Zigzag Graphene Nanoribbons Research Articles

Mechanical spin splitting in zigzag graphene nanoribbons

Mechanical spin splitting in zigzag graphene nanoribbons

Impact of valley degeneracy on the thermoelectric properties of zig-zag graphene nanoribbons with staggered sublattice potentials and transverse electric fields.

This study investigates the band inversion of flat bands in zig-zag graphene nanoribbons (ZGNRs) using a tight-binding model. The band inversion results from symmetry breaking in the transverse direction, achievable through deposition on specific substrates such as separated silicon carbide or hexagonal boron nitride sheets. Upon band inversion, ZGNRs exhibit electronic structures characterized by valley degeneracy and band gap properties, which can be modulated by transverse electric fields. To explore the impact of this level degeneracy on thermoelectric properties, we employ Green's function techniques to calculate thermoelectric quantities in ZGNR segments with staggered sublattice potentials and transverse electric fields. Two carrier transport scenarios are considered: the chemical potential is positioned above and below the highest occupied molecular orbital. We analyze thermionic-assisted transport (TAT) and direct ballistic transport (DBT). Level degeneracy enhances the electric power factors of ZGNRs by increasing electrical conductance, while the Seebeck coefficient remains robust in the TAT scenario. Conversely, in DBT, the enhancement of the power factor primarily stems from improvements in the Seebeck coefficient at elevated temperatures.

Utilizing armchair and zigzag nanoribbons for improved detection of SO2 Toxicity with graphene biosensor

Graphene nanoribbons (GNRs), with their distinctive structural and electronic characteristics, offer significant potential for use as biosensors in the detection of sulfur dioxide (SO₂) levels. This study employs Density Functional Theory (DFT) to evaluate the sensitivity of armchair graphene nanoribbons (AGNRs) to SO₂ gas. Specifically, we investigate the influence of SO₂ molecules on the electronic and transport characteristics of both pure and Cr-doped zigzag graphene nanoribbons (ZGNRs) and Cr-doped AGNRs. Key electronic properties, including band structure, adsorption energy, and density of states (DOS), were analyzed following SO₂ adsorption. The results indicate that Cr doping leads to significant changes in the electronic properties of AGNRs upon SO₂ exposure, including alterations in the Fermi surface that result in band separation and the formation of a forbidden band. The adsorption energy of Cr-doped AGNR increased from 0.07 eV (pristine AGNR) to 0.55 eV (Cr-doped AGNR), nearly eight times higher, indicating strong chemisorption of SO₂. These findings suggest that Cr-doped AGNRs exhibit high sensitivity to SO₂, making them promising candidates for gas detection. Furthermore, this study reveals that SO₂ adsorption in the armchair direction results in a more pronounced peak-to-valley ratio compared to the zigzag direction, highlighting distinct characteristics in SO₂ adsorption behavior. These findings could facilitate the development of advanced sensors with improved sensitivity and selectivity for environmental monitoring and safety applications.

The incorporation of armchair and zigzag boron nitride nanoribbons in graphene monolayers: An examination of the structural, electronic, and magnetic properties

The opening of an energy gap and generating magnetism in graphene are certainly the most significant and urgent topics in your current research. The majority of proposed applications for it require the ability to modify its electronic structure and induce magnetism in it. Here, using first-principles calculations utilizing the PBE and HSE06 functionals, we examine the structural, energetic, electronic, magnetic, and phonon transport characteristics of armchair graphene and boron nitride nanoribbons (aGNRs and aBNNRs), and zigzag graphene and boron nitride nanoribbons (zGNRs and zBNNRs) with varying widths. We shall emphasize the impact of incorporating aBNNRs and zBNNRs of varying widths into graphene monolayers (GMLs). The findings suggest that zBNNRs are easier to insert into GMLs than aBNNRs. A study of the average formation energies of graphene and boron nitride nanoribbons reveals that BNNRs have a formation energy that is at least twenty times greater than GNRs. We have observed energy gaps that can be classified into three distinct families in aGNRs, aBNNRs, and aBNNRs inserted into GML. In the zGNRs and zBNNRs inserted in GML, depending on the width, different magnetic orderings (antiferromagnetic, ferrimagnetic, and ferromagnetic), and electronic behaviors are observed (metallic, semimetallic, semiconductor, and topological insulator).

Investigation of Electric Field Tunable Optical and Electrical Characteristics of Zigzag and Armchair Graphene Nanoribbons: An Ab Initio Approach.

