Ngoc Thanh Thuy Tran

π-Bonding-dominated energy gaps in graphene oxide

The chemical bonding in graphene oxide with oxygen concentrations from 50% to 1% is investigated using first-principle calculations. The energy gaps are mainly determined by the competition of the orbital hybridizations in the C–C, O–O, and C–O bonds. They are very sensitive to changes in the oxygen concentration and distribution. Five types of π-bonding exist on moving from full to vanishing adsorption, namely complete termination, partial suppression, 1D bonding, deformed planar bonding, and the well-behaved type. They can account for the finite and gapless characteristics, corresponding to O-concentrations of >25% and <3%, respectively. The feature-rich chemical bonding dominates the band structures and density of states, leading to diverse electronic properties.

Chemical bonding-induced rich electronic properties of oxygen adsorbed few-layer graphenes.

The electronic properties of graphene oxides enriched by strong chemical bonding are investigated using first-principles calculations. They are very sensitive to the changes in the number of graphene layers, stacking configuration, and distribution of oxygen. The feature-rich electronic structures exhibit destruction or distortion of the Dirac cone, opening of a band gap, anisotropic energy dispersions, O- and (C,O)-dominated energy dispersions, and extra critical points. All of the few-layer graphene oxides are semi-metals except for the semiconducting monolayer ones. For the former, the distorted Dirac-cone structures and the O-dominated energy bands near the Fermi level are revealed simultaneously. The orbital-projected density of states (DOS) has many special structures mainly coming from a composite energy band, the parabolic and partially flat ones. The DOS and spatial charge distributions clearly indicate the critical orbital hybridizations in O-O, C-O and C-C bonds, being responsible for the diversified properties.

Adatom doping-enriched geometric and electronic properties of pristine graphene: a method to modify the band gap

We have investigated the way in which the concentration and distribution of adatoms affect the geometric and electronic properties of graphene. Our calculations were based on the use of first principle under the density functional theory which reveal various types of π-bonding. The energy band structure of this doped graphene material may be explored experimentally by employing angle-resolved photo-emission spectroscopy (ARPES) for electronic band structure measurements and scanning tunneling spectroscopy (STS) for the density-of-states (DOS) both of which have been calculated and reported in this paper. Our calculations show that such adatom doping is responsible for the destruction or appearance of the Dirac-cone structure.

Coverage-dependent essential properties of halogenated graphene: A DFT study

The significant halogenation effects on the essential properties of graphene are investigated by the first-principles method. The geometric structures, electronic properties, and magnetic configurations are greatly diversified under the various halogen adsorptions. Fluorination, with the strong multi-orbital chemical bondings, can create the buckled graphene structure, while the other halogenations do not change the planar s bonding in the presence of single-orbital hybridization. Electronic structures consist of the carbon-, adatom- and (carbon, adatom)-dominated energy bands. All halogenated graphenes belong to holedoped metals except that fluorinated systems are middle-gap semiconductors at sufficiently high concentration. Moreover, the metallic ferromagnetism is revealed in certain adatom distributions. The unusual hybridization-induced features are clearly evidenced in many van Hove singularities of density of states. The structure- and adatom-enriched essential properties are compared with the measured results, and potential applications are also discussed.