AVS 50th International Symposium
    Surface Science Thursday Sessions
       Session SS-ThA

Paper SS-ThA5
Gas Sensing Mechanism of SnO@sub 2@

Thursday, November 6, 2003, 3:20 pm, Room 328

Session: Oxide Reactions and Catalysis
Presenter: M. Batzill, Tulane University
Authors: M. Batzill, Tulane University
B. Katsiev, Tulane University
A. Chaka, National Institute of Standards and Technology
U. Diebold, Tulane University
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Stannic oxide is widely used as a gas sensing material for reducing and oxidizing gases. Variations in the surface oxygen concentration of metal-oxide gas sensors play an important role for explaining their response to a change in the surrounding gas phase. Here we show for different low index SnO@sub 2@ surfaces that non-stoichiometric surface terminations are favored at a low oxidation potential of the environment (e.g. UHV conditions). Under such conditions the low-energy (110) surface forms complex surface reconstructions in order to accommodate the loss of surface oxygen. The (101) and (001) surfaces, on the other hand, retain bulk terminations for both stoichiometric and reduced surfaces. The stability of these surfaces is explained on ground of the dual valency of Sn (SnII and SnIV) and the rutile-structure of SnO@sub 2@ that allow the (001) and (101) surfaces to attain a Sn@super 2+@O@super 2-@ stoichiometry by removal of bridging oxygen atoms. The surface structures have been determined by low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). For reduced surfaces, angle resolved UPS was employed to characterize the dispersion of the surface electronic states. The variation of the surface composition has been measured by temperature programmed ion scattering spectroscopy. The experimental results are verified by density functional theory calculations that show the stability of different surface phases as a function the oxygen chemical potential. This variable surface composition accompanied by a change in the electronic structure is proposed to be the fundamental process of the gas sensing mechanism for SnO@sub 2@.