Graphene Nanoribbon Electrodes Research Articles

Axisymmetric All-Carbon Devices with High-Spin Filter Efficiency, Large-Spin Rectifying, and Strong-Spin Negative Differential Resistance Properties

We propose the perfect all-carbon axisymmetric spintronic devices consisting of a zigzag-edged trigonal graphene (ZTG) linked to left and right zigzag-edged graphene nanoribbons (ZGNR) electrodes via carbon atomic chains (CACs). To ensure the stability of the system, the edge carbon atoms are passivated by hydrogen atoms. The self-consistent density functional theory (DFT) calculations show that the simple all-carbon system possesses the prefect spin-filtering property at a wide voltage region from −1.0 to 1.0 V. More importantly, the proposed system can act as a perfect dual spin diode in the antiparallel (AP) spin configuration, and the single-spin rectifying ratio can reach 103. When we add the number of the CACs linked to the left ZGNR electrode, the device shows the obvious single-spin negative differential resistance (NDR) behavior, which originates from the appearance of the localized states in the region of the left ZGNR electrode and ZTG. Meanwhile, the perfect spin-filtering and dual spin-diode ...

SrTiO3‐Based Resistive Switching Memory Device with Graphene Nanoribbon Electrodes

We demonstrate the resistive switching behavior on SrTiO3 (STO) (100) single‐crystalline substrate with graphene nanoribbon (GNR) electrodes. The planar GNR was fabricated on STO substrate by means of dip‐pen nanolithography and polystyrene‐etching techniques. The nanogap for the GNR electrodes was induced by electroburning, which was performed by applying a voltage across the GNR. The nanoscale GNR/STO/GNR RRAM device showed bipolar resistive switching behavior with low set/reset voltages and current as well as good retention characteristics. The bipolar resistive switching behavior might be attributed to roles of oxygen vacancies, originating from intrinsic characteristics of dislocation of STO single crystal.

Effect of electrode twisting on electronic transport properties of atomic carbon wires

We investigate the electron transport properties in atomic carbon wires between two zigzag graphene nanoribbon (ZGNR) electrodes by applying nonequilibrium Green's functions in combination with the density-functional theory. It shows that the ZGNR electrode twisting can modulate the conductance of the atomic carbon wire-graphene junctions remarkably. Typical currents of devices with odd carbon wires are much higher than currents of devices with even carbon wires to exhibit even-odd behavior. The negative differential resistance behaviors are only found in the devices with odd carbon wires. When the right ZGNR electrode is twisted, the curvatures of the current–voltage characteristics change remarkably upon twisted angles. The current will decrease by up to 5 orders of magnitude when the twisted angle reaches to 90°. That means the atomic carbon wire-graphene junctions can be made as a mechanical switching.

Negative differential resistance and stable conductance switching behaviors of salicylideneaniline molecular devices sandwiched between armchair graphene nanoribbon electrodes

By applying nonequilibrium Green's functions in combination with the density-functional theory, we investigate the electron transport properties of the salicylideneaniline molecule sandwiched between two armchair graphene nanoribbon (AGNR) electrodes. It shows that the width of the AGNR electrodes plays a significant role in the transport properties of the salicylideneaniline molecular junctions. The current–voltage characteristics of the salicylideneaniline molecule sandwiched between 8AGNR electrodes can perform a stable conductance switching behavior at the bias region [1.2 V, 1.6 V] when the molecule translates between the trans-enol form and the trans-keto form. When the electrodes change to 7AGNR, a remarkable negative differential resistance behavior can be found in the salicylideneaniline molecular device at the trans-keto form. That means the salicylideneaniline molecule can perform different functions when it connects to the different AGNR electrodes.

Characteristics of classical Kirchhoff's superposition law in carbon atomic wires connected in parallel

The classical Kirchhoff's superposition law is hard to realize in the molecular scale devices because the coupling between the juxtaposed molecules can lead to constructive or destructive quantum interferences [Vazquez et al. nature nanotechnology 2012, 7, 663; Zhu et al. Phys. Rev. B 2014, 89, 085427]. In view of this, we try to eliminate the quantum interference between the juxtaposed molecules by increasing the distance between them. Simple junctions of carbon atomic wire(s) coupled to zigzag graphene nanoribbon electrodes are chosen as our model. Interestingly, fine Kirchhoff's superposition law phenomenon is found when the distance between the two carbon atomic wires reaches 15.5 Å. At the distance 15.5 Å, the conductance for the double carbon atomic wire (DCAW) configuration is 1.96 times of that for single carbon atomic wire (SCAW) configuration and the current across the DCAW configuration keeps nearly two times of that across the SCAW configuration at the applied biases. In addition, the conductance superposition effect becomes better when the distance between the two wires increases further and the spin filtering effect is enhanced in the DCAW configuration.

