Nanostructured gas sensors by electron beam evaporation

Electron beam (E-beam) evaporation process offers extensive possibilities for controlling film structure and morphology with desired properties such as dense coating, high thermal efficiency, low contamination, high reliability and high productivity. In this work, we have applied the E-beam process to fabricate nanostructured gas sensors, i.e., WO
3
, SnO
2
, CNT-WO
3
, CNT-SnO
2
. The nanostructure sensing elements were characterized by scanning electron microscopy and transmission electron microscopy. Various gases with variable concentrations were used to test the sensing properties and selectivity of the gas sensors at different operating temperatures. Based on the operating temperatures within a range of 350–400 °C, the SnO
2
and WO
3
gas sensors were found to exhibit good response to alcohol and hydrogen, respectively. Doping CNT in SnO
2
and WO
3
dramatically improves the sensitivity and selectivity of the gas sensors. Moreover, CNT can reduce the operating temperature (from around 350–400°C to 250 °C) leading to reduction in power consumption which is one of the major problems for metal oxide gas sensor. The sensing mechanism of these gas sensors will be demonstrated.