1.
Torriani, IL; Silva, JC; Autreto, PAS; Galvao, DS; Caldas, MJ; Graeff, CFO
Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents Journal Article
In: Acta Crystalographica A, vol. 64, pp. C552, 2009.
@article{torriani2009low,
title = {Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents},
author = {Torriani, IL and Silva, JC and Autreto, PAS and Galvao, DS and Caldas, MJ and Graeff, CFO},
url = {http://journals.iucr.org/a/issues/2008/a1/00/a39972/a39972.pdf},
year = {2009},
date = {2009-01-01},
journal = {Acta Crystalographica A},
volume = {64},
pages = {C552},
abstract = {In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
2.
Caetano, Ewerton WS; Freire, Valder N; Santos, Sergio G dos; Galvao, Douglas S; Sato, Fernando
Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties Journal Article
In: arXiv preprint arXiv:0903.2080, 2009.
@article{caetano2009m,
title = {Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties},
author = {Caetano, Ewerton WS and Freire, Valder N and Santos, Sergio G dos and Galvao, Douglas S and Sato, Fernando},
url = {http://arxiv.org/abs/0903.2080},
year = {2009},
date = {2009-01-01},
journal = {arXiv preprint arXiv:0903.2080},
abstract = {Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist M"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO → LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist M\"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO → LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.
3.
Rocha, Tulio CR; Sato, Fernando; Dantas, Socrates O; Galvao, Douglas S; Zanchet, Daniela
New Insights on the Growth of Anisotropic Nanoparticles from Total Energy Calculations Journal Article
In: The Journal of Physical Chemistry C, vol. 113, no. 28, pp. 11976–11979, 2009.
@article{rocha2009new,
title = {New Insights on the Growth of Anisotropic Nanoparticles from Total Energy Calculations},
author = {Rocha, Tulio CR and Sato, Fernando and Dantas, Socrates O and Galvao, Douglas S and Zanchet, Daniela},
url = {http://pubs.acs.org/doi/abs/10.1021/jp903794y},
year = {2009},
date = {2009-01-01},
journal = {The Journal of Physical Chemistry C},
volume = {113},
number = {28},
pages = {11976--11979},
publisher = {American Chemical Society},
abstract = {The growth mechanism of anisotropic metallic nanoparticles is still an open and polemical question. The common observation of the existence of nonspherical (not the most stable) shapes in varied experimental conditions is not fully understood. In this work, based on results from total energy calculations for different shapes and sizes of Ag nanoparticles, we provide new insights of why anisotropic structures are commonly found in different preparation conditions. We show that, assuming the presence of a particle shape distribution in the beginning of the growth process, anisotropic nanoparticles can preferentially grow over spherical ones due to the fact that the energy required to build larger anisotropic structures could be less than the one required to build isotropic structures. These results suggest that many previous works in literature shall be revisited accordingly to these new finds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The growth mechanism of anisotropic metallic nanoparticles is still an open and polemical question. The common observation of the existence of nonspherical (not the most stable) shapes in varied experimental conditions is not fully understood. In this work, based on results from total energy calculations for different shapes and sizes of Ag nanoparticles, we provide new insights of why anisotropic structures are commonly found in different preparation conditions. We show that, assuming the presence of a particle shape distribution in the beginning of the growth process, anisotropic nanoparticles can preferentially grow over spherical ones due to the fact that the energy required to build larger anisotropic structures could be less than the one required to build isotropic structures. These results suggest that many previous works in literature shall be revisited accordingly to these new finds.
4.
E. W. S.; Freire Caetano, V. N. ; dos Santos
Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties Journal Article
In: THE JOURNAL OF CHEMICAL PHYSICS, vol. 128, pp. 164719, 2008.
@article{Caetano2008,
title = {Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties},
author = {Caetano, E. W. S.; Freire, V. N.; dos Santos, S. G.; Galvao, D. S.,and Sato, F.},
url = {http://scitation.aip.org/content/aip/journal/jcp/128/16/10.1063/1.2908739},
year = {2008},
date = {2008-04-29},
journal = {THE JOURNAL OF CHEMICAL PHYSICS},
volume = {128},
pages = {164719},
abstract = {Results of classical force field geometry optimizations for twisted graphenenanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO−4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO→LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Results of classical force field geometry optimizations for twisted graphenenanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO−4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO→LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.
