Garcia-Mandayo, G. (Gemma)
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- Influence of the test-chamber shape on the performance of conductometric gas sensors(Elsevier, 2022) Bou-Ali, M.M. (M. Mounir); Souto-Canteli, I. (Íñigo); Martín-Mayor, A. (Alain); Garcia-Mandayo, G. (Gemma); Parellada-Monreal, L. (Laura)In this article, CFD simulations results are presented as a key tool to the comprehension of the target gas con- centration evolution in a test chamber, at different working conditions. The simulation results are compared with the experimental data, which shows a qualitative good correlation with the evolution of the concentration gradient detected. The experiments were carried out using an aluminum gas test chamber, where a WO3 based conductometric sensor is introduced. The results demonstrate how the response time is dependent on the sensor working conditions. Analyzing the CFD and experimental results, some assumptions for this behavior are proposed. The WO3 sensor needs a Pt heating element, which is heated up to 300 ◦C. As the response is highly temperature-dependent, the temperature distribution on the sensor surface was measured by an IR thermo- graphic camera. The simulation results show that the temperature distribution matches with those obtained experimentally. To validate the model, a mesh and time step convergence study was also implemented
- Bessel beams as a versatile tool to generate embedded devices in optical glasses(2024) Fantova-Sarasa, J. (Jorge); Rodríguez-González, A. (Ainara); Del-Hoyo, J. (Jesús); Olaizola-Izquierdo, S.M. (Santiago Miguel); Garcia-Mandayo, G. (Gemma)Beam shaping offers many opportunities to both streamline and accelerate laser fabrication processes, closing the gap between lab research and large-scale manufacturing. In the field of embedded devices, a Bessel beam configuration allows for large volume engraving of transparent materials in a single laser pass. In this work, we take advantage of femtosecond Bessel beams with a length of 340 mu m and a diameter of 1 mu m to generate diffractive elements within three distinct optical glasses. This strategy represents a chemical-free and cost-effective alternative to the conventional manufacturing of holographic elements based on photoresist micro-patterning. Despite the different nonlinear effects taking place in each material, we report the successful fabrication of diffraction gratings operating at either normal or Bragg incidence, with efficiencies in the first combined order of up to 70%. Our experimental results show the potential of Bessel beams as a tool to produce buried light devices in a wide variety of glass materials.
- Study of deposition parameters and growth kinetics of ZnO deposited by aerosol assisted chemical vapor deposition(ROYAL SOC. CHEMISTRY., 2021-06) Olaizola, S.M. (Santiago Miguel); Urionabarrenetxea, E. (Ernesto); Castaño-Carmona, E. (Enrique); Ayerdi-Olaizola, I. (Isabel); Sánchez-Martín, S. (Sergio); Garcia-Mandayo, G. (Gemma)Aerosol-assisted Chemical Vapor Deposition (AACVD) is a thermally activated CVD technique that uses micro-droplets as deposition precursors. An AACVD system with a custom-designed reaction chamber has been implemented to grow ZnO thin films using zinc chloride as a precursor. The present work aims to study the impact of the deposition parameters on the thin film, as well as the microstructure evolution and growth kinetics. Aerosol flow has an effect on the density of nucleation sites and on the grain size. The temperature affects the morphology of the grown ZnO, showing a preferential orientation along the c-axis for 350 degrees C, 375 degrees C and 400 degrees C substrate temperatures. The microstructural evolution and the growth kinetics are also presented. A different evolution behavior has been observed for 350 degrees C, where nucleation site density is the highest at the early stages and it decreases over time in contrast with the cases of 375 degrees C and 400 degrees C, where there is an initial increase and a subsequent decrease. The activation energy of the chemical reaction is 1.06 eV. The optical characterization of the material has been performed through reflection measurements showing a relationship between the spectrum and the ZnO film thickness. The electrical characterization has been done by means of an interdigital capacitor, with which it is possible to measure the grain and grain boundary resistance of the material. Both resistances are of the order of 10(5)-10(6) omega.
- Single-step fabrication of highly tunable blazed gratings using triangular-shaped femtosecond laser pulses(2024) Fantova-Sarasa, J. (Jorge); Olaizola, S.M. (Santiago Miguel); Rodríguez-González, A. (Ainara); Gómez-Aranzadi, M. (Mikel); Lens, J. (José); Beldarrain, O. (Oihane); Omeñaca-Segura, L. (Luís); Garcia-Mandayo, G. (Gemma)Blazed gratings are periodic surface structures of great interest for applications such as friction control, light trapping, and spectrometry. While different laser processing methods have been explored to produce these elements, they have not yet surpassed conventional surface manufacturing techniques, often based on lithography processes or mechanical ruling. This work introduces a new approach based on the combination of ultrashort pulses and triangular beam shaping, which enables the generation of asymmetrical grooves in a single step. The main advantage of this strategy is that by simply changing the laser processing direction we can induce a significant modification in the ratio of asymmetry between the sidewall angles of the machined channels. The paper includes a comprehensive study, which has been supported by statistical tools, of the effect of this and other experimental parameters on the morphology of grooves machined on stainless steel. As a result, we achieved a wide range of geometries, with asymmetry ratios spanning from 1 to 5 and channel depths between 3 and 15 mu m. Furthermore, we demonstrate the validity of the approach through the successful manufacture of blazed gratings of various slopes. The results reflect the versatility and cost-efficiency of the proposed fabrication strategy, and thus its potential to streamline the production of sawtooth gratings and other devices that are based on asymmetrical features.
