Probing Bi2Te3 thin nanoplates by Raman Spectroscopy*

Two infrared (IR)-active vibrational modes centered at 93 and 113 cm$^{-1}$ are observed in Raman spectra from as-grown thin nanoplates (NPs) of topological insulator Bi$_2$Te$_3$. The presence of IR modes in Raman scattering reveals a breakdown of inversion symmetry in thin NPs grown on SiO$_2$. Both Raman and IR modes are preserved after typical device fabrication processes, suggesting the robustness of surface properties. In NPs transferred to another SiO$_2$ substrate, the IR modes are absent, and the Raman spectra are similar to those from bulk samples. These differences could be attributed to interactions between the SiO$_2$ substrate and the as-grown NPs.