Stability, edge passivation effect, electronic and transport properties of POPGraphene nanoribbons.

POPGraphene is a theoretically predicted 2D carbon allotrope which presents a unit cell with 5-8-5 carbon rings. It presents metallic behavior and has a low diffusion energy barrier, which suggests applications as an anode material in batteries. Motivated by the fact that nanoribbons present different properties to their 2D counterparts, in this work two kinds of POPGraphene nanoribbons were proposed, with (POPGNRH) and without (POPGNR) hydrogen edge passivation, and their electronic and transport properties were investigated, in order to characterize them and verify the influence of hydrogen edge passivation. Density functional theory was employed for structure optimization and combined with the Non-Equilibrium Green's Function to obtain the electronic transport properties. We predict that both nanoribbons are stable and can be obtained experimentally. Furthermore, hydrogen passivation reduces the bands around the Fermi level and shift them toward the region of negative energies, which can be seen from the presence of NDR in the transport properties of the hydrogenated device. The electronic transport properties suggest that POPGNR shows Field effect transistor behavior in the analyzed range and POPGNRH shows the same behavior, but in the range of -0.70 V to 0.70 V. Also, due to the presence of NDR, POPGNRH presents Resonant Tunneling Diode behavior in the range of ±0.70 V to ±1.00 V. Therefore, the results suggest applications for both nanoribbons in the field of molecular electronics.

Molecular junction by tunneling in 1D and quasi-1D systems.

We have investigated electron tunneling through two one-dimensional (1D) molecular junctions based on first-principles simulations using the density functional theory combined with the non-equilibrium Green's functions methodology. The first junction, composed of left and right carbyne wire electrodes with a sodium atom in between, is atomically thin. The second one is quasi-one-dimensional (quasi-1D) and consists of two single-wall carbon nanotube electrodes, closed on the tips and again a sodium atom in the scattering region. Although the bridging atom bonds weakly to the electrodes in both systems, it strongly affects the electronic transport properties, such as electron transmission, current-voltage relation, differential conductance, density of states and eigenchannels. This is demonstrated by comparing with the results obtained from the corresponding systems for both the 1D and the quasi-1D junctions in the absence of the central sodium atom. The revealed transport properties are sensitive to the molecular geometry. This helps future molecular electronic device design.