201.
Sato, Fernando; Lagos, Maureen; Autreto, Pedro; Ugarte, Daniel; Galvao, Douglas
On the Lifetime of Suspended Atomic Chains Formed from Stretched Metallic Gold Nanowires Journal Article
In: Physicae, vol. 8, no. 8, 2009, (Invited Paper).
@article{sato2009lifetime,
title = {On the Lifetime of Suspended Atomic Chains Formed from Stretched Metallic Gold Nanowires},
author = {Sato, Fernando and Lagos, Maureen and Autreto, Pedro and Ugarte, Daniel and Galvao, Douglas},
url = {http://physicae.ifi.unicamp.br/physicae/article/viewArticle/109},
year = {2009},
date = {2009-01-01},
journal = {Physicae},
volume = {8},
number = {8},
abstract = {Metallic nanowires have been object of intense theoretical and experimental works in the lastyears. In spite of the large number of studies for such systems some fundamental aspects remain open and polemical questions. In this work we report preliminary results for the study of the final steps of Au suspended atomic chains (LACs) with different number of atoms as a function of tem-perature. We have carried out classical molecular dynamics simulations using tight-binding models with a second moment approximations. Our results suggest a more complex phenomenon than previously anticipated. The dynamics of chain rupture seems to be determined beyond thermodynamics contributions and the bond breaking patterns were observed to be chain-length dependent.
},
note = {Invited Paper},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metallic nanowires have been object of intense theoretical and experimental works in the lastyears. In spite of the large number of studies for such systems some fundamental aspects remain open and polemical questions. In this work we report preliminary results for the study of the final steps of Au suspended atomic chains (LACs) with different number of atoms as a function of tem-perature. We have carried out classical molecular dynamics simulations using tight-binding models with a second moment approximations. Our results suggest a more complex phenomenon than previously anticipated. The dynamics of chain rupture seems to be determined beyond thermodynamics contributions and the bond breaking patterns were observed to be chain-length dependent.
202.
Torriani, IL; Silva, JC; Autreto, PAS; Galvao, DS; Caldas, MJ; Graeff, CFO
Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents Journal Article
In: Acta Crystalographica A, vol. 64, pp. C552, 2009.
@article{torriani2009low,
title = {Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents},
author = {Torriani, IL and Silva, JC and Autreto, PAS and Galvao, DS and Caldas, MJ and Graeff, CFO},
url = {http://journals.iucr.org/a/issues/2008/a1/00/a39972/a39972.pdf},
year = {2009},
date = {2009-01-01},
journal = {Acta Crystalographica A},
volume = {64},
pages = {C552},
abstract = {In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
203.
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}
}
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.
204.
Hall, Lee J; Coluci, Vitor R; Galvao, Douglas S; Kozlov, Mikhail E; Zhang, Mei; Dantas, Socrates O; Baughman, Ray H
Sign change of Poisson's ratio for carbon nanotube sheets Journal Article
In: Science, vol. 320, no. 5875, pp. 504–507, 2008.
@article{hall2008sign,
title = {Sign change of Poisson's ratio for carbon nanotube sheets},
author = {Hall, Lee J and Coluci, Vitor R and Galvao, Douglas S and Kozlov, Mikhail E and Zhang, Mei and Dantas, Socrates O and Baughman, Ray H},
url = {http://www.sciencemag.org/content/320/5875/504.short},
year = {2008},
date = {2008-01-01},
journal = {Science},
volume = {320},
number = {5875},
pages = {504--507},
publisher = {American Association for the Advancement of Science},
abstract = {Most materials shrink laterally like a rubber band when stretched, so their Poisson's ratios are positive. Likewise, most materials contract in all directions when hydrostatically compressed and decrease density when stretched, so they have positive linear compressibilities. We found that the in-plane Poisson's ratio of carbon nanotube sheets (buckypaper) can be tuned from positive to negative by mixing single-walled and multiwalled nanotubes. Density-normalized sheet toughness, strength, and modulus were substantially increased by this mixing. A simple model predicts the sign and magnitude of Poisson's ratio for buckypaper from the relative ease of nanofiber bending and stretch, and explains why the Poisson's ratios of ordinary writing paper are positive and much larger. Theory also explains why the negative in-plane Poisson's ratio is associated with a large positive Poisson's ratio for the sheet thickness, and predicts that hydrostatic compression can produce biaxial sheet expansion. This tunability of Poisson's ratio can be exploited in the design of sheet-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Most materials shrink laterally like a rubber band when stretched, so their Poisson's ratios are positive. Likewise, most materials contract in all directions when hydrostatically compressed and decrease density when stretched, so they have positive linear compressibilities. We found that the in-plane Poisson's ratio of carbon nanotube sheets (buckypaper) can be tuned from positive to negative by mixing single-walled and multiwalled nanotubes. Density-normalized sheet toughness, strength, and modulus were substantially increased by this mixing. A simple model predicts the sign and magnitude of Poisson's ratio for buckypaper from the relative ease of nanofiber bending and stretch, and explains why the Poisson's ratios of ordinary writing paper are positive and much larger. Theory also explains why the negative in-plane Poisson's ratio is associated with a large positive Poisson's ratio for the sheet thickness, and predicts that hydrostatic compression can produce biaxial sheet expansion. This tunability of Poisson's ratio can be exploited in the design of sheet-derived composites, artificial muscles, gaskets, and chemical and mechanical sensors.
