Direct Observation of the Epitaxial Growth of Bismuth Telluride Topological Insulators from One-Dimensional...

As extraordinary topological insulators, 2D bismuth telluride (Bi₂Te₃) nanosheets have been synthesized and controlled with a few-layer structure by a facile and fast solvothermal process. The detail-oriented growth evolution of 2D Bi₂Te₃ in an ethylene glycol reducing solution is discovered and recorded for direct observation of the liquid-solid interactions through the use of environmental SEM. At the initial synthesis stage, Te nanowires are rapidly synthesized and observed in solution. In the next stage, Bi nanoclusters slowly adhere to the Te nanowires and react to form hierarchical Te-Bi₂Te₃ nanostructured materials. Additionally, the Te nanowires shorten in-plane in an orderly manner, while the Bi₂Te₃ nanosheets exhibit directional out-of-plane epitaxial growth. In the last procedure, Bi₂Te₃ nanosheets with a clear hexagonal appearance can be largely obtained. Experiments performed under these rigorous conditions require careful consideration of the temperature, time, and alkaline environment for each reaction process. In addition, the yield of a wider and thinner Bi₂Te₃ nanosheet is synthesized by manipulating the crystal growth with an optimal alkaline concentration, which is found through statistical analysis of the AFM results. In the UV-Vis-NIR spectroscopy results, the main peak in the spectrum tends to redshift, while the other peak in the ultraviolet range decreases during Bi₂Te₃ nanosheet synthesis, facilitating a rapid understanding of the trends in the morphological evolution of the Bi₂Te₃ materials in solution. By rationalizing the above observations, we are the first to report the success of environmental SEM, HAADF-STEM, and UV-Vis-NIR spectroscopy for confirming the Bi₂Te₃ nanosheet formation mechanism and the physical properties in the solvent media. This research promotes the future optimization of promising Bi₂Te₃ nanomaterials that can be used in the fabrication of thermoelectric and topological components.