889 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
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
Minimalist design of a robust real-time quantum random number generator
We present a simple and robust construction of a real-time quantum random
number generator (QRNG). Our minimalist approach ensures stable operation of
the device as well as its simple and straightforward hardware implementation as
a stand-alone module. As a source of randomness the device uses measurements of
time intervals between clicks of a single-photon detector. The obtained raw
sequence is then filtered and processed by a deterministic randomness
extractor, which is realized as a look-up table. This enables high speed
on-the-fly processing without the need of extensive computations. The overall
performance of the device is around 1 random bit per detector click, resulting
in 1.2 Mbit/s generation rate in our implementation
Tailoring electronic properties of multilayer phosphorene by siliconization
Controlling a thickness dependence of electronic properties for
two-dimensional (2d) materials is among primary goals for their large-scale
applications. Herein, employing a first-principles computational approach, we
predict that Si interaction with multilayer phosphorene (2d-P) can result in
the formation of highly stable 2d-SiP and 2d-SiP compounds with a weak
interlayer interaction. Our analysis demonstrates that these systems are
semiconductors with band gap energies that can be governed by varying the
thickness and stacking order. Specifically, siliconization of phosphorene
allows to design 2d-SiP materials with significantly weaker thickness
dependence of electronic properties than that in 2d-P and to develop ways for
their tailoring. We also reveal the spatial dependence of electronic properties
for 2d-SiP highlighting difference in effective band gaps for different
layers. Particularly, our results show that central layers in the multilayer 2d
systems determine overall electronic properties, while the role of the
outermost layers is noticeably smaller
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