Raman spectroscopy of a few layers of bismuth telluride nanoplatelets.

We can shape the electronic and phonon properties of BiTe crystals the variation of the number of layers. Here, we report a Raman study with the aid of first-principles calculations on few-layered BiTe 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 (A, E, and A) 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 A 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 BiTe systems.