- Nuevas estrategias de catalizado y filtrado para la mejora de prestaciones en sensores de monóxido de carbono basados en nanopartículas de óxido de estaño.(2011-04-05T10:05:04Z) Garcia-Mandayo, G. (Gemma); Castaño-Carmona, E. (Enrique)El continuo y sostenido avance que se ha producido en los últimos años en el sector de las microtecnologías y los microsistemas ha dado lugar a un creciente desarrollo de procesos altamente controlados, desarrollados en ambiente de sala limpia, cuya aplicación se ha extendido a campos como el de la fabricación de sensores. El atractivo de estas técnicas radica en su repetibilidad, en la reducción de consumos y en la miniaturización de los dispositivos así fabricados. Si en este panorama se introduce la creciente demanda de dispositivos sensores tanto en ámbitos industriales como domésticos, resulta comprensible la adopción de las mencionadas técnicas para llegar a la obtención de los denominados microsensores, en alusión tanto a la miniaturización de los mismos como a las microtecnologías mediante las que se fabrican. Por otra parte, en el ámbito de la llamada sociedad del bienestar, el uso creciente del gas natural en los hogares ha incrementado el riesgo tanto de explosiones por escape de metano (principal componente del gas natural) como de envenenamiento por presencia de monóxido de carbono, gas procedente de combustiones deficientes y tóxico incluso en muy bajas concentraciones. Esto ha desembocado en la elaboración de normativas de detección de monóxido de carbono en ambientes domésticos, de previsible obligatoriedad en un futuro próximo, así como en una creciente demanda de sensores de gas. De todo lo expuesto nace el objetivo de este trabajo, que comprende el diseño y fabricación de un microsensor para detección de monóxido de carbono en ámbitos domésticos, previo estudio del material a utilizar como película sensible, en este caso el óxido de estaño. Por consiguiente, la realización del trabajo ha consistido en una primera etapa de estudio exhaustivo de las prestaciones del óxido de estaño como material sensor, para determinar su proceso y parámetros de fabricación haciendo uso de microtecnologías. Los valores de respuesta obtenidos mediante los dispositivos fabricados son superiores a los valores reseñados por otros autores que también apuestan por las técnicas de película delgada. Uno de los mayores problemas que presentan los dispositivos sensores de gas en general es su falta de selectividad ante posibles gases interferentes que puedan estar presentes en la atmósfera en la que se utilizan. En este trabajo se propone el uso de un filtro integrado que consigue la eliminación en gran medida de la señal procedente del etanol, uno de los interferentes más importantes en el ámbito doméstico. En una segunda etapa del trabajo se ha abordado el diseño del microdispositivo sensor de gas, que incorpora, además de la película, la fabricación de un calefactor integrado que es necesario optimizar. Además de las técnicas de procesado de película delgada, son necesarias técnicas de propias del desarrollo de microsistemas, tales como el micromecanizado del silicio o el pegado anódico de silicio contra pyrex, para la consecución de un dispositivo acabado y susceptible de ser encapsulado para su uso final. El trabajo se ha concluido con el estudio de las prestaciones del dispositivo fabricado en cuanto a consumo de potencia y estabilidad temporal. Cabe subrayar la doble vertiente de este trabajo. En primer lugar se debe señalar su aplicación en el sector gasodoméstico a través del proyecto llevado a cabo conjuntamente con la empresa Sociedad de Gas de Euskadi y avalada por las comunicaciones a los congresos del sector IGU 99 e IGRC 2001, así como por las patentes que la empresa ha realizado en relación con la fabricación del prototipo. En segundo lugar, hay que reseñar el interés científico reflejado en las publicaciones en revistas de ámbito internacional (Sensors & Actuators e IEEE Sensors Journal), así como por varias comunicaciones a congresos de alcance tanto nacional (VI Reunión Nacional de Materiales, CDE 99 y CDE 2001) como internacional (Sensor 99 y Eurosensors XVI).
- Low temperature NO2 gas sensing with ZnO nanostructured by laser interference lithography(RSC Advances, 2021) Sánchez-Martín, S. (Sergio); Olaizola, S.M. (Santiago Miguel); Castaño-Carmona, E. (Enrique); Garcia-Mandayo, G. (Gemma); Ayerdi-Olaizola, I. (Isabel)ZnO conductometric gas sensors have been widely studied due to their good sensitivity, cost-efficiency, long stability and simple fabrication. This work is focused on NO2 sensing, which is a toxic and irritating gas. The developed sensor consists of interdigitated electrodes covered by a ZnO sensing layer. ZnO has been grown by means of the aerosol assisted chemical vapor deposition technique and then nanostructured by laser interference lithography with a UV laser. The SEM and XRD results show vertically oriented growth of ZnO grains and a 2D periodic nanopatterning of the material with a period of 800 nm. Nanostructuring lowers the base resistance of the developed sensors and modifies the sensor response to NO2. Maximum sensitivity is obtained at 175 C achieving a change of 600% in sensor resistance for 4 ppm NO2 versus a 400% change for the non-nanostructured material. However, the most relevant results have been obtained at temperatures below 125 C. While the non-nanostructured material does not respond to NO2 at such low temperatures, nanostructured ZnO allows NO2 sensing even at room temperature. The room temperature sensing capability possibly derives from the increase of both the surface defects and the surface-to-volume ratio. The long stability and the gas sensing under humid conditions have also been tested, showing improvements of sensitivity for the nanostructured sensors.