The role of oxygen vacancies in the sensing properties of SnO2 nanocrystals

SnO2 nanocrystals (6 nm) were prepared by a wet chemical route and heat-treated at 500degC. The nanocrystals were characterized by X-ray photoelectron spectroscopy, conductometric measurements and cathodoluminescence spectroscopy. The results, interpreted with the aid of molecular modeling carried out in the frame of the Density Functional Theory (DFT), indicated that the nanocrystals contain topographically well-defined surface oxygen vacancies. The NO2 adsorption properties of the oxygen vacancies, investigated by DFT modeling, indicated that the in-plane oxygen vacancies facilitate the NO2 adsorption at low operating temperatures, and that the bridging oxygen vacancies enhance the charge transfer from the surface to the adsorbate. Thus an actively transducing surface is obtained through generation of surface oxygen vacancies. If this enhancing phenomenon is complemented with the grain size effects, remarkable gas-responses can be obtained.