Silicene, germanene and stanene are part of a monoelemental class of two-dimensional (2D) crystals termed 2D-Xenes (X = Si, Ge, Sn and so on) which, together with their ligand-functionalized derivatives referred to as Xanes, are comprised of group IVA atoms arranged in a honeycomb lattice — similar to graphene but with varying degrees of buckling. Their electronic structure ranges from trivial insulators, to semiconductors with tunable gaps, to semi-metallic, depending on the substrate, chemical functionalization and strain. More than a dozen different topological insulator states are predicted to emerge, including the quantum spin Hall state at room temperature, which, if realized, would enable new classes of nanoelectronic and spintronic devices, such as the topological field-effect transistor. The electronic structure can be tuned, for example, by changing the group IVA element, the degree of spin–orbit coupling, the functionalization chemistry or the substrate, making the 2D-Xene systems promising multifunctional 2D materials for nanotechnology. This Perspective highlights the current state of the art and future opportunities in the manipulation and stability of these materials, their functions and applications, and novel device concepts.
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We thank C. Grazianetti, E. Cinquanta, L. Tao, M. Fanciulli, V.V. Afanas'ev, A. Stesmans, W. Vandenberghe, M. Fischetti, A. Dimoulas, D. Tsoutsou, C. Pirri and M. Ezawa for fruitful discussions. We also thank J. Wozniak of UT-Austin TACC Center for the renderings of Fig. 3. A.M. is partially supported by the National Research Council of Italy (CNR) under the joint lab project 'SFET' (2014 call). J.G. acknowledges partial support from the Center for Emergent Materials: an NSF MRSEC under award number DMR-1420451, partial support from NSF EFRI-1433467, and the Camille and Henry Dreyfus Foundation. M.H acknowledges financial support from the KU Leuven Research Funds, project GOA/13/011. A.M. and M.H. also acknowledge partial financial support from the EU-FP7 FET-Open grant no. 270749 ('2D-Nanolattices' project). Y.X. acknowledges support from Tsinghua University Initiative Scientific Research Program and the National Thousand-Young-Talents Program. S.C.Z. is supported by the Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under contract DE-AC02-76SF00515 and by FAME, one of six centres of STARnet, a Semiconductor Research Corporation programme sponsored by MARCO and DARPA. D.A acknowledges support from the Army Research Office (ARO), the Presidential Early Career Award for Engineers and Scientists (PECASE), and the Gordon and Betty Moore Foundation.
The authors declare no competing financial interests.
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Molle, A., Goldberger, J., Houssa, M. et al. Buckled two-dimensional Xene sheets. Nature Mater 16, 163–169 (2017). https://doi.org/10.1038/nmat4802
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