http://scholar.google.com/citations?hl=en&user=95SvbM8AAAAJ
1.
Xifan Wang Sidong Lei, Bo Li
Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry Journal Article
Em: Nature Nanotechnology, vol. 11, pp. 465–471, 2016.
@article{Lei2016,
title = {Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry},
author = {Sidong Lei, Xifan Wang, Bo Li, Jiahao Kang, Yongmin He, Antony George, Liehui Ge, Yongji Gong, Pei Dong, Zehua Jin, Gustavo Brunetto, Weibing Chen, Zuan-Tao Lin, Robert Baines, Douglas S. Galvão, Jun Lou, Enrique Barrera, Kaustav Banerjee, Robert Vajtai & Pulickel Ajayan},
url = {http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.323.html},
doi = {10.1038/nnano.2015.323},
year = {2016},
date = {2016-02-01},
journal = {Nature Nanotechnology},
volume = {11},
pages = {465–471},
abstract = {Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid–base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p–n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid–base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid–base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p–n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid–base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.
2.
S Fang ZF Liu, FA Moura
Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles Journal Article
Em: Science, vol. 349, não 6246, pp. 404-404, 2015.
@article{Liu2015,
title = {Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles},
author = {ZF Liu, S Fang, FA Moura, JN Ding, N Jiang, J Di, M Zhang, X Lepró, DS Galvão, CS Haines, NY Yuan, SG Yin, DW Lee, R Wang, HY Wang, W Lv, C Dong, RC Zhang, MJ Chen, Q Yin, YT Chong, R Zhang, X Wang, MD Lima, R Ovalle-Robles, D Qian, H Lu, RH Baughman},
url = {http://www.sciencemag.org/content/349/6246/400.full.pdf},
doi = {10.1126/science.aaa7952},
year = {2015},
date = {2015-07-24},
journal = {Science},
volume = {349},
number = {6246},
pages = {404-404},
abstract = {Superelastic conducting fibers with improved properties and functionalities are needed
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Superelastic conducting fibers with improved properties and functionalities are needed
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.
3.
Chandra Sekhar Tiwary Mohamad A Kabbani, Pedro AS Autreto
Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes Journal Article
Em: Nature Communications, vol. 6, pp. 7291, 2015.
@article{Kabbani2015,
title = {Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes},
author = {Mohamad A Kabbani, Chandra Sekhar Tiwary, Pedro AS Autreto, Gustavo Brunetto, Anirban Som, KR Krishnadas, Sehmus Ozden, Ken P Hackenberg, Yongi Gong, Douglas S Galvao, Robert Vajtai, Ahmad T Kabbani, Thalappil Pradeep, Pulickel M Ajayan},
url = {http://www.nature.com/ncomms/2015/150615/ncomms8291/full/ncomms8291.html},
doi = {10.1038/ncomms8291},
year = {2015},
date = {2015-06-15},
journal = {Nature Communications},
volume = {6},
pages = {7291},
abstract = {Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.
4.
Vinod, Soumya; Tiwary, Chandra Sekhar; da Silva Autreto, Pedro Alves; Taha-Tijerina, Jaime; Ozden, Sehmus; Chipara, Alin Cristian; Vajtai, Robert; Galvao, Douglas S; Narayanan, Tharangattu N; Ajayan, Pulickel M
Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers Journal Article
Em: Nature Communications, vol. 5, 2014.
@article{vinod2014low,
title = {Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers},
author = {Vinod, Soumya and Tiwary, Chandra Sekhar and da Silva Autreto, Pedro Alves and Taha-Tijerina, Jaime and Ozden, Sehmus and Chipara, Alin Cristian and Vajtai, Robert and Galvao, Douglas S and Narayanan, Tharangattu N and Ajayan, Pulickel M},
url = {http://www.nature.com/ncomms/2014/140729/ncomms5541/full/ncomms5541.html},
year = {2014},
date = {2014-01-01},
journal = {Nature Communications},
volume = {5},
publisher = {Nature Publishing Group},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
5.
SB Legoas LD Machado, JS Soares
Dynamics of the formation of carbon nanotube serpentines Journal Article
Em: Physical Review Letters, vol. 110, não 10, pp. 105502, 2013.
@article{machado2013dynamics,
title = {Dynamics of the formation of carbon nanotube serpentines},
author = {LD Machado, SB Legoas, JS Soares, N Shadmi, A Jorio, E Joselevich, DS Galvão},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.105502},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {110},
number = {10},
pages = {105502},
publisher = {American Physical Society},
abstract = {Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] reported the experimental realization of carbon nanotube S-like shaped nanostructures, the so-called carbon nanotube serpentines. We report here results from multimillion fully atomistic molecular dynamics simulations of their formation. We consider one-μm-long carbon nanotubes placed on stepped substrates with and without a catalyst nanoparticle on the top free end of the tube. A force is applied to the upper part of the tube during a short period of time and turned off; then the system is set free to evolve in time. Our results show that these conditions are sufficient to form robust serpentines and validates the general features of the “falling spaghetti model” proposed to explain their formation.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] reported the experimental realization of carbon nanotube S-like shaped nanostructures, the so-called carbon nanotube serpentines. We report here results from multimillion fully atomistic molecular dynamics simulations of their formation. We consider one-μm-long carbon nanotubes placed on stepped substrates with and without a catalyst nanoparticle on the top free end of the tube. A force is applied to the upper part of the tube during a short period of time and turned off; then the system is set free to evolve in time. Our results show that these conditions are sufficient to form robust serpentines and validates the general features of the “falling spaghetti model” proposed to explain their formation.
6.
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
Em: Science, vol. 338, não 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.
7.
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
Em: Physical Review Letters, vol. 106, não 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.
8.
Lagos, MJ; Sato, Fernando; Bettini, Jeferson; Rodrigues, Varlei; Galvao, Douglas S; Ugarte, Daniel
Observation of the smallest metal nanotube with a square cross-section Journal Article
Em: Nature Nanotechnology, vol. 4, não 3, pp. 149–152, 2009.
@article{lagos2009observation,
title = {Observation of the smallest metal nanotube with a square cross-section},
author = {Lagos, MJ and Sato, Fernando and Bettini, Jeferson and Rodrigues, Varlei and Galvao, Douglas S and Ugarte, Daniel},
url = {http://www.nature.com/nnano/journal/v4/n3/abs/nnano.2008.414.html},
year = {2009},
date = {2009-01-01},
journal = {Nature Nanotechnology},
volume = {4},
number = {3},
pages = {149--152},
publisher = {Nature Publishing Group},
abstract = {Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms1, 2, 3 and helical wires4, 5 have been produced by stretching metal junctions. Here, we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms1, 2, 3 and helical wires4, 5 have been produced by stretching metal junctions. Here, we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation.
9.
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
Em: Physical Review Letters, vol. 100, não 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.
10.
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
Em: Science, vol. 320, não 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.
11.
Rodrigues, V; Sato, F; Galvao, DS; Ugarte, D
Size limit of defect formation in pyramidal Pt nanocontacts Journal Article
Em: Physical Review Letters, vol. 99, não 25, pp. 255501, 2007.