Electronic properties of Z-shaped graphene nanoribbon under uniaxial strain

Based on tight-binding approximation and a generalized Green's function method, the effect of uniaxial strain on the electron transport properties of Z-shaped graphene nanoribbon (GNR) composed of an armchair GNR sandwiched between two semi-infinite metallic armchair GNR electrodes is numerically investigated. Our results show that the increase of uniaxial strain enhances the band gap and leads to a metal-to-semiconductor transition for Z-shaped GNR. Furthermore, in the Landauer–Büttiker formalism, the current–voltage characteristics, the noise power resulting from the current fluctuations and Fano factor of strained Z-shaped GNR are explored. It is found the threshold voltage for the current and the noise power increased so that with reinforcement of the uniaxial strain parameter strength, the noise power goes from the Poisson limit to sub-Poisson region at higher bias voltages.

The integrated spintronic functionalities of an individual high-spin state spin-crossover molecule between graphene nanoribbon electrodes

The spin-polarized transport properties of a high-spin-state spin-crossover molecular junction with zigzag-edge graphene nanoribbon electrodes have been studied using density functional theory combined with the nonequilibrium Green’s-function formalism. The molecular junction presents integrated spintronic functionalities such as negative differential resistance behavior, spin filter and the spin rectifying effect, associated with the giant magnetoresistance effect by tuning the external magnetic field. Furthermore, the transport properties are almost unaffected by the electrode temperature. The microscopic mechanism of these functionalities is discussed. These results represent a step toward multifunctional molecular spintronic devices on the level of the individual spin-crossover molecule.

Magnetic transport properties of DBTAA-based nanodevices with graphene nanoribbon electrodes

Based on the density functional theory combined with the nonequilibrium Green’s function formalism, the magnetic transport properties of dibenzotetraaza[14]annulene (DBTAA) and transition metal (TM)-DBTAA (TM=Fe and Co) sandwiched between two ferromagnetic zigzag-edge graphene nanoribbon electrodes are investigated. The results show that giant magnetoresistance, spin-filtering and spin-polarized current rectifying effects can be realized simultaneously in the DBTAA system by modulating the external magnetic field. Introducing of TM atoms has obvious effects on these spin-related effects. The mechanisms of these intriguing phenomena are proposed and these phenomena would be instructive in the design of high-performance magnetic nanodevices.

Magnetic transport properties of a trigonal graphene sandwiched between graphene nanoribbon electrodes

Magnetic transport behaviors of a zigzag-edge trigonal graphene (ZTG) constructed as a nanodevice with zigzag graphene nanoribbon (ZGNR) electrodes are investigated, and various magnetic configurations are considered. It is found that excellent magnetic device natures, such as the perfect (100%) spin polarization in a large bias region, spin-resolved rectification ratios approaching 105, and the giant magnetoresistance effect up to 1015%, can be achieved, which is indeed an extremely high value as compared with previously reported theoretical one, ∼107%, for complete ZGNR-based magnetic devices and experimental ones, ∼104%, for the MgO tunnel junction. This can be attributed to unique transmission features due to the strong modulating ability of ZTG for the magnetic transport. These results suggest that the ZTG might possess some advantages in nature for developing magnetic devices.

Negative differential resistance in boron nitride graphene heterostructures: physical mechanisms and size scaling analysis.

Hexagonal boron nitride (hBN) is drawing increasing attention as an insulator and substrate material to develop next generation graphene-based electronic devices. In this paper, we investigate the quantum transport in heterostructures consisting of a few atomic layers thick hBN film sandwiched between graphene nanoribbon electrodes. We show a gate-controllable vertical transistor exhibiting strong negative differential resistance (NDR) effect with multiple resonant peaks, which stay pronounced for various device dimensions. We find two distinct mechanisms that are responsible for NDR, depending on the gate and applied biases, in the same device. The origin of first mechanism is a Fabry-Pérot like interference and that of the second mechanism is an in-plane wave vector matching when the Dirac points of the electrodes align. The hBN layers can induce an asymmetry in the current-voltage characteristics which can be further modulated by an applied bias. We find that the electron-phonon scattering suppresses the first mechanism whereas the second mechanism remains relatively unaffected. We also show that the NDR features are tunable by varying device dimensions. The NDR feature with multiple resonant peaks, combined with ultrafast tunneling speed provides prospect for the graphene-hBN-graphene heterostructure in the high-performance electronics.

