Zigzag MoS2 Nanoribbons Research Articles

High performance piezotronic thermoelectric devices based on zigzag MoS2 nanoribbon

Piezotronic and piezophototronic devices have high performance due to the coupling of piezoelectric and semiconductor properties. Strain-induced polarization can effectively modulate the energy band structure and electrical conductivity in low-dimensional structures. In this study, piezotronic effect on the thermoelectric properties of MoS2 zigzag nanoribbons is theoretically investigated. The thermoelectric efficiency (ZT) and Seebeck coefficient of piezotronic thermoelectric devices can be increased by 44 times and 6 times, respectively. This work not only investigates piezotronic effect on thermoelectric properties, but also paves a new way to design high-performance thermoelectric devices.

Effect of strain-induced polarization field on band structure of MoS2 nanoribbon

Single-layered transition metal dichalcogenides (TMDs) materials show intriguing device application potential due to their superior adjustability under various mechanisms. External strain can produce huge polarization fields inside two-dimensional piezoelectric semiconductor materials to modulate the relevant properties. In this paper, the strain-induced polarization field in monolayer zigzag MoS2 nanoribbon is specifically discussed. For comparison, we also study the deformation potential by means of the strain-modified bond lengths and hopping energies. The edge states and band gap indicate a distinct change due to polarization field. This work can put forward feasible perspectives for designing low-dimensional materials-based devices.

Tunable spin-photovoltaic effect in zigzag MoS2 nanoribbons

This article introduces a method for generating spin-polarized photocurrent through light radiation on zigzag MoS2 nanoribbons. In this regard, we investigate local manipulation by exposing edge states to (i) a ferromagnetic, (ii) an antiferromagnetic exchange field, (iii) a parallel and an antiparallel electric field. These local manipulations at the edges with intrinsic spin-orbit interaction could produce a spin-polarized photocurrent and manipulate optical properties. Even at one edge of the nanoribbon, applying the exchange field could induce a fully spin polarization by light irradiation. Efficient quantum efficiency, significant optical spin polarization, and spin-polarized photocurrent make zigzag MoS2 nanoribbon an effective structure for improving the performance of spin-photovoltaic devices.

Tunable thermal conductivity of single layer MoS2 nanoribbons: an equilibrium molecular dynamics study

Thermal transport in single-layer MoS2 nanoribbons (SLMOSNRs) has been comprehensively studied using equilibrium molecular dynamics (EMD) simulations based on the Green–Kubo formulation. The room-temperature thermal conductivity of a pristine ~ 10 nm × 4 nm zigzag MoS2 nanoribbon is computed to be ~ 117 W m−1 K−1 using the Stillinger–Weber (SW) interatomic potential. The thermal conductivity is also studied as a function of temperature and the dimensions of the sample. The thermal conductivity of SLMOSNRs is found to decrease with increasing temperature due to increased phonon–phonon Umklapp scattering, while it shows the opposite trend as the length is increased. With increasing length, the thermal conductivity initially increases rapidly but gradually less so. The thermal conductivity exhibits a similar trend with increasing sample width. Moreover, the impact of defect engineering, an effective tool for tailoring the thermal transport in single-layer MoS2 by considering various defects, namely point vacancies, bi-vacancies, and edge vacancies, is studied. The results of this study show that the thermal conductivity of SLMOSNRs with defects is significantly reduced compared with their pristine counterparts. The reduction of the thermal conductivity with increasing defect concentration is greater at low than high concentration. To study the underlying mechanism responsible for such characteristics, the phonon density of states (PDOS) of SLMOSNRs is calculated. This study provides a detailed demonstration of how the thermal transport characteristics of MoS2 nanostructures can be tuned, promoting the potential application of MoS2 in thermoelectric and nanoelectronic devices.

Effect of Nitrogen doping on the electronic transport of zigzag MoS2 nanoribbons

Abstract Two-dimensional materials have attracted extensive attention in many applications. Based on the first-principles technique, we investigate the electronic transport properties of zigzag MoS2 nanoribbons (Z-MoS2NRs) in which the S atom is substituted by N atom at three different positions. By calculating the formation energy, we find that the S atom at the S-edge of the Z-MoS2NR can be more easily replaced by the N atom. The ground state of the perfect Z-MoS2NR is changed when the N atom is doped. Besides, the relationship between the current and the voltage demonstrate that the Z-MoS2NRs with N doping at the S-edge or in the center still show negative differential resistance (NDR) effect. Besides, the impact of N doping at different positions on the spin-up and spin-down currents of the Z-MoS2NRs is different when the bias voltage varies within a certain range.