@article{rodrigues2007size,
title = {Size limit of defect formation in pyramidal Pt nanocontacts},
author = {Rodrigues, V and Sato, F and Galvao, DS and Ugarte, D},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.99.255501},
year = {2007},
date = {2007-01-01},
journal = {Physical Review Letters},
volume = {99},
number = {25},
pages = {255501},
publisher = {American Physical Society},
abstract = {We report high resolution transmission electron microscopy and ab initio calculation results for defect formation in sharp pyramidal Pt nanocontacts. Our results show that there is a size limit to the existence of twins (extended structural defects). These defects are always present but blocked away from the tip axes. They may act as scattering planes, influencing the electron conductance for Pt nanocontacts at room temperature and Ag/Au nanocontacts at low temperature (<150 K).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report high resolution transmission electron microscopy and ab initio calculation results for defect formation in sharp pyramidal Pt nanocontacts. Our results show that there is a size limit to the existence of twins (extended structural defects). These defects are always present but blocked away from the tip axes. They may act as scattering planes, influencing the electron conductance for Pt nanocontacts at room temperature and Ag/Au nanocontacts at low temperature (<150 K).
12.
Bettini, Jefferson; Sato, Fernando; Coura, Pablo Zimmerman; Dantas, SO; Galvao, Douglas Soares; Ugarte, Daniel
Experimental realization of suspended atomic chains composed of different atomic species Journal Article
Em: Nature Nanotechnology, vol. 1, não 3, pp. 182–185, 2006.
@article{bettini2006experimental,
title = {Experimental realization of suspended atomic chains composed of different atomic species},
author = {Bettini, Jefferson and Sato, Fernando and Coura, Pablo Zimmerman and Dantas, SO and Galvao, Douglas Soares and Ugarte, Daniel},
url = {http://www.nature.com/nnano/journal/v1/n3/full/nnano.2006.132.html},
year = {2006},
date = {2006-01-01},
journal = {Nature Nanotechnology},
volume = {1},
number = {3},
pages = {182--185},
publisher = {Nature Publishing Group},
abstract = {Research into nanostructured materials frequently relates to pure substances. This contrasts with industrial applications, where chemical doping or alloying is often used to enhance the electrical or mechanical properties of materials1. However, the controlled preparation of doped nanomaterials has been much more difficult than expected because the increased surface-area-to-volume ratio can, for instance, lead to the expulsion of impurities (self-purification)2. For nanostructured alloys, the influence of growth methods and the atomic structure on self-purification is still open to investigation2, 3. Here, we explore, experimentally and with molecular dynamics simulations, to what extent alloying persists in the limit that a binary metal is mechanically stretched to a linear chain of atoms. Our results reveal a gradual evolution of the arrangement of the different atomic elements in the narrowest region of the chain, where impurities may be expelled to the surface or enclosed during elongation.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Research into nanostructured materials frequently relates to pure substances. This contrasts with industrial applications, where chemical doping or alloying is often used to enhance the electrical or mechanical properties of materials1. However, the controlled preparation of doped nanomaterials has been much more difficult than expected because the increased surface-area-to-volume ratio can, for instance, lead to the expulsion of impurities (self-purification)2. For nanostructured alloys, the influence of growth methods and the atomic structure on self-purification is still open to investigation2, 3. Here, we explore, experimentally and with molecular dynamics simulations, to what extent alloying persists in the limit that a binary metal is mechanically stretched to a linear chain of atoms. Our results reveal a gradual evolution of the arrangement of the different atomic elements in the narrowest region of the chain, where impurities may be expelled to the surface or enclosed during elongation.
13.
Campos, Paulo RA; de Oliveira, Viviane M; Giro, Ronaldo; Galvao, Douglas S
Emergence of prime numbers as the result of evolutionary strategy Journal Article
Em: Physical Review Letters, vol. 93, não 9, pp. 098107, 2004.
@article{campos2004emergence,
title = {Emergence of prime numbers as the result of evolutionary strategy},
author = {Campos, Paulo RA and de Oliveira, Viviane M and Giro, Ronaldo and Galvao, Douglas S},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.098107},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {9},
pages = {098107},
publisher = {American Physical Society},
abstract = {We investigate by means of a simple theoretical model the emergence of prime numbers as life cycles, as those seen for some species of cicadas. The cicadas, more precisely the Magicicadas, spend most of their lives below the ground and then emerge and die in a short period of time. The Magicicadas display an uncommon behavior: their emergence is synchronized and these periods are usually prime numbers. In the current work, we develop a spatially extended model at which preys and predators coexist and can change their evolutionary dynamics through the occurrence of mutations. We verified that prime numbers as life cycles emerge as a result of the evolution of the population. Our results seem to be a first step in order to prove that the development of such strategy is selectively advantageous, especially for those organisms that are highly vulnerable to attacks of predators.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We investigate by means of a simple theoretical model the emergence of prime numbers as life cycles, as those seen for some species of cicadas. The cicadas, more precisely the Magicicadas, spend most of their lives below the ground and then emerge and die in a short period of time. The Magicicadas display an uncommon behavior: their emergence is synchronized and these periods are usually prime numbers. In the current work, we develop a spatially extended model at which preys and predators coexist and can change their evolutionary dynamics through the occurrence of mutations. We verified that prime numbers as life cycles emerge as a result of the evolution of the population. Our results seem to be a first step in order to prove that the development of such strategy is selectively advantageous, especially for those organisms that are highly vulnerable to attacks of predators.
14.
Legoas, Sergio B; Rodrigues, Varlei; Ugarte, Daniel; Galvao, Douglas S
Contaminants in suspended gold chains: An ab initio molecular dynamics study Journal Article
Em: Physical Review Letters, vol. 93, não 21, pp. 216103, 2004.
@article{legoas2004contaminants,
title = {Contaminants in suspended gold chains: An ab initio molecular dynamics study},
author = {Legoas, Sergio B and Rodrigues, Varlei and Ugarte, Daniel and Galvao, Douglas S},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.216103},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {21},
pages = {216103},
publisher = {American Physical Society},
abstract = {Recently, we have proposed that the origin of anomalously long interatomic distances in suspended gold chains could be the result of carbon contamination during sample manipulation [S. B. Legoas et al., Phys. Rev. Lett. 88, 076105 (2002)]. More recently, however, other works have proposed that hydrogen instead of carbon should be the most probable contaminant. We report ab initio molecular dynamics results for different temperatures considering different possible contaminants. Our results show that at nonzero temperatures (more realistic to simulate the experimental conditions) hydrogen may be ruled out and carbon atoms remain the best candidate for contamination.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, we have proposed that the origin of anomalously long interatomic distances in suspended gold chains could be the result of carbon contamination during sample manipulation [S. B. Legoas et al., Phys. Rev. Lett. 88, 076105 (2002)]. More recently, however, other works have proposed that hydrogen instead of carbon should be the most probable contaminant. We report ab initio molecular dynamics results for different temperatures considering different possible contaminants. Our results show that at nonzero temperatures (more realistic to simulate the experimental conditions) hydrogen may be ruled out and carbon atoms remain the best candidate for contamination.
