The effect of the Bi source on optical properties of Bi2Te3 nanostructures

Abstract Bi 2 Te 3 nanostructures were synthesized by using different Bi sources via a simple solvothermal process, in which Bi 2 O 3 and BiCl 3 were used as the Bi sources. Optical properties of Bi 2 Te 3 nanostructures prepared with Bi 2 O 3 and BiCl 3 as the Bi sources were investigated by micro-Raman spectroscopy. The Raman scattering spectrum of Bi 2 Te 3 hexagonal nanoplates prepared by using Bi 2 O 3 as the Bi source shows that the infrared (IR) active mode A 1 u , which must be odd parity and is Raman forbidden for bulk crystal due to its inversion symmetry, is greatly activated and shows up clearly in the Raman scattering spectrum. We attribute the appearance of the infrared active A 1 u mode in the Raman spectrum to crystal symmetry breaking of Bi 2 Te 3 hexagonal nanoplates. However, the Raman scattering spectrum of Bi 2 Te 3 nanostructures with irregular shape prepared by using BiCl 3 as the Bi source only exhibits the two characteristic Raman modes of Bi 2 Te 3 crystals. Micro-Raman measurements on Bi 2 Te 3 nanostructures with different morphologies offer us a potential way to tailor optical properties of Bi 2 Te 3 nanostructures by controlling the morphologies of the nanostructures, which is very important for practical applications of Bi 2 Te 3 nanostructures in thermoelectric devices.