A tin oxide (SnO2)/arc-discharge single walled carbon nanotubes (SWNTs) hybrid material based sensor was developed for the detection of NH3 and O3 at room temperature. The gas sensitive composite thin films were prepared using sol gel and dip coating techniques, and characterized by transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Overall, the hybrid material based sensor is found to have an enhanced sensitivity as compared to pure SnO2 or pure SWNTs based sensors. An optimum annealing temperature of the composite of 300 °C was determined. The detection limit at room temperature was evaluated at 1 ppm and lower than 20 ppb for NH3 and O3, respectively. Moreover, the hybrid sensor exhibited a fast response (few minutes), a good sensitivity and a full recovery at room temperature. The sensor efficiency has also been demonstrated to strongly depend on the SWNT source used for sensor fabrication (4 different commercial sources have been tested). These results open the way towards further optimized hybrid sensors.

The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365 degrees C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface. (C) 2009 Elsevier Ltd. All rights reserved.

Résumé (à complèter)

Cet exposé fait le point sur le potentiel des spectroscopies vibrationnelles Raman et infrarouge pour l'étude des propriétés d'auto-assemblage (ex situ et in situ ) des silices hybrides. La sensibilité de ces techniques à la compétition des interactions covalentes et non covalentes est particulièrement décrite.

Fourier transformed infrared microreflectance spectroscopy is used to probe and compare the consequences of thermal quenching or ionic implantation on the structure of silica. A linear change in the main structural feature associated with Si-O-Si vibration with fictive temperature (T-f) is observed up to T-f = 1400 degrees C. Ionic implantation is shown to shift the frequency of the main IR Si-O-Si vibration toward much lower wavenumbers, for all deposited energies, indicating that a comparison can be drawn between fictive temperature and irradiation effects. Extrapolating the linear changes in the IR structural bands obtained as a function of T-f for the implanted samples, we show that two structural (nu(TO)) and (nu(B)) contributions are not affected by ionic implantation, as they would be by a unique very high T-f. In the case of ionic implantation, we also evidence the development of some specific structural contributions indicating a depolymerization of silica network. (C) 2009 American Institute of Physics.