Z.Q. Fan

Rectifying behaviors induced by BN-doping in trigonal graphene with zigzag edges

Based on nonequilibrium Green’s functions in combination with density-function theory, the transport properties of trigonal graphenes, with the vertex carbon atom substituted by one phosphorus or boron atom and bounded through a B-N pair, coupled to gold electrodes are investigated. The rectification behavior can be observed because a potential barrier similar to the p-n junction is formed in the B-N region of central molecule. When the size of a central molecule is enlarged, rectification ratio is improved greatly since the barrier height in it is enhanced as well.

All-carbon sp-sp2 hybrid structures: Geometrical properties, current rectification, and current amplification

All-carbon sp-sp2 hybrid structures comprised of a zigzag-edged trigonal graphene (ZTG)and carbon chains are proposed and constructed as nanojunctions. It has been found that such simple hybrid structures possess very intriguing propertiesapp:addword:intriguing. The high-performance rectifying behaviors similar to macroscopic p-n junction diodes, such as a nearly linear positive-bias I-V curve (metallic behavior), a very small leakage current under negative bias (insulating behavior), a rather low threshold voltage, and a large bias region contributed to a rectification, can be predicted. And also, a transistor can be built by such a hybrid structure, which can show an extremely high current amplification. This is because a sp-hybrid carbon chain has a special electronic structure which can limit the electronic resonant tunneling of the ZTG to a unique and favorable situation. These results suggest that these hybrid structures might promise importantly potential applications for developing nano-scale integrated circuits.

The site effects of B or N doping on I-V characteristics of a single pyrene molecular device

Using the non-equilibrium Green’s function method combined with the density functional theory, the electronic transport properties of boron (B) or nitrogen (N) doped pyrene molecular devices are investigated. The results show that effects of B or N doping on I-V characteristics of a single pyrene molecular device are not constant and can be changed by varying doped sites. More importantly, significant negative differential resistance (NDR) behaviors are found in B-doped pyrene molecular devices. The peak-to-valley ratio which is a typical character of NDR behavior is also sensitive to the B doped site.Using the non-equilibrium Green’s function method combined with the density functional theory, the electronic transport properties of boron (B) or nitrogen (N) doped pyrene molecular devices are investigated. The results show that effects of B or N doping on I-V characteristics of a single pyrene molecular device are not constant and can be changed by varying doped sites. More importantly, significant negative differential resistance (NDR) behaviors are found in B-doped pyrene molecular devices. The peak-to-valley ratio which is a typical character of NDR behavior is also sensitive to the B doped site.

Edge contact dependent spin transport for n-type doping zigzag-graphene with asymmetric edge hydrogenation

Spin transport features of the n-type doping zigzag graphene nanoribbons (ZGNRs) with an edge contact are investigated by first principle methods, where ZGNRs are C–H2 bonded at one edge while C–H bonded at the other to form an asymmetric edge hydrogenation. The results show that a perfect spin filtering effect (100%) in such ZGNR nanojunctions can be achieved in a very large bias region for the unchanged spin states regardless of bias polarities, and the nanojunction with a contact of two C–H2 bonded edges has larger spin polarized current than that with a contact of two C–H bonded edges. The transmission pathways and the projected density of states (PDOS) demonstrate that the edge of C-H2 bonds play a crucial role for the spin magnetism and spin-dependent transport properties. Moreover, the negative differential resistance (NDR) effect is also observed in the spin-polarized current.

Controllable low-bias negative differential resistance and rectifying behaviors induced by symmetry breaking

Incorporating the characteristic of pyramidal electrode and symmetry breaking of molecular structure, we theoretically design a molecular device to perform negative differential resistance and rectifying behaviors simultaneously. The calculated results reveal that low-bias negative differential resistance behaviors can appear symmetrically when tetraphenyl molecule connects to pyramidal gold electrodes. However, as one phenyl of tetraphenyl molecule is replaced by a pyrimidyl, the symmetry breaking on the molecule will break the symmetry of negative differential resistance behavior. The peak-to-valley ratio on negative bias region is larger than that on positive bias region to perform a low-bias rectifying behavior. More importantly, increasing the symmetry breaking can further weaken these two behaviors which propose an effective way to modulate them.

