Phonon confinement studies in nanocrystalline anatase‐TiO₂ thin films by micro Raman spectroscopy

Abstract

Raman studies were performed on titania thin films prepared by polyethylene glycol (PEG) assisted, low-temperature, sol-gel method. The Raman spectra of the films show a systematic blue shift in the peak position and a broadening in the full width at half-maximum (FWHM) when compared with those of the bulk anatase TiO 2 powder. Several reports have appeared indicating this kind of peak shift and broadening of FWHM, which were attributed to the confinement of phonons in the anatase nanocrystallites. In this paper, we report an analysis of quantum size effect in the Raman spectra of nanocrystalline TiO 2 thin films performed by utilizing the phonon dispersion relation of the anatase phase which has been obtained from a work based on density functional perturbation theory (DFPT). For comparison purposes the quantum size effect calculations have also been done utilizing the dispersion relations of the rutile phase. There is good agreement between the crystallite sizes evaluated from the equally weighted Raman line intensity of the dispersion relations obtained from the DFPT and those determined by X-ray diffraction.

“Black” TiO2 Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H2-Evolution

“…These observations are in line with models that indicate phonon confinement by a decrease of the effective particle size. In fact, if various models for phonon confinement [33][34][35] (see SI) are applied to the shifts in peak position and the changes in the FWHM at the Eg peak, the corresponding length scale results as ~10-20 nm -this well in line with direct observation of voids in the TEM walls with spacings at ≈ 20 nm (Fig. 2h).…”

Characterisation Studies of the Structure and Properties of As-Deposited and Annealed Pulsed Magnetron Sputtered Titania Coatings

“…This implies that even though peak positions in these samples are characteristic to crystalline rutile formation there is no long range ordering in these samples and the Raman shifts are most likely represented by amorphous vibrations. It has been suggested that peak broadening occurs due to nanocrystallinity and quantum confinement effects, and that there is a characteristic dependency between grain size and peak position and broadening in Raman analysis [23,[25][26][27]. Finally Li Bassi et al [22] pointed out that materials with smaller particles (~4.4 nm) have Raman spectrum similar to that of amorphous materials, which could also be the case here.…”

Erratum to: Sol–gel synthesis of mesoporous WO3–TiO2 composite thin films for photochromic devices

“…In addition, in the Raman spectrum of the WO 3 -TiO 2 composite film annealed at 600°C (Fig. 1C), the mode emerging at 151.5 cm -1 is due to the crystallization of the TiO 2 in the anatase form [45]. Also, the anatase main band is high-frequency shifted (151.5 cm -1 ) with respect to the value of commercial anatase TiO 2 powder (142.5 cm -1 ), indicating that the TiO 2 is constituted of TiO 2 nanoparticles.…”

“…Also, the anatase main band is high-frequency shifted (151.5 cm -1 ) with respect to the value of commercial anatase TiO 2 powder (142.5 cm -1 ), indicating that the TiO 2 is constituted of TiO 2 nanoparticles. A phonon confinement model has been applied to establish a relation between the crystallite sizes and the main Raman peak position of TiO 2 , and the observed shift corresponds to a crystallite size of *5 nm [45]. Compared with the WO 3 sample annealed at 500°C, which had amorphous TiO 2 , formation of the orthorhombic phase of WO 3 in the WO 3 -TiO 2 composite film heat treated at 600°C has been favored by the presence of crystalline anatase.…”