Zigzag Phosphorene Nanoribbons Research Articles

Modulating the electronic transport properties of zigzag phosphorene nanoribbons through the coupling with the chromium triiodide molecules

Based on density functional theory (DFT) and non-equilibrium Green's function (NEGF) method, we have investigated spin-dependent electronic transport properties of zigzag phosphorene nanoribbons (ZPNRs) coupled with chromium triiodide (CrI3) molecules. Three different adsorption models have been considered: CrI3 molecule is placed on ZPNR surface (C-type), and CrI3 molecule is lateral adsorbed on the edge of ZPNR with its molecule panel vertical (V-type) or parallel (P-type). We discovered that ZPNR's electrical transport clearly displays spin polarization, owing to the coupling between ZPNR and CrI3 molecules. And spin-polarization is tightly dependent on the absorbing manners. Moreover, the negative differential resistance (NDR) characteristics can be observed from current-voltage curves and modulated by absorbing molecules. Furthermore, we also discovered that CrI3 is vertically adsorbed on the surface of the ZPNRs has a better spin-polarization efficiency than the other two cases.

Spintronic performance of bent zigzag phosphorene nanoribbons: effects of mechanical deformation and gate voltage.

This study explores the spintronic properties of an innovative device incorporating in-plane bent zigzag phosphorene nanoribbons (ZPNRs). The device features ZPNRs with a channel length of 23.4 nm, bent into circular arcs with varying curvatures. We investigate the impact of mechanical deformation and gate voltage on the spin-dependent properties, including the density of states, transmission coefficients, and spin Seebeck coefficient (SSC). Our results demonstrate that the device exhibits a spin-semiconducting phase with tunable spin-splitting characteristics and spin-dependent transport properties, both of which are influenced by the curvature. An increase in the bending parameter markedly enhances spin splitting, leading to the SSC attaining values as high as 1.35 mV K-1. Moreover, the application of gate voltage further enhances both spin polarization and spin current. The significant impact of mechanical deformation and gate voltage on spintronic performance showcases the potential of bent ZPNRs for advanced applications.

Structure-search-revealed edge reconstruction in two-dimensional materials: The case of phosphorene nanoribbons

The edge structures of two-dimensional materials are important for the property control of corresponding nanoribbons, but possible edge reconstructions are difficult to resolve. Taking phosphorene nanoribbons as an example, we have employed the structure-searching program IM2ODE to discover new structures for both zigzag and armchair edges of bare phosphorene nanoribbons. The edge atoms of these low-energy nanoribbons are generally 3-fold coordinated, and the edge energies are significantly lower than those directly cut from the monolayer. Moreover, we can build low-energy sinuous edges along the diagonal direction based on the bonding features of phosphorus atoms. Further electronic structure studies also reveal that zigzag phosphorene nanoribbons undergo cell doubling and metal-insulator transition similar to Peierls distortion, indicating that the edges experience self-passivation and become stabilized. As similar edge reconstructions can exist in many other two-dimensional materials and it may be difficult to construct the edges by hand, our structure-searching approach provides reliable insights and certain rules can be discovered to elucidate various structure reconstructions.

Electronic transport and thermoelectric properties of phosphorene nanodisk under an electric field

The Seebeck coefficient is an important quantity in determining the thermoelectric efficiency of a material. Phosphorene is a two-dimensional material with a puckered structure, which makes its properties anisotropic. In this work, a phosphorene nanodisk (PDisk) with a radius of 3.1 nm connected to two zigzag phosphorene nanoribbons is studied, numerically, by the tight-binding and non-equilibrium Green’s function (NEGF) methods in the presence of transverse and perpendicular electric fields. Our results show that the change in structure from a zigzag ribbon to a disk form creates an energy gap in the structure, such that for a typical nanodisk with a radius of 3.1 nm, the size of the energy gap is 3.88 eV. Besides, with this change, the maximum Seebeck coefficient increases from 1.54 to 2.03 mV/K. Furthermore, we can control the electron transmission and Seebeck coefficients with the help of the electric fields. The numerical results show that with the increase of the electric field, the transmission coefficient decreases and the Seebeck coefficient changes. The effect of a perpendicular electric field on the Seebeck coefficient is weaker than a transverse electric field. For an applied transverse electric field of 0.3 V/nm, the maximum Seebeck coefficient enhances to 2.09 mV/K.

