Abstract
We have investigated the structural stabilities and electronic properties for AA and the Bernal-stacked AB bilayer zigzag graphene nanoribbons (ZZGNRs) using first-principles calculations within density functional theory. The AB-stacked ZZGNR exhibits the spin-polarized state, while the AA-stacked ZZGNR has the nonmagnetic ground state, being more energetically stable than the AB-stacked one. For the AA-stacked ZZGNR, the interaction between the so-called edge states rather than the van der Waals (vdW) interaction plays an important role: the occupied up-spin and the unoccupied down-spin states at one end of ZZGNR interact with each other, and vice versa at the other end, forming the non-spin-polarized bonding and antibonding states at the zigzag edge. Thus, the structural stability for the AA-stacked ZZGNR is dominated by the trade-off between the edge–edge interaction and the vdW interaction of the basal plane of GNRs.
Highlights
Graphene, a two-dimensional (2D) sheet of sp2-bonded carbon atoms in a honeycomb arrangement, has attracted enormous attention[1] because of its extraordinary electronic[2,3] and thermal[4−6] properties
zigzag graphene nanoribbons (ZZGNRs) increases and approaches that of bilayer graphene, because the relative contribution of the edge−edge interaction with respect to the total interaction between graphene nanoribbons (GNRs) decreases with increasing N
The stabilities of the AA- and AA′-stacked ZZGNRs are dominated by the trade-off between the van der Waals (vdW) interaction of the basal plane of GNRs and the edge−edge interaction attributed to the edge-localized states
Summary
A two-dimensional (2D) sheet of sp2-bonded carbon atoms in a honeycomb arrangement, has attracted enormous attention[1] because of its extraordinary electronic[2,3] and thermal[4−6] properties. Graphene is a zero-gap semiconductor, and many attempts have been made to modulate the electronic properties with an external electric field[7−10] and heteroatoms[11−13] for future applications in carbon-based nanoelectronic devices. A fabrication of graphene nanoribbons (GNRs), has been thought as one of the methods for the modulation of electronic properties of graphene. GNRs have been realized experimentally,[14−20] over the past few decades, a considerable number of theoretical studies have been made on the remarkable structural and electronic properties of GNRs.[21−23] GNRs have two basic shapes with armchair and zigzag edges. It has been well known that the electronic properties of GNRs depend strongly on edge shapes. ZZGNRs are expected to be magnetic materials[28−30] and materials for spintronic devices.[31,32] Such peculiar electronic structures are attributed to the localized state near the zigzag edge, the socalled edge state consisting of nonbonding pz orbitals.[24−34]
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