Exploring the spin polarization and electronic transport properties for zigzag MoS2 nanoribbons with antisite defects

The spin polarization and electronic transport of zigzag MoS 2 nanoribbons (ZMoS 2 NRs) with two kinds of antisite defects are explored based on density functional theory and nonequilibrium Green's function . The study of the band structure indicates that the defective ZMoS 2 NRs keep the metallic property under antisite defects. From the transmission spectra under the zero bias voltage, it can be observed that the spin up and spin down transmission coefficients at the Fermi level become smaller for the defective two-probe devices when compared with the perfect ZMoS 2 NRs. It suggests that the antisite defects will suppress the transport ability. An obvious negative differential resistance (NDR) phenomenon can be seen from the spin-resolved current-voltage curves for the perfect and defective devices. Due to the antisite defects, the current flowing through the two defective devices is lower than that of the perfect counterpart. Besides, the reduced hop current and bond current in the spin down pathway cause the dramatic drop of the spin down current. An excellent spin filtering effect is found in the ZMoS 2 NRs with antisite defects than the perfect ZMoS 2 NRs. • The spin polarization and electronic transport properties of Z-SbNRs with antisite defects are investigated. • The spin up and spin down transmission coefficients at the Fermi level become smaller for the defective devices. • An obvious negative differential resistance phenomenon is observed from the spin-resolved current-voltage curves. • Excellent spin filtering effect is found in the ZMoS 2 NRs with antisite defects.

Near-room-temperature spin caloritronics in a magnetized and defective zigzag MoS2 nanoribbon

Using a tight-binding approach and first-principles calculations combined with the nonequilibrium Green’s function method, the thermal spin transport in a zigzag molybdenum disulfide ($$\hbox{MoS}_2$$) nanoribbon in the proximity of a ferromagnetic insulator that induces a local exchange magnetic field in the center of the nanoribbon is investigated. It is found that a pure spin current and perfect spin Seebeck effect with zero charge current can be generated by applying a thermal gradient and local exchange magnetic field without a bias voltage near room temperature. Furthermore, it is shown that this nanoscale device can act as a spin Seebeck diode for the control of thermal and spin information in spin caloritronics applications. Finally, the impact of structural defects including edge and Stone–Wales defects on the spin figure of merit is studied. It is then shown that the spin figure of merit can be higher for a magnetized and defective $$\hbox{MoS}_2$$ nanoribbon. The results of this work facilitate deep understanding of the effects of structural defects on the thermoelectric properties of $$\hbox{MoS}_2$$ nanoribbons and indicate their great potential for use in spin caloritronics devices for operation at room temperature.

The spin-transport properties of single edge oxidized zigzag MoS2 nanoribbon

Abstract Based on density functional theory and combined with non-equilibrium Green's function, we investigate the electronic, magnetic and transport properties of zigzag MoS2 nanoribbons which is passivated by oxygen atoms at the single Mo edge (ZMoS2ONRs). At ferromagnetic ground magnetic state, the magnetic moment is found to concentrate on the non-passivated edge. Due to the oxygen passivation, the negative differential resistance effect discovered in the bare zigzag MoS2 nanoribbons disappears. Besides, the electron transport pathway is located at the passivated side and the transport current is mainly contributed by spin-down channels. The findings provide more possibilities for its application in spintronics and nanoelectronic devices.

Edge effects on Li atom adsorption and migration of MoS2 zigzag nanoribbons

In this paper, the effects of the two edges, i.e., S and Mo terminals for zigzag MoS2 nanoribbons, on Li atom adsorption and migration were studied from first principles. The lattice constants of NRs are width-dependent. The adsorption energy of single or multi-lithium adatoms is stronger when they are bound to the top of Mo atoms and when a Li atom is closer to the edge of a nanoribbon, particularly the S terminal edge. The symmetric two-sided adsorption configuration is more to form for multi-lithium adatoms. In addition, Li atoms initially adsorbed at the S or Mo terminal edge always prefer to diffuse along their corresponding edges. For other ones, they prefer to diffuse towards their nearby S or Mo terminal edge. These results indicate that zigzag MoS2 nanoribbons can significantly increase the Li binding energy while providing a high mobility path for Li. We hope our theoretical studies will inspire experimental studies on zigzag MoS2 nanoribbons for use as cathode materials.

The effect of structural defects on the electron transport of MoS2 nanoribbons based on density functional theory

Using non-equilibrium Green’s function method and density functional theory, we study the effect of line structural defects on the electron transport of zigzag molybdenum disulfide (MoS2) nanoribbons. Here, the various types of non-stoichiometric line defects greatly affect the electron conductance of MoS2 nanoribbons. Although such defects would be lead to the electron scattering, they can increase the transmission of charge carriers by creating new channels. In addition, the presence of S bridge defect in the zigzag MoS2 nanoribbon leads to more the transmission of charge carriers in comparison with the Mo–Mo bond defect. Also, we find that the different atomic orbitals and their bonding structure at the edge affect the electron conductance of MoS2 nanoribbons. Moreover, we calculate the spin-dependent transport of MoS2 nanoribbons and showed that the spin polarization increases at the non-zigzag edges and remains even in the presence of the defect. This study presents a deep understanding of created properties in MoS2 nanoribbons due to the presence of structural defects.