5.
Rodrigues, Varlei; Sato, Fernando; Galvao, Douglas S; Ugarte, Daniel
Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts Journal Article
In: arXiv preprint arXiv:0707.4187, 2007.
@article{rodrigues2007small,
title = {Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts},
author = {Rodrigues, Varlei and Sato, Fernando and Galvao, Douglas S and Ugarte, Daniel},
url = {http://xxx.tau.ac.il/abs/0707.4187},
year = {2007},
date = {2007-01-01},
journal = {arXiv preprint arXiv:0707.4187},
abstract = {We report high resolution transmission electron microscopy and ab initio calculation results for the defect formation in Pt nanocontacts (NCs). Our results show that there is a size limit to the existence of twins (extended structural defects). Defects are always present but blocked away from the tip axes. The twins may act as scattering plane, influencing contact electron transmission for Pt NC at room temperature and Ag/Au NC at low temperature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We report high resolution transmission electron microscopy and ab initio calculation results for the defect formation in Pt nanocontacts (NCs). Our results show that there is a size limit to the existence of twins (extended structural defects). Defects are always present but blocked away from the tip axes. The twins may act as scattering plane, influencing contact electron transmission for Pt NC at room temperature and Ag/Au NC at low temperature.
6.
Rodrigues, V; Sato, F; Galvao, DS; Ugarte, D
Size limit of defect formation in pyramidal Pt nanocontacts Journal Article
In: Physical Review Letters, vol. 99, no. 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).
7.
Lorite, Gabriela S; Coluci, Vitor R; da Silva, Maria Ivonete N; Deziderio, Shirlei N; Graeff, Carlos Frederico O; Galvao, Douglas S; Cotta, Monica A
Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties Journal Article
In: Journal of Applied Physics, vol. 99, no. 11, pp. 113511, 2006.
@article{lorite2006synthetic,
title = {Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties},
author = {Lorite, Gabriela S and Coluci, Vitor R and da Silva, Maria Ivonete N and Deziderio, Shirlei N and Graeff, Carlos Frederico O and Galvao, Douglas S and Cotta, Monica A},
url = {http://scitation.aip.org/content/aip/journal/jap/99/11/10.1063/1.2200401},
year = {2006},
date = {2006-01-01},
journal = {Journal of Applied Physics},
volume = {99},
number = {11},
pages = {113511},
publisher = {AIP Publishing},
abstract = {In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy(AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy(AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.
8.
Coura, Pablo Z; Legoas, Sergio B; Moreira, Anderson S; Sato, Fernando; Rodrigues, Varlei; Dantas, Socrates O; Ugarte, Daniel; Galvao, Douglas S
On the structural and stability features of linear atomic suspended chains formed from gold nanowires stretching Journal Article
In: Nano Letters, vol. 4, no. 7, pp. 1187–1191, 2004.
@article{coura2004structural,
title = {On the structural and stability features of linear atomic suspended chains formed from gold nanowires stretching},
author = {Coura, Pablo Z and Legoas, Sergio B and Moreira, Anderson S and Sato, Fernando and Rodrigues, Varlei and Dantas, Socrates O and Ugarte, Daniel and Galvao, Douglas S},
url = {http://pubs.acs.org/doi/abs/10.1021/nl049725h},
year = {2004},
date = {2004-01-01},
journal = {Nano Letters},
volume = {4},
number = {7},
pages = {1187--1191},
publisher = {American Chemical Society},
abstract = {Metallic nanowires (NWs) have been intensily investigated in the past years, but details on
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metallic nanowires (NWs) have been intensily investigated in the past years, but details on
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.
9.
Braga, Scheila F; Coluci, Vitor R; Legoas, Sergio B; Giro, Ronaldo; Galvao, Douglas S; Baughman, Ray H
Structure and dynamics of carbon nanoscrolls Journal Article
In: Nano Letters, vol. 4, no. 5, pp. 881–884, 2004.
