Zinc oxide (ZnO) hollow hemisphere (HS) and urchin-like (UL) structures were fabricated and examined for application to a gas sensor. Films of hollow ZnO-HS arrays floating over substrates were synthesized via Zn sputtering onto the template of a polystyrene sphere array followed by oxidation. Growing ZnO nanorods upon HS surfaces via a hydrothermal method formed hollow ZnO-UL structures. The thicknesses of the HS films and the lengths of nanorods in the UL structures were varied to obtain the maximum response to NO gas. Both sensor structures showed a sensing of tens of parts per billion of levels of NO concentrations with good response and gas selectivity. The highest response was realized through the thinness and the open porosity of the structures. The surface depletion determined the sensor response signal for the sensor geometry with the highest response.
Tin oxide-single wall carbon nanotube (SWCNT) nano composites are synthesized for gas sensor application. The fabrication includes deposition of porous SWCNTs on thermally oxidized SiO2 substrates followed by rheotaxial growth of Sn and thermal oxidation at 300, 400, 500, and 600 degrees C in air. The effects of oxidation temperature on morphology, microstructure, and gas sensing properties are investigated for process optimization. The tin monoxide oxidized at 400 degrees C showed the highest response at the operating temperature of 200 degrees C. Under the optimized test condition, the composite structure showed better response than both structures of SWCNTs and thin film SnO.
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