Half-metallicity in strained phosphorene nanoribbons

We investigate the effect of nonuniform strains on the electronic properties of zigzag phosphorene nanoribbons (ZPNR) within a self-consistent computational model. We show that a nonuniform strain induces spin-splitting even at low values of strain. Moreover, a further increase of strain causes considerable spin splitting with a tunable spin-dependent energy gap until a critical value where the half-metallicity (HM) occurs. Interestingly, the black ZPNRs with different ribbon widths show the HM under out-of-plane tensile and in-plane compressive strains. Moreover, the critical values to realize HM can vary considerably depending on the ribbon width and the direction of strain. The results show that the nonuniform strain can be a practical way to enhance flexible spintronic in phosphorene-based devices.

The effect of edge passivation of phosphorene nanoribbons with different atoms and arrangements on their electronic and transport properties

Through density functional theory (DFT), we investigate the electronic and transport properties of zigzag phosphorene nanoribbons (ZPNRs) and armchair phosphorene nanoribbons (APNRs) passivated with only H or O, or both H and O with different arrangements, systematically. According to the calculated cohesive energies, all structures are stable. Also, the simulation results reveal a semiconductor-to-metal transition in zigzag groups, but all the APNRs are semiconductors. We see the direct-to-indirect energy bandgap transition in armchair groups, while all the semiconductors of zigzag groups have a direct energy bandgap. We also study the effect of external transverse electric field on electronic properties. The applying electric field changes the energy bandgap leading to a semiconductor-to-metal transition at a certain electric field. In addition, the direct-to-indirect bandgap transition and vice versa occurs for some samples. Moreover, edge passivation has a significant effect on transport properties. The breakdown voltage of the devices changes from 0 to 1.94 eV, and we observe negative differential resistance (NDR) for some devices. The results indicate that passivated phosphorene nanoribbons are possible, and their properties can effectively be tuned by the arrangement, type of edge atoms, and external electric field, which make these structures a promising candidate for feasible nanodevices.

Enhanced Spin Thermopower in Phosphorene Nanoribbons via Edge-State Modifications.

We investigated spin-dependent thermoelectric transport in zigzag phosphorene nanoribbons with a ferromagnetic stripe. We explored the possibility to enhance the spin thermopower via modifications of the edge states in zigzag ribbons. Two methods are proposed to modulate the edge transport: one is applying gate voltages on the edges; the other is including notches on the ribbon edges. The transport gap is enlarged by the edge-state modifications, which enhance the charge and spin Seebeck coefficients almost twofold. Our results suggest phosphorene to be a promising material for thermoelectric applications and open a possibility to design a tunable spin-thermoelectric device.

Direct mapping of edge states in bilayer zigzag phosphorene nanoribbons into a SSH ladder model and optimizing their thermoelectric performance via edge state engineering

We theoretically investigate the thermoelectric properties of zigzag bilayer phosphorene nanoribbons (ZBPNR). We first, draw an analogy between the extended Su-Schrieffer-Heeger (SSH) ladder and ZBPNR edge states and obtain their corresponding band structure and wave functions analytically. Then, by applying the energy filtering method, we show that the electric power and thermoelectric efficiency of the ZBPNRs can be improved remarkably in the presence of mid-gap edge states. We also argue how to engineer the edge modes to further optimize thermoelectric power and efficiency of the system by applying periodic point potentials at the boundaries.

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.

Dual spin filtering and negative differential resistance effects in vanadium doped zigzag phosphorene nanoribbons with different edge passivations

By applying density functional theory combined with nonequilibrium Green’s function, we investigate the electronic and transport properties of V-doped zigzag phosphorene nanoribbons (ZPNRs) with different edge passivations. The results show that the electronic and transport properties of vanadium-doped ZPNRs (V-ZPNRs) can be tuned by the edge passivation types. V-ZPNRs passivated by sulfur atoms possess stronger conductivity than bared ones, and edge passivation by hydrogen and halogen (F and Cl) atoms can transform V-ZPNRs from magnetic metals to magnetic semiconductors. Moreover, due to the edge passivation by hydrogen and halogen atoms, V-ZPNRs exhibit dual spin polarizability and negative differential resistance effects. The findings provide theoretical support in modulating the electronic transport properties of ZPNRs, which may be useful in designing phosphorene-based spintronic devices.

