Energy Band Gap Modification of Graphene Deposited on a Multilayer Hexagonal Boron Nitride Substrate
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Energy Band Gap Modification of Graphene Deposited on a Multilayer Hexagonal Boron Nitride Substrate
Celal Yelgel1 and Gyaneshwar P. Srivastava1 1 School
of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, U.K.
ABSTRACT The equilibrium geometry and electronic structure of graphene deposited on a multilayer hexagonal boron nitride (h-BN) substrate has been investigated using the density functional and pseudopotential theories. We found that the energy band gap for the interface between a monolayer graphene (MLG) and a monolayer BN (MLBN) lies between 47 and 62 meV, depending on the relative orientations of the layers. In the most energetically stable configuration the binding energy is found to be approximately 40 meV per C atom. Slightly away from the Dirac point, the dispersion curve is linear, with the electron speed almost identical to that for isolated graphene. The dispersion relation becomes reasonably quadratic for the interface between MLG and 4-layer-BN, with a relative effective mass of 0.0047. While the MLG/MLBN superlattice is metallic, the thinnest armchair nanoribbon of MLG/MLBN interface is semiconducting with a gap of 1.84 eV. INTRODUCTION The energy band gap tuning in the zero-band gap graphene is considered very desirable for electronic devices. There are reports of band gap opening in graphene with hydrogenation [1], graphene-substrate interaction [2, 3] and by absorption of molecules [6]. Recent investigations have been demonstrated that a small band gap can be opened by depositing graphene on a four-layer hexagonal boron nitride (h-BN) substrate [3, 4, 5]. Using a chemical-solution-derived method, starting from single-crystalline h-BN, Han and co-workers successfully synthesised BN mono-atomic layer [7]. Alem et al. [8] have also achieved a successful ex-situ isolation of suspended single h-BN using a combination of mechanical exfoliation and reactive ion etching. An exciting development in graphene science is the successful fabrication of gated graphene layers on h-BN substrates [9, 10, 11]. Graphene/BN heterobilayers have also been grown on Ru(0001) substrate through chemical vapor deposition technique[12]. More recently, theoretical investigations of disorder-limited electrical conductivity of monolayer and bilayer graphene on h-BN substrate have been presented [13]. It is, therefore, timely and important to investigate modifications of the electronic properties of graphene deposited on a mono- and multi-layer h-BN substrate. In the present work, we have employed the plane wave pseudopotential method, within the density functional scheme, to investigate the equilibrium atomic geometry and electronic structure of graphene adsorbed on a h-BN substrate. We have shown that this system is a tiny-gap semiconductor for graphene on a monolayer h-BN. There is no significant difference in the band gap by increasing the number of h-BN layers. The importance of the interlayer interaction and stacking patterns of graphene/BN is clearly explained for band gap tuning in graphene. We have
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