Properties Of Graphene Nanoribbons Research Articles

From defect to effect: controlling electronic transport in chevron graphene nanoribbons

While bottom-up synthesis allows for precise control over the properties of graphene nanoribbons (GNRs), the use of certain precursor molecules can result in edge defects, such as missing benzene rings that resemble a ‘bite’. We investigate the adverse effect of the ‘bite’ defects on the electronic transport properties in three chevron-type GNRs and discover that the extent of scattering is governed by the different defect positions. Applying the concepts learned in single GNRs, we engineer defects in two nanostructures to construct prototypical components for nanoelectronics. First, we design a switch, consisting of three laterally fused fluorenyl-chevron GNRs, and place a pair of ‘bite’ defects to effectively allow the switching between four binary states corresponding to distinct current pathways. Second, we show that conscientious placement of a ‘bite’ defect pair can increase conductance between two leads in a triple chevron GNR junction. Overall, we outline how the incorporation of ‘bite’ defects affects transport properties in chevron-type nanostructures and provide a guide on how to design nanoelectronic components.

Reverse strain-induced snake states in graphene nanoribbons

Strain can tailor the band structures and properties of graphene nanoribbons (GNRs) with the well-known emergent pseudo-magnetic fields and the corresponding pseudo-Landau levels (pLLs). We design one type of the zigzag GNR (ZGNR) with reverse strains, producing pseudo-magnetic fields with opposite signs in the lower and upper half planes. Therefore, electrons propagate along the interface as "snake states", experiencing opposite Lorentz forces as they cross the zero field border line. By using the Landauer-Buttiker formalism combined with the nonequilibrium Green's function method, the existence and robustness of the reverse strain-induced snake states are further studied. Furthermore, the realization of long-thought pure valley currents in monolayer graphene systems is also proposed in our device.

Small Size, Big Impact: Recent Progress in Bottom-Up Synthesized Nanographenes for Optoelectronic and Energy Applications.

Bottom‐up synthesized graphene nanostructures, including 0D graphene quantum dots and 1D graphene nanoribbons, have recently emerged as promising candidates for efficient, green optoelectronic, and energy storage applications. The versatility in their molecular structures offers a large and novel library of nanographenes with excellent and adjustable optical, electronic, and catalytic properties. In this minireview, recent progress on the fundamental understanding of the properties of different graphene nanostructures, and their state‐of‐the‐art applications in optoelectronics and energy storage are summarized. The properties of pristine nanographenes, including high emissivity and intriguing blinking effect in graphene quantum dots, superior charge transport properties in graphene nanoribbons, and edge‐specific electrochemistry in various graphene nanostructures, are highlighted. Furthermore, it is shown that emerging nanographene‐2D material‐based van der Waals heterostructures provide an exciting opportunity for efficient green optoelectronics with tunable characteristics. Finally, challenges and opportunities of the field are highlighted by offering guidelines for future combined efforts in the synthesis, assembly, spectroscopic, and electrical studies as well as (nano)fabrication to boost the progress toward advanced device applications.

The Effect of 555-777 Defect on Mechanical Properties of Graphene Nanoribbon

In this study, the effects of 555-777 defect on Young’s modulus, fracture strength and fracture strain of armchair graphene nanoribbons (AGNRs) and zigzag graphene nanoribbons (ZGNRs) were investigated by using Molecular Dynamics simulations under uniaxial tension. The simulation results show that 555-777 defect significantly reduces the fracture strength and fracture strain of AGNRs and ZGNRs, but has little effect on Young's modulus. The influence of 555-777 defect on the mechanical properties of AGNRs is greater than that of ZGNRs. This study provides a better understanding of mechanical properties of graphene nanoribbons.

Energetics and magnetism of topological graphene nanoribbons

The topological properties of graphene nanoribbons (GNRs) have received a significant amount of attention in emerging fields such as spintronics and quantum computing. This study is focused on the energetics and magnetism of symmetry-protected junction state arrays, which are realized in the alternating periodic structures of two topologically different armchair GNRs. We found that the antiferromagnetic states require at least eight unit cells for each segment of the periodic armchair GNRs, where the armchair GNRs whose numbers of carbon atoms in a row are seven and nine are connected with a junction structure. We also found the junction structure that provides more stable antiferromagnetic states. Furthermore, we propose an end (armchair GNRs/vacuum interface) structure to avoid disturbing the global topological properties of the junction state array. This means that if the topological end states (non-trivial phases of the Su, Schrieffer, and Heeger model or Majorana fermions) exist, they are properly formed at the endmost junctions without the requirement for extra effort such as long end extension. We believe that this study can add new guidelines and challenges for realizing graphene-based quantum computing.

Recent advances in graphene nanoribbons for biosensing and biomedicine.

