Solution-Based Iron Doping of Solvothermally Grown Hexagonal Bismuth Telluride Nanoplates

Theoretical studies have shown that impurity addition in the form of magnetic or non-magnetic nanoparticles, to a topological material such as Bismuth Telluride (Bi₂Te₃), is an interesting route to study the correlation of symmetry-breaking and coherent spin transport. Moreover, a solution-based synthesis method to form the Bi₂Te₃crystals and dope them can expand the parameter space for exploring dopant-host interactions. In this work, we study the distribution and chemical nature of iron nanoparticles that electronically dope single-crystal Bi₂Te₃ nanoplates. Using a solvothermal method, Bi₂Te₃ nanoplates are reacted with iron salts (FeCl₂) to promote the formation of metallic iron interfaces. The presence of a reducing agent (L(+)-ascorbic acid) along with FeCl₂ results in a homogeneous dispersion of iron across the Bi₂Te₃nanoplate surface. In comparison, non-reduced iron doping results in the growth of iron/iron oxide nanoparticles on the nanoplate edges. Counterintuitive to elemental analysis which showed a lower iron atomic percent in the reduced iron-doped Bi₂Te₃sample, transport measurements on thin films indicate a higher metallic iron concentration, which oxidizes gradually upon ambient exposure. In comparison, non-reduced iron-doped Bi₂Te₃thin films exhibited a lower conductivity to begin with and faster air degradation, suggesting iron oxide growth during the doping process itself. The thermoelectric power factor also expresses the modifications from oxidation providing an indirect probe of the dopant’s influence on the host Bi₂Te₃’s electronic properties. Interestingly, in the oxidized state, magnetic force microscopy images showed a distinct difference in the formation of magnetic phases for non-reduced and reduced iron. We observed that oxidation post-doping does not form magnetic phases, whereas oxidation during the doping process is suitable for obtaining magnetically doped Bi₂Te₃ nanoplates. Our results reveal a unique synthesis approach to obtain magnetic/non-magnetic impurity doping of the topologically relevant Bi₂Te₃ using a solution-based route.