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 similar to 25 nm, the Raman spectrum of rutile TiO2 nanocrystals displays an additional low-frequency, possibly surface vibrational, mode at similar to 105 cm(-1). The disorder-activated, high-frequency surface modes seen in the Raman spectrum of rutile SnO2 nanocrystals are absent. The E-g and A(1g) 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.