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Theoretical Study On Electronic Structures And Transport Properties Of New Carbon Based Nano-Materials

Posted on:2012-07-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:L N ChenFull Text:PDF
GTID:1481303353989459Subject:Materials computational science and virtual engineering
Abstract/Summary:PDF Full Text Request
Fullerene, Carbon Nanotubes and Graphene nanoribbon are new carbon based nano-materials. Due to their unique geometry structures and special electrical properties, they show the great and potential applied value in nano-electronics field. By using the first-principles methods within the framework of density functional theory and Nonequilibrium Green's functions method, the eletronic structures and transport properties of three carbon based nano-materials were studied. The results are summarized as follows:(1) The effect of atomic hydrogen adsorption on the transport properties of fullerenes C6o molecular devices is studied. It is found that when two hydrogen adatoms are located at the side of a six-membered ring in C6o molecule, the transport properties of C60 molecular devices coupled to Au chain electrodes depend on the relative sites of two hydrogen adatoms. Obtained results show that the adsorption of meta-position enhances the transmission ability in low bias voltage. However, the adsorption of adjacent-position and para-position suppresses the transmission ability, and the negative differential resistance disappears. The negative differential resistance is caused by the effect of coupling between frontier molecule orbits and electrode.(2) The electronic structures and transport properties of single-walled carbon nanotube (SWCNT) with Boron/Nitrogen (B/N) pair doping. It is found that B/N pairs are easier to insert into the lattice of SWCNT than separate B/N atoms. The gap of SWCNT increases with the increase of the impurity concentration of B/N pair. At the same impurity concentration of B/N pairs, the gap of SWCNT can change significantly with the change of the relative impurity position. Furthermore, the impurity causes the inhibition of the transmission peak near the fermi level, leading to the conductivity decreases in the system. The physical origin of these phenomena is the symmetry breaking of SWCNT.(3) The effect of atomic hydrogen adsorption and vacancy defect on the eletronic structures of SWCNT is studied. It is found that the electronic structure and magnetism of SWCNT is mainly determinded the number of atoms adding to or missing from two sublattices. When the adsorption or defect destroys the?conjugated system of SWCNT, sublattice imbalance causes the appearance of spin-polarized band and local magnetization. However, the adsorption or defect retain the?conjugated system of SWCNT, sublattice balance lead to the degeneration of spin and nonmagnetic metallic behavior. These results provided theoretic foundation for experimental Hydrogen sensors based on SWCNT.(4) The graphene nanoribbons with B/N doping and multivacancies defect is investigated. The armchair graphene nanoribbons (AGNRs) with B or N doping are metallic, and the electronic structures of the AGNRs with a pair of B or N doping vary with the different parity of ribbon width. However, the energy gap is oscillatory with the increase of the ribbon width in the AGNRs with B/N pair doping. The defect configuration, the doping type, and ribbon symmetry have an important effect on the electronic structures of zigzag graphene nanoribbons (ZGNRs). The ZGNRs with multivacancies defect show the half-metallic behavior under certain condition. Furthermore, the electronic transport properties of crisscross GNRs change significantly with the change of N-doped position in low bias voltage. By changing the N-doped position, the negative differential resistance is realized. The reseach provides ideas for the design of nanoelectronics and spintronic devices based on GNRs.
Keywords/Search Tags:Carbon based nano-materials, First-principle, Nonequilibrium Green's functions method, electronic structure, transport property, Doping, Defect
PDF Full Text Request
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