Coupling annealing fabrication of WO3 nano-rods/thin-film integral structure for the enhancement of NO2 gas sensing

Tungsten trioxide (WO3) thin film gas sensor is compatible with integrated circuit technology and can be used in smart integral system. However, the poor sensitivity limits its application. We proposed an coupling annealing method to prepare WO3 nano-rods/thin film integral structure from tungsten thin film. The tungsten thin film was annealed by rapid thermal process in oxygen atmosphere. And then, the structure evolution of as prepared WO3 thin film with tube annealing temperature was investigated. The integral structured of nanorods on thin film were obtained at 650 degrees C of tube annealing temperature. This structure shows the response to 5 ppm NO2 gas at 150 degrees C can reach up to 8.43. The excellent sensitivity performance is related to the nanorods and the homogeneous junctions generated between the nanorod and film. The adsorption energy, density of states and charge density difference between NO2 and WO3 obtained from density functional theory calculations suggest that WO3 can undergo a large charge transfer between molecules with NO2 after annealing coupling. This is attributed to the modulation of electrons by homogeneous junctions. The proposed nanorods and thin film integral structure will enhance the application of WO3 in integral system with integrated circuit.