Topotactic synthesis of the overlooked multilayer silicene intercalation compound SrSi₂

Abstract

Silicene, a 2D honeycomb lattice of Si atoms similar to graphene, is expected to be a platform for nanoelectronics and home to novel quantum phenomena. Unlike graphene, free-standing silicene is notoriously difficult to stabilize, while strong hybridization of silicene with substrates destroys its desirable properties. On the other hand, Dirac cones of silicene are effectively realized in a bulk - stoichiometric ionic multilayer silicene intercalation compound CaSi2. Besides, a number of new 2D silicene-based materials are synthesized employing CaSi2 as a precursor. However, the rather complex atomic structure of CaSi2 and fresh opportunities of physical and chemical breakthroughs drive the search for alternative compounds with silicene networks. Here, a new polymorph of SrSi2 is synthesized, enjoying both the structure of intercalated multilayer silicene and the simplest possible stacking of silicene sheets. The MBE-quality synthesis accomplished on Si(001) and Si(111) surfaces leads to epitaxial films of SrSi2 with orientation controlled by the substrate, as revealed by XRD, RHEED and electron microscopy studies. The structural SrSi2/Si relation is mirrored in the transport properties of the films.

Engineering of Magnetically Intercalated Silicene Compound: An Overlooked Polymorph of EuSi2

“…In our case, the obvious difficulty is that the substrate (Si) is also a reactant. When synthesis of Sr‐intercalated multilayer silicene is attempted in such a manner, the backbone of bulk Si provides the required stabilization—the layered structure prevails over the ground‐state cubic SrSi 2 for the growths on both Si(111) and Si(001). Unfortunately, the same approach fails for europium—molecular beam epitaxy (MBE) reactions of Eu with Si(111) and Si(001) produce epitaxial films of the stable tetragonal polymorph of EuSi 2 .…”

“…Two different templates of trigonal SrSi 2 on Si are available for the growth of EuSi 2 . One is single‐crystalline SrSi 2 epitaxially grown on Si(111) (without any stabilizing layers), with silicene layers parallel to the surface of the film.…”

“…A thin (9 nm) film of SrSi 2 is grown at 500 °C by directing a beam of Sr atoms (10 −8 Torr) at the film surface following the procedure described in Ref. . The structure of the grown Sr‐intercalated multilayer silicene compound is confirmed in situ by the characteristic image of RHEED ( Figure a).…”

“…Therefore, nontrivial synthetic routes for engineering alternatives to CaSi 2 should be devised. Quite recently we succeeded in the synthesis of Sr‐intercalated multilayer silicene—a novel polymorph of SrSi 2 . Its synthesis is achieved by stabilizing the structure with the silicon lattice.…”

“…In contrast to CaSi 2 the stacking of layers in SrSi 2 is regular (… AA …). It is remarkable that the orientation of silicene layers in the thin films of SrSi 2 on Si is determined by the orientation of the Si surface …”