Selective gas-sensing properties of surface ruthenated tin oxide
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Selective gas-sensing properties of surface ruthenated tin oxide V. A. Chaudhary, I. S. Mulla, and K. Vijayamohanana) Physical and Materials Chemistry Division, National Chemical Laboratory, Pune-411008, India (Received 15 July 1997; accepted 19 March 1998)
Gas-sensing properties of a novel surface functionalized tin oxide material have been studied to demonstrate the possibility of selectivity control by surface state formation. Covalent anchoring of ruthenium oxide on the tin oxide surface (ruthenated tin oxide) is found to give considerable enhancement in sensitivity (320) as well as selectivity to 1000 ppm of liquified petroleum gas (LPG) at 300 ±C compared to the sensitivity (4) of pure tin oxide samples. The amount and distribution of grafted ruthenium oxide on the surface of tin oxide seems to be the most important parameter controlling the change in electrical transport with LPG gas adsorption.
I. INTRODUCTION
Manipulating the morphology of semiconducting surfaces1–3 through surface functionalization has attracted much interest recently. A primary goal is to artificially create surface states in the mid-gap region using strained modes of growth of separate chemical identities, and the misfits distributed at the grain boundaries in the surface can lead to unusual physical and chemical properties. For example, adsorption energy can be higher on the misfit regions and the discontinuity in the adsorption potential can give rise to unusual selectivity effects for semiconducting oxide gas sensors. More specifically, the electron-electron interaction in the presence of periodically enhanced disorders in these twodimensional systems can affect the adsorbate-adsorbent interaction and the range of adsorption potential, leading to the additional mechanism of sensitivity improvement. This is to be contrasted with the conventional approach of selectivity control of semiconducting oxide gas sensors where noble metals and certain transition metal oxides are used to control the characteristics of adsorbed oxygen species through doping.4 –7 In the present study we report a very simple way of controlling the selectivity of tin oxide gas sensor by chemical self-organization of ruthenium cations on the tin oxide surface. More specifically, the surface of polycrystalline tin oxide samples have been functionalized by allowing adatom formation from solution so that the nature and distribution (coverage) of the ruthenium cations can be easily controlled by varying the concentration of the solution and time. Although RuO2 has been extensively used both for contact configurations and also for doping, this is the first report of the preparation and characterization of surface functionalization of SnO2 along with enhanced gas-sensing behavior. Because of the considerable influence of surface and interfacial mor-
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e-mail: [email protected] J. Mater. Res., Vol. 14, No. 1, Jan 1999
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