Abstract
This paper deals with experimental investigations of ZnO nanostructures, consisting of a mixture of nanoparticles and nanowires, obtained by the chemical (hydrothermal) method. The influences of both oxidizing (NO2) and reducing gases (H2, NH3), as well as relative humidity (RH) on the physical and chemical properties of ZnO nanostructures were tested. Carrier gas effect on the structure interaction with gases was also tested; experiments were conducted in air and nitrogen (N2) atmospheres. The effect of investigated gases on the resistance of the ZnO nanostructures was tested over a wide range of concentrations at room temperature (RT) and at 200 °C. The impact of near- ultraviolet (UV) excitation (λ = 390 nm) at RT was also studied. These investigations indicated a high response of ZnO nanostructures to small concentrations of NO2. The structure responses to 1 ppm of NO2 amounted to about: 600% in N2/230% in air at 200 °C (in dark conditions) and 430% in N2/340% in air at RT (with UV excitation). The response of the structure to the effect of NO2 at 200 °C is more than 105 times greater than the response to NH3, and more than 106 times greater than that to H2 in the relation of 1 ppm. Thus the selectivity of the structure for NO2 is very good. What is more, the selectivity to NO2 at RT with UV excitation increases in comparison at elevated temperature. This paper presents a great potential for practical applications of ZnO nanostructures (including nanoparticles) in resistive NO2 sensors.
Highlights
Within the group of nanostructured semiconductors with a wide band gap, zinc oxide (ZnO) is a material which has been comprehensively investigated due to its interesting physical and chemical properties and the possibility of its potential extensive application in solar cells, ultraviolet (UV) photodetectors, and light emitters [1,2,3,4]
In order to investigate the electrical properties of ZnO nanostructures, a resistive structure on an interdigital transducer (IDT) was made
In order to compare the reaction of the ZnO nanostructures affected by external atmospheres, temperature and light excitation the results for the same structure are presented in the text
Summary
Within the group of nanostructured semiconductors with a wide band gap, zinc oxide (ZnO) is a material which has been comprehensively investigated due to its interesting physical and chemical properties and the possibility of its potential extensive application in solar cells, ultraviolet (UV) photodetectors, and light emitters [1,2,3,4]. The investigations concerning gas sensors based on ZnO are already well advanced [20,29,36] Those structures are tested at elevated temperature (from 200 ◦C even up to 700 ◦C) [18,36]. The investigated material showed promising NO2 sensing properties at RT with ultraviolet excitation and at elevated temperature (200 ◦C) With this approach, objective results and conclusions were obtained about the influence of gaseous environments, qualitatively, and quantitatively.
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