Fabrication and gas sensing performance of parallel assemblies of metal oxide nanotubes supported by porous aluminum oxide membranes

We describe a conductometric chemical sensor architecture based upon an assembly of parallel metal oxide nanotubes. In this design, an aluminum oxide membrane serves as both a template for growth of the sensing nanotubes and a scaffold to support the nanotubes and the top/bottom electrical contacts for sensing measurements. Important advantages of this sensing architecture are: (1) analyte molecules are detected within the nanotube interior thereby maximizing sensitivity; and (2) metal contacts for resistance measurements are easily and reproducibly established at the ends of the nanotubes. We demonstrate a proof-of-concept for this approach by fabricating and evaluating tungsten trioxide (WO3) nanotube-based conductometric devices. Nanotubes are formed in membrane pores (diameter approximate to 200 nm, length approximate to 60 mu m) by sol-gel deposition and characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photorelectron spectroscopy (XPS). Thin film Au contacts are deposited on the top/bottom of the WO3-coated membranes such that the tube-ends remain open, enabling conductometric sensing along the length of the WO3 nanotubes. The nanotube assemblies detect oxidizing (nitrogen dioxide) and reducing (methanol) gases at 200 degrees C, and exhibit responses two to three orders-of-magnitude greater than a planar WO3-film sensor. The enhanced sensitivity is attributed to the large surface area presented by the interior of the nanotube assemblies. Published by Elsevier B.V.