@article{braga2004structure,
title = {Structure and dynamics of carbon nanoscrolls},
author = {Braga, Scheila F and Coluci, Vitor R and Legoas, Sergio B and Giro, Ronaldo and Galvao, Douglas S and Baughman, Ray H},
url = {http://pubs.acs.org/doi/abs/10.1021/nl0497272},
year = {2004},
date = {2004-01-01},
journal = {Nano Letters},
volume = {4},
number = {5},
pages = {881--884},
publisher = {American Chemical Society},
abstract = {Carbon nanotube scrolls (CNSs) provide an interesting form of carbon that ideally consists of a single sheet of graphite that is spiral wrapped
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Carbon nanotube scrolls (CNSs) provide an interesting form of carbon that ideally consists of a single sheet of graphite that is spiral wrapped
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators
10.
Galvao, Douglas Soares; Rodrigues, Varlei; Ugarte, Daniel; Legoas, Sergio Benites
The role of carbon contamination in metallic nanowires Journal Article
In: Materials Research, vol. 7, no. 2, pp. 339–342, 2004.
@article{galvao2004role,
title = {The role of carbon contamination in metallic nanowires},
author = {Galvao, Douglas Soares and Rodrigues, Varlei and Ugarte, Daniel and Legoas, Sergio Benites},
url = {http://www.scielo.br/scielo.php?pid=S1516-14392004000200020&script=sci_arttext},
year = {2004},
date = {2004-01-01},
journal = {Materials Research},
volume = {7},
number = {2},
pages = {339--342},
publisher = {SciELO Brasil},
abstract = {Metallic nanowires have attracted much attention in the last years due to new phenomena such as quantum conductance and the existence of unexpected long interatomic distances attaining 0.3-0.5 nm. These large distances represented a challenge for physical interpretation. In this work we present experimental data from high-resolution transmission electron microscopy and results from ab initio calculations for suspended gold chains and show that these large distances can be easily explained by the presence of carbon atoms as contaminants. In principle the present conclusions can be also applied to other metallic nanowires (such as Ag and Pt) whose structures also present large interatomic distances.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Metallic nanowires have attracted much attention in the last years due to new phenomena such as quantum conductance and the existence of unexpected long interatomic distances attaining 0.3-0.5 nm. These large distances represented a challenge for physical interpretation. In this work we present experimental data from high-resolution transmission electron microscopy and results from ab initio calculations for suspended gold chains and show that these large distances can be easily explained by the presence of carbon atoms as contaminants. In principle the present conclusions can be also applied to other metallic nanowires (such as Ag and Pt) whose structures also present large interatomic distances.
2009
10.
Torriani, IL; Silva, JC; Autreto, PAS; Galvao, DS; Caldas, MJ; Graeff, CFO
Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents Journal Article
In: Acta Crystalographica A, vol. 64, pp. C552, 2009.
Abstract | Links | BibTeX | Tags: Melanin, Structure
@article{torriani2009low,
title = {Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents},
author = {Torriani, IL and Silva, JC and Autreto, PAS and Galvao, DS and Caldas, MJ and Graeff, CFO},
url = {http://journals.iucr.org/a/issues/2008/a1/00/a39972/a39972.pdf},
year = {2009},
date = {2009-01-01},
journal = {Acta Crystalographica A},
volume = {64},
pages = {C552},
abstract = {In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.},
keywords = {Melanin, Structure},
pubstate = {published},
tppubtype = {article}
}
In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.
9.
Caetano, Ewerton WS; Freire, Valder N; Santos, Sergio G dos; Galvao, Douglas S; Sato, Fernando
Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties Journal Article
In: arXiv preprint arXiv:0903.2080, 2009.
Abstract | Links | BibTeX | Tags: Graphene, Mobius, NanoRibbons, Structure
@article{caetano2009m,
title = {Mobius and twisted graphene nanoribbons: stability, geometry and electronic properties},
author = {Caetano, Ewerton WS and Freire, Valder N and Santos, Sergio G dos and Galvao, Douglas S and Sato, Fernando},
url = {http://arxiv.org/abs/0903.2080},
year = {2009},
date = {2009-01-01},
journal = {arXiv preprint arXiv:0903.2080},
abstract = {Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist M"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO → LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {Graphene, Mobius, NanoRibbons, Structure},
pubstate = {published},
tppubtype = {article}
}
Results of classical force field geometry optimizations for twisted graphene nanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist M\"obius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO-4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO → LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.
8.
