The electrical rectifying properties of a single-molecule nanowire from the type donor−π-bridge−acceptor are investigated by means of the nonequilibrium Green's function method, combined with density functional theory (NEGF−DFT). The investigated nanowire is an oligo-1,4-phenylene ethylene with π-donor and π-acceptor groups attached on opposite sides of the molecule. The donor and acceptor wires are separated by a π-bridge, in contrast to the Aviram−Ratner rectifier, which is a donor−σ-bridge−acceptor diode. A model more similar to the real molecular electronic device is considered with relaxation of the molecular geometry, under the interaction with external electric field, taking into account its influence on the electronic properties of the nanowire. An asymmetric current−bias (I−V) diagram is observed, with a conductance ratio of 7. The analysis of the spatial distribution of frontier orbitals, the highest occupied molecular orbital−lowest unoccupied molecular orbital ( HOMO−LUMO) gaps, and the transmission spectra give an inside view of the observed results.
Graphene layers have been targeted in the last years as excellent host materials for sensing a remarkable variety of gases and molecules. Such sensing abilities can also benefit other important scientific fields such as medicine and biology. This has automatically led scientists to probe graphene as a potential platform for sequencing DNA strands. In this work, we use robust numerical tools to model the dynamic and electronic properties of molecular sensor devices composed of a graphene nanopore through which DNA molecules are driven by external electric fields. We performed molecular dynamic simulations to determine the relation between the intensity of the electric field and the translocation time spent by the DNA to pass through the pore. Our results reveal that one can have extra control on the DNA passage when four additional graphene layers are deposited on the top of the main graphene platform containing the pore in a 2 × 2 grid arrangement. In addition to the dynamic analysis, we carried electronic transport calculations on realistic pore structures with diameters reaching nanometer scales. The transmission obtained along the graphene sensor at the Fermi level is affected by the presence of the DNA. However, it is rather hard to distinguish the respective nucleobases. This scenario can be significantly altered when the transport is conducted away from the Fermi level of the graphene platform. Under an energy shift, we observed that the graphene pore manifests selectiveness toward DNA nucleobases.
We propose a possible route to achieve high thermoelectric efficiency in molecular junctions by combining a local chemical tuning of the molecular electronic states with the use of semiconducting electrodes. The former allows to control the position of the highest-occupied molecular orbital ͑HOMO͒ transmission resonance with respect to the Fermi energy while the latter fulfills a twofold purpose: the suppression of electronlike contributions to the thermopower and the cutoff of the HOMO transmission tails into the semiconductor band gap. As a result a large thermopower can be obtained. Our results strongly suggest that large figures of merit in such molecular junctions can be achieved.
The optical photoswitching of conductivity of a diarylperfluorocyclopentene nanowire is investigated using Green's function method combined with density functional theory. A model closer to the real molecular electronic device is considered with relaxation of the molecular geometry under the interaction with external electric field. The ratio of conductance for the closed-and open-ring forms is on the order of magnitude 10 2 . The influence of the HOMO-LUMO gaps and the spatial distributions of frontier molecular orbitals on the quantum transport through the molecular wire is investigated.
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