Structure Of Graphene Nanoribbons Research Articles

Implications of the edge states for the band structure of armchair graphene nanoribbons

Implications of the edge states for the band structure of armchair graphene nanoribbons

Implications for electronic structures of S-doped graphene nanoribbons from a DFTB algorithm at atomic scale

Self-consistent charge density functional tight binding simulations were used to provide implications for the effect of S atoms’ doping on geometrical structures and electronic states in armchair graphene nanoribbons with different widths. The geometric configurations, energy, charge density differences, Mulliken charges, and molecular orbitals at HOMO and LUMO energy levels are characterized. Besides the changes of bond length and bond angles, the calculation results indicate that the band structures and bandgaps of the graphene nanoribbons is affected by the nanoribbon width as well as S doping positions, where the ribbons exhibit metallic or semiconductor properties. Doping S atoms result significant changes in the charge density differences and Mulliken charges on the atoms near the doped atom. At the same time, the HOMOs and LUMOs also present differences.

Effects of nanocutting environments on the electronic structure of armchair-type graphene nanoribbons: the first-principles study

In order to investigate the effect of nanocutting environment on the electronic structure of armchair-type graphene nanoribbons, this paper adopts a first-principle computational approach to study the effect of different substrates and solutions, such as on the motion of electrons in the middle and outer orbitals of graphene nanoribbons, by observing the energy band structure, the value of the band gap, and the density of the split-wave states. The results show that the adsorption of Si and C atoms at the edge of the nanoribbon leads to a decrease in the band gap value. The adsorption of Al and O atoms at the edges of graphene nanoribbons leads to a decrease in the nanoribbon band gap value to 0 eV. Different substrate atoms mainly affect the p-orbital electron motion in the nanobelt. Bare-edge graphene nanoribbons are indirect bandgap structures, and graphene nanoribbons with H, O and OH atoms adsorbed at the edges of the nanoribbons are direct bandgap structures. Edge O-isation leads to a nanobelt band gap of 0, which exhibits metallic properties. The edge H-isation nanoribbon band gap is higher than the bare edge nanoribbon band gap. Nanoribbon edge OH-isation reduces the nanoribbon band gap value. Nanoribbon edge adsorption of atoms in solution affects p-orbital electron motion. The formation energy of five-ring defects and seven-ring defects is low, and the defects are easier to form. The edges containing defects all reduce the band gap values of graphene nanoribbons. The defects mainly affect the p-orbital electron motion, leading to differences in the band gap values. The bandgap decreases with increasing nanobelt width, and the bandgap value conforms to 3 N+2<3 N<3 N+1, with regular fluctuations in the curve with period 3. The larger the band gap, the smaller the curvature of the curve at the extremes, and the sparser the curve. In this paper, the electronic structures of different edge structures are analysed from a quantum mechanical point of view, and the synthesis of these results will provide theoretical guidance for obtaining high-quality semiconductor nanoribbons by mechanochemical nanocutting.

Magneto-plasmon of AA-stacked bilayer graphene nanoribbons at finite temperature

Magneto-band structures of AA-stacked bilayer graphene nanoribbons with armchair and zigzag (BLAGNR and BLZGNR) edges are calculated by the pz-orbital tight-binding model. At zero field, BLAGNR is a semiconductor or metal determined by its width. Magnetic field can reduce band-gap and exhibit crossing bands. For metallic BLZGNRs, crossing bands shift and parabolic bands are separated more widely with magnetic field; however, partial flat bands keep unchanged. Temperature significantly increases plasmon frequency and strength for semiconducting BLAGNRs, but slightly affects those of metallic BLAGNRs and BLZGNRs. Magnetic field, for gapped BLAGNRs, can effectively reduce the threshold temperature for inducing plasmon. Whether magneto-plasmon frequency and critical momentum of dispersion relation increase or decrease is strongly sensitive to nanoribbon’s geometry. Field-modulated plasmons with a wide range of frequency could provide potential applications in waveguides and optical sensors.

Terahertz plasmonic resonances in coplanar graphene nanoribbon structures

We analyze plasmonic oscillations in the coplanar graphene nanoribbon (GNR) structures induced by the applied terahertz (THz) signals and calculate the GNR impedance. The plasmonic oscillations in the GNR structures are associated with the electron and hole inductances and the lateral inter-GNR capacitance. A relatively low inter-GNR capacitance enables the resonant excitation of the THz plasmonic oscillations in the GNR structures with long GNRs. The GNR structures under consideration can be used in different THz devices as the resonant structures incorporated in THz detectors, THz sources using resonant-tunneling diodes, photomixers, and surface acoustic wave sensors.