15.
Gonzalez, JC; Rodrigues, V; Bettini, J; Rego, LGC; Rocha, AR; Coura, PZ; Dantas, SO; Sato, F; Galvao, DS; Ugarte, D
Indication of unusual pentagonal structures in atomic-size Cu nanowires Journal Article
Em: Physical Review Letters, vol. 93, não 12, pp. 126103, 2004.
@article{gonzalez2004indication,
title = {Indication of unusual pentagonal structures in atomic-size Cu nanowires},
author = {Gonzalez, JC and Rodrigues, V and Bettini, J and Rego, LGC and Rocha, AR and Coura, PZ and Dantas, SO and Sato, F and Galvao, DS and Ugarte, D},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.126103},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {12},
pages = {126103},
publisher = {APS},
abstract = {We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of ∼0.45 nm and ∼4.5 conductance quanta.
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of ∼0.45 nm and ∼4.5 conductance quanta.
16.
Otero, Roberto; Hummelink, Frauke; Sato, Fernando; Legoas, Sergio B; Thostrup, Peter; Lægsgaard, Erik; Stensgaard, Ivan; Galvao, Douglas S; Besenbacher, Flemming
Lock-and-key effect in the surface diffusion of large organic molecules probed by STM Journal Article
Em: Nature Materials, vol. 3, não 11, pp. 779–782, 2004.
@article{otero2004lock,
title = {Lock-and-key effect in the surface diffusion of large organic molecules probed by STM},
author = {Otero, Roberto and Hummelink, Frauke and Sato, Fernando and Legoas, Sergio B and Thostrup, Peter and Lægsgaard, Erik and Stensgaard, Ivan and Galvao, Douglas S and Besenbacher, Flemming},
url = {http://www.nature.com/nmat/journal/v3/n11/full/nmat1243.html},
year = {2004},
date = {2004-01-01},
journal = {Nature Materials},
volume = {3},
number = {11},
pages = {779--782},
publisher = {Nature Publishing Group},
abstract = {A nanoscale understanding of the complex dynamics of large molecules at surfaces is essential for the bottom-up design of molecular nanostructures1, 2, 3, 4, 5, 6, 7, 8. Here we show that we can change the diffusion coefficient of the complex organic molecule known as Violet Lander (VL, C108H104) on Cu(110) by two orders of magnitude by using the STM at low temperatures to switch between two adsorption configurations that differ only in the molecular orientation with respect to the substrate lattice. From an interplay with molecular dynamics simulations, we interpret the results within a lock-and-key model similar to the one driving the recognition between biomolecules: the molecule (key) is immobilized only when its orientation is such that the molecular shape fits the atomic lattice of the surface (lock); otherwise the molecule is highly mobile.
Introduction
},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
A nanoscale understanding of the complex dynamics of large molecules at surfaces is essential for the bottom-up design of molecular nanostructures1, 2, 3, 4, 5, 6, 7, 8. Here we show that we can change the diffusion coefficient of the complex organic molecule known as Violet Lander (VL, C108H104) on Cu(110) by two orders of magnitude by using the STM at low temperatures to switch between two adsorption configurations that differ only in the molecular orientation with respect to the substrate lattice. From an interplay with molecular dynamics simulations, we interpret the results within a lock-and-key model similar to the one driving the recognition between biomolecules: the molecule (key) is immobilized only when its orientation is such that the molecular shape fits the atomic lattice of the surface (lock); otherwise the molecule is highly mobile.
Introduction
Introduction
17.
VR Coluci SB Legoas, SF Braga
Molecular-dynamics simulations of carbon nanotubes as gigahertz oscillators Journal Article
Em: Physical Review Letters, vol. 90, não 5, pp. 055504, 2003.
@article{legoas2003molecularb,
title = {Molecular-dynamics simulations of carbon nanotubes as gigahertz oscillators},
author = {SB Legoas, VR Coluci, SF Braga, PZ Coura, SO Dantas, DS Galvao},
year = {2003},
date = {2003-01-01},
journal = {Physical Review Letters},
volume = {90},
number = {5},
pages = {055504},
abstract = {Recently, Zheng and Jiang [Phys. Rev. Lett. 88, 045503 (2002)] have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nano-oscillators in the several gigahertz range. In this Letter, we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nano-oscillators are dynamically stable when the radii difference values between inner and outer tubes are of ∼3.4 Å. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recently, Zheng and Jiang [Phys. Rev. Lett. 88, 045503 (2002)] have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nano-oscillators in the several gigahertz range. In this Letter, we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nano-oscillators are dynamically stable when the radii difference values between inner and outer tubes are of ∼3.4 Å. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations.
18.
Legoas, Sergio B; Galvao, Douglas S; Rodrigues, Varlei; Ugarte, Daniel
Origin of anomalously long interatomic distances in suspended gold chains Journal Article
Em: Physical Review Letters, vol. 88, não 7, pp. 076105, 2002.
@article{legoas2002origin,
title = {Origin of anomalously long interatomic distances in suspended gold chains},
author = {Legoas, Sergio B and Galvao, Douglas S and Rodrigues, Varlei and Ugarte, Daniel},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.88.076105},
year = {2002},
date = {2002-01-01},
journal = {Physical Review Letters},
volume = {88},
number = {7},
pages = {076105},
publisher = {American Physical Society},
abstract = {The discovery of long bonds in gold atom chains has represented a challenge for physical interpretation. In fact, interatomic distances frequently attain 3.0–3.6 Å values, and distances as large as 5.0 Å may be occasionally observed. Here we studied gold chains by transmission electron microscopy and performed theoretical calculations using cluster ab initio density functional formalism. We show that the insertion of two carbon atoms is required to account for the longest bonds, while distances above 3 Å may be due to a mixture of clean and one C atom contaminated bonds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The discovery of long bonds in gold atom chains has represented a challenge for physical interpretation. In fact, interatomic distances frequently attain 3.0–3.6 Å values, and distances as large as 5.0 Å may be occasionally observed. Here we studied gold chains by transmission electron microscopy and performed theoretical calculations using cluster ab initio density functional formalism. We show that the insertion of two carbon atoms is required to account for the longest bonds, while distances above 3 Å may be due to a mixture of clean and one C atom contaminated bonds.
19.
A Camilo Jr PMVB Barone, DS Galvao
Theoretical approach to identify carcinogenic activity of polycyclic aromatic hydrocarbons Journal Article
Em: Physical Review Letters, vol. 77, não 6, pp. 1186, 1996.
