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We present an atomistic simulation of thermoelectric properties in cove-edged graphene nanoribbons (CGNRs) via the nonequilibrium Green's function. Different from gapless zigzag graphene nanoribbons (ZGNRs), CGNRs exhibit a noticeable bandgap. Such a bandgap can be modulated by varying three structural parameters (namely, the width N, the distance between adjacent coves m, as well as the shortest offset n) of CGNRs, which can give rise to the transition from semiconducting to semi-metallic. Due to the less dispersive phonon bands and the decrease in the number of phonon channels of CGNRs, they are found to have the lower phonon thermal conductance than ZGNRs. Modulation of CGNRs can produce over tenfold improvement of the maximum of ZT compared to ZGNRs. This improvement is due to the promotion of the Seebeck coefficient together with the degradation of the phonon thermal conductance of CGNRs compared to ZGNRs. [ABSTRACT FROM AUTHOR]

This study delves into the thermoelectric properties of armchair black phosphorene nanoribbons while considering the presence of line edge roughness. Employing the tight‐binding method in conjunction with non‐equilibrium Green's function techniques and Landauer formulas, the impact of various parameters on thermoelectric performance is explored. These findings reveal that the electrical conductivity and, consequently, the power factor exhibits an increasing trend with expanding ribbon length and width. This behavior can be attributed to heightened collision rates, particularly in narrow ribbons, induced by line edge roughness as length increases. Remarkably, the Seebeck coefficient at the Fermi energy corresponding to the maximum power factor remains nearly constant across different widths, lengths, temperatures, and transport regimes. Furthermore, the thermoelectric figure of merit (ZT) demonstrates a positive correlation with both ribbon length and width. In narrow widths and lengths ≈1000 nm, the power factor and figure of merit exhibit an upward trend with ribbon width. However, with further increases in ribbon width, the influence of line edge roughness on thermal conductivity diminishes. Consequently, the figure of merit decreases due to the rise in thermal conductivity. Notably, the thermoelectric figure of merit is higher for short and narrow ribbons and long and wider ribbons. [ABSTRACT FROM AUTHOR]

Based on density functional theory (DFT) and nonequilibrium Green's function (NEGF) framework, to study the monolayer (ML) blue phosphorene (BlueP) doped with C along zigzag direction, such as the structural stability, and electronic and transport properties. Interestingly, we found that doping engineering strategies can effectively transform monolayer ML ZBlueP doped with C into a spintronic nanodevice with a few unique transport properties. Firstly, our model showed a magnificently giant magnetoresistance (GMR) up to 10 $ ^4 $ 4 under low bias. Secondly, a rectifier with a large rectification ratio (RR) of 10 $ ^5 $ 5 was observed. Lastly, negative differential resistance with a peak-to-valley current ratio (PVCR) of 10 $ ^4 $ 4 was observed. Our research shows a promising route towards the development of high-performance ML ZBlueP spintronics technology by doping with C atom. Our results indicate that our models have immense potential for application in nanoscale spintronic devices. [ABSTRACT FROM AUTHOR]

To investigate the effect of quantum confinement on the thermoelectric properties of armchair graphene (AGNRs) at different temperatures, we have used density functional theory-based tight-binding (DFTB) together with the non-equilibrium Green's function (NEGF). In this study, we focus on eight different widths of AGNR, namely the ribbon width, which ranges from 3 to 10. The results demonstrate that the band structure may be altered by changing the ribbon width, leading to changes in the electrical components of thermoelectric efficiency. Also, decreasing ribbon width increases the band gap and effect of phonon edge scattering on thermal conductance for the AGNR series. Thus, it has a higher Seebeck coefficient and figure of merit (ZT) than wider AGNRs. Also, it is found that the ZT is increasing as temperatures rise, where the Fermi distribution broadens and excites more states in adjacent bands as the temperature rises. These results suggest that engineered graphene nanoribbons have the potential to produce high ZT values and are an attractive contender for use in the development of future thermoelectric generators. [ABSTRACT FROM AUTHOR]

In this study, we employ density functional theory and non-equilibrium Green's function methods to investigate the electronic and photoelectric response properties of one-dimensional hexagonal ZnX (X = S, Se) nanoribbons (NRs). Remarkably, armchair (ARM) NRs demonstrate superior photoelectric response in the visible and near-ultraviolet regions. It is worth noting that for all considered photon energies, the photocurrent exhibits a cosine dependence on the polarization angle, which is consistent with the photogalvanic effect. when the width of NR is eight atoms, the zinc blende ZnSe/ARM NR-based device achieves a maximum extinction ratio of 63.9 at the photon energy of 3.0 eV. The significant photocurrent and high polarization sensitivity suggest the potential of ZnX NRs for applications in optoelectronic devices, particularly in visible and near-ultraviolet light detection. [ABSTRACT FROM AUTHOR]

Molecular switches based on functionalized graphene nanoribbons (GNRs) are of great interest in the development of nanoelectronics. In experiment, it was found that a significant difference in the conductance of an anthraquinone derivative can be achieved by altering the pH value of the environment. Building on this, in this work we investigate the underlying mechanism behind this effect and propose a general design principle for a pH based GNR-based switch. The electronic structure of the investigated systems is calculated using density functional theory and the transport properties at the quasi-stationary limit are described using nonequilibrium Green's function and the Landauer formalism. This approach enables the examination of the local and the global transport through the system. The electrons are shown to flow along the edges of the GNRs. The central carbonyl groups allow for tunable transport through control of the oxidation state via the pH environment. Finally, we also test different types of GNRs (zigzag vs. armchair) to determine which platform provides the best transport switchability. [ABSTRACT FROM AUTHOR]