Impact of uniaxial strain on physical properties of zigzag graphene nanoribbons with topological defects

The synergistic regulation mechanism of uniaxial strain, topological defects, edge passivation atom and nanoribbon width on the geometric and electronic structures of zigzag graphene nanoribbons have been studied systematically by first-principles. It is found that the average formation energy and strain energy of X-N 1 N 2-LD-ZGNR (X = H, F and O, as well as, N 1 = N 2 = 3, 4 and 5) increase with the increase of uniaxial strain, and this relationship is also dependent of edge passivation atom species and nanoribbon width. And the edge of 55-LD-ZGNR passivating with O and F atoms is more beneficial than H atom for system stability. The stress–strain curve shows that the limiting strain of zigzag graphene nanoribbon depends on edge passivation atom species and nanoribbon width. The Young’s modulus in the case of ε > 3% and Poisson’s ratio except O-33-LD-ZGNR at ε = 1% of X-N 1 N 2-LD-ZGNR decrease with the increase of the tensile strain, and is dependent of nanoribbon width and edge atom species. And O-55-LD-ZGNR is easier than F-55-LD-ZGNR and H-55-LD-ZGNR to be stretched or compressed. The magnetism is induced in both H-55-LD-ZGNR and F-55-LD-ZGNR, and remains with the increases of uniaxial tension strain. What is more, magnetic property of O-55-LD-ZGNR can be regulated by applying uniaxial strain, and the band gap of the O-N 1 N 2-LD-ZGNR (N 1 = N 2 = 3, 4 and 5) system can be regulated by adjusting the uniaxial tensile strain and nanoribbon width. Our research provides a new method to open the graphene band gap, which can provide some new theoretical guidance for the application of graphene in electronic devices and other fields. The band gap of the O-LD-ZGNDR system is opened as the uniaxial tensile strain increases.

Topological Structure Realized in Cove-Edged Graphene Nanoribbons via Incorporation of Periodic Pentagon Rings.

Cove-edged zigzag graphene nanoribbons are predicted to show metallic, topological, or trivial semiconducting band structures, which are precisely determined by their cove offset positions at both edges as well as the ribbon width. However, due to the challenge of introducing coves into zigzag-edged graphene nanoribbons, only a few cove-edged graphene nanoribbons with trivial semiconducting bandgaps have been realized experimentally. Here, we report that the topological band structure can be realized in cove-edged graphene nanoribbons by embedding periodic pentagon rings on the cove edges through on-surface synthesis. Upon noncontact atomic force microscopy and scanning tunneling spectroscopy measurements, the chemical and electronic structures of cove-edged graphene nanoribbons with periodic pentagon rings have been characterized for different lengths. Combined with theoretical calculations, we find that upon inducing periodic pentagon rings the cove-edged graphene nanoribbons exhibit nontrivial topological structures. Our results provide insights for the design and understanding of the topological character in cove-edged graphene nanoribbons.

Impacts of Graphene Nanoribbon Production Methods on Oxygen‐Reduction Electrocatalysis in Different Environments

AbstractGraphene‐based materials have emerged as highly promising catalysts for enhancing oxygen reduction reaction (ORR), a pivotal process in diverse energy conversion applications and the production of eco‐friendly oxidants like hydrogen peroxide (H2O2). To design exceptionally efficient catalysts tailored to specific applications, it is essentially crucial to have a thorough understanding of their electrocatalytic behaviour. This involves ascribing functions to structural characteristics like defects and exploring heteroatom doping in graphene matrices. In this work, we study the synthesis of graphene nanoribbons (GNRs) derived from multi‐walled carbon nanotubes (MWCNTs) and their doping with nitrogen (N) and phosphorus (P). We investigate how edge defects and oxygenated groups retained from the MWCNT opening process impact both the doping process and GNR electrocatalytic characteristics, with a focus on their relevance to ORR. Our findings underscore the need to optimize GNR structures and doping strategies for specific reaction conditions. We demonstrate how GNR characteristics are effectively influenced by varying MWCNT opening methods, ultimately affecting ORR performance and H2O2 selectivity. The findings show that when MWCNTs are opened to create GNRs with a broader distribution of oxygen atoms across the basal plane and fewer exposed edges, N‐insertion enhances catalytic activity, resulting in improved ORR performance. However, this alteration reduces H2O2 selectivity in both acidic and alkaline media. On the other hand, generating GNRs with abundant edges and widespread oxygen functional groups on both the basal plane and edges yields a high oxygen group concentration. This configuration not only facilitates phosphorus insertion at the edges but also plays a crucial role in enhancing ORR performance, leading to selectivities of over 92 % for H2O2 production in alkaline media. This study not only advances our understanding of graphene‐based catalysts but also offers meaningful contributions and insights into the development of more efficient and sustainable electrochemical technologies in the realm of energy conversion.

