Interaction of Silicene and Germanene with Non-Metallic Substrates

Abstract

Silicene, the silicon counterpart of graphene, has recently attracted a lot of attention as an alternative 2D materials to graphene for nanoelectronic devices. So far, the likely existence of silicene on Ag(111) surfaces has recently been reported, by combining experimental and first-principles simulations (1,2). The growth of silicene has also been reported on other metallic substrates, like (0001) ZrB2 (3) and (111)Ir (4).However, the characterization of the electronic and electrical properties of silicene on metallic substrates is very challenging, since these properties can be largely dominated by the substrates. In addition, potential applications of silicene in nanoelectronic devices will also require its growth on non-metallic substrates.We report here on the theoretical study of the interaction of silicene and germanene (2D Ge counterpart of graphene) with non-metallic substrates, using first-principles simulations. We first studied the weak (van der Waals) interaction between silicene or germanene with metal chalcogenide substrates (5,6). The buckling of the silicene/germanene layer is found to be correlated to the in-plane lattice mismatch between the free-standing silicene or germanene layer and the metal dichalcogenide layer. Highly buckled silicene (e.g. on MoS2) is predicted to be metallic, while low buckled silicene (on e.g. GaSe) is predicted to have Dirac cones at the K-points.We next investigated the interaction between silicene or germanene with (0001) ZnS or (0001) ZnSe surfaces (7,8). In this case, part of the Si (Ge) atoms form covalent bonds with the substrate, leading to the opening of a gap in their energy band structure. Very interestingly, the value of this energy gap can be controlled by an out-of-plane electric field, leading to field-driven semiconductor to metal transitions at these interfaces – which could be very promising for the potential use of silicene and germanene in field effect transistors.Part of this work has been financially supported by the European Project “2D Nanolattices” within the Future and Emerging Technologies (FET) program of the European Commission, under FET-grant number 270749, as well as the KU Leuven Research Funds, project GOA/13/011.