1,595 research outputs found
Conductivity of epitaxial and CVD graphene with correlated line defects
Transport properties of single-layer graphene with correlated one-dimensional
defects are studied using the time-dependent real-space Kubo-Greenwood
formalism. Such defects are present in epitaxial graphene, comprising atomic
terraces and steps due to the substrate morphology, and in polycrystalline
chemically-vapor-deposited (CVD) graphene due to the grain boundaries, composed
of a periodic array of dislocations, or quasi-periodic nanoripples originated
from the metal substrate. The extended line defects are described by the
long-range Lorentzian-type scattering potential. The dc conductivity is
calculated numerically for different cases of distribution of line defects.
This includes a random (uncorrelated) and a correlated distribution with a
prevailing direction in the orientation of lines. The anisotropy of the
conductivity along and across the line defects is revealed, which agrees with
experimental measurements for epitaxial graphene grown on SiC. We performed a
detailed study of the conductivity for different defect correlations,
introducing the correlation angle alpha_max (i.e. the maximum possible angle
between any two lines). We find that for a given electron density, the relative
enhancement of the conductivity for the case of fully correlated line defects
in comparison to the case of uncorrelated ones is larger for a higher defect
density. Finally, we study the conductivity of realistic samples where both
extended line defects as well as point-like scatterers such as adatoms and
charged impurities are presented.Comment: 8 pages, 7 figure
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Influence of correlated impurities on conductivity of graphene sheets: Time-dependent real-space Kubo approach
Exact numerical calculations of the conductivity of graphene sheets with
random and correlated distributions of disorders have been performed using the
time-dependent real-space Kubo formalism. The disorder was modeled by the
long-range Gaussian potential describing screened charged impurities and by the
short-range potential describing neutral adatoms both in the weak and strong
scattering regime. Our central result is that correlation in the spatial
distribution for the strong short-range scatterers and for the long-range
Gaussian potential do not lead to any enhancement of the conductivity in
comparison to the uncorrelated case. Our results strongly indicate that the
temperature enhancement of the conductivity reported in the recent study (Yan
and Fuhrer, Phys. Rev. Lett. 107, 206601 (2011)) and attributed to the effect
of dopant correlations was most likely caused by other factors not related to
the correlations in the scattering potential.Comment: 14 pages, 10 figure
Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene
The chapter generalizes results on influence of uniaxial strain and
adsorption on the electron states and charge transport or localization in
graphene with different configurations of imperfections (point defects):
resonant (neutral) adsorbed atoms either oxygen- or hydrogen-containing
molecules or functional groups, vacancies or substitutional atoms, charged
impurity atoms or molecules, and distortions. To observe electronic properties
of graphene-admolecules system, we applied electron paramagnetic resonance
technique in a broad temperature range for graphene oxides as a good basis for
understanding the electrotransport properties of other active carbons. Applied
technique allowed observation of possible metal-insulator transition and
sorption pumping effect as well as discussion of results in relation to the
granular metal model. The electronic and transport properties are calculated
within the framework of the tight-binding model along with the Kubo-Greenwood
quantum-mechanical formalism. Depending on electron density and type of the
sites, the conductivity for correlated and ordered adsorbates is found to be
enhanced in dozens of times as compared to the cases of their random
distribution. In case of the uniaxially strained graphene, the presence of
point defects counteracts against or contributes to the band-gap opening
according to their configurations. The band-gap behaviour is found to be
nonmonotonic with strain in case of a simultaneous action of defect ordering
and zigzag deformation. The amount of localized charge carriers (spins) is
found to be correlated with the content of adsorbed centres responsible for the
formation of potential barriers and, in turn, for the localization effects.
Physical and chemical states of graphene edges, especially at a uniaxial strain
along one of them, play a crucial role in electrical transport phenomena in
graphene-based materials.Comment: 16 pages, 10 figure
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