205.
Martins, Bruno VC; Brunetto, Gustavo; Sato, Fernando; Coluci, Vitor R; Galvao, Douglas S
Designing conducting polymers using bioinspired ant algorithms Journal Article
In: Chemical Physics Letters, vol. 453, no. 4, pp. 290–295, 2008.
@article{martins2008designing,
title = {Designing conducting polymers using bioinspired ant algorithms},
author = {Martins, Bruno VC and Brunetto, Gustavo and Sato, Fernando and Coluci, Vitor R and Galvao, Douglas S},
url = {http://www.sciencedirect.com/science/article/pii/S0009261408000845},
year = {2008},
date = {2008-01-01},
journal = {Chemical Physics Letters},
volume = {453},
number = {4},
pages = {290--295},
publisher = {Elsevier},
abstract = {Ant algorithms are inspired in real ants and the main idea is to create virtual ants that travel into the space of possible solutions depositing virtual pheromone proportional to how good a specific solution is. This creates an autocatalytic (positive feedback) process that can be used to generate automatic solutions to very difficult problems. In the present work we show that these algorithms can be used coupled to tight-binding Hamiltonians to design conducting polymers with pre-specified properties. The methodology is completely general and can be used for a large number of optimizations problems in materials science.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ant algorithms are inspired in real ants and the main idea is to create virtual ants that travel into the space of possible solutions depositing virtual pheromone proportional to how good a specific solution is. This creates an autocatalytic (positive feedback) process that can be used to generate automatic solutions to very difficult problems. In the present work we show that these algorithms can be used coupled to tight-binding Hamiltonians to design conducting polymers with pre-specified properties. The methodology is completely general and can be used for a large number of optimizations problems in materials science.
206.
Coluci, Vitor R; Hall, Lee J; Kozlov, Mikhail E; Zhang, Mei; Dantas, Socrates O; Galvao, Douglas S; Baughman, Ray H
Modeling the auxetic transition for carbon nanotube sheets Journal Article
In: Physical Review B, vol. 78, no. 11, pp. 115408, 2008.
@article{coluci2008modeling,
title = {Modeling the auxetic transition for carbon nanotube sheets},
author = {Coluci, Vitor R and Hall, Lee J and Kozlov, Mikhail E and Zhang, Mei and Dantas, Socrates O and Galvao, Douglas S and Baughman, Ray H},
url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.78.115408},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B},
volume = {78},
number = {11},
pages = {115408},
publisher = {APS},
abstract = {A simple model is developed to predict the complex mechanical properties of carbon nanotube sheets (buckypaper) [L. J. Hall et al., Science 320, 504 (2008)]. Fabricated using a similar method to that deployed for making writing paper, these buckypapers can have in-plane Poisson’s ratios changed from positive to negative, becoming auxetic, as multiwalled carbon nanotubes are increasingly mixed with single-walled carbon nanotubes. Essential structural features of the buckypapers are incorporated into the model: isotropic in-plane mechanical properties, nanotubes preferentially oriented in the sheet plane, and freedom to undergo stress-induced elongation by both angle and length changes. The expressions derived for the Poisson’s ratios enabled quantitative prediction of both observed properties and remarkable new properties obtainable by structural modification.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A simple model is developed to predict the complex mechanical properties of carbon nanotube sheets (buckypaper) [L. J. Hall et al., Science 320, 504 (2008)]. Fabricated using a similar method to that deployed for making writing paper, these buckypapers can have in-plane Poisson’s ratios changed from positive to negative, becoming auxetic, as multiwalled carbon nanotubes are increasingly mixed with single-walled carbon nanotubes. Essential structural features of the buckypapers are incorporated into the model: isotropic in-plane mechanical properties, nanotubes preferentially oriented in the sheet plane, and freedom to undergo stress-induced elongation by both angle and length changes. The expressions derived for the Poisson’s ratios enabled quantitative prediction of both observed properties and remarkable new properties obtainable by structural modification.
207.
Nakabayashi, D; Moreau, ALD; Coluci, VR; Galvao, DS; Cotta, MA; Ugarte, D
Carbon nanotubes as reinforcement elements of composite nanotools Journal Article
In: Nano letters, vol. 8, no. 3, pp. 842–847, 2008.