In recent years, a new type of quasi-one-dimensional graphene-based material, graphene nanoribbons (GNRs), has attracted increasing attention. The limited domain width and rich edge configurations of GNRs endow them with unique properties and wide applications in comparison to two-dimensional graphene. This review article mainly focuses on the electrical, chemical and other properties of GNRs, and further introduces the typical preparation methods of GNRs, including top-down and bottom-up strategies. Then, their biosensing and biomedical applications are highlighted in detail, such as biosensors, photothermal therapy, drug delivery, etc. Finally, the challenges and future prospects in the synthesis and application of functionalized GNRs are discussed. It is expected that GNRs will have significant practical use in biomedical applications in the future.

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.

Thermoelectricity in graphene nanoribbons: Structural effects of nanopores

Abstract The thermoelectric (TE) properties of graphene nanoribbon (GNR) with various regularly structured nanopores (NPs) are studied in detail. Describing the system within a tight-binding (TB) framework we compute all the TE quantities using the Landauer integrals. Results show a significant reduction in thermal conductance along with higher thermopower on the incorporation of most of the NPs, considered in this work, which enhances the TE performance. The different NP structures, such as the circle, rectangle, particular configuration of an isosceles triangle, etc., are found to have a higher figure of merit (FOM). A strategy is also proposed to enhance FOM by increasing the height of NPs across the junction. In light of the simplicity of our proposed models with such promising prospects, we strongly believe that NP-GNR system can be highly effective as an efficient TE device in the commercial market in the near future.

Living annulative π-extension polymerization for graphene nanoribbon synthesis.

The properties of graphene nanoribbons (GNRs)1-5-such as conductivity or semiconductivity, charge mobility and on/off ratio-depend greatly on their width, length and edge structure. Existing bottom-up methods used to synthesize GNRs cannot achieve control over all three of these parameters simultaneously, and length control is particularly challenging because of the nature of step-growth polymerization6-18. Here we describe a living annulative π-extension (APEX)19 polymerization technique that enables rapid and modular synthesis of GNRs, as well as control over their width, edge structure and length. In the presence of palladium/silver salts, o-chloranil and an initiator (phenanthrene or diphenylacetylene), the benzonaphthosilole monomer polymerizes in an annulative manner to furnish fjord-type GNRs. The length of these GNRs can be controlled by simply changing the initiator-to-monomer ratio, achieving the synthesis of GNR block copolymers. This method represents a type of direct C-H arylation polymerization20 and ladder polymerization21, activating two C-H bonds of polycyclic aromatic hydrocarbons and constructing one fused aromatic ring per chain propagation step.

Calculation and Analysis of Graphene Nanoribbons Field Effect Transistor Structure and Characteristics

Because there is no gap between conduction band and valence band of graphene, it is difficult to achieve switching characteristics when transistors are fabricated. In order to open the graphene band gap, researchers have explored many methods, such as tailoring Shi Mocheng quantum dots, nanobelts, nano grids or laying graphene on a special substrate, one of the feasible ways is to regulate the electrical properties of graphene by doping. Through the analysis on the structure and properties of graphene band calculation, with the help of computer aided simulation, the ID and VG characteristics analysis of the Schottky barrier graphene field effect transistor (SBFET) and MOS structure of graphene field effect transistor (MOSFET) are investigated in this study. The results are of high reference value for the study of the structure and properties of graphene nanoribbons.

Graphene Nanoribbon Simulator of Vacancy Defects On Electronic Structure

Graphene Nanoribbon Simulator (GNRSIM) is developed using MATLAB Graphical User Interface Development Environment to study the electronics properties of graphene nanoribbons (GNRs). The main focus of this research is the simulation effects of single vacancy 1 in graphene nanoribbons lattices on electronic structure. The band structure and density of states are explored by using tight binding approximation where a Hamiltonian operator with nearest-neighbor interactions is introduced. The simulator has a wide range of input parameters where user can select armchair or zigzag GNR. The size of the lattices namely width and length can be varied. The location of the vacancy defect can be pinpoint by providing the row and column of the missing atom. The limitation of GNRSIM at present is that it can only accept a single atom vacancy. GNRSIM is able to be executed as a standalone application software in understanding the fundamental properties of semiconductor material and device engineering through ab-initio calculations.

Edge-oxidation effects on the thermoelectric properties in graphene nanoribbons

The thermal, electrical and thermoelectric properties in edge modified zigzag graphene nanoribbon are analyzed carefully by nonequilibrium Green's function formalism combined with first principles calculation. Epoxy (-O-) and hydroxyl groups (-OH) are considered for the ZGNR edge modification (ZGNR-O and ZGNR-OH). The results show that ZGNR-O and ZGNR-OH both can suppress obviously the phonon transport, leading to low phonon thermal conductance. While ZGNR-O and ZGNR-OH hardly suppress electron transport within the positive energy, which induces one conductance quantum plateau can be observed in ZGNR-O and ZGNR-OH. At the negative energies, ZGNR-O can suppress obviously the electron transport, which induces violent fluctuation of electronic transmissions, leading to high Seebeck coefficient and enhanced thermopower.

