Zigzag Phosphorene Nanoribbon Research Articles

Electrically controllable spin filtering in zigzag phosphorene nanoribbon based normal–antiferromagnet–normal junctions

We investigated the electric controllable spin-filtering effect in a zigzag phosphorene nanoribbon (ZPNR) based normal–antiferromagnet–normal junction. Two ferromagnets are closely coupled to the edges of the nanoribbon and form the edge-to-edge antiferromagnetism. Under an in-plane electric field, the two degenerate edge bands of the edge-to-edge antiferromagnet split into four spin-polarized sub-bands and a 100% spin-polarized current can be easily induced with the maximal conductance 2e 2/h. The spin polarization changes with the strength of the electric field and the exchange field, and changes sign at opposite electric fields. The spin-polarized current switches from one edge to the other by reversing the direction of the electric field. The edge current can also be controlled spatially by changing the electric potential of the scattering region. The manipulation of edge current is useful in spin-transfer-torque magnetic random-access memory and provides a practical way to develop controllable spintronic devices.

Crossed Andreev reflection in zigzag phosphorene nanoribbon based ferromagnet/superconductor/ferromagnet junctions

We study the crossed Andreev reflection in zigzag phosphorene nanoribbon based ferromagnet/superconductor/ferromagnet junction. Only edge states, which are entirely detached from the bulk gap, involved in the transport processes. The perfect crossed Andreev reflection, with the maximal nonlocal conductance -2e^{2}/h, is addressed by setting the electric potentials of the leads and device properly. At this situation, the local Andreev reflection and the electron tunneling are completely eliminated, the incoming electrons can only be reflected as electrons or transmitted as holes, corresponding to the electron reflection and the crossed Andreev reflection respectively.The nonlocal conductance oscillates periodically with the length and the electric potential of the superconductor. Our study shows that the phosphorene based junction can be used as the quantum device to generate entangled-electrons.

Tuning of the electronic structures and spin-dependent transport properties of phosphorene nanoribbons by vanadium substitutional doping

Based on vanadium-doped zigzag phosphorene nanoribbon (ZPNRs), we investigate the electronic structures and spin-dependent transport properties by the first-principles calculations in combination with the nonequilibrium Green's function approach. We find that the ZPNRs can be tuned from nonmagnetic metals to magnetic metals or half-metals by different doping positions, which are caused by the hybridization among different electron orbitals under the crystal field. Moreover, a robust negative differential resistance effect is observed in all studied devices, and a perfect spin-filter effect with almost 100% spin polarization can be found under low bias. We analyze the transport properties in detail from the viewpoint of the transmission spectrum and molecular energy levels. These results indicate that the vanadium-doped ZPNRs have potential applications as multi-functional spintronic devices. • Zigzag phosphorene nanoribbons can be tuned from nonmagnetic metals to magnetic metals or half-metals. • Robust negative differential resistance effect is observed. • Perfect spin-filter effect with almost 100% spin polarization can be found. • We analyze the transport properties in detail.

Double-Fano resonance in a two-level quantum system coupled to zigzag Phosphorene nanoribbon

Double-level quantum systems are good candidates for revealing coherent quantum transport properties. Here, we consider quantum interference effects due to the formation of a two-level system (TLS) coupled to the edge channel of a zigzag Phosphorene nanoribbon (ZPNR). Using the tight-binding approach, we first demonstrate the formation of a TLS in bulk Phosphorene sheet due to the existence of two nearby vacancy impurities. Then, we show that such a TLS can couple to the quasi-one-dimensional continuum of the edge states in a ZPNR which results in the appearance of two-dip Fano-type line shapes. To this end, we generalize the Lippmann–Schwinger approach to study the scattering of edge electrons in a ZPNR by two coupled impurity defects. We obtain an analytical expression of the transmission coefficient which shows that the positions and widths of the antiresonances can be controlled by changing the intervacancy distance as well as their distance from the edge of the ribbon. This work constitutes a clear example of the multiple Fano resonances in mesoscopic transport.

