161.
Machado, Leonardo D; Legoas, Sergio B; Galvao, Douglas S
Multi-Million Fully Atomistic Molecular Dynamics Simulations of Yarn Formation from Carbon Nanotube Forests Proceedings
Cambridge University Press, vol. 1407, 2012.
@proceedings{machado2012multi,
title = {Multi-Million Fully Atomistic Molecular Dynamics Simulations of Yarn Formation from Carbon Nanotube Forests},
author = {Machado, Leonardo D and Legoas, Sergio B and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8537115&fulltextType=RA&fileId=S1946427412007105},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1407},
pages = {mrsf11--1407},
publisher = {Cambridge University Press},
abstract = {In this work we present preliminary results from multi-million fully atomistic classical molecular dynamics simulations carried out to test different existing mechanisms that have been proposed in the literature to explain the drawing of yarns from carbon nanotube forests. Despite the fact that it has been almost ten years since yarns were first drawn, there are still controversies on the mechanisms and necessary conditions that can produce yarns and sheets drawn from carbon nanotube forests. Moreover, few works have tried to understand at atomistic level the details of yarn drawing mechanisms, and no fully atomistic simulations have been carried out so far on this particular subject. Our preliminary results suggest that only direct van der Waals interactions among large bundles seem not to be enough to explain the yarn drawing process. Bundle interconnectors (such as small bundles connecting large bundles) were observed to play a critical role in our simulations. Depending on the topology of these interconnectors it was possible to observe from the simulations fibers/yarn formation from proposed structural models. These models were built based on structural information inferred from scanning electron microscopy data.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
In this work we present preliminary results from multi-million fully atomistic classical molecular dynamics simulations carried out to test different existing mechanisms that have been proposed in the literature to explain the drawing of yarns from carbon nanotube forests. Despite the fact that it has been almost ten years since yarns were first drawn, there are still controversies on the mechanisms and necessary conditions that can produce yarns and sheets drawn from carbon nanotube forests. Moreover, few works have tried to understand at atomistic level the details of yarn drawing mechanisms, and no fully atomistic simulations have been carried out so far on this particular subject. Our preliminary results suggest that only direct van der Waals interactions among large bundles seem not to be enough to explain the yarn drawing process. Bundle interconnectors (such as small bundles connecting large bundles) were observed to play a critical role in our simulations. Depending on the topology of these interconnectors it was possible to observe from the simulations fibers/yarn formation from proposed structural models. These models were built based on structural information inferred from scanning electron microscopy data.
162.
Legoas, SB; dos Santos, RPB; Troche, KS; Coluci, VR; Galvao, Douglas S
On the Existence of Ordered Phases of Encapsulated Diamondoids into Carbon Nanotubes Proceedings
Cambridge University Press, vol. 1407, 2012.
@proceedings{legoas2012existence,
title = {On the Existence of Ordered Phases of Encapsulated Diamondoids into Carbon Nanotubes},
author = {Legoas, SB and dos Santos, RPB and Troche, KS and Coluci, VR and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8539583&fileId=S194642741200704X},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1407},
pages = {mrsf11--1407},
publisher = {Cambridge University Press},
abstract = {We have investigated some diamondoids encapsulation into single walled carbon nanotubes (with diameters ranging from1.0 up to 2.2 nm) using fully atomistic molecular dynamics simulations. Diamondoids are the smallest hydrogen-terminated nanosized diamond-like molecules. Diamondois have been investigated for a large class of applications, ranging from oil industry to pharmaceuticals. Molecular ordered phases were observed for the encapsulation of adamantane, diamantane, and dihydroxy diamantanes. Chiral ordered phases, such as; double, triple, 4- and 5-stranded helices were also observed for those diamondoids. Our results also indicate that the modification of diamondoids through chemical functionalization with hydroxyl groups can lead to an enhancement of the molecular packing inside the carbon nanotubes in comparison to non-functionalized molecules. For larger diamondoids (such as, adamantane tetramers), we have not observed long-range ordering, but only a tendency of incomplete helical structural formation.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
We have investigated some diamondoids encapsulation into single walled carbon nanotubes (with diameters ranging from1.0 up to 2.2 nm) using fully atomistic molecular dynamics simulations. Diamondoids are the smallest hydrogen-terminated nanosized diamond-like molecules. Diamondois have been investigated for a large class of applications, ranging from oil industry to pharmaceuticals. Molecular ordered phases were observed for the encapsulation of adamantane, diamantane, and dihydroxy diamantanes. Chiral ordered phases, such as; double, triple, 4- and 5-stranded helices were also observed for those diamondoids. Our results also indicate that the modification of diamondoids through chemical functionalization with hydroxyl groups can lead to an enhancement of the molecular packing inside the carbon nanotubes in comparison to non-functionalized molecules. For larger diamondoids (such as, adamantane tetramers), we have not observed long-range ordering, but only a tendency of incomplete helical structural formation.