Hydrogen passivation tunes edge magnetism in the ZMoS2NR with a sulfur vacancy

We performed density functional theory study on electronic structure, magnetic properties and stability of zigzag MoS2 nanoribbons with a S vacancy (ZMoS2NRs-VS) and considered their different edge passivation. The ZMoS2NR-VS systems are magnetic metals with ferromagnetic (FM) edge states. The magnetic moments are greatly influenced by the site of S vacancy and edge passivation because the vacancy and edge states significantly change the structure of the systems. Importantly, we can achieve distinct FM states such as both edge FM and single edge FM states in the ZMoS2NRs-VS by tuning edge passivated pattern. Additionally, edge passivation can not only tune the magnetism of the ZMoS2NRs-VS but also enhance their stability by eliminating dangling bonds. These interesting findings on the ZMoS2NRs may open the possibility of their application in nanodevices and spintronics.

Flexible modulation of electronic and magnetic properties of zigzag H-MoS2 nanoribbons by crack defects

The effects of crack defects on electronic and magnetic properties of zigzag MoS2 nanoribbons are investigated systematically by first-principles calculations based on spin-polarized density functional theory. We find that not only the electronic and spin transport ability of zigzag MoS2 nanoribbons can be enhanced significantly by the armchair crack defects, but also their magnetism could be modulated flexibly by crack defects. Our study suggests that the introduction of crack defect is a feasible way to modulate the electronic and magnetic properties of zigzag MoS2 nanoribbons. We further propose that the crack defects may also provide a useful tool for improving the performance of devices.

Achieving half-metallicity in zigzag MoS2 nanoribbon with a sulfur vacancy by edge passivation

We performed density functional theory calculations to investigate the electronic and magnetic properties of zigzag MoS2 nanoribbons with a S vacancy (ZMoS2NRs-VS). The systems are all magnetic with magnetism concentrated on the edge Mo and S atoms. Interestingly, ZMoS2NR-VS can be tuned from metallicity to half-metallicity. Moreover, passivation of functional groups such as H, F, OH or NH2 with a passivated concentration of 25% can not only provide half-metallicity in ZMoS2NR-VS but also enhance the stability of the system. These diverse electronic and magnetic properties might open great opportunities for MoS2 materials in spintronics in the future.

Structural and magnetic properties of MoS2 monolayer zigzag nanoribbon doped by Ti, V, Cr, and Mn

In order to find new functions of monolayer MoS2 in nanoelectronics or spin electronic devices, using spin-polarized density functional theory (DFT) calculations with on-site coulomb interaction (U), we investigated substitutional doping of Mo atoms of monolayer zigzag MoS2 nanoribbon (ZZ-MoS2 NR) by transition metals (TM) (where TM = Ti, V, Cr, Mn) at the Mo-edge, S-edge, and the middle of the NRs. The results of this study indicate the NR widened irrespective of the doped TM position and type, and the Mo-edge was found as the easiest substitutional position. For ZZ-MoS2 NR doped by Mn, Cr or V atoms, the preferred magnetic coupling state is the edge atoms of S at the S-edge, exhibiting the same spin polarization with TM (named the FM1 state), attributing the NR with metallic magnetism. For Ti-doped monolayer ZZ-MoS2 NR, in addition to the FM1 state, other preferred magnetic coupling state was observed in which the edge atoms of S at the S-edge exhibit the opposite spin polarization with that of Ti (named the FM2 state). Thus, the NR doped by Ti atom possesses metallic (FM1 state) or half-metallic (FM2 state) magnetism. The total magnetic moments of the ZZ-MoS2 NR doped by TM follows a linear relationship as a function of the TM dopants (Mn, Cr, V, and Ti). Under >4% applied strain, the NR doped by Ti atom only presents the characteristics of half-metallic magnetism as the initial one in the FM2 state, and its total magnetic moment always remained 0 μB, i.e., it was not affected by the width of the NR. This study provides a rational route of tuning the magnetic properties of ZZ-MoS2 NRs for their promising applications in nanoelectronics and spin electronic devices.

Phase transition and field effect topological quantum transistor made of monolayer MoS2

We study topological phase transitions and topological quantum field effect transistor in monolayer molybdenum disulfide (MoS2) using a two-band Hamiltonian model. Without considering the quadratic (q2) diagonal term in the Hamiltonian, we show that the phase diagram includes quantum anomalous Hall effect, quantum spin Hall effect, and spin quantum anomalous Hall effect regions such that the topological Kirchhoff law is satisfied in the plane. By considering the q2 diagonal term and including one valley, it is shown that MoS2 has a non-trivial topology, and the valley Chern number is non-zero for each spin. We show that the wave function is (is not) localized at the edges when the q2 diagonal term is added (deleted) to (from) the spin-valley Dirac mass equation. We calculate the quantum conductance of zigzag MoS2 nanoribbons by using the nonequilibrium Green function method and show how this device works as a field effect topological quantum transistor.

