Semiconductor Gas Sensors Based on SnO2 Thick Films

Abstract

ABSTRACT. Some physical and chemical aspects about the behaviour of semiconductor gas sensors are discussed. Discussion is restricted to sintered Sn02 which is usually in the form of a thick film. Since we have concentrated on electrical studies of the response characteristics of Sn02 thick films in our laboratory, the discussion also has an emphasis on the transducing properties (conductance signals) of the sensor. Initially, some electrical properties of Sn02 are reviewed. Subsequently a description of the general form of conductance in sintered samples is presented. From the chemical point of view, the central role of the oxygen ions, 0; and 0-, on the Sn02 surface is analysed in connection with the conductance response at a constant temperature and after quick temperature changes. The role of the adsorption/desorption mechanism is emphasized. Some discussion about the surface defect mechanism is also included. The use of catalysts and promoters to improve sensor properties, together with some peculiar effects related to electrode materials are also discussed.

Organometallic approach for platinum and palladium doping of tin and tin oxide nanoparticles: structural characterisation and gas sensor investigations

“…This organometallic complex then appears as a convenient potential precursor for the doping of tin nanoparticles, and we observed indeed that [Pt 2 (dba) 3 ] also decomposed in the presence of colloidal tin/tin oxide nanoparticles suspended in anisole, when exposed to 1 atm of carbon monoxide.…”

“…We recently demonstrated that the reaction of [Pt 2 (dba) 3 ] with carbon monoxide in THF leads to the formation of well crystallized platinum nanoparticles of uniform size centred near 1.2 nm 41 which can be easily functionalized through coordination of various ligands at their surface. This organometallic complex then appears as a convenient potential precursor for the doping of tin nanoparticles, and we observed indeed that [Pt 2 (dba) 3 ] also decomposed in the presence of colloidal tin/tin oxide nanoparticles suspended in anisole, when exposed to 1 atm of carbon monoxide.…”

“…Metal oxides are widely employed as sensitive element in gas sensors [1][2][3][4] and commercial devices produced by a typical ceramic manufacturing process have been available for a long time. 5 Such devices are able to detect low concentration of flammable or toxic gases at a ppm level but their lack of selectivity and long term stability remains their weak points, and improving the cross sensitivities between gases such as CO, H 2 , hydrocarbons and NO 2 remains a major problem.…”

“…[39][40][41] We demonstrate in this paper that these Pd and Pt organometallic complexes can effectively be used as precursors to surface doping tin nanoparticles through very mild conditions and with an accurate control of morphology. The reaction with CO of [Pt 2 (dba) 3 ] or [Pd(dba) 3 ] in anisole containing tin nanoparticles indeed leads to the formation of tin/platinum or tin/palladium nanoparticles. Partial aspects of this work, including essentially X-ray absorption experiments of the tin/palladium particles, have been previously reported.…”

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Platinum and palladium surface doped tin nanoparticles have been obtained by decomposition of [Pt 2 (dba) 3 ] and [Pd(dba) 2 ] organometallic precursors, respectively, in a colloidal suspension of tin/ tin oxide core-shell nanoparticles of uniform size (E13 nm), in anisole under 1 bar of carbon monoxide at room temperature. The particles can be isolated as pure solids and present effective doping ratios [Pt]/[Sn] and [Pd]/[Sn] of 2.5 and 3.1%, respectively.

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