The Electronic Transport Mechanism And Computational Design Of Functional Molecular Devices

In recent years, there have been increasing interest and development efforts in minia-turizing electronic devices. The carbon based molecular devices are considered as the most ideal substitute for the current silicon based semiconductor devices. In this the-sis, we have performed first-principles combined with nonequilibrium Green’s function calculations on the transport properties of some new and significant functional molecu-lar devices. The physics and chemical methods including molecular tailoring, doping, hybridized connection and weak π-π intermolecular interaction for tuning the perfor-mance of devices have been studied. We also have explored the humidity effects on the electronic transport properties in carbon based molecular device.An armchair graphene nanoribbon based spintronic device is designed by means of molecular tailoring, and the spin dependent electronic transport properties are studied. The calculational results show that this spintronic device with Rectifying and perfect spin filtering behavior. Furthermore, the rectifying performance can be effectively tuned by edge doping. These results provide new idea for Multi-function integrated in a single-molecule.A hybridized structure constructed by zigzag boron nitride nanoribbon (ZBNNR) and zigzag graphene nanoribbon (ZGNR) is proposed, and their band structures and elec-tronic transport properties are investigated. The results show that the band gap of the hybridized structure can be effectively tuned and the transitions from insulator to semi-conductor, to half-semiconductor and even to metal can be realized by changing the width of ZGNR. However, the band gap of the hybridized structure can not be obviously tuned by changing the width of ZBNNR. It is found that the diversified transitions of the band structure originates from the Mulliken population and charge transfer in the hybridized structure. Moreover, we can also observe spin polarized currents and NDR behavior in the molecular devices which is constructed by this hybridized structure. These results provide new ideas in the design of spin filters and molecular switching.The spin-dependent transport mechanisms of the spiral graphene nanoribbons (SGNRs) in carbon nanotube have been investigated. The results show that when the SGNRs with zigzag edges, we can observe spin polarized currents in the molecular devices; and it can not be observed when the SGNRs with armchair edges. It is found that it can form loop currents in the SGNRs systems with zigzag edges, and the spin polarized transport behav- ior just originates from the magnetic moment which produced by loop currents. However, the loop currents are not be observed when the SGNRs with armchair edges, thus the spin polarized currents completely disappear in this system. More interestingly, the transitions from metal to semiconductor can be realized by changing the width of the SGNRs with armchair edges. These results will have significant application in the design of molecular devices.We have investigated the electronic transport properties of double C60molecules based electronic device with different intermolecular interactions. The results show that the electronic transport properties vary with the types of the intermolecular interaction. A fast electrical switching behavior based on NDR has been found when two molecules are coupled by the weak π-π interaction. However, in the strong coupled system, we can only observe NDR which the current gradually decrease as the bias increase. Compared to the solid bonding, the weak interaction is found to induce resonant tunneling, which is responsible for the fast response to the applied electric field and hence the velocity of switching. These results are very useful for designing high performance molecular devices.We investigate the effect of humidity on the electronic transport properties in single C60molecule based electronic device. The results show that the humidity has a great effect on electronic transport properties and its instability. It is found that different humidity may form varied localized potential barrier, which is a very important factor to affect the stability of electronic transport in the molecular device. It is suggested that humidity is a very import factor influencing the stability of electronic transport in nanoscale electronic system and it should not be neglected.