Magnetic structure and magnetic transport characteristics of nanostructures based on armchair-edged graphene nanoribbons

Exploring half-metallic nanostructures with a high Curie temperature and a wide half-metallic gap is a crucial solution for developing high-performance spintronic devices. Using the first-principles method, we design a new magnetic structure based on edge modification of armchair-edged graphene nanoribbons by Mn and F atoms (AGNR–Mn–F2). It is found that such a structure is an excellent half-metal with a wide bandgap (∼1.2 eV) and a stable magnetic ordering by a very high Curie temperature (Tc > 700 K) as well as being predicted to stably exist in a very large chemical potential range in experiment by the Gibbs free energy. And it is also shown that it possesses an outstanding magnetic device nature, such as a spin polarization of 100% in a very large bias region, a dual spin diode-like rectification ratio up to 105, and a spin-valve feature with a giant magnetoresistance approaching 108%, indicating a promising application for developing spintronic devices.

Altering regularities of electronic transport properties in twisted graphene nanoribbons

Based on density-function theory combined with nonequilibrium Green’s function method, the electronic transport properties of twisted armchair- and zigzag-edge graphene nanoribbons (AGNRs and ZGNRs) are investigated. Results show that electronic transport properties are sensitive to twisting deformations for semiconductor-type AGNRs, but are robust against twisting deformations for quasi-metallic AGNRs and ZGNRs. The electronic conduction becomes weaker gradually for moderate-gap semiconductor-type AGNRs, but gets stronger for wide-gap semiconductor-type AGNRs when the twisted angle increases to 120°. While for quasi-metallic AGNRs and ZGNRs, the electronic conduction is strong and obeys Ohm’s law of resistance strictly. Mechanisms for such results are suggested.

Electronic and spin transport properties in zigzag silicene nanoribbons with edge protrusions

We investigate the electronic transport properties of zigzag-edged silicene nanoribbons (ZSiNRs) with one or two protrusions at the edges using the density functional theory combined with nonequilibrium Greens function method. It is found that the protrusion generally breaks down the edge state along the same edge, which carries current in the junction. For the ZSiNR having an even number of zigzag chains in its width, the protrusions can increase the conductance except for the case of two symmetric protrusions. For ZSiNRs with an odd number of zigzag chains in its width, the introduction of edge protrusions can suppress currents. We also investigate the spin-dependent transport properties of ZSiNR-based devices with antiparallel (AP) magnetism configuration. Interestingly, only non- and symmetric-protrusion models with a width of an even number of zigzag chains show a perfect spin filter effect.

Tunable negative differential resistance in a single cruciform diamine molecule with zigzag graphene nanoribbon electrodes

We investigate the electronic transport properties of a single cruciform diamine molecule connected to zigzag graphene nanoribbon electrodes by using the non-equilibrium Greens function formalism with density functional theory. Negative differential resistance behavior can be discovered in the current–voltage curve of this molecular device. Then, one hydrogen atom in the molecule is replaced by an electron-donating group (–NH2) or an electron-withdrawing group (–NO2) in order to modulate the devices electronic transport properties. The results show the replacement of –NH2 on two different functionalized sites (R1 and R2) are all ineffective on the devices current–voltage characteristic. However, the replacement of –NO2 on R1 and R2 can enlarge the devices electron transport ability to different extents. More importantly, the original negative differential resistance behavior is also enhanced markedly. The above results offer us a new effective way to control the conductance and to modulate the negative differential resistance behavior in the single molecular device with zigzag graphene nanoribbon electrodes.

Tunnable rectifying performance of in-plane metal–semiconductor junctions based on passivated zigzag phosphorene nanoribbons

Using first principles density functional theory, we perform a systematic study of the band structures of passivated zigzag phosphorene nanoribbons (ZPNRs) and the transport properties of in-plane metal–semiconductor junctions. It is found that the ZPNR passivated by H, Cl or F atoms is a semiconductor, and the ZPNR passivated by C, O or S atoms is a metal. Therefore, ZPNRs with different passivated atoms can be fabricated into an in-plane metal–semiconductor junction. The calculated current–voltage characteristics indicate that these in-plane metal–semiconductor junctions can exhibit excellent rectification behavior. More importantly, we find that the type of passivated atom plays a very important role in the rectification ratio of this in-plane metal–semiconductor junction. The findings are very useful for the further design of functional nanodevices based on ZPNRs.