Gas sensors based on metal semiconducting oxides heterostructured: investigation of microstructural and electrical properties

• Grant number: 23/09790-6
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: August 01, 2023
• End date: July 31, 2028
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Luís Fernando da Silva
• Grantee: Mayron Silva Castro
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 22/02927-3 - Gas sensors based on n-type semiconductors operating at room temperature: investigation of their performance and mechanisms involved, AP.PNGP.PI

Abstract

Great efforts have been directed to the development of portable and easy-to-operate gas sensing devices that allow the efficient monitoring of small concentrations of toxic species in a quantitative and selective way. Resistive gas sensors based on semiconducting metal oxides (SMOx) stand out due to their good sensitivity and fair stability. Despite being promising, the operating temperatures of sensors based on this class of materials are relatively high, discouraging their application in commercial devices. An efficient strategy to reduce its operating temperature consists of partially or completely replacing the traditional thermal activation by photoactivation. In this regard, the combination of two SMOx, by the formation of nanoheterostructures, has enabled the use of SMOx at mild temperatures, in addition to enhancing the sensing properties of these materials. Despite the potential, few works have been dedicated to the study of the photoactivation process of nanoheterostructures, especially in the reasoned description of the mechanisms involved. Another challenge in the area is the processing of these materials in a simple and reproducible way. In this sense, chemical synthesis methods have allowed obtaining micro and/or nano-sized materials exhibiting high quality and particular properties. Furthermore, works reported in the literature show that the sensing properties of SMOx are strongly affected by the processing method employed, due to possible changes in microstructural and surface characteristics. Therefore, in this Direct Doctorate project we propose the preparation of nanoheterostructures of ZnO/SnO2, SnO2/WO3 and ZnO/WO3 in the form of thin films through two different methodologies: the method of polymeric precursors, and chemical vapor deposition (CVD). Samples will be characterized using a variety of techniques, such as X-ray diffraction (XRD), electron microscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The evaluation of the sensing properties of the samples will be carried out by electrical characterizations (DC and AC), with the samples exposed to different analytes (e.g., BTEX, ethanol, acetone and NO2), in addition to different percentages of relative humidity. For the study of the effect of photoactivation on the sensing properties, the samples will be irradiated with different wavelengths (UV and visible) using commercial LEDs. Additionally, "in-situ and operando" measurements will be performed using spectroscopic techniques (impedance and photoluminescence). These analyzes will allow understanding the role of the device regions involved in the gas detection process, as well as possible changes in the electronic properties of the samples during interaction with the analyte. (AU)