Raman scattering by thin film nanomosaic rutile TiO_2

摘要

Thin TiO_2 films with rutile short-range atomic order grown at room temperature have a nanostructure of rectangular domains based on a faulted rutile structure. Raman scattering by nanomosaic rutile in single layer TiO_2 and TiO_2—Al_2O_3 nanolaminate films is reported here. In all architectures, the E_g phonon mode frequency is similar to bulk but the A_(1g) mode frequency is significantly blueshifted. These results are different from published Raman scattering spectra of other nanocrystalline rutile TiO_2. A model for nanomosaic rutile is presented in which TiO_6 octahedra in the faulted regions are severely distorted with a lengthened equatorial Ti-O bond and a shortened apical Ti-O bond. The observed A_(1g) mode blueshift is a consequence of the shortened apical bond.