Large rectification ratio induced by nitrogen (boron) doping in graphene nanoribbon electrodes for OPE junctions

Using nonequilibrium Green's function method combined with density functional theory, we present electronic transport properties for a molecular device constructed by an oligomeric phenylene ethynylenes (OPE) molecule between two zigzag-edge graphene nanoribbon (zGNR) electrodes. Nitrogen and boron dopants are introduced into one electrode, which makes the molecular junctions to have obvious rectifying behaviors. The conductance properties are closely related to the position and the kind of impurity atoms in electrodes. Moreover, the I–V curve of the junction, which is boron doping at the edge, displays unidirectional features in the studied bias region, and large rectification ratios up to 103 are obtained. The mechanism of the performance is analyzed in terms of transmission spectra combined with molecular projected self-consistent Hamiltonian and electrode band structures under different bias voltages. Symmetry analyses of the Bloch wave functions of the corresponding subbands and the frontier molecular orbitals are also applied to reveal the rectifying behavior.

Designing multi-functional devices based on two benzene rings molecule modulated with Co and N atoms

We investigate the electronic transport properties in molecular devices consisting of two phenyl-rings connected by Co and N atoms by using nonequilibrium Green’s function method and density function theory. The molecule is coupled to two zigzag graphene nanoribbon electrodes. It is found that giant magnetoresistance effect exists in both the coplanar and the perpendicular conformations at low biases. And the total current decreases a lot, on order of 100, when the orientation of the phenyl ring changes from coplanar site to perpendicular site. This indicates a molecular switcher via conformational control. What’s more, perfect dual spin-filtering effect and rectifying behavior can be realized by modulating the external magnetic field. So a multi-functional device is achieved in our designed molecular junction. Detailed explanations via transmission spectra, distribution of molecular projected self-consistent Hamiltonian states are given to the above useful phenomenon.

Effects of amino-nitro side groups on electron device of oligo p-phenylenevinylene molecular between ZGNR electrodes

We study the electronic transport property for a molecular device of an oligo (p-phenylenevinylene) (OPV) molecule without or with different side groups between two zigzag-edged graphene nanoribbon (ZGNR) electrodes. By using ab initio calculations based on density-functional theory, the effects of negative differential resistance (NDR) and spin-rectifying in I–V characteristics are revealed and explained for the proposed molecular device. Our analysis indicates that the NDR behavior comes from the conduction orbital being suppressed under certain bias voltage, while the rectifying effect is because of the asymmetry distribution of the highest occupied molecular orbital or the lowest unoccupied molecular one as well as the corresponding coupling between the molecule and electrodes. Interestingly, the transport property of the device can be improved by introducing amino-nitro side groups to the OPV molecule. The NDR behavior can be much enhanced for molecule with amino side group, and the rectification can be improved for molecule with amino and nitro side groups, respectively. In particular, the NDR behavior of peak to valley ratio can be much enhanced and a molecular rectifier which offers rectification ratio of more than three orders of magnitude up to 2863 by adding NH2 and NO2 side groups to OPV molecule, respectively.

High performance bipolar spin filtering and switching functions of poly-(terphenylene-butadiynylene) between zigzag graphene nanoribbon electrodes

Using the nonequilibrium Green’s function method combined with spin-polarized DFT, we investigate the spin-resolved electronic transport properties of devices made of poly-(terphenylene-butadiynylene) (PTB) between zigzag graphene nanoribbon (ZGNR) electrodes.

Spin transport properties in lower n-acene-graphene nanojunctions.