Graphene nanoribbons (GNRs), categorized into zigzag and armchair types, hold significant promise in electronics due to their unique properties. In this study, optical properties of zigzag and armchair GNRs are investigated using density functional theory (DFT) in conjunction with Kubo-Greenwood formalism. Our findings reveal that optical characteristics of both GNR types can be extensively modulated through the application of a transverse electric field, e.g., the refractive index of the a zigzag GNR is shown to vary in the range of n = 0.3 and n = 9.9 for the transverse electric field values between 0 V/Å and 10 V/Å. Additionally, electrical transmission spectra and the electrical conductivities of the GNRs are studied using DFT combined with non-equilibrium Green's function formalism, again uncovering a strong dependence on the transverse electric field. For example, the conductance of the armchair GNR is shown to vary in the range of G = 6 μA/V and G = 201 μA/V by the transverse electric field. These results demonstrate the potential of GNRs for use in electronically controlled optoelectronic devices, promising a broad range of applications in advanced electronic systems.

Investigating Transmission Coefficients of AB-Stacked Bilayer Graphene Nanoribbons with Varied Edge Configurations

In this study, the transmission coefficients of AB-stacked bilayer graphene nanoribbons (AB-BGNRs) with different edge configurations, specifically zigzag and armchair edges, are comprehensively investigated. These coefficients are modeled and simulated using the tight-binding (TB) model and non-equilibrium Green’s function (NEGF) formalism. The impact of edge structures on the electronic properties of AB-BGNRs is highlighted, providing insights into their potential applications in nanoelectronics devices. Significant variations between zigzag and armchair-edged bilayer graphene nanoribbons (BGNRs) are demonstrated, emphasizing the importance of edge configuration in device performance. This study contributes to the fundamental understanding of edge effects in bilayer graphene and paves the way for the design of more efficient graphene-based electronic devices.

Quantum discord in zigzag graphene nanoribbons

Based on Hubbard model with the Hartree-Fock approximation, we study the properties of quantum discord (QD) between the nearest-neighbor sites A and B in zigzag graphene nanoribbons thermalized with a reservoir at temperature T. Several influences of the site position, on-site Coulomb repulsion U, temperature, and ribbon width on QD are discussed in detail. The results show that QD is robust against thermal fluctuations, and QD for the leg pairs along the zigzag chain near ribbon edges is always larger than that for the rung pairs linking two adjacent zigzag chains. QD for the rung pairs increases and then approaches to saturation as the ribbon width increases, where the velocity of saturation is strongly correlated to U. Moreover, for rung pairs the values of U at the QD peaks perform the scaling behaviors with increasing ribbon width.

Role of twist in modulating the electronic and thermoelectric properties of zigzag graphene nanoribbons

Role of twist in modulating the electronic and thermoelectric properties of zigzag graphene nanoribbons

On-Surface Synthesis of Graphene Nanoribbons and Spin Chains

Recent advances in on-surface synthesis has allowed the selective fabrication of a number of prototypical types of graphene nanoribbons. The thereby achieved properties include width-dependent electronic band gaps in armchair graphene nanoribbons, edge-localized states in zigzag graphene nanoribbons and topological band engineering in width-modulated topological graphene nanoribbons. More recently, on-surface synthesis of magnetic nanographenes has been reported. Here, the spin originates from unpaired electrons present in nanographenes with controlled sublattice imbalance or topological frustration. The corresponding magnetic moments live in p-orbitals and are hence largely delocalized, which allows for chemical control over their exchange interaction when covalently linking several molecular building blocks. Here, I will present synthesis of various prototypical magnetic nanographenes and the possibility to covalently link them to form coupled spin systems where exchange coupling can exceed 100 meV. Using halogen-substituted precursors, we achieve the on-surface synthesis-based deterministic bottom-up fabrication of various spin chains including a triangulene spin-1 chain revealing the predicted Haldane gap and fractional excitations at the chain termini or a strictly alternating spin-½ chain with chemically engineered coupling strengths J1 and J2 . Scanning tunneling microscopy and spectroscopy is used to explore length- and site-dependent magnetic excitations. Furthermore, we apply hydrogenation to achieve spin site passivation and controlled tip-based local reactivation to fabricate and characterize specific spin patterns in one-dimensional spin chains and spin clusters.

Perfect Spin Filtering, Giant Magnetoresistance, and Rectification Behavior Induced by V‐Doped Zigzag Graphene Nanoribbons

AbstractEmploying the constructs of density functional theory (DFT) and the Nonequilibrium Green's Function (NEGF), the investigation extensively explores the electronic and transport properties of zigzag graphene nanoribbons (ZGNRs) doped with vanadium (V). Notably, this inquiry unveils that strategic doping can transform V‐doped ZGNRs into spintronic nanodevices with distinctive transport attributes. Initially, the simulations showcase remarkably high spin‐filtering efficiencies (SFEs) at certain bias voltages. Furthermore, a giant magnetoresistance (GMR) peaking at 6.87 10 is detected. In conclusion, the examination discerns a spin rectifier that exhibits a significant rectification ratio (RR) of 9.62 10. This research delineates a viable trajectory for the refinement of high‐performance spintronics in ZGNRs via vanadium doping. The implications of this study indicate that the model harbors considerable promise for application in miniature spintronic devices.

