Estudo dos mecanismos de condução e defeitos de interface em semicondutores não-estequiométricos com diferentes morfologias
Carregando...
Data
2023-04-12
Autores
Ortega, Pedro Paulo da Silva
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
O monóxido de carbono é um gás altamente tóxico responsável por milhares de mortes anualmente ao redor do mundo. Por ser um gás inodoro, incolor e insípido, os seres humanos não são capazes de notar sua presença no ambiente, sendo necessário que um alarme os alerte. Assim sendo, este trabalho tem por objetivo estudar as propriedades sensoriais de matrizes de dióxido de cério dopadas com európio sintetizadas pelo método hidrotermal assistido por micro-ondas com diferentes morfologias, a partir das quais foram fabricados filmes espessos visando a sua aplicação em sensores de monóxido de carbono, além de avaliar suas propriedades fotocatalíticas e fotoluminescentes. Os filmes foram depositados sobre substratos de alumina com eletrodos de ouro pela técnica de screen-printing. De todas as amostras preparadas, as com morfologias de nanopartículas pura e dopada com európio, e as com nanobastões, nanocubos e nanopoliedros (todas dopadas com európio) foram as que apresentaram os melhores resultados. As análises por XRD indicaram que a fase tipo fluorita do CeO2 foi obtida com sucesso, com picos bem definidos e sem segundas fases. As análises por espectroscopia de espalhamento Raman apresentaram um único modo referente ao cluster [CeO8] e espalhamentos de segunda ordem referentes a vacâncias de oxigênio. A caracterização fotocatalítica das amostras mostrou que a melhor performance foi a dos nanopoliedros, que descoloriram cerca de 56% de RhB em 60 minutos de irradiação UV. Os pós contendo as nanoestruturas foram utilizados para fabricar filmes espessos para aplicações em dispositivos sensores de gás. As temperaturas de ensaio mais altas (380°C e 450°C) apresentaram os melhores resultados frente o sensoriamento do monóxido de carbono e foram escolhidas para realizar as outras caracterizações. Os testes realizados com umidade mostraram que algumas amostras foram particularmente sensíveis à presença de moléculas de água, como os nanobastões. As nanopartículas esféricas dopadas mostraram ser pouco influenciadas pela umidade. A resposta dos sensores aumentou com o aumento da concentração de CO utilizada, sendo observado que algumas foram capazes de detectar moléculas de CO apenas em temperaturas mais altas. Portanto, o desenvolvimento de diferentes morfologias de nanoestruturas de céria dopada com európio apresentou ótimas possiblidades para modificação dessas amostras, possibilitando aplicações na área de sensores de gás, fotocatálise, dispositivos LED, etc.
Carbon monoxide is a highly toxic gas responsible for thousands of deaths around the world annually. Since it is colorless, odorless, and tasteless, human beings are not able to notice its presence and need an alarm to alert them. This work aims to study the sensor properties of europium doped cerium dioxide matrices synthesized by the microwave assisted hydrothermal method with different morphologies, from which sensor thick films will be fabricated, aiming their applications in carbon monoxide detection devices, as well as their photocatalytic and photoluminescent properties. The sensor films were deposited on alumina substrates with interdigitated gold using the screen-printing technique. Of all samples prepared, the ones with nanoparticles morphology (pure and doped), nanorods, nanocubes e nanopolyhedrons (all doped with europium) presented the best results. The XRD analyzes showed that the fluorite phase of CeO2 was successfully obtained, with well-defined peaks and no second phases. The analysis by Raman spectrometry showed a single mode referring to the [CeO8] cluster and second order scattering referring to oxygen vacancies. The photocatalytic characterization of the samples showed that the best performance was that of the nanopolyhedrons, which decolorized about 56% of RhB in 60 minutes of UV irradiation. The samples containing the nanostructures were used to make thick films for applications in gas sensing devices. The highest test temperatures (380°C and 450°C) showed the best results against carbon monoxide sensing and were chosen to perform the other characterizations. Tests carried out with humidity showed that some samples were particularly sensitive to the presence of water molecules, such as nanorods. Doped spherical nanoparticles were shown to be little influenced by the relative humidity. The response of the sensors increased with the increase in the concentration of CO used, and it was observed that some were able to detect CO molecules only at higher temperatures. Therefore, the development of different morphologies of Eu-doped ceria nanostructures presented great possibilities for handling these samples, allowing applications in gas sensors, photocatalysis, LED devices, etc.
Carbon monoxide is a highly toxic gas responsible for thousands of deaths around the world annually. Since it is colorless, odorless, and tasteless, human beings are not able to notice its presence and need an alarm to alert them. This work aims to study the sensor properties of europium doped cerium dioxide matrices synthesized by the microwave assisted hydrothermal method with different morphologies, from which sensor thick films will be fabricated, aiming their applications in carbon monoxide detection devices, as well as their photocatalytic and photoluminescent properties. The sensor films were deposited on alumina substrates with interdigitated gold using the screen-printing technique. Of all samples prepared, the ones with nanoparticles morphology (pure and doped), nanorods, nanocubes e nanopolyhedrons (all doped with europium) presented the best results. The XRD analyzes showed that the fluorite phase of CeO2 was successfully obtained, with well-defined peaks and no second phases. The analysis by Raman spectrometry showed a single mode referring to the [CeO8] cluster and second order scattering referring to oxygen vacancies. The photocatalytic characterization of the samples showed that the best performance was that of the nanopolyhedrons, which decolorized about 56% of RhB in 60 minutes of UV irradiation. The samples containing the nanostructures were used to make thick films for applications in gas sensing devices. The highest test temperatures (380°C and 450°C) showed the best results against carbon monoxide sensing and were chosen to perform the other characterizations. Tests carried out with humidity showed that some samples were particularly sensitive to the presence of water molecules, such as nanorods. Doped spherical nanoparticles were shown to be little influenced by the relative humidity. The response of the sensors increased with the increase in the concentration of CO used, and it was observed that some were able to detect CO molecules only at higher temperatures. Therefore, the development of different morphologies of Eu-doped ceria nanostructures presented great possibilities for handling these samples, allowing applications in gas sensors, photocatalysis, LED devices, etc.
Descrição
Palavras-chave
Semicondutores, Nanoestruturas, Morfologias, Sensor de gás, Meio ambiente, Semiconductors, Nanostructures, Morphologies, Gas sensor, Environment, Detectores, Microscopia eletrônica de varredura, Materiais nanoestruturados