Electronic properties and quantum transport in Graphene-based nanostructures (original) (raw)
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Electronic transport properties of graphene nanoribbons
Journal of Physics: Conference Series, 2009
We will present brief overview on the electronic and transport properties of graphene nanoribbons focusing on the effect of edge shapes and impurity scattering. The low-energy electronic states of graphene have two non-equivalent massless Dirac spectrum. The relative distance between these two Dirac points in the momentum space and edge states due to the existence of the zigzag type graphene edges are decisive to the electronic and transport properties of graphene nanoribbons. In graphene nanoribbons with zigzag edges, two valleys related to each Dirac spectrum are well separated in momentum space. The propagating modes in each valley contain a single chiral mode originating from a partially flat band at band center. This feature gives rise to a perfectly conducting channel in the disordered system, if the impurity scattering does not connect the two valleys, i.e. for long-range impurity potentials. On the other hand, the low-energy spectrum of graphene nanoribbons with armchair edges is described as the superposition of two non-equivalent Dirac points of graphene. In spite of the lack of well-separated two valley structures, the single-channel transport subjected to long-ranged impurities is nearly perfectly conducting, where the backward scattering matrix elements in the lowest order vanish as a manifestation of internal phase structures of the wavefunction. Symmetry considerations lead to the classification of disordered zigzag ribbons into the unitary class for long-range impurities, and the orthogonal class for short-range impurities. However, no such crossover occurs in armchair nanoribbons.
Electronic Transport Properties of Assembled Carbon Nanoribbons
ACS Nano, 2012
Graphitic nanowiggles (GNWs) are 1D systems with segmented graphitic nanoribbon GNR edges of varying chiralities. They are characterized by the presence of a number of possible different spin distributions along their edges and by electronic band-gaps that are highly sensitive to the details of their geometry. These two properties promote these experimentally observed carbon nanostructures as some of the most promising candidates for developing high-performance nanodevices. Here, we highlight this potential with a detailed understanding of the electronic processes leading to their unique spin-state dependent electronic quantum transport properties. The three classes of GNWs containing at least one zigzag edge (necessary to the observation of multiple-magnetic states) are considered in two distinct geometries: a perfectly periodic system and in a one-GNW-cell system sandwiched between two semi-infinite terminals made up of straight GNRs. The present calculations establish a number of elementary rules to relate fundamental electronic transport functionality, electronic energy, the system geometry, and spin state.
Carbon, 2008
Numerical calculations have been performed to elucidate unconventional electronic transport properties in disordered nanographene ribbons with zigzag edges (zigzag ribbons). The energy band structure of zigzag ribbons has two valleys that are well separated in momentum space, related to the two Dirac points of the graphene spectrum. The partial flat bands due to edge states make the imbalance between left- and right-going modes in each valley, i.e. appearance of a single chiral mode. This feature gives rise to a perfectly conducting channel in the disordered system, i.e. the average of conductance 〈g〉〈g〉 converges exponentially to 1 conductance quantum per spin with increasing system length, provided impurity scattering does not connect the two valleys, as is the case for long-range impurity potentials. Ribbons with short-range impurity potentials, however, through inter-valley scattering, display ordinary localization behavior. Symmetry considerations lead to the classification of disordered zigzag ribbons into the unitary class for long-range impurities, and the orthogonal class for short-range impurities. The electronic states of graphene nanoribbons with general edge structures are also discussed, and it is demonstrated that chiral channels due to the edge states are realized even in more general edge structures except for armchair edges.