While synthesizing quasi-one-dimensional nanoribbons, there is a finite probability that edges have cove-edge defects. This paper focuses on the structural, electronic, and transport properties of cove-edge aluminum nitride nanoribbons (AlNNR) using density functional theory and the non-equilibrium Green's function (NEGF) method. The cove-edge AlNNRs are thermodynamically stable and exhibit metallic behavior. Interestingly, the calculated current–voltage characteristics of the cove-edge AlNNR-based nanodevices show negative differential resistance (NDR). The H-AlN-Cove nanodevice exhibits high peak-to-valley current ratio (PVCR) of the order of 107. The calculated PVCR of the H-AlN-Cove nanodevice is 106 times higher than that of the silicene nanoribbon (SiNR) and graphene nanoribbon (GNR), and 104 times higher than that of the phosphorene nanoribbon (PNR) and arsenene nanoribbons (ANR)-based devices respectively. The NDR feature with high PVCR provides a prospect for the cove-edge AlNNR in nanodevice applications. [ABSTRACT FROM AUTHOR]

Electronic structures and magnetotransport properties of topological Dirac semimetal (TDSM) nanoribbons are studied by adopting the tight-binding lattice model and the Landauer–Büttiker formula based on the non-equilibrium Green's function. For concreteness, the TDSM material Cd3As2 grown along the experimentally accessible [110] crystallographic direction is taken as an example. We found that the electronic structures of the TDSM nanoribbon depend on both the strength and direction of the magnetic field (MF). The transversal local charge density (LCD) distribution of the electronic states in the TDSM nanoribbon is moved gradually from the center toward the hinge of each surface as a [010] direction MF strength is increased, forming the two-sided hinge states. However, one-sided surface states are generated in the TDSM nanoribbon when a [001] direction MF is applied. As a result, one-sided hinge states can be achieved once a tilted MF is placed to the TDSM nanoribbon. The underlying physical mechanism of the desired one-sided hinge states is attributed to both the orbital and Zeeman effects of the MF, which is given by analytical analyses. In addition, typical Aharonov–Bohm interference patterns are observed in the charge conductance of the two-terminal TDSM nanoribbon with a tilted MF. This conductance behaviour originates from the unique interfering loop shaped by the one-sided hinge states. These findings may not only further our understanding on the external-field-induced higher-order (HO) topological phases but also provide an alternative method to probe the HO boundary states. [ABSTRACT FROM AUTHOR]

Enhancing the thermoelectric performance in engineered graphene nanoribbons is used to produce thermoelectric nanodevices, which are important in many applications. By using a chemical doping method, armchair graphene nanoribbons (AGNRs) can have thermoelectric properties that are tunable. We predicted that changing the number and geometrical pattern of zinc oxide (ZnO) dimers in an AGNR can engineer thermoelectric properties, so we used density functional-based tight binding (DFTB) combined with the non-equilibrium Green's function (NEGF) to investigate the geometric, electronic, and thermoelectric properties of the AGNR with and without various dopants of ZnO dimers. With three forms of ZnO dimers, ortho, meta, and para dimers, different concentration ratios of Zn and O atoms are used. Our results indicate that the electronic features of AGNR are influenced not only by the concentrations of ZnO dimers but also by the geometrical pattern of ZnO dimers in the AGNR. These results are helpful in better understanding the effect of chemical doping on the transport properties of AGNRs and in motivating nanodevices to improve their thermoelectric performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We propose a graphene nanoribbon pumping device and study its quantum charge and spin pumping properties for both adiabatic and non-adiabatic regimes by using the Keldysh non-equilibrium Green's function and renormalization procedure. We show that the adiabatic regime is suitable for the generation of high charge current, while the non-adiabatic regime is appropriate for the generation of fully spin polarized and pure spin currents. Also, it is shown that the proposed device can act as a perfect and controllable spin filter. Moreover, we investigate the effects of width and edge of graphene nanoribbons and show that the pumped charge current in the zigzag graphene nanoribbon (ZGNR) strongly depends on nanoribbon width so that the maximum pumped current for width with even numbers of carbon chains is about one order of magnitude larger than that with odd numbers. In contrast with ZGNR, in armchair graphene nanoribbon, the pumped currents with even and odd numbers have the same order of magnitude. [ABSTRACT FROM AUTHOR]

Creating a good contact between electrodes and graphene nanoribbons (GNRs) has been a long-standing challenge in searching for the next GNR-based nanoelectronics. This quest requires the controlled fabrication of sub-20 nm metallic gaps, a clean GNR transfer minimizing damage and organic contamination during the device fabrication, as well as work function matching to minimize the contact resistance. Here, we transfer 9-atom-wide armchair-edged GNRs (9-AGNRs) grown on Au(111)/mica substrates to pre-patterned platinum electrodes, yielding polymer-free 9-AGNR field-effect transistor devices. Our devices have a resistance in the range of 106–108 Ω in the low-bias regime, which is 2–4 orders of magnitude lower than previous reports. Density functional theory calculations combined with the non-equilibrium Green's function method explain the observed p-type electrical characteristics and further demonstrate that platinum gives strong coupling and higher transmission in comparison to other materials, such as graphene. [ABSTRACT FROM AUTHOR]

Germanium selenide (GeSe) nanoribbons as quasi-one-dimensional materials are expected to host fascinating tunable electronic properties due to the edge state and quantum confinement effect. Herein, the effect on the electronic structures and transport properties of zigzag GeSe nanoribbon (ZGeSeNR) of different functional passivation groups is systematically studied using a combination of density functional theory and the non-equilibrium Green's function. The N-, P-, and S-passivated ZGeSeNRs are metallic, while the F-, Cl-, OH-, and H-passivated ones exhibit semiconductor properties. The rectification behavior is found in lateral ZGeSeNR heterojunctions composed of a metal–semiconductor contact, and the rectification performance can be modulated by changing the edge passivation group, the ribbon width, and the length of the scattering region. Especially, the highest rectification ratio (RR) reaches 9.2 × 106 in the S–H–ZGeSeNR heterojunctions, in which the left and right half-edge atoms are passivated by the S and H groups, respectively. These results are useful for the design of nanoscale rectifiers based on ZGeSeNRs. [ABSTRACT FROM AUTHOR]

