Structural characterization of pure and magnetic-doped Bi₂Se₃ nanoparticles

Abstract

Nanoparticles made of “pure” and Ni-“doped” Bi₂Se₃ prototype topological insulators were successfully prepared using the chemical hot-injection method. In both cases, the reaction is kept for a relatively long period, where samples are taken from the reaction flask at successive time steps. High resolution transmission electron microscopy revealed significant morphology differences for the pure and Ni-doped samples at all reaction times. The pure Bi₂Se₃ samples exhibit spiral-like shapes turning into large sheets with wires-like features at very long reaction times, whereas the Ni-doped samples evolve, with the reaction time, from highly spherical, partially elongated, and finally well-defined nanorods. In addition, Co-doped Bi₂Se₃ samples, prepared under the same conditions, exhibit large non-uniform flakes at long reaction time. The crystallinity of all pure and magnetic-doped samples was ensured from electron diffraction, and quantitatively obtained from X-ray diffraction measurements. The latter justified the same rhombohedral crystal structure for both the pure and magnetically doped samples, and the absence of other phases. The energy dispersive X-ray spectroscopy was used to quantify the present elements, where the Bi, Se, Ni, and Co peaks were identified. The present study provides a way for tuning the nanoparticles size/morphology of Bi₂Se₃ and related-compounds by the slight addition of magnetic dopants, which subsequently allows the engineering of various Bi₂Se₃-based nanoarchitectures.