A HIGHLY SENSITIVE GAS SENSOR BASED ON A

TUNGSTEN OXIDE NANOTUBE-ARRAY FORMED IN

NANOPORE ALUMINUM OXIDE MEMBRANES

 

Reit Artzi-Gerlitz1*, Kurt D. Benkstein1, David L. Lahr1, Joshua L. Hertz1, Christopher B. Montgomery1, John E. Bonevich2, Steve Semancik1 and Michael J. Tarlov1

1Chemical Science and Technology Laboratory, 2Materials Science and Engineering Laboratory,

National Institute of Standards and Technology

100 Bureau Dr., Gaithersburg, MD 20899, USA

 

 

Nanostructured materials are promising for sensing applications due to their enhanced surface area. Assembly of nanostructures or high-porosity structures further contributes to increased surface area, facile gas diffusion and, hence, higher sensitivity. We report on a tungsten trioxide (WO3) nanotube-array gas sensor fabricated using a porous aluminum oxide membrane as the template. Continuous, open-ended WO3 nanotubes were formed in the pores (d=200 nm, l=60 m) using a sol-gel process, with multiple coating and sintering steps. The WO3 coated membranes structure was determined by dissolving the aluminum oxide template, and the exposed nanotubes were thoroughly characterized by scanning electron and transmission electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. The measurements confirmed the open-pore structure and the chemical state of the nanotubes, and indicated that the nanotube walls are composed of poly-crystalline grains with a diameter of ≈ 60 nm to 80 nm. For electrical characterization and to enable chemiresistive-sensing measurements, porous Au contacts were deposited by thermal evaporation on the top and the bottom of the WO3-coated alumina membranes. The nanotube-array sensor readily detected 200 ppb (nmol/mol) of nitrogen dioxide (a hazardous pollutant) in air, at temperatures ranging from 37 C to 200 C, with enhanced sensitivity at lower temperatures. The electrical sensing response of the nanotube-array sensor to 20 ppm (mol/mol) of NO2 at 200C was measured to be three orders of magnitude larger than that of a non-porous WO3 film-based sensor, which was prepared with the same sol-gel process. We attribute the extraordinary sensitivity to the high surface area of the array (~0.1 m2 internal surface area calculated, as compared to 410-4 m2 geometric surface area) and the multiple grain boundaries of the poly-crystalline nanotubes. Furthermore, the open-pore structure enables gas to access the interior surfaces of the nanotubes, which results in high gas-sensing responses.

 

Contact information:

Reit Artzi-Gerlitz

Mentor: Michael Tarlov

NIST-CSTL-836.04

 

Tel: 301-975-3142

Fax: 301-975-2643

 

 

100 Bureau Dr., MS 8362

Bldg. 221, Rm B324

Gaithersburg, MD 20899-8362

reit.artzi-gerlitz@nist.gov

Category: materials

Not Sigma-Xi members