@article{barone1996theoretical,
title = {Theoretical approach to identify carcinogenic activity of polycyclic aromatic hydrocarbons},
author = {PMVB Barone, A Camilo Jr, DS Galvao},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.77.1186},
doi = {10.1103/PhysRevLett.77.1186},
year = {1996},
date = {1996-01-01},
journal = {Physical Review Letters},
volume = {77},
number = {6},
pages = {1186},
publisher = {American Physical Society},
abstract = {Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules that can induce chemical carcinogenesis. Their carcinogenic powers vary in a large range, from the very strong carcinogens to the inactive ones. Many models have been proposed to explain the PAHs' carcinogenic activity, but all of them present some failures. Here we introduce a new methodology to identify PAHs' carcinogenic activity based on the concept of electronic local density of states (LDOS). We show that the analysis of the molecular energy levels in association with the LDOS calculated over the ring which contains the highest bond order of the molecule allows simple rules to identify whether a specific PAH molecule will present (or not) carcinogenic activity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules that can induce chemical carcinogenesis. Their carcinogenic powers vary in a large range, from the very strong carcinogens to the inactive ones. Many models have been proposed to explain the PAHs' carcinogenic activity, but all of them present some failures. Here we introduce a new methodology to identify PAHs' carcinogenic activity based on the concept of electronic local density of states (LDOS). We show that the analysis of the molecular energy levels in association with the LDOS calculated over the ring which contains the highest bond order of the molecule allows simple rules to identify whether a specific PAH molecule will present (or not) carcinogenic activity.
20.
Baughman, RH; Galvao, DS
Crystalline networks with unusual predicted mechanical and thermal properties Journal Article
Em: Nature, vol. 365, não 6448, pp. 735–737, 1993.
@article{baughman1993crystalline,
title = {Crystalline networks with unusual predicted mechanical and thermal properties},
author = {RH Baughman and DS Galvao},
url = {http://www.nature.com/nature/journal/v365/n6448/abs/365735a0.html},
doi = {10.1038/365735a0},
year = {1993},
date = {1993-01-01},
journal = {Nature},
volume = {365},
number = {6448},
pages = {735--737},
publisher = {Nature Publishing Group},
abstract = {Most materials shrink laterally and become less dense when stretched. Materials that both expand laterally (that is, have negative Poisson's ratio) and densify when stretched are of interest both from the fundamental and the practical points of view1–5. A few monocrystalline phases with negative Poisson's ratio are known3,4, but these do not densify when stretched. Here we present molecular-mechanics calculations for some hypothetical phases of carbon which exhibit both kinds of behaviour. The properties derive from the presence of bonds that act as hinges in extended helical chains. Other unusual properties of these phases include negative thermal expansion, dopant-controlled porosity and low-temperature polymorphism. Such structures can be envisaged for polyacetylene, polydiacetylene, polyphenylene and (BN)x phases, as well as for variants of some known, structurally related inorganic phases.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Most materials shrink laterally and become less dense when stretched. Materials that both expand laterally (that is, have negative Poisson's ratio) and densify when stretched are of interest both from the fundamental and the practical points of view1–5. A few monocrystalline phases with negative Poisson's ratio are known3,4, but these do not densify when stretched. Here we present molecular-mechanics calculations for some hypothetical phases of carbon which exhibit both kinds of behaviour. The properties derive from the presence of bonds that act as hinges in extended helical chains. Other unusual properties of these phases include negative thermal expansion, dopant-controlled porosity and low-temperature polymorphism. Such structures can be envisaged for polyacetylene, polydiacetylene, polyphenylene and (BN)x phases, as well as for variants of some known, structurally related inorganic phases.
2016
20.
Xifan Wang Sidong Lei, Bo Li
Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry Journal Article
Em: Nature Nanotechnology, vol. 11, pp. 465–471, 2016.
Resumo | Links | BibTeX | Tags: Chalcogenides, Modelling, Synthesis, top20
@article{Lei2016,
title = {Surface functionalization of two-dimensional metal chalcogenides by Lewis acid–base chemistry},
author = {Sidong Lei, Xifan Wang, Bo Li, Jiahao Kang, Yongmin He, Antony George, Liehui Ge, Yongji Gong, Pei Dong, Zehua Jin, Gustavo Brunetto, Weibing Chen, Zuan-Tao Lin, Robert Baines, Douglas S. Galvão, Jun Lou, Enrique Barrera, Kaustav Banerjee, Robert Vajtai & Pulickel Ajayan},
url = {http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.323.html},
doi = {10.1038/nnano.2015.323},
year = {2016},
date = {2016-02-01},
journal = {Nature Nanotechnology},
volume = {11},
pages = {465–471},
abstract = {Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid–base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p–n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid–base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.
},
keywords = {Chalcogenides, Modelling, Synthesis, top20},
pubstate = {published},
tppubtype = {article}
}
Precise control of the electronic surface states of two-dimensional (2D) materials could improve their versatility and widen their applicability in electronics and sensing. To this end, chemical surface functionalization has been used to adjust the electronic properties of 2D materials. So far, however, chemical functionalization has relied on lattice defects and physisorption methods that inevitably modify the topological characteristics of the atomic layers. Here we make use of the lone pair electrons found in most of 2D metal chalcogenides and report a functionalization method via a Lewis acid–base reaction that does not alter the host structure. Atomic layers of n-type InSe react with Ti4+ to form planar p-type [Ti4+n(InSe)] coordination complexes. Using this strategy, we fabricate planar p–n junctions on 2D InSe with improved rectification and photovoltaic properties, without requiring heterostructure growth procedures or device fabrication processes. We also show that this functionalization approach works with other Lewis acids (such as B3+, Al3+ and Sn4+) and can be applied to other 2D materials (for example MoS2, MoSe2). Finally, we show that it is possible to use Lewis acid–base chemistry as a bridge to connect molecules to 2D atomic layers and fabricate a proof-of-principle dye-sensitized photosensing device.
2015
19.
S Fang ZF Liu, FA Moura
Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles Journal Article
Em: Science, vol. 349, não 6246, pp. 404-404, 2015.
Resumo | Links | BibTeX | Tags: Carbon Nanotube Forests, Finite Elements, Superelastic, top20
@article{Liu2015,
title = {Hierarchically buckled sheath-core fibers for superelastic electronics, sensors, and muscles},
author = {ZF Liu, S Fang, FA Moura, JN Ding, N Jiang, J Di, M Zhang, X Lepró, DS Galvão, CS Haines, NY Yuan, SG Yin, DW Lee, R Wang, HY Wang, W Lv, C Dong, RC Zhang, MJ Chen, Q Yin, YT Chong, R Zhang, X Wang, MD Lima, R Ovalle-Robles, D Qian, H Lu, RH Baughman},
url = {http://www.sciencemag.org/content/349/6246/400.full.pdf},
doi = {10.1126/science.aaa7952},
year = {2015},
date = {2015-07-24},
journal = {Science},
volume = {349},
number = {6246},
pages = {404-404},
abstract = {Superelastic conducting fibers with improved properties and functionalities are needed
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.},
keywords = {Carbon Nanotube Forests, Finite Elements, Superelastic, top20},
pubstate = {published},
tppubtype = {article}
}
Superelastic conducting fibers with improved properties and functionalities are needed
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.
for diverse applications. Here we report the fabrication of highly stretchable (up to 1320%)
sheath-core conducting fibers created by wrapping carbon nanotube sheets oriented in
the fiber direction on stretched rubber fiber cores. The resulting structure exhibited
distinct short- and long-period sheath buckling that occurred reversibly out of phase
in the axial and belt directions, enabling a resistance change of less than 5% for a
1000% stretch. By including other rubber and carbon nanotube sheath layers, we
demonstrated strain sensors generating an 860% capacitance change and electrically
powered torsional muscles operating reversibly by a coupled tension-to-torsion
actuation mechanism. Using theory, we quantitatively explain the complementary effects
of an increase in muscle length and a large positive Poisson’s ratio on torsional actuation
and electronic properties.
