Role of 3D-paired pentagon–heptagon defects in electronic and transport properties of zigzag graphene nanoribbons

Abstract

Electronic and transport properties of 11 zigzag graphene nanoribbons (11-z-GNRs) with two types of 3D-paired pentagon–heptagon defects (3D-PPHDs) are studied using density functional theory combined with non-equilibrium Green’s function method. The C ad-dimers that have been introduced to z-GNRs to form these 3D-PPHDs have induced local strains forcing the C-bonds in the ad-dimers to hybridize in sp3-like rather than sp2-like orbitals. Such transformations that cause extra electrons to accumulate around the 3D-PPHDs are responsible for the variations in the electronic and transport properties of the defected z-GNRs. Density of states (DOS) for 11-z-GNRs containing either type of 3D-PPHDs, compared with that of the pristine 11-z-GNR, exhibits a peak at a particular energy level below the Fermi level, within its first plateau. Each peak, corresponding to a dip in the related zero-bias conductance profile, is attributed to electrons trapped in the localized states around the same energy level. The current–voltage (I–V) characteristics are almost linear for 11-z-GNR defected by either type of 3D-PPHD. Presence of a 3D-PPHD, made by addition of a single C ad-dimer, above an 11-z-GNR super-cell decreases its average conductance by 10.7 %, while a 3D-PPHD made by addition of two C ad-dimers to the opposite sides of the same 11-z-GNR super-cell decreases its conductance by 23 %.