dos Santos, Ricardo P; Machado, Leonardo D; Legoas, Sergio B; Galvao, Douglas S
Tribological Properties of Graphene and Boron-Nitride Layers: A Fully Atomistic Molecular Dynamics Study Proceedings
Cambridge University Press, vol. 1407, 2012.
@proceedings{dos2012tribological,
title = {Tribological Properties of Graphene and Boron-Nitride Layers: A Fully Atomistic Molecular Dynamics Study},
author = {dos Santos, Ricardo P and Machado, Leonardo D and Legoas, Sergio B and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8537106&fileId=S1946427412007063},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1407},
pages = {mrsf11--1407},
publisher = {Cambridge University Press},
abstract = {Graphene has been one of the most important subjects in materials science in the last years. Recently, the frictional characteristics of atomically thin sheets were experimentally investigated using atomic force microscopy (AFM). A new mechanism to explain the enhanced friction for these materials, based on elastic compliance has been proposed. Here, we have investigated the tribological properties of graphene and boron-nitride (single and multi-layers) membranes using fully atomistic molecular dynamics simulations. These simulations were carried out using classical force fields, as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. The used structural models contain typically hundreds of thousands of atoms. In order to mimic the experimental conditions, an artificial AFM tip was moved over the membranes and the tribological characteristics determined in terms of forces and energies. Our results are in good agreement with the available experimental data. They show that the observed enhanced tribological properties can be explained in terms of out-of-plane geometrical distortions and elastic waves propagation. They validate the general features of the model proposed by Lee et al. (Science 328, 76 (2010).},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
Autreto, Pedro AS; Flores, Marcelo Z; Legoas, Sergio B; Santos, Ricardo PB; Galvao, Douglas S
Cambridge University Press, vol. 1284, 2011.
@proceedings{autreto2011fully,
title = {A Fully Atomistic Reactive Molecular Dynamics Study on the Formation of Graphane from Graphene Hydrogenated Membranes.},
author = {Autreto, Pedro AS and Flores, Marcelo Z and Legoas, Sergio B and Santos, Ricardo PB and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8364784&fileId=S1946427411013583},
year = {2011},
date = {2011-01-01},
journal = {MRS Proceedings},
volume = {1284},
pages = {mrsf10--1284},
publisher = {Cambridge University Press},
abstract = {Using fully reactive molecular dynamics methodologies we investigated the structural and dynamical aspects of the fluorination mechanism leading to fluorographene formation from graphene membranes. Fluorination tends to produce significant defective areas on the membranes with variation on the typical carbon-carbon distances, sometimes with the presence of large holes due to carbon losses. The results obtained in our simulations are in good agreement with the broad distribution of values for the lattice parameter experimentally observed. We have also investigated mixed atmospheres composed by H and F atoms. When H is present in small quantities an expressive reduction on the rate of incorporation of fluorine was observed. On the other hand when fluorine atoms are present in small quantities in a hydrogen atmosphere, they induce an increasing on the hydrogen incorporation and the formation of locally self-organized structure of adsorbed H and F atoms.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
Santos, Ricardo PB; Autreto, Pedro AS; Legoas, Sergio B; Galvao, Douglas S
Cambridge University Press, vol. 1344, 2011.
@proceedings{santos2011dynamics,
title = {The Dynamics of Formation of Graphane-like Fluorinated Graphene Membranes (Fluorographene): A Reactive Molecular Dynamics Study},
author = {Santos, Ricardo PB and Autreto, Pedro AS and Legoas, Sergio B and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayFulltext?type=1&fid=8237871&jid=OPL&volumeId=1284&issueId=-1&aid=8237869},
year = {2011},
date = {2011-01-01},
journal = {MRS Proceedings},
volume = {1344},
pages = {mrss11--1344},
publisher = {Cambridge University Press},
abstract = {Recently, Elias et al. (Science 323, 610 (2009).) reported the experimental realization of
the formation of graphane from hydrogenation of graphene membranes under cold plasma
exposure. In graphane, the carbon-carbon bonds are in sp3
configuration, as opposed to the sp2
hybridization of graphene, and the C–H bonds exhibit an alternating pattern (up and down with
relation to the plane defined by the carbon atoms). In this work we have investigated, using
reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms up and
down alternating pattern) in graphane-like structures. Our results show that a significant
percentage of uncorrelated H frustrated domains are formed in the early stages of the
hydrogenation process, leading to membrane shrinkage and extensive membrane corrugations.
