Boron-doped Graphene Nanoribbon Research Articles

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.

The effect of line edge roughness defect on the electronic transport properties of Boron-doped graphene nanoribbon rectifier

A rectifying behavior is achieved by means of boron doping in defected armchair graphene nanoribbon (AGNR). In the proposed AGNR device, the effect of line edge roughness (LER) is investigated on the electronic and transport characteristics. Moreover, the width of AGNR is changed by 6, 7 and 8 atoms in the fixed length, and the position of the boron doping is changed in the center or edge of the left electrode. The electronic features of the devices are analyzed through density function theory and non-equilibrium Green’s function method. The LER defect and any change in the doping position or the width of AGNR affect the energy alignments, molecular orbital levels, transfer functions and density of states (DOS) that lead to a change in the rectifying behavior of the device. Without the LER defect, rectifying ratio at the ribbon width of 7w in the presence of boron doping at the center, and edge is achieved 16 and 5.88, respectively. But interestingly, by considering the LER defect in the same situation these values increase to 362 and 102, respectively.

The adsorption, diffusion and capacity of lithium on novel boron-doped graphene nanoribbon: A density functional theory study

Inspired by the experimental synthesis of novel boron-doped graphene nanoribbon (BGNR), we have performed density functional theory (DFT) calculations to reveal the adsorption behaviors of lithium (Li) atoms on BGNR. We systematically studied the adsorption, diffusion and capacity of Li on BGNR with 7 carbon atoms in width. It is found that due to the doping effects of boron (B) atoms, BGNR exhibits a narrower band gap than graphene nanoribbon (GNR) with the same width. Individual Li atom exhibits much stronger binding on BGNR than that on GNR, attributing to the stronger LiC interaction caused by doping of B atoms. A zigzag diffusion path along the growth direction of BGNR is confirmed for diffusion of Li. The maximum theoretical storage capacity of Li on BGNR is determined as 783 mAh/g, which is 15 times than that on GNR with same width (52 mAh/g). Our results demonstrated that doping of B atoms greatly enhances the adsorption and storage performance of Li, which provides a theoretical foundation of researches on the novel BGNR and other similar structures for adsorption and storage of Li.

Boron-Doped Graphene Nanoribbons: Electronic Structure and Raman Fingerprint

We investigate the electronic and vibrational properties of bottom-up synthesized aligned armchair graphene nanoribbons of N = 7 carbon atoms width periodically doped by substitutional boron atoms (B-7AGNRs). Using angle-resolved photoemission spectroscopy and density functional theory calculations, we find that the dopant-derived valence and conduction band states are notably hybridized with electronic states of Au substrate and spread in energy. The interaction with the substrate leaves the bands with pure carbon character rather unperturbed. This results in an identical effective mass of ≈0.2 m0 for the next-highest valence band compared with pristine 7AGNRs. We probe the phonons of B-7AGNRs by ultrahigh-vacuum (UHV) Raman spectroscopy and reveal the existence of characteristic splitting and red shifts in Raman modes due to the presence of substitutional boron atoms. Comparing the Raman spectra for three visible lasers (red, green, and blue), we find that interaction with gold suppresses the Raman signal from B-7AGNRs and the energy of the green laser (2.33 eV) is closer to the resonant E22 transition. The hybridized electronic structure of the B-7AGNR-Au interface is expected to improve electrical characteristics of contacts between graphene nanoribbon and Au. The Raman fingerprint allows the easy identification of B-7AGNRs, which is particularly useful for device fabrication.

Electronic Properties of Substitutionally Boron-Doped Graphene Nanoribbons on a Au(111) Surface

High quality graphene nanoribbons (GNRs) grown by on-surface synthesis strategies with atomic precision can be controllably doped by inserting heteroatoms or chemical groups in the molecular precursors. Here, we study the electronic structure of armchair GNRs substitutionally doped with di-boron moieties at the center, through a combination of scanning tunneling spectroscopy, angle-resolved photoemission, and density functional theory simulations. Boron atoms appear with a small displacement towards the surface signaling their stronger interaction with the metal. We find two boron-rich flat bands emerging as impurity states inside the GNR band gap, one of them particularly broadened after its hybridization with the gold surface states. In addition, the boron atoms shift the conduction and valence bands of the pristine GNR away from the gap edge, and leave unaffected the bands above and below, which become the new frontier bands and have negligible boron character. This is due to the selective mixing of boron states with GNR bands according to their symmetry. Our results depict that the GNRs band structure can be tuned by modifying the separation between di-boron moieties.

