Size-dependent modifications of the Raman spectrum of rutile TiO2

Crystallite-size-dependent variations in the Raman spectrum of rutile TiO2 have been characterized and compared with those of the well-investigated rutile SnO2. For an average crystallite size below ∼25nm, the Raman spectrum of rutile TiO2 nanocrystals displays an additional low-frequency, possibly surface vibrational, mode at ∼105cm−1. The disorder-activated, high-frequency surface modes seen in the Raman spectrum of rutile SnO2 nanocrystals are absent. The Eg and A1g vibrational modes of rutile TiO2 show systematic redshifts, broadening, and intensity reductions with decreasing crystallite size, which are consistent with phonon confinement behavior. A phonon confinement model provides reasonable crystallite size quantification, as in the case of rutile SnO2 and RuO2.