This might explain the significant broad distribution of values of lattice parameter
experimentally observed. For comparison purposes we have also analyzed fluorinated graphanelike
structures. Our results show that similarly to H, F atoms also create significant uncorrelated
frustrated domains on graphene membranes. },
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
the formation of graphane from hydrogenation of graphene membranes under cold plasma
exposure. In graphane, the carbon-carbon bonds are in sp3
configuration, as opposed to the sp2
hybridization of graphene, and the C–H bonds exhibit an alternating pattern (up and down with
relation to the plane defined by the carbon atoms). In this work we have investigated, using
reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms up and
down alternating pattern) in graphane-like structures. Our results show that a significant
percentage of uncorrelated H frustrated domains are formed in the early stages of the
hydrogenation process, leading to membrane shrinkage and extensive membrane corrugations.
This might explain the significant broad distribution of values of lattice parameter
experimentally observed. For comparison purposes we have also analyzed fluorinated graphanelike
structures. Our results show that similarly to H, F atoms also create significant uncorrelated
frustrated domains on graphene membranes.
Coutinho, Samir S; Azevedo, David L; Galvao, Douglas S
Tuning Electronic and Structural Properties of Triple Layers of Intercalated Graphene and Hexagonal Boron Nitride: An Ab-initio Study. Journal Article
In: MRS Proceedings, vol. 1307, pp. mrsf10–1307, 2011.
@article{coutinho2011tuning,
title = {Tuning Electronic and Structural Properties of Triple Layers of Intercalated Graphene and Hexagonal Boron Nitride: An Ab-initio Study.},
author = {Coutinho, Samir S and Azevedo, David L and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8330317&fileId=S1946427411003642},
year = {2011},
date = {2011-01-01},
journal = {MRS Proceedings},
volume = {1307},
pages = {mrsf10--1307},
publisher = {Cambridge University Press},
abstract = {Recently, several experiments and theoretical studies demonstrated the possibility of tuning or modulating band gap values of nanostructures composed of bi-layer graphene, bi-layer hexagonal boron-nitride (BN) and hetero-layer combinations. These triple layers systems present several possibilities of stacking. In this work we report an ab initio (within the formalism of density functional theory (DFT)) study of structural and electronic properties of some of these stacked configurations. We observe that an applied external electric field can alter the electronic and structural properties of these systems. With the same value of the applied electric field the band gap values can be increased or decreased, depending on the layer stacking sequences. Strong geometrical deformations were observed. These results show that the application of an external electric field perpendicular to the stacked layers can effectively be used to modulate their inter-layer distances and/or their band gap values.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Martins, BVC; Galvao, DS
Curved graphene nanoribbons: structure and dynamics of carbon nanobelts Journal Article
In: Nanotechnology, vol. 21, no. 7, pp. 075710, 2010.
@article{martins2010curved,
title = {Curved graphene nanoribbons: structure and dynamics of carbon nanobelts},
author = {Martins, BVC and Galvao, DS},
url = {http://iopscience.iop.org/0957-4484/21/7/075710},
year = {2010},
date = {2010-01-01},
journal = {Nanotechnology},
volume = {21},
number = {7},
pages = {075710},
publisher = {IOP Publishing},
abstract = {Carbon nanoribbons (CNRs) are graphene (planar) structures with a large aspect ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into spiral-like structures, i.e. carbon nanoscrolls (CNSs) with a large aspect ratio. In this work we investigated the energetics and dynamical aspects of CNBs formed from rolling up CNRs. We have carried out molecular dynamics simulations using reactive empirical bond-order potentials. Our results show that, similarly to CNSs, CNB formation is dominated by two major energy contributions, the increase in the elastic energy due to the bending of the initial planar configuration (decreasing structural stability) and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers (increasing structural stability). Beyond a critical diameter value these scrolled structures can be even more stable (in terms of energy) than their equivalent planar configurations. In contrast to CNSs that require energy-assisted processes (sonication, chemical reactions, etc) to be formed, CNBs can be spontaneously formed from low temperature driven processes. Long CNBs (length of ~30.0 nm) tend to exhibit self-folded racket-like conformations with formation dynamics very similar to the one observed for long carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled structures. Possible synthetic routes to fabricate CNBs from graphene membranes are also addressed.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Flores, Marcelo ZS; Autreto, Pedro AS; Legoas, Sergio B; Galvao, Douglas S
Graphene to graphane: a theoretical study Journal Article
In: Nanotechnology, vol. 20, no. 46, pp. 465704, 2009.