Silver Nanoparticle/Boron-Doped Graphene Nanoribbon Nanocomposite for Effective Surface Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) provides high sensitivity and selectivity on molecule detection, making it attractive for biomedical and chemical detections. Generally there are two mechanisms to influence the SERS enhancement: electromagnetic mechanism (EM) created by the metals with surface plasmon resonance (SPR) property and chemical mechanism (CM) due to the charge transfer between the molecule and the substrate. The development of synthetic method to produce nanostructures with controllable EM and CM properties will lead to important advances on both fundamental study and innovative applications for SERS-based biomedical detections. Graphene nanoribbons (GNRs) represent a unique structure of carbon nanomaterials with controlled electronic properties by tuning their widths, making them can be potentially useful as the SERS-active substrate and used in other applications including energy, composites, biomedical and electronics. Here we report a rational design to develop a SERS-active nanocomposite with improved EM and CM properties. Toward this goal, we prepared silver (Ag)/Boron-doped GNR (B-GNR) composites using a sequential reaction route. First we synthesized GNRs with averaged width around 4 to 5 nm by the chemical unzipping of singled-walled carbon nanotubes (SWCNTs). Additionally, the prepared GNRs were doped with B atoms by a controlled carbonthemic reaction under argon (Ar) flow at atmospheric pressure and the B dopant concentration was about 1.4 atomic percentage (atom%) according to the X-ray photoelectron spectroscopy (XPS) analysis. Ag NPs with 10 nm averaged size were decorated onto the B-GNRs surface through an atmospheric-pressure microplasma-assisted redox reaction. Detailed materials characterizations including transmission electron microscopy and UV-Vis spectroscopy show that Ag/B-GNR composites were successfully synthesized in our experiment. We further systematically studied the Raman response of the Ag/B-GNR composite using Rhodamine 6G (R6G) as the Raman probe molecules. The result indicates that the Ag/GNR composite shows superior SERS performance with low detection concentration of 10-12 M of R6G and high enhance factor (EF) of 1.9x1012. We furthermore systematically studied the CM enhancement via different probing molecules and substrates. Results show that SERS performance is strongly influenced by the charge transfer mechanism induced by the energy gap between the substrate Fermi level and the LUMO energy of probing molecules. Our study provide the conception to design the applicable SERS substrates. Figure 1

Potential Application of Novel Boron-Doped Graphene Nanoribbon as Oxygen Reduction Reaction Catalyst

The development of carbon-based metal-free electrocatalysts for oxygen reduction reaction (ORR) is essential for large-scale commercial applications of fuel cells. Using density functional theory computations, we explore the potentials of a novel boron-doped graphene nanoribbon (BGNR) as an excellent electrocatalyst for ORR in an acidic environment. The plausible reaction pathways are studied, and the optimal reaction mechanism is identified. Our results show that ORR at BGNR prefers to proceed through a four-electron OOH pathway. The overpotential for ORR on BGNR is calculated to be 0.38 V, which is lower than that on the Pt-based catalysts (0.45 V). For comparison, we study the catalytic activity of the single B-doped graphene nanoribbon (S-BGNR) and B-doped graphene (BG) for ORR. Remarkably, the para-B distribution on BGNR leads to high affinity for O2 adsorption and excellent catalytic activity, which is superior to S-BGNR and BG. Our results indicate that BGNR is a promising metal-free ORR catalyst f...

Detecting CO, NO and NO2 gases by Boron-doped graphene nanoribbon molecular devices

Combining nonequilibrium Green’s function method and density functional theory, an azulene-like dipole molecule sandwiched between two graphene nanoribbon (GNR) electrodes are explored to gas sensors. Both the pristine zigzag edged GNR and Boron-doped armchair-edged GNR are considered in this study. It shows that certain specific toxic molecules CO, NO and NO2 would adsorb on the doped Boron atoms of the GNR, resulting in a dramatic change in the current–voltage profile. Changes in the subbands of electrodes, induced by gas adsorption, are responsible for the variation of current. The devices are thus demonstrated to be sensitive nanosensors for these toxic gases.

Atomically controlled substitutional boron-doping of graphene nanoribbons.

Boron is a unique element in terms of electron deficiency and Lewis acidity. Incorporation of boron atoms into an aromatic carbon framework offers a wide variety of functionality. However, the intrinsic instability of organoboron compounds against moisture and oxygen has delayed the development. Here, we present boron-doped graphene nanoribbons (B-GNRs) of widths of N=7, 14 and 21 by on-surface chemical reactions with an employed organoboron precursor. The location of the boron dopant is well defined in the centre of the B-GNR, corresponding to 4.8 atom%, as programmed. The chemical reactivity of B-GNRs is probed by the adsorption of nitric oxide (NO), which is most effectively trapped by the boron sites, demonstrating the Lewis acid character. Structural properties and the chemical nature of the NO-reacted B-GNR are determined by a combination of scanning tunnelling microscopy, high-resolution atomic force microscopy with a CO tip, and density functional and classical computations.

Highly-dispersed boron-doped graphene nanoribbons with enhanced conductibility and photocatalysis.

