Electric Field Induced Raman Scattering (EFIRS) Investigation in TiO2 Nano-crystallites

Nanosized TiO2 crystallites, a semiconductor with a wide energy gap of about 3.2 eV, as a new material, has many excellent properties, such as high efficient photocatalytic effect, high mechanical surface resistence and also environmental and biological applications. In recent years the electric-field-induced Raman scattering (EFIRS) has become an attractive tool to probe the changes in the electric fields in space-charge layers at semiconductor surfaces and interfaces, [1-2]. EFIRS can cause either an enhancement of the lattice allowed modes or an activation of theoretically forbidden modes. The influence of EFIRS has previously been examined for some semiconductors such as ZnO, GaAs, CdS, etc. It can be claimed that the external electric fields can significantly influence phonon modes in semiconductors and its piezoelectric character, [3-4]. In this work, we have investigated the effect of the external electric fields, up to about 17 kV/cm, on the phonon modes of TiO2 nanocrystallites by using the excitation energies of a 532 nm laser, which lower than the TiO2 band gap energy. In the present work, we report the fabrications of TiO2 nanoparticles in our lab by a simple modified sol-gel process. The synthesized TiO2 nanocrystallites then were characterized by XRD, SEM and back scattering Raman techniques and the effects of an external DC electric field on the lattice internal and external modes of the nanocrystallites were investigated by the recorded in situ Raman data. Our results show that the applied external electic fileld can make a strong interaction and widening of the Raman active modes, the intensity quenching and possible peak shifts in the Raman spectra can be observed