The Design And Analysis On Graphene-Based Molecular Device

Molecule-based devices, as the next generation of electronic devices, have draw lots of attentions, and many works have been made both experimentally and theoretically. But its realistic applications are still restricted by its instability in transport and low-performance. So, many researchers are trying to find some new theoretical mechanism and use new building materials. Graphene is recognized as a novel and very prospective material for future generations of nanoelectronic and nanospintronic devices due to its unique physical properties and chemical stability. Thus, in this paper, we have designed several graphene-based molecule devices and applied the first-principle method based on the DFT and the NEGF technique to perform studies on their transport characteristic.Firstly, we introduced the research background of graphene, molecular electronics and the first-principle method. Secondly, we designed a molecule rectifier built by sandwiching a combined nanostructure of two trigonal graphenes with different edge modifications between two Au electrodes. Calculated results show that the molecule rectifier, the left zigzag-edge trigonal graphene is terminated by nonmetal (metal) atoms and the right zigzag-edge trigonal graphene is terminated by H atoms, has a forward (reverse) rectification, and the stronger the nonmetallic (metallic) behaviors for atom terminated at edge of the left zigzag-edge trigonal graphene, the larger its rectification ratio. Thirdly, we investigated the effect of the electrodes’ band gap on the rectifying behaviors for a donor-acceptor molecular diode. This study implies that using graphene with a large bandgap as electrodes might be a novel effective pathway to greatly raise rectifying behaviors of a donor-acceptor molecule and the maximum rectification ratio can reach a value more than 4000. Fourthly, we explored the spin polarization effects of zigzag-edge graphene electrodes on the rectifying performance of the D-a-A molecular diode. It has been found that its rectifying behaviors strongly depends on the spin-polarized states of ZGNRs electrodes, when electrodes take the AFM state (anti-ferromagnetic state), it has a best rectifying behavior. Next, we designed a new type of doped carbon-based molecule rectifier with unexpectedly high rectification ratios,109-1011, in a larger bias region. They are much higher values than 105-107 for macroscopic p-n junction diodes, and the typical behaviors for conventional diodes are clearly observed as well, such as a nearly linear positive-bias I-V characteristic, a negligible small negative-bias leakage current, and a low threshold voltage. In the end, we report first-principles calculations on the electronic properties, spin magnetism, and potential applications of the functionalized hexagonal armchair graphene nanoflakes (GNFs). Based on the suitable hexagonal defective GNFs, we design a field effect transistor (FET) and a bipolar field-effect spin-filtering (BFESF) device, and find that they both exhibit extremely high performances. For this FET, its ON/OFF ratio reaches-105, and for this BFESF device, the spin polarization nearly reaches 100% with different spin directions only by altering signs of gate voltages. All in all, we are look forward that our theoretical explorations can be helpful to the realistic applications of molecule devices.