Annealing atmosphere-mediated N-doped In2O3 homojunctions toward synergistic enhancement of NO2 gas sensing via oxygen vacancy engineering

In this work, In 2 O 3 nanosheets were fabricated on the surface of Al 2 O 3 ceramic tubes via an in-situ synthesis approach. The effects of three annealing atmospheres (O 2 , air, and N 2 ) on their micro-morphologies and gas-sensing properties were systematically investigated. The gas-sensing test results demonstrate that the In 2 O 3 nanosheet sensor annealed in N 2 atmosphere exhibits the optimal sensing performance towards 50 ppm NO 2 . At an operating temperature of 160 °C, its response value reaches 241.8, which is 4 times that of the sample annealed in oxygen and 1.5 times that of the sample annealed in air, respectively. Meanwhile, this sensor also exhibits a rapid response time of 15 s, along with excellent selectivity and repeatability. Combined characterizations and density functional theory (DFT) calculations reveal that nitrogen atmosphere annealing enables In 2 O 3 nanosheets to generate abundant oxygen vacancies (with a content of 44.67%), while simultaneously facilitating the formation of homojunctions and N-doping. These defect structures can significantly enhance the adsorption energy between NO 2 and In 2 O 3 as well as the charge transfer efficiency, thereby achieving the optimization of gas-sensing performance.