Force-constant model for the vibrational modes in black-phosphorene and phosphorene nanoribbons (PNRs)

We present in this paper, force constant model developed for Black phosphorene in order to reproduce the vibrationnal properties calculated from density functional theory. The results of this model are compared with the experimental data available from Raman spectroscopy measurements. Excellent agreement is obtained between calculation and Raman experiment. On the basis of the resulting force model, the non-resonant Raman spectra of a large number of armchair and zigzag phosphorene nanoribbons (PNRs) are calculated using the bond polarizability model in the framework of spectral moments method. We have found a good agreement with group theory concerning the number of the Raman-active modes of black phosphorene. We report the effect of the edge and width on the vibrational properties of PNRs by increasing the width, the main characteristic feature is dictated by Ag2 Raman active mode. It exhibits different characteristic for armchair and zigzag edges. The mode is upshifted under armchair edge and downshifted in the zigzag one. Moreover, we observe additional Raman modes as a function of the ribbon width and we propose an equation, ωmin = A/L (A = 98 cm−1 nm), to estimate the PNRs width L from the knowledge of the lowest Raman frequency mode ωmin.

Lateral heterostructures of zigzag phosphorene nanoribbons as a platform for high performance 5 nm transistor

By performing first-principle transport calculations, we propose that lateral heterostructures of zigzag phosphorene nanoribbons (ZPNRs) with the different passivated edges, can represent a powerful platform for the high performance field-effect transistors (FETs). The ZPNR with H-passivated edge is a semiconductor with a band gap of 1.39 eV. However, the ZPNRs with zigzag edges and cliff edges all exhibit the metallic characters. Two 5 nm Schottky barrier FETs consisting of H-passivated ZPNR and unpassivated ZPNRs with zigzag or cliff edges all can overcome the short channel effect. More importantly, the 5 nm Schottky barrier FET consisting of H-passivated ZPNR and unpassivated ZPNRs with cliff edge at a supply voltage of 0.64 V exhibits ION/IOFF ratio larger than 103, which satisfy the requirements of the high-performance transistor outlined by the ITRS (International Technology Roadmap for Semiconductors). Therefore, the transistor model of ZPNRs in this paper provides a valuable idea for the design of short channel transistors in the future.

Even–odd effect of the thermoelectric information for zigzag phosphorene nanoribbons under an electric field

We study the thermoelectric properties of zigzag-edge phosphorene nanoribbon with N chains (N-ZPNR) under a perpendicular electric field (PEF). By adopting the tight-binding Hamiltonian combined with the nonequilibrium Green’s function method, it is demonstrated that the maximum value of the Seebeck coefficients for both 40- and 41-ZPNRs can reach 4 mV/K. Interestingly, there is an even–odd effect on the thermoelectric properties when a PEF is applied, which originates from the structure symmetry of N-ZPNR and can result in different behavior of edge states for even and odd cases. Specifically, the increasement induced by the external field of the Seebeck coefficient for 41-ZPNR with odd number of chains is much more pronounced than that for 40-ZPNR with even number. Moreover, the introduction of the Anderson disorder to the system can suppress the transmission but enhance the Seebeck coefficients for both even and odd cases.

Robust charge spatial separation and linearly tunable band gap of low-energy tube-edge phosphorene nanoribbon.

Versatile applications have been proposed for phosphorene nanoribbons (PNRs), whose properties depend strongly on the edge structures. Recently, a unique tube-reconstruction at the zigzag edge (ZZ[Tube]) of PNRs was discovered to be the lowest configuration. Therefore, studies on PNRs should be reconsidered. In this paper, we systemically explore the width and strain effects on zigzag PNRs with different edge structures, including ZZ[Tube], ZZ and ZZ[ad] edges. ZZ PNRs always have small band gaps which are nearly independent of both width and strain. A remarkable band gap exists in ZZ[ad] PNRs which increases with a decrease in the ribbon width but is not sensitive to strain. In contrast, the band gaps of ZZ[Tube] PNRs change from 1.08 to 0.70 eV as the width increases from 12 to 65 Å. In addition, the band gaps of ZZ[Tube] PNRs show a linear response under a certain range of strain. In addition, the carrier effective masses (0.50 m0 for electrons and 0.94 m0 for holes) of ZZ[Tube] PNRs are much lower than for ZZ[ad], and the VBM and CBM charges are robustly spatially separated even under strains ranging from −5% to 5%. Their ease of formation, lowest energy, light effective mass, linear band gap response to strain and robust charge spatial separation provide ZZ[Tube] PNRs with potentially excellent performance in microelectronic and opto-electric applications.