163.
Lagos, MJ; Autreto, PAS; Galvao, DS; Ugarte, D
Correlation between Quantum Conductance and Atomic Arrangement of Silver Atomic-Size Nanowires Journal Article
In: arXiv preprint arXiv:1206.2551, 2012, (Draft version of: Correlation between quantum conductance and atomic arrangement of atomic-size silver nanowires Journal of Applied Physics, 111 (12), pp. 124316, 2012.).
@article{lagos2012correlation,
title = {Correlation between Quantum Conductance and Atomic Arrangement of Silver Atomic-Size Nanowires},
author = {Lagos, MJ and Autreto, PAS and Galvao, DS and Ugarte, D},
url = {http://arxiv.org/abs/1206.2551},
year = {2012},
date = {2012-01-01},
journal = {arXiv preprint arXiv:1206.2551},
abstract = {We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction. We have observed drastic changes in conductance and structural properties of Ag nanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wire (3/3) along the (001) crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior.},
note = {Draft version of:
Correlation between quantum conductance and atomic arrangement of atomic-size silver nanowires
Journal of Applied Physics, 111 (12), pp. 124316, 2012.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction. We have observed drastic changes in conductance and structural properties of Ag nanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wire (3/3) along the (001) crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior.
164.
Lagos, MJ; Autreto, PAS; Galvao, DS; Ugarte, D
Correlation between quantum conductance and atomic arrangement of atomic-size silver nanowires Journal Article
In: Journal of Applied Physics, vol. 111, no. 12, pp. 124316, 2012.
@article{lagos2012correlationb,
title = {Correlation between quantum conductance and atomic arrangement of atomic-size silver nanowires},
author = {Lagos, MJ and Autreto, PAS and Galvao, DS and Ugarte, D},
url = {http://scitation.aip.org/content/aip/journal/jap/111/12/10.1063/1.4729805},
year = {2012},
date = {2012-01-01},
journal = {Journal of Applied Physics},
volume = {111},
number = {12},
pages = {124316},
publisher = {AIP Publishing},
abstract = {We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires (NWs) generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction. We have observed drastic changes in conductance and structuralproperties of Agnanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements, and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structuralproperties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Agwire (3/3) along the [001] crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the effect of thermal effects on the structural and transport response of Ag atomic-size nanowires (NWs) generated by mechanical elongation. Our study involves both time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction. We have observed drastic changes in conductance and structuralproperties of Agnanowires generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements, and quantum transport calculations, we have been able to obtain a consistent correlation between the conductance and structuralproperties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Agwire (3/3) along the [001] crystallographic direction, whose formation is enhanced. These results illustrate the high complexity of analyzing structural and quantum conductance behaviour of metal atomic-size wires; also, they reveal that it is extremely difficult to compare NW conductance experiments performed at different temperatures due to the fundamental modifications of the mechanical behavior.
165.
Perim, Eric; Fonseca, Alexandre F; Galvao, Douglas S
When Small is Different: The Case of Membranes Inside Tubes Proceedings
Cambridge University Press, vol. 1451, 2012.
@proceedings{perim2012small,
title = {When Small is Different: The Case of Membranes Inside Tubes},
author = {Perim, Eric and Fonseca, Alexandre F and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8637821&fileId=S1946427412012523},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1451},
pages = {15--20},
publisher = {Cambridge University Press},
abstract = {Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales.
166.
dos Santos, Ricardo P; Autreto, Pedro A; Perim, Eric; Brunetto, Gustavo; Galvao, Douglas S
On the Unzipping Mechanisms of Carbon Nanotubes: Insights from Reactive Molecular Dynamics Simulations Proceedings
Cambridge University Press, vol. 1451, 2012.
