Anharmonicity of optical phonon modes in copper doped rutile TiO2 nanorod composed microflowers

Abstract

Anharmonicity and impurities have a significant impact on the dynamic and optical properties of crystalline solids. In this report, we have performed temperature-dependent Raman spectroscopy in the range of 300–800 K for hydrothermally synthesized titanium dioxide (TiO2) nanorod composed microflowers doped with Cu. X-ray diffraction and high resolution transmission electron microscopy confirm the pure rutile phase of both pristine and Cu doped TiO2. The most intense Eg and A1g modes exhibit a frequency redshift, and the linewidth increases with temperature, which leads to Fano line shape type asymmetry. The anharmonicity induced phonon frequency shift as a function of temperature was well fitted using the Klemens model by combining three and four-phonon coupling processes. The Raman modes soften with the increasing concentration of Cu doping. The Cu dopant acts as an impurity, which manifests defect states to tune the bandgap and shorten the phonon lifetime and anharmonicity. Such an anharmonic effect can lead to applications in the sensing devices with suitable thermal and electrical conductivities.

In-situ monitoring of plasmon-induced nanoscale photocatalytic activity from Au-decorated TiO2 microflowers

“…Firstly, the Au decoration on the surface of TiO 2 suppresses the out-of-plane vibration of O atoms, and stress develops, which causes the shift of the Raman peak position. Secondly, it is reported that the E g vibrational mode gets red-shifted with increasing temperature [43,49]. It is also demonstrated that localized heat is generated in Au upon photoexcitation near its SPR.…”

“…The TiO 2 seed layer was prepared on Si using the radio-frequency sputtering deposition technique with working pressure 5 × 10 −3 mbar and in an Ar flow rate of 15 sccm. Subsequently, TiO 2 microflowers were grown on the seeded substrate using the hydrothermal method as described in our earlier publication [43]. An appropriate quantity of HCl was added with deionized water, stirred well for 15 min, and an appropriate amount of titanium butoxide was added to the above solution dropwise and stirred until a clear solution was obtained.…”

“…In general, the rutile phase of TiO 2 has four vibrational modes at 143 (B 1g ), 447 (E g ), 612 (A 1g ), and 826 cm −1 (B 2g ). The peak at around 240 cm −1 is attributed to multi-phonon scattering, which is also a signature of rutile TiO 2 [43]. The intensity of B 2g is small and broad, so it is not distinguished.…”

Influence of defects on the linear and nonlinear optical properties of Cu-doped rutile TiO2 microflowers

“…However, from the ICP-OES measurement, the actual doping % was found to be approximately 50% of the initial value taken at the time of the experiment as reported in our previous work. 34…”

Anharmonicity induced faster decay of hot phonons in rutile TiO2 nanorods: a Raman spectromicroscopy study

“…The TD peak shift of a Raman phonon mode provides valuable information on the effect of thermal perturbation on phonon scattering processes and causes Raman peak broadening due to reduced lifetime with thermal expansion of the crystal lattice. Raman study on anatase TiO 2 nanorods (TNRs) has been carried out to a great extent, 50–52 whereas that od rutile phase has been carried out only by a few research groups, 40,53,54 and carrying out more studies is required to present a holistic picture about the different aspects related to anharmonicity in low dimensional TiO 2 .…”