ifang Hu

The electronic properties of graphene nanoribbons with boron/nitrogen codoping

The electronic properties of graphene nanoribbons with boron/nitrogen codoping at different sites are investigated by performing first-principles calculations based on density functional theory. The calculated results show that the band structures of these doping configurations have distinctly changed around the Fermi level with gradual increasing the distance between nitrogen atom and boron atom. Doping positions regulate the electronic structure of the graphene nanoribbons. Interestingly, our results exhibit both semiconducting and half-metallic behavior in response to the boron/nitrogen codoping at different sites without an applied electronic field, opening a possibility in spintronics device application.

Chirality effects in atomic vacancy-limited transport in metallic carbon nanotubes.

We use first principles density functional theory combined with nonequilibrium Greens function technique to investigate the electronic and transport properties of metallic armchair and zigzag carbon nanotubes (CNTs) with different kinds of multivacancy defects. While the existence of a small band gap in pristine zigzag (12,0) CNTs lowers its conductance compared to pristine armchair (7,7) CNTs, transport properties in the presence of multi (hexa)-vacancy are superior in the former nanostructure, that is more sensitive to defect size and topology than the latter. In addition, in the zigzag structures hexavacancy nanotubes have higher conductance than divancancy nanotubes, which is due to the presence of midgap states that reduce the transmission gap and enhance the conductance.

Effects of nitrogen in Stone-Wales defect on the electronic transport of carbon nanotube

The effects of nitrogen substitutional doping in Stone-Wales (SW) defect on the transport properties of single-walled nanotubes are simulated by using density functional theory and nonequilibrium Green’s functions. It is found that the nitrogen in SW produces half-filled band near the Fermi level in which the electron effective mass varies with the changing of the position of nitrogen. The total transmission coefficients nearby the Fermi level increase and the others decrease after doping. The nitrogen doping and SW defect enhance the transport property of semiconducting (8, 0) and weaken that of quasimetallic (9, 0).

Atomic vacancy defects in the electronic properties of semi-metallic carbon nanotubes

We investigate the electronic properties of semimetallic (12,0) carbon nanotubes in the presence of a variety of monovacancy, divacancy, and hexavacancy defects, by using first principle density functional theory combined with nonequilibrium Green’s function technique. We show that defect states related to the vacancies hybridize with the extended states of the nanotubes to modify the band edge, and change the energy gap. As a consequence, the nanotube conductance is not a monotonic function of the defect size and geometry. Paradoxically, tetravacancy and hexavacancy nanotubes have higher conductance than divacancy nanotubes, which is due to the presence of midgap states originating from the defect, thereby enhancing the conductance.

Curvature effects on electronic properties of small radius nanotube

The authors use the density functional theory associated with nonequilibrium Green function to calculate (2,2) and (3,3) single-walled nanotubes. The result of T(E) imply that π or π* band has been suppressed at certain electronic energy region result in the effect of curvature induce complex hybridization procedure. In view of the I-V characteristics of (2,2) tube, it is found that the current curve appears to have an oscillation behavior. These peculiar electronic transport properties of small diameter tube directly relate to a large curvature effect, which may be useful for the manufacture of electronic applications.

Effect of nitrogen-vacancy complex defects on the electronic transport of carbon nanotube

Effect of nitrogen-vacancy complex defects on the transport properties of single-walled nanotubes are simulated using density functional theory and nonequilibrium Green’s functions. We find that the defect state in carbon nanotubes becomes spatially localized and develops one half-filled impurity band near the Fermi level for either N-vacancy or N3-vacancy defect. The impurity bands are favorable to the electronic transport of the semiconducting nanotube (8, 0) but weaken that of metallic (4, 4). The studied results show that the differential conductance of the nanotubes behaves obvious oscillation characteristic.

TRANSPORT PROPERTIES OF SINGLE-WALLED CARBON NANOTUBE WITH INTRAMOLECULAR JUNCTIONS

Using density-functional theory (DFT) combined with non-equilibrium Greens function (NEGF), we have investigated the transport properties of carbon nanotubes with S–S, M–S, and M–M heterojunctions. The results show that the local states associated with topological defects arise at the junctions. The position and width of local states strongly depend on the configurations of the topological defects and their arrangement. The (7, 0)–(8, 0) and (8, 0)–(9, 0) heterojunctions present semiconducting characteristics. The (6, 0)–(9, 0) heterojunction maintains metallic properties. However, the 5/6/6/7 defects in the nanostructure decrease the electronic transport. More importantly, our results indicate that the I–V characteristics of the heterojunctions could be effectively controlled by gate voltage.

Negative differential resistance induced by SiNx co-dopant in armchair graphene nanoribbon

By adopting density functional theory in combination with nonequilibrium Greens functions, we investigated the electronic structure and transport properties of silicon/nitrogen (Si/N) co-doping armchair graphene nanoribbons (AGNRs) with SiNx co-dopant incorporated in neighboring carbon atoms. The results demonstrate that the electronic structure can be modulated by introducing SiNx co-dopants in AGNRs. The striking negative differential resistance behaviors in the range of low bias can be observed in Si/N co-doped AGNR devices. These remarkable properties suggest the potential application of Si/N co-doping AGNRs in molectronics.

Rectifying behaviors introduced by nitrogen-vacancy complex in spiral chirality single walled carbon nanotube device

By applying nonequilibrium Greens functions in combination with density-functional theory, the effects of nitrogen-vacancy complex on electronic transport properties are investigated in spiral chirality single walled carbon nanotube device. The results show that rectifying behaviors can be tuned by introducing the complex defects with vacancy and nitrogen atoms. Moreover, current-voltage characteristics and negative differential conductance behavior can also be observed in this model. The mechanisms for these interesting phenomena are suggested.

THE EFFECTS OF CO-DOPING OF B AND N ON THE ELECTRONIC TRANSPORT OF SINGLE-WALLED CARBON NANOTUBES

Based on first-principle calculation, the geometry and electronic transport properties of the boron and nitrogen co-doping single-walled carbon nanotubes are investigated by using density functional theory combined with non-equilibrium Greens functions. The results show that the BN atoms energetically tend to form covalent bond of BN along axis in the nanotubes. In contrast to solely B or N doping, the co-doping do not generate accepter or donor subbands near the Fermi level. The co-doping give rise to the reduction of band gap in semiconducting (10, 0) tube and, furthermore, introduces the band gap to the metallic (5, 5) tube.