Room-temperature semiconductor gas sensor based on nonstoichiometric tungsten oxide nanorod film

Porous tungsten oxide films were deposited onto a sensor substrate with a Si bulk-micromachined hotplate, by drop-coating isopropyl alcohol solution of highly crystalline tungsten oxide (WO2.72) nanorods with average 75 nm length and 4 nm diameter. The temperature-dependent gas sensing characteristics of the films have been investigated over the mild temperature range from 20 to 250 degrees C. While the sensing responses for ammonia vapor showed increase in electrical conductivity at temperatures above 150 degrees C as expected for n-type metal oxide sensors, they exhibited the opposite behavior of unusual conductivity decrease below 100 degrees C. Superb sensing ability of the sensors at room temperature in conjunction with their anomalous conductivity behavior might be attributed to unique nanostructural features of very thin, nonstoichiometric WO2.72. (c) 2005 American Institute of Physics.