By performing extensive density functional theory calculations combined with non‐equilibrium Green's function technique, we predict the rhombic porous carbon nitride nanoribbon (rPCNNR) and the vertical rPCNNR junction exhibiting high thermoelectric figure of merit (ZT) values of 0.57 and 2.1 at room temperature respectively. Theoretical results reveal that the ZT value of rPCNNR is significantly larger than that of armchair graphene nanoribbon with the almost same width (~0.035) due to the large Seebeck coefficients and the significantly decreased thermal conductance of rPCNNR, where the phonon states are blocked by the built‐in porous structure and rhombic edge in rPCNNR. The ZT value is further enhanced to be 2.1 in the vertical rPCNNR junction, which is achieved by the synergy effect between the dramatically suppressed thermal conductance in in‐plane direction due to the weak van der Waals interaction between two rPCNNRs, the almost unchanged Seebeck coefficients, and the good electron conductivity provided by the strong overlapping of delocalized VB‐ and CB‐derived states in the scattering region. These presented findings highlight rPCNNR as a promising candidate in building flexible devices with high thermoelectric performance. [ABSTRACT FROM AUTHOR]

Structural and physical properties of armchair MoSi2N4 nanoribbons substitutionally doped by 3d transition metals (TM) at Mo sites are investigated using the density functional theory combined with the non-equilibrium Green's function method. TM doping can convert the nonmagnetic direct semiconductor into device materials of a broad variety, including indirect semiconductors, half semiconductors, metals, and half metals. Furthermore the 100% spin filtering behavior in spin-up and spin-down half metals, a negative differential resistance with peak-to-valley ratio over 140 and a rectification effect with ratio over 130 are predicted, as well as semiconductor behavior with high spin polarization. [ABSTRACT FROM AUTHOR]

The spin-photo current in single layer stanene and germanene under a linearly polarized light is theoretically investigated based on the tight-binding Hamiltonian combined with the nonequilibrium Green's function at room temperature. The results show that by considering the simultaneous effect of the linear illumination and a vertical external electric field without any magnetic exchange element, pure spin-photo current without charge current is generated in two-dimensional lattices with a large intrinsic spin–orbit coupling. The necessity of enhanced spin life-time for detection of spin polarization can be explained by spin-valley locking concept. Spin-valley locking arises in buckled two-dimensional materials as a result of the large spin–orbit coupling and electric-field reversible valley spin polarization. Equal absorption of the linearly illumination at both valleys with different spin polarization, leads to pure spin-photo current injection. In addition, an acceptable photoresponsivity has been reported in a broad range of photon energy. The numerical results indicate high quantum efficiency with a maximum of nearly 83% and 50% for stanene and germanene, respectively. This work may pave theoretical reference toward design of new spin-optoelectronic devices based on satanene and germanene junctions with high performance. [ABSTRACT FROM AUTHOR]

Thermoelectrics as a way to use waste heat, is essential in electronic industries, but its low performance at operational temperatures makes it inappropriate in practical applications. Tailoring graphene can change its properties. In this work, we are interested in studying the transport properties of S-shape graphene structures with the single vacancy (SV) and double vacancy (DV) models. The structures are composed of a chiral part, which is an armchair graphene nanoribbon, and two zigzag graphene ribbons. We investigate the changes in the figure of merit by means of the Seebeck coefficient, electronic conductance, and electronic and phononic conductances with the vacancies in different device sizes. The transport properties of the system are studied by using the non-equilibrium Green's function method, so that the related Hamiltonians (dynamical matrices) are obtained from the tight-binding (force constant) model. The maximum figure of merit (ZT) obtains for the DVs in all lengths. Physical properties of such a system can be tuned by controlling various parameters such as the location and the type of the defects, and the device size. Our findings show that lengthening the structure can reduce phononic contribution, and single vacancies than double vacancies can better distinguish between electronic thermal conductance behavior and electronic conductance one. Namely, vacancy engineering can significantly increase thermoelectric performance. In the large devices, the SVs can increase the ZT up to 2.5 times. [ABSTRACT FROM AUTHOR]

A semi‐analytical theoretical model is presented, which describes the operation of a selective molecular sensor employing a double resonance between a dipole‐active molecular vibration mode, tunable surface plasmons in a periodic structure of graphene nanoribbons (NRs), and the incident light, in the THz‐to‐IR range, used for testing. The model is based on the solution of Maxwell's equations for the NR structure deposited on a dielectric substrate, using the electromagnetic Green's function, and is extended to the case of an additional (buffer) layer present between the NRs and the substrate. Both the graphene NRs and the layer of adsorbed molecules are considered as 2D, since their thicknesses are very small in comparison with the wavelength of the incident light. The model is applied to different molecular systems, the protein studied by Rodrigo et al. [Science2015, 349, 165], for which an excellent agreement with experimental data is obtained, and an organometallic molecule Cd(CH3)2. Two different assumptions concerning the way of sticking of the analyte molecules to the sensor's surface are considered and the limitations of these sensing principles are discussed. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS 2 ) is a layered transition metal dichalcogenide (TMDC), which has a direct bandgap of 1.8 eV in its monolayer form. This large bandgap makes MoS 2 a good candidate for use in transistors. Density-functional theory studies the effect of strain and width on the electronic band structure. Furthermore, the transport properties of MoS 2 -bare and MoS 2 -passivated armchair nanoribbons are presented. We focus on the quantum conductance and band structure of the MoS 2 -bare and MoS 2 -passivated armchair nanoribbons by applying the Wannier function, and Non-Equilibrium Green's Function approaches for different widths and strains in the range −15 to + 15%. Our results indicate that MoS 2 -passivated armchair nanoribbons are good candidates for transistors, composites, and the fabrication of flexible electronic devices. [ABSTRACT FROM AUTHOR]

