Study of the conduction mechanisms and interface defects in non-stoichiometric semiconductors with different morphologies

Author(s)

Pedro Paulo da Silva Ortega

• Document type: Doctoral Thesis
• Press: Guaratinguetá. 2023-06-05.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Engenharia. Guaratinguetá
• Defense date: 2023-04-12
• Advisor: Alexandre Zirpoli Simões; Miguel Adolfo Ponce; Miguel Angel Ramírez Gil

Abstract

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. (AU)

• FAPESP's process: 18/26550-0 - Study of the conduction mechanisms and interface defects in non-stoichiometric semiconductors with different morphologies
• Grantee: Pedro Paulo da Silva Ortega
• Support Opportunities: Scholarships in Brazil - Doctorate