@article{nakabayashi2008carbon,
title = {Carbon nanotubes as reinforcement elements of composite nanotools},
author = {Nakabayashi, D and Moreau, ALD and Coluci, VR and Galvao, DS and Cotta, MA and Ugarte, D},
url = {http://pubs.acs.org/doi/abs/10.1021/nl0729633},
year = {2008},
date = {2008-01-01},
journal = {Nano letters},
volume = {8},
number = {3},
pages = {842--847},
publisher = {American Chemical Society},
abstract = {Nanotechnology is stimulating the development of nanomanipulators, including tips to interact with individual nanosystems. Fabricating nanotips fulfilling the requirements of shape (size, aspect ratio), mechanical, magnetic, and electrical properties is a material science challenge. Here, we report the generation of reinforced carbon−carbon composite nanotools using a nanotube (CNTs) covered by an amorphous carbon matrix (shell); the CNT tip protruded and remained uncoated to preserve apex size. Unsuitable properties such as flexibility and vibration could be controlled without deteriorating the CNT size, strength, and resilience. Nanomanipulation experiments and molecular dynamics simulations have been used to study the mechanical response of these composite beams under bending efforts. AFM probes based on these C−C composite high aspect ratio tips generated excellent image resolution and showed no degradation after acquiring several hundred (400) images.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Nanotechnology is stimulating the development of nanomanipulators, including tips to interact with individual nanosystems. Fabricating nanotips fulfilling the requirements of shape (size, aspect ratio), mechanical, magnetic, and electrical properties is a material science challenge. Here, we report the generation of reinforced carbon−carbon composite nanotools using a nanotube (CNTs) covered by an amorphous carbon matrix (shell); the CNT tip protruded and remained uncoated to preserve apex size. Unsuitable properties such as flexibility and vibration could be controlled without deteriorating the CNT size, strength, and resilience. Nanomanipulation experiments and molecular dynamics simulations have been used to study the mechanical response of these composite beams under bending efforts. AFM probes based on these C−C composite high aspect ratio tips generated excellent image resolution and showed no degradation after acquiring several hundred (400) images.
208.
Coluci, Vitor R; Fonseca, Alexandre F; Galvao, Douglas S; Daraio, Chiara
Entanglement and the nonlinear elastic behavior of forests of coiled carbon nanotubes Journal Article
In: Physical Review Letters, vol. 100, no. 8, pp. 086807, 2008.
@article{coluci2008entanglement,
title = {Entanglement and the nonlinear elastic behavior of forests of coiled carbon nanotubes},
author = {Coluci, Vitor R and Fonseca, Alexandre F and Galvao, Douglas S and Daraio, Chiara},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.086807},
year = {2008},
date = {2008-01-01},
journal = {Physical Review Letters},
volume = {100},
number = {8},
pages = {086807},
publisher = {American Physical Society},
abstract = {Helical or coiled nanostructures have been objects of intense experimental and theoretical studies due to their special electronic and mechanical properties. Recently, it was experimentally reported that the dynamical response of a foamlike forest of coiled carbon nanotubes under mechanical impact exhibits a nonlinear, non-Hertzian behavior, with no trace of plastic deformation. The physical origin of this unusual behavior is not yet fully understood. In this Letter, based on analytical models, we show that the entanglement among neighboring coils in the superior part of the forest surface must be taken into account for a full description of the strongly nonlinear behavior of the impact response of a drop ball onto a forest of coiled carbon nanotubes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Helical or coiled nanostructures have been objects of intense experimental and theoretical studies due to their special electronic and mechanical properties. Recently, it was experimentally reported that the dynamical response of a foamlike forest of coiled carbon nanotubes under mechanical impact exhibits a nonlinear, non-Hertzian behavior, with no trace of plastic deformation. The physical origin of this unusual behavior is not yet fully understood. In this Letter, based on analytical models, we show that the entanglement among neighboring coils in the superior part of the forest surface must be taken into account for a full description of the strongly nonlinear behavior of the impact response of a drop ball onto a forest of coiled carbon nanotubes.
209.
Coluci, Vitor R; Sato, Fernando; Braga, Scheila F; Skaf, Munir S; Galvao, Douglas S
Rotational dynamics and polymerization of C60 in C60-cubane crystals: A molecular dynamics study Journal Article
In: The Journal of Chemical Physics, vol. 129, no. 6, pp. 064506, 2008.
