Shuqi Zheng

Controlled synthesis of tellurium nanowires and nanotubes via a facile, efficient, and relatively green solution phase method

Single-crystal trigonal tellurium nanowires and nanotubes were synthesized using a facile, efficient, and relatively green solution phase method with ethylene glycol as solvent and an alternative reducing agent in the presence of NaOH. Large-scale production of slender nanowires and hollow nanotubes with average diameters of 72 and 240 nm, respectively, was achieved by increasing the temperature from 170 °C to 200 °C. Tellurium morphology from nanowires to nanotubes was also controlled by adjusting the NaOH dosage. Scanning electron micrographs show that low temperature or NaOH insufficiency promotes the formation of slender nanowires but counteracts the synthesis of tellurium nanotubes. Detailed reaction equations based on the NaOH dosage were obtained. Preferential growth orientation of [001] was observed in the nanowire and nanotube through high-resolution transmission electron microscopy. Further formation mechanisms dependent on time were systematically studied.

High-Yield Synthesis, Controllable Evolution, and Thermoelectric Properties of Te/Bi2Te3 Heterostructure Nanostrings

Te/Bi2Te3 heterostructure nanostrings composed of multiple hexagon Bi2Te3 nanosheets, which were strung together by Te nanowires, were rationally designed and synthesized via an in situ growth process. High-yield heterostructure products were obtained via the two-step solution phase method. The rhombohedral Bi2Te3 nanosheets and hexagonal phase Te nanowires were characterized using x-ray diffractometer patterns and high-resolution transmission electron microscopy images. Detailed scanning electron microscopy and transmission electron microscopy images revealed that the lengths of the nanostrings were approximately 3.6xa0μm, and the diameters of the Bi2Te3 nanosheets were approximately 290xa0nm. The results indicated that the dimensions and morphologies of the Te/Bi2Te3 heterostructure nanostrings can be controlled by regulating the dosage of Bi(NO3)3·5H2O from 0xa0mmol to 3xa0mmol, and the number of the Bi2Te3 nanosheets can be adjusted by controlling the concentration of N2H4·H2O. Exceedingly low thermal conductivities from 0.45xa0Wxa0m−1xa0K−1 to 0.49xa0Wxa0m−1xa0K−1 were demonstrated by the measurements of the thermoelectric properties at near-room temperature from 350xa0K to 500xa0K. The phonon scattering mechanisms were systematically analyzed using three-dimensional schematic structure models.