Modeling and Simulation of the Electronic Properties in Graphene Nanoribbons of Varying Widths and Lengths Using Tight-Binding Hamiltonian

Modeling and Simulation of the Electronic Properties in Graphene Nanoribbons of Varying Widths and Lengths Using Tight-Binding Hamiltonian

Monodisperse N‐Doped Graphene Nanoribbons Reaching 7.7 Nanometers in Length

AbstractThe properties of graphene nanoribbons are highly dependent on structural variables such as width, length, edge structure, and heteroatom doping. Therefore, atomic precision over all these variables is necessary for establishing their fundamental properties and exploring their potential applications. An iterative approach is presented that assembles a small and carefully designed molecular building block into monodisperse N‐doped graphene nanoribbons with different lengths. To showcase this approach, the synthesis and characterisation of a series of nanoribbons constituted of 10, 20 and 30 conjugated linearly‐fused rings (2.9, 5.3, and 7.7 nm in length, respectively) is presented.

Monodisperse N-Doped Graphene Nanoribbons Reaching 7.7 Nanometers in Length.

The properties of graphene nanoribbons are highly dependent on structural variables such as width, length, edge structure, and heteroatom doping. Therefore, atomic precision over all these variables is necessary for establishing their fundamental properties and exploring their potential applications. An iterative approach is presented that assembles a small and carefully designed molecular building block into monodisperse N‐doped graphene nanoribbons with different lengths. To showcase this approach, the synthesis and characterisation of a series of nanoribbons constituted of 10, 20 and 30 conjugated linearly‐fused rings (2.9, 5.3, and 7.7 nm in length, respectively) is presented.

Electrical Transport Properties of Graphene Nanoribbons with Green Function

Electrical Transport Properties of Graphene Nanoribbons with Green Function

Fluorination-enriched electronic and magnetic properties in graphene nanoribbons.

The feature-rich electronic and magnetic properties of fluorine-doped graphene nanoribbons are investigated by the first-principles calculations. They arise from the cooperative or competitive relations among the significant chemical bonds, finite-size quantum confinement and edge structure. There exist C-C, C-F, and F-F bonds with multi-orbital hybridizations. Fluorine adatoms can create p-type metals or concentration- and distribution-dependent semiconductors, depending on whether the π bonding is seriously suppressed by the top-site chemical bonding. Furthermore, five kinds of spin-dependent electronic and magnetic properties cover the non-magnetic and ferromagnetic metals, non-magnetic semiconductors, and anti-ferromagnetic semiconductors with/without spin splitting. The diverse essential properties are clearly revealed in the spatial charge distribution, spin density, and orbital-projected density of states.

Thermal transport of graphene and graphene nanoribbon: a summary review

Thermal conductivity of materials is a critical part of electronic components in ever-smaller electronic devices, high-power engines and thermoelectric conversion devices. Thus, the subject of thermal transport of graphene nanoribbons, as the first example of truly two-dimensional materials, is attracting tremendous attention for both fundamental research and potential applications. Here, we give a review of recent studies on thermal properties focusing on recently reported experimental and theoretical progresses in graphene nanoribbons. We further discuss underlying mechanisms of thermal transport in graphene nanoribbons, and suggest possible methods to tune thermal properties of graphene nanoribbons.

Electronic Transport in Oxidized Zigzag Graphene Nanoribbons

ABSTRACT The electronic and transport properties of graphene nanoribbons strongly depends on different types of adatoms. Oxygen as adatom on graphene is expected to resemble oxidized graphene sheets and enable in understanding their transport properties. Here, we report the transport properties of oxygen adsorbed zigzag edge saturated graphene nanoribbon. It is interesting to note that increasing the number of oxygen adatoms on graphene sheets lift the spin degeneracy as observed in the transmission profile of graphene nanoribbons. The relative orientation of the oxygen atom on the graphene basal plane is detrimental to flow of spin current in the nanoribbon.

Effect of Boron (Nitrogen)-Divacancy Complex Defects on the Electronic Properties of Graphene Nanoribbon

We report the effect of boron (nitrogen)-divacancy complex defects on the electronic properties of graphene nanoribbon by means of density functional theory. It is found that the defective subbands appear in the conduction band and valence band in accordance with boron (nitrogen)-divacancy defect, respectively; the impurity subbands don’t lead to the transition from the metallic characteristic to a semiconducting one. These complex defects affect the electronic band structures around the Fermi level of the graphene nanoribbon; the charge densities of these configurations have also changed distinctly. It is hoped that the theoretical results are helpful in designing the electronic device.