@article{coluci2008rotational,
title = {Rotational dynamics and polymerization of C60 in C60-cubane crystals: A molecular dynamics study},
author = {Coluci, Vitor R and Sato, Fernando and Braga, Scheila F and Skaf, Munir S and Galvao, Douglas S},
url = {http://scitation.aip.org/content/aip/journal/jcp/129/6/10.1063/1.2965885},
year = {2008},
date = {2008-01-01},
journal = {The Journal of Chemical Physics},
volume = {129},
number = {6},
pages = {064506},
publisher = {AIP Publishing},
abstract = {We report classical and tight-binding molecular dynamics simulations of the C60fullerene and cubane molecular crystal in order to investigate the intermolecular dynamics and polymerization processes. Our results show that, for 200 and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations, while C60fullerenes show rotational motions. Fullerenes perform “free” rotational motions at short times (≲1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (≳10 ps). The mechanisms underlying these dynamics are presented. Random copolymerizations among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure. Changes in the radial distribution function and electronic density of states indicate the coexistence of amorphous and crystalline phases. The different conformational phases that cubanes and fullerenes undergo during the copolymerization process are discussed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report classical and tight-binding molecular dynamics simulations of the C60fullerene and cubane molecular crystal in order to investigate the intermolecular dynamics and polymerization processes. Our results show that, for 200 and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations, while C60fullerenes show rotational motions. Fullerenes perform “free” rotational motions at short times (≲1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (≳10 ps). The mechanisms underlying these dynamics are presented. Random copolymerizations among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure. Changes in the radial distribution function and electronic density of states indicate the coexistence of amorphous and crystalline phases. The different conformational phases that cubanes and fullerenes undergo during the copolymerization process are discussed.
210.
Konstantinova, Elena; Camilo Jr, Alexandre; Barone, Paulo MVB; Dantas, Socrates O; Galvao, Douglas S
Some electronic properties of saturated and unsaturated cubane oligomers using DFT-based calculations Journal Article
In: Journal of Molecular Structure: THEOCHEM, vol. 868, no. 1, pp. 37–41, 2008.
@article{konstantinova2008some,
title = {Some electronic properties of saturated and unsaturated cubane oligomers using DFT-based calculations},
author = {Konstantinova, Elena and Camilo Jr, Alexandre and Barone, Paulo MVB and Dantas, Socrates O and Galvao, Douglas S},
url = {http://www.sciencedirect.com/science/article/pii/S016612800800448X},
year = {2008},
date = {2008-01-01},
journal = {Journal of Molecular Structure: THEOCHEM},
volume = {868},
number = {1},
pages = {37--41},
publisher = {Elsevier},
abstract = {Cubanes and cubane-based molecular structures attract considerable interest as structural units which represent a new class of materials with remarkable properties. These structures are potentially useful for a variety of industrial applications and, for this reason, deserve detailed study. One of the options is to use cubane-based structures to synthesize a new class of conducting polymers with small energy band gap. In the present work we use the DFT-based methods to perform geometrical optimization and obtain some electronic properties for cubane, cubatriene, saturated and unsaturated oligomers containing different number of cubane and cubatriene building units. Our results indicate that the energy difference between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) manifests a small decrease with the growing units number for saturated or unsaturated oligomers. This energy difference is strongly dependent on the presence of hydrogen atoms and is greater for unsaturated structures.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Cubanes and cubane-based molecular structures attract considerable interest as structural units which represent a new class of materials with remarkable properties. These structures are potentially useful for a variety of industrial applications and, for this reason, deserve detailed study. One of the options is to use cubane-based structures to synthesize a new class of conducting polymers with small energy band gap. In the present work we use the DFT-based methods to perform geometrical optimization and obtain some electronic properties for cubane, cubatriene, saturated and unsaturated oligomers containing different number of cubane and cubatriene building units. Our results indicate that the energy difference between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) manifests a small decrease with the growing units number for saturated or unsaturated oligomers. This energy difference is strongly dependent on the presence of hydrogen atoms and is greater for unsaturated structures.
211.
Moreira, DA; Albuquerque, EL; da Silva, LR; Galvao, DS
Low-temperature specific heat spectra considering nonextensive long-range correlated quasiperiodic DNA molecules Journal Article
In: Physica A: Statistical Mechanics and its Applications, vol. 387, no. 22, pp. 5477–5482, 2008.
@article{moreira2008low,
title = {Low-temperature specific heat spectra considering nonextensive long-range correlated quasiperiodic DNA molecules},
author = {Moreira, DA and Albuquerque, EL and da Silva, LR and Galvao, DS},
url = {http://www.sciencedirect.com/science/article/pii/S0378437108005347},
year = {2008},
date = {2008-01-01},
journal = {Physica A: Statistical Mechanics and its Applications},
volume = {387},
number = {22},
pages = {5477--5482},
publisher = {North-Holland},
abstract = {We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q-gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q-gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum.
212.
Rurali, R; Cartoixa, X; Galvao, DS
Large electromechanical response in silicon nanowires predicted from first-principles electronic structure calculations Journal Article
In: Physical Review B, vol. 77, no. 7, pp. 073403, 2008.