Vacancy defected blue and black phosphorene nanoribbons as gas sensor of NOx and SOx molecules

Black phosphorene, due to its high chemical activity and large surface-to-volume ratio, indicates potential application for gas sensing. Additionally, recently synthesized blue phosphorene has attracted a lot of attention because of its properties, appropriate for applications in different fields. In this work, the sensing properties of vacancy defected black and blue phosphorene nanoribbons for NOx and SOx molecules are analyzed with density functional theory. Adsorption energy and adsorbate/phosphorene distance are studied for sensing molecules on pristine black/blue phosphorene nanoribbons which show the sensing capability of these materials. In order to further develop the sensor performance, considering the vacancy defect in the host material is suggested. Due to comprehensively analysing the effect of vacancy defect in the terms of sensor response, the I-V characteristics of defected blue/black phosphorene-based FET structures are calculated. Calculation results confirm that, vacancy defect increases the adsorption energies of all examined molecules on phosphorene-based substrates but calculated I-V values show small changes in current responses of armchair black/blue phosphorene nanoribbons in both pristine and defected forms. However, in the case of zigzag phosphorene nanoribbons, great current modifications before and after sensing process are obtained. Consequently, our results present a promising application of vacancy defected zigzag phosphorene nanoribbon in gas sensing.

Electromechanical and magnetic response in zigzag phosphorene nanoribbons

Abstract We investigate the electromechanical and magnetic response of normal-zigzag phosphorene nanoribbons (nZPNRs) to the Dresselhaus spin-orbit coupling (SOC) and Rashba SOC, electric fields, exchange fields, and uniaxial strains. It is found that, when the typical exchange fields, developed by combining a ferromagnetic (FM) state with one of the antiferromagnetic (AFM) states, are applied to the system, spin and charge band splitting occur, simultaneously. We show that a zigzag phosphorene nanoribbon, when exposed to an FM and/or an AFM exchange field, as well as a transverse electric field, behaves as a half-metal, meaning that one spin state electrons are allowed to move. Furthermore, we demonstrate that the phosphorene nanoribbon undergoes a topological phase transition under a transverse electric field. By tuning the above parameters, one can control the transport properties of the system. Our results may have important applications in designing of spintronic devices based on phosphorene.

Transport properties of Z-shaped phosphorene nanoribbon devices

By using first-principles calculations and the non-equilibrium Green’s function, we theoretically study the electronic transport properties of a [Formula: see text]-shaped phosphorene nanoribbon (PNR) device, which is called ZSZ-PNR because it is composed of a left zigzag PNR electrode, an intermediate skewed armchair PNR (saPNR), and a right zigzag PNR electrode. First, we investigate the influences of the length and the width of the central saPNR on the ZSZ-PNR transport. The results show that the negative differential conductance (NDC) always appears in the case of the short central saPNR, and is independent of its width, while the NDC is inclined to vanish with the increase of the length. Also, an anomaly on the current–voltage ([Formula: see text]–[Formula: see text]) curves is observed for the ZSZ-PNR with a short saPNR. Next, the transport properties are analyzed according to the evolution of the energy bands of the electrodes, the molecular energy levels (MELs) of the central saPNR, as well as the transmission coefficients, the transmission eigenstates, and the eigenstates of the self-consistent Hamiltonian of the saPNR. Finally, we use a top gate and two parallel gates to manipulate the transport of the ZSZ-PNR, and find that all these gates can strengthen or suppress the ZSZ-PNR transport.

The effect of strain on the zigzag and armchair phosphorene nanoribbon

Abstract In this work, the band structure and electronic properties of different nanoribbons of phosphorene along two typical crystal directions of armchair (AM) and zigzag (ZZ) were investigated under compression and tensile strain by density functional theory. The results were compared to the band structure and electronic properties of phosphorene monolayer at similar conditions. The electronic properties of armchair nanoribbons revealed to be resistant to tensile strain in the direction of the armchair, consistent to phosphorene monolayer, but they undergo band structure change due to the applied compression strain at armchair direction. By comparing the effects of strain on the zigzag nanoribbon and phosphorene monolayer, it was found that the zigzag direction neither tolerates the tensile strain nor resists compression strain.

