Raman study of SnO2 nanograins under different annealing temperature

SnO2 nano-crystalline grains with sizes in the range of 4-80 nm are systematically investigated using Raman spectroscopy. Besides SnO2 fundamental-frequeney modes, a few weak Raman modes and a very strong and broad photoluminescence peak at about 700 nm can be observed. Our results show that bulk properties of nano-SnO2 diminish but the defect-, surface-, and size-related features display as grain size decreases. A critical size that divides respective predominance is determined to be about 20 nm. Bulk spectra with spectroscopic line broadening and position shifting, a surface mode and interface mode around 571 cm(-1) and 351 cm(-1), as well as the O-H vibration modes of the water molecules in SnO2 narrograins are characteristics of Raman spectra of nano-SnO2 with grain size below 20 nm. They are related to the microstructure change of the narrograins, i.e. they reflect the change of grain size, surface, and the interaction between nanograins.