Low-pressure hydrogen sensing mechanism based on the field emission of defect-controlled ZnO nanorods

Abstract

ZnO nanostructures are widely used for detecting hydrogen at atmospheric pressure by measuring variation in resistance. However, low-pressure gas sensing using ZnO is still underdeveloped due to the weak resistance effect. Herein, we report a low-pressure hydrogen sensing method based on the field emission of defect-controlled ZnO nanorods in a wide pressure range from 10⁻³ to 10⁻⁷ Pa. The investigation reveals that while hydrogen atoms adsorb on the site of the oxygen defect, the field emission of ZnO could increase with the reduction of the effective work function (WF) of ZnO, leading to improved hydrogen sensing performance. Conversely, the effective WF of ZnO will increase with hydrogen adsorption on the site of the zinc defect. In addition, the sensing performance could be enhanced with increasing contents of oxygen defects. This study not only provides insight into the low-pressure hydrogen sensing mechanism from the field emission of ZnO but also expands the understanding of the electronic properties of the ZnO nanomaterial with various defects and under different annealing conditions.