Solution-based iron doping of solvothermally grown 2D hexagonal bismuth telluride

Abstract

In this work, we examine the formation of iron-based magnetic domains on two-dimensional (2D) single-crystal bismuth telluride plates. Using solvothermal chemical methods, 2D bismuth telluride (Bi2Te3) single crystalline nanoplates were reacted with iron salts (FeCl2) to achieve electrical doping. The use of a reducing agent [L(+)-ascorbic acid] along with FeCl2 resulted in homogeneous dispersion of iron across the crystal, whereas non-reduced iron doping achieved edge growth of iron/iron oxide nanoparticles. High-resolution analytical electron microscopy was used to examine the iron nanoparticle accumulation and morphology at nanoplate edges for non-reduced materials and iron dispersions within the crystals in the case of reduction. Our analysis revealed little variation in the atomic uptake of iron in any form over a range of solution-dopant concentrations. However, structural analysis and transport measurements clearly indicate the tendency of the dopant nanoparticles to oxidize quickly. The Seebeck coefficient and power factor also express modifications with exposure to oxidation, providing an indirect probe of the dopant modification to the host Bi2Te3’s electronic properties. Importantly, however, magnetic force microscopy images show a distinct difference in the formation of magnetic phases with and without the use of reducing agents during iron doping. This suggests that oxidation post-doping does not form magnetic phases, whereas oxidation during the doping process is suitable for obtaining magnetically doped Bi2Te3 nanocrystals.