Publication: Alta eficiencia termoeléctrica en películas delgadas nanoestructuradas de SiGe, Cu₂Se y Ag₂Se depositadas por pulverización catódica
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2018-05-17
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Universidad Complutense de Madrid
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Abstract
Los materiales termoel ectricos convierten energ a t ermica en energ a el ectrica y viceversa. Las ventajas de los materiales termoel ectricos son que no poseen partes m oviles, son dispositivos de larga duraci on, son silenciosos, pueden utilizarse en aplicaciones para enfriar y calentar, y tambi en pueden emplearse para la recuperaci on de energ a proveniente del calor residual. En los ultimos a~nos se han propuesto diferentes alternativas prometedoras destinadas a conseguir sistemas con coe cientes zT superiores a 1. Un coe ciente zT de 1 supone una e ciencia de generaci on de energ a el ectrica a partir de energ a t ermica de un 10% del l mite te orico, dado por el ciclo de Carnot, mientras que un valor de 4 supondr a un 30 %. Para este prop osito, esto es, estudiar c omo aumentar la e ciencia termoel ectrica en distintos materiales, en primer lugar se han obtenido pel culas delgadas de Si0;8Ge0;2 a trav es de un sistema de pulverizaci on cat odica de ultra alto vac o construido para este n. El primer objetivo ha sido lograr obtener pel culas delgadas de Si0;8Ge0;2 policristalinas con bajos valores de conductividad t ermica (cercanos a los reportados en la literatura para los nanohilo) y a bajas temperaturas de fabricaci on. Adicionalmente, un segundo objetivo ha consistido en la fabricaci on de nanomallas de Si0;8Ge0;2 con un control del tama~no de poro y del espesor de la nanoestructura. Este nuevo enfoque en la fabricaci on se realiza en un unico paso, sin necesidad de procesos litogr a cos o tratamientos t ermicos adicionales.
Thermoelectric materials are those that convert thermal energy into electrical energy and vice-versa. The advantages of thermoelectric devices are many, such as being solid state devices, that is, with no mobile parts and no noise, and they are durable, among others. They can be used in applications for heating and cooling, but more importantly, they can be used to recover wasted heat converting it into electrical energy. In the last years there have been di erent promising ways of obtaining thermoelectric systems with gures of merit zT higher than 1. A zT of 1 means to have an electric energy generation e ciency from thermal gradients of 10% of the theoretical limit, which is given by the Carnot cycle, while a value of zT of 4 would mean a 30% e ciency. In order to study one route of increasing the thermoelectric e ciency of di erent materials, thin lms of Si0;8Ge0;2 have been fabricated with a sputtering system at ultrahigh vacuum, which was constructed speci cally to this purpose. The rst objective was to obtain polycrystalline thin lms of Si0;8Ge0;2 fabricated at low temperatures and with reduced thermal conductivity (with values near the ones reported in literature for nanowires of the same material). Additionally, a second objective consisted in the fabrication of nano-meshes of Si0;8Ge0;2 with controlled pore size and thickness of the nano-structure. This new approach in the fabrication was performed in a single step, without any lithographical process or additional thermal treatments...
Thermoelectric materials are those that convert thermal energy into electrical energy and vice-versa. The advantages of thermoelectric devices are many, such as being solid state devices, that is, with no mobile parts and no noise, and they are durable, among others. They can be used in applications for heating and cooling, but more importantly, they can be used to recover wasted heat converting it into electrical energy. In the last years there have been di erent promising ways of obtaining thermoelectric systems with gures of merit zT higher than 1. A zT of 1 means to have an electric energy generation e ciency from thermal gradients of 10% of the theoretical limit, which is given by the Carnot cycle, while a value of zT of 4 would mean a 30% e ciency. In order to study one route of increasing the thermoelectric e ciency of di erent materials, thin lms of Si0;8Ge0;2 have been fabricated with a sputtering system at ultrahigh vacuum, which was constructed speci cally to this purpose. The rst objective was to obtain polycrystalline thin lms of Si0;8Ge0;2 fabricated at low temperatures and with reduced thermal conductivity (with values near the ones reported in literature for nanowires of the same material). Additionally, a second objective consisted in the fabrication of nano-meshes of Si0;8Ge0;2 with controlled pore size and thickness of the nano-structure. This new approach in the fabrication was performed in a single step, without any lithographical process or additional thermal treatments...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 28-09-2017