@article{rurali2008large,
title = {Large electromechanical response in silicon nanowires predicted from first-principles electronic structure calculations},
author = {Rurali, R and Cartoixa, X and Galvao, DS},
url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.77.073403},
year = {2008},
date = {2008-01-01},
journal = {Physical Review B},
volume = {77},
number = {7},
pages = {073403},
publisher = {American Physical Society},
abstract = {We study by means of first-principles electronic structure calculations the electromechanical response, i.e., the structural modifications upon charge injection, of ⟨100⟩ silicon nanowires. We show that, at variance with sp2 carbon nanostructures, the response is remarkably linear, discriminates between injected charge of different signs, and is up to one order of magnitude larger than in carbon nanotubes.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We study by means of first-principles electronic structure calculations the electromechanical response, i.e., the structural modifications upon charge injection, of ⟨100⟩ silicon nanowires. We show that, at variance with sp2 carbon nanostructures, the response is remarkably linear, discriminates between injected charge of different signs, and is up to one order of magnitude larger than in carbon nanotubes.
213.
Lagos, M; Sato, F; Bettini, J; Rdrigues, V; Galvao, D; Ugarte, D
Atomic-size Silver Nanotube Book Section
In: EMC 2008 14th European Microscopy Congress 1--5 September 2008, Aachen, Germany, pp. 493–494, Springer Berlin Heidelberg, 2008, (Book Chapter).
@incollection{lagos2008atomic,
title = {Atomic-size Silver Nanotube},
author = {Lagos, M and Sato, F and Bettini, J and Rdrigues, V and Galvao, D and Ugarte, D},
url = {http://link.springer.com/chapter/10.1007%2F978-3-540-85156-1_247},
year = {2008},
date = {2008-01-01},
booktitle = {EMC 2008 14th European Microscopy Congress 1--5 September 2008, Aachen, Germany},
pages = {493--494},
publisher = {Springer Berlin Heidelberg},
abstract = {The atomic arrangement of nanosystems may be quite different from the traditional materials; surface energy minimization plays a dominant role in this size range, and accounts for many of these new structures. Graphitic nanotubes [1] represent the best example, being fromed by a rolled the graphitic layer, which is tradionally flat. Subsequently the rolling of the compact (111) atomic planes was reported for gold nanowires (NW) generated by mechanical stretching [2]. But, we may expect many more surprises from the interplay between atomic and electronic structure.},
note = {Book Chapter},
keywords = {},
pubstate = {published},
tppubtype = {incollection}
}
The atomic arrangement of nanosystems may be quite different from the traditional materials; surface energy minimization plays a dominant role in this size range, and accounts for many of these new structures. Graphitic nanotubes [1] represent the best example, being fromed by a rolled the graphitic layer, which is tradionally flat. Subsequently the rolling of the compact (111) atomic planes was reported for gold nanowires (NW) generated by mechanical stretching [2]. But, we may expect many more surprises from the interplay between atomic and electronic structure.
214.
Coluci, Vitor; Sato, Fernando; Braga, Scheila F; Skaf, Munir S; Galvao, Douglas S
A molecular dynamics study of the rotational dynamics and polymerization of C60 in C60-cubane crystals Journal Article
In: MRS Proceedings, vol. 1130, pp. 1130–W06, 2008.
@article{coluci2008molecular,
title = {A molecular dynamics study of the rotational dynamics and polymerization of C60 in C60-cubane crystals},
author = {Coluci, Vitor and Sato, Fernando and Braga, Scheila F and Skaf, Munir S and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7973166&fileId=S1946427400024088},
year = {2008},
date = {2008-01-01},
journal = {MRS Proceedings},
volume = {1130},
pages = {1130--W06},
publisher = {Cambridge University Press},
abstract = {Recently, heteromolecular crystals of fullerene C60 and cubane (C8H8) have been synthesized. For some temperatures the C60 molecules are free to rotate whereas cubanes behave like a static bearing in a so-called rotor-stator phases. In this work we report classical and tight-binding molecular dynamics simulations in order to investigate the rotor-stator dynamics and polymerization processes. Our results show that, for 200 K and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations within the timescale of our simulations, while C60 fullerenes show rotational motions. Fullerenes perform “free” rotational motions at short times (< 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (> 10 ps). Random copolymerization among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, heteromolecular crystals of fullerene C60 and cubane (C8H8) have been synthesized. For some temperatures the C60 molecules are free to rotate whereas cubanes behave like a static bearing in a so-called rotor-stator phases. In this work we report classical and tight-binding molecular dynamics simulations in order to investigate the rotor-stator dynamics and polymerization processes. Our results show that, for 200 K and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations within the timescale of our simulations, while C60 fullerenes show rotational motions. Fullerenes perform “free” rotational motions at short times (< 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (> 10 ps). Random copolymerization among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure.
215.
