Excitation of lattice vibrations in nanostructured anatase TiO2 frequently occurs at energy values differing from that found for the corresponding bulk phase. Particularly, investigations have long aimed at establishing a correlation between the low-frequency E-g(1) mode and the mean crystallite size on the basis of phonon-confinement models. Here, we report a detailed Raman study, supported by X-ray diffraction analyses, on anatase TiO2 nanocrystals with rod-shaped morphology and variable geometric parameters, prepared by colloidal wet-chemical routes. By examining the anomalous shifts of the E-g(1) mode in the spectra of surfactant-capped nanorods and in those of corresponding organic-free derivatives (obtained by a suitable thermal oxidative treatment), an insight into the impact of exposed facets and of the coherent crystalline domain size on Raman-active lattice vibrational modes has been gained. Our investigation offers a ground for clarifying the current lack of consensus as to the applicability of phonon-confinement models for drawing information on the size of surface-functionalized TiO2 nanocrystals upon analysis of their Raman features.
Comparative Raman Study of Organic-Free and Surfactant-Capped Rod-Shaped Anatase TiO2 Nanocrystals
COZZOLI, Pantaleo Davide
Conceptualization
2014-01-01
Abstract
Excitation of lattice vibrations in nanostructured anatase TiO2 frequently occurs at energy values differing from that found for the corresponding bulk phase. Particularly, investigations have long aimed at establishing a correlation between the low-frequency E-g(1) mode and the mean crystallite size on the basis of phonon-confinement models. Here, we report a detailed Raman study, supported by X-ray diffraction analyses, on anatase TiO2 nanocrystals with rod-shaped morphology and variable geometric parameters, prepared by colloidal wet-chemical routes. By examining the anomalous shifts of the E-g(1) mode in the spectra of surfactant-capped nanorods and in those of corresponding organic-free derivatives (obtained by a suitable thermal oxidative treatment), an insight into the impact of exposed facets and of the coherent crystalline domain size on Raman-active lattice vibrational modes has been gained. Our investigation offers a ground for clarifying the current lack of consensus as to the applicability of phonon-confinement models for drawing information on the size of surface-functionalized TiO2 nanocrystals upon analysis of their Raman features.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
