40 research outputs found
Heat conduction in 2D strongly-coupled dusty plasmas
We perform non-equilibrium simulations to study heat conduction in
two-dimensional strongly coupled dusty plasmas. Temperature gradients are
established by heating one part of the otherwise equilibrium system to a higher
temperature. Heat conductivity is measured directly from the stationary
temperature profile and heat flux. Particular attention is paid to the
influence of damping effect on the heat conduction. It is found that the heat
conductivity increases with the decrease of the damping rate, while its
magnitude agrees with previous experimental measurement.Comment: 4 pages, 2 figures, presented in SCCS2008 conferenc
Dynamic polarization of graphene by moving external charges: random phase approximation
We evaluate the stopping and image forces on a charged particle moving
parallel to a doped sheet of graphene by using the dielectric response
formalism for graphene's -electron bands in the random phase approximation
(RPA). The forces are presented as functions of the particle speed and the
particle distance for a broad range of charge-carrier densities in graphene. A
detailed comparison with the results from a kinetic equation model reveal the
importance of inter-band single-particle excitations in the RPA model for high
particle speeds. We also consider the effects of a finite gap between graphene
and a supporting substrate, as well as the effects of a finite damping rate
that is included through the use of Mermin's procedure. The damping rate is
estimated from a tentative comparison of the Mermin loss function with a HREELS
experiment. In the limit of low particle speeds, several analytical results are
obtained for the friction coefficient that show an intricate relationship
between the charge-carrier density, the damping rate, and the particle
distance, which may be relevant to surface processes and electrochemistry
involving graphene.Comment: 14 pages, 10 figures, accepted for publication in Phys. Rev.
Donut and dynamic polarization effects in proton channeling through carbon nanotubes
We investigate the angular and spatial distributions of protons of the energy
of 0.223 MeV after channeling through an (11,~9) single-wall carbon nanotube of
the length of 0.2 m. The proton incident angle is varied between 0 and 10
mrad, being close to the critical angle for channeling. We show that, as the
proton incident angle increases and approaches the critical angle for
channeling, a ring-like structure is developed in the angular distribution -
donut effect. We demonstrate that it is the rainbow effect. When the proton
incident angle is between zero and a half of the critical angle for channeling,
the image force affects considerably the number and positions of the maxima of
the angular and spatial distributions. However, when the proton incident angle
is close to the critical angle for channeling, its influence on the angular and
spatial distributions is reduced strongly. We demonstrate that the increase of
the proton incident angle can lead to a significant rearrangement of the
propagating protons within the nanotube. This effect may be used to locate
atomic impurities in nanotubes as well as for creating nanosized proton beams
to be used in materials science, biology and medicine.Comment: 17 pages, 14 figure
Wave spectra of 2D dusty plasma solids and liquids
Brownian dynamics simulations were carried out to study wave spectra of
two-dimensional dusty plasma liquids and solids for a wide range of
wavelengths. The existence of a longitudinal dust thermal mode was confirmed in
simulations, and a cutoff wavenumber in the transverse mode was measured.
Dispersion relations, resulting from simulations, were compared with those from
analytical theories, such as the random-phase approximation (RPA),
quasi-localized charged approximation (QLCA), and harmonic approximation (HA).
An overall good agreement between the QLCA and simulations was found for wide
ranges of states and wavelengths after taking into account the direct thermal
effect in the QLCA, while for the RPA and HA good agreement with simulations
were found in the high and low temperature limits, respectively.Comment: 26 pages, 9 figure
Friction force on slow charges moving over supported graphene
We provide a theoretical model that describes the dielectric coupling of a 2D
layer of graphene, represented by a polarization function in the Random Phase
Approximation, and a semi-infinite 3D substrate, represented by a surface
response function in a non-local formulation. We concentrate on the role of the
dynamic response of the substrate for low-frequency excitations of the combined
graphene-substrate system, which give rise to the stopping force on slowly
moving charges above graphene. A comparison of the dielectric loss function
with experimental HREELS data for graphene on a SiC substrate is used to
estimate the damping rate in graphene and to reveal the importance of phonon
excitations in an insulating substrate. A signature of the hybridization
between graphene's pi plasmon and the substrate's phonon is found in the
stopping force. A friction coefficient that is calculated for slow charges
moving above graphene on a metallic substrate shows an interplay between the
low-energy single-particle excitations in both systems.Comment: 13 pages, 5 figures, submitted to Nanotechnology for a special issue
related to the NGC 2009 conference (http://asdn.net/ngc2009/index.shtml
Invited Lecture INTERACTIONS OF IONS WITH CARBON NANO-STRUCTURES
Abstract. Investigation into the properties of carbon nano-structures, involving fullerene molecules, carbon nanotubes, and the most recently contrived graphene, has been growing at a relentless rate over the past decade or so owing to prospects of their applications in nanotechnology. While interactions with particle beams have been an important part of this research endeavor in the context of various spectroscopic techniques (TEM, EELS, ...), the use of energetic electron and ion beams has recently emerged as a novel engineering tool for modifications of atomic structure and electronic properties of carbon nano-structures In that context, the most widely studied themes in literature are concerned with changes in carbon nanotubes upon exposure to the ion-beam irradiation at energies ranging from several tens of eV to some MeV. On the other hand, the empty cylindrical space in individual carbon nanotubes, and a high degree of their ordering and alignment in structures called ropes or bundles, provide unique means for achieving the effect of ion channeling. Prospects of realization and a range of possible applications of ion channeling through carbon nanotubes at energies from keV to TeV have stimulated an active research area, which was recently reviewed After assessing some key experimental facts and the status of computer simulations of ion irradiation effects on carbon nanotubes, I shall discuss several problems arising in modeling of ion interactions with carbon nanotube
Analytical expression for stopping force acting on a slow charged particle moving parallel to a thick graphene-sapphire-graphene structure
We derive an analytical expression for the stopping force acting on an external charged particle moving parallel to a sandwich-like structure consisting of two undoped graphene sheets separated by a layer of Al2O3 (sapphire)
Interactions of ions with graphene-sapphire-graphene composite system: Stopping force and image force
We derive general expressions for the stopping and image forces on an external charged particle moving parallel to a sandwich-like structure consisting of two doped graphene sheets separated by a layer of Al2O3 (sapphire