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DFT comparison of structural and electronic properties of graphene and germanene: Monolayer and bilayer systems

Abstract:

Two-dimensional honeycomb systems such as graphene and graphene-related materials have attracted enormous technological interest due to the wide range of applications from composites to conductive coatings. Based on density functional calculations we present a comparison of structural and electronic properties of monolayer (and bilayer) graphene and germanene, particularly, germanene have been synthesized on MoS2 with the Dirac cone properties. Our results show that germanene prefers a buckled structural conformation, which is slight more stable respect to its planar conformation. The well-known structure of graphene is compared with the buckled and planar structures of germanene at level of local density approximation. Graphene and germanene, in monolayer pristine conformations, exhibit massless Dirac fermions close to the K point. However, in germanene the top valence and bottom conduction bands are found at lower energies respect to graphene corresponding bands. The Fermi velocity in germanene is around 30% lower compared to graphene. Bilayer graphene show an anisotropic Dirac cone, while in bilayer germanene a small band gap at K point of ∼0.05 eV is detected. Our results are found to be in agreement with previous theoretical reports, and these pretend to give a compressible description from fundamental point of view.