Electronic Structures and Optical Properties of Partially and Fully Fluorinated Graphene

In this Letter, we study the electronic structures and optical properties of partially and fully fluorinated graphene by a combination of ab initio $G_0{W}_0$ calculations and large-scale multiorbital tight-binding simulations. We find that, for partially fluorinated graphene, the appearance of paired fluorine atoms is more favorable than unpaired atoms. We also show that different types of structural disorder, such as carbon vacancies, fluorine vacancies, fluorine vacancy clusters and fluorine armchair and zigzag clusters, will introduce different types of midgap states and extra excitations within the optical gap. Furthermore, we argue that the local formation of $s{p}^3$ bonds upon fluorination can be distinguished from other disorder inducing mechanisms which do not destroy the $s{p}^2$ hybrid orbitals by measuring the polarization rotation of passing polarized light.

Figure 1

In-plane (a),(b) and out-of-plane (c),(d) optical conductivity of partially and fully fluorinated graphene with different concentration of randomly distributed unpaired or paired fluorine adatoms. The density of states of graphene and ${\mathrm{CF}}_{0.1}$ are plotted as inserts of panels (a),(b) and reveal midgap states in the unpaired case (see the sharp peak close to the neutrality point).

Figure 2

Left column: Atomic structure with different types of structural disorder. The red dots indicate fluorine adatoms. Middle and right columns: density of states and optical conductivity of fully or highly fluorinated graphene with different types of structural disorder. From top to bottom: Fully or highly fluorinated graphene with (a) randomly distributed carbon vacancies, (b) randomly distributed fluorine vacancies, (c) randomly distributed fluorine vacancy clusters, (d) randomly distributed fluorine armchair clusters, (e) randomly distributed fluorine zigzag clusters. For several types of disorder, characteristic defect states and features in optical spectra can be identified.

Figure 3

Comparison of optical conductivity with and without intra-atomic dipole contribution in graphene (top) and fluorographene (bottom).