Electronic Properties Of Graphene Nanoribbons Research Articles

Electronic Properties of Graphene Nanoribbons Doped with Pyrrole-Like Nitrogen

Electronic Properties of Graphene Nanoribbons Doped with Pyrrole-Like Nitrogen

Precision Synthesis of Boron‐Doped Graphene Nanoribbons: Recent Progress and Perspectives

AbstractStructurally precision graphene nanoribbons (GNRs) have attracted great interest considering their prospective applications as organic carbon materials for nanoelectronics. The electronic properties of GNRs not only critically depend on the edge structure and width but also on the heteroatom type, doping position, and concentration. Motivated by the recent undisputable progress in the synthesis of stable boron‐doped polycyclic aromatic hydrocarbons (B‐PAHs), considerable efforts have been devoted to the precision synthesis of the corresponding boron‐doped GNRs (B‐GNRs) via bottom‐up synthesis approach in recent years in view of the extraordinary ability of boron doping on modulating their physiochemical properties. In this review, an overview of the bottom‐up organic synthesis of B‐GNRs, including the precursor design and synthesis, structure characterization of the resulting B‐GNRs, and investigation of their electronic properties is provided. Moreover, the future challenges and perspectives regarding the bottom‐up synthesis of B‐GNRs are also discussed. The authors hope that this review will further stimulate the synthesis and device integrations of B‐GNRs with a combined effort from different disciplines.

Synergistic effect of Cu decoration and N doping in divacancy defected graphene nanoribbons on hydrogen gas sensing properties: DFT study

Density functional theory (DFT) calculations have been employed to analyze the molecular hydrogen interaction on Cu decorated nitrogen doped divacancy defected graphene nanoribbons (GNRs). In this study, 5-8-5 double vacancy has been specified as a functional defect in order to study their effect on the electronic properties of GNRs. Divacancies are considered to be thermodynamically more favorable than monovacancies because of low formation energy. Moreover, the introduction of nitrogen defects had a massive influence on adsorption properties. The adsorption capability of the complex systems improved as the concentration of nitrogen atoms increased, but when four nitrogen atoms were doped, the efficiency decreased significantly. Aside from adsorption energy, other parameters such as bonding distance, charge transfer; electronic properties were examined and found to be consistent with the previous findings. Our results suggested that simultaneous doping of nitrogen atoms and Cu decorated defected GNR could be a potential material for hydrogen sensing and could be utilized for future applications. Hence, it is worth noting that adding appropriate dopants and defects to the graphene-based gas sensors could greatly improve their sensitivity.

The electronic properties of graphene nanoribbons and the offset logarithm function

Graphene Nanoribbons (GN), being an important class of next-generation carbon materials, are of immense interest and find innumerable applications in diverse fields. A variation of the generalized Lambert W function, called the Offset Logarithm function, has been found to have important applications in fields such as physics, engineering and nanotechnology. We study the electronic properties of zigzag GN and use the generalized Lambert W function to study the eigenvalue equations of the massless Dirac equation applied to zigzag GN. We have studied the effects of nanoribbon width and determined the parameters that significantly affect the obtained solutions.

Electronic Properties of Graphene Nanoribbons with Zigzag Armchair Edges

We have studied the electronic properties of graphene nanoribbons with zigzag armchair edges. We have calculated the local density of states, the single particle special function, the optical conductivity and the conductance for different geometries. We have also studied the disordered effects. The influence of disorder on the transport behavior of tight binding approach has been accepted. The conductance of edge contacted graphene nanoribbon sensitivity was found dependent on the lead graphene nanoribbon matching conditions. In this respect armchair graphene nanoribbon enabled a somewhat better current injection. Dangling bonds on the graphene nanoribbon side of the interface substantially reduced the conductance. The typical conductance of disordered graphene nanoribbons sandwiched between graphene leads in a junction set up exhibited a negative differential conductivity whenever new transport channels become available by increasing the Fermi level. This accentuates the efficiency of Anderson localization function manifested a precursor of the transition from a current carrying to an Anderson disorder induced insulating behavior which takes place when the size of the disordered active graphene region becomes infinite. The obtained results were found in good agreement with previously obtained results.

Electronic Properties of Graphene Nanoribbons With Defects

Graphene nanoribbons (GNRs) are the most important emerging Graphene structures for nanoelectronic and sensor applications. GNRs with perfect lattices have been extensively studied, but fabricated GNRs contain lattice defects the effect of which on their electronic properties has not been studied extensively enough. In this paper, we apply the Non-Equilibrium Green's function (NEGF) method combined with tight-binding Hamiltonians to investigate the effect of lattice defects on the conductance of GNRs. We specifically study, butterfly shaped GNRs, which operate effectively as switches, and have been used in CMOS-like architectures. The cases of the most usual defects, namely the single and double vacancy have been analytically examined. The effect of these vacancies was computed by placing them in different regions and with various numbers on GNR nano-devices, namely edges, main body, contacts and narrow regions. The computation results are presented in the form of energy dispersion diagrams as well as diagrams of maximum conductance as a function of the number of lattice defects. We also present results on the defect tolerance of the butterfly shaped GNR devices.

