NO₂ Gas Sensing Mechanism of ZnO Thin-Film Transducers: Physical Experiment and Theoretical Correlation Study

Abstract

In this work, ZnO thin films were investigated to sense NO2, a gas exhausted by the most common combustion systems polluting the environment. To this end, ZnO thin films were grown by RF sputtering on properly designed and patterned substrates to allow the measurement of the electrical response of the material when exposed to different concentrations of the gas. X-ray diffraction was carried out to correlate the material’s electrical response to the morphological and microstructural features of the sensing materials. Electrical conductivity measurements showed that the transducer fabricated in this work exhibits the optimal performance when heated at 200 °C, and the detection of 0.1 ppm concentration of NO2 was possible. Ab initio modeling allowed the understanding of the sensing mechanism driven by the competitive adsorption of NO2 and atmospheric oxygen mediated by heat. The combined theoretical and experimental study here reported provides insights into the sensing mechanism which will aid the optimization of ZnO transducer design for the quantitative measurement of NO2 exhausted by combustion systems which will be used, ultimately, for the optimized adjustment of combustion resulting into a reduced pollutants and greenhouse gases emission.

Laser-induced periodic surface structures on ZnO thin film for high response NO2 detection

“…Many conductometric NO 2 sensor devices have been tested during the last decade, as it can cause severe respiratory diseases for long exposures, but the NO 2 detection mechanism in semiconductors is still under investigation [34].…”

Reading at exposed surfaces: theoretical insights into photocatalytic activity of ZnWO4

“…In recent years, several studies have attempted to establish correlation between the morphology, properties, and applications for both micro-and nano-materials [20][21][22][23][24][25][26][27] . For example, in the field of catalysis, the presence of high-index facets at the crystal morphology is more desirable, in comparison with their low-index faced counterparts, because they have low coordinated surface atoms that are exposed on such facets, which can serve as highly catalytic active sites [28][29][30] .…”

Ultrasensitive and bifunctional ZnO nanoplates for an oxidative electrochemical and chemical sensor of NO2: implications towards environmental monitoring of the nitrite reaction

“…This change in resistivity can be used for the chemical detection and determination of NO 2 . There are many reports [58][59][60][61][62][63][64] for enhanced gas sensing behaviours of ZnO based systems and the mechanism is explained by "spill-over effect", which means that especially at the nano-regime ZnO NPs enhance the active surface with nonstoichiometric amounts of oxygen species. Moreover, the ZnO NPs in this work showed no evidence of forming metallic (Zn) particles either at the surface or in the interior of the ZnO NPs.…”

“…8) and ZnO. 9 Among these, ZnO is a cheap, stable and nontoxic material and it is possible to further improve its chemical and physical properties by controlling its dimensions in a micro/nano-regime. This motivated us to develop a new, cost effective, safer synthetic method for the synthesis of its nanostructures by a chemical approach, taking into consideration energy and environmental factors.…”