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Discrete plasticity in sub-10-nm-sized gold crystals.

Zheng H, Cao A, Weinberger CR, Huang JY, Du K, Wang J, Ma Y, Xia Y, Mao SX - Nat Commun (2010)

Bottom Line: Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking.Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure.These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.

ABSTRACT
Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking. Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure. These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years.

No MeSH data available.


Related in: MedlinePlus

Tensile loading test of an Au nanocrystal.This tensile test (see also Supplementary Movie 1) shows that surface steps act as the dislocation sources (see also Supplementary Movie 2). (a–c) Sequential HRTEM images showing the emission of a dislocation from a free surface. The insets in a, b Fourier-filtered images (reconstructed using the spatial frequencies of the (111) planes) of the black square area, respectively. The scale bar in each figure represents 3 nm. (d, e) The strain mapping of the white-boxed area in HRTEM images before a and after b shows the nucleation of a partial dislocation. The black arrowheads indicate the site for dislocation nucleation. Open circles on the upper right part of the two figures represent the twinning lamella. (f) A quantitative strain analysis of the black-boxed region in d and e; frequency is the number of atoms with that strain divided by the total number of atoms in the black-boxed area in d and e. (g–k) MD simulations illustrating the atomic process of nucleation (h), propagation of the leading partial producing a stacking fault (i) and the nucleation of the trailing partial (j), where bL and bT mark the location of leading and trailing partials, respectively. Eventually, the combined perfect dislocation leaves out of the sample (k). Colours are assigned to the atoms according to a local crystallinity classification visualized by common neighbour analysis (see Methods for details).
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f1: Tensile loading test of an Au nanocrystal.This tensile test (see also Supplementary Movie 1) shows that surface steps act as the dislocation sources (see also Supplementary Movie 2). (a–c) Sequential HRTEM images showing the emission of a dislocation from a free surface. The insets in a, b Fourier-filtered images (reconstructed using the spatial frequencies of the (111) planes) of the black square area, respectively. The scale bar in each figure represents 3 nm. (d, e) The strain mapping of the white-boxed area in HRTEM images before a and after b shows the nucleation of a partial dislocation. The black arrowheads indicate the site for dislocation nucleation. Open circles on the upper right part of the two figures represent the twinning lamella. (f) A quantitative strain analysis of the black-boxed region in d and e; frequency is the number of atoms with that strain divided by the total number of atoms in the black-boxed area in d and e. (g–k) MD simulations illustrating the atomic process of nucleation (h), propagation of the leading partial producing a stacking fault (i) and the nucleation of the trailing partial (j), where bL and bT mark the location of leading and trailing partials, respectively. Eventually, the combined perfect dislocation leaves out of the sample (k). Colours are assigned to the atoms according to a local crystallinity classification visualized by common neighbour analysis (see Methods for details).

Mentions: Figure 1 shows the tensile loading of an Au nanocrystal under a strain rate of 10−3 s−1. The beam is orientated along the [11̄0] and the tensile loading direction is [001] (Fig. 1a). Figure 1a shows an abundance of {111} facets, which have the lowest surface energy, separated by surface steps on the Au crystal surface. It should be noted that the {111} facets are also frequently encountered in as-synthesized FCC nanocrystals18. Interestingly, a pre-existing twin boundary is present as well. On tensile loading, dislocation emission from the grain boundary near the left contact was observed (Supplementary Figs S1 and S2, Supplementary Movie 1 and Supplementary Discussion).


Discrete plasticity in sub-10-nm-sized gold crystals.

Zheng H, Cao A, Weinberger CR, Huang JY, Du K, Wang J, Ma Y, Xia Y, Mao SX - Nat Commun (2010)

Tensile loading test of an Au nanocrystal.This tensile test (see also Supplementary Movie 1) shows that surface steps act as the dislocation sources (see also Supplementary Movie 2). (a–c) Sequential HRTEM images showing the emission of a dislocation from a free surface. The insets in a, b Fourier-filtered images (reconstructed using the spatial frequencies of the (111) planes) of the black square area, respectively. The scale bar in each figure represents 3 nm. (d, e) The strain mapping of the white-boxed area in HRTEM images before a and after b shows the nucleation of a partial dislocation. The black arrowheads indicate the site for dislocation nucleation. Open circles on the upper right part of the two figures represent the twinning lamella. (f) A quantitative strain analysis of the black-boxed region in d and e; frequency is the number of atoms with that strain divided by the total number of atoms in the black-boxed area in d and e. (g–k) MD simulations illustrating the atomic process of nucleation (h), propagation of the leading partial producing a stacking fault (i) and the nucleation of the trailing partial (j), where bL and bT mark the location of leading and trailing partials, respectively. Eventually, the combined perfect dislocation leaves out of the sample (k). Colours are assigned to the atoms according to a local crystallinity classification visualized by common neighbour analysis (see Methods for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3105591&req=5

f1: Tensile loading test of an Au nanocrystal.This tensile test (see also Supplementary Movie 1) shows that surface steps act as the dislocation sources (see also Supplementary Movie 2). (a–c) Sequential HRTEM images showing the emission of a dislocation from a free surface. The insets in a, b Fourier-filtered images (reconstructed using the spatial frequencies of the (111) planes) of the black square area, respectively. The scale bar in each figure represents 3 nm. (d, e) The strain mapping of the white-boxed area in HRTEM images before a and after b shows the nucleation of a partial dislocation. The black arrowheads indicate the site for dislocation nucleation. Open circles on the upper right part of the two figures represent the twinning lamella. (f) A quantitative strain analysis of the black-boxed region in d and e; frequency is the number of atoms with that strain divided by the total number of atoms in the black-boxed area in d and e. (g–k) MD simulations illustrating the atomic process of nucleation (h), propagation of the leading partial producing a stacking fault (i) and the nucleation of the trailing partial (j), where bL and bT mark the location of leading and trailing partials, respectively. Eventually, the combined perfect dislocation leaves out of the sample (k). Colours are assigned to the atoms according to a local crystallinity classification visualized by common neighbour analysis (see Methods for details).
Mentions: Figure 1 shows the tensile loading of an Au nanocrystal under a strain rate of 10−3 s−1. The beam is orientated along the [11̄0] and the tensile loading direction is [001] (Fig. 1a). Figure 1a shows an abundance of {111} facets, which have the lowest surface energy, separated by surface steps on the Au crystal surface. It should be noted that the {111} facets are also frequently encountered in as-synthesized FCC nanocrystals18. Interestingly, a pre-existing twin boundary is present as well. On tensile loading, dislocation emission from the grain boundary near the left contact was observed (Supplementary Figs S1 and S2, Supplementary Movie 1 and Supplementary Discussion).

Bottom Line: Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking.Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure.These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.

ABSTRACT
Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking. Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure. These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years.

No MeSH data available.


Related in: MedlinePlus