Selective adsorption of harmful molecules on zigzag phosphorene nanoribbon for sensing applications

Abstract Using density functional theory (DFT) and non-equilibrium Green's function method (NEGF), we investigate the electronic structures and transport properties of hydrogenated zigzag phosphorene nanoribbon (ZPNR) after adsorption of four typical harmful molecules. The results show that SO3 and CCl4 are both tending to adsorb on the top site of hydrogenated ZPNR. The NH3 and CH4 are both tending to adsorb on a hollow site of hydrogenated ZPNR. Hydrogenated ZPNR exhibits a strong adsorption of SO3, and the corresponding adsorption energy and charge transfer are largest in four harmful molecules. Moreover, we found the adsorptions of CH3, CH4 and CCl4 have little effect on the band structure of hydrogenated ZPNR. However, the adsorption of SO3 can reduce the band gap of hydrogenated ZPNR obviously. The findings of the present work confirm that the hydrogenated ZPNR has strong selectivity of the absorbability.

Two-impurity entanglement generation by electron scattering in zigzag phosphorene nanoribbons

In this paper, we investigate how two on-side doped impurities with net magnetic moments in an edge chain of a zigzag phosphorene nanoribbon~(zPNR) can be entangled by scattering of the traveling edge-state electrons. To this end, in the first step, we employ the Lippmann-Schwinger equation as well as the Green's function approach to study the scattering of the free traveling electrons from two magnetic impurities in a one-dimensional tight-binding chain. Then, following the same formalism, that is shown that the behavior of two on-side spin impurities in the edge chain of a zPNR in responding to the scattering of the edge-state traveling electrons is very similar to what happens for the one-dimensional chain. In both cases, considering a known incoming wave state, the reflected and transmitted parts of the final wave state are evaluated analytically. Using the obtained results, the related partial density matrices and the reflection and transmission probabilities are computable. Negativity as a measure of the produced entanglement in the final state is calculated and the results are discussed. Our theoretical model actually proposes a method, which is perhaps experimentally performable to create the entanglement in the state of the impurities.

Probing decoupled edge states in a zigzag phosphorene nanoribbon via RKKY exchange interaction

Phosphorene is an anisotropic puckered two-dimensional ($2$D) hexagonal lattice of phosphorus atoms. The edge modes in a zigzag phosphorene nanoribbon (ZPNR) are quasi-flat in nature and fully isolated from the bulk states, which are unique in comparison to the other hexagonal lattices like graphene, silicene etc. We theoretically investigate the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between two magnetic impurities placed on the nanoribbon, and extract the signatures of the flat edge states via the behavior of it. Due to the complete separation of the edge states from the bulk, we can isolate the edge mode contribution via the RKKY interaction from that of the bulk by tuning the external gate potential when both the impurities are placed at the same edge. The bulk induced RKKY interaction exhibits very smooth oscillation with the distance between the two impurities, whereas for edge modes it fluctuates very rapidly. We also explore the effect of tensile strain both in absence and presence of gate voltage and reveal that the RKKY interaction strength can be boosted under suitable doping, when both the impurities are within the bulk.

Half metal phase in the zigzag phosphorene nanoribbon

Exploring half-metallic nanostructures is a crucial solution for developing high-performance spintronic devices. Black phosphorene is an emerging two-dimensional material possessing strong anisotropic band structure and high mobility. Based on the first principles calculations, we investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons (ZPNRs) with three different functionalization groups (OH/CN, OH/NO2, NH2/NO2) at the edges. We find that the interplay between edge functionalization and edge oxidation can induce the half metal phase in the ZPNRs, and the half metal phase can be controlled by the external transverse in-plane electric field and the proportion of the functional groups and edge oxidation. The results may pave a new way to construst nanoscale spintronic devices based on black phosphorene nanoribbons.

Strain modification on electronic transport of the phosphorene nanoribbon

We demonstrate theoretically how local strains can be tailored to control quantum transport of carriers on monolayer armchair and zigzag phosphorene nanoribbon. We find that the electron tunneling is forbidden when the in-plane strain exceeds a critical value. The critical strain is different for different crystal orientation of the ribbons, widths, and incident energies. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent. Moreover, for the zigzag-phosphorene nanoribbon, the two-fold degenerate quasi-flat edge band splits completely under certain strain. These properties provide us an efficient way to control the transport of monolayer phosphorene-based microstructure.

