442 research outputs found
Kinks, rings, and rackets in filamentous structures
Carbon nanotubes and biological filaments each spontaneously assemble into
kinked helices, rings, and "tennis racket" shapes due to competition between
elastic and interfacial effects. We show that the slender geometry is a more
important determinant of the morphology than any molecular details. Our
mesoscopic continuum theory is capable of quantifying observations of these
structures, and is suggestive of their occurrence in other filamentous
assemblies as well.Comment: This paper was originally published in PNAS 100: 12141-12146 (2003).
The present version has corrected Eq. 3, A1, and A2, and some minor typo
Multi-shell gold nanowires under compression
Deformation properties of multi-wall gold nanowires under compressive loading
are studied. Nanowires are simulated using a realistic many-body potential.
Simulations start from cylindrical fcc(111) structures at T=0 K. After
annealing cycles axial compression is applied on multi-shell nanowires for a
number of radii and lengths at T=300 K. Several types of deformation are found,
such as large buckling distortions and progressive crushing. Compressed
nanowires are found to recover their initial lengths and radii even after
severe structural deformations. However, in contrast to carbon nanotubes
irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure
Structural stability and energetics of single-walled carbon nanotubes under uniaxial strain
A (10x10) single-walled carbon nanotube consisting of 400 atoms with 20
layers is simulated under tensile loading using our developed O(N) parallel
tight-binding molecular-dynamics algorithms. It is observed that the simulated
carbon nanotube is able to carry the strain up to 122% of the relaxed tube
length in elongation and up to 93% for compression. Young s modulus, tensile
strength, and the Poisson ratio are calculated and the values found are 0.311
TPa, 4.92 GPa, and 0.287, respectively. The stress-strain curve is obtained.
The elastic limit is observed at a strain rate of 0.09 while the breaking point
is at 0.23. The frequency of vibration for the pristine (10x10) carbon nanotube
in the radial direction is 4.71x10^3 GHz and it is sensitive to the strain
rate.Comment: 11 pages, 8 figure
Single- and multi-walled carbon nanotubes viewed as elastic tubes with Young's moduli dependent on layer number
The complete energy expression of a deformed single-walled carbon nanotube
(SWNT) is derived in the continuum limit from the local density approximation
model proposed by Lenosky {\it et al.} \lbrack Nature (London) {\bf 355}, 333
(1992)\rbrack and shows to be content with the classic shell theory by which
the Young's modulus, the Poisson ratio and the effective wall thickness of
SWNTs are obtained as TPa, , , respectively.
The elasticity of a multi-walled carbon nanotube (MWNT) is investigated as the
combination of the above SWNTs of layer distance and the
Young's modulus of the MWNT is found to be an apparent function of the number
of layers, , varying from 4.70TPa to 1.04TPa for N=1 to .Comment: 4 pages, 1 figur
Extreme structure and spontaneous lift of spin degeneracy in doped perforated bilayer graphenes
Extreme structure and spin states of doped and undoped perforated bigraphenes was studied using DFT simulations. It was found that folded nanopores possess extremely high curvature of 0.34 Å−1. Dramatic structural deformation causes severe changes of the chemical properties of carbon atoms localized at the nanopores converting the folded edges to local oxidative fragments. It was found that asymmetrical coordination of either Li, Ca, or Al to the nanopores is coupled with electron transfer from metal to edge carbon atoms and breakdown of local inversion symmetry. Li-, Ca-, and Al-doped perforated AA bigraphene revealed ferromagnetic spin ordering with magnetic moments of 0.38, 0.14, and 0.32μB/unit cell, respectively, and spin polarization energy gain of 0.037eV for Ca-doped superlattice. It was shown that ferromagnetic spin ordering of bigraphene nanopores contradicts to the Nagaoka's theorem, which excludes strong electron correlations as a reason of spin polarization. Spontaneous lift of spin degeneracy was interpreted in terms of perturbing intense local electrostatic fields from extra electron charges localized at the nanopore edges, coupled with breakdown of space inversion and local translation invariances. It was shown that spin energy splitting is proportional to the matrix elements calculated on Bloch states with opposite wavevectors and perturbing electrostatic fields
Atomistic Simulations of Nanotube Fracture
The fracture of carbon nanotubes is studied by atomistic simulations. The
fracture behavior is found to be almost independent of the separation energy
and to depend primarily on the inflection point in the interatomic potential.
The rangle of fracture strians compares well with experimental results, but
predicted range of fracture stresses is marketly higher than observed. Various
plausible small-scale defects do not suffice to bring the failure stresses into
agreement with available experimental results. As in the experiments, the
fracture of carbon nanotubes is predicted to be brittle. The results show
moderate dependence of fracture strength on chirality.Comment: 12 pages, PDF, submitted to Phy. Rev.
Nonlinear resonance in a three-terminal carbon nanotube resonator
The RF-response of a three-terminal carbon nanotube resonator coupled to
RF-transmission lines is studied by means of perturbation theory and direct
numerical integration. We find three distinct oscillatory regimes, including
one regime capable of exhibiting very large hysteresis loops in the frequency
response. Considering a purely capacitive transduction, we derive a set of
algebraic equations which can be used to find the output power (S-parameters)
for a device connected to transmission lines with characteristic impedance
.Comment: 16 pages, 8 figure
Coil Formation in Multishell Carbon Nanotubes: Competition between Curvature Elasticity and Interlayer Adhesion
To study the shape formation process of carbon nanotubes, a string equation
describing the possible existing shapes of the axis-curve of multishell carbon
tubes (MCTs) is obtained in the continuum limit by minimizing the shape energy,
that is the difference between the MCT energy and the energy of the
carbonaceous mesophase (CM). It is shown that there exists a threshold relation
of the outmost and inmost radii, that gives a parameter regime in which a
straight MCT will be bent or twisted. Among the deformed shapes, the regular
coiled MCTs are shown being one of the solutions of the string equation. In
particular,the optimal ratio of pitch and radius for such a coil is
found to be equal to , which is in good agreement with recent
observation of coil formation in MCTs by Zhang et al.Comment: RevTeX, no figure, 12 pages, to appear in Phys. Rev. Let
In-situ observation of graphene sublimation and edge reconstructions
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