@article{flores2009graphene,
title = {Graphene to graphane: a theoretical study},
author = {Flores, Marcelo ZS and Autreto, Pedro AS and Legoas, Sergio B and Galvao, Douglas S},
url = {http://iopscience.iop.org/0957-4484/20/46/465704},
year = {2009},
date = {2009-01-01},
journal = {Nanotechnology},
volume = {20},
number = {46},
pages = {465704},
publisher = {IOP Publishing},
abstract = {Graphane is a two-dimensional system consisting of a single layer of fully saturated (sp3 hybridization) carbon atoms. In an ideal graphane structure C–H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms). In this work we have investigated, using ab initio and reactive molecular dynamics simulations, the role of H frustration (breaking the H atoms' up and down alternating pattern) in graphane-like structures. Our results show that a significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hydrogenation process leading to membrane shrinkage and extensive membrane corrugations. These results also suggest that large domains of perfect graphane-like structures are unlikely to be formed, as H frustrated domains are always present.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Legoas, Sergio B; Autreto, Pedro AS; Flores, Marcelo ZS; Galvao, Douglas S
Graphene to graphane: the role of H frustration in lattice contraction Journal Article
In: arXiv preprint arXiv:0903.0278, 2009.
@article{legoas2009graphene,
title = {Graphene to graphane: the role of H frustration in lattice contraction},
author = {Legoas, Sergio B and Autreto, Pedro AS and Flores, Marcelo ZS and Galvao, Douglas S},
url = {http://arxiv.org/abs/0903.0278},
year = {2009},
date = {2009-01-01},
journal = {arXiv preprint arXiv:0903.0278},
abstract = {Graphane is a two-dimensional system consisting of a single planar layer of fully saturated (sp3 hybridization) carbon atoms with H atoms attached to them in an alternating pattern (up and down with relation to the plane defined by the carbon atoms). Stable graphane structures were theoretically predicted to exist some years ago and just experimentally realized through hydrogenation of graphene membranes. In this work we have investigated using textit{ab initio} and reactive molecular dynamics the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like structures. Our results show that H frustration significantly contributes to lattice contraction. The dynamical aspects of converting graphene to graphane is also addressed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Caetano, Ewerton WS; Freire, Valder N; Santos, Sergio G dos; Galvao, Douglas S; Sato, Fernando
Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties Journal Article
In: arXiv preprint arXiv:0903.2080, 2009.
@article{caetano2009m,
title = {Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties},
author = {Caetano, Ewerton WS and Freire, Valder N and Santos, Sergio G dos and Galvao, Douglas S and Sato, Fernando},
url = {http://arxiv.org/abs/0903.2080},
year = {2009},
date = {2009-01-01},
journal = {arXiv preprint arXiv:0903.2080},
abstract = {Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist M"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO → LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
E. W. S.; Freire Caetano, V. N. ; dos Santos
Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties Journal Article
In: THE JOURNAL OF CHEMICAL PHYSICS, vol. 128, pp. 164719, 2008.
@article{Caetano2008,
title = {Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties},
author = {Caetano, E. W. S.; Freire, V. N.; dos Santos, S. G.; Galvao, D. S.,and Sato, F.},
url = {http://scitation.aip.org/content/aip/journal/jcp/128/16/10.1063/1.2908739},
year = {2008},
date = {2008-04-29},
journal = {THE JOURNAL OF CHEMICAL PHYSICS},
volume = {128},
pages = {164719},
abstract = {Results of classical force field geometry optimizations for twisted graphenenanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO−4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO→LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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