NiO/SnO2 hybrid nanowires showed an enhanced sensitivity against NO2 gas of ppm concentrations (5–15ppm) when compared to pristine SnO2 counterpart without the NiO decoration. The hybrid structure involved uniform deposition of NiO nano-islands with a size less than 10nm in diameter on surface of the SnO2 nanowires. A fivefold increase on the sensing response, i.e., from 1.65 to 9.34, was found for the NiO/SnO2 hybrid nanowires at NO2 concentration of 15ppm at 250°C. This is attributable to the formation of local p-n heterojunctions at the NiO/SnO2 interface so that an enlarged electronic depletion layer was resulted near the surface. Accordingly, the reduced channel width for carriers migration impeded electron transportation and led to the increased electrical resistance upon reacted with the dilute NO2 gas mixtures.
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