@proceedings{dos2012unzipping,
title = {On the Unzipping Mechanisms of Carbon Nanotubes: Insights from Reactive Molecular Dynamics Simulations},
author = {dos Santos, Ricardo P and Autreto, Pedro A and Perim, Eric and Brunetto, Gustavo and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8652294&fileId=S1946427412013292},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1451},
pages = {3--8},
publisher = {Cambridge University Press},
abstract = {Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges.
167.
Dos Santos, RPB; Perim, E; Autreto, PAS; Brunetto, Gustavo; Galvao, DS
On the unzipping of multiwalled carbon nanotubes Journal Article
In: Nanotechnology, vol. 23, no. 46, pp. 465702, 2012.
@article{dos2012unzippingb,
title = {On the unzipping of multiwalled carbon nanotubes},
author = {Dos Santos, RPB and Perim, E and Autreto, PAS and Brunetto, Gustavo and Galvao, DS},
url = {http://iopscience.iop.org/0957-4484/23/46/465702},
year = {2012},
date = {2012-01-01},
journal = {Nanotechnology},
volume = {23},
number = {46},
pages = {465702},
publisher = {IOP Publishing},
abstract = {Graphene nanoribbons (GNRs) are very interesting structures which can retain graphene's high carrier mobility while presenting a finite bandgap. These properties make GNRs very valuable materials for the building of nanodevices. Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for GNR controlled and large-scale production, although some of the details of the CNT unzipping processes are not completely known. In this work we have investigated CNT unzipping processes through fully atomistic molecular dynamics simulations using reactive force fields (ReaxFF). Multiwalled CNTs of different dimensions and chiralities under induced mechanical stretching were considered. Our results show that fracture patterns and stress profiles are highly CNT chirality dependent. Our results also show that the 'crests' (partially unzipped CNT regions presenting high curvature), originating from defective CNT areas, can act as a guide for the unzipping processes, which can explain the almost perfectly linear cuts frequently observed in unzipped CNTs.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Graphene nanoribbons (GNRs) are very interesting structures which can retain graphene's high carrier mobility while presenting a finite bandgap. These properties make GNRs very valuable materials for the building of nanodevices. Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for GNR controlled and large-scale production, although some of the details of the CNT unzipping processes are not completely known. In this work we have investigated CNT unzipping processes through fully atomistic molecular dynamics simulations using reactive force fields (ReaxFF). Multiwalled CNTs of different dimensions and chiralities under induced mechanical stretching were considered. Our results show that fracture patterns and stress profiles are highly CNT chirality dependent. Our results also show that the 'crests' (partially unzipped CNT regions presenting high curvature), originating from defective CNT areas, can act as a guide for the unzipping processes, which can explain the almost perfectly linear cuts frequently observed in unzipped CNTs.
168.
Lima, Marcio D; Li, Na; De Andrade, Monica Jung; Fang, Shaoli; Oh, Jiyoung; Spinks, Geoffrey M; Kozlov, Mikhail E; Haines, Carter S; Suh, Dongseok; Foroughi, Javad; Kim, Seon Jeong; Chen, Yongsheng; Ware, Taylor; Shin, Min Kyoon; Machado, Leonardo D; Fonseca, Alexandre F; Madden, John DW; Voit, Walter E; Galvao, Douglas S; Baughman, Ray H
Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yarn muscles Journal Article
In: Science, vol. 338, no. 6109, pp. 928–932, 2012.
@article{lima2012electrically,
title = {Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yarn muscles},
author = {Lima, Marcio D and Li, Na and De Andrade, Monica Jung and Fang, Shaoli and Oh, Jiyoung and Spinks, Geoffrey M and Kozlov, Mikhail E and Haines, Carter S and Suh, Dongseok and Foroughi, Javad and Kim, Seon Jeong and Chen, Yongsheng and Ware, Taylor and Shin, Min Kyoon and Machado, Leonardo D and Fonseca, Alexandre F and Madden, John DW and Voit, Walter E and Galvao, Douglas S and Baughman, Ray H
},
url = {http://www.sciencemag.org/content/338/6109/928.short},
year = {2012},
date = {2012-01-01},
journal = {Science},
volume = {338},
number = {6109},
pages = {928--932},
publisher = {American Association for the Advancement of Science},
abstract = {Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average 11,500 revolutions/minute or delivers 3% tensile contraction at 1200 cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average 11,500 revolutions/minute or delivers 3% tensile contraction at 1200 cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.
169.
Autreto, Pedro A; Lagos, Maureen J; Ugarte, Daniel; Galvao, Douglas S
Correlation Between Quantum Conductance and Atomic Arrangement of Silver Atomic-Size Nanocontacts Proceedings
Cambridge University Press, vol. 1429, 2012.
