Applied Surface Science 256 (2010) 5783–5788 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Structural and electronic properties of H-passivated graphene A.Z. AlZahrani a,∗ , G.P. Srivastava b a Physics Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21589, Saudi Arabia b School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK article info Article history: Available online 29 March 2010 Keywords: Graphene Graphane Density functional theory Local density approximation Pseudopotential method Hydrogen passivation abstract The atomic and electronic structures of graphane (hydrogen-passivated graphene) are theoretically inves- tigated using the local density approximation (LDA) of the density functional theory (DFT) and the pseudopotential method. Our total energy calculations suggest that the chairlike configuration for graphane is more energetically stable than the boatlike and tablelike configurations by approximately 0.129 eV/cell and 0.655 eV/cell, respectively. Our calculations suggest that the LDA band gap of the chair- like structure is approximately 3.9 eV. The equilibrium geometry and the band structure of the chairlike conformer are investigated and compared with the available experimental and theoretical data. We fur- ther present total and partial charge density to reveal the orbital nature of the highest occupied and the lowest unoccupied states. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Graphene [1], a single hexagonal atomic sheet of carbon atoms from bulk graphite, has attracted immense interest due to its fas- cinating electronic properties [2,3]. The electronic structure of graphene is based on sp 2 -bonded carbons with ‘bonding’  and ‘anti-bonding’  ∗ degenerated states at the K edge of its hexag- onal Brillouin zone. Moreover, the linear band dispersion at the so-called Dirac point is considered as a special feature of graphene, leading to high mobility charge carriers. Very recently, Castro Neto et al. [4] have reviewed the basic electronic properties of graphene. These properties, along with others, provide potentially promising applications for carbon-based electronics and optical devices. Adsorption of molecules on graphene has been the subject of various theoretical [5–12] and experimental [13,14] investiga- tions. Wehling et al. [7] have presented first-principles studies of water adsorption on graphene and the influence of SiO 2 sub- strate. Their investigations suggested that graphene on the SiO 2 substrate is more sensitive to water adsorbates than perfect suspended graphene. Nakamura and co-workers [8,9] have inves- tigated the structural and electronic properties of the graphene sheet upon oxygen adsorption. First-principles calculations pre- dicted that the oxygen-adsorbed graphene shows the structural bistability between the epoxy group phase (oxygen atom joined by single bonds to two adjacent carbon atoms) and the ether group phase (two hydrocarbon groups linked by an oxygen atom). Their calculations suggested that the ether group structure is the ∗ Corresponding author. Tel.: +966 26952287. E-mail address: azalzahrani@kau.edu.sa (A.Z. AlZahrani). most energetically preferable for adsorption involving both sides of the sheet, while the one-side adsorption structure appears only as a meta-stable phase. They also found that a finite energy gap at the K point emerges and its magnitude increases as the ratio O/C increases. Further, Leenaerts et al. [10,11] have reported on the main charge transfer mechanisms upon adsorption of small molecules on graphene, such as NH 3 and NO 2 . They concluded that there are two main mechanisms for charge transfer when molecules adsorb on graphene. Small charge transfer takes place due to orbital hybridisation (orbital mixing) for all molecules. Large charge transfer takes place when the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the molecules lie close enough to the Dirac point. Recently, the hydrogen-passivated graphene (viz. graphane) has attracted great attention because of the resultant dramatical changes in graphene’s band gap [15–17]. These changes could open the gate for enormous technological and industrial applications for graphane, such as hydrogen storage and two dimensional nano- electronics. It is predicted that graphane is semiconductor with two possible configurations: a chairlike and boatlike. In the for- mer conformer the hydrogen atoms are alternatively attached to the carbon atoms on both sides of the plane. In the other con- former the hydrogen atoms are alternatively attached in pairs to the carbon atoms in both sides. Sofo et al. [15] have studied the adsorption of hydrogen atoms on both sides of the graphene plane in an alternating manner, leading to both the chairlike and boatlike configurations. Their total energy calculations suggested that the chairlike is more energetically preferable than the boatlike model. They also found that the energy gap, at the centre of the Brilloiun zone, of the graphene is opened by 3.5 eV for the chairlike and 3.7 eV for the boatlike conformer. Boukhvalov et al. [16] have also 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.03.088