Predicting edge-localized monovacancy defects in zigzag graphene nanoribbons from Floquet quasienergy spectrum

Predicting edge-localized monovacancy defects in zigzag graphene nanoribbons from Floquet quasienergy spectrum

One-Dimensional Magnetic Conduction Channels across Zigzag Graphene Nanoribbon/Hexagonal Boron Nitride Heterojunctions.

We examine the electronic structure of recently fabricated in-plane heterojunctions of zigzag graphene nanoribbons embedded in hexagonal boron nitride. We focus on hitherto unexplored interface configurations in which both edges of the nanoribbon are bonded to the same chemical species, either boron or nitrogen atoms. Using ab initio and mean-field Hubbard model calculations, we reveal the emergence of one-dimensional magnetic conducting channels at these interfaces. These channels originate from the energy shift of the magnetic interface states that is induced by charge transfer between the nanoribbon and hexagonal boron nitride. We further address the response of these heterojunctions to external electric and magnetic fields, demonstrating the tunability of energy and spin splittings in the electronic structure. Our findings establish that zigzag graphene nanoribbon/hexagonal boron nitride heterojunctions are a suitable platform for exploring and engineering spin transport in the atomically thin limit, with potential applications in integrated spintronic devices.

Edge magnetism in zigzag graphene nanoribbons with Rashba spin–orbit coupling

We study the edge magnetism in zigzag graphene nanoribbons (ZGNRs) described by the mean-field Hubbard model with the controllable Rashba spin–orbit coupling (RSOC) at finite temperatures. The results show that the edge magnetic moments are robust against thermal fluctuation. Moreover, the magnitude of such edge magnetism can be significantly enhanced by the on-site Coulomb repulsion U, whereas RSOC yields the opposite effect. However, RSOC plays a crucial role in tuning the edge magnetism, which can drive the phase transition from the antiferromagnetic state into the ferromagnetic state in ZGNRs. When the ribbon width increases, the magnitudes of the edge magnetic moments under the weak U are apt to increase until reaching saturation. If U is large enough, the edge magnetism is almost independent of ribbon width. These versatile magnetic properties of ZGNRs could be useful in promising spintronics applications.

Effects of vacancies on quantum transport of zigzag graphene nanoribbons

Using the Green’s function method, we investigate the effect of vacancies on conductance and local density of states (LDOS) in zigzag graphene nanoribbons within a symmetric and asymmetric potential wells. The results differ from ideal ribbons in that there are no conductance plateaus and a decline in conductance for varied N (number of atoms in the unit cell) and M (number of unit cells) values following vacancy incorporation. LDOS and conductance in symmetrical and asymmetrical circumstances are examined alongside vacancies and accordingly, they are affecting the respective edge states.

Insights into the electronic, optical, and catalytic properties of finite biphenylene nanoribbons: First-principles study

The electronic, optical, and catalytic properties of finite two-dimensional biphenylene nanoribbons are investigated using density functional theory calculations. The nanoribbons are energetically and dynamically stable as confirmed by the negative formation energy ∼ -7 eV and the real vibrational frequencies, respectively. Increasing the length of nanoribbons in the zigzag or armchair directions reduces the energy gap, with modest oscillations in the former case. In contrast to zigzag graphene nanoribbons, biphenylene ones have nonmagnetic spin ordering due to the passivation of the unpaired electrons at the zigzag edges by the 4C- rings connecting the benzene rings. The UV–vis spectra exhibit redshifts, with size increases in both the armchair and zigzag directions, which validate the electronic computations' results. Simulating the catalytic performance of oxygen evolution reaction shows remarkable performance with a low overpotential of 0.12 V. Thus, biphenylene nanoribbons with desirable electronic and catalytic properties are attractive anode materials for water-splitting cells.

Phase diagram and crossover phases of topologically ordered graphene zigzag nanoribbons: role of localization effects

We computed the phase diagram of zigzag graphene nanoribbons as a function of on-site repulsion, doping, and disorder strength. The topologically ordered phase undergoes topological phase transitions into crossover phases, which are new disordered phases with non-universal topological entanglement entropy that exhibits significant variance. We explored the nature of non-local correlations in both the topologically ordered and crossover phases. In the presence of localization effects, strong on-site repulsion and/or doping weaken non-local correlations between the opposite zigzag edges of the topologically ordered phase. In one of the crossover phases, both e−/2 solitonic fractional charges and spin-charge separation were absent; however, charge-transfer correlations between the zigzag edges were possible. Another crossover phase contains solitonic e−/2 fractional charges but lacks charge transfer correlations. We also observed properties of non-topological, strongly disordered, and strongly repulsive phases. Each phase on the phase diagram exhibits a different zigzag-edge structure. Additionally, we investigated the tunneling of solitonic fractional charges under an applied voltage between the zigzag edges of undoped topologically ordered zigzag ribbons, and found that it may lead to a zero-bias tunneling anomaly.

