Structural and spectral properties of SnO2 nanocrystal prepared by microemulsion technique

Extrafine SnO2 nanocrystals as small as 2.4 nm were synthesized by the microemulsion method. The grain sizes and crystallization process were measured and investigated by X-ray diffraction. Two growth processes were proposed, and the activation energies of 4.3 and 23 KJ/mol were obtained for respective low-and fast-growth processes. TEM micrographs and the selected-area diffraction recorded their morphology and crystallization, well crystallized at about 773 K. All the IR modes measured by FT-IR spectrometer were assigned. The 616 cm-1 mode after annealing at 673 K showed fine crystallization. The temperature dependence of the Raman spectra shows that increase in intensity and decrease in linewidth of the 636 cm-1 mode with the increasing grain size indicate a phonon confinement effect. A new 330 cm-1 Raman mode originally inactive in bulk, was observed in the SnO2 nanocrystal by size effect. A low frequency mode at 76 cm-1 shifts to 38 cm-1 as the temperature goes up 873 K, which can be characterized to determine the SnO2 grain sizes.