A Numerical Analysis of Electronic and Optical Properties of the Zigzag MoS2 Nanoribbon Under Uniaxial Strain

In this paper, we investigate the transmission spectrum, current–voltage ( ${I}$ – ${V}$ ) characteristics and dielectric function of the zigzag MoS2 nanoribbon with and without a uniaxial tensile strain. By considering only the nearest neighbor atoms, we will first calculate the band structure for this material using the tight-binding method. Then, we present the transmission spectrum and the ${I}$ – ${V}$ characteristics by employing nonequilibrium Green’s function formalism in conjunction with the Landauer formula. Due to the presence of edge states, in the zigzag nanoribbons, this material demonstrates a metallic behavior. We also study the aforementioned parameters in the presence of the strain in the range of 10%–20%. Results indicate that applying a tensile strain of the order of 10% opens up a direct gap within the energy bands. This gap increases upon increasing the strain. Furthermore, the current increases with increase in the tensile strain as well as the number of atoms at the ribbon’s edge. Our numerical simulations also predict possible transitions between subbands. Strain intensifies the amplitude of the dielectric function at lower energies. These results can be instrumental for the design of nanoscale photonic devices based on the nanoribbon MoS2.

Spin Transport in Electric-Barrier-Modulated Ferromagnetic/Normal/Ferromagnetic Monolayer Zigzag MoS2 Nanoribbon Junction

In this paper, with the three-band tight-binding model and non-equilibrium Green’s function technique, we investigate spin transport in electric-barrier-modulated Ferromagnetic/Normal/Ferromagnetic (F/N/F) monolayer (ML) zigzag MoS2 nanoribbon junction. The results demonstrate that once the double electric barriers structure emerges, the oscillations of spin conductances become violent, especially for spin-down conductance, the numbers of resonant peaks increase obviously, thus we can obtain [Formula: see text] spin polarization in the low energy region. It is also found that with the intensity of the exchange field enhancement, the resonant peaks of spin-up and spin-down conductances move in the opposite direction in a certain energy region. As a consequence, the spin-down conductance can be filtered out completely. The findings here indicate that the present structure may be considered as a good candidate for spin filter.

Spin-filtering, negative differential resistance, and giant magnetoresistance in (2 × 1) reconstructed zigzag MoS2 nanoribbons

Based on density functional theory combined with nonequilibrium Green's function method, we have investigated the spin-polarized transport properties of the (2 × 1) reconstructed zigzag MoS2 nanoribbon (ZMoS2NR)-based devices. The results show that these devices can exhibit multiple high-performance spin-dependent transport properties by modulating the applied magnetic field, including spin-filtering, negative differential resistance and giant magnetoresistance effects. These effects are explained by the spin band structures around the Fermi level, as well as their symmetries. Moreover, all effects are robust regardless of the nanoribbon width. These findings suggest the (2 × 1) reconstructed ZMoS2NRs have great potential in the field of spintronics.

Spin Caloritronic Transport of (2×1) Reconstructed Zigzag MoS2 Nanoribbons**Supported by the Natural Science Foundation of Shandong Province under Grant No ZR2016AM11.

Using first-principles density functional theory combined with nonequilibrium Green’s function method, we investigate the spin caloritronic transport properties of (2×1) reconstructed zigzag MoS2 nanoribbons. These systems can exhibit obvious spin Seebeck effect. Furthermore, by tuning the external magnetic field, a thermal giant magnetoresistance up to 104% can be achieved. These spin caloritronic transport properties are understood in terms of spin-resolved transmission spectra, band structures, and the symmetry analyses of energy bands around the Fermi level.

Perfect valley polarization in MoS2

We study perfect valley polarization in a molybdenum disulfide MoS2 nanoribbon monolayer using two bands Hamiltonian model and non-equilibrium Green's function method. The device consists of a one-dimensional quantum wire of MoS2 monolayer sandwiched between two zigzag MoS2 nanoribbons such that the sites A and B of the honeycomb lattice are constructed by the molecular orbital of Mo atoms, only. Spin-valley coupling is seen in energy dispersion curve due to the inversion asymmetry and time-reversal symmetry. Although, the time reversal symmetry is broken by applying an external magnetic field, the valley polarization is very small. A valley polarization equal to 46% can be achieved using an exchange field of 0.13 eV. It is shown that a particular spin-valley combination with perfect valley polarization can be selected based on a given set of exchange field and gate voltage as input parameters. Therefore, the valley polarization can be detected by detecting the spin degree of freedom.