Rocha, Tulio CR; Sato, Fernando; Dantas, Socrates O; Galvao, Douglas S; Zanchet, Daniela
New Insights on the Growth of Anisotropic Nanoparticles from Total Energy Calculations Journal Article
In: The Journal of Physical Chemistry C, vol. 113, no. 28, pp. 11976–11979, 2009.
Abstract | Links | BibTeX | Tags: growth, Nanoparticles, Structure
@article{rocha2009new,
title = {New Insights on the Growth of Anisotropic Nanoparticles from Total Energy Calculations},
author = {Rocha, Tulio CR and Sato, Fernando and Dantas, Socrates O and Galvao, Douglas S and Zanchet, Daniela},
url = {http://pubs.acs.org/doi/abs/10.1021/jp903794y},
year = {2009},
date = {2009-01-01},
journal = {The Journal of Physical Chemistry C},
volume = {113},
number = {28},
pages = {11976--11979},
publisher = {American Chemical Society},
abstract = {The growth mechanism of anisotropic metallic nanoparticles is still an open and polemical question. The common observation of the existence of nonspherical (not the most stable) shapes in varied experimental conditions is not fully understood. In this work, based on results from total energy calculations for different shapes and sizes of Ag nanoparticles, we provide new insights of why anisotropic structures are commonly found in different preparation conditions. We show that, assuming the presence of a particle shape distribution in the beginning of the growth process, anisotropic nanoparticles can preferentially grow over spherical ones due to the fact that the energy required to build larger anisotropic structures could be less than the one required to build isotropic structures. These results suggest that many previous works in literature shall be revisited accordingly to these new finds.},
keywords = {growth, Nanoparticles, Structure},
pubstate = {published},
tppubtype = {article}
}
The growth mechanism of anisotropic metallic nanoparticles is still an open and polemical question. The common observation of the existence of nonspherical (not the most stable) shapes in varied experimental conditions is not fully understood. In this work, based on results from total energy calculations for different shapes and sizes of Ag nanoparticles, we provide new insights of why anisotropic structures are commonly found in different preparation conditions. We show that, assuming the presence of a particle shape distribution in the beginning of the growth process, anisotropic nanoparticles can preferentially grow over spherical ones due to the fact that the energy required to build larger anisotropic structures could be less than the one required to build isotropic structures. These results suggest that many previous works in literature shall be revisited accordingly to these new finds.
2008
7.
E. W. S.; Freire Caetano, V. N. ; dos Santos
Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties Journal Article
In: THE JOURNAL OF CHEMICAL PHYSICS, vol. 128, pp. 164719, 2008.
Abstract | Links | BibTeX | Tags: DFT, Graphene, Mobis, NanoRibbons, Structure
@article{Caetano2008,
title = {Mobius and twisted graphene nanoribbons: Stability, geometry, and electronic properties},
author = {Caetano, E. W. S.; Freire, V. N.; dos Santos, S. G.; Galvao, D. S.,and Sato, F.},
url = {http://scitation.aip.org/content/aip/journal/jcp/128/16/10.1063/1.2908739},
year = {2008},
date = {2008-04-29},
journal = {THE JOURNAL OF CHEMICAL PHYSICS},
volume = {128},
pages = {164719},
abstract = {Results of classical force field geometry optimizations for twisted graphenenanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO−4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO→LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.},
keywords = {DFT, Graphene, Mobis, NanoRibbons, Structure},
pubstate = {published},
tppubtype = {article}
}
Results of classical force field geometry optimizations for twisted graphenenanoribbons with a number of twists Nt varying from 0 to 7 (the case Nt=1 corresponds to a half-twist Möbius nanoribbon) are presented in this work. Their structural stability was investigated using the Brenner reactive force field. The best classical molecular geometries were used as input for semiempirical calculations, from which the electronic properties (energy levels, HOMO, LUMO orbitals) were computed for each structure. CI wavefunctions were also calculated in the complete active space framework taking into account eigenstates from HOMO−4 to LUMO+4, as well as the oscillator strengths corresponding to the first optical transitions in the UV-VIS range. The lowest energy molecules were found less symmetric than initial configurations, and the HOMO-LUMO energy gaps are larger than the value found for the nanographene used to build them due to electronic localization effects created by the twisting. A high number of twists leads to a sharp increase of the HOMO→LUMO transition energy. We suggest that some twisted nanoribbons could form crystals stabilized by dipolar interactions.
2007
6.