18.
Chandra Sekhar Tiwary Mohamad A Kabbani, Pedro AS Autreto
Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes Journal Article
Em: Nature Communications, vol. 6, pp. 7291, 2015.
Resumo | Links | BibTeX | Tags: Carbon Nanotubes, Chemical Reactions, Electronic Structure, Molecular Dynamics, top20
@article{Kabbani2015,
title = {Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes},
author = {Mohamad A Kabbani, Chandra Sekhar Tiwary, Pedro AS Autreto, Gustavo Brunetto, Anirban Som, KR Krishnadas, Sehmus Ozden, Ken P Hackenberg, Yongi Gong, Douglas S Galvao, Robert Vajtai, Ahmad T Kabbani, Thalappil Pradeep, Pulickel M Ajayan},
url = {http://www.nature.com/ncomms/2015/150615/ncomms8291/full/ncomms8291.html},
doi = {10.1038/ncomms8291},
year = {2015},
date = {2015-06-15},
journal = {Nature Communications},
volume = {6},
pages = {7291},
abstract = {Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.},
keywords = {Carbon Nanotubes, Chemical Reactions, Electronic Structure, Molecular Dynamics, top20},
pubstate = {published},
tppubtype = {article}
}
Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.
2014
17.
Vinod, Soumya; Tiwary, Chandra Sekhar; da Silva Autreto, Pedro Alves; Taha-Tijerina, Jaime; Ozden, Sehmus; Chipara, Alin Cristian; Vajtai, Robert; Galvao, Douglas S; Narayanan, Tharangattu N; Ajayan, Pulickel M
Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers Journal Article
Em: Nature Communications, vol. 5, 2014.
Links | BibTeX | Tags: foams, Fracture, Graphene, Mechanical Properties, top20
@article{vinod2014low,
title = {Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers},
author = {Vinod, Soumya and Tiwary, Chandra Sekhar and da Silva Autreto, Pedro Alves and Taha-Tijerina, Jaime and Ozden, Sehmus and Chipara, Alin Cristian and Vajtai, Robert and Galvao, Douglas S and Narayanan, Tharangattu N and Ajayan, Pulickel M},
url = {http://www.nature.com/ncomms/2014/140729/ncomms5541/full/ncomms5541.html},
year = {2014},
date = {2014-01-01},
journal = {Nature Communications},
volume = {5},
publisher = {Nature Publishing Group},
keywords = {foams, Fracture, Graphene, Mechanical Properties, top20},
pubstate = {published},
tppubtype = {article}
}
2013
16.
SB Legoas LD Machado, JS Soares
Dynamics of the formation of carbon nanotube serpentines Journal Article
Em: Physical Review Letters, vol. 110, não 10, pp. 105502, 2013.
Resumo | Links | BibTeX | Tags: Carbon Nanotubes, Molecular Dynamics, Serpentines, top20
@article{machado2013dynamics,
title = {Dynamics of the formation of carbon nanotube serpentines},
author = {LD Machado, SB Legoas, JS Soares, N Shadmi, A Jorio, E Joselevich, DS Galvão},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.110.105502},
year = {2013},
date = {2013-01-01},
journal = {Physical Review Letters},
volume = {110},
number = {10},
pages = {105502},
publisher = {American Physical Society},
abstract = {Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] reported the experimental realization of carbon nanotube S-like shaped nanostructures, the so-called carbon nanotube serpentines. We report here results from multimillion fully atomistic molecular dynamics simulations of their formation. We consider one-μm-long carbon nanotubes placed on stepped substrates with and without a catalyst nanoparticle on the top free end of the tube. A force is applied to the upper part of the tube during a short period of time and turned off; then the system is set free to evolve in time. Our results show that these conditions are sufficient to form robust serpentines and validates the general features of the “falling spaghetti model” proposed to explain their formation.
},
keywords = {Carbon Nanotubes, Molecular Dynamics, Serpentines, top20},
pubstate = {published},
tppubtype = {article}
}
Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] reported the experimental realization of carbon nanotube S-like shaped nanostructures, the so-called carbon nanotube serpentines. We report here results from multimillion fully atomistic molecular dynamics simulations of their formation. We consider one-μm-long carbon nanotubes placed on stepped substrates with and without a catalyst nanoparticle on the top free end of the tube. A force is applied to the upper part of the tube during a short period of time and turned off; then the system is set free to evolve in time. Our results show that these conditions are sufficient to form robust serpentines and validates the general features of the “falling spaghetti model” proposed to explain their formation.
2012
15.
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
Em: Science, vol. 338, não 6109, pp. 928–932, 2012.
Resumo | Links | BibTeX | Tags: Actuation, Artificial Muscles, Carbon Nanotubes, top20, Yarns
@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 = {Actuation, Artificial Muscles, Carbon Nanotubes, top20, Yarns},
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.
2011
14.
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
Em: Physical Review Letters, vol. 106, não 6, pp. 065501, 2011.
Resumo | Links | BibTeX | Tags: DFT, Mechanical Properties, Metallic Nanowires, New Structures, top20
@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 = {DFT, Mechanical Properties, Metallic Nanowires, New Structures, top20},
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.
2009
13.
Lagos, MJ; Sato, Fernando; Bettini, Jeferson; Rodrigues, Varlei; Galvao, Douglas S; Ugarte, Daniel
Observation of the smallest metal nanotube with a square cross-section Journal Article
Em: Nature Nanotechnology, vol. 4, não 3, pp. 149–152, 2009.
Resumo | Links | BibTeX | Tags: Metallic Nanowires, New Structures, Smallest nanotube, TEM, top20
@article{lagos2009observation,
title = {Observation of the smallest metal nanotube with a square cross-section},
author = {Lagos, MJ and Sato, Fernando and Bettini, Jeferson and Rodrigues, Varlei and Galvao, Douglas S and Ugarte, Daniel},
url = {http://www.nature.com/nnano/journal/v4/n3/abs/nnano.2008.414.html},
year = {2009},
date = {2009-01-01},
journal = {Nature Nanotechnology},
volume = {4},
number = {3},
pages = {149--152},
publisher = {Nature Publishing Group},
abstract = {Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms1, 2, 3 and helical wires4, 5 have been produced by stretching metal junctions. Here, we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation.},
keywords = {Metallic Nanowires, New Structures, Smallest nanotube, TEM, top20},
pubstate = {published},
tppubtype = {article}
}
Understanding the mechanical properties of nanoscale systems requires a range of measurement techniques and theoretical approaches to gather the relevant physical and chemical information. The arrangements of atoms in nanostructures and macroscopic matter can be different, principally due to the role of surface energy, but the interplay between atomic and electronic structure in association with applied mechanical stress can also lead to surprising differences. For example, metastable structures such as suspended chains of atoms1, 2, 3 and helical wires4, 5 have been produced by stretching metal junctions. Here, we report the spontaneous formation of the smallest possible metal nanotube with a square cross-section during the elongation of silver nanocontacts. Ab initio calculations and molecular simulations indicate that the hollow wire forms because this configuration allows the surface energy to be minimized, and also generates a soft structure capable of absorbing a huge tensile deformation.