Nakabayashi, D; Ugarte, D; Moreau, ALD; Coluci, VR; Galvao, DS; Cotta, MA
Carbon nanotubes as R-bars of high aspect ratio composite nanotools Technical Report
2008.
@techreport{nakabayashi2008carbonb,
title = {Carbon nanotubes as R-bars of high aspect ratio composite nanotools},
author = {Nakabayashi, D and Ugarte, D and Moreau, ALD and Coluci, VR and Galvao, DS and Cotta, MA},
url = {http://lnls.cnpem.br/ar2008/},
year = {2008},
date = {2008-01-01},
abstract = {Nano technology requires the development of nano scale tools to manipulate nano systems. From the point of view of materials science, this represents a serious challenge, because nano tools must meet a series of stringent requirements of shape (size, aspect ratio), mechanical, magnetic and electrical properties. We have developed long and narrow carbon-carbon composite nano tips using carbon nanotubes covered by an amorphous carbon shell; the very small nano tube tip remained uncoated to preserve apex size. This configuration renders the system stiffer and allows for the control of flexibility and vibrations. In addition, we have maintained the important nano tube properties of size, strength and resilience. Nano manipulation experiments in situ in a high resolution scanning electron microscope were used to optimize the tips behavior and molecular dynamics simulations were used to study the mechanical response. Finally, we performed a practical application in atomic force microscopy. Composite tips yielded excellent image resolution and showed remarkable wear resistance (no degradation of image quality after acquiring several hundred images). },
keywords = {},
pubstate = {published},
tppubtype = {techreport}
}
Nano technology requires the development of nano scale tools to manipulate nano systems. From the point of view of materials science, this represents a serious challenge, because nano tools must meet a series of stringent requirements of shape (size, aspect ratio), mechanical, magnetic and electrical properties. We have developed long and narrow carbon-carbon composite nano tips using carbon nanotubes covered by an amorphous carbon shell; the very small nano tube tip remained uncoated to preserve apex size. This configuration renders the system stiffer and allows for the control of flexibility and vibrations. In addition, we have maintained the important nano tube properties of size, strength and resilience. Nano manipulation experiments in situ in a high resolution scanning electron microscope were used to optimize the tips behavior and molecular dynamics simulations were used to study the mechanical response. Finally, we performed a practical application in atomic force microscopy. Composite tips yielded excellent image resolution and showed remarkable wear resistance (no degradation of image quality after acquiring several hundred images).
216.
Coluci, Vitor R; Pugno, Nicola M; Dantas, Socrates O; Galvao, Douglas S; Jorio, Ado
Atomistic simulations of the mechanical properties of'super'carbon nanotubes Journal Article
In: Nanotechnology, vol. 18, no. 33, pp. 335702, 2007.
@article{coluci2007atomistic,
title = {Atomistic simulations of the mechanical properties of'super'carbon nanotubes},
author = {Coluci, Vitor R and Pugno, Nicola M and Dantas, Socrates O and Galvao, Douglas S and Jorio, Ado},
url = {http://iopscience.iop.org/0957-4484/18/33/335702
},
year = {2007},
date = {2007-01-01},
journal = {Nanotechnology},
volume = {18},
number = {33},
pages = {335702},
publisher = {IOP Publishing},
abstract = {The mechanical properties of the so-called 'super' carbon nanotubes (STs) are investigated using classical molecular dynamics simulations. The STs are built from single-walled carbon nanotubes (SWCNTs) connected by Y-like junctions forming an ordered carbon nanotube network that is then rolled into a seamless cylinder. We observed that the ST behaviour under tensile tests is similar to the one presented by fishing nets. This interesting behaviour provides a way to vary the accessible channels to the inner parts of STs by applying an external mechanical load. The Young's modulus is dependent on the ST chirality and it inversely varies with the ST radius. Smaller reduction of breaking strain values due to temperature increase is predicted for zigzag STs compared to SWCNTs. The results show that, for STs with radius ~5 nm, the junctions between the constituent SWCNTs play an important role in the fracture process. The Young's modulus and tensile strength were estimated for hierarchical higher-order STs using scaling laws related to the ST fractal dimension. The obtained mechanical properties suggest that STs may be used in the development of new porous, flexible, and high-strength materials.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The mechanical properties of the so-called 'super' carbon nanotubes (STs) are investigated using classical molecular dynamics simulations. The STs are built from single-walled carbon nanotubes (SWCNTs) connected by Y-like junctions forming an ordered carbon nanotube network that is then rolled into a seamless cylinder. We observed that the ST behaviour under tensile tests is similar to the one presented by fishing nets. This interesting behaviour provides a way to vary the accessible channels to the inner parts of STs by applying an external mechanical load. The Young's modulus is dependent on the ST chirality and it inversely varies with the ST radius. Smaller reduction of breaking strain values due to temperature increase is predicted for zigzag STs compared to SWCNTs. The results show that, for STs with radius ~5 nm, the junctions between the constituent SWCNTs play an important role in the fracture process. The Young's modulus and tensile strength were estimated for hierarchical higher-order STs using scaling laws related to the ST fractal dimension. The obtained mechanical properties suggest that STs may be used in the development of new porous, flexible, and high-strength materials.
