Metal oxide nanoarchitectures for environmental sensing.

Metal oxide materials are widely used for gas sensing. Capable of operating at elevated temperatures and in harsh environments, they are mechanically robust and relatively inexpensive and offer exquisite sensing capabilities, the performance of which is dependent upon the nanoscale morphology. In this paper we first review different routes for the fabrication of metal oxide nanoarchitectures useful to sensing applications, including mesoporous thin films, nanowires, and nanotubes. Two sensor test cases are then presented. The first case examines the use of highly uniform nanoporous Al2O3 for humidity sensing; we find that such materials can be successfully used as a wide-range humidity sensor. The second test case examines the use of TiO2 nanotubes for hydrogen sensing. Going from a nitrogen atmosphere to one containing 1000 ppm of hydrogen, at 290 degrees C, 22-nm-diameter titania nanotubes demonstrate a 10(4) change in measured resistance with no measurement hysteresis.