Ultrasensitive NO2 gas sensors using tungsten oxide nanowires with multiple junctions self-assembled on discrete catalyst islands via on-chip fabrication

An effective fabrication of networked nanowire sensors with multiple junctions, which were obtained by selectively growing tungsten oxide nanowires directly on the arrays of discrete catalyst islands, was demonstrated for highly sensitive NO2 gas sensors. Junction density was controlled by altering growth time for superior NO2 gas response. The optimum sensor exhibited remarkably high response (Rg/Ra) to 10 ppm NO2 (Rg/Ra ∼ 144.3), negligible cross-responses to 100 ppm CO, H2, and NH3 (Rg/Ra ∼ 1.3-1.7), and ultralow detection limit (∼0.33 ppb) at 250 °C. In addition, the sensor exhibited good reversibility for up to 15 cycles of air-to-gas switching under sensing at relatively high temperatures of up to 350 °C. The methodology illustrated in the present work aims to overcome the disadvantages of nanowire sensors grown on an ordinary continuous catalyst layer and to make these sensors suitable for large-scale fabrication via microelectronic technology.