Modulation of Dirac points and band-gaps in graphene via periodic fullerene adsorption

The structural, energetic and electronic properties of periodic graphene nanobud (PGNB) with small-diameter fullerenes (C20, C34, C42, and C60) adsorbed have been investigated by first-principles plane wave method. The bond-to-ring cycloaddition is found to be energetically most stable among various configurations and the minimum energy paths of different-sized fullerenes attaching to graphene indicate that smaller fullerene shows lower energy barriers due to its larger surface curvature. For perfectly ordered adsorption, band structures analyses by both density functional theory (DFT) and tight binding (TB) methods show that the Dirac cone of graphene can be generally preserved despite the sp2 to sp3 bond hybridization change for selected carbon atoms in graphene sheet. However, the position of the Dirac points inside the Brillouin zone has a shift from the hexagonal corner and can be effectively modulated by changing the fullerenes’ concentration. For practical applications, we show that a considerable band gap (∼0.35 eV) can be opened by inducing randomness in the orientation of the fullerene adsorption and an effective order parameter is identified that correlates well with the magnitude of the band gap opening.