Atomically precise graphene nanoribbons: interplay of structural and electronic properties.

Graphene nanoribbons hold great promise for future applications in nanoelectronic devices, as they may combine the excellent electronic properties of graphene with the opening of an electronic band gap – not present in graphene but required for transistor applications. With a two-step on-surface synthesis process, graphene nanoribbons can be fabricated with atomic precision, allowing precise control over width and edge structure. Meanwhile, a decade of research has resulted in a plethora of graphene nanoribbons having various structural and electronic properties. This article reviews not only the on-surface synthesis of atomically precise graphene nanoribbons but also how their electronic properties are ultimately linked to their structure. Current knowledge and considerations with respect to precursor design, which eventually determines the final (electronic) structure, are summarized. Special attention is dedicated to the electronic properties of graphene nanoribbons, also in dependence on their width and edge structure. It is exactly this possibility of precisely changing their properties by fine-tuning the precursor design – offering tunability over a wide range – which has generated this vast research interest, also in view of future applications. Thus, selected device prototypes are presented as well.

Electronic Properties of Graphene Nanoribbons

Nowadays, graphene physics is aimed at finding a way to control the band gap of graphene, which is necessary for application of graphene in nanoelectronics. The purpose of this work is to investigate the systems that break an inversion symmetry of a hexagonal lattice. The electronic properties of armchair and zigzag graphene nanoribbons are obtained and the dependence of the electronic properties on the edge effects is shown.

Band Depopulation of Graphene Nanoribbons Induced by Chemical Gating with Amino Groups.

The electronic properties of graphene nanoribbons (GNRs) can be precisely tuned by chemical doping. Here we demonstrate that amino (NH2) functional groups attached at the edges of chiral GNRs (chGNRs) can efficiently gate the chGNRs and lead to the valence band (VB) depopulation on a metallic surface. The NH2-doped chGNRs are grown by on-surface synthesis on Au(111) using functionalized bianthracene precursors. Scanning tunneling spectroscopy resolves that the NH2 groups significantly upshift the bands of chGNRs, causing the Fermi level crossing of the VB onset of chGNRs. Through density functional theory simulations we confirm that the hole-doping behavior is due to an upward shift of the bands induced by the edge NH2 groups.

Electronic properties of graphene nanoribbons with line-edge roughness doped with nitrogen and boron

Abstract Graphene has enormous potential in nanoelectronics because of its remarkable electronic properties. Pristine graphene is a zero-bandgap semimetal nanomaterial unsuitable for logic devices. Graphene nanoribbons (GNRs), which are strips of graphene, have gained considerable research attention. During the fabrication of GNRs, a number of carbon atoms are removed from the ribbons' edges by cutting processes, thereby causing line-edge roughness, which is common in typical graphene. Substitution doping is a crucial method to adjust the electronic properties of materials. Based on the nearest-neighbour tight-binding method and non-equilibrium Green's function formalism, a GNR tight-binding model is presented. This research focuses on 13-armchair-edged GNRs with line-edge roughness that are doped with nitrogen or boron. Furthermore, the band structure and local density of states of both pristine and non-pristine GNRs are analysed. This study confirms that the line-edge roughness effect causes band-gap reduction. In addition, p-type doping decreases the band gap further than n-type doping. Nevertheless, the line-edge roughness effect is more prominent than the effect caused by doping. The study determines the effects and interaction of non-idealities, namely, substitutional impurities and vacancies, in GNRs having edge roughness.

A comparative study of substrates disorder on mobility in the Graphene nanoribbon: Charged impurity, surface optical phonon, surface roughness

The effects of substrate on the electronic properties of Graphene remains unclear. Many theoretical and experimental efforts have been done to clarify this discrepancy. In this work, we studied the electronic transport in armchair Graphene nanoribbons (AGNR) in the presence of substrate's disorder. The three main substrate's disorders -- surface roughness, charged impurity and surface optical phonon -- are investigated. Non-Equilibrium Green's function along with the tight-binding model is employed to investigate the electronic properties of Graphene Nanoribbons. The effects of these disorders are investigated individually, finally, the effects of them are compared to determine the dominant source of scattering.

