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Density functional theory investigations of graphene-based heterostructures
Ebnonnasir, Abbas
Ebnonnasir, Abbas
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2013
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Abstract
Graphene, a two-dimensional single crystal of carbon atoms arranged in a honeycomb lattice, is attractive for applications in nanoelectromechanical devices; in high-performance, low-power electronics, and as transparent electrodes. The present study employs Density Functional Theory (DFT) to identify the atomic and electronic structure of graphene (Gr) on three different types of substrates: transition metals (nickel, palladium), insulators (hBN) and semiconductors (MoS2). Our DFT calculations show that graphene layer on Ni(111) and Ni(110) becomes metallic owing to large binding energies and strong hybridization between nickel and carbon bands. Furthermore, in Gr/Gr/palladium systems, we find that the electrostatic dipoles at the Gr/palladium and Gr/Gr interfaces are oppositely oriented. This leads to a work function of bilayer graphene domains on palladium (111) higher than that of monolayer graphene; the strengths of these dipoles are sensitive to the relative orientation between the two graphene layers and between the graphene and palladium (111). Additionally, the binding energy of graphene on palladium (111) depends on its orientation. We elucidate the physical origin of the effect of growing graphene on hBN/Ni(111) on the binding of hBN to a Ni(111) substrate, and on the electronic properties of hBN. We find that hBN/Ni has two configurational minima, one chemisorbed and one physisorbed, whose properties are not altered when graphene is placed atop hBN. However, a switch from chemisorbed to physisorbed hBN on Ni can occur due to the processing conditions during graphene growth; this switch is solely responsible for changing the hBN layer from metallic to insulating, and not the interactions with graphene. Finally, we find that the relative orientation between graphene and MoS2 layers affects the value and the nature of the bandgap of MoS2, while keeping the electronic structure of graphene unaltered. This relative orientation does not affect the binding energy or the distance between graphene and MoS2 layers. However, it changes the registry between the two layers, which strongly influences the value and type of the bandgap in MoS2.
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