Nonequilibrium Green's function formalism is used to set the chemiresistor device for analyzing the sensing ability of pristine and metal-doped (Al, Fe and Mn) armchair graphene nanoribbons (AGNRs) for the detection of hydrogen halide gases — HF, HCl and HBr. Metal doping is found to enhance the adsorptive strength and sensing ability of the ribbon. On Al-AGNR, all three halide gases follow dissociative chemisorption while on Fe-AGNR and Mn-AGNR, these gases adsorb nondissociatively. The computed current–voltage characteristics indicate selective response of Mn-AGNR toward HF and of Fe-AGNR toward HBr. The origin of this selectivity has been discussed in terms of difference in the density-of-state profiles of the studied AGNR systems. Sensing properties of pristine armchair graphene nanoribbon (AGNR) and metal doped AGNRs (M-AGNRs; M=Al, Mn, Fe) are explored for selective detection of HF, HCl and HBr gases. Study of I-V characteristics reveal selective sensing capabilities of M-AGNRs. Origin of selectivity is explained based on differences in DOS profiles. [ABSTRACT FROM AUTHOR]

To explore the edge deformation effects on the performance of a graphene quantum ring gas sensor, we considered an armchair hexagonal graphene ring connected to two semi-infinite armchair graphene nanoribbons. We calculated the current through the graphene ring upon exposure to CO, NO, CO2, and NH3 gas molecules. It is shown that the behavior of current vs bias voltage depends on the inner and outer radii, and it is independent of the graphene quantum ring width. The effect of temperature resulting from nonequilibrium Green's function (Fermi–Dirac distribution) related to leads has been investigated. The substantial finding is that the current value remains unchanged up to room temperature at a perfect graphene quantum ring and, indeed, the sensor performance is unrelated to temperature. In a deformed graphene quantum ring, the influence of temperature on sensor performance is insignificant so that it is ineffective. Furthermore, the deformation in the edges can be accidental in the formation process, which we have simulated by randomly removing the atoms of the edges, or deformation can be manual, which was simulated by removing successive edge atoms from the ring sides. In the presence of edge deformation at a constant voltage, the difference between current values related to adsorption of NO, CO, and NH3 gas molecules and the pristine ring increases. In fact, the edge deformation improves the selectivity and the sensitivity of the graphene ring gas sensor. Single vacancy and double vacancies decrease the graphene ring sensor's performance. This underlines the importance of precision in the fabrication of nonedge parts of a graphene ring, although edge deformation is worthwhile in the improvement of the gas sensor. [ABSTRACT FROM AUTHOR]

The effect of vacancies on electronic properties of a zigzag graphene nanoribbon is studied. Vacancies are created by removing carbon atoms on the edge and in the bulk. A tight-binding Huckel model and Green's function methodology are employed to calculate conductance, total density of states, and local density of states (LDOS). The results show interesting behaviors that are notably different from the perfect ribbon, including transmission zeros and modulation in conductance, and changes in the LDOS of neighboring atoms, indicating the formation of localized states. A drop in the highest conductance step by a unit of 2 e2/h is observed for all cases, suggesting the loss of a transmission mode with creation of a vacancy. Interestingly, large increases in LDOS of individual atoms are found at the same energy as transmission zeros or dips in conductance near the Fermi energy. These changes can be shown to be localized near the vacancy, suggesting the formation of localized states that may be causing the conductance dips because of destructive interference between channels. [ABSTRACT FROM AUTHOR]

Phosphorene is a graphene-like material with an intermediate band gap, in contrast to zero-gap graphene and large-gap dichalcogenides or hexagonal boron nitride (hBN), which makes it more suitable for nanoelectronic devices. However, inducing band-gap modulation in freestanding phosphorene nanoribbons (PNRs) is problematic, as high in-plane electric fields are necessary to close the gap. We perform here a detailed investigation concerning the substrate influence on the electric-field control exerted by an external gate, using the density functional theory–non-equilibrium Green's functions (DFT-NEGF) framework. It is established that the interaction with a hexagonal boron nitride supporting layer significantly enhances the gap modulation. Furthermore, we address the issue of contacting the PNRs, by using conducting graphene nanoribbons embedded in the support hBN layer. Within this setup, a measurable spin polarization is achieved owing to the anti-ferromagnetic coupling between the edges of the graphene nanoribbons. [ABSTRACT FROM AUTHOR]

The transport and thermoelectric properties of finite textured graphene nanoribbons (t-GNRs) connected to electrodes with various coupling strengths are theoretically studied in the framework of the tight-binding model and Green's function approach. Due to quantum constriction induced by the indented edges, such t-GNRs behave as serially coupled graphene quantum dots (SGQDs). These types of SGQDs can be formed by tailoring zigzag GNRs (ZGNRs) or armchair GNRs (AGNRs). Their bandwidths and gaps can be engineered by varying the size of the quantum dot and the neck width at indented edges. Effects of defects and junction contact on the electrical conductance, Seebeck coefficient, and electron thermal conductance of t-GNRs are calculated. When a defect occurs in the interior site of textured ZGNRs (t-ZGNRs), the maximum power factor within the central gap or near the band edges is found to be insensitive to the defect scattering. Furthermore, we found that SGQDs formed by t-ZGNRs have significantly better electrical power outputs than those of textured ANGRs due to the improved functional shape of the transmission coefficient in t-ZGNRs. With a proper design of contact, the maximum power factor (figure of merit) of t-ZGNRs could reach 90 % ( 95 % ) of the theoretical limit. [ABSTRACT FROM AUTHOR]