Modeling of lightly-doped drain and source contact with boron and nitrogen in graphene nanoribbon

Graphene, a monolayer carbon atoms arranged in hexagonal honeycomb lattice possesses impressive electronic properties. It is utilized as channel, source and drain contact in graphene nanoribbon field-effect transistor (GNRFET). Zigzag graphene nanoribbon (ZGNR) is used as semi-metallic drain and source terminal to a pristine armchair graphene nanoribbon (AGNR) that acts as a semiconducting channel. In addition, a single dopant, either nitrogen or boron is added to create lightly-doped drain and source contact. The electronic properties of graphene nanoribbon (GNR) with lightly-doped drain and source contacts are obtained from tight-binding approach. With self-energy matrices, the lightly-doped contacts Hamiltonian matrices are combined with the pristine channel Hamiltonian matrix. The density of states (DOS) are simulated based on the non-equilibrium Green's Function (NEGF) formalism. Our findings are then compared with published research work. Furthermore, it is demonstrated that the DOS of the overall GNR structure still retain a small band gap and possess semiconducting properties when the channel is connected to semi-metallic contact at the drain and source terminal.

Ab initio study of electronic properties of armchair graphene nanoribbons passivated with heavy metal elements

In this study, electronic properties of graphene nanoribbons with armchair edges (AGNRs) have been investigated with Density Functional Theory (DFT). Effects of heavy metal (HM) elements, including Zinc (Zn), Cadmium (Cd) and Mercury (Hg) atoms on electronic behavior of AGNRs have been calculated by passivating for both one and two edges of AGNRs in detail. To explain the electronic behavior of investigated AGNRs, the electronic band structure, the density of states (DOS), total energy have been calculated. Energetically favorable structures have been determined using calculated binding energy values. The obtained bandgap values of investigated structures changes between 0.30 and 0.64 eV. Increasing atomic number of passivation atoms have led to an increment in the bandgap of AGNRs.

DFT Investigation of Graphene Nanoribbon As a Potential Nanobiosensor for Tyrosine Amino Acid

We investigated (2,2) graphene nanoribbon (GNR) as a nanobiosensor for tyrosine (C9H11NO3) amino acid detection using density functional theory (DFT) calculations. The geometric, energetic, and electronic properties, which include the bond length, charge, adsorption energies, HOMO energies, Fermi level energies, LUMO energies, energy gaps, work functions, dipole moments and reactivity descriptors were calculated by DFT/B3LYP with 6-31G(d) basis set for the GNR in free mode and interacted with the tyrosine (Tyr) molecule. The molecular electrostatic potential and the electron density surfaces have been constructed. Moreover, we used orbital analysis counting the density of states (DOS) to finding out the possible orbital hybridization of these hybrid structures. Based on the results, it was found that GNR shows high reactivity toward Tyr, and, in the favorable state, the calculated adsorption energy is about 2.610 eV. It is shown that the electronic properties of GNR are strongly sensitive to the presence of Tyr molecule. Therefore, we believe that these hybrid structures of nanobiosensors are able to sense the smallest amino acid constructing block of proteins, and the GNRs have the potential to be used in sensor devices.

Edge functionalization of finite graphene nanoribbon superlattices

The effect of chemical functionalization on the electronic properties of graphene nanoribbon superlattices with zigzag and armchair terminations is investigated using the density functional theory. The calculated positive binding energies imply that all the considered structures are stable before and after chemical modifications. The superlattices with armchair edges are characterized by a wide energy gap while those with zigzag edges have a narrow energy gap. The energy gap in superlattices with armchair edges nearly independent of their length while it strongly decreases and almost closes in superlattices with zigzag edges. The energy gap is comparably sensitive to the width variations in both types of the superlattices. It was found that the electric dipole moment increases with increasing the width in the case of armchair while it oscillates in zigzag superlattices. The electric dipole moment can be enhanced by chemical functionalization with COOH and NH2 groups. The effect of this functionalization is moderate for the energy gap, but the adsorption of tetracyanoquinodimethane transforms the system from insulator (Eg = 2.66 eV) to a narrow band gap semiconductor (Eg = 0.25 eV). The adsorption energy of tetracyanoquinodimethane and tetrathiafulvalene molecules can be enhanced by chemical functionalization which makes graphene superlattices useful for sensor applications and wastewater treatment.