Magneto-electronic property in zigzag phosphorene nanoribbons doped with transition metal atom

The magneto-electronic properties of zigzag phosphorene nanoribbons (ZPNRs) doped, respectively, with iron (Fe), cobalt (Co) and nickel (Ni) atoms are investigated by the first-principles method based on density functional theory. The calculated results show that the structures of doped and undoped ZPNR are stable because their binding energy and Gibbs free energy are negative, and the Forcite annealing dynamics simulation shows that the thermal stabilities of all doped ZPNRs are extremely high. The ground states of pristine ZPNRs and ZPNRs doped with Co atoms are nonmagnetic states, while the ground states of ZPNRs doped with Fe or Ni atoms are ferromagnetic states. When they are in the nonmagnetic states, the pristine ZPNRs and ZPNRs doped with Co atoms turn into semiconductors, while the ZPNRs doped with Fe or Ni atoms become metals. The undoped ZPNRs are direct band gap semiconductors, while the ZPNRs doped with Co atoms are indirect band gap semiconductors, and the band gaps of the latter are smaller than those of the former. The changes of the properties of the ZPNRs are due to the introduction of impurity energy band into the energy band structures. The spin-polarized calculation displays that the pristine ZPNRs and ZPNRs doped with Co atoms are non-magnetic, and the ZPNRs doped with Fe or Ni atoms are magnetic but only in the ferromagnetic state. In the ferromagnetic state, the ZPNRs doped with Fe atoms are spin semiconductors, while the ZPNR doped with Ni atoms are spin half-metals. This means that the half-metal feature can be realized by doping Ni atom into ZPNR. The magnetism of ZPNRs doped with Fe or Ni atoms is mainly contributed by impurity atoms, and the occurrence of magnetism is due to the existence of unpaired electrons in ZPNR. The doping position has a certain influence on the electromagnetic properties of ZPNR. In the ferromagnetic state, the ZPNRs are half-metals when the Ni atoms are doped near the edge of the nanoribbons, while the ZPNRs are spin semiconductors as the Ni atoms are doped near the symmetric center of the nanoribbons. These results might be of significance for developing the phosphorene based electronic nanodevices

A first-principles study on zigzag phosphorene nanoribbons terminated by transition metal atoms* *Project supported by the National Natural Science Foundation of China (Grant No. 11564008), the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2017GXNSFAA198195), and the Shanghai Supercomputer Center.

We have investigated the electronic and magnetic properties of zigzag phosphorene nanoribbons (ZPNRs) with transition metal (TM) passivated atoms, it can be found that the ZPNRs with TM passivated atoms exhibit different magnetisms except for the Ni-passivated system. Meanwhile, the results show that the magnetic moments of ZPNRs with TM passivated atoms are larger than that of ZPNRs with other passivated non-metals/groups. Interestingly, it can be found that Fe-passivated ZPNR exhibits magnetic semiconducting character, which provides the possbility for the application of phosphorene in information storage. For Mn-passivated ZPNRs, it exhibits the half-metallicity. These results may be useful for potential applications of phosphorene in electronic and high-performance spintronic devices.

The effect of Rashba spin–orbit interaction on the spin-polarized transport of zigzag phosphorene nanoribbons

Spin transport features of zigzag phosphorene nanoribbons (ZPNRs) are investigated in the presence of the perpendicular electric field (), the exchange field , and Rashba spin–orbit interaction (RSOI). To this end, the non-equilibrium Green’s function method is used based on the tight-binding model, which can be described by the Landauer–Büttiker formalism. Interestingly, spin-filtering and spin-flipping are observed only for incoming up (down) spins in the presence of the exchange field with anti-parallel configuration (parallel configuration). Furthermore, changing the magnitude and direction of for the parallel and anti-parallel configurations of the exchange field in the presence of RSOI can induce and control the ON/OFF state of the current, the band gap, the spin polarization, spin-flipping, and spin-filtering in the system. The obtained results could be utilized to construct novel nanostructures and also to maximize the efficiency of spintronic devices based on ZPNRs.

