Atomic-level mediation in structural interparameter tradeoff of zinc oxide nanowires-based gas sensors: ZnO nanofilm/ZnO nanowire homojunction array

摘要

The gas response of metal oxide-based gas sensors is determined by atomic scale defects associated with oxygen vacancies and surface area of the sensing element. In this study, we corroborated a facile strategy to manipulate the surface area and the density of oxygen vacancies (OVs) of ZnO nanowires (NWs) simultaneously using atomic layer deposition (ALD)-assisted conformal coating of homogeneous, thickness-tailored ZnO nanofilms. A comprehensive exploration of structural and chemical features of ZnO nanofilms/ZnO NWs homojunction reveals that the surface area and density of OVs can be manipulated by altering the thickness of the ZnO nanofilms. Resistive-type semiconductor gas sensors were fabricated on the thickness-tailored ZnO nanofilms/ZnO NWs homojunction. As a consequence, the optimized gas response values of the ZnO nanofilms/ZnO NWs formed by 50 ALD cycles were estimated to be 84.2% (20 ppm NO2), 45.9% (20 ppm NH3), 35.8% (2% CH4), 29.2% (100 ppm H-2), and 31.2% (2% C3H8). The gas detection limit corresponded to 2 ppm for NO2, 2 ppm for NH3, 10 ppm for H-2, 0.2% for CH4, and 0.2% for C3H8. In addition, we ascertained that the surface area was a critical factor for enhancing the gas response up to 50 ALD cycles, whereas the density of OVs was more critical than the surface area for gas sensing performance with increasing the ALD cycles (50 cycles).