Raman surface vibration modes in nanocrystalline SnO2:: Correlation with gas sensor performances

Raman surface vibration modes have been measured for SnO2 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 NO2 species diluted in a N-2 carrier. The influence of the nanostructure surface on the sensor signal exhibits opposite trends for CO than for NO2 detection. As the Raman surface vibration modes, 400-700 cm(-1), band intensity increases, the sensor response for CO increases too, while that of NO2 diminishes, giving an excellent inverse correlation between the sensor response for CO and NO,. This correlation is fulfilled for all the samples except those that are distorted by the presence of an excess of contamination caused by OH- groups together with Cl- ions introduced by the chemical synthesis procedure.