@proceedings{autreto2012correlation,
title = {Correlation Between Quantum Conductance and Atomic Arrangement of Silver Atomic-Size Nanocontacts},
author = {Autreto, Pedro A and Lagos, Maureen J and Ugarte, Daniel and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8717061&fileId=S1946427412015011},
year = {2012},
date = {2012-01-01},
journal = {MRS Proceedings},
volume = {1429},
pages = {mrss12--1429},
publisher = {Cambridge University Press},
abstract = {In this work we have studied the importance of thermal effects on the structural and transport properties of Ag atomic-size nanowires (NWs) generated by mechanical stretching. Our study involve time-resolved atomic high resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction combined with quantum transport calculations. We have observed drastic changes in conductance and structural properties of Ag NWs generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements and theoretical modeling, we have been able to establish a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wires along the [001] crystallographic direction.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
In this work we have studied the importance of thermal effects on the structural and transport properties of Ag atomic-size nanowires (NWs) generated by mechanical stretching. Our study involve time-resolved atomic high resolution transmission electron microscopy imaging and quantum conductance measurement using an ultra-high-vacuum mechanically controllable break junction combined with quantum transport calculations. We have observed drastic changes in conductance and structural properties of Ag NWs generated at different temperatures (150 and 300 K). By combining electron microscopy images, electronic transport measurements and theoretical modeling, we have been able to establish a consistent correlation between the conductance and structural properties of Ag NWs. In particular, our study has revealed the formation of metastable rectangular rod-like Ag wires along the [001] crystallographic direction.
170.
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}
}
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).
171.
PAS Autreto MJ Lagos, SB Legoas
Temperature effects on the occurrence of long interatomic distances in atomic chains formed from stretched gold nanowires Journal Article
In: Nanotechnology, vol. 22, no. 9, pp. 095705, 2011.
@article{Lagos2011,
title = {Temperature effects on the occurrence of long interatomic distances in atomic chains formed from stretched gold nanowires},
author = {MJ Lagos, PAS Autreto, SB Legoas, F Sato, V Rodrigues, DS Galvao, D Ugarte},
url = {http://iopscience.iop.org/0957-4484/22/9/095705},
year = {2011},
date = {2011-03-04},
journal = {Nanotechnology},
volume = {22},
number = {9},
pages = {095705},
abstract = {The origin of long interatomic distances in suspended gold atomic chains formed from stretched nanowires remains the object of debate despite the large amount of theoretical and experimental work. Here, we report new atomic resolution electron microscopy observations acquired at room and liquid-nitrogen temperatures and theoretical results from ab initio quantum molecular dynamics on chain formation and stability. These new data are suggestive that the long distances are due to contamination by carbon atoms originating from the decomposition of adsorbed hydrocarbon molecules.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The origin of long interatomic distances in suspended gold atomic chains formed from stretched nanowires remains the object of debate despite the large amount of theoretical and experimental work. Here, we report new atomic resolution electron microscopy observations acquired at room and liquid-nitrogen temperatures and theoretical results from ab initio quantum molecular dynamics on chain formation and stability. These new data are suggestive that the long distances are due to contamination by carbon atoms originating from the decomposition of adsorbed hydrocarbon molecules.
172.
Lagos, Maureen J; Sato, Fernando; Galvao, Douglas S; Ugarte, Daniel
Mechanical deformation of nanoscale metal rods: when size and shape matter Journal Article
In: Physical Review Letters, vol. 106, no. 5, pp. 055501, 2011.
@article{lagos2011mechanical,
title = {Mechanical deformation of nanoscale metal rods: when size and shape matter},
author = {Lagos, Maureen J and Sato, Fernando and Galvao, Douglas S and Ugarte, Daniel},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.055501},
year = {2011},
date = {2011-01-01},
journal = {Physical Review Letters},
volume = {106},
number = {5},
pages = {055501},
publisher = {American Physical Society},
abstract = {Face centered cubic metals deform mainly by propagating partial dislocations generating planar fault ribbons. How do metals deform if the size is smaller than the fault ribbons? We studied the elongation of Au and Pt nanorods by in situ electron microscopy and ab initio calculations. Planar fault activation barriers are so low that, for each temperature, a minimal rod size is required to become active for releasing elastic energy. Surface effects dominate deformation energetics; system size and shape determine the preferred fault gliding directions which induce different tensile and compressive behavior.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Face centered cubic metals deform mainly by propagating partial dislocations generating planar fault ribbons. How do metals deform if the size is smaller than the fault ribbons? We studied the elongation of Au and Pt nanorods by in situ electron microscopy and ab initio calculations. Planar fault activation barriers are so low that, for each temperature, a minimal rod size is required to become active for releasing elastic energy. Surface effects dominate deformation energetics; system size and shape determine the preferred fault gliding directions which induce different tensile and compressive behavior.
