Electronic structure and transport properties of sulfur-passivated graphene nanoribbons

Abstract

Electronic structure of newly synthesized sulfur-terminated graphene nanoribbons (S-GNRs) has been presented from the calculations based on ab initio density functional theory and non-equilibrium Green's function (NEGF) method. The calculations reveal that zigzag-edged S-GNRs (Z-S-GNRs) are thermodynamically more stable than armchair edged S-GNRs (A-S-GNRs). It has been observed that the band gap of S-GNRs depends both on ribbon width and edge symmetry. The calculated band gap, in case of A-S-GNRs, is also supported by the presence of threshold bias in the I-V characteristics obtained from NEGF formalism. It is shown that all A-S-GNRs having width up to 1.50 nm are semiconducting but the Z-S-GNRs of similar widths are metallic. For A-S-GNRs, the width dependent band-gap hierarchy follows three different trends which seem to be different from that of H-passivated GNRs. The band-gaps for A-S-GNRs arise from both quantum confinement as well as crucial effect of edge, where the passivating S atoms play an important role. Band-gap may be further tuned by introducing other passivating atoms like Se and Te. The semiconducting ribbons, when attached to doped metallic ribbons, show negative differential resistance phenomena as indicated by the observed I-V characteristics.