Nanofios de SnO2: estudo e caracterização de dispositivos sensores de ozônio

Abstract

This work involves the production, characterization and optimization of electronic devices based on SnO2 nanowires in order to study the electronic transport and ozone detection properties of these devices. The surfaces of SnO2 nanowires are responsible for giving the material sensing qualities for different chemical species, such as ozone. This work investigated the electronic properties of devices based on a single nanowire and a network of nanowires and their responses when subjected to different environments in which the exposure time and the amount of the gas of interest at room temperature were controlled. The SnO2 samples were characterized using electron microscopy images which showed the formation of randomly distributed nanowires on the growth substrates with lengths in the order of tens to hundreds of micrometres and typical widths between tens of nanometres and micrometres. X-ray diffraction patterns confirmed the SnO2 isomorphous phase with tetragonal symmetry, rutile type and P42/mnm space group for all samples. Transport experiments were conducted to analyze the transport mechanisms: Thermal activation (high temperatures) and Variable Range Hopping (low temperatures) were observed. The results, in terms of ozone detection, showed that the response time to exposure to the gas at room temperature was fast (t<2 min) compared to literature data, as well as demonstrating high detection sensitivity. In order to optimize the device's gain, illuminating the devices with Ultraviolet Light proved to be very effective in the process of “cleaning” the sensors after each ozone exposure cycle. In comparison with data from the literature, the devices developed here demonstrate great efficiency when working at room temperature, with expressive responses and high reproducibility for ozone concentrations in the order of hundreds of ppb. In addition, the process for manufacturing the samples and devices is low-cost and easily scalable.