217.
Coluci, VR; Dantas, SO; Jorio, A; Galvao, DS
Mechanical properties of carbon nanotube networks by molecular mechanics and impact molecular dynamics calculations Journal Article
In: Physical Review B, vol. 75, no. 7, pp. 075417, 2007.
@article{coluci2007mechanical,
title = {Mechanical properties of carbon nanotube networks by molecular mechanics and impact molecular dynamics calculations},
author = {Coluci, VR and Dantas, SO and Jorio, A and Galvao, DS},
url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.75.075417},
year = {2007},
date = {2007-01-01},
journal = {Physical Review B},
volume = {75},
number = {7},
pages = {075417},
publisher = {APS},
abstract = {We report a theoretical investigation of the mechanical properties of idealized networks formed by single-walled carbon nanotubes showing crossbar and hexagonal architectures. The study was performed by using molecular mechanics calculations and impact dynamics simulations based on bond-order empirical potential. The studied networks were predicted to have elasticity modulus of ∼10–100GPa and bulk modulus of ∼10GPa. The results show a transition from high to moderate flexibility during the deformation stages. This behavior was associated with the existence of two deformation mechanisms presented by the network related to the nanotube stretching and junction bending processes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report a theoretical investigation of the mechanical properties of idealized networks formed by single-walled carbon nanotubes showing crossbar and hexagonal architectures. The study was performed by using molecular mechanics calculations and impact dynamics simulations based on bond-order empirical potential. The studied networks were predicted to have elasticity modulus of ∼10–100GPa and bulk modulus of ∼10GPa. The results show a transition from high to moderate flexibility during the deformation stages. This behavior was associated with the existence of two deformation mechanisms presented by the network related to the nanotube stretching and junction bending processes.
218.
Coluci, VR; Braga, SF; Baughman, RH; Galvao, DS
Prediction of the hydrogen storage capacity of carbon nanoscrolls Journal Article
In: Physical Review B, vol. 75, no. 12, pp. 125404, 2007.
@article{coluci2007prediction,
title = {Prediction of the hydrogen storage capacity of carbon nanoscrolls},
author = {Coluci, VR and Braga, SF and Baughman, RH and Galvao, DS},
url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.75.125404},
year = {2007},
date = {2007-01-01},
journal = {Physical Review B},
volume = {75},
number = {12},
pages = {125404},
publisher = {APS},
abstract = {Classical grand-canonical Monte Carlo simulations were performed to investigate the equilibrium hydrogen storage capacity of carbon nanoscrolls. The results show that hydrogen molecules can be absorbed in the internal cavity as well as on the external surface of the scroll when the interlayer spacing is less than 4.4Å. When the interlayer spacing is increased to 6.4Å, by assuming spacing increase due to intercalation of other species, the hydrogen molecules can also be incorporated in the interlayer galleries, doubling the gravimetric storage capacity and reaching 5.5wt% hydrogen per weight carbon at 150K and 1MPa. Our results showed that intercalated carbon nanoscrolls may be a promissing material for hydrogen storage.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Classical grand-canonical Monte Carlo simulations were performed to investigate the equilibrium hydrogen storage capacity of carbon nanoscrolls. The results show that hydrogen molecules can be absorbed in the internal cavity as well as on the external surface of the scroll when the interlayer spacing is less than 4.4Å. When the interlayer spacing is increased to 6.4Å, by assuming spacing increase due to intercalation of other species, the hydrogen molecules can also be incorporated in the interlayer galleries, doubling the gravimetric storage capacity and reaching 5.5wt% hydrogen per weight carbon at 150K and 1MPa. Our results showed that intercalated carbon nanoscrolls may be a promissing material for hydrogen storage.
219.
Braga, SF; Coluci, VR; Baughman, RH; Galvao, DS
Hydrogen storage in carbon nanoscrolls: An atomistic molecular dynamics study Journal Article
In: Chemical Physics Letters, vol. 441, no. 1, pp. 78–82, 2007.