Even–odd effect of spin-dependent transport and thermoelectric properties for ferromagnetic zigzag phosphorene nanoribbons under an electric field

We study the spin-dependent transport and thermoelectric properties of ferromagnetic zigzag-edge phosphorene nanoribbon with N chains (N-ZPNR) modulated by a perpendicular electric field (PEF). By adopting the Hubbard model Hamiltonian combined with the self-consistent calculation, and using the nonequilibrium Green’s function method, we obtain the band structure, spin-dependent transmission coefficients and Seebeck coefficients. It is demonstrated that the bands are split with spin-up and -down ones for both 12- and 13-ZPNR in the ferromagnetic state, and both ZPNRs show spin-semiconducting behavior with the spin gap of value 1 eV. Interestingly, there is an even–odd effect on the spin-dependent transport and thermoelectric properties when a PEF is applied, which originates from the structure symmetry of N-ZPNR and can result in different behavior of edge states for even and odd cases. The electric field lifts the degeneracy of the two edge bands for both spin-up and -down channels in 12-ZPNR, however, it only bends the spin-up edge bands and shifts the spin-down ones upward without splitting in 13-ZPNR. In addition, we find that the spin Seebeck coefficients exhibit wide plateaus and their maximum values can reach unprecedented giant 5 mV K−1 for both ZPNRs. The spin Seebeck coefficients for both ZPNRs decrease gradually as temperature increasing. As the electric field increasing, the value of the plateau in the spin Seebeck coefficient for 12-ZPNR decreases gradually, however, the plateau almost has no variation for 13-ZPNR in this case. This different responses of spin Seebeck coefficients to the PEF between even and odd cases originate from the different edge state responses to the electric field, and we provide the explanation from the corresponding spin-up and spin-down Seebeck coefficients. Our results reveal that ferromagnetic ZPNRs are perfectly spin-polarized, and are promising candidates for spin caloritronics with high efficiency.

Gate-voltage induced giant spin Seebeck effect in phosphorene nanoribbons

Using the tight-binding approximation combined with the mean-field Hubbard model and a Green's function approach, we designed a spin thermoelectric device in which the electrodes and the channel region consist of zigzag phosphorene nanoribbons. Our theoretical results show that applying a gate voltage only in the channel region induces a spin-semiconducting behavior with spin-polarized midgap states. Furthermore, the appearance of the localized and asymmetric electron-hole transmission coefficients induces a giant spin Seebeck effect with a spin-dependent current by applying a thermal gradient. Additionally, the spin-Seebeck values for zigzag phosphorene nanoribbons could be larger than those calculated for magnetized zigzag graphene nanoribbons. More interestingly, the values and the direction of the spin Seebeck effect as well as the spin-dependent currents can be easily manipulated by controlling the applied gate voltage or the magnetic state of the channel at room temperature.

Spin photocurrents in zigzag phosphorene nanoribbons: From infrared to ultraviolet

Using the self-consistent non-equilibrium Green’s function model and the mean-field Hubbard approximation, we studied the possibility of inducing the spin-photovoltaic effects in zigzag phosphorene nanoribbons. We numerically showed that an applied electric field could induce a spin-semiconducting behavior with anisotropic and localized band structures around the Fermi energy in the antiferromagnetic zigzag phosphorene nanoribbons. Moreover, a tunable energy gap with an electric field could induce a spin photocurrent in a wide range of photon energies. Interestingly, increasing the electric field strength induces the spin-valve effect from terahertz to infrared irradiation. Furthermore, ferromagnetic zigzag phosphorene nanoribbons reveal a spin-dependent photoresponsivity, which is induced by infrared to ultraviolet frequencies. These results could enhance photovoltaic effects with a generation of the spin photocurrent in phosphorene junctions.