Using density functional theory and non-equilibrium Green’s function method, we designed several zigzag graphene-graphyne nanoribbon heterojunction devices and investigated their spin-dependent transport and optoelectronic properties. Our results show that the heterojunctions have outstanding giant magnetoresistance (GMR) effect. The GMR value is as high as 106%. According to the symmetry and connection way, for the ferromagnetic states the heterojunctions may produce two spin currents and exhibit significant rectification behaviors. Furthermore, spin-polarized photocurrents can be generated by irradiating the devices with infrared, visible or ultraviolet light. More importantly, in these heterojunctions we found that the behavior of the spin-up (spin-down) photocurrent for the ferromagnetic state is similar to that of the spin-down (spin-up) photocurrent for the antiferromagnetic state. This novel effect provides an efficient way to control the spin transport in the systems.Download high-res image (133KB)Download full-size image

•There exist Dirac cones in three-dimensional (3D) graphene.•The thermoelectric performance of 3D graphene is excellent.•The defective 3D graphene has better thermoelectric performance.The electronic and thermoelectric properties of a new carbon bulk material, three-dimensional (3D) graphene, are investigated in this study. Our results show that 3D graphene has unique electronic structure, i.e., near the Fermi level there exist Dirac cones. More importantly, the thermoelectric performance of 3D graphene is excellent, at room temperature the thermoelectric figure of merit (ZT) is 0.21, an order of magnitude higher than that of graphene. By introducing line defects, the ZT of 3D graphene could be enhanced to 1.52, indicating 3D graphene is a powerful candidate for constructing novel thermoelectric materials.

•Fen/AGNR (n = 1–4) systems have high stabilities and large magnetic moments.•Fen/AGNR is half metal with 100% spin polarization (n = 1–3) or semiconductor (n = 4).•By tuning cluster size, Fen/AGNR can serve as possible candidates for designing new nanodevices with different functions.Using density functional theory, the structural stabilities, electronic and magnetic properties of Fen (n = 1–4) cluster adsorbed on armchair graphene nanoribbon (AGNR), Fen/AGNR, are systematically investigated. We found that the Fen/AGNR systems have high stabilities and large magnetic moments. For different-sized Fen, Fen/AGNR can be half-metal with 100% spin polarization (n = 1–3) or semiconductor (n = 4). These excellent electronic and magnetic properties show that Fen/AGNR systems can serve as possible candidates for designing new nanodevices with different functions.

Highlights•Full-boron fullerene B40 was applied to design molecular device.•Large rectification ratio was observed in the molecular device.•The molecular device has excellent optical properties and can be used as photodetector.All-boron fullerene B40 is a highly stable molecule, which has been successfully synthesized in recent experiment. In this paper, with Au as two electrodes, the single-molecule device Au–B40–Au was investigated by using density functional theory and non-equilibrium Green׳s function method. The results show that the device can exhibit large rectification ratio and significant negative differential resistance. More importantly, the photocurrent of the device has different responses in the infrared, visible and ultraviolet regions. The excellent optoelectronic properties ensure that the device can be used as photodetector.

•The hydrogen storage capacities of FeC5H5, Fe2C5H5 and (FeC5H5)∞ were investigated.•The hydrogen storage capacities of FeC5H5 and Fe2C5H5 are 7.63 wt% and 10.15 wt%.•(FeC5H5)∞ can adsorb H2 molecules, and the hydrogen storage capacity is 1.62 wt%.•The magnetic and electrical properties of (FeC5H5)∞ are sensitive to additional H2.Based on density functional theory, the capacities of FeC5H5, Fe2C5H5 and one-dimensional (FeC5H5)∞ nanowire as hydrogen storage media were investigated. The results show that FeC5H5 and Fe2C5H5 can adsorb five and ten H2 molecules, respectively, and form stable FeC5H5(H2)5 and Fe2C5H5(H2)10 systems. The hydrogen storage capacities of the two systems are 7.63 wt% and 10.15 wt%, while the average adsorption energies are 0.49 and 0.73 eV/H2, indicating that FeC5H5 and Fe2C5H5 are excellent hydrogen storage media. In addition, (FeC5H5)∞ nanowire can also adsorb H2 molecules (1.62 wt%). Most importantly, the magnetic and electrical properties of the nanowire are sensitive to the additional H2, thus (FeC5H5)∞ can be used for selecting and detecting H2 molecules.

The chemical bonds and magnetic and quantum transport properties of small-sized transition-metal-pentalene sandwich clusters TM2nPnn+1 (TM = V, Cr, Mn, Co, and Ni; n = 1, 2) were investigated by using density functional theory and nonequilibrium Green’s function method. Theoretical results show that TM2nPnn+1 sandwiches have high stabilities. The TM–TM bond order gradually decreases with the increase of 3d electron number of TM atoms and TM2nPnn+1 could exhibit different spin states. With Au as two electrodes, significant spin-filter capability was observed in TM2nPnn+1, and such a filter can be switched on/off by changing the spin state. In addition, giant magnetoresistance was also found in the systems. These interesting quantum transport properties indicate that TM2nPnn+1 sandwiches are promising materials for designing molecular junction with different functions.

•Different-sized vanadium–naphthalene sandwich clusters are all very stable and could exhibit rich magnetic properties.•The spin-filter capability and negative differential resistance can be observed in these systems.•The giant magnetoresistance effect was also found in the sandwiches and the transport properties can be adjusted according to cluster size.Using density functional theory and non-equilibrium Green’s function technique, we performed theoretical investigations on the magnetic and transport properties of V2n(C10H8)n+1 (n = 1–4) sandwich clusters. For the ground states, our results show that all the clusters are stable and possess ferromagnetic orders. The smaller clusters have higher stabilities, and our predictions are in agreement with the experimental observation. The double exchange mechanism plays an important role in determining the magnetic properties of the systems. Furthermore, with Ni as electrodes, the clusters exhibit interesting transport properties such as significant spin-filter capability, negative differential resistance feature and giant magnetoresistance effect. These findings suggest that V2n(C10H8)n+1 sandwiches are excellent candidates for application in spintronics and organic electronics.The giant magnetoresistance effects of different-sized vanadium–naphthalene sandwich clusters.

In present paper, detailed investigations on the magnetic and quantum transport properties of Mnn(B3N3H6)n+1 (n = 1–4) sandwich clusters were performed by using density functional theory and non-equilibrium Green’s function technique. The calculated results show that these clusters are stable and adopt ferromagnetic orders as the ground states. When coupled to Ni electrodes, the sandwiches could exhibit novel quantum transport properties such as high spin-filter capabilities and negative differential resistance effects, indicating that these sandwich systems could be viewed as a new kind of spin filter.

Highlights•Full-boron fullerene B40 was applied to design molecular device.•Large rectification ratio was observed in the molecular device.•The molecular device has excellent optical properties and can be used as photodetector.All-boron fullerene B40 is a highly stable molecule, which has been successfully synthesized in recent experiment. In this paper, with Au as two electrodes, the single-molecule device Au–B40–Au was investigated by using density functional theory and non-equilibrium Green׳s function method. The results show that the device can exhibit large rectification ratio and significant negative differential resistance. More importantly, the photocurrent of the device has different responses in the infrared, visible and ultraviolet regions. The excellent optoelectronic properties ensure that the device can be used as photodetector.