Raman Line Shapes of Optical Phonons of Different Symmetries in Anatase TiO2 Nanocrystals

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• 作者：Satyaprakash Sahoo ; A. K. Arora ; V. Sridharan
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：October 1, 2009
• 年：2009
• 卷：113
• 期：39
• 页码：16927-16933
• 全文大小：270K
• 年卷期：v.113,no.39(October 1, 2009)
• ISSN：1932-7455

文摘

Raman spectroscopic investigations of phonons of different symmetries in anatase TiO₂ nanocrystals synthesized by the sol−gel method are carried out. Out of six Raman active phonons, the line shapes of two E_g modes and one B_1g mode have been analyzed quantitatively to distinguish between the contributions of laser-induced local heating, phonon confinement effects, and defects to the line broadening. The line shape asymmetry arising from confinement of optical phonons in the 397 cm⁻¹ B_1g mode is found to be of opposite nature than those in the 144 and 639 cm⁻¹ E_g modes. This arises due to the negative dispersion of the 397 cm⁻¹ B_1g phonon dispersion curve. The measured spectra show larger broadening than those predicted by a phonon confinement model. The excess broadening, attributed to intrinsic defects, is found to be least for the 144 cm⁻¹ E_g mode and largest for the 397 cm⁻¹ B_1g mode. In addition, finite laser power of the excitation wavelength is found to raise the temperature of the nanocrystals, with heating being maximum for the smallest size nanocrystals.