173.
Machado, Leonardo D; Legoas, Sergio B; Soares, Jaqueline S; Shadmi, Nitzan; Jorio, Ado; Joselevich, Ernesto; Galvao, Douglas S
Cambridge University Press, vol. 1284, 2011.
@proceedings{machado2011formation,
title = {On the formation of carbon nanotube serpentines: insights from multi-million atom molecular dynamics simulation},
author = {Machado, Leonardo D and Legoas, Sergio B and Soares, Jaqueline S and Shadmi, Nitzan and Jorio, Ado and Joselevich, Ernesto and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8194288&fileId=S194642741100220X},
year = {2011},
date = {2011-01-01},
journal = {MRS Proceedings},
volume = {1284},
pages = {mrsf10--1284},
publisher = {Cambridge University Press},
abstract = {In this work we present preliminary results from molecular dynamics simulations for carbon nanotubes serpentine dynamics formation. These S-like nanostructures consist of a series of parallel and straight nanotube segments connected by alternating U-turn shaped curves. Nanotube serpentines were experimentally synthesized and reported in recent years, but up to now no atomistic simulations have been carried out to address the dynamics of formation of these structures. We have carried out fully atomistic molecular dynamics simulations in the framework of classical mechanics with a standard molecular force field. Multi-million atoms structures formed by stepped substrates with a carbon nanotube (about 1 micron in length) placed on top of them have been considered in our simulations. A force is applied to the upper part of the tube during a short period of time and then turned off and the system set free to evolve in time. Our results showed that these conditions are sufficient to form robust serpentines and validate the general features of the ‘falling spaghetti mechanism’ previously proposed to explain their formation.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
In this work we present preliminary results from molecular dynamics simulations for carbon nanotubes serpentine dynamics formation. These S-like nanostructures consist of a series of parallel and straight nanotube segments connected by alternating U-turn shaped curves. Nanotube serpentines were experimentally synthesized and reported in recent years, but up to now no atomistic simulations have been carried out to address the dynamics of formation of these structures. We have carried out fully atomistic molecular dynamics simulations in the framework of classical mechanics with a standard molecular force field. Multi-million atoms structures formed by stepped substrates with a carbon nanotube (about 1 micron in length) placed on top of them have been considered in our simulations. A force is applied to the upper part of the tube during a short period of time and then turned off and the system set free to evolve in time. Our results showed that these conditions are sufficient to form robust serpentines and validate the general features of the ‘falling spaghetti mechanism’ previously proposed to explain their formation.
174.
Autreto, PAS; Lagos, MJ; Sato, F; Bettini, J; Rocha, AR; Rodrigues, V; Ugarte, D; Galvao, DS
Intrinsic Stability of the Smallest Possible Silver Nanotube Journal Article
In: Physical Review Letters, vol. 106, no. 6, pp. 065501, 2011.
@article{autreto2011intrinsic,
title = {Intrinsic Stability of the Smallest Possible Silver Nanotube},
author = {Autreto, PAS and Lagos, MJ and Sato, F and Bettini, J and Rocha, AR and Rodrigues, V and Ugarte, D and Galvao, DS},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.065501},
year = {2011},
date = {2011-01-01},
journal = {Physical Review Letters},
volume = {106},
number = {6},
pages = {065501},
publisher = {American Physical Society},
abstract = {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 3.6G0 for this new family of nanotubes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
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 3.6G0 for this new family of nanotubes.
175.
Lagos, MJ; Autreto, PAS; Legoas, SB; Sato, F; Rodrigues, V; Galvao, DS; Ugarte, D
Temperature effects on the occurrence of long interatomic distances in atomic chains formed from stretched gold nanowires Journal Article
In: Nanotechnology, vol. 22, no. 9, pp. 095705, 2011.