Electronic structure of defects and quantum transport in carbon nanotubes
Physica B: Condensed Matter, 2006
Understanding of the electronic structure and the electrical transport properties on the nanoscale becomes increasingly important for the development of the next-generation nanodevices. We have developed a first-principles pseudopotential method to calculate the quantum conductance as well as the self-consistent charge distributions of nanostructures and studied the electronic structure and quantum conductance of carbon nanotubes with impurities or defects. Even if the carbon nanotube is metallic instead of semiconducting, boron and nitrogen atoms create acceptor-like and donor-like states which act as scattering centers for conducting electrons. Various defect geometries such as Stone-Wales defects are considered which give rise to interesting localized states and the corresponding conductance characteristics. These localized states are in resonance with the extended states of the metallic nanotube and form quasibound states with broadened energy levels leading to novel conductance behaviors. For semiconducting carbon nanotubes, it is shown that various defects located at the junction of two different tubes can produce both shallow and deep defect levels. Theoretical predictions are closely compared with recent scanning tunneling microscopy and scanning tunneling spectroscopy data.
Electronic structure and quantum transport in carbon nanotubes
Applied Physics A: Materials Science & Processing, 1998
The electrical properties of various forms of carbon nanotubes are presented with particular emphasis placed on individual multi-wall and single-wall tubes. After a brief survey of the electronic structure of single-wall carbon nanotubes, electronic transport mechanisms are overviewed in relation with the dimensionality of the carbon system. Typical quantum aspects of low temperature electronic conduction for low dimensionality encountered in some carbon nanotubes are discussed.
Impact of charge impurities on transport properties of graphene nanoribbons
Applied Physics Letters, 2013
Previous experimental studies have shown qualitative dependence of transport property of graphene nanoribbons on external charged impurities. We have measured transport properties of a graphene nanoribbon at increasing coverage of charged impurities in an ultra high vacuum environment. We discovered an exact relationship between the source-drain and gate gaps at increasing charged impurity density. In addition, we found that graphene nanoribbons have different electronic screening as compared to bulk graphene. Our study paves the way for controlling transport property of nanoribbons using extrinsic impurities. V
Vertical and In-Plane Electronic Transport of Graphene Nanoribbon/Nanotube Heterostructures
Nanomaterials
All-carbon systems have proven to present interesting transport properties and are often used in electronic devices. Motivated by recent resonant responses measured on graphene/fullerene junction, we propose coupled nanoribbons/carbon-nanotube heterostructures for use as charge filters and to allow tuned transport. These hybrid systems are engineered as a four-terminal device, and we explore multiple combinations of source and collector leads. The armchair-edge configuration results in midgap states when the transport is carried through top/bottom terminals. Such states are robust against the lack of perfect order on the tube and are revealed as sharp steps in the characteristic current curves when a bias potential is turned on. The zigzag-edge systems exhibit differential negative resistance, with features determined by the details of the hybrid structures.
Vacancy effects on electronic and transport properties of graphene nanoribbons
APS, 2015
We analytically study vacancy effects on electronic and transport properties of graphene nanoribbons and nanodots using Green’s function approach. For semiconducting systems, the presence of a vacancy induces a zero-energy midgap state. The spatial pattern of the wave functions critically depends on the atomistic edge structures, and can be used as an unambiguous probe of the edge structure. For metallic systems, the mid-gap vacancy state does not exist. In these systems, the vacancy mainly works as a source of electronic scattering and modifies electronic transmission. We derive that the electronic transmission coefficient can be written as T = cos2(α), where α denotes the phase angle of the on-site Green’s function at the vacancy site of the ideal systems. At small energies, T exhibits distinctly different functional form depending on edge structures.
Transport properties of branched graphene nanoribbons
Applied Physics Letters, 2008
The electronic transport properties of three-terminal graphene nanoribbon T-junctions are investigated using a quantum tight binding molecular dynamics scheme. The transport properties are found to depend very sensitively on the geometric features of the branches of the junctions. This dependence is even more pronounced than the corresponding dependence in the case of T-shaped single wall carbon nanotubes. This is attributed to the strong dependence of the conductivity of the nanoribbons on their chirality, width, and length. An additional factor that influences the conductivity of the T-junction nanoribbons is associated with the junction itself, i.e., the way the branches are interconnected.