Highly-dispersed boron-doped graphene nanoribbons (B-GNRs), prepared by a simple vacuum activation method, exhibit p-type semiconductor properties and provide many more zigzag- and armchair-edges to facilitate control of the bandgap. B-GNRs are used for the photodegradation of Rhodamine B in order to demonstrate their excellent conductivity and photocatalytic activity.

Atomistic Boron-Doped Graphene Field-Effect Transistors: A Route toward Unipolar Characteristics

We report fully quantum simulations of realistic models of boron-doped graphene-based field-effect transistors, including atomistic details based on DFT calculations. We show that the self-consistent solution of the three-dimensional (3D) Poisson and Schrödinger equations with a representation in terms of a tight-binding Hamiltonian manages to accurately reproduce the DFT results for an isolated boron-doped graphene nanoribbon. Using a 3D Poisson/Schrödinger solver within the non-equilibrium Green's function (NEGF) formalism, self-consistent calculations of the gate-screened scattering potentials induced by the boron impurities have been performed, allowing the theoretical exploration of the tunability of transistor characteristics. The boron-doped graphene transistors are found to approach unipolar behavior as the boron concentration is increased and, by tuning the density of chemical dopants, the electron-hole transport asymmetry can be finely adjusted. Correspondingly, the onset of a mobility gap in the device is observed. Although the computed asymmetries are not sufficient to warrant proper device operation, our results represent an initial step in the direction of improved transfer characteristics and, in particular, the developed simulation strategy is a powerful new tool for modeling doped graphene nanostructures.

Electronic Properties of Nitrogen-/Boron-Doped Graphene Nanoribbons With Armchair Edges

Calculation of electronic structures has been performed for graphene nanoribbons with eight-armchair edges containing nitrogen or boron substitutional impurity by using <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ab initio</i> density functional theory. It is found that the electronic structures of the doped graphene nanoribbon are different from those of doped carbon nanotubes. The impurity levels are autoionized, so that the relevant charge carriers occupy the conduction or valence bands. The donor and acceptor levels are derived mainly from the lowest unoccupied orbital and highest occupied orbital of pristine graphene nanoribbon, respectively. N introduces an impurity level above the donor level, while an impurity level introduced by B is below the acceptor level. The doped graphene nanoribbons with armchair edges are inactive compared to the doped carbon nanotubes around the impurity site, which may indicate that the doped graphene nanoribbons with armchair edges could be more stable than the doped carbon nanotubes at the ambient.

A theoretical study of chemical doping and width effect on zigzag graphene nanoribbons

Abstract The energetics and the electronic properties of nitrogen- and boron-doped graphene nanoribbons with zigzag edges have been investigated using density functional theory calculations. For the optimized geometry configurations, vibrational frequency analysis and wavefunction stability tests have been carried out. Different doping site optimizations for a model nanoribbon have been performed and formation energy values of these sites revealed that zigzag edgesite for both of the dopants were the most favorable one. The effect of doping on the molecular orbital energies, HOMO–LUMO distributions, and density of states have been studied as well. It is found that molecular orbital distributions for pure zigzag nanoribbons are located in the zigzag edges while they exhibit different behaviors for the doped cases.

Half-Metallicity in Undoped and Boron Doped Graphene Nanoribbons in the Presence of Semilocal Exchange-Correlation Interactions

We perform density functional calculations on one-dimensional zigzag edge graphene nanoribbons (ZGNRs) of different widths, with and without edge doping including semilocal exchange correlations. Our study reveals that, although the ground state of edge-passivated (with hydrogen) ZGNRs prefers to be anti-ferromagnetic, the doping of both of the edges with boron atoms stabilizes the system in a ferromagnetic ground state. Both the local and semilocal exchange correlations result in half-metallicity in edge-passivated ZGNRs at a finite cross-ribbon electric field. However, the ZGNR with boron edges shows half-metallic behavior irrespective of the ribbon width even in the absence of electric field and this property sustains for any field strength, opening a huge possibility of applications in spintronics.

Electronic and Transport Properties of Boron-Doped Graphene Nanoribbons

We report a spin polarized density functional theory study of the electronic and transport properties of graphene nanoribbons doped with boron atoms. We considered hydrogen terminated graphene (nano)ribbons with width up to 3.2 nm. The substitutional boron atoms at the nanoribbon edges (sites of lower energy) suppress the metallic bands near the Fermi level, giving rise to a semiconducting system. These substitutional boron atoms act as scattering centers for the electronic transport along the nanoribbons. We find that the electronic scattering process is spin-anisotropic; namely, the spin-down (up) transmittance channels are weakly (strongly) reduced by the presence of boron atoms. Such anisotropic character can be controlled by the width of the nanoribbon; thus, the spin-up and spin-down transmittance can be tuned along the boron-doped nanoribbons.