2008
12.
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
Em: Physical Review Letters, vol. 100, não 8, pp. 086807, 2008.
Resumo | Links | BibTeX | Tags: Carbon Nanotube Forests, Entanglement, Mechanical Properties, top20
@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 = {Carbon Nanotube Forests, Entanglement, Mechanical Properties, top20},
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.
11.
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
Em: Science, vol. 320, não 5875, pp. 504–507, 2008.
Resumo | Links | BibTeX | Tags: Artificial Muscles, Auxetics, Carbon Nanotube Forests, sheets, top20
@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 = {Artificial Muscles, Auxetics, Carbon Nanotube Forests, sheets, top20},
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.
2007
10.
Rodrigues, V; Sato, F; Galvao, DS; Ugarte, D
Size limit of defect formation in pyramidal Pt nanocontacts Journal Article
Em: Physical Review Letters, vol. 99, não 25, pp. 255501, 2007.
Resumo | Links | BibTeX | Tags: DFT, Metallic Nanowires, Platinum, Structure, TEM, top20
@article{rodrigues2007size,
title = {Size limit of defect formation in pyramidal Pt nanocontacts},
author = {Rodrigues, V and Sato, F and Galvao, DS and Ugarte, D},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.99.255501},
year = {2007},
date = {2007-01-01},
journal = {Physical Review Letters},
volume = {99},
number = {25},
pages = {255501},
publisher = {American Physical Society},
abstract = {We report high resolution transmission electron microscopy and ab initio calculation results for defect formation in sharp pyramidal Pt nanocontacts. Our results show that there is a size limit to the existence of twins (extended structural defects). These defects are always present but blocked away from the tip axes. They may act as scattering planes, influencing the electron conductance for Pt nanocontacts at room temperature and Ag/Au nanocontacts at low temperature (<150 K).},
keywords = {DFT, Metallic Nanowires, Platinum, Structure, TEM, top20},
pubstate = {published},
tppubtype = {article}
}
We report high resolution transmission electron microscopy and ab initio calculation results for defect formation in sharp pyramidal Pt nanocontacts. Our results show that there is a size limit to the existence of twins (extended structural defects). These defects are always present but blocked away from the tip axes. They may act as scattering planes, influencing the electron conductance for Pt nanocontacts at room temperature and Ag/Au nanocontacts at low temperature (<150 K).
2006
9.
Bettini, Jefferson; Sato, Fernando; Coura, Pablo Zimmerman; Dantas, SO; Galvao, Douglas Soares; Ugarte, Daniel
Experimental realization of suspended atomic chains composed of different atomic species Journal Article
Em: Nature Nanotechnology, vol. 1, não 3, pp. 182–185, 2006.
Resumo | Links | BibTeX | Tags: Metallic Nanowires, Molecular Dynamics, TEM, top20
@article{bettini2006experimental,
title = {Experimental realization of suspended atomic chains composed of different atomic species},
author = {Bettini, Jefferson and Sato, Fernando and Coura, Pablo Zimmerman and Dantas, SO and Galvao, Douglas Soares and Ugarte, Daniel},
url = {http://www.nature.com/nnano/journal/v1/n3/full/nnano.2006.132.html},
year = {2006},
date = {2006-01-01},
journal = {Nature Nanotechnology},
volume = {1},
number = {3},
pages = {182--185},
publisher = {Nature Publishing Group},
abstract = {Research into nanostructured materials frequently relates to pure substances. This contrasts with industrial applications, where chemical doping or alloying is often used to enhance the electrical or mechanical properties of materials1. However, the controlled preparation of doped nanomaterials has been much more difficult than expected because the increased surface-area-to-volume ratio can, for instance, lead to the expulsion of impurities (self-purification)2. For nanostructured alloys, the influence of growth methods and the atomic structure on self-purification is still open to investigation2, 3. Here, we explore, experimentally and with molecular dynamics simulations, to what extent alloying persists in the limit that a binary metal is mechanically stretched to a linear chain of atoms. Our results reveal a gradual evolution of the arrangement of the different atomic elements in the narrowest region of the chain, where impurities may be expelled to the surface or enclosed during elongation.
},
keywords = {Metallic Nanowires, Molecular Dynamics, TEM, top20},
pubstate = {published},
tppubtype = {article}
}
Research into nanostructured materials frequently relates to pure substances. This contrasts with industrial applications, where chemical doping or alloying is often used to enhance the electrical or mechanical properties of materials1. However, the controlled preparation of doped nanomaterials has been much more difficult than expected because the increased surface-area-to-volume ratio can, for instance, lead to the expulsion of impurities (self-purification)2. For nanostructured alloys, the influence of growth methods and the atomic structure on self-purification is still open to investigation2, 3. Here, we explore, experimentally and with molecular dynamics simulations, to what extent alloying persists in the limit that a binary metal is mechanically stretched to a linear chain of atoms. Our results reveal a gradual evolution of the arrangement of the different atomic elements in the narrowest region of the chain, where impurities may be expelled to the surface or enclosed during elongation.
2004
8.
Campos, Paulo RA; de Oliveira, Viviane M; Giro, Ronaldo; Galvao, Douglas S
Emergence of prime numbers as the result of evolutionary strategy Journal Article
Em: Physical Review Letters, vol. 93, não 9, pp. 098107, 2004.
Resumo | Links | BibTeX | Tags: Cellular Automata, Cicadas, Patterns, Prime Numbers, top20
@article{campos2004emergence,
title = {Emergence of prime numbers as the result of evolutionary strategy},
author = {Campos, Paulo RA and de Oliveira, Viviane M and Giro, Ronaldo and Galvao, Douglas S},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.098107},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {9},
pages = {098107},
publisher = {American Physical Society},
abstract = {We investigate by means of a simple theoretical model the emergence of prime numbers as life cycles, as those seen for some species of cicadas. The cicadas, more precisely the Magicicadas, spend most of their lives below the ground and then emerge and die in a short period of time. The Magicicadas display an uncommon behavior: their emergence is synchronized and these periods are usually prime numbers. In the current work, we develop a spatially extended model at which preys and predators coexist and can change their evolutionary dynamics through the occurrence of mutations. We verified that prime numbers as life cycles emerge as a result of the evolution of the population. Our results seem to be a first step in order to prove that the development of such strategy is selectively advantageous, especially for those organisms that are highly vulnerable to attacks of predators.},
keywords = {Cellular Automata, Cicadas, Patterns, Prime Numbers, top20},
pubstate = {published},
tppubtype = {article}
}
We investigate by means of a simple theoretical model the emergence of prime numbers as life cycles, as those seen for some species of cicadas. The cicadas, more precisely the Magicicadas, spend most of their lives below the ground and then emerge and die in a short period of time. The Magicicadas display an uncommon behavior: their emergence is synchronized and these periods are usually prime numbers. In the current work, we develop a spatially extended model at which preys and predators coexist and can change their evolutionary dynamics through the occurrence of mutations. We verified that prime numbers as life cycles emerge as a result of the evolution of the population. Our results seem to be a first step in order to prove that the development of such strategy is selectively advantageous, especially for those organisms that are highly vulnerable to attacks of predators.
