Isomeric effects tuning the electron transport in carotenoid derivatives: from ohmic to rectifier behavior

Electronic and transport properties of new carbon nanoribbons with 5-8-5 carbon rings: tuning stability by the edge shape effect

We predicted the existence of five carbon nanoribbons based on POPGraphene, by first-principles calculations. We investigated the role of the shape of the edges in stability, structural, electronic, and transport properties. Density functional theory (DFT) was implemented to relax the unit cell nanoribbons, and DFT combined with non-equilibrium Greens functions was used to obtain the transport properties of molecular devices. Our results strongly suggest that all nanoribbons are stable, and can be feasibly obtained through experiment. Furthermore, the edge termination with pentarings is an important factor in the stability of nanoribbons. The electronic properties show that the three zigzag nanoribbons have a metallic behavior and the two armchair ones are semiconductors, but with a very tiny indirect bandgap of 0.053 eV and 0.050 eV. The transport properties show that the presence of partially filled steep bands crossing deeper into the Fermi level triggers high conductivity in molecular devices and the presence of flat bands decreases the device conductivity. The presence of sub-bandgap regions triggers the rise of negative differential resistance (NDR) regions in the device operation. The molecular device behavior is strongly dependent on the shape of the edges, presenting characteristics of field effect transistors (FETs), lighting emitting diodes (LEDs), or resonant tunneling diodes (RTDs), depending on the edge termination and operation range.

Electron scattering processes in steroid molecules via NEGF-DFT: The opening of conduction channels by central oxygen

We present a careful analysis of the electron transport in a variety of steroid derivatives attached among Au (111) electrodes. Our discussion is based on the non-equilibrium Green's function formalism coupled to the density functional theory, as well as appropriate parameters, such as the current-voltage behavior, differential conductance, rectification ratio, transmittance, the projected density of states, and the corresponding eigenchannels. The systems investigated present antagonistic features. While the cholesterol has no appreciable electrical rectification and works as an insulator, cortisol presents an evident diode-like behavior with an intense micro-ampere current with a strong peak at ca. 0.3 eV. This characteristic is a consequence of the systematic remotion of saturated carbon chains, and the inclusion of oxygen atoms. These results can help to understand biological processes involving these molecules besides designing new devices for applications in 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.