Rodrigues, Varlei; Sato, Fernando; Galvao, Douglas S; Ugarte, Daniel
Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts Journal Article
In: arXiv preprint arXiv:0707.4187, 2007.
Abstract | Links | BibTeX | Tags: Defects, DFT, Metallic Nanowires, Structure, TEM
@article{rodrigues2007small,
title = {Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts},
author = {Rodrigues, Varlei and Sato, Fernando and Galvao, Douglas S and Ugarte, Daniel},
url = {http://xxx.tau.ac.il/abs/0707.4187},
year = {2007},
date = {2007-01-01},
journal = {arXiv preprint arXiv:0707.4187},
abstract = {We report high resolution transmission electron microscopy and ab initio calculation results for the defect formation in Pt nanocontacts (NCs). Our results show that there is a size limit to the existence of twins (extended structural defects). Defects are always present but blocked away from the tip axes. The twins may act as scattering plane, influencing contact electron transmission for Pt NC at room temperature and Ag/Au NC at low temperature.},
keywords = {Defects, DFT, Metallic Nanowires, Structure, TEM},
pubstate = {published},
tppubtype = {article}
}
We report high resolution transmission electron microscopy and ab initio calculation results for the defect formation in Pt nanocontacts (NCs). Our results show that there is a size limit to the existence of twins (extended structural defects). Defects are always present but blocked away from the tip axes. The twins may act as scattering plane, influencing contact electron transmission for Pt NC at room temperature and Ag/Au NC at low temperature.
5.
Rodrigues, V; Sato, F; Galvao, DS; Ugarte, D
Size limit of defect formation in pyramidal Pt nanocontacts Journal Article
In: Physical Review Letters, vol. 99, no. 25, pp. 255501, 2007.
Abstract | 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
4.
Lorite, Gabriela S; Coluci, Vitor R; da Silva, Maria Ivonete N; Deziderio, Shirlei N; Graeff, Carlos Frederico O; Galvao, Douglas S; Cotta, Monica A
Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties Journal Article
In: Journal of Applied Physics, vol. 99, no. 11, pp. 113511, 2006.
Abstract | Links | BibTeX | Tags: Electronic Structure, Melanin, Structure
@article{lorite2006synthetic,
title = {Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties},
author = {Lorite, Gabriela S and Coluci, Vitor R and da Silva, Maria Ivonete N and Deziderio, Shirlei N and Graeff, Carlos Frederico O and Galvao, Douglas S and Cotta, Monica A},
url = {http://scitation.aip.org/content/aip/journal/jap/99/11/10.1063/1.2200401},
year = {2006},
date = {2006-01-01},
journal = {Journal of Applied Physics},
volume = {99},
number = {11},
pages = {113511},
publisher = {AIP Publishing},
abstract = {In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy(AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.},
keywords = {Electronic Structure, Melanin, Structure},
pubstate = {published},
tppubtype = {article}
}
In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy(AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.
2004
3.
Coura, Pablo Z; Legoas, Sergio B; Moreira, Anderson S; Sato, Fernando; Rodrigues, Varlei; Dantas, Socrates O; Ugarte, Daniel; Galvao, Douglas S
On the structural and stability features of linear atomic suspended chains formed from gold nanowires stretching Journal Article
In: Nano Letters, vol. 4, no. 7, pp. 1187–1191, 2004.
Abstract | Links | BibTeX | Tags: Liinear Atomic Chains, Metallic Nanowires, Molecular Dynamics, Structure, TEM
@article{coura2004structural,
title = {On the structural and stability features of linear atomic suspended chains formed from gold nanowires stretching},
author = {Coura, Pablo Z and Legoas, Sergio B and Moreira, Anderson S and Sato, Fernando and Rodrigues, Varlei and Dantas, Socrates O and Ugarte, Daniel and Galvao, Douglas S},
url = {http://pubs.acs.org/doi/abs/10.1021/nl049725h},
year = {2004},
date = {2004-01-01},
journal = {Nano Letters},
volume = {4},
number = {7},
pages = {1187--1191},
publisher = {American Chemical Society},
abstract = {Metallic nanowires (NWs) have been intensily investigated in the past years, but details on
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.},
keywords = {Liinear Atomic Chains, Metallic Nanowires, Molecular Dynamics, Structure, TEM},
pubstate = {published},
tppubtype = {article}
}
Metallic nanowires (NWs) have been intensily investigated in the past years, but details on
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.
their formation are still not completely understood. In this work we report high resolution
transmission electron microscopy data and molecular dynamics simulation results for gold
NW elongation. Our results show that different initial crystallographic orientations lead to
very differentiated linear atomic suspended chain (LAC) formations and strongly support that
kinetic aspects are the dominant mechanisms determining the LAC morphologies.