An array of QDs on a one-dimensional periodic structure of graphene nanoribbons as a nanoscale plasmonic grating

An array of QDs on a one-dimensional periodic structure of graphene nanoribbons as a nanoscale plasmonic grating

Exploring the Potential of Heteroatom-Doped Graphene Nanoribbons as a Catalyst for Oxygen Reduction

In this study, we created a series of N, S, and P-doped and co-doped carbon catalysts using a single graphene nanoribbon (GNR) matrix and thoroughly evaluated the impact of doping on ORR activity and selectivity in acidic, neutral, and alkaline conditions. The results obtained showed no significant changes in the GNR structure after the doping process, though changes were observed in the surface chemistry in view of the heteroatom insertion and oxygen depletion. Of all the dopants investigated, nitrogen (mainly in the form of pyrrolic-N and graphitic-N) was the most easily inserted and detected in the carbon matrix. The electrochemical analyses conducted showed that doping impacted the performance of the catalyst in ORR through changes in the chemical composition of the catalyst, as well as in the double-layer capacitance and electrochemically accessible surface area. In terms of selectivity, GNR doped with phosphorus and sulfur favored the 2e− ORR pathway, while nitrogen favored the 4e− ORR pathway. These findings can provide useful insights into the design of more efficient and versatile catalytic materials for ORR in different electrolyte solutions, based on functionalized carbon.

Relationship Between Stress Modulated Metallicity and Plasmon in Graphene Nanoribbons.

Nanoscale quantum plasmon is an important technology that restricts the application of optics, electricity, and graphene photoelectric devices. Establishing a structure-effect relationship between the structure of graphene nanoribbons (GNRs) under stress regulation and the properties of plasmons is a key scientific issue for promoting the application of plasmons in micro-nano photoelectric devices. In this study, zigzag graphene nanoribbon (Z-GNR) and armchair graphene nanoribbon (A-GNR) models of specific widths were constructed, and density functional theory (DFT) was used to study their lattice structure, energy band, absorption spectrum, and plasmon effects under different stresses. The results showed that the Z-GNR band gap decreased with increasing stress, and the A-GNR band gap changed periodically with increasing stress. The plasmon effects of the A-GNRs and Z-GNRs appeared in the visible region, whereas the absorption spectrum showed a redshift trend, indicating the range of the plasmon spectrum also underwent significant changes. This study provides a theoretical basis for the application of graphene nanoribbons in the field of optoelectronics under strain-engineering conditions.

Study of the energy spectrum of a few one-dimensional and quasi one-dimensional lattices through tight binding and density functional theory

A graphene nanoribbon (GNR) is a strip of carbon atoms having sp2 hybridization. It has wide application in nanoelectronics and opto-electronics. Usual fields of application are found in field effect transistors, interconnects, logic gates, sensors, energy storage, and photovoltaics. A single unit graphene nanoribbon is a long strip of graphene rings. Such a GNR structure may be seen as two one-dimensional carbon chains that are suitable connected with bonds. We have done tight binding calculations and density functional theory simulation of carbon chains. We study the single bond and double bond one-dimensional carbon chain and the alternate bond (t1-t2), also called a bond order system in one dimension and quasi one-dimensional chain. We find evidence for the emergence of multiple gaps in the energy spectrum of these systems. We have mapped the alternate bond system to the Su–Schrieffer–Heeger model (with a small modification) in one dimension and quasi one dimension. This is the first time such a mapping has been attempted and a comprehensive theoretical and computational study of these chains has been performed.

Visualizing Ribbon-to-Ribbon Heterogeneity of Chemically Unzipped Wide Graphene Nanoribbons by Silver Nanowire-Based Tip-Enhanced Raman Scattering Microscopy.

