Synthesis and characterization of high-purity, single phase hexagonal Bi2Te3 nanostructures

Abstract

In order to synthesize defect free, highly crystalline single phase nanostructured bismuth chalcogenides, we have investigated the effects of several reaction conditions including, solvents, temperatures, reaction time, and reducing agents. A small variation in the reaction method resulted in Bi₂Te₃ with different morphologies, ranging from nanosize particles, rods, platelets, and tubes to nanosheets. The materials were characterized by powder X-ray crystallography, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, and four-probe current (I)–voltage (V) analysis. An optimized reaction condition allowed the synthesis of single-phase, impurity-free hexagonal nanoplates with size varying between 50 nm and 500 nm and thickness varying between 45 nm and 55 nm in a reproducible manner. The Raman spectra of the optimized hexagonal plates and sheets showed infra red (IR)-active modes around 118 cm⁻¹ resulting from symmetry breaking, a characteristic feature of nanostructured Bi₂Te₃. Additional peaks at 94 cm⁻¹ in the nanosheets, resulting from the surface phonon mode further confirmed the ultrathin Bi₂Te₃ structures. The I–V measurements on the optimized surface showed an n-type semiconducting behavior. The surface current measured as a function of applied voltage is two orders of magnitude higher than that across the stacked pellet in ambient conditions and much higher compared to previously published data on few quintuplet-thick Bi₂Te₃ nanofilms. The highlights of this study are the optimal solvothermic reaction conditions and their impact on obtaining defect free, highly crystalline single phase bismuth chalcogenides.