Semiconducting SnO₂ thin films are often used as an active element in gas sensors technologies¹. An emerging application is the use as electrode or sensitive element in biochip technologies². These two applications require a good control of the composition, microstructure and physical properties of the film. The films have been fabricated from metal-organic precursors by using a submicroscopic aerosol pyrolysis deposition method. This elaboration method allows obtaining films with small amounts of catalytic metallic aggregates such as Pt or Pd by codeposition. This incorporation can drastically improve the films sensitivity to polluting gas. The best sensitivity is obtained from a low concentration of the metal in the film. A previous local microstructural analysis of Pt-doped SnO₂ thin films prepared by this deposition method have shown that the porosity of the films is significantly affected by finely varying the metal amounts³. To correlate these local structural evolutions with statistical information on the film porosity, X-ray reflectivity analysis has been performed from a series of films loaded with various contents of Pt (0 at. % to 6 at. % in the precursor solution calculated as [Pt]/([Sn] + [Pt] + [O])) To obtain a reliable X-ray reflectivity data, larger samples (e.g. 2 to 4 inch Si wafers) have been prepared by using a specific large area deposition method. The results indicate that the film density increases with increasing loading (from ~75% to 95% of SnO₂ bulk value for used range of Pt contents in the precursor solution). The films analysis is combined with Transmission Electron Microscopy and Atomic Force Microscopy microstructural analysis. Results will be discussed in terms of potential improvement for applications in chemical sensor technologies.

¹ M. Gaidi et al., J. Electrochem. Soc. 147 (8) (2000) 3131

² V. Stambouli et al. Sensors and Actuators B 113 (2006) 1025

³ I. Matko et al., J. Electrochem. Soc. 149 (8) (2002) H153.

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