Effects of edge reconstruction on the common groups terminated zigzag phosphorene nanoribbon

Edge configuration plays an important role in the electronic properties of nano-structures. In this work, we perform first-principles calculations to study the effects of the cooperation between neighbor groups on the edge configuration and the electronic properties of zigzag-PNRs (ZPNRs) terminated by common groups H, F, O, S and OH. We find that the cooperation has little effect on the H(F)-terminated ZPNRs, but gives rise to an edge reconstruction for the O(S)-terminated ZPNRs. The edge reconstruction derives from the repulsion between neighbor O atoms and the distortion of the P skeleton induced by the p state coupling among the edge, second edge and third edge P atoms. In comparison to the H-terminated ZPNRs, O-terminated ZPNRs are also a semiconductor and enlarge the band gap, but bring about an extra transport channel for the charge transport at the edge and decreases the effective mass of the electron and hole. OH-terminated ZPNRs also undergo a doubling of the unit cell (UC) along the periodic direction because of the different directions of the neighbor O–H bonds. In comparison with the H-terminated ZPNRs, OH-terminated ZPNRs show a similar band gap and electronic effective mass, but increase the effective mass of the hole.

Two dimensional Schottky contact structure based on in-plane zigzag phosphorene nanoribbon

We investigate the transport properties of Schottky contact structure based on zigzag phosphorene nanoribbon (ZPNR) by using the non-equilibrium Green's function formalism with density functional theory. The calculated band structures show the unpassivated ZPNR is metal and the H-passivated ZPNR is semiconductor. The in-plane contact structure of unpassivated ZPNR and H-passivated ZPNR leads to the formation of a Schottky barrier, which results in rectifying current-voltage characteristics. The rectification ratio (RR) can reach to 103 in the bias region from 0.3 V to 0.5 V. By extending the length of H-passivated ZPNR in Schottky contact structure, the currents of the Schottky contact structure are decreased, but the RR can be enlarged obviously. When the length of H-passivated ZPNR is four times than that of the unpassivated ZPNR, the average RR increases to 106 in the bias region from 0.3 V to 0.5 V and the maximal RR is boosted up to 107 at 0.45 V.

Tuning of the electronic and transport properties of phosphorene nanoribbons by edge types and edge defects

By performing first-principle quantum transport calculations, we investigated the effects of the edge types and edge defects on the electronic and transport properties of phosphorene nanoribbons (PNRs). The calculated band structures show the PNRs with the zigzag and cliff edges are all metallic. The conductance of the cliff phosphorene nanoribbon (CPNR) is higher than that of the zigzag phosphorene nanoribbon (ZPNR). The low bias negative differential resistance behavior is only found in the ZPNR and the peak-to-valley current ratio is up to 102. More over, we found the carrier transport channels under low bias of ZPNR and CPNR mainly locate on the edges. The current-voltage characteristics show the defects induced by removing the phosphorus atoms from the edge can decrease the conductance of the ZPNR and CPNR obviously. The low bias negative differential resistance behavior of the ZPNR also can be weakened or removed by the edge defects.

Spin filtering in a magnetized zigzag phosphorene nanoribbon

Using the Keldysh non-equilibrium Green’s function method and applying the Landauer–Büttiker formula, the spin-dependent electron transport properties of a zigzag phosphorene nanoribbon at zero temperature are studied. The depositing of two ferromagnetic strips on the edges of the nanoribbon induces exchange fields with parallel and anti-parallel configurations. An external perpendicular electric field is also applied to manipulate the spin-dependent electron conductance properties. Due to the order of the zigzag phosphorene nanoribbon edge bands near zero Fermi energy, parallel and anti-parallel configurations result in different properties. For anti-parallel configuration, spin filtering only occurs in the presence of a perpendicular electric field, while in the parallel case spin filtering takes place both in the absence and in the presence of an electric field. Although spin filtering properties are invariant against the inversion of the direction of the electric field in a parallel configuration, this inversion changes the spin filtering type for anti-parallel configurations.

Homostructured negative differential resistance device based on zigzag phosphorene nanoribbons

Robust negative differential resistance as well as quite large currents are observed in zigzag phosphorene nanoribbon homostructures.