Resonance Raman spectroscopic study for radial vibrational modes in ultra‐thin walled TiO₂ nanotubes

Abstract

The study reports the observation of radial vibrational modes in ultra‐thin walled anatase TiO2 nanotube powders grown by rapid breakdown anodization technique using resonant Raman spectroscopic study. The as‐grown tubes in the anatase phase are around 2–5 nm in wall thickness, 15–18 nm in diameter and few microns in length. The Eg(ν1,ν5,ν6) phonon modes with molecular vibrations in the radial direction are predominant in the resonance Raman spectroscopy using 325 nm He–Cd excitation. Multi‐phonons including overtones and combinational modes of Eg(ν1,ν5,ν6) are abundantly observed. Fröhlich interaction owing to electron–phonon coupling in the resonance Raman spectroscopy of ultra‐thin wall nanotubes is responsible for the observation of radial vibrational modes. Finite size with large surface energy in these nanotubes energetically favor only one mode, B1g(ν4) with unidirectional molecular vibrations in the parallel configuration out of the three Raman modes with molecular vibration normal to the radial modes. Enhanced specific heat with increasing temperatures in these nanotubes as compared to that reported for nanoparticles of similar diameter may possibly be related to the presence of the prominent radial mode along with other energetic phonon mode. The findings elucidate the understanding of total energy landscape for TiO2 nanotubes. Copyright © 2015 John Wiley & Sons, Ltd.

Assessment of the Cr doping and size effects on the Raman‐active modes of rutile TiO2 by UV/Visible polarized Raman spectroscopy

“…Characteristic modification of phonon modes in addition to the Raman‐active modes in anatase TiO 2 has been previously reported in presence of Fe and Al as dopants . Besides, Fröhlich interactions due to resonance conditions have been proposed to be responsible of the activation of some of these multiscattering phonon modes in nanosized anatase, as reported by Antony et al . Also, Dou and Persson emphasized the role of the Fröhlich phonon–electron coupling in the polaron effective mass due to the strong ionic Ti─O bond character and the presence of structure distortions in rutile TiO 2 with importance in the dielectric properties due to the large LO–TO energy split of the A 2u mode.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part X

“…Antony and co‐workers used resonance Raman spectroscopy to study the radial vibrational modes in ultra‐thin walled TiO 2 nanotubes. Their findings elucidate the understanding of the total energy landscape for TiO 2 nanotubes . Baibarac et al .…”

“…Their findings elucidate the understanding of the total energy landscape for TiO 2 nanotubes. [59] Baibarac et al used anti-Stokes Raman spectroscopy as a method to identify the metallic and semiconducting configurations of double-walled carbon nanotubes. The procedure exploits the difference between the intensities of recorded anti-Stokes Raman spectrum and the anti-Stokes spectrum calculated by applying the Boltzmann formulas to the recorded Stokes spectrum.…”

Fabrication of porous and visible light active ZnO nanorods and ZnO@TiO2core–shell photocatalysts for self-cleaning applications

“…Based on the group theory, six Raman active phonon modes are obtained; A 1g + 2B 1g + 3E g . 40 After coating TiO 2 on the ZnO NRs, an intense peak near 143 cm À1 confirms the anatase phase of TiO 2 and a small peak at 440 cm À1 is due to the hexagonal phase of ZnO. 41 The respective peaks at 144, 197 and 638 cm À1 are assigned to the E g vibrational mode of the TiO 2 .…”