49 research outputs found
Electronic transport in polycrystalline graphene
Most materials in available macroscopic quantities are polycrystalline.
Graphene, a recently discovered two-dimensional form of carbon with strong
potential for replacing silicon in future electronics, is no exception. There
is growing evidence of the polycrystalline nature of graphene samples obtained
using various techniques. Grain boundaries, intrinsic topological defects of
polycrystalline materials, are expected to dramatically alter the electronic
transport in graphene. Here, we develop a theory of charge carrier transmission
through grain boundaries composed of a periodic array of dislocations in
graphene based on the momentum conservation principle. Depending on the grain
boundary structure we find two distinct transport behaviours - either high
transparency, or perfect reflection of charge carriers over remarkably large
energy ranges. First-principles quantum transport calculations are used to
verify and further investigate this striking behaviour. Our study sheds light
on the transport properties of large-area graphene samples. Furthermore,
purposeful engineering of periodic grain boundaries with tunable transport gaps
would allow for controlling charge currents without the need of introducing
bulk band gaps in otherwise semimetallic graphene. The proposed approach can be
regarded as a means towards building practical graphene electronics.Comment: accepted in Nature Material
Effect of Peierls transition in armchair carbon nanotube on dynamical behaviour of encapsulated fullerene
The changes of dynamical behaviour of a single fullerene molecule inside an
armchair carbon nanotube caused by the structural Peierls transition in the
nanotube are considered. The structures of the smallest C20 and Fe@C20
fullerenes are computed using the spin-polarized density functional theory.
Significant changes of the barriers for motion along the nanotube axis and
rotation of these fullerenes inside the (8,8) nanotube are found at the Peierls
transition. It is shown that the coefficients of translational and rotational
diffusions of these fullerenes inside the nanotube change by several orders of
magnitude. The possibility of inverse orientational melting, i.e. with a
decrease of temperature, for the systems under consideration is predicted.Comment: 9 pages, 6 figures, 1 tabl
Electrically driven thermal light emission from individual single-walled carbon nanotubes
Light emission from nanostructures exhibits rich quantum effects and has
broad applications. Single-walled carbon nanotubes (SWNTs) are one-dimensional
(1D) metals or semiconductors, in which large number of electronic states in a
narrow range of energies, known as van Hove singularities, can lead to strong
spectral transitions. Photoluminescence and electroluminescence involving
interband transitions and excitons have been observed in semiconducting SWNTs,
but are not expected in metallic tubes due to non-radiative relaxations. Here,
we show that in the negative differential conductance regime, a suspended
quasi-metallic SWNT (QM-SWNT) emits light due to joule-heating, displaying
strong peaks in the visible and infrared corresponding to interband
transitions. This is a result of thermal light emission in 1D, in stark
contrast with featureless blackbody-like emission observed in large bundles of
SWNTs or multi-walled nanotubes. This allows for probing of the electronic
temperature and non-equilibrium hot optical phonons in joule-heated QM-SWNTs
Conducting linear chains of sulphur inside carbon nanotubes
Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (∼800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ∼450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ∼90 GPa to become metallic
Conductance quantization in multiwalled carbon nanotubes
We present results of carbon nanotube conductance measurements. The experiments were performed
using an scanning probe microscope (SPM) system where a carbon nanotube fiber is connected
to the SPM tip and then lowered into a liquid mercury contact. Experiments were also performed using
a modified transmission electron microscope (TEM) specimen holder supplied with piezo and micrometer
positioning system. Thus the contacting process of the nanotubes with the mercury could be monitored
while simultaneously recording the conductance. These measurements and observations confirm previously
reported conductance quantization (Frank et al.: Science 280, 1744 (1998)) of the nanotubes while providing
additional details concerning the mercury nanotube contacts.We also report conductance versus voltage
characteristics of carbon nanotube