Hybrid metal oxide and multiwall carbon nanotube films for low temperature gas sensing

Active layers for detecting NO2 have been obtained by adding a low amount of oxygen-functionalized MWCNTs to three different types of metal oxides (SnO2, WO3 or TiO2). We show that the responsiveness towards NO2 of micro-sensors based on some of the resulting metal oxide/MWCNT hybrid films is considerably improved. In particular, the sensors based on hybrid SnO2/MWCNTs films present excellent sensitivity towards NO2 when operated at room temperature. Additionally, the sensors show a total recovery of their baseline resistance and reasonable response and recovery times. A mechanism of response based on the development of two depletion layers, one at the surface of metal oxide grains and another at the interface of the n-metal oxide/p-MWCNT hetero-structure, is postulated as responsible for the improvement observed. Our results suggest that there should be an optimum amount of carbon nanotubes to be added to each specific metal oxide in order to enhance sensitivity.