@article{lagos2011temperature,
title = {Temperature effects on the occurrence of long interatomic distances in atomic chains formed from stretched gold nanowires},
author = {Lagos, MJ and Autreto, PAS and Legoas, SB and Sato, F and Rodrigues, V and Galvao, DS and Ugarte, D},
url = {http://iopscience.iop.org/0957-4484/21/48/485702},
year = {2011},
date = {2011-01-01},
journal = {Nanotechnology},
volume = {22},
number = {9},
pages = {095705},
publisher = {IOP Publishing},
abstract = {We have studied the changes induced by thermal effects in the structural and transport response of Au nanowires generated by mechanical elongation. We have used time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using a mechanically controllable break junction. Our results showed remarkable differences in the NW evolution for experiments realized at 150 and 300 K, which modifies drastically the conductance response during elongation. Molecular dynamics and electronic transport calculations were used to consistently correlate the observed structural and conductance behavior. These results emphasize that it is essential to take into account the precise atomic arrangement of nanocontacts generated by mechanical stretching to understand electrical transport properties. Also, our study shows that much care must be taken when comparing results obtained in different experimental conditions, mainly different temperatures.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have studied the changes induced by thermal effects in the structural and transport response of Au nanowires generated by mechanical elongation. We have used time-resolved atomic resolution transmission electron microscopy imaging and quantum conductance measurement using a mechanically controllable break junction. Our results showed remarkable differences in the NW evolution for experiments realized at 150 and 300 K, which modifies drastically the conductance response during elongation. Molecular dynamics and electronic transport calculations were used to consistently correlate the observed structural and conductance behavior. These results emphasize that it is essential to take into account the precise atomic arrangement of nanocontacts generated by mechanical stretching to understand electrical transport properties. Also, our study shows that much care must be taken when comparing results obtained in different experimental conditions, mainly different temperatures.
176.
Perim, Eric; Galvao, Douglas S
Stability and Dynamics of Boron Nitride Nanoscrolls Proceedings
Cambridge University Press, vol. 1307, 2011.
@proceedings{perim2011stability,
title = {Stability and Dynamics of Boron Nitride Nanoscrolls},
author = {Perim, Eric and Galvao, Douglas S},
url = {http://journals.cambridge.org/action/displayFulltext?type=1&fid=8200678&jid=OPL&volumeId=1307&issueId=-1&aid=8200676},
year = {2011},
date = {2011-01-01},
journal = {MRS Proceedings},
volume = {1307},
pages = {mrsf10--1307},
publisher = {Cambridge University Press},
abstract = {We report here molecular dynamics results for boron nitride nanoscroll structures
(BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to
carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping
layers. The energy balance between losses and gains (due to elastic deformations and van der
Waals interactions, respectively) when the structure is rolled up leads to the existence of a
critical value of the internal scroll diameter where stable or metastable structures can be formed.
The mechanisms of scroll formation and stability as a function of their chirality were also
investigated.},
keywords = {},
pubstate = {published},
tppubtype = {proceedings}
}
We report here molecular dynamics results for boron nitride nanoscroll structures
(BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to
carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping
layers. The energy balance between losses and gains (due to elastic deformations and van der
Waals interactions, respectively) when the structure is rolled up leads to the existence of a
critical value of the internal scroll diameter where stable or metastable structures can be formed.
The mechanisms of scroll formation and stability as a function of their chirality were also
investigated.
(BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to
carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping
layers. The energy balance between losses and gains (due to elastic deformations and van der
Waals interactions, respectively) when the structure is rolled up leads to the existence of a
critical value of the internal scroll diameter where stable or metastable structures can be formed.
The mechanisms of scroll formation and stability as a function of their chirality were also
investigated.
177.
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}
}
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.
178.
Azevedo, David L; Sato, Fernando; Gomes de Sousa Filho, Antonio; Galvao, Douglas S
In: Molecular Simulation, vol. 37, no. 9, pp. 746–751, 2011.
