106 research outputs found
Nanoelectromechanical coupling in fullerene peapods probed via resonant electrical transport experiments
Fullerene peapods, that is carbon nanotubes encapsulating fullerene
molecules, can offer enhanced functionality with respect to empty nanotubes.
However, the present incomplete understanding of how a nanotube is affected by
entrapped fullerenes is an obstacle for peapods to reach their full potential
in nanoscale electronic applications. Here, we investigate the effect of C60
fullerenes on electron transport via peapod quantum dots. Compared to empty
nanotubes, we find an abnormal temperature dependence of Coulomb blockade
oscillations, indicating the presence of a nanoelectromechanical coupling
between electronic states of the nanotube and mechanical vibrations of the
fullerenes. This provides a method to detect the C60 presence and to probe the
interplay between electrical and mechanical excitations in peapods, which thus
emerge as a new class of nanoelectromechanical systems.Comment: 7 pages, 3 figures. Published in Nature Communications. Free online
access to the published version until Sept 30th, 2010, see
http://www.nature.com/ncomms/journal/v1/n4/abs/ncomms1034.htm
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
Visualizing the orientational dependence of an intermolecular potential
Scanning probe microscopy can now be used to map the properties of single molecules with intramolecular precision by functionalization of the apex of the scanning probe tip with a single atom or molecule. Here we report on the mapping of the three-dimensional potential between fullerene (C₆₀) molecules in different relative orientations, with sub-Angstrom resolution, using dynamic force microscopy (DFM). We introduce a visualization method which is capable of directly imaging the variation in equilibrium binding energy of different molecular orientations. We model the interaction using both a simple approach based around analytical Lennard–Jones potentials, and with dispersion-force-corrected density functional theory (DFT), and show that the positional variation in the binding energy between the molecules is dominated by the onset of repulsive interactions. Our modelling suggests that variations in the dispersion interaction are masked by repulsive interactions even at displacements significantly larger than the equilibrium intermolecular separation
Molecular modeling of temperature dependence of solubility parameters for amorphous polymers
A molecular modeling strategy is proposed to describe the temperature (T) dependence of solubility parameter (δ) for the amorphous polymers which exhibit glass-rubber transition behavior. The commercial forcefield “COMPASS” is used to support the atomistic simulations of the polymer. The temperature dependence behavior of δ for the polymer is modeled by running molecular dynamics (MD) simulation at temperatures ranging from 250 up to 650 K. Comparing the MD predicted δ value at 298 K and the glass transition temperature (Tg) of the polymer determined from δ–T curve with the experimental value confirm the accuracy of our method. The MD modeled relationship between δ and T agrees well with the previous theoretical works. We also observe the specific volume (v), cohesive energy (Ucoh), cohesive energy density (ECED) and δ shows a similar temperature dependence characteristics and a drastic change around the Tg. Meanwhile, the applications of δ and its temperature dependence property are addressed and discussed
Radial Corrugations of Multi-Walled Carbon Nanotubes Driven by Inter-Wall Nonbonding Interactions
We perform large-scale quasi-continuum simulations to determine the stable cross-sectional configurations of free-standing multi-walled carbon nanotubes (MWCNTs). We show that at an inter-wall spacing larger than the equilibrium distance set by the inter-wall van der Waals (vdW) interactions, the initial circular cross-sections of the MWCNTs are transformed into symmetric polygonal shapes or asymmetric water-drop-like shapes. Our simulations also show that removing several innermost walls causes even more drastic cross-sectional polygonization of the MWCNTs. The predicted cross-sectional configurations agree with prior experimental observations. We attribute the radial corrugations to the compressive stresses induced by the excessive inter-wall vdW energy release of the MWCNTs. The stable cross-sectional configurations provide fundamental guidance to the design of single MWCNT-based devices and shed lights on the mechanical control of electrical properties
Glass transition with decreasing correlation length during cooling of Fe50Co50 superlattice and strong liquids
The glass transition GT is usually thought of as a structural arrest that
occurs during the cooling of a liquid, or sometimes a plastic crystal, trapping
a metastable state of the system before it can recrystallize to stabler forms1.
This phenomenon occurs in liquids of all classes, most recently in bulk
metallic glassformers2. Much theoretical interest has been generated by the
dynamical heterogeneity observed in cooling of fragile liquids3, 4, and many
have suggested that the slow-down is caused by a related increasing correlation
length 5-9. Here we report both kinetics and thermodynamics of arrest in a
system that disorders while in its ground state, exhibits a large !Cp on arrest
(!Cp = Cp,mobile - Cp,arrested), yet clearly is characterized by a correlation
length that is decreasing as GT is approached from above. We show that GT
kinetics in our system, the disordering superlattice Fe50Co50, satisfy the
kinetic criterion for ideally 'strong' glassformers10, and since !Cp behavior
through Tg also correlates10, we propose that very strong liquidsand very
fragile liquids exist on opposite flanks of an order-disorder transition - one
that is already known for model systems
Explaining why simple liquids are quasi-universal
It has been known for a long time that many simple liquids have surprisingly
similar structure as quantified, e.g., by the radial distribution function. A
much more recent realization is that the dynamics are also very similar for a
number of systems with quite different pair potentials. Systems with such
non-trivial similarities are generally referred to as "quasi-universal". From
the fact that the exponentially repulsive pair potential has strong virial
potential-energy correlations in the low-temperature part of its thermodynamic
phase diagram, we here show that a liquid is quasi-universal if its pair
potential can be written approximately as a sum of exponential terms with
numerically large prefactors. Based on evidence from the literature we moreover
conjecture the converse, i.e., that quasi-universality only applies for systems
with this property
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