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Raman surface vibration modes have been measured for SnO 2 nanocrystalline powders with grain sizes of 3-36 nm and a specific surface area up to 180 m 2 g -1 , which were prepared by four different routes of chemical synthesis. The influence on these surface vibration modes of the treatment temperature, the crystallite size, and the specific surface area has been studied and bands at 245, 257, 286, 310-350, and 400-700 cm -1 have been identified. The 400-700 cm -1 band intensity has been found proportional to the surface active area. Likewise, the correlation of the 400-700 cm -1 band intensity with the sensing mechanisms have been analyzed from the sensor response of the prepared thick-film gas sensors against reducing CO and oxidizing NO 2 species diluted in a N 2 carrier. The influence of the nanostructure surface on the sensor signal exhibits opposite trends for CO than for NO 2 detection. As the Raman surface vibration modes, 400-700 cm -1 , band intensity increases, the sensor response for CO increases too, while that of NO 2 diminishes, giving an excellent inverse correlation between the sensor response for CO and NO 2 . This correlation is fulfilled for all the samples except those that are distorted by the presence of an excess of contamination caused by OHgroups together with Clions introduced by the chemical synthesis procedure.

International audienceMetal oxide (SnO₂, TiO₂, In₂O₃, ZnO) sols are prepared by various sol-gel processes in such a way as to hinder the condensation reactions. The obtained sols are injected at 160 °C into a solution of tetradecene and dodecylamine, and kept under heating for different periods of time. Depending on the starting sol, variously crystallized oxide nanoparticles are obtained, whose phase compositions and chemical structure have been studied by X-ray diffraction (XRD) and Fourier transform IR spectroscopy. The elimination of the organic residuals has been carried out by thermal treatment, and the thermal evolution of the nanoparticles has been studied by thermal analyses and Raman spectroscopy. High-resolution transmission electron microscopy studies coupled with XRD measurements show that the thermal treatment does not markedly affect the particle size, which remains in the nanometer-sized regime (from 3.5 to 8.5 nm, depending on the system), except in the case of ZnO. The thermally purified and stabilized powders, drop-coated onto alumina substrates with pre-deposited electrical contacts, have been tested as gas-sensing devices, displaying outstanding sensing properties even at room temperature