The Development and Evaluation of TiO 2 Nanoparticle Films for Conductometric Gas Sensing on MEMS Microhotplate Platform
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The Development and Evaluation of TiO2 Nanoparticle Films for Conductometric Gas Sensing on MEMS Microhotplate Platforms Kurt D. Benkstein, Christopher B. Montgomery, Mark D. Vaudin1 and Steve Semancik Chemical Science and Technology Laboratory, National Institute of Standards and Technology 100 Bureau Drive, MS 8362, Gaithersburg, MD 20899-8362, U.S.A. 1 Materials Science and Engineering Laboratory ABSTRACT Over the past decade, MEMS microhotplate devices have been developed at the National Institute of Standards and Technology to support semiconductor metal oxide films for use in conductometric gas sensor arrays. In most cases, the materials have been based on compact thin films of SnO2 or TiO2 deposited by single-source precursor chemical vapor deposition. Of particular interest to our group is the enhancement of the sensitivity of the microsensors to trace gas species by inducing nanostructured porosity and large internal surface areas in the films. In this presentation, we discuss the development of nanostructured sensor materials based on porous TiO2 nanoparticle thin films. The preparation and evaluation of pure and Nb-doped TiO2 nanoparticle films are described. The films on the MEMS microhotplate substrates are evaluated as conductometric gas sensors based on the critical performance elements of sensitivity, stability, speed and selectivity. The sensor performance, and specifically the sensitivity, of the novel nanoparticle TiO2 films is compared with that of traditional compact CVD-derived films.
INTRODUCTION Metal oxide films have been of great interest for use in several types of gas sensing schemes, including cases involving optical, physical and electrical transduction. Conductometric sensors rely on the interaction of reducing or oxidizing analyte gases at or with the surface of the metal oxide film to cause changes in electrical conduction through the film. Sensors based on metal oxides have been widely studied and used because metal oxide films are stable in many environments and over a wide temperature range, are sensitive to many potential analytes, respond quickly and reversibly, and are inexpensive [1, 2]. The metal oxide films can be prepared and deposited using a variety of methods, with generally good control of film morphology [3-5]. Films based on metal oxide nanoparticles have attracted great interest for chemical sensors [1-14] owing largely to the inherently high internal surface area of the porous films. Several nano-structured metal oxides have been used to prepare nanoparticle-based sensor films, including SnO2, TiO2 and In2O3 [2-8]. These materials have been effective in detecting a variety of gas species such as NO2, CO2, water and alcohols [2-8]. The enhanced surface area is enticing because it equates to a larger active area when compared to the projected geometric area of the film. For any type of application that relies on interaction with the surface of the material (i.e., conductometric sensing), a porous nanoparticle film potentially offers a much greater activity th
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