35 research outputs found
Site-dependent hydrogenation on graphdiyne
Graphene is one of the most important materials in science today due to its
unique and remarkable electronic, thermal and mechanical properties. However in
its pristine state, graphene is a gapless semiconductor, what limits its use in
transistor electronics. In part due to the revolution created by graphene in
materials science, there is a renewed interest in other possible graphene-like
two-dimensional structures. Examples of these structures are graphynes and
graphdiynes, which are two-dimensional structures, composed of carbon atoms in
sp2 and sp-hybridized states. Graphdiynes (benzenoid rings connecting two
acetylenic groups) were recently synthesized and some of them are intrinsically
nonzero gap systems. These systems can be easily hydrogenated and the relative
level of hydrogenation can be used to tune the band gap values. We have
investigated, using fully reactive molecular dynamics (ReaxFF), the structural
and dynamics aspects of the hydrogenation mechanisms of graphdiyne membranes.
Our results showed that the hydrogen bindings have different atom incorporation
rates and that the hydrogenation patterns change in time in a very complex way.
The formation of correlated domains reported to hydrogenated graphene is no
longer observed in graphdiyne cases.Comment: Submitted to Carbo
Mechanical Properties and Fracture Dynamics of Silicene Membranes
As graphene became one of the most important materials today, there is a
renewed interest on others similar structures. One example is silicene, the
silicon analogue of graphene. It share some the remarkable graphene properties,
such as the Dirac cone, but presents some distinct ones, such as a pronounced
structural buckling. We have investigated, through density functional based
tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF),
the mechanical properties of suspended single-layer silicene. We calculated the
elastic constants, analyzed the fracture patterns and edge reconstructions. We
also addressed the stress distributions, unbuckling mechanisms and the fracture
dependence on the temperature. We analysed the differences due to distinct edge
morphologies, namely zigzag and armchair
Surface Effects on the Mechanical Elongation of AuCu Nanowires: De-alloying and the Formation of Mixed Suspended Atomic Chains
We report here an atomistic study of the mechanical deformation of AuxCu(1-x)
atomic-size wires (NWs) by means of high resolution transmission electron
microscopy (HRTEM) experiments. Molecular dynamics simulations were also
carried out in order to obtain deeper insights on the dynamical properties of
stretched NWs. The mechanical properties are significantly dependent on the
chemical composition that evolves in time at the junction; some structures
exhibit a remarkable de-alloying behavior. Also, our results represent the
first experimental realization of mixed linear atomic chains (LACs) among
transition and noble metals; in particular, surface energies induce chemical
gradients on NW surfaces that can be exploited to control the relative LAC
compositions (different number of gold and copper atoms). The implications of
these results for nanocatalysis and spin transport of one-atom-thick metal
wires are addressed.Comment: Accepted to Journal of Applied Physics (JAP
Dynamical Aspects Of The Unzipping Of Multiwalled Boron Nitride Nanotubes.
Boron nitride nanoribbons (BNNRs) exhibit very interesting magnetic properties, which could be very useful in the development of spintronic based devices. One possible route to obtain BNNRs is through the unzipping of boron nitride nanotubes (BNNTs), which have been already experimentally realized. In this work, different aspects of the unzipping process of BNNTs were investigated through fully atomistic molecular dynamics simulations using a classical reactive force field (ReaxFF). We investigated multiwalled BNNTs of different diameters and chiralities. Our results show that chirality plays a very important role in the unzipping process, as well as the interlayer coupling. These combined aspects significantly change the fracturing patterns and several other features of the unzipping processes in comparison to the ones observed for carbon nanotubes. Also, similar to carbon nanotubes, defective BNNTs can create regions of very high curvature which can act as a path to the unzipping process.1519147-5
Boron Nitride Nanotube Peapod under Ultrasonic Velocity Impacts: A Fully Atomistic Molecular Dynamics Investigation
In this work, we investigated the mechanical response and fracture dynamics
of boron nitride nanotubes (BNNTs)-peapods under ultrasonic velocity impacts
(from 1 km/s to 6 km/s) against a solid target. BNNT-peapods are BNNTs
containing an encapsulated linear arrangement of C60 molecules. We carried out
fully atomistic reactive (ReaxFF) molecular dynamics simulations. We have
considered the case of horizontal and vertical shootings. Depending on the
velocity values we observed tube bending, tube fracture, and C60 ejection. One
interesting result was tube unzipping with the formation of bilayer nanoribbons
'incrusted' with C60 molecules.Comment: 1
Intrinsic Stability Of The Smallest Possible Silver Nanotube.
Recently, Lagos et al. [Nature Nanotech. 4, 149 (2009)] reported the discovery of the smallest possible Ag nanotube with a square cross section. Ab initio density functional theory calculations strongly support that the stability of these hollow structures is structurally intrinsic and not the result of contamination by light atoms. We also report the first experimental observation of the theoretically predicted corrugation of the hollow structure. Quantum conductance calculations predict a unique signature of 3.6 G0 for this new family of nanotubes.10606550
A Nonzero Gap Two-Dimensional Carbon Allotrope from Porous Graphene
Graphene is considered one of the most promising materials for future
electronic. However, in its pristine form graphene is a gapless material, which
imposes limitations to its use in some electronic applications. In order to
solve this problem many approaches have been tried, such as, physical and
chemical functionalizations. These processes compromise some of the desirable
graphene properties. In this work, based on ab initio quantum molecular
dynamics, we showed that a two-dimensional carbon allotrope, named biphenylene
carbon (BPC) can be obtained from selective dehydrogenation of porous graphene.
BPC presents a nonzero bandgap and well-delocalized frontier orbitals.
Synthetic routes to BPC are also addressed.Comment: Published on J. Phys. Chem. C, 2012, 116 (23), pp 12810-1281
Dynamical aspects of the unzipping of multiwalled boron nitride nanotubes
Boron nitride nanoribbons (BNNRs) exhibit very interesting magnetic properties, which could be very useful in the development of spintronic based devices. One possible route to obtain BNNRs is through the unzipping of boron nitride nanotubes (BNNTs), which have been already experimentally realized. In this work, different aspects of the unzipping process of BNNTs were investigated through fully atomistic molecular dynamics simulations using a classical reactive force field (ReaxFF). We investigated multiwalled BNNTs of different diameters and chiralities. Our results show that chirality plays a very important role in the unzipping process, as well as the interlayer coupling. These combined aspects significantly change the fracturing patterns and several other features of the unzipping processes in comparison to the ones observed for carbon nanotubes. Also, similar to carbon nanotubes, defective BNNTs can create regions of very high curvature which can act as a path to the unzipping process.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP