NO2-sensing properties of WO3 nanorods prepared by glancing angle DC magnetron sputtering

In this work, the NO2-sensing properties of the tungsten trioxide (WO3) nanorods prepared by dc magnetron sputtering with glancing-angle deposition (GLAD) technique are comparatively studied with that of WO3 thin film deposited by normal sputtering process. The crystal structure and morphologies were characterized by grazing-incidence X-ray diffraction and field emission scanning electron microscopy, respectively. As-deposited WO3 structure deposited at glancing angle of 85° exhibited amorphous crystal structure with uniform isolated columnar nanorod morphology with average length, diameter and spacing between nanorods of around 400 nm, 50 nm and 10 nm, respectively. Annealing at 400 and 500 °C resulted in polycrystalline phase and more porous nanorod network with very large effective surface area. The NO2 sensing response of WO3 nanorods was found to be higher than that of WO3 thin film by a factor of 2-5 depending on operating temperature and gas concentration. In addition, WO3 nanorod annealed at 500 °C exhibited an optimum response of ∼27-2.0 ppm of NO2 at 250 °C. Therefore, GLAD using reactive dc magnetron sputtering has been demonstrated as a practical method for fabrication of well-aligned metal oxide nanostructures and is potential for gas-sensing applications.