Based on the density functional theory in combination with the nonequilibrium Green's function formalism, we study the structural, electronic, and transport properties of SS-pSiC2 NRs under a sequence of uniaxial strains in the range from 10% compression to 10% stretch. The pentagon network of SS-pSiC2 NRs is still maintained, but the bond length along the strained direction is largely changed under this strain. The electronic band structure and bandgap are strongly affected by the uniaxial compressive strain. The evolution of the bandgap vs the strain is linear. With a bias voltage of 2 V, the current of the 10% compressed sample increased 75 times, and the current of the 10% stretched sample increased 2.5 times compared to the one of the relaxed sample. The I–V characteristic of SS-pSiC2 NRs seems to be more sensitive to compressive strain than the stretch strain. Our calculations may indicate new applications of strain structures in electromechanical devices based on SS-pSiC2 NRs. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and nonequilibrium Green’s function (NEGF) framework are used to explore the structural, spin-polarized electronic, and spin-based transport properties of edge-hydrogenated zigzag aluminum nitride nanoribbons (ZAlNNRs). The proposed ZAlNNR is observed to be structurally stable and exhibits half-metallic nature in the magnetic state. The quantum transport property of the proposed two-terminal device model of 1H-AlN-1H demonstrates the bipolar spin-filter characteristics along with giant magnetoresistance (GMR), spin-based peak to valley current ratio (spin-PVCR), and spin-based rectification ratio (spin-RR) of the order of 1015, 1012, and 108, respectively. The calculated GMR and spin-RR of the 1H-AlN-1H device are 107 and 102 times higher than zigzag silicene nanoribbon (ZSiNR) and doped-zigzag graphene nanoribbon (doped ZGNR), respectively. The observed GMR, spin-PVCR, and spin-rectifying behavior of the reported ZAlNNR device could be deployed for multifunctional spintronic device applications. [ABSTRACT FROM AUTHOR]

• The spin-dependent electronic transport properties of zigzag phosphorene nanoribbons (ZPNRs);. • The electronic transport through the ZPNRs shows apparent spin polarization;. • The spin polarization is tightly dependent on the absorbing manners;. • Negative differential resistance characteristic can be observed on current-voltage curves. 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 (CrI 3) molecules. Three different adsorption models have been considered: CrI 3 molecule is placed on ZPNR surface (C-type), and CrI 3 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 CrI 3 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 CrI 3 is vertically adsorbed on the surface of the ZPNRs has a better spin-polarization efficiency than the other two cases. [ABSTRACT FROM AUTHOR]

Similar to graphene nanoribbons, boron nitride nanoribbons are prone to twist intrinsically. Hence, investigating the effect of local torsion on the electromechanical properties of boron nitride nanoribbons (9-cells) is of great importance. By using the density functional theory in combination with the non-equilibrium Green's function method, the effect of local torsion on the structural evolution and electrical transport of armchair boron nitride nanoribbons is investigated here. In addition, the electrical transport, current–voltage and Local density of state (LDOS) are studied. It is shown that local twist can change the transport properties of the boron nitride nanoribbons significantly. The current at a given bias can switch on/off or change many times with twist angle, which is related to twist-induced changes in electronic structures of boron nitride nanoribbons. The results of the current work can provide a valuable guideline for design and implementation of boron nitride nanoribbons in nanoelectromechanical systems and devices. [ABSTRACT FROM AUTHOR]

The spin-photo current in single layer stanene and germanene under a linearly polarized light is theoretically investigated based on the tight-binding Hamiltonian combined with the nonequilibrium Green's function at room temperature. The results show that by considering the simultaneous effect of the linear illumination and a vertical external electric field without any magnetic exchange element, pure spin-photo current without charge current is generated in two-dimensional lattices with a large intrinsic spin–orbit coupling. The necessity of enhanced spin life-time for detection of spin polarization can be explained by spin-valley locking concept. Spin-valley locking arises in buckled two-dimensional materials as a result of the large spin–orbit coupling and electric-field reversible valley spin polarization. Equal absorption of the linearly illumination at both valleys with different spin polarization, leads to pure spin-photo current injection. In addition, an acceptable photoresponsivity has been reported in a broad range of photon energy. The numerical results indicate high quantum efficiency with a maximum of nearly 83% and 50% for stanene and germanene, respectively. This work may pave theoretical reference toward design of new spin-optoelectronic devices based on satanene and germanene junctions with high performance. [ABSTRACT FROM AUTHOR]

Graphene nanoribbons (GNRs) are narrow strips of graphene which show interesting electronic properties. The occurrence of defects (vacancy, line, impurity) in GNR can alter these properties. This work investigates the role of line defects on transmission probability for AGNR (armchair) for Ny = 3n, Ny = 3n + 1, and Ny = 3n + 2 systems. It is observed that the bandgap of these AGNRs can be tailored by inducing one and multiple line defects. The effect of defect position of the line defects in the above-mentioned AGNR systems is studied within a framework of a non-interacting tight-binding approach. The energy band diagrams (E–k diagrams) for these systems with one and multiple line defects are plotted and analyzed. Also, the two-terminal electron transport of these AGNRs with one and multiple line defects is obtained by using the non-equilibrium Green's function (NEGF) methodology. This work opens up the possibility of controlling the bandgaps of AGNRs through multiple line defects for device applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate the spin-dependent electron transport properties of a zigzag silicene nanoribbon (ZSiNR) by using spin-polarized density functional theory and the non-equilibrium Green's function method. The results show that such a ZSiNR with an FM configuration exists the perfect dual spin filtering and dual spin diode effects when the bias voltage was applied. These phenomena still exist in ZSiNRs with different widths. As the ribbon width increases, the progressively smaller bias voltage is required to trigger a polarized current. Therefore, such a ZSiNR in FM configuration is a good candidate for spintronic devices. [ABSTRACT FROM AUTHOR]