2.
Braga, Scheila F; Coluci, Vitor R; Legoas, Sergio B; Giro, Ronaldo; Galvao, Douglas S; Baughman, Ray H
Structure and dynamics of carbon nanoscrolls Journal Article
In: Nano Letters, vol. 4, no. 5, pp. 881–884, 2004.
Abstract | Links | BibTeX | Tags: Molecular Dynamics, Scrolls, Structure
@article{braga2004structure,
title = {Structure and dynamics of carbon nanoscrolls},
author = {Braga, Scheila F and Coluci, Vitor R and Legoas, Sergio B and Giro, Ronaldo and Galvao, Douglas S and Baughman, Ray H},
url = {http://pubs.acs.org/doi/abs/10.1021/nl0497272},
year = {2004},
date = {2004-01-01},
journal = {Nano Letters},
volume = {4},
number = {5},
pages = {881--884},
publisher = {American Chemical Society},
abstract = {Carbon nanotube scrolls (CNSs) provide an interesting form of carbon that ideally consists of a single sheet of graphite that is spiral wrapped
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators},
keywords = {Molecular Dynamics, Scrolls, Structure},
pubstate = {published},
tppubtype = {article}
}
Carbon nanotube scrolls (CNSs) provide an interesting form of carbon that ideally consists of a single sheet of graphite that is spiral wrapped
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators
to form a nanotube. We here use molecular dynamics simulations to investigate CNS formation, stability, and the structural effects due to
charge injection. CNS formation is seen to automatically occur when a critical overlap between sheet layers is achieved for the partially curled
sheet. We find that charge injection causes unwinding of the CNSs, which might be important for the application of CNSs as nanomechanical
actuators
1.
Galvao, Douglas Soares; Rodrigues, Varlei; Ugarte, Daniel; Legoas, Sergio Benites
The role of carbon contamination in metallic nanowires Journal Article
In: Materials Research, vol. 7, no. 2, pp. 339–342, 2004.
Abstract | Links | BibTeX | Tags: Contaminantes, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, Structure
@article{galvao2004role,
title = {The role of carbon contamination in metallic nanowires},
author = {Galvao, Douglas Soares and Rodrigues, Varlei and Ugarte, Daniel and Legoas, Sergio Benites},
url = {http://www.scielo.br/scielo.php?pid=S1516-14392004000200020&script=sci_arttext},
year = {2004},
date = {2004-01-01},
journal = {Materials Research},
volume = {7},
number = {2},
pages = {339--342},
publisher = {SciELO Brasil},
abstract = {Metallic nanowires have attracted much attention in the last years due to new phenomena such as quantum conductance and the existence of unexpected long interatomic distances attaining 0.3-0.5 nm. These large distances represented a challenge for physical interpretation. In this work we present experimental data from high-resolution transmission electron microscopy and results from ab initio calculations for suspended gold chains and show that these large distances can be easily explained by the presence of carbon atoms as contaminants. In principle the present conclusions can be also applied to other metallic nanowires (such as Ag and Pt) whose structures also present large interatomic distances.},
keywords = {Contaminantes, Electronic Structure, Linear Atomic Chains, Metallic Nanowires, Structure},
pubstate = {published},
tppubtype = {article}
}
Metallic nanowires have attracted much attention in the last years due to new phenomena such as quantum conductance and the existence of unexpected long interatomic distances attaining 0.3-0.5 nm. These large distances represented a challenge for physical interpretation. In this work we present experimental data from high-resolution transmission electron microscopy and results from ab initio calculations for suspended gold chains and show that these large distances can be easily explained by the presence of carbon atoms as contaminants. In principle the present conclusions can be also applied to other metallic nanowires (such as Ag and Pt) whose structures also present large interatomic distances.
http://scholar.google.com/citations?hl=en&user=95SvbM8AAAAJ
