more Here we report on the electroactivity properties of Langmuir-Blodgett (LB) films of the hole-transport molecule 4,4´,4´´-tris [3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA). Fairly stable Langmuir films at the air-water interface are accomplished, despite the non-amphiphilic character of the molecule. The Reflection-Absorption Infrared Spectroscopy (RAIRS) and Fourier Transform Infrared (FT-IR) analysis revealed that the molecules arrange with no neat preferential orientation, in agreement with the amorphous glassy nature of this starburst molecule. However, there is a tendency of the molecules to organize in a more planar conformation due to the intermolecular stacking induced by the LB technique. On the other hand, the fundamental electrochemistry (by Cyclic Voltammetry, CV) of the films is also analyzed. The CV studies of both solution and films reveal that both the solid Wavelength / nm Wavelength / nm m m--MTDATA MTDATA electrooxidization Wavelength / nm Wavelength / nm m m--MTDATA MTDATA electrooxidization state and the electrolyte's anions clearly affect the m-MTDATA's electroactivity, exhibiting a unique and broad redox process instead of the two reversible oxidations observed in solution. The oxidization mechanism is discussed. Finally, the spectroelectrochemistry studies evidence that the oxidization of the films leads to new absorption bands, among which it should be pointed up the emerging bands in the NIR region ascribed to intervalence charge transfer (IVCT) between the generated aminyl radical cations.

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