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

Bi2Te3 nanostructures were synthesized by using different Bi sources via a simple solvothermal process, in which Bi2O3 and BiCl3 were used as the Bi sources. Optical properties of Bi2Te3 nanostructures prepared with Bi2O3 and BiCl3 as the Bi sources were investigated by micro-Raman spectroscopy. The Raman scattering spectrum of Bi2Te3 hexagonal nanoplates prepared by using Bi2O3 as the Bi source shows that the infrared (IR) active mode A(1u), 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(1u) mode in the Raman spectrum to crystal symmetry breaking of Bi2Te3 hexagonal nanoplates. However, the Raman scattering spectrum of Bi2Te3 nanostructures with irregular shape prepared by using BiCl3 as the Bi source only exhibits the two characteristic Raman modes of Bi2Te3 crystals. Micro-Raman measurements on Bi2Te3 nanostructures with different morphologies offer us a potential way to tailor optical properties of Bi2Te3 nanostructures by controlling the morphologies of the nanostructures, which is very important for practical applications of Bi2Te3 nanostructures in thermoelectric devices. (C) 2011 Elsevier Ltd. All rights reserved.