Bi 2TeI is also a topological crystalline insulators (TCIs), for which the protecting symmetry are mirror planes 24. Stackings of these 2D TI layers result in a 3D WTI (weakly interacting TI). Each of these sandwich-like layer packages is a 2D TI with metallic edge states protected by time-inversion symmetry and a calculated bulk bandgap of 80 meV (ref. The crystal structure of Bi 2TeI is a stack of uncharged three atoms thick layers and puckered bismuth layers with the periodic sequence –– (Fig. This work focuses on the exfoliation of Bi 2TeI, which is an exceptional topological quantum material 19, 20 exhibiting coexisting topological surface states. LPE has the great advantage of being scalable and of producing freestanding flakes in a dispersion, which can then be processes with common techniques, such as spin-coating or printing. Instead of manual cleavage, liquid phase exfoliation (LPE) by sonication 16, 17, can be implemented to prepare thin sheets of TIs 18. However, both procedures are either hard to control or extremely time-consuming, and thus inefficient for production on larger scale. Even atomic force microscopy was used for the exfoliation of TI materials 15. Some review articles summarize the attempts to exfoliate layered TI materials with a simple micromechanical cleavage technique using adhesive tape 13, 14. It appears more attractive to use top–down methods, in which TI films are exfoliated from high quality crystals. The latter allows very good control, but is complicated and expensive, and thus can hardly be used in industrial processes. Common techniques include chemical and physical vapor deposition 9, 10 and molecular beam epitaxy 11, 12. The latter exhibit topologically nontrivial surface states only at particular surfaces (indicated by the invariants) and may be obtained from stacking 2D TIs along the out-of-plane direction.Īpplications in micro- or nanoelectronics require thin TI films of high quality, as well as a reasonable processing and scalability. A TI must be a bulk semiconductor with nontrivial \(\mathbb\) 2 classification and dimensionality, TIs may be classified in to 2D TIs (a quantum spin Hall state) and 3D strong and weak TIs (WTI). These two properties make TIs highly desirable materials for quantum computing and spintronics 4, 5 by virtue of the topology and symmetry of their band structure 1, 6. Their spin is locked orthogonal to their propagation direction, i.e., attaching a spin current to electrons traveling into a particular direction. Highly mobile electrons that are protected against backscattering by time-inversion symmetry and topology exist on the surface of TIs 1, 2, 3. Topological insulators (TIs) are a relatively new class of quantum materials, which are currently heavily investigated for their intriguing fundamental properties, as well as possible applications in future electronic and spintronic devices. By heat treatment and sonication in isopropyl alcohol and poly(vinylpyrrolidone), crystalline Bi 2TeI sheets with a thickness of ~50 nm were obtained and can therefore be considered for further processing toward microelectronic applications. ![]() ![]() We developed an effective, scalable protocol for LPE of freestanding nanoflakes from Bi 2TeI crystals. Bi 2TeI is a weak 3D TI, which leads to protected edge states at the side facets of a crystal, as well as a topological crystalline insulator, which is responsible for protected states at the top and bottom faces. A suitable approach is the liquid phase exfoliation (LPE) of TI crystals that have layered structures. For application, crystalline thin films are requested in sufficient quantity. Being bulk semiconductors, their nontrivial topology at the electronic bandgap enables dissipation-free charge and spin transport in protected metallic surface states. The emergence of topological insulators (TIs) raised high expectations for their application in quantum computers and spintronics.
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