@article{braga2007hydrogen,
title = {Hydrogen storage in carbon nanoscrolls: An atomistic molecular dynamics study},
author = {Braga, SF and Coluci, VR and Baughman, RH and Galvao, DS},
url = {http://www.sciencedirect.com/science/article/pii/S0009261407005209},
year = {2007},
date = {2007-01-01},
journal = {Chemical Physics Letters},
volume = {441},
number = {1},
pages = {78--82},
publisher = {North-Holland},
abstract = {We report molecular dynamics results on the hydrogen uptake in carbon nanoscrolls (CNs). CNs are formed from helically wrapped graphite layers. We observed that at low temperatures significant H2 storage is possible, but at higher temperatures thermal energies drastically reduce this capacity. Only a small fraction of hydrogen is adsorbed between scroll layers. Using temperature as the sorption/desorption variable we have observed that hydrogen can be released from the CN by temperature increase and can be readsorbed when the system is cooled. Higher capacities are expected if the CNs interlayer spacings are increased, making them an attractive nanostructure for H2 storage having fast kinetics for charge/discharge.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report molecular dynamics results on the hydrogen uptake in carbon nanoscrolls (CNs). CNs are formed from helically wrapped graphite layers. We observed that at low temperatures significant H2 storage is possible, but at higher temperatures thermal energies drastically reduce this capacity. Only a small fraction of hydrogen is adsorbed between scroll layers. Using temperature as the sorption/desorption variable we have observed that hydrogen can be released from the CN by temperature increase and can be readsorbed when the system is cooled. Higher capacities are expected if the CNs interlayer spacings are increased, making them an attractive nanostructure for H2 storage having fast kinetics for charge/discharge.
220.
Braga, Scheila Furtado; Galvao, Douglas Soares
Molecular dynamics simulation of single wall carbon nanotubes polymerization under compression Journal Article
In: Journal of Computational Chemistry, vol. 28, no. 10, pp. 1724–1734, 2007.
@article{braga2007molecular,
title = {Molecular dynamics simulation of single wall carbon nanotubes polymerization under compression},
author = {Braga, Scheila Furtado and Galvao, Douglas Soares},
url = {http://onlinelibrary.wiley.com/store/10.1002/jcc.20684/asset/20684_ftp.pdf?v=1&t=i52l5iyb&s=94cda082eed01cd61890fffe50aad5e26cdda7d1},
year = {2007},
date = {2007-01-01},
journal = {Journal of Computational Chemistry},
volume = {28},
number = {10},
pages = {1724--1734},
publisher = {Wiley Subscription Services, Inc., A Wiley Company},
abstract = {Single wall carbon nanotubes (SWCNTs) often aggregate into bundles of hundreds of weakly interacting
tubes. Their cross-polymerization opens new possibilities for the creation of new super-hard materials. New mechanical
and electronic properties are expected from these condensed structures, as well as novel potential applications. Previous
theoretical results presented geometric modifications involving changes in the radial section of the compressed tubes
as the explanation to the experimental measurements of structural changes during tube compression. We report here
results from molecular dynamics simulations of the SWCNTs polymerization for small diameter arm chair tubes under
compression. Hydrostatic and piston-type compression of SWCNTs have been simulated for different temperatures and
rates of compression. Our results indicate that large diameter tubes (10,10) are unlike to polymerize while small diameter
ones (around 5 Å) polymerize even at room temperature. Other interesting results are the observation of the appearance
of spontaneous scroll-like structures and also the so-called tubulane motifs, which were predicted in the literature more
than a decade ago},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Single wall carbon nanotubes (SWCNTs) often aggregate into bundles of hundreds of weakly interacting
tubes. Their cross-polymerization opens new possibilities for the creation of new super-hard materials. New mechanical
and electronic properties are expected from these condensed structures, as well as novel potential applications. Previous
theoretical results presented geometric modifications involving changes in the radial section of the compressed tubes
as the explanation to the experimental measurements of structural changes during tube compression. We report here
results from molecular dynamics simulations of the SWCNTs polymerization for small diameter arm chair tubes under
compression. Hydrostatic and piston-type compression of SWCNTs have been simulated for different temperatures and
rates of compression. Our results indicate that large diameter tubes (10,10) are unlike to polymerize while small diameter
ones (around 5 Å) polymerize even at room temperature. Other interesting results are the observation of the appearance
of spontaneous scroll-like structures and also the so-called tubulane motifs, which were predicted in the literature more
than a decade ago
tubes. Their cross-polymerization opens new possibilities for the creation of new super-hard materials. New mechanical
and electronic properties are expected from these condensed structures, as well as novel potential applications. Previous
theoretical results presented geometric modifications involving changes in the radial section of the compressed tubes
as the explanation to the experimental measurements of structural changes during tube compression. We report here
results from molecular dynamics simulations of the SWCNTs polymerization for small diameter arm chair tubes under
compression. Hydrostatic and piston-type compression of SWCNTs have been simulated for different temperatures and
rates of compression. Our results indicate that large diameter tubes (10,10) are unlike to polymerize while small diameter
ones (around 5 Å) polymerize even at room temperature. Other interesting results are the observation of the appearance
of spontaneous scroll-like structures and also the so-called tubulane motifs, which were predicted in the literature more
than a decade ago
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