Ke-Qiu Chen

Negative differential resistance and rectifying behaviors in phenalenyl molecular device with different contact geometries

The electronic transport properties in phenalenyl molecular device are studied by using nonequilibrium Green’s functions in combination with the density-functional theory. The results show that the electronic transport properties are strongly dependent on the contact geometry. The negative differential resistance behavior with large peak to valley ratio is observed when the molecule contacts the Au electrodes through two second-nearest sites or one second-nearest site and one third-nearest site, while the rectifying performance is observed only when the molecule contacts the Au electrodes through one second-nearest site and one third-nearest site. The mechanisms are proposed for these phenomena.

Transition from insulator to metal induced by hybridized connection of graphene and boron nitride nanoribbons

A hybridized structure constructed by zigzag boron nitride nanoribbon and zigzag graphene nanoribbon is proposed, and their band structures and electronic transport properties are calculated by applying first-principles calculations. The results show that the band gap of the hybridized structure can be tuned and transitions from insulator to metal can be realized by changing the unit number of zigzag graphene nanoribbon. The currents with different spin polarization display different behavior.

Effect of length and size of heterojunction on the transport properties of carbon-nanotube devices

By applying nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of molecular junctions constructed by the mirror symmetrical straight carbon-nanotube heterojunctions. The results show that the length and size of heterojunction play an important role in the electronic transport properties of these systems. The negative differential resistance behavior can be observed in such devices with certain length and size of heterojunction. A mechanism is suggested for the negative differential resistance behavior.

Theoretical investigation of the negative differential resistance in squashed C60 molecular device

By applying nonequilibrium Green’s function and first-principles calculation, we investigate the transport behavior of squashed C60 molecular devices. The results show that the electronic transport properties are affected obviously by the deformation of C60 molecule. Negative differential resistance is found in such system and can be tuned by the deformation degree of the molecule. A mechanism for the negative differential resistance behavior is suggested.

Negative differential resistance induced by intermolecular interaction in a bimolecular device

Using nonequilibrium Green’s functions in combination with the density-functional theory, we study the electronic transport properties of the molecular device constructed by two cofacial oligo(phenylene ethynylene) molecules and gold electrodes. The results show that negative differential resistance can be observed when the intermolecular distance closes to a certain value. We propose that a combination of the splitting of the molecular orbitals due to the intermolecular interaction and the change of the coupling between the molecules and the electrodes at different biases might be responsible for the negative differential resistance behavior.

Electronic transport properties in doped C60 molecular devices

By applying nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of molecular junctions constructed by C60, C59N, and C59B. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance behavior can be observed in a certain bias range for C60 molecular junction but cannot be observed in C59N and C59B molecular junctions. A mechanism is proposed for the doping effect and negative differential resistance behavior.

Effects of symmetry and Stone–Wales defect on spin-dependent electronic transport in zigzag graphene nanoribbons

Spin-dependent electronic transport properties in zigzag graphene nanoribbons (ZGNRs) are studied using first-principles quantum transport calculations. The effects of the symmetry and defect have been considered. The results show that when the spin polarization is considered, both symmetric and asymmetric ZGNRs present semiconductor behavior, which is different from spin-unpolarized result. The symmetry of ZGNRs plays an important role in electron transport behavior. Asymmetric ZGNR displays monotonic transport behavior. However, in symmetric ZGNRs systems, negative differential resistance is observed. The influence of defect is more obvious in symmetric ZGNRs than in asymmetric systems. A physical analysis of these results is given.

Thermal transport by phonons in zigzag graphene nanoribbons with structural defects

The thermal transport properties by phonons in zigzag graphene nanoribbons with structural defects are investigated by using nonequilibrium phonon Greens function formalism. We find that the combined effect of the edge and local defect plays an important role in determining the thermal transport properties. In the limit T → 0, the thermal conductance approaches the universal quantum value 3κ(0)(κ(0) = π(2)k(B)(2)T/3h) even when structural defects are presented in graphene nanoribbons. The thermal transport shows a noticeable transformation from quantum to classical features with increasing temperature in the system. A suggestion to tune the thermal conductance by modulating structural defects and the ribbon width in graphene nanoribbons is presented.

Nitrogen doping-induced rectifying behavior with large rectifying ratio in graphene nanoribbons device

By applying nonequilibrium Green’s functions in combination with density-function theory, we investigate the electronic transport properties of armchair graphene nanoribbons devices with one undoped and one nitrogen-doped armchair graphene nanoribbons electrode. For the doped armchair graphene nanoribbons electrode, an N dopant is considered to substitute the center or edge carbon atom. The results show that the electronic transport properties are strongly dependent on the width of the ribbon and the position of the N dopant. The rectifying behavior with large rectifying ratio can be observed and can be modulated by changing the width of the ribbon or the position of the N dopant. A mechanism for the rectifying behavior is suggested.

Negative differential resistance behaviors in porphyrin molecular junctions modulated with side groups

By applying nonequilibrium Green’s functions in combination with the density-functional theory, we investigate the electronic transport properties of molecular junctions constructed by the porphyrin molecule with donor or acceptor side groups. The results show that the side groups play important role on the electron transport properties. Negative differential resistance (NDR) is observed in such devices. Especially for the molecule with electron-donating group (−NH2), two NDR appear at different bias voltage regions, and the origins for both NDR behavior are different. A mechanism is proposed for the NDR behavior.