@article{azevedo2011van,
title = {van der Waals potential barrier for cobaltocene encapsulation into single-walled carbon nanotubes: classical molecular dynamics and ab initio study},
author = {Azevedo, David L and Sato, Fernando and Gomes de Sousa Filho, Antonio and Galvao, Douglas S},
url = {http://www.tandfonline.com/doi/abs/10.1080/08927022.2010.537093#.VLfBForF-2o},
year = {2011},
date = {2011-01-01},
journal = {Molecular Simulation},
volume = {37},
number = {9},
pages = {746--751},
publisher = {Taylor & Francis Group},
abstract = {In this work, we carried out geometry optimisations and classical molecular dynamics for the problem of cobaltocene (CC) encapsulation into different carbon nanotubes (CNTs) ((7,7), (8,8), (13,0) and (14,0) tubes were used). CCs are molecules composed of two aromatic pentagonal rings (C5H5) sandwiching one cobalt atom. From our simulation results, we observed that CC was encapsulated into CNTs (8,8), (13,0) and (14,0). However, for CNT (7,7), the encapsulation could not occur, in disaggrement with some previous works in the literature. Our results show that the encapsulation process is mainly governed by van der Waals potential barriers.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this work, we carried out geometry optimisations and classical molecular dynamics for the problem of cobaltocene (CC) encapsulation into different carbon nanotubes (CNTs) ((7,7), (8,8), (13,0) and (14,0) tubes were used). CCs are molecules composed of two aromatic pentagonal rings (C5H5) sandwiching one cobalt atom. From our simulation results, we observed that CC was encapsulated into CNTs (8,8), (13,0) and (14,0). However, for CNT (7,7), the encapsulation could not occur, in disaggrement with some previous works in the literature. Our results show that the encapsulation process is mainly governed by van der Waals potential barriers.
179.
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}
}
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.
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.
180.
Legoas, SB; Dos Santos, RPB; Troche, KS; Coluci, VR; Galvao, DS
Ordered phases of encapsulated diamondoids into carbon nanotubes Journal Article
In: Nanotechnology, vol. 22, no. 31, pp. 315708, 2011.
@article{legoas2011ordered,
title = {Ordered phases of encapsulated diamondoids into carbon nanotubes},
author = {Legoas, SB and Dos Santos, RPB and Troche, KS and Coluci, VR and Galvao, DS},
url = {http://iopscience.iop.org/0957-4484/22/31/315708},
year = {2011},
date = {2011-01-01},
journal = {Nanotechnology},
volume = {22},
number = {31},
pages = {315708},
publisher = {IOP Publishing},
abstract = {Diamondoids are hydrogen-terminated nanosized diamond fragments that are present in petroleum crude oil at low concentrations. These fragments are found as oligomers of the smallest diamondoid, adamantane (C10H16). Due to their small size, diamondoids can be encapsulated into carbon nanotubes to form linear arrangements. We have investigated the encapsulation of diamondoids into single walled carbon nanotubes with diameters between 1.0 and 2.2 nm using fully atomistic simulations. We performed classical molecular dynamics and energy minimizations calculations to determine the most stable configurations. We observed molecular ordered phases (e.g. double, triple, 4- and 5-stranded helices) for the encapsulation of adamantane, diamantane, and dihydroxy diamantane. Our results also indicate that the functionalization of diamantane with hydroxyl groups can lead to an improvement on the molecular packing factor when compared to non-functionalized compounds. Comparisons to hard-sphere models revealed differences, especially when more asymmetrical diamondoids were considered. For larger diamondoids (i.e., adamantane tetramers), we have not observed long-range ordering but only a tendency to form incomplete helical structures. Our calculations predict that thermally stable (at least up to room temperature) complex ordered phases of diamondoids can be formed through encapsulation into carbon nanotubes.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Diamondoids are hydrogen-terminated nanosized diamond fragments that are present in petroleum crude oil at low concentrations. These fragments are found as oligomers of the smallest diamondoid, adamantane (C10H16). Due to their small size, diamondoids can be encapsulated into carbon nanotubes to form linear arrangements. We have investigated the encapsulation of diamondoids into single walled carbon nanotubes with diameters between 1.0 and 2.2 nm using fully atomistic simulations. We performed classical molecular dynamics and energy minimizations calculations to determine the most stable configurations. We observed molecular ordered phases (e.g. double, triple, 4- and 5-stranded helices) for the encapsulation of adamantane, diamantane, and dihydroxy diamantane. Our results also indicate that the functionalization of diamantane with hydroxyl groups can lead to an improvement on the molecular packing factor when compared to non-functionalized compounds. Comparisons to hard-sphere models revealed differences, especially when more asymmetrical diamondoids were considered. For larger diamondoids (i.e., adamantane tetramers), we have not observed long-range ordering but only a tendency to form incomplete helical structures. Our calculations predict that thermally stable (at least up to room temperature) complex ordered phases of diamondoids can be formed through encapsulation into carbon nanotubes.
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