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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.

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Scroll-like colloidal quasi-two-dimensional CdS x Se1–x nanoplatelets (NPLs) with a thickness of five monolayers and average lateral dimensions of 100 nm over the whole composition range (0 ≤ x ≤ 1) were synthesized by using a mixture of chalcogenide precursors. According to X-ray diffraction and X-ray energy dispersive spectroscopy mapping in a scanning transmission electron microscope, as-synthesized NPLs are solid solutions with a uniform elemental distribution in each individual nanoplatelet. A change in composition leads to the continuous shift and gradual broadening of exciton absorption and photoluminescence (PL) lines in the visible blue and near-ultraviolet light range. Detailed analysis of optical properties, including temperature-dependent PL spectroscopy, revealed the nonmonotonic behavior of several optical parameters (average phonon temperature, electron–phonon interaction coefficient, and Stokes shift) starting from a sulfur content of ∼40% in alloyed NPLs. This behavior may be attributed to the local composition fluctuations within CdS x Se1–x solid solution nanoplatelets.

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