We investigate theoretically the electronic transport properties in narrow graphene ribbons with an adatom-induced defect. It is found that the lowest conductance step of a metallic graphene nanoribbon may develop a dip even down to zero at certain values of the Fermi energy due to the defect. Accompanying the occurrence of the conductance dip, a loop current develops around the defect. We show how the properties of the conductance dip depend on the parameters of the defect, such as the relative position and severity of the defect as well as the width and edges of the graphene ribbons. In particular, for metallic armchair-edges graphene nanoribbons, whether the conductance dip appears or not, they can be controlled by choosing the position of the single defect.
High-quality BN-Graphene-BN nanoribbon capacitors with double side-gates of graphene are experimentally realized. Graphene electronic properties can be significantly modulated by the double side-gates. The modulation effects are very obvious and followed the metallic electrode behavior of numerical simulations, while the theoretically predicted negative quantum capacitance was not observed, possibility due to the over-estimated or weakened interactions between the graphene nanoribbon and side-gate electrodes.
Graphene plasmonics is a rapidly growing field with multiple potential applications. One of the standard ways to study plasmons in graphene is by fabricating an array of graphene nanoribbons where nanoribbon edges provide the efficient photon-plasmon coupling. We systematically analyze the problem of optical plasmonic response in such systems and demonstrate the purely geometric nature of the size quantization condition for graphene plasmons. Accurate numerical calculations allowed us to tabulate the universal geometric parameters of plasmon size quantization, which is expected to become usefu…
The electronic and magnetic properties of zigzag graphene nanoribbons with asymmetric notches along their edges are investigated by first principle density functional theory calculations. It is found that the electronic and magnetic properties of the asymmetrically-notched graphene nanoribbons are closely related with the depth of notches, but weekly dependent on the length of notches. As the relative depth of notch increases, the energy level of spin-up and spin-down becomes greatly shifted, associated with the gradual increase of magnetic momentum. The asymmetric band shift allows the asymme…
In this paper we propose an analytical method to calculate the band structures of graphene-like nanoribbons of the armchair type with arbitrary line defects or uniaxial strains. The model is based on the tight-binding model and the standing wave assumption for the armchair nanoribbons. It gives accurate band results for large supercell systems. Within this method, we analyze different local states near the line defect in the graphene and boron-nitride nanoribbons. We also derive the analytical expression for the local states in a semi-infinite graphene nanoribbon by this method and the transfe…
The geometric, electronic and magnetic properties of strained graphene nanoribbons were investigated using spin polarized calculations within the framework of density functional theory. Cases of compressive stress along the longer axis of a nanoribbon and tensile stress at the midpoint and perpendicular to the plane of the nanoribbon were considered. Significant structural changes were observed including the formation of nanoripples. The calculated electronic and magnetic properties strongly depend on the size and shape of nanoribbons. The tunable magnetic properties of strained nanoribbons ca…
We use time dependent perturbation theory to study quantum size effects on the terahertz nonlinear response of metallic graphene armchair nanoribbons of finite length under an applied electric field. Our work shows that quantization due to the finite length of the nanoribbon, the applied field profile, and the broadening of the graphene spectrum all play a significant role in the resulting nonlinear conductances. In certain cases, these effects can significantly enhance the nonlinearity over that for infinitely-long metallic armchair graphene nanoribbon.
Graphene nanoribbons' electronic transport properties strongly depend on the type of edge, armchair, zigzag or other, and on edge functionalization that can be used for band-gap engineering. For only partly hydrogenated edges interesting magnetic properties are predicted. Electric charge accumulates at edges and corners. Scanning force microscopy has so far shown the centre of graphene nanoribbons with atomic resolution using a quartz crystal tuning fork sensor of high stiffness. Weak long-range electrostatic forces related to the charge accumulation on the edges of graphene nanoribbons could …
An odd number of zigzag edges in armchair graphene nanoribbons and their mechanical properties (e.g., Young's modulus, Poisson ratio and shear modulus) have potential interest for bandgap engineering in graphene based optoelectronic devices. In this paper, we consider armchair graphene nanoribbons passivated with hydrogen at the armchair edges and then apply the strain for tuning the bandgaps. Using density functional theory calculations, our study finds that the precise control of strain can allow tuning the bandgap from semiconductor to mettalic and then again switching back to semiconductor…
Random fluctuations of the shot-noise power in disordered graphene nanoribbons are studied. In particular, we calculate the distribution of the shot noise of nanoribbons with zigzag and armchair edge terminations. We show that the shot noise statistics is different for each type of these two graphene structures, which is a consequence of presence of different electron localizations: while in zigzag nanoribbons electronic edge states are Anderson localized, in armchair nanoribbons edge states are absent, but electrons are anomalously localized. Our analytical results are verified by tight bindi…
Thermoelectric properties of Graphene Nanoribbons doped by magnetic impurities Fe and Co are carried out in room temperature. We report on a study of the band structure dependent properties such as electrical conductivity, charge of carriers and Seebeck coefficients. We investigate the thermoelectric properties using the Semi-classical Boltzmann method. The electronic band structure of doped nanoribbons are evaluated by using density-functional theory in which the Hubbard interaction is considered. In this work we compare the different types of the nanoribbons and their thermoelectric features…
Using the partition-free time-dependent Landauer-B{ü}ttiker formalism for transient current correlations, we study the traversal times taken for electrons to cross graphene nanoribbon (GNR) molecular junctions. We demonstrate electron traversal signatures that vary with disorder and orientation of the GNR. These findings can be related to operational frequencies of GNR-based devices and their consequent rational design.
It is shown that apart from well-known factors, like temperature, substrate, and edge reconstruction effects, also the presence of external contacts is destructive for the formation of magnetic moments at the edges of graphene nanoribbons. The edge magnetism gradually decreases when graphene/electrode interfaces become more and more transparent for electrons. In addition to the graphene/electrode coupling strength, also the aspect ratio parameter, i.e. a width/length ratio of the graphene nanoribbon, is crucial for the suppression of edge magnetism. The present theory uses a tight-binding meth…
Confinement in two-dimensional transition metal dichalcogenides is an attractive platform for trapping single charge and spins for quantum information processing. Here, we present low temperature electron transport through etched 50-70nm MoS2 nanoribbons showing current oscillations as a function of gate voltage. On further investigations current through the device forms diamond shaped domains as a function of source-drain and gate voltage. We associate these current oscillations and diamond shaped current domains with Coulomb blockade due to single electron tunneling through a quantum dot for…
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…
A pseudo-magnetic field kink can be realized along a graphene nanoribbon using strain engineering. Electron transport along this kink is governed by snake states that are characterized by a single propagation direction. Those pseudo-magnetic fields point towards opposite directions in the K and K' valleys, leading to valley polarized snake states. In a graphene nanoribbon with armchair edges this effect results in a valley filter that is based only on strain engineering. We discuss how to maximize this valley filtering by adjusting the parameters that define the stress distribution along the g…
One of the ways to use graphene in field effect transistors is to introduce a band gap by quantum confinement effect [1]. That is why narrow graphene nanoribbons (GNRs) with width less than 50nm are considered to be essential components in future graphene electronics. The growth of graphene on sidewalls of SiC(0001) mesa structures using scalable photolithography was shown to produce high quality GNR with excellent transport properties [2-7]. Such epitaxial graphene nanoribbons are very important in fundamental science but if GNR are supposed to be used in advanced nanoelectronics, high qualit…