In this study, we employed density functional theory (DFT) and the nonequilibrium Green's function (NEGF) framework to examine the quantum transport properties of Ti-doped zigzag blue phosphorene (ZblueP) nanoribbons at various doping levels. Our objective was to investigate the structural stability, electronic, and transport characteristics of our models. Interestingly, we discovered that doping engineering techniques can effectively convert a monolayer (ML) of ZblueP doped with Ti into a spintronic nanodevice possessing a handful of unique transport attributes using the generalized gradient approximation (GGA) treatment. First off, our models demonstrated an high dual spin-filtering efficiencies (SFEs) at low bias. Secondly, we observed a giant magnetoresistance (GMR) of up to 1.81 × 10 5. Lastly, we noticed a spin rectifier with a substantial rectification ratio (RR) of 1.32 × 10 7. Our research points to a promising pathway for the advancement of high-performance ML ZblueP spintronics technology through Ti doping. Our findings suggest that the considered model holds significant potential for use in nanoscale spintronic devices. [Display omitted] • Assessment of structural stability alongside electronic and transport properties. • Demonstrated high dual spin-filtering efficiencies at low bias. • Observed giant magnetoresistance reaching 1.81 × 10 5. • Significant spin rectification with a rectification ratio of 1.32 × 10 7. [ABSTRACT FROM AUTHOR]

Two-dimensional polyaniline with a C 3 N structure is a newly fabricated layered material that is expected to have fascinating electronic, thermal, mechanical, and chemical properties. By performing first-principles calculations based on density functional theory and the nonequilibrium Green's function, we first perform a stoichiometric study of the energy bands of armchair C 3 N nanoribbons (AC 3 NNRs) without and with H-passivation. The results show that the pristine AC 3 NNRs are metals, whereas the H-passivated nanoribbons are either direct or indirect band gap semiconductors with different edge configurations. Interestingly, additional transport calculations demonstrate that the AC 3 NNR-based heterojunction shows good rectification behavior. The average rectification ratio (RR) can reach up to 1 0 3 under voltage bias within the range from 0.2 to 0.4 V. In particular, extending the length of the scattering region in the heterojunction, which leads to a reduction in the current passing through the junction, allows the RR to be enlarged obviously. The average value of RR increases to a magnitude of the order of 1 0 4 under bias voltages in the range from 0.25 to 0.4 V, with a boosted maximum of up to 1 0 5 at 0.35 V. The findings of this work may be helpful in the design of functional nanodevices based on AC 3 NNRs in the future. [Display omitted] • First numerical simulation on the electronic property for armchair C 3 N nanoribbons without or with H passivation. • The planar heterojunctions show a diode behavior, this is mainly because of the internal Schottky barrier and the role of structural asymmetry. • Length-dependent channel effect of heterojunction has been observed with the rectification ratio reaching up to 105. [ABSTRACT FROM AUTHOR]

In this work, spin transport in corrugated armchair graphene nanoribbons (AGNRs) is studied. We survey combined effects of spin-orbit interaction and surface roughness, employing the non-equilibrium Green's function formalism and multi-orbitals tight-binding model. Rough substrate surfaces have been statistically generated and the hopping parameters are modulated based on the bending and distance of corrugated carbon atoms. The effects of surface roughness parameters, such as roughness amplitude and correlation length, on spin transport in AGNRs are studied. The increase of surface roughness amplitude results in the coupling of σ and π bands in neighboring atoms, leading to larger spin flipping rate and therefore reduction of the spin-polarization, whereas a longer correlation length makes AGNR surface smoother and increases spin-polarization. Moreover, spin diffusion length of carriers is extracted and its dependency on the roughness parameters is investigated. In agreement with experimental data, the spin diffusion length for various substrate ranges between 2 and 340 μm. Our results indicate the importance of surface roughness on spin-transport in graphene. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We have designed high-efficient spin-filtering junctions composed of graphene and silicon carbide nanoribbons. We have calculated the spin and charge transport in the junction by non-equilibrium Green's function formalism combined with the density functional theory to find its spin-dependent electrical conductance, thermal conductance and Seebeck coefficient. In addition, the effect of Si and C atoms vacancies on the transport properties of the junction has been carefully investigated. The enhanced spin-filtering is clearly observed due to the edge and vacancy effects. On the other hand, vacancy defects increase the electrical and spin conductances of the junctions. The results show that the considered junctions are half-metal with reduced thermal conductance which makes them a suitable spin-dependent thermoelectric device. Our results predict the promising potential of the considered junctions for application in spintronic devices. [ABSTRACT FROM AUTHOR]

The structural stability, spin-polarized electronic and transport properties of edge-hydrogenated zigzag boron nitride nanoribbons (ZBNNRs) are investigated using density functional theory (DFT) combined with a non-equilibrium Green’s function (NEGF) approach. The considered structures are observed to be energetically stable in the magnetic ground state. The calculated spin-dependent transport properties indicate that a selective-edge hydrogenated ZBNNR device shows bipolar spin filter characteristics. Interestingly, high spin giant magnetoresistance (GMR) and a rectification ratio (RR) are observed of the order of 1015 and 1010, respectively. The observed GMR and rectification behavior in edge-hydrogenated ZBNNRs have potential applications for designing future spintronic nanodevices. [ABSTRACT FROM AUTHOR]

In this article, tight binding model and nonequilibrium Green’s function technique have been used to investigate the electronic properties of armchair black phosphorene nanoribbons in ballistic transport regime as well as in the presence of line-edge roughness. The results indicate that although the ballistic electrical conductance is almost independent of ribbon width for the narrow ribbons and has no significant changes by temperature, at the presence of line-edge roughness, the electrical conductance varies by temperature and could be highly dependent on the ribbon width, especially in the case of long channels. In contrast to the graphene nanoribbons in which the line-edge roughness limited effective mean free path (MFP) is about tens of nanometer, in the black phosphorene nanoribbons, the effective MFP could be as high as ${2}~\mu \text{m}$ in ribbons with width of about 5 nm. For ribbons wider than 3 nm, the line-edge roughness scattering is almost negligible in comparison with electron–phonon scattering. [ABSTRACT FROM AUTHOR]

