Facile synthesis of ultra-small Bi2Te3 nanoparticles, nanorods and nanoplates and their morphology-dependent Raman spectroscopy

a r t i c l e i n f o Keywords: Bi2Te3 Nanorod Nanoparticle Nanoplate Raman TEM High-crystalline 0D, 1D and 2D ultra-small Bi 2 Te 3 nanocrystals were synthesized using the pyrolysis of organ-ometallic compound method. The Bi 2 Te 3 nanocrystals was studied with transmission electron microscopy (TEM). Samples synthesized at 35 °C possessed a dominant morphology of 0D nanoparticles or 1D nanorods, while samples synthesized at temperatures higher than 75 °C possessed a dominant morphology of 2D nanoplates. Phonon vibrations were investigated by Raman spectroscopy. The 2D nanoplates showed similar Raman features as few-quintuple-thick Bi 2 Te 3 layers, while the 0D and 1D nanostructures showed a blue-shifted A 1g 2 mode and a much stronger A 1u mode. This is the first report regarding the morphology effect on the Raman-active phonon modes of Bi 2 Te 3 nanocrystals. Bismuth telluride based alloys have received extensive attention by virtue of their excellent TE performance at room temperature. Bulk Bi 2 Te 3-based alloys possess a ZT value close to 1 [1]. However, in order for TE power generation to become competitive to other power generation approaches, a ZT value of 4 is required [2]. Theoretical studies showed that making bulk TE materials into nanostructures could enhance their performance by decreasing their phonon thermal conductivity. Hicks et al. showed that the ZT value of Bi 2 Te 3 quantum well might be 9 times higher than the bulk value [3] and the ZT value of 1D Bi 2 Te 3 nanowire could be increased to ~ 14 from the bulk value [4]. Despite the progress in the synthesis of Bi 2 Te 3 nanocrystals [5–8], the synthesis of pure-phase Bi 2 Te 3 nanoparticles smaller than 10 nm still remains a challenge due to the high reactivity between bismuth and tellurium salts. To summarize, Bi 2 Te 3 nanoparticles can be synthesized via methods like co-precipitation [9], reverse micelle [10], micro-emulsion [11], reduction of metal-organo complexes [12], and hydrothermal (solvothermal) method [8]. Due to the application of high pressure, hydrothermal (solvothermal) approaches normally result in oversized Bi 2 Te 3 nanocrystals [8]. Purkayastha et al. [11] developed a micro-emulsion method to synthesize Bi 2 Te 3 nanoparticles of 5 nm, however the XRD results showed the existence of sulfur-related impurities. Scheele et al. [12] used a two-step reduction method to produce nanoparticles of 7 nm, but there …