Search

Resumen del trabajo presentado en la 18th European Conference on Thermoelectrics , celebrada en Barcelona (España), del 14 al 18 de septiembre de 2022, In order to reduce the complexity of developing nanostructured thermoelectric materials, and thus, obtain enhanced properties for applications, we report the template-assisted electrochemical deposition of bismuth telluride inside commercial membranes. The objective is to develop efficient, cost-effective, flexible and wearable thermoelectric generators (TEGs) by the use of low cost and scalable fabrication techniques along with a reduction in the amount of material used when compared to thin films. The use of different nanoporous membranes gives rise to different nanostructured morphologies, given that the electrochemical process produces a replica of the initial porous structure. Here we will fabricate thermoelectric 3D nanostructures inside flexible templates (made of polyester and cellulose) by electrochemical deposition as it has been previously done inside alumina templates [A. Ruiz-Clavijo., O. Caballero-Calero, M. Martín-González, Nanomaterials, 8 (2018) 345]. The morphology has been studied with SEM and Tomography, the crystalline orientation with XRD, the composition with EDX, and also Raman spectroscopy has been used to characterize the structures. Then, different transport measurements have been carried on. In fact, a certain increase is expected, as it was proved in [A. Ruiz-Clavijo., O. Caballero-Calero, C. V. Manzano, X. Maeder, A. Beardo, X. Cartoixa¿, X. Álvarez, M. Martín-González, ACS Applied Energy Materials, 4 (2021). 13556-13566] for 3D interconnected nanowire networks of bismuth telluride inside alumina. In that paper we showed the importance of increasing surface to volume ratio, as well as the relevance of nano-features in the structure, in order to improve the efficiency. In this case, the nanostructure is not as ordered as 3D nanowire network, but similar features are present, and they should have an impact in the final efficiency. Finally, further metallic contacts made of electrodeposited gold and/or nickel will be also fabricated in order to improve their electrical contacts and test such nanostructures as thermoelectric generators.

Trabajo presentado en el XVI Congreso Nacional de Materiales CNMAT 2022, celebrado en Ciudad Real (España), del 28 de junio al 1 de julio de 2022, La técnica de pulverización catódica operada en geometría de ángulo oblicuo es bien conocida por permitir el crecimiento de películas delgadas nanocolumnares sobre sustratos planos. En otro tipo de sustratos, e.g. rugosos o litografiados, la casuística es variada, apareciendo estructuras complejas y diversas, incluso para espesores del orden de la micra. Estos resultados sugieren la existencia de una fuerte conexión entre el crecimiento de la película y la topografía del sustrato, que podría utilizarse para obtener un mayor control nanoestructural. En esta presentación se analiza teórica y experimentalmente la relación entre ambos aspectos al utilizar la técnica de pulverización catódica a ángulo oblicuo. Se demuestra la posibilidad de crecer estructuras singulares como, por ejemplo, cruces nanopilares o incluso de huecos dentro de una matriz compacta, ordenados de acuerdo a un patrón regular con distancias típicas del orden de cientos de nanómetros (ver Figura 1). Se describe, por lo tanto, el marco conceptual que permitiría que las técnicas actuales de litografía superficial se puedan utilizar como técnicas efectivas de control nanoestructural de películas delgadas. Como resultado, se demuestran varios principios que definen los diferentes estadios de la deposición que servirían como guías para el diseño inteligente del sustrato e inducir crecimientos a la carta. Estos principios se han validado experimentalmente al crecer diferentes películas delgadas sobre un total de 16 sustratos litografiados con diferentes topografías, patrones y escalas típicas por debajo de la micra, así como en otros sustratos con rugosidad intrínseca sometidos a diferentes tipos de pulido.

Trabajo presentado en NanoSpain2022, celebrado en Madrid (España), del 17 al 20 de mayo de 2022, In this work, we present different nano-structures of bismuth telluride based on scalable and low cost fabrication techniques. The objective is to improve the thermoelectric performance of this material grown by electrochemical deposition, and then use these nanostructures to develop efficient flexible thermoelectric generators (TEGs) which will allow the conversion of wasted heat around room temperature into usable electrical energy. The main advantage of nanostructures over thin films or bulk is that they should increase the thermoelectric performance of the bismuth telluride (which is the most used thermoelectric material for room temperature appilcations) by lowering its thermal conductivity. This has been already proved for 3D interconnected nanowire networks of bismuth telluride [1]. In that work, we showed that both the increasing of the surface to volume ratio and the influence of the nanostructure in the the phonon scattering phenomena are the main responsibles of the improvement, but the templates used in that case were made of non-flexible alumina. Here, we will use two different flexible commercial templates to obtain nanostructured thermoelectric materials by template-assisted electrochemical deposition of bismuth telluride: polyester membranes (obtaining an intrincate 3D nanostructure) and cellulose membranes (obtaining a highly porous structure). As it was previously done with the growth of bismuth telluride inside alumina templates [2], the nanostructured bismuth telluride grown inside the flexible templates will be then characterized to optimize the fabricartion parameters to obtain highly oriented, stoichiometric material in such nanostructures.