In this contribution, we aim at investigating the mechanism of biosensing in graphene‐based materials from first principles. Inspired by recent experiments, we construct an atomistic model composed of a pyrene molecule serving as a linker fragment, which is used in experiment to attach certain aptamers, and a defective zigzag graphene nanoribbons (ZGNRs). Density functional theory including dispersive interaction is employed to study the energetics of the linker absorption on the defective ZGNRs. Combining non‐equilibrium Green's function and the Landauer formalism, the total current‐bias voltage dependence through the device is evaluated. Modifying the distance between the linker molecule and the nanojunction plane reveals a quantitative change in the total current‐bias voltage dependence, which correlates to the experimental measurements. In order to illuminate the geometric origin of these variation observed in the considered systems, the local currents through the device are investigated using the method originally introduced by Evers and co‐workers. In our new implementation, the numerical efficiency is improved by applying sparse matrix storage and spectral filtering techniques, without compromising the resolution of the local currents. Local current density maps qualitatively demonstrate the local variation of the interference between the linker molecule and the nanojunction plane. [ABSTRACT FROM AUTHOR]

In this paper, first-principle calculation methods based on density functional theory are used to study the electronic structure of arsenic nitride nanoribbons (AsNNR), arsenic nitride nanoribbons passivated by hydrogen at the edges (HAsNNR), and arsenic nitride nanoribbons oxidized at the edges (OAsNNR). The results show that the spin-polarized nanoribbons are energy favorable than the non-spin-polarized nanoribbons. The zigzag type OAsNNR exhibits ferromagnetic (FM) half-metallic state. The non-equilibrium Green's function is used to study spin-polarized current of OAsNNR, and the full spin-polarized current is obtained by calculation. [ABSTRACT FROM AUTHOR]

In view of the experimental breakthrough and unique geometric structure, through using the nonequilibrium Green's function combined with density functional based tight-binding method, in this paper we investigate the thermoelectric performance of four metastable graphene allotrope nanoribbons. Compared to graphene nanoribbon, our calculations show that the four metastable graphene allotrope nanoribbons possess larger electronic band gap and Seebeck coefficient. Meanwhile, owing to intrinsic distortion structure, the phonon transport in these metastable nanoribbons is suppressed, and gives rise to lower thermal conductance. Such synergy effects make them hosting better thermoelectric conversion efficiency, for instance, the room temperature thermoelectric figure of merits in phagraphene and tetra penta-hepta-graphene nanoribbons is about 0.32 and 0.33, while that is merely 0.1 for graphene nanoribbon. The results not only reveal the intrinsic thermoelectric properties of the four metastable graphene allotrope nanoribbons, but also provide useful guidelines in designing related thermoelectric devices. [ABSTRACT FROM AUTHOR]

Steep-slope switching is effective to reduce the required energy for switching, however, at least 60 mV of gate voltage is required to modulate the current by an order of magnitude at room temperature. In this article, a numerical study of cold-source transistors based on chiral graphene nanoribbons (CGNRs) is presented. In cold-source transistors, the high-energy electrons are filtered out to break the room-temperature limitation, which can be realized by using CGNRs with narrow density of states (DOS) distribution. Our numerical results indicate that CGNR transistors can achieve sub-60 mv/decade subthreshold swing and similar ON-state current to conventional transistor. Moreover, the effect of the DOS distribution of CGNRs on the transport characteristics is investigated. This work provides a potential option for low-power electron devices and provides guidance for the design of cold-source transistors. [ABSTRACT FROM AUTHOR]

Recently, some photodetectors based on graphene have been proposed. In all of these works, current generation was carried out by separation of photo-excited carriers using an electric field, either internal or external. In this work, a new method of producing current which is based on different transmission coefficients for electrons and holes when they travel toward any of the two contacts is proposed. To this end, a single Stone-Wales defect close to one of the two contacts was used to break the channel symmetry. In order to confirm the idea, the non-equilibrium Green's function formalism in real space in conjunction with the tight binding method was used in simulations. In addition, to clarify the results, we present a classical model in which different diffusion constants are assumed for the left going and the right going carriers. Additional simulations for different positions of the defect, different lengths of the ribbon, and different bias voltages were performed, and the results are included in this study. [ABSTRACT FROM AUTHOR]

Device miniaturization and low-energy dissipation are two urgent requirements in future spintronics devices. The narrowest zigzag graphene nanoribbons (ZGNRs), which are composed of just two coupled carbon-atom chains connected with carbon tetragons, are promising candidates that meet both of the above requirements well. Using the first-principles calculations combined with non-equilibrium Green's function approach, thermal spin-dependent transport through this kind of narrow ZGNR is investigated, and several exotic thermal spin-resolved transport properties are uncovered: (i) when an external magnetic field is applied, the ZGNRs are transited from the intrinsic semiconducting to the metallic state, and the thermal colossal magnetoresistance effect occurs with order of magnitudes up to 104 at room temperature; (ii) the thermal spin-dependent currents display a thermal negative differential resistance effect, and a well-defined spin-Seebeck effect (SSE) together with a pure thermal spin current occurs; and (iii) under suitable device temperature settings, a nearly perfect spin-filtering effect occurs in these narrowest ZGNRs. The theoretical results not only uncover the narrowest nanoribbon structures to realize the SSE and other inspiring thermal spin transport features, but also push carbon-based material candidates towards thermoelectric conversion device applications. [ABSTRACT FROM AUTHOR]

