79 research outputs found
The Structure of Graphene on Graphene/C60/Cu Interfaces: A Molecular Dynamics Study
Two experimental studies reported the spontaneous formation of amorphous and
crystalline structures of C60 intercalated between graphene and a substrate.
They observed interesting phenomena ranging from reaction between C60 molecules
under graphene to graphene sagging between the molecules and control of strain
in graphene. Motivated by these works, we performed fully atomistic reactive
molecular dynamics simulations to study the formation and thermal stability of
graphene wrinkles as well as graphene attachment to and detachment from the
substrate when graphene is laid over a previously distributed array of C60
molecules on a copper substrate at different values of temperature. As graphene
compresses the C60 molecules against the substrate, and graphene attachment to
the substrate between C60s ("C60s" stands for plural of C60) depends on the
height of graphene wrinkles, configurations with both frozen and non-frozen
C60s structures were investigated in order to verify the experimental result of
stable sagged graphene when the distance between C60s is about 4 nm and height
of graphene wrinkles is about 0.8 nm. Below the distance of 4 nm between C60s,
graphene becomes locally suspended and less strained. We show that this happens
when C60s are allowed to deform under the compressive action of graphene. If we
keep the C60s frozen, spontaneous "blanketing" of graphene happens only when
the distance between them are equal or above 7 nm. Both above results for the
existence of stable sagged graphene for C60 distances of 4 or 7 nm are shown to
agree with a mechanical model relating the rigidity of graphene to the energy
of graphene-substrate adhesion. In particular, this study might help the
development of 2D confined nanoreactors that are considered in literature to be
the next advanced step on chemical reactions.Comment: 7 pages, 4 figure
Reversible Actuation of -Borophene Nanoscrolls
In this work, we proposed and investigated the structural and electronic
properties of boron-based nanoscrolls (armchair and zigzag) using the DFTB+
method. We also investigated the electroactuation process (injecting and
removing charges). A giant electroactuation was observed, but the results show
relevant differences between the borophene and carbon nanoscrolls. The
molecular dynamics simulations showed that the scrolls are thermally and
structurally stable for a large range of temperatures (up to 600K) and the
electroactuation process can be easily tuned and can be entirely reversible for
some configurations.Comment: 21 pages, 6 figures, 1 tabl
On the mechanical, thermoelectric, and excitonic properties of Tetragraphene monolayer
Two-dimensional carbon allotropes have attracted much attention due to their
extraordinary optoelectronic and mechanical properties, which can be exploited
for energy conversion and storage applications. In this work, we use density
functional theory simulations and semi-empirical methods to investigate the
mechanical, thermoelectric, and excitonic properties of Tetrahexcarbon (also
known as Tetragraphene). This quasi-2D carbon allotrope exhibits a combination
of squared and hexagonal rings in a buckled shape. Our findings reveal that
tetragraphene is a semiconductor material with a direct electronic bandgap of
2.66 eV. Despite the direct nature of the electronic band structure, this
material has an indirect exciton ground state of 2.30 eV, which results in an
exciton binding energy of 0.36 eV. At ambient temperature, we obtain that the
lattice thermal conductivity for tetragraphene is approximately 118 W/mK.
Young's modulus and the shear modulus of tetragraphene are almost isotropic,
with maximum values of 286.0 N/m and 133.7 N/m, respectively, while exhibiting
a very low anisotropic Poisson ratio value of 0.09
Exploring the Elastic Properties and Fracture Patterns of Me-Graphene Monolayers and Nanotubes through Reactive Molecular Dynamics Simulations
Me-graphene (MeG) is a novel two-dimensional (2D) carbon allotrope. Due to
its attractive electronic and structural properties, it is important to study
the mechanical behavior of MeG in its monolayer and nanotube topologies. In
this work, we conducted fully atomistic reactive molecular dynamics simulations
using the Tersoff force field to investigate their mechanical properties and
fracture patterns. Our results indicate that Young's modulus of MeG monolayers
is about 414 GPa and in the range of 421-483 GPa for the nanotubes investigated
here. MeG monolayers and MeGNTs directly undergo from elastic to complete
fracture under critical strain without a plastic regime.Comment: 10 pages, 01 table, and 05 figure
Giant and tunable anisotropy of nanoscale friction in graphene
CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISThe nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.The nanoscale friction between an atomic force microscopy tip and graphene is investigated using friction force microscopy (FFM). During the tip movement, friction forces are observed to increase and then saturate in a highly anisotropic manner. As a result, the friction forces in graphene are highly dependent on the scanning direction: under some conditions, the energy dissipated along the armchair direction can be 80% higher than along the zigzag direction. In comparison, for highly-oriented pyrolitic graphite (HOPG), the friction anisotropy between armchair and zigzag directions is only 15%. This giant friction anisotropy in graphene results from anisotropies in the amplitudes of flexural deformations of the graphene sheet driven by the tip movement, not present in HOPG. The effect can be seen as a novel manifestation of the classical phenomenon of Euler buckling at the nanoscale, which provides the non-linear ingredients that amplify friction anisotropy. Simulations based on a novel version of the 2D Tomlinson model (modified to include the effects of flexural deformations), as well as fully atomistic molecular dynamics simulations and first-principles density-functional theory (DFT) calculations, are able to reproduce and explain the experimental observations.619CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPERJ - FUNDAÇÃO CARLOS CHAGAS FILHO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISSem informaçãoSem informação2013/08293-7, 2014/15521-9Sem informaçãoAll authors aknowledge the financial support from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ). R.P. acknowledges Fundação de Amparo a Pesquisa do Estado de São Paulo (Fapesp) for financial support through Grant #2014/15521-9. D.S.G. thanks the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant # 2013/08293-7. Computer simulations carried out during this research were supported by resources supplied by the Center for Scientific Computing (NCC/GridUNESP) of the São Paulo State University (UNESP). L.G.C. acknowledges FAPEMIG and the grant PRONAMETRO (52600.056330/2012). B.F acknowledges FAPEMIG and the grant PRONAMETRO (52600.030929/2014)
Defect-Free Carbon Nanotube Coils
Carbon nanotubes are promising building blocks for various nanoelectronic
components. A highly desirable geometry for such applications is a coil.
However, coiled nanotube structures reported so far were inherently defective
or had no free ends accessible for contacting. Here we demonstrate the
spontaneous self-coiling of single-wall carbon nanotubes into defect-free coils
of up to more than 70 turns with identical diameter and chirality, and free
ends. We characterize the structure, formation mechanism, and electrical
properties of these coils by different microscopies, molecular dynamics
simulations, Raman spectroscopy, and electrical and magnetic measurements. The
coils are highly conductive, as expected for defect-free carbon nanotubes, but
adjacent nanotube segments in the coil are more highly coupled than in regular
bundles of single-wall carbon nanotubes, owing to their perfect crystal
momentum matching, which enables tunneling between the turns. Although this
behavior does not yet enable the performance of these nanotube coils as
inductive devices, it does point a clear path for their realization. Hence,
this study represents a major step toward the production of many different
nanotube coil devices, including inductors, electromagnets, transformers, and
dynamos
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