Electronic structure of graphene nanoribbons on hexagonal boron nitride

Hexagonal boron nitride is an ideal dielectric to form two-dimensional heterostructures due to the fact that it can be exfoliated to be just few atoms thick and its a very low density of defects. By placing graphene nanoribbons on high quality hexagonal boron nitride it is possible to create ideal quasi one dimensional (1D) systems with very high mobility. The availability of high quality one-dimensional electronic systems is of great interest also given that when in proximity to a superconductor they can be effectively engineered to realize Majorana bound states. In this work we study how a boron nitride substrate affects the electronic properties of graphene nanoribbons. We consider both armchair and zigzag nanoribbons. Our results show that for some stacking configurations the boron nitride can significantly affect the electronic structure of the ribbons. In particular, for zigzag nanoribbons, due to the lock between spin and sublattice degree of freedom at the edges, the hexagonal boron nitride can induce a very strong spin-splitting of the spin polarized, edge sates. We find that such spin-splitting can be as high as 40~meV.

Electronic transport through hybrid armchair graphane/graphene nanoribbons

Modulation of the electronic properties of graphene nanoribbons (GNRs) is an important issue for their application in nanoelectronics. Armchair GNRs (AGNRs) are semiconductors with energy gaps related to their width. Armchair graphane nanoribbons (AGaNRs) are insulators with wide gaps. Considering the gap size hierarchy of AGNRs, we construct a series of hybrid nanoribbon by substituting AGaNRs into AGNRs to tune the charge transport of the nanoribbons. Based on the non-equilibrium Green's function method combined with the density functional theory, it is interesting to find that the energy gaps of these nanoribbons do not increase monotonically with the increasing proportion of AGaNRs as one expects intuitively. The charge transport of these systems can be enhanced or reduced due to the incorporation of AGaNRs. It suggests that such hybridization is an efficient way to modulate the electronic properties of the systems. Detailed analyses via transmission spectra, distribution of molecular projected self-consistent Hamiltonian states, frontier molecular orbital position and transmission pathways are given for a deeper insight.

Energy bandgap engineering of graphene nanoribbon by doping phosphorous impurities to create nano-heterostructures: A DFT study

Energy bandgap engineering is used to produce semiconductor heterostructure systems that perform processes such as the resonant tunneling in nanoelectronics and the solar energy conversion in solar cell applications. However, the performance of such systems degrades as their size is reduced. Graphene-based nanoelectronics has appeared as a candidate to enable high performance down to the single-molecule scale. Here, graphene nanoribbons (GNRs) can have bandgaps that are tunable by using chemical doping method. We have been predicted that bandgap engineering within a GNR may be achieved by varying the number and geometrical pattern of phosphorus (P) impurities in the GNS, so that we have carried out first-principles calculations of the energetic and electronic properties of P-doped GNR based on density functional theory (DFT) with Gaussian 09W packages. The geometric and electronic properties of the GNR with and without various dopants of phosphorus impurities were performed and discussed. Our results show that the electronic properties of GNR do not only depend on the phosphorus impurity concentrations, but also depend on the geometrical pattern of phosphorus impurities in the GNR. As a result, we can bandgap engineering of GNR by doping phosphorous impurities to create semiconductor heterostructure, which can be used in many important applications.

Electronic properties of graphene nanoribbons doped with zinc, cadmium, mercury atoms

The effect of substitutional impurities as Zinc (Zn), Cadmium (Cd) and Mercury (Hg) on electronic properties of graphene nanoribbons (GNRs) was investigated by using Density Functional Theory (DFT). A substantial change in the electronic properties of GNR structures was observed while changing the position of dopant atom from the edge to the center of armchair graphene nanoribbons (AGNRs) and zigzag graphene nanoribbons (ZGNRs). The calculations are shown that the electronic band gap of GNRs can be controlled depending on the position of dopant atoms. The calculated electronic band structures for both AGNRs and ZGNRs show spin-dependent metallic or semiconductor behavior according to the position of dopant atoms. From the Density of States (DOS) information, quasi-zero-dimensional (Q0D) and quasi-one-dimensional (Q1D) type behaviors are observed. It is shown that because the doped ZGNRs had the lowest total energies, ZGNRs are energetically more stable than AGNRs.

Mechanical and electronic properties of graphene nanomesh heterojunctions

It is well known that introducing periodic holes into graphene can be used to obtain semiconducting graphene nanomeshes (GNM). Using Molecular Dynamics (MD) simulations as well as semi-empirical Extended Hückel (EH) method, the mechanical and electronic properties of GNM heterojunction are studied. In this study the mechanical and electronic properties of graphene nanoribbons with different hole sizes and different hole shapes (circular, square and equilateral triangle) were studied. Midgap states were observed near the Fermi level, which are also affected by the geometries of the holes. Dependence of the properties on the density (ρ) was also investigated for each geometry. It has been found that GNM is significantly brittle compared to pristine graphene nanoribbons. It is observed that the relationship between the hole shape and size and the band gap is different for armchair and zigzag chirality.