Graphene nanoribbons (GNRs), a quasi-one-dimensional form of graphene, have gained tremendous attention due to their potential for next-generation nanoelectronic devices. The chemical unzipping of carbon nanotubes is one of the attractive fabrication methods to obtain single-layered GNRs (sGNRs) with simple and large-scale production. The authors recently found that unzipping from double-walled carbon nanotubes (DWNTs), rather than single- or multi-walled, results in high-yield production of crystalline sGNRs. However, details of the resultant GNR structure, as well as the reaction mechanism, are not fully understood due to the necessity of nanoscale spectroscopy. In this regard, silver nanowire-based tip-enhanced Raman spectroscopy (TERS) is applied for single GNR analysis and investigated ribbon-to-ribbon heterogeneity in terms of defect density and edge structure generated through the unzipping process. The authors found that sGNRs originated from the inner walls of DWNTs showed lower defect densities than those from the outer walls. Furthermore, TERS spectra of sGNRs exhibit a large variety in graphitic Raman parameters, indicating a large variation in edge structures. This work at the single GNR level reveals, for the first time, ribbon-to-ribbon heterogeneity that can never be observed by diffraction-limited techniques and provides deeper insights into unzipped GNR structure as well as the DWNT unzipping reaction mechanism.

The Effect of Anionic and Cationic Charge Carriers on the Supercapacitive Behavior of Graphene Nanoribbons

As worldwide energy consumption continues to increase, so too does the demand for improved energy storage technologies. Supercapacitors have attracted a lot of attention due to their quick charging/discharging rate, high power density, and long-term cycling stability in comparison to conventional batteries.1 Graphene nanoribbons (GNRs) with ultrathin two-dimensional structures and unique properties received a lot of attention recently as potential materials for electrochemical energy storage and specifically supercapacitors.2,3 GNRs maintain graphene’s unique lattice structure in one dimension and provide more open-edge structures compared to graphene, thus allowing faster ion diffusion, which makes GNRs highly promising for energy storage systems.2,3 GNRs have unique characteristics such as exceptional electrical conductivity, a highly modifiable surface area, strong chemical stability, low toxicity, great mechanical behavior, and the ability to tune properties for the desired application.This presentation provides an overview of the production of GNRs from carbon nanotubes and their application in supercapacitors. The physical/chemical structure of GNRs was evaluated using XRD, TEM, FT-IR, Raman spectroscopy, and XPS. Since the selection of the cation and anion has been reported to have a dramatic effect on the specific capacitance of the studied materials,4 the supercapacitive behavior of GNR was thoroughly investigated in various media (H2SO4, KOH, K2SO4 ), using different loadings and different evaluation systems (three and two-electrode systems). GNRs, in all of the tested media, showed good stability (retained 95% of their capacitance over 10,000 cycles at a high current density of 10 A/g), a wide potential window (up to 1.7 V), and a relatively high capacitance (≈ 400-800 F/g). The best medium for GNRs highest supercapacitance in correlation with their surface chemical structure will be discussed.

Semi-Empirical Pseudopotential Method for Graphene and Graphene Nanoribbons.

We implemented a semi-empirical pseudopotential (SEP) method for calculating the band structures of graphene and graphene nanoribbons. The basis functions adopted are two-dimensional plane waves multiplied by several B-spline functions along the perpendicular direction. The SEP includes both local and non-local terms, which were parametrized to fit relevant quantities obtained from the first-principles calculations based on the density-functional theory (DFT). With only a handful of parameters, we were able to reproduce the full band structure of graphene obtained by DFT with a negligible difference. Our method is simple to use and much more efficient than the DFT calculation. We then applied this SEP method to calculate the band structures of graphene nanoribbons. By adding a simple correction term to the local pseudopotentials on the edges of the nanoribbon (which mimics the effect caused by edge creation), we again obtained band structures of the armchair nanoribbon fairly close to the results obtained by DFT. Our approach allows the simulation of optical and transport properties of realistic nanodevices made of graphene nanoribbons with very little computation effort.

Magnetism in Nonplanar Zigzag Edge Termini of Graphene Nanoribbons.

Graphene nanoribbons (GNRs) and nanographenes synthesized by on-surface reaction using tailor-made molecular precursors offer an ideal playground for a study of magnetism towards nano-spintronics. Although the zigzag edge of GNRs has been known to host magnetism, underlying metal substrates usually veil the edge-induced Kondo effect. Here, we report the on-surface synthesis of unprecedented, π-extended 7-armchair GNRs using 7-bromo-12-(10-bromoanthracen-9-yl)tetraphene as the precursor. Characterizations by scanning tunneling microscopy/spectroscopy revealed unique rearrangement reactions leading to pentagon- or pentagon/heptagon-incorporated, nonplanar zigzag termini, which demonstrated Kondo resonance even on bare Au(111). Density functional theory calculations indicate that the nonplanar structure significantly reduces the interaction between the zigzag terminus and the Au(111), leading to a recovery of the spin localization of the zigzag edge. Such distortion of planar GNR structures offers a degree of freedom to control the magnetism on metal substrates.

