Topochemische Pseudomorphose eines Chlorids in ein Bismutid

Freestanding Nanolayers of a Wide-Gap Topological Insulator through Liquid-Phase Exfoliation

The layered salt Bi14 Rh3 I9 is a weak three-dimensional (3D) topological insulator (TI), that is, a stack of two-dimensional (2D) TIs. It has a wide non-trivial band gap of 210 meV, which is generated by strong spin-orbit coupling, and possesses protected electronic edge-states. In the structure, charged layers of∞ 2 [ (Bi4 Rh)3 I]2+ honeycombs and∞ 1 [ Bi2 I8 ]2- chains alternate. The non-trivial topology of Bi14 Rh3 I9 is an inherent property of the 2D intermetallic fragment. Here, the exfoliation of Bi14 Rh3 I9 was performed using two different chemical approaches: (a) through a reaction with n-butyllithium and poly(vinylpyrrolidone), (b) through a reaction with betaine in dimethylformamide at 55 °C. The former yielded few-layer sheets of the new compound Bi12 Rh3 I, while the latter led to crystalline sheets of Bi14 Rh3 I9 with a thickness down to 5 nm and edge-lengths up to several ten microns. X-ray diffraction and electron microscopy proved that the structure of Bi14 Rh3 I9 remained intact. Thus, it was assumed that the particles are still TIs. Dispersions of these flakes now allow for next steps towards the envisioned applications in nanoelectronics, such as the study of quantum coherence in deposited films, the combination with superconducting particles or films for the generation of Majorana fermions, or studies on their behavior under the influence of magnetic or electric fields or in contact with various materials occurring in devices. The method presented generally allows to exfoliate layers with high specific charges and thus the use of layered starting materials beyond van der Waals crystals.

The Weak 3D Topological Insulator Bi12 Rh3 Sn3 I9

Topological insulators (TIs) gained high interest due to their protected electronic surface states that allow dissipation-free electron and information transport. In consequence, TIs are recommended as materials for spintronics and quantum computing. Yet, the number of well-characterized TIs is rather limited. To contribute to this field of research, we focused on new bismuth-based subiodides and recently succeeded in synthesizing a new compound Bi₁₂ Rh₃ Sn₃ I₉ , which is structurally closely related to Bi₁₄ Rh₃ I₉ - a stable, layered material. In fact, Bi₁₄ Rh₃ I₉ is the first experimentally supported weak 3D TI. Both structures are composed of well-defined intermetallic layers of _∞ ² [(Bi₄ Rh)₃ I]²⁺ with topologically protected electronic edge-states. The fundamental difference between Bi₁₄ Rh₃ I₉ and Bi₁₂ Rh₃ Sn₃ I₉ lies in the composition and the arrangement of the anionic spacer. While the intermetallic 2D TI layers in Bi₁₄ Rh₃ I₉ are isolated by _∞ ¹ [Bi₂ I₈ ]^2- chains, the isoelectronic substitution of bismuth(III) with tin(II) leads to _∞ ² [Sn₃ I₈ ]^2- layers as anionic spacers. First transport experiments support the 2D character of this material class and revealed metallic conductivity.