ZnO nanowires synthesized by CSS and their application as a hydrogen gas sensor

Zinc oxide nanowires (ZnO-NWs) were synthesized through two simple processes on silicon substrates. The first step was to obtain the zinc nanowires (Zn-NWs) by close spaced sublimation (CSS) on a quartz substrate. The second step was the transformation of Zn-NWs to ZnO-NWs by a simple thermal annealing in air environment. In the synthesis process a zinc pellet source was used as the source material, where the temperatures of the source, the temperature of the substrate, and the growth time were fixed at 350°C, 325°C, and 5 minutes respectively, using a nitrogen environment at atmospheric pressure conditions. Afterwards, the as-prepared Zn-NWs sample was heated at 400°C for 30 minutes in open tube conditions. In addition, a conductimetric gas sensor was fabricated using the annealed Zn-NWs based film. The sensor was tested to hydrogen at moderate temperatures (200-400°C) for several concentrations (95-1492 ppm). The results revealed that the ZnO-NWs have a high response to hydrogen at high temperatures and high concentrations. The response and recovery times depend on the hydrogen concentration. The response time for almost all conditions is of the order of 2 minutes. These results are very promising for the development of hydrogen solid state gas sensors based on zinc oxide nanowires.