A series of n-acene-graphene (n = 3, 4, 5, 6) devices, in which n-acene molecules are sandwiched between two zigzag graphene nanoribbon (ZGNR) electrodes, are modeled through the spin polarized density functional theory combined with the non-equilibrium Green's function technique. Our theoretical results show that for n-acene molecules ranging from anthracene to hexacene, the spin-polarized electronic states near the Fermi level can be induced by the spin-polarized ZGNR electrodes, which strengthen gradually to facilitate the electronic transport. A nearly 100% spin filtering ratio and a dual-orientation spin-rectifying effect are observed in a wide range of bias voltage. Importantly, an over 8000% giant magnetoresistance is obtained in the low bias range from -0.1 V to +0.1 V. Moreover, negative differential resistance behaviors are detected in these devices. The potential mechanisms of these intriguing phenomena are proposed and these findings would be instructive for the design and synthesis of high-performance graphene-based spin-related devices.

Side-gate modulation effects on high-quality BN-Graphene-BN nanoribbon capacitors

High-quality BN-Graphene-BN nanoribbon capacitors with double side-gates of graphene have been experimentally realized. The double side-gates can effectively modulate the electronic properties of graphene nanoribbon capacitors. By applying anti-symmetric side-gate voltages, we observed significant upward shifting and flattening of the V-shaped capacitance curve near the charge neutrality point. Symmetric side-gate voltages, however, only resulted in tilted upward shifting along the opposite direction of applied gate voltages. These modulation effects followed the behavior of graphene nanoribbons predicted theoretically for metallic side-gate modulation. The negative quantum capacitance phenomenon predicted by numerical simulations for graphene nanoribbons modulated by graphene side-gates was not observed, possibly due to the weakened interactions between the graphene nanoribbon and side-gate electrodes caused by the Ga+ beam etching process.

Spin filtering behaviors for a carbon chain connected with armchair- and zigzag-edged graphene nanoribbon electrodes

Using the non-equilibrium Green’s function method combined with the density functional theory, we investigate the spin transport properties of carbon chains connected with armchair- and zigzag-edged graphene nanoribbon (ZGNR) electrodes at finite bias with the parallel magnetism configuration. When spin polarized electrons are injected into carbon chains from the ZGNR electrode, the β-spin current is nearly zero, while the α-spin current shows large values in the calculated bias region, thus the spin polarization 100% can be achieved, which is a promising pathway for developing a spin filter.

Rectifying, giant magnetoresistance, spin-filtering, newgative differential resistance, and switching effects in single-molecule magnet Mn(dmit)2-based molecular device with graphene nanoribbon electrodes

By applying the density functional theory and the nonequilibrium Green’s function formalism, we investigate the spin transport properties of a single-molecule magnet Mn(dmit)2 sandwiched between two ferromagnetic zigzag-edge graphene nanoribbon electrodes. The results show that the system can present large rectifying, giant magnetoresistance, spin-filtering and negative differential resistance effects with the help of magnetic field modulation. Moreover, an improved switching effect can also be realized by changing the orientation between planes of two dmit ligands. Therefore, the system will provide the possibilities for a multifunctional molecular device design.

Perfect Spin-Filtering in 4H-TAHDI-Based Molecular Devices: the Effect of N-Substitution

Based on the non-equilibrium Green's function formalism and spin-polarized density functional theory calculations, we investigate the spin transport properties of HDI and terahydrotetraazahexacene diimide (4H-TAHDI) with two ferromagnetic zigzag-edge graphene nanoribbon electrodes. Compared with HDI, four carbon atoms in the hexacene part of 4H-TAHDI are substituted by nitrogen atoms. The results show that the nitrogen substitution can improve significantly the spin-filtering performance and 4H-TAHDI can be used as a perfect spin filter. Our study indicates that suitable chemical substitution is a possible way to realize high-efficiency spin filters.

Spin-dependent transport properties of an armchair boron-phosphide nanoribbon embedded between two graphene nanoribbon electrodes

Using non-equilibrium Green׳s function and ab initio calculations we investigate structural, electronic, and transport properties of a junction consisting of armchair hexagonal boron phosphide nanoribbon (ABPNR) contacted by two semi-infinite electrodes composed of armchair graphene nanoribbons (AGNRs). We consider three different configurations including the pristine AGNR–BP–GNR and substitutions for Iron atoms, namely on phosphorus and boron atoms at one edge of the BP nanoribbon. The spin current polarization in all these cases is extracted for each structure and bias. Such hybrid system is found to exhibit not only significant spin-filter efficiency (SFE) but also tunable negative differential resistance (NDR).