Conductivity‐Type Sensor Based on CNT‐WO3 Composite for NO 2 Detection

The CNTs with 20–50 nm in diameter were directly grown on Au microgap electrode by means of thermal CVD at 700∘C for 60 minutes under EtOH‐Ar‐H2 atmosphere (6 kPa). The CNTs with entangled shape formed the network structure with contacting each other. In the CNTs‐WO3 composite, WO3 grains with disk shape (50–200 nm) were independently trapped. The CNTs‐WO3 composite sensor showed the fairly good sensor response (Ra/Rg = 3.8 at 200∘C). The sensor response was greatly improved with CNTs‐WO3 composite, comparing with that of CNT sensor (Ra/Rg = 1.05). This phenomenon can be explained by formation of p‐n junction, between CNT(p) and WO3(n), and thus improvement of NO2 adsorption. The sensor response was decreased with increasing the WO3 amount in CNTs‐WO3 composite, suggesting the electronic conduction due to WO3 connection.