An investigation on NO2 sensing mechanism and shielding behavior of WO3 nanosheets

NO2 sensor based on WO3 nanosheets was fabricated and its basic sensing mechanism was investigated. It is found that sensor response of WO3 nanosheets is linearly proportional with concentrations of NO2. It is revealed that the linear response could be theoretically derived from assumption of the grain controlled conductivity, which is caused by the tiny thickness of nanosheet. With the same assumption, the sensor resistance of WO3 nanosheets can be analytically derived and expressed by NO2. However, in order to achieve a linear sensor response, NO2 concentrations should be large enough to overcome an electronic shielding behavior of O2, which could cause an insensitive and non-linear sensor response. Based on the grain controlled conductivity, the electronic shielding behavior has been theoretically explained and found to be well consistent with experimental results observed in WO3 nanosheets.