(Digital Presentation) P-n Heterostructured Mos for NOx Gas Sensing
Authors: Shynybekov Yernar , Turlybekuly Amanzhol , Soltabayev Baktiyar , Mentbayeva Almagul 
Published: September 2023

The significant air pollution caused mainly by exhaust and factory emissions has become a considerable hazard to human survival and development [1]. Nitrogen oxides (NOx) are a family of poisonous and highly reactive gases which forming at fuel high temperatures burn [2]. As an industrial source, such as power plants, industrial boilers, cement kilns, and turbines, NOx pollution is emitted by automobiles, trucks and various non-road vehicles (e.g., construction equipment, boats, etc.) [3]. Hazardous compounds such as NOx with negative environmental and human health consequences, must be controlled to avoid ecological disasters [4]. Metal-oxide-semiconductors (MOSs) as a class of chemoresistive sensors have attracted great attention in environmental monitoring, automotive emission monitoring and food safety testing, due to their low production cost, high sensitivity, simplicity of use and their ability to detect various gases [5].
Due to its inherent advantages in charge carrier mobility, chemical activity, and redox potential, TiO2 (n-type) is a widely used and extensively researched MOSs. At the same time, CuO is also known to be an active transition-metal based semiconductor (p-type) having a lower electrical resistance value as well as a narrow band gap. A promising strategy for improving the gas sensitivity at room temperature (RT) is to apply p-n heterostructures to modulate resistance more strongly. The active surface area and nanoarchitecture affect the gas sensors' sensitivity. The provision of porous MOSs nanostructures to improve the diffusion channel and increase the adsorption of target gas molecules is the most promising means of achieving enhanced sensitivity [6-7]. The mentioned structures may be created using the glancing angle deposition (GLAD) reactive magnetron sputtering method. The TiO2/CuO heterostructure gas sensors were synthesized by reactive magnetron sputtering using the GLAD. The application CuO layer improves the gas sensor device's sensitivity due to electron-hole pair recombination and a reduction in the concentration of charge carriers in the TiO2 and CuO layers. The identical circumstances of 10 ppm and RT were used for each gas selectivity test. It demonstrates the potential of using heterostructured CuO/TiO2 nanorods as N2O gas sensors. Dynamic gas response analysis shows that the response time is only 47s, whereas the recovery time is 80s. The dynamic gas sensing measurements at various N2O gas concentrations exhibit excellent linearity at 50 ppb to 5 ppm range. The sensor's gas response was 2% at a very low N2O concentration (50 ppb) and 9.8% at 5 ppm. Thus, the research findings indicate that the p-n heterostructured CuO/TiO2 nanorods synthesized by reactive magnetron sputtering using the glancing angle deposition show fast response and recovery times in ultra-low N2O gas concentration in RT. It can be used as excellent N2O gas sensors for quickly monitoring air pollution.

Acknowledgements.

This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (Grant No. AP13067814) and Nazarbayev University under the Collaborative Research Program (Grant No. 021220CRP0122).

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