7.
Legoas, Sergio B; Rodrigues, Varlei; Ugarte, Daniel; Galvao, Douglas S
Contaminants in suspended gold chains: An ab initio molecular dynamics study Journal Article
Em: Physical Review Letters, vol. 93, não 21, pp. 216103, 2004.
Resumo | Links | BibTeX | Tags: DFT, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, top20
@article{legoas2004contaminants,
title = {Contaminants in suspended gold chains: An ab initio molecular dynamics study},
author = {Legoas, Sergio B and Rodrigues, Varlei and Ugarte, Daniel and Galvao, Douglas S},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.216103},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {21},
pages = {216103},
publisher = {American Physical Society},
abstract = {Recently, we have proposed that the origin of anomalously long interatomic distances in suspended gold chains could be the result of carbon contamination during sample manipulation [S. B. Legoas et al., Phys. Rev. Lett. 88, 076105 (2002)]. More recently, however, other works have proposed that hydrogen instead of carbon should be the most probable contaminant. We report ab initio molecular dynamics results for different temperatures considering different possible contaminants. Our results show that at nonzero temperatures (more realistic to simulate the experimental conditions) hydrogen may be ruled out and carbon atoms remain the best candidate for contamination.},
keywords = {DFT, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, top20},
pubstate = {published},
tppubtype = {article}
}
Recently, we have proposed that the origin of anomalously long interatomic distances in suspended gold chains could be the result of carbon contamination during sample manipulation [S. B. Legoas et al., Phys. Rev. Lett. 88, 076105 (2002)]. More recently, however, other works have proposed that hydrogen instead of carbon should be the most probable contaminant. We report ab initio molecular dynamics results for different temperatures considering different possible contaminants. Our results show that at nonzero temperatures (more realistic to simulate the experimental conditions) hydrogen may be ruled out and carbon atoms remain the best candidate for contamination.
6.
Gonzalez, JC; Rodrigues, V; Bettini, J; Rego, LGC; Rocha, AR; Coura, PZ; Dantas, SO; Sato, F; Galvao, DS; Ugarte, D
Indication of unusual pentagonal structures in atomic-size Cu nanowires Journal Article
Em: Physical Review Letters, vol. 93, não 12, pp. 126103, 2004.
Resumo | Links | BibTeX | Tags: Copper Nanowires, Linear Atomic Chains, Metallic Nanowires, Molecular Dynamics, TEM, top20
@article{gonzalez2004indication,
title = {Indication of unusual pentagonal structures in atomic-size Cu nanowires},
author = {Gonzalez, JC and Rodrigues, V and Bettini, J and Rego, LGC and Rocha, AR and Coura, PZ and Dantas, SO and Sato, F and Galvao, DS and Ugarte, D},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.93.126103},
year = {2004},
date = {2004-01-01},
journal = {Physical Review Letters},
volume = {93},
number = {12},
pages = {126103},
publisher = {APS},
abstract = {We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of ∼0.45 nm and ∼4.5 conductance quanta.
},
keywords = {Copper Nanowires, Linear Atomic Chains, Metallic Nanowires, Molecular Dynamics, TEM, top20},
pubstate = {published},
tppubtype = {article}
}
We present a study of the structural and quantum conductance properties of atomic-size copper nanowires generated by mechanical stretching. The atomistic evolution was derived from time-resolved electron microscopy observations and molecular dynamics simulations. We have analyzed the quantum transport behavior by means of conductance measurements and theoretical calculations. The results suggest the formation of an unusual and highly stable pentagonal Cu nanowire with a diameter of ∼0.45 nm and ∼4.5 conductance quanta.
5.
Otero, Roberto; Hummelink, Frauke; Sato, Fernando; Legoas, Sergio B; Thostrup, Peter; Lægsgaard, Erik; Stensgaard, Ivan; Galvao, Douglas S; Besenbacher, Flemming
Lock-and-key effect in the surface diffusion of large organic molecules probed by STM Journal Article
Em: Nature Materials, vol. 3, não 11, pp. 779–782, 2004.
Resumo | Links | BibTeX | Tags: Landers, Molecular Dynamics, Molecular Electronics, STM, top20
@article{otero2004lock,
title = {Lock-and-key effect in the surface diffusion of large organic molecules probed by STM},
author = {Otero, Roberto and Hummelink, Frauke and Sato, Fernando and Legoas, Sergio B and Thostrup, Peter and Lægsgaard, Erik and Stensgaard, Ivan and Galvao, Douglas S and Besenbacher, Flemming},
url = {http://www.nature.com/nmat/journal/v3/n11/full/nmat1243.html},
year = {2004},
date = {2004-01-01},
journal = {Nature Materials},
volume = {3},
number = {11},
pages = {779--782},
publisher = {Nature Publishing Group},
abstract = {A nanoscale understanding of the complex dynamics of large molecules at surfaces is essential for the bottom-up design of molecular nanostructures1, 2, 3, 4, 5, 6, 7, 8. Here we show that we can change the diffusion coefficient of the complex organic molecule known as Violet Lander (VL, C108H104) on Cu(110) by two orders of magnitude by using the STM at low temperatures to switch between two adsorption configurations that differ only in the molecular orientation with respect to the substrate lattice. From an interplay with molecular dynamics simulations, we interpret the results within a lock-and-key model similar to the one driving the recognition between biomolecules: the molecule (key) is immobilized only when its orientation is such that the molecular shape fits the atomic lattice of the surface (lock); otherwise the molecule is highly mobile.
Introduction
},
keywords = {Landers, Molecular Dynamics, Molecular Electronics, STM, top20},
pubstate = {published},
tppubtype = {article}
}
A nanoscale understanding of the complex dynamics of large molecules at surfaces is essential for the bottom-up design of molecular nanostructures1, 2, 3, 4, 5, 6, 7, 8. Here we show that we can change the diffusion coefficient of the complex organic molecule known as Violet Lander (VL, C108H104) on Cu(110) by two orders of magnitude by using the STM at low temperatures to switch between two adsorption configurations that differ only in the molecular orientation with respect to the substrate lattice. From an interplay with molecular dynamics simulations, we interpret the results within a lock-and-key model similar to the one driving the recognition between biomolecules: the molecule (key) is immobilized only when its orientation is such that the molecular shape fits the atomic lattice of the surface (lock); otherwise the molecule is highly mobile.
Introduction
Introduction
2003
4.
VR Coluci SB Legoas, SF Braga
Molecular-dynamics simulations of carbon nanotubes as gigahertz oscillators Journal Article
Em: Physical Review Letters, vol. 90, não 5, pp. 055504, 2003.