In this paper, we perform a systematical investigation on searching for defect γ -graphyne nanoribbons (γ -GYNRs) with optimal thermoelectric performance by utilizing nonequilibrium Green's function combined with Bayesian optimization. The calculations show that Bayesian optimization could quickly and accurately identify the optimal structure with best thermoelectric efficiency. Even in the worst round of optimization, optimal structure could be obtained by only calculating 719 structure candidates (merely 4.35% of all the 16512 candidates). The room temperature thermoelectric figure of merit of optimal defect γ -GYNR (length 11.846 nm, width 1.453 nm) could approach 2.315, which is 5 times of that of pristine γ -GYNR. The obvious advantage of optimal defect γ -GYNR is mainly attributed to the maximum balance of weakening of thermal power factor (side effect) and suppression of thermal conductance (positive effect). Through analyzing the pair correlation function, we also find that the correlations between perfect (defect) unit and perfect (defect) unit are both extremely low for defect γ -GYNRs with high thermoelectric conversion efficiency. The findings presented in this work indicate the effectiveness and superiority of Bayesian optimization in designing defect γ -GYNRs, and could provide new insights for exploring other low-dimensional materials with excellent thermoelectric properties. [Display omitted] [ABSTRACT FROM AUTHOR]

We theoretically investigate spin-dependent Seebeck effects for a system consisting of a narrow graphene nanoribbon (GNR) contacted to square lattice ferromagnetic (FM) electrodes with noncollinear magnetic moments. Both zigzag-edge graphene nanoribbons (ZGNRs) and armchair-edge graphene nanoribbons (AGNRs) were considered. Compared with our previous work with two-dimensional honeycomb-lattice FM leads, a more realistic model of two-dimensional square-lattice FM electrodes is adopted here. Using the nonequilibrium Green's function method combining with the tight-binding Hamiltonian, it is demonstrated that both the charge Seebeck coefficient SC and the spin-dependent Seebeck coefficient SS strongly depend on the geometrical contact between the GNR and the leads. In our previous work, SC for a semiconducting 15-AGNR system near the Dirac point is two orders of magnitude larger than that of a metallic 17-AGNR system. However, SC is the same order of magnitude for both metallic 17-AGNR and semiconducting 15-AGNR systems in the present paper because of the lack of a transmission energy gap for the 15-AGNR system. Furthermore, the spin-dependent Seebeck coefficient SS for the systems with 20-ZGNR, 17-AGNR, and 15-AGNR is of the same order of magnitude and its maximum absolute value can reach 8 μV/K. The spin-dependent Seebeck effects are not very pronounced because the transmission coefficient weakly depends on spin orientation. Moreover, the spin-dependent Seebeck coefficient is further suppressed with increasing angle between the relative alignments of magnetization directions of the two leads. Additionally, the spin-dependent Seebeck coefficient can be strongly suppressed for larger disorder strength. The results obtained here may provide valuable theoretical guidance in the experimental design of heat spintronic devices. [ABSTRACT FROM AUTHOR]

Using nonequilibrium Green's function in combination with the spin-polarized density functional theory, the spin-dependent transport properties of boron and nitrogen doped zigzag graphene nano-ribbons (ZGNRs) heterojunctions with single or double edge-saturated hydrogen have been investigated. Our results show that the perfect spin-filtering effect (100%), rectifying behavior and negative differential resistance can be realized in the ZGNRs-based systems. And the corresponding physical analysis has been given. [ABSTRACT FROM AUTHOR]

Localized magnetic impurity centres in graphene can interact through the π-electrons, leading to an effective Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. A RKKY-type study is presented for graphene ribbons with zigzag edges. Specifically investigations of how the edges modify the interaction between two localized magnetic moments are made by using a tight-binding Hamiltonian to describe the hopping of the π-electrons between adjacent sites and a contact term for interactions with the localized moments. In terms of a Green's function formalism for the excitation spectrum, which comprises modified bulk modes and two different types of localized edge modes, explicit analytical expressions are obtained for the RKKY interaction for any two magnetic sites on the graphene ribbon. The results enable us to determine the RKKY contributions that arise individually from the bulk-like modes and from the two types of edge modes in the zigzag geometry. The importance of these contributions varies depending on the proximity of the magnetic impurities to each other and to an edge. [ABSTRACT FROM AUTHOR]

Using non-equilibrium green function with density functional theory, the present study investigates the transport properties of decorated zigzag graphene nanoribbon with a copper cluster. We have represented the decoration of zigzag graphene nanoribbon with single copper atom and cluster con- taining two and three copper atoms. In all the cases, copper atoms tend to occupy the edge state. In addition, we have shown that copper can alter the current-voltage characteristic of zigzag graphene nanoribbon and create new ?uctuations and negative differential resistance. These alternations are made due to discontinuity in the combination of orbitals along the graphene nanoribbon. Decoration alters these discontinuities and creates more visible ?uctuations. However, in low bias voltages, the changes are similar in all the cases. The study demonstrates that in the decorated zig- zag graphene nanoribbon, the edge states are the main states for transporting electron from one electrode to another. [ABSTRACT FROM AUTHOR]

In this paper, spin transport properties of aluminum-doped zigzag silicon carbide nanoribbons (Al-ZSiC NRs) are investigated using the first-principle calculations and the nonequilibrium Green's function method. The results show an approximately perfect spin filtering (100%) for three considered models and undoped structure at ferromagnetic state in the presence of bias voltage. In particular, a weak negative differential resistance (NDR) phenomenon can be obtained in a certain system when replacing the edge Si atom with the Al-doping atom. Indeed, edge states play a crucial role in spin-dependent transport and magnetic properties of ZSiC NRs, such as the NDR effect. Furthermore, the significant rectifying ratio (RR) is obtained under bias voltage only for one given configuration. When the same spin states overlap in the bias window (BW), spin-dependent transmission and the spin current display a non-zero value; however, the mismatch of the same spin states within the BW region causes to vanish the transmission spectra. The controllable manipulation of threshold voltage, spin filtering efficiency, NDR behavior, and RR effect can be achieved by substituting of silicon with Al atom in ZSiC NRs. These results shed new light on our understanding of silicon carbide-based nanodevices with appealing spintronic applications. [ABSTRACT FROM AUTHOR]