Ouyang Fang-Ping

DNA translocation through graphene nanopores: a first-principles study

With first-principles transport simulation, a biosensor device built from a graphene nanoribbon containing a nanopore is designed for DNA sequencing. The four DNA nucleobases can be distinguished from one another by detecting the transverse-currents of this device. To investigate the transport properties and mechanisms of such a device, we examine the motion effects of nucleobases. The analysis of the transmission spectra and frontier orbital energy shows that the transverse-currents variation of the device strongly results from the long-range interaction between nucleobases and the device. This interaction makes transverse-currents ultra-sensitive to the molecule inside the pore. By rotating the nucleotides inside the pore, the transverse-currents of the device vary along with the changes of molecular orientation. Due to the long-range interaction, when nucleobases chain translocates through nanopore of the device, the influences of adjacent nucleobases on transverse-currents cannot be ignored. These novel effects of nucleobases on the transport capacity of the device provide some theoretical guidance for the design of graphene-based nanopore sensor devices.

Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study

By using the first-principles calculations, the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal?semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.

Negative differential resistance behaviour in N-doped crossed graphene nanoribbons

By using first-principles calculations and nonequilibrium Greens function technique, we study elastic transport properties of crossed graphene nanoribbons. The results show that the electronic transport properties of molecular junctions can be modulated by doped atoms. Negative differential resistance (NDR) behaviour can be observed in a certain bias region, when crossed graphene nanoribbons are doped with nitrogen atoms at the shoulder, but it cannot be observed for pristine crossed graphene nanoribbons at low biases. A mechanism for the negative differential resistance behaviour is suggested.

A simple Scheme for Generating an n-Qubit W State in a Trapped-Ion System without a Lamb–Dicke Limit

A simple and scalable scheme is proposed to generate a n-qubit W state in a trapped-ion system without the Lamb–Dicke limit. The n-qubit W state can be generated by the interaction between the ions and the laser field if the collective mode is initially prepared in the single-phonon state and each ion is in the ground state. The scheme only requires a single laser and avoids laser manipulation of the individual ion. The time required to complete the process decreases with the number of ions. The present scheme is not limited to small values of the LD parameter, which greatly enhances operation speeds.

Ab initio study of transport properties of an all-carbon molecular switch based on C20 molecule

Choosing closed-ended armchair (5, 5) single-wall carbon nanotubes (CCNTs) as electrodes, we have investigated the electron transport properties across a carbon molecular junction consisting of a C20 molecule sandwiched between two semi-infinite carbon nanotubes. It is shown that the Landauer conductance of this carbon hybrid system can be tuned within several orders of magnitude not only by varying the tube-C20 distance, but more importantly by changing the orientation of the C20 molecule and rotating the C20 molecule or one of the tubes around the symmetry axis of the system at fixed distances. This fact could make this all-carbon molecular system a possible candidate for a nano-electronic switching device. Moreover, our study also reveals that molecular configuration selection and structural relaxation would play an important role in the design of such devices.

Electronic Structure and Edge Modification of Armchair MoS 2 Nanoribbons

The geometries and electronic properties of armchair MoS2 nanoribbons were investigated by the first-principles method based on density functional theory. It was found that the stability and electronic properties of armchair MoS2 nanoribbons sensitively depend on edge modification. Increasing the number of hydrogen atoms on the edge caused the nanoribbons to become more stable and transition between indirect-gap semiconductor, semi-metal and direct-gap semiconductor. The band structure and densities of states of the nanoribbons indicated that low energy bands contributed to edge states. Different hydrogen adsorption patterns on each edge induce two kinds of edge state on the nanoribbons and these two kinds of edge state have little effect on each other. The relationships between the bandgap and width of three types of nanoribbons were studied. Nanoribbons terminated with zero or eight hydrogen atoms in each unit cell have a bandgap that oscillates with width in a period of three, while the bandgap changes nonperiodically in those terminated with four hydrogen atoms.

Electronic Transport Properties of Graphene Nanoribbons with Nanoholes

Based on the density of the general theory, the structures of ziqzag graphene nanoribbons (ZGNRs) (N=17, N is the number of carbon chain) with nanoholes are optimized and then get the transport property of the electrons in these systems with different holes through the calculation. The results show that the conductance is not only related to the quantum confinement effect, but also confined by the symmetry of the hole and the configuration of the diagonal symmetry is larger than the longitudinal symmetry′s in the presence of a single-hole. In the case of two holes, the conduction of the system is advanced with the growth of the distance between the two holes because of the coupling effect. At the same time, we can get some quantum phenomenon which can be explained by the model of one-dimensional double barrier.

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair (5, 5) single-wall carbon nanotubes (CCNTs) as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models: the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20–C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.

Design and First-principles Study of a Fullerene Molecular Device

By using open-ended armchair (6, 6) single-wall carbon nanotubes as electrodes, we investigate the electron transport properties of an all-carbon molecular junction based on the C82 molecule. We find the most stable system among different isomers by performing structural optimization calculations of the C82 isomers and the C82 extended molecules. The calculated results show that the C82–C2(3) isomer and the C82 extended molecule with C82–C2v isomer are most stable. For the all-carbon hybrid system consisting of C82–C2v extended molecules, it is shown that the Landauer conductance can be tuned over several orders of magnitude both by changing the distance between two electrodes and by changing the orientation of the C82 molecule or rotating one of the tubes around the symmetry axis of the system at a fixed distance. Also, we find the most stable distance between two electrodes from the total energy curve. This fact could make this all-carbon molecular system a possible candidate for a nanoelectronic switch. Moreover, we interpret the conductance mechanism for such a molecular device.