Raman spectroscopy of a few layers of bismuth telluride nanoplatelets

We can shape the electronic and phonon properties of Bi₂Te₃ crystals via the variation of the number of layers. Here, we report a Raman study with the aid of first-principles calculations on few-layered Bi₂Te₃ systems ranging from 5 to 24 nm layer thickness using 1.92, 2.41 and 2.54 eV excitation energies. We examine how the frequency position, intensity and lineshape of the main Raman modes (A¹_1g, E²_g, and A²_1g) behave by the variation of the layer thickness and excitation energy. We observed a frequency dispersion on the number of layers of the main modes, indicating changes in the inter- and intra-layers interaction. A resonant Raman condition is reached for all modes for samples with 11 and 18 nm thickness because of van Hove singularities at the electronic density of states. Also, the Breit-Wigner-Fano line shape of the A²_1g mode shows an increase of electron-phonon coupling for thick layers. These results suggest a relevant influence of numbers of layers on the Raman scattering mechanics in Bi₂Te₃ systems.