Electronic Properties of Single‐Layer and Bilayer Graphene Nanoribbons

Herein, a tight‐binding description is utilized to investigate electronic structures and density of states of single‐layer (SL) and bilayer (BL) graphene ribbons with and without the influence of external electric fields. Analyses are implemented to reveal the similarity and difference among electronic properties of three types of structures (specifically SL and BL ribbons with AA and AB stackings). Moreover, both armchair and zigzag edge orientations are considered. It is indicated in the results that variation in electronic properties of these structures in the presence of external electric fields depends on both structural form and edge orientation. The following two points are demonstrated: 1) a transverse field has a significant effect on adjusting bandgap of the zigzag configurations, whereas a vertical electric field has a distinct impact on energy bands of armchair edge structures, and 2) among considered structures, AB‐stacking BL ribbons are invariably the structures that are most strongly influenced by external fields. Interestingly, AB‐stacking BL ribbons are also capable of enlarging bandgap with both edge terminations. Herein, an insight into how the electronic structure and charge distribution of both SL and BL graphene nanoribbons can be controlled not only in armchair but also in zigzag edge terminations using electric stimulants is provided by the results.

Magnetic force microscopy study of induced magnetism in graphene nanoribbons influenced by magnetic nanoparticles

Nanoscale analysis of magnetic properties of graphene nanoribbons (GNRs) conjugated with magnetic nanoparticles has been studied in this work. The effect of varying concentrations of Fe3O4 and Ni nanoparticles on the magnetic domain structure of GNRs has been investigated using magnetic force microscopy (MFM). A variable external magnetic field was applied to the samples, and an evident variation in the domain structure with a change in the magnetic field was observed. It was found that magnetic properties and the imaged magnetic domain structure are influenced by the concentration of magnetic nanoparticles conjugated with GNRs. The vibrating sample magnetometry (VSM) studies support the nano-domain studies done using MFM such that the trend observed for the saturation magnetization obtained from vibrating sample magnetometry (VSM) matches that of the phase difference obtained using MFM.

Reconfigurable GNR based elliptical dielectric resonator antenna for THz band applications

This article presents a novel approach to investigating a reconfigurable Dielectric Resonator antenna using Graphene Nano Ribbon (GNR) in the terahertz band. Two Elliptical shape DRAs are merged to realize High gain and radiation efficiency. The Roger-6010 is utilized to construct an Elliptical shape Dielectric Resonator (EDRA), and GNR structures are constructed on top of it to achieve reconfigurability. The radiation performance of projected EDRA is investigated in terms of 10 dB Impedance bandwidth, reflection coefficient, surface current, directivity, radiation efficiency, and gain in the frequency range from 0.55-to-0.75-THz. The proposed EDRA design has an impedance bandwidth of 15.64 %, a peak gain of 11.9dBi, peak directivity of 13.1dBi, and radiation efficiency of 97.3 %. Moreover, the reconfigurability nature is investigated by the chemical potential of the surface conductivity of graphene and then GNR-based EDRA radiation parameters. The projected EDRA is suitable for various applications in the THz band.

Nonlinear thermal transport in graphene nanoribbon: A molecular dynamics study

Effects of different factors on the thermal conductivity of graphene nanoribbons (GNRs) is investigated using nonequilibrium molecular dynamics (NEMD) simulations with LAMMPS code, taking advantage of the optimized Tersoff interatomic potential. The influences of temperature, size, and layer number on thermal transport are considered for both zigzag and armchair GNRs. It is found that increasing the size (length⩽40 nm and width⩽10 nm) enhances the thermal conductivity of both GNR types by a power-law relationship at room temperature. In contrast, the thermal conductivity of GNRs drastically drops as the temperature rises in the range of 50–500 K. The power-law reduction of conductivity, owing to the temperature increase, is faster in zigzag GNR than in armchair one. In addition, in the range of 1–10 layers, the thermal conductivity experiences a power-law decrease with increasing number of GNRs layers because of the out-of-plane scattering of phonons. Our results reveal how boundary scattering, growing phonon number and Umklapp scattering govern nonlinear thermal transport mechanism. This study also demonstrates a dramatic influence of the edge structure of GNR on thermal conduction.