Size-dependent modifications of the first-order Raman spectra of nanostructured rutile TiO2

The crystallite-size-dependent Raman spectral modifications observed for a suite of rutile TiO2 nanocrystals are analyzed and compared to the characteristics of the Raman spectra that were reported for nanoscale rutile TiO2 domains/crystallites embedded in thin films. The strong E-g and A(1g) modes display disparate size dependencies in the various rutile nanostructures. The redshifts of the Raman frequencies, asymmetric peak broadening, and intensity/linewidth ratio reductions with decreasing crystallite size observed for nanopowder samples are consistent with phonon confinement. The nonsystematic Raman spectral modifications that are inconsistent with phonon confinement documented for the nanoscale rutile within thin films suggest that intrinsic crystallographic or extrinsic matrix influences can interfere and overprint the confinement effects.