1,868 research outputs found
Neutral-cluster implantation in polymers by computer experiments
In this work we perform atomistic model potential molecular dynamics
simulations by means of state-of-the art force-fields to study the implantation
of a single Au nanocluster on a Polydimethylsiloxane substrate. All the
simulations have ben performed on realistic substrate models containing up to
4.6 millions of atoms having depths up to 90 nm and lateral dimensions up to 25
nm. We consider both entangled-melt and cross-linked Polydimethylsiloxane
amorphous structures. We show that even a single cluster impact on the
Polydimethylsiloxane substrate remarkably changes the polymer local temperature
and pressure. Moreover we observe the presence of craters created on the
polymer surface having lateral dimensions comparable to the cluster radius and
depths strongly dependent on the implantation energy. Present simulations
suggest that the substrate morphology is largely affected by the cluster impact
and that most-likely such modifications favor the the penetration of the next
impinging clusters
Gap opening in graphene by shear strain
We exploit the concept of strain-induced band structure engineering in
graphene through the calculation of its electronic properties under uniaxial,
shear, and combined uniaxial-shear deformations. We show that by combining
shear deformations to uniaxial strains it is possible modulate the graphene
energy gap value from zero up to eV. Interestingly enough, the use of a
shear component allows for a gap opening at moderate absolute deformation,
safely smaller than the graphene failure strain.Comment: to appear on PRB - Rapid Communicatio
Thermal transport in nanocrystalline graphene investigated by approach-to-equilibrium molecular dynamics simulations
Approach-to-equilibrium molecular dynamics simulations have been used to
study thermal transport in nanocrystalline graphene sheets. Nanostructured
graphene has been created using an iterative process for grain growth from
initial seeds with random crystallographic orientations. The resulting cells
have been characterized by the grain size distribution based on the radius of
gyration, by the number of atoms in each grain and by the number of atoms in
the grain boundary. Introduction of nanograins with a radius of gyration of 1
nm has led to a significant reduction in the thermal conductivity to 3% of the
value in single crystalline graphene. Analysis of the vibrational density of
states has revealed a general reduction of the vibrational intensities and
broadening of the peaks when nanograins are introduced which can be attributed
to phonon scattering in the boundary layer. The thermal conductivity has been
evaluated as a function of the grain size with increasing size up to 14 nm and
it has been shown to follow an inverse rational function. The grain size
dependent thermal conductivity could be approximated well by a function where
transport is described by a connection in series of conducting elements and
resistances (at boundaries).Comment: 9 pages, 9 figure
Order-disorder phase change in embedded Si nano-particles
We investigated the relative stability of the amorphous vs crystalline
nanoparticles of size ranging between 0.8 and 1.8 nm. We found that, at
variance from bulk systems, at low T small nanoparticles are amorphous and they
undergo to an amorphous-to-crystalline phase transition at high T. On the
contrary, large nanoparticles recover the bulk-like behavior: crystalline at
low T and amorphous at high T. We also investigated the structure of
crystalline nanoparticles, providing evidence that they are formed by an
ordered core surrounded by a disordered periphery. Furthermore, we also provide
evidence that the details of the structure of the crystalline core depend on
the size of the nanoparticleComment: 8 pages, 5 figure
An investigation of the SCOZA for narrow square-well potentials and in the sticky limit
We present a study of the self consistent Ornstein-Zernike approximation
(SCOZA) for square-well (SW) potentials of narrow width delta. The main purpose
of this investigation is to elucidate whether in the limit delta --> 0, the
SCOZA predicts a finite value for the second virial coefficient at the critical
temperature B2(Tc), and whether this theory can lead to an improvement of the
approximate Percus-Yevick solution of the sticky hard-sphere (SHS) model due to
Baxter [R. J. Baxter, J. Chem. Phys. 49, 2770 (1968)]. For SW of non vanishing
delta, the difficulties due to the influence of the boundary condition at high
density already encountered in an earlier investigation [E. Schoell-Paschinger,
A. L. Benavides, and R. Castaneda-Priego, J. Chem. Phys. 123, 234513 (2005)]
prevented us from obtaining reliable results for delta < 0.1. In the sticky
limit this difficulty can be circumvented, but then the SCOZA fails to predict
a liquid-vapor transition. The picture that emerges from this study is that for
delta --> 0, the SCOZA does not fulfill the expected prediction of a constant
B2(Tc) [M. G. Noro and D. Frenkel, J. Chem. Phys. 113, 2941 (2000)], and that
for thermodynamic consistency to be usefully exploited in this regime, one
should probably go beyond the Ornstein-Zernike ansatz.Comment: 40 pages, 13 figures. Previous Sec. 2 on the Yukawa potential has
been removed. Only the square-well potential is considered in this versio
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