Surface modification of solid state gas sensors

The phenomenon of electrical conductivity being controlled by the chemical state of a surface grafted reactive centre, resulting in a room temperature gas response, is demonstrated. The reactive centres can be chosen to be specific to a particular gas, providing a route to new types of gas detectors tailored for a particular application. Generalization of the phenomenon was verified. Surface grafting of Ti, Ru and Pt centres onto SnO_2; Ti and Pt centres onto TiO_2 ; and Pt centres onto BaSn_0_._9_7Sb_0_._0_3O_3 resulted in a room temperature gas sensitivity specific to each system. Surface grafting of Ru centres onto SnO_2 resulted in additional electronic states in the SnO_2 band gap associated with surface Ru species, revealed by XPS and correlated with resistance increase of the material. An electronic interaction between grafted Ru centres and the SnO_2 support was manifested in conductivity being controlled by the surface state of the Ru. Variations in the chemical state of the surface grafted Ru caused by gas chemisorption were revealed by XPS and this was correlated with conductivity change measured as gas response of the device at room temperature. The samples were characterized by EXAFS to confirm the structure of the surface Ru species, TPD, UV- visible spectroscopy, XPS and electrical measurements. DFT molecular cluster calculations were also performed to ascertain the origin of the gas response. The mechanism of the room temperature CO response of SnO_2 decorated with small Pt particles was refined. In this case Pt was applied by common impregnation techniques. The conductivity was shown to be controlled by the surface state of the Pt. The CO response at room temperature was found to be specific to the presence of Pt(ll) species. The mechanism was assigned to CO chemisorption onto Pt(ll), resulting in charge transfer, measured as conductivity increase. The samples were characterized by XPS, TPD, SEM, mass spectrometry and electrical measurements. Comparison of the results presented for Pt decorated BaSn_0_._9_7Sb_0_._0_3O_3 and BaFeO_3 demonstrated the phenomenon to be general providing that Pt particles act as surface traps, controlling the conductivity. (author)Available from British Library Document Supply Centre-DSC:DXN050488 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo