Fabrication of WO3 nanodot-based microsensors highly sensitive to hydrogen

A novel approach that involves electrochemical anodising for fabricating WO3 nanodot-based microsensors is presented. The formation of gas sensing film is assisted by a nanoporous anodic alumina layer grown from a thin layer of aluminium sputtering-deposited over a thin layer of tungsten (Al/W bilayer). The anodic film annealed at 500 degrees C consists of a self-ordered array of WO3 nanodots (similar to 50 nm), each composed of few nanocrystallites (similar to 9 nm) having thermostable tetragonal structure. The processes for forming the WO3 nanodot active films are fully compatible with standard technology for fabrication of sensor chips on a micromachined silicon wafer. Characterization of the WO3 nanodot film was performed by field-emission scanning electron microscopy, atomic force microscopy and X-ray diffraction analysis. A study of the ability of the WO3 nanodot-based microsensors to detect H-2, CO, ethanol and relative humidity was presented for the first time. High sensitivity to hydrogen, with linear response characteristic was obtained in the range of low H-2 concentrations (5-20 ppm). The gas sensing mechanism of the WO3 nanodot-based sensors was discussed. (C) 2010 Elsevier B.V. All rights reserved.