Comparative investigation of the bulk and electronic properties of dimethyl disulphide adsorbed indium doped zigzag graphene nanoribbon: A DFT Study

For the purpose of understanding the adsorption process using the density functional theory method, the bulk and electronic properties of the complex consisting of dimethyl disulphide (C2H6S2) and indium doped zigzag graphene nanoribbon are investigated. Also, a comparison with the electronic and bulk characteristics of indium-doped zigzag graphene nanoribbon is made with molecule adsorbed zigzag graphene nanoribbon. Following complete geometric optimization, the electronic and bulk characteristics are calculated. The stated complex’s structural changes exhibit observable differences, prompting further research based on its electronic properties. Calculating the complex’s various electronic properties reveals that it possesses semi metallic behavior.

Analyzing the electronic and conductive characteristics of zigzag graphene nanoribbons upon NOx and N2O Adsorption: An ab-initio study

Achieving a cleaner and more sustainable environment relies on the precise identification and elimination of toxic gases. Addressing this imperative, our current study utilizes a symmetric zigzag graphene nanoribbon (ZGNR)-based sensor device to effectively detect gases from the NOx family at low concentrations. The ZGNR serves as the channel element within a simulated sensing device, with its electrodes connected to a variable direct voltage (d.c) source. The performance of the device is validated by monitoring changes in adsorption energy, charge transfer, dipole moment, recovery time and conductance. The manuscript utilizes non-equilibrium Green’s function (NEGF) theory and density functional theory (DFT). These theories serve as the foundation for electronic structure calculations, supplemented by the application of the Landauer-Büttiker equation for computing electrical characteristics.Three common gasses namely NO, NO2, and N2O have been taken into consideration for ZGNR-based sensor device detection. Notably, the suggested sensor device exhibits a higher sensor response (S= 4.63) and a selectivity of about 21% for NO gas. This is likely due to the high adsorption energy (-1.07 eV), and large dipole moment (4.86×10−30Cm) that substantiate larger charge transfer (-0.14e) as compared to NO2 and N2O.Meanwhile, the ZGNR sensor device shows great gas sensing performances, including excellent selectivity, repeatability (due to small recovery time of 103.00 and 0.01 microseconds), and stability. It can therefore be explored as a sensor device that is comparable as well as superior to various carbon-based chemical entities of both 1D and 2D nanomaterials.

Optically and electrically controlled switchers and electron beam splitters based on topological edge states

Recently, topological edge states have attracted rapid attention for designing low-power consumption electronics due to their topological protection and suppression of backscattering. We study the transport properties of inner and outer edge states in a three-terminal device composed of hybrid zigzag graphene nanoribbons based on our derived formulas of local bond current and transmission coefficient with the wave-function matching technique. Particularly, by electrically modulating inner edge state in the conductor region, the valley current can be flipped as the charge current that is switched into one lead or split into two transmitted leads, leading to the charge switchers and electron beam splitters when the incident lead and transmitted leads are set as antichiral inner edge state and chiral edge states, respectively. Furthermore, when three leads are both modulated as antichiral inner edge state by the spatially varying off-resonant circularly polarized (ORCP) light, the charge switchers and electron beam splitters are accordingly converted into the valley switchers and electron beam splitters. The behavior of the switchers and splitters originates from the cooperative effects of the lager wave-vector mismatch between different valleys, and the distributions of lateral and vertical inner edge states. Moreover, the proposed devices could be cut off by the staggered electric field due to the gap effect, and are robust against the edge magnetism and the spin-orbit coupling. These findings are expected to apply for optically and electrically controlled topological devices.

Chiral symmetry breaking and topological charge of zigzag graphene nanoribbons

Interacting quasi-one-dimensional zigzag graphene nanoribbons display gapped edge excitations. Although the self-consistent Hartree–Fock fields break chiral symmetry, our work demonstrates that zigzag graphene nanoribbons maintain their status as short-range entangled symmetry-protected topological insulators. The relevant symmetry involves combined mirror and time-reversal operations. In undoped ribbons displaying edge ferromagnetism, the band gap edge states with a topological charge form on the zigzag edges. An analysis of the anomalous continuity equation elucidates that this topological charge is induced by the gap term. In low-doped zigzag ribbons, where the ground state exhibits edge spin density waves, this topological charge appears as a nearly zero-energy edge mode. Our system is outside the conventional classification for topological insulators.