Structural and Electronic Properties of Graphene upon Molecular Adsorption: DFT Comparative Analysis

Since its discovery in 2004 (Nobel prize in 2010), graphene -a single sheet of carbon atoms forming the thinnest free standing material to datehas attracted enormous interest due to its potentially tunable and exotic structural and electronic properties (Castro Neto et al., 2009; Geim & Novolselov, 2007; Katsnelson et al., 2006, 2007; Novoselov et al., 2004, 2007; Ohta et al., 2006; Y. Zhang et al., 2005). The pristine graphene is characterized as a zerogap semiconductor with bonding and antibonding * bands touch in a single point at the Fermi level (EF) at the corner of the Brillouin zone, and close to this so-called Dirac point the bands display a linear dispersion, leading to extremely high charge carriers mobility at room temperature of approximately 15,000 cm2/V.s (Geim & Novolselov, 2007) which is significantly higher than that of the widely-used semiconductor, namely silicon (Si), of approximately 1400 cm2/V.s. Like carbon nanotubes, measurements (Lee et al., 2008) have shown that graphene is extremely strong and rigid compared to Si-based materials. These incredibly fascinating properties alongside the high thermal conductivity suggest that graphene is an excellent candidate for the applications in the circuits beyond the conventional complementary metal-oxide semiconductor technology and many other potential applications. Moreover and recently, the possibility of using graphene as a highly-sensitive gas sensor has been reported as the good sensor properties of carbon nanotubes are already known. It was shown that the increase of the concentration of graphene charge carrier induced by adsorbed gas molecules can be used to make highly sensitive sensors. These highly-sensitive properties of graphene can be attributed to the fact that graphene is a low-dimensional structure with only a surface but no volume which increase the chemical reaction of adsorbates and the surface atoms. Additionally, the high conductivity of graphene even in low charge density is another reason for being a highly-sensitive sensor. Having established the importance of pristine graphene in many potential applications, the adsorption of single atoms (Chan et al., 2008; Farjam & Rafii-Tabar, 2009; Han et al., 2007; Hao et al., 2006; Li et al., 2008; Mao et al., 2008; Medeiros, 2010; Yang, 2009) and molecules (Duplock et al., 2004; Elias et al., 2009; Giannozzi et al., 2003; Ito et al., 2008; Leenaerts et al., 2008, 2009; Nakamura et al., 2008; Novoselov et al., 2004; Pinto et al., 2009; Sanyal et al.,