Abstract :
Raman spectra acquired from SnO2 nanocrystals with different sizes show a size-independent Raman mode at ∼574 cm−1. The intensity increases as the nanocrystal size decreases and this tendency is contrary to that of the normal bulk Raman modes. By considering the existence of oxygen vacancies at the nanocrystal surface, we adopt the density functional theory to calculate the Raman spectra with different oxygen vacancy positions and concentrations. The results clearly demonstrate that the in-plane oxygen vacancy is responsible for the 574 cm−1 mode and the intensity enhancement is a result of the higher in-plane oxygen vacancy concentration.