Resumo | BibTeX | Tags: Carbon Nanotubes, Molecular Dynamics, Oscillators, top20
@article{legoas2003molecularb,
title = {Molecular-dynamics simulations of carbon nanotubes as gigahertz oscillators},
author = {SB Legoas, VR Coluci, SF Braga, PZ Coura, SO Dantas, DS Galvao},
year = {2003},
date = {2003-01-01},
journal = {Physical Review Letters},
volume = {90},
number = {5},
pages = {055504},
abstract = {Recently, Zheng and Jiang [Phys. Rev. Lett. 88, 045503 (2002)] have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nano-oscillators in the several gigahertz range. In this Letter, we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nano-oscillators are dynamically stable when the radii difference values between inner and outer tubes are of ∼3.4 Å. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations.},
keywords = {Carbon Nanotubes, Molecular Dynamics, Oscillators, top20},
pubstate = {published},
tppubtype = {article}
}
Recently, Zheng and Jiang [Phys. Rev. Lett. 88, 045503 (2002)] have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nano-oscillators in the several gigahertz range. In this Letter, we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nano-oscillators are dynamically stable when the radii difference values between inner and outer tubes are of ∼3.4 Å. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations.
2002
3.
Legoas, Sergio B; Galvao, Douglas S; Rodrigues, Varlei; Ugarte, Daniel
Origin of anomalously long interatomic distances in suspended gold chains Journal Article
Em: Physical Review Letters, vol. 88, não 7, pp. 076105, 2002.
Resumo | Links | BibTeX | Tags: DFT, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, TEM, top20
@article{legoas2002origin,
title = {Origin of anomalously long interatomic distances in suspended gold chains},
author = {Legoas, Sergio B and Galvao, Douglas S and Rodrigues, Varlei and Ugarte, Daniel},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.88.076105},
year = {2002},
date = {2002-01-01},
journal = {Physical Review Letters},
volume = {88},
number = {7},
pages = {076105},
publisher = {American Physical Society},
abstract = {The discovery of long bonds in gold atom chains has represented a challenge for physical interpretation. In fact, interatomic distances frequently attain 3.0–3.6 Å values, and distances as large as 5.0 Å may be occasionally observed. Here we studied gold chains by transmission electron microscopy and performed theoretical calculations using cluster ab initio density functional formalism. We show that the insertion of two carbon atoms is required to account for the longest bonds, while distances above 3 Å may be due to a mixture of clean and one C atom contaminated bonds.},
keywords = {DFT, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, TEM, top20},
pubstate = {published},
tppubtype = {article}
}
The discovery of long bonds in gold atom chains has represented a challenge for physical interpretation. In fact, interatomic distances frequently attain 3.0–3.6 Å values, and distances as large as 5.0 Å may be occasionally observed. Here we studied gold chains by transmission electron microscopy and performed theoretical calculations using cluster ab initio density functional formalism. We show that the insertion of two carbon atoms is required to account for the longest bonds, while distances above 3 Å may be due to a mixture of clean and one C atom contaminated bonds.
1996
2.
A Camilo Jr PMVB Barone, DS Galvao
Theoretical approach to identify carcinogenic activity of polycyclic aromatic hydrocarbons Journal Article
Em: Physical Review Letters, vol. 77, não 6, pp. 1186, 1996.
Resumo | Links | BibTeX | Tags: top20
@article{barone1996theoretical,
title = {Theoretical approach to identify carcinogenic activity of polycyclic aromatic hydrocarbons},
author = {PMVB Barone, A Camilo Jr, DS Galvao},
url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.77.1186},
doi = {10.1103/PhysRevLett.77.1186},
year = {1996},
date = {1996-01-01},
journal = {Physical Review Letters},
volume = {77},
number = {6},
pages = {1186},
publisher = {American Physical Society},
abstract = {Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules that can induce chemical carcinogenesis. Their carcinogenic powers vary in a large range, from the very strong carcinogens to the inactive ones. Many models have been proposed to explain the PAHs' carcinogenic activity, but all of them present some failures. Here we introduce a new methodology to identify PAHs' carcinogenic activity based on the concept of electronic local density of states (LDOS). We show that the analysis of the molecular energy levels in association with the LDOS calculated over the ring which contains the highest bond order of the molecule allows simple rules to identify whether a specific PAH molecule will present (or not) carcinogenic activity.},
keywords = {top20},
pubstate = {published},
tppubtype = {article}
}
Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules that can induce chemical carcinogenesis. Their carcinogenic powers vary in a large range, from the very strong carcinogens to the inactive ones. Many models have been proposed to explain the PAHs' carcinogenic activity, but all of them present some failures. Here we introduce a new methodology to identify PAHs' carcinogenic activity based on the concept of electronic local density of states (LDOS). We show that the analysis of the molecular energy levels in association with the LDOS calculated over the ring which contains the highest bond order of the molecule allows simple rules to identify whether a specific PAH molecule will present (or not) carcinogenic activity.
1993
1.
Baughman, RH; Galvao, DS
Crystalline networks with unusual predicted mechanical and thermal properties Journal Article
Em: Nature, vol. 365, não 6448, pp. 735–737, 1993.
Resumo | Links | BibTeX | Tags: top20
@article{baughman1993crystalline,
title = {Crystalline networks with unusual predicted mechanical and thermal properties},
author = {RH Baughman and DS Galvao},
url = {http://www.nature.com/nature/journal/v365/n6448/abs/365735a0.html},
doi = {10.1038/365735a0},
year = {1993},
date = {1993-01-01},
journal = {Nature},
volume = {365},
number = {6448},
pages = {735--737},
publisher = {Nature Publishing Group},
abstract = {Most materials shrink laterally and become less dense when stretched. Materials that both expand laterally (that is, have negative Poisson's ratio) and densify when stretched are of interest both from the fundamental and the practical points of view1–5. A few monocrystalline phases with negative Poisson's ratio are known3,4, but these do not densify when stretched. Here we present molecular-mechanics calculations for some hypothetical phases of carbon which exhibit both kinds of behaviour. The properties derive from the presence of bonds that act as hinges in extended helical chains. Other unusual properties of these phases include negative thermal expansion, dopant-controlled porosity and low-temperature polymorphism. Such structures can be envisaged for polyacetylene, polydiacetylene, polyphenylene and (BN)x phases, as well as for variants of some known, structurally related inorganic phases.},
keywords = {top20},
pubstate = {published},
tppubtype = {article}
}
Most materials shrink laterally and become less dense when stretched. Materials that both expand laterally (that is, have negative Poisson's ratio) and densify when stretched are of interest both from the fundamental and the practical points of view1–5. A few monocrystalline phases with negative Poisson's ratio are known3,4, but these do not densify when stretched. Here we present molecular-mechanics calculations for some hypothetical phases of carbon which exhibit both kinds of behaviour. The properties derive from the presence of bonds that act as hinges in extended helical chains. Other unusual properties of these phases include negative thermal expansion, dopant-controlled porosity and low-temperature polymorphism. Such structures can be envisaged for polyacetylene, polydiacetylene, polyphenylene and (BN)x phases, as well as for variants of some known, structurally related inorganic phases.
