Influence of External Gaseous Environments on the Electrical Properties of ZnO Nanostructures Obtained by a Hydrothermal Method

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 (NO(2)) and reducing gases (H(2), NH(3)), 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 (N(2)) 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 NO(2). The structure responses to 1 ppm of NO(2) amounted to about: 600% in N(2)/230% in air at 200 °C (in dark conditions) and 430% in N(2)/340% in air at RT (with UV excitation). The response of the structure to the effect of NO(2) at 200 °C is more than 10(5) times greater than the response to NH(3), and more than 10(6) times greater than that to H(2) in the relation of 1 ppm. Thus the selectivity of the structure for NO(2) is very good. What is more, the selectivity to NO(2) 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 NO(2) sensors.