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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

Dislocation slip and deformation twinning with their quantitative strain analysis.(a, b) In a, individual slip dominates the plastic deformation for a [001] loading, whereas in b twinning is the main deformation mode for [110] loading, see also Supplementary Movies 1, 2 and 3. (c, d) Sequential images captured before and after the twinning partials are emitted; the double arrowheads indicate the location of the deformation twins. The scale bar in each figure represents 4 nm. (e, f) The strain mapping of the HRTEM images of c and d, respectively, showing a strain relaxation immediately after the twin formation. Likewise, the open circles are drawn to represent the twinning partials. (g) A quantitative strain analysis, performed using the LADIA software, of the black-box region in e and f, showing data before (green curve) and after twinning (red curve). All images are taken along the [11̄0] zone axis. The surface steps indicated by the arrowheads are caused by partial dislocation slip and the double arrowheads show the deformation twins.
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f4: Dislocation slip and deformation twinning with their quantitative strain analysis.(a, b) In a, individual slip dominates the plastic deformation for a [001] loading, whereas in b twinning is the main deformation mode for [110] loading, see also Supplementary Movies 1, 2 and 3. (c, d) Sequential images captured before and after the twinning partials are emitted; the double arrowheads indicate the location of the deformation twins. The scale bar in each figure represents 4 nm. (e, f) The strain mapping of the HRTEM images of c and d, respectively, showing a strain relaxation immediately after the twin formation. Likewise, the open circles are drawn to represent the twinning partials. (g) A quantitative strain analysis, performed using the LADIA software, of the black-box region in e and f, showing data before (green curve) and after twinning (red curve). All images are taken along the [11̄0] zone axis. The surface steps indicated by the arrowheads are caused by partial dislocation slip and the double arrowheads show the deformation twins.

Mentions: We also found that the tensile loading direction affects the deformation mechanisms of sub-10-nm Au significantly. Figure 4a,b (see Supplementary Movies 4 and 5) shows that slip and twinning are favoured under 〈001〉 and 〈110〉 tensile loading directions, respectively, which confirms theoretical predictions5. The dominant effect is the Schmid law, which indicates that the slip system with highest Schmid factor is preferred on the deformation modes in small-scale materials. For the 〈001〉 orientation, the Schmid factor for the trailing partial is higher than the leading partial, which suggests that slip is preferred. However, for the 〈110〉 direction, the Schmid factor for leading partial is higher, which therefore enhances the propensity of twinning5.


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)

Dislocation slip and deformation twinning with their quantitative strain analysis.(a, b) In a, individual slip dominates the plastic deformation for a [001] loading, whereas in b twinning is the main deformation mode for [110] loading, see also Supplementary Movies 1, 2 and 3. (c, d) Sequential images captured before and after the twinning partials are emitted; the double arrowheads indicate the location of the deformation twins. The scale bar in each figure represents 4 nm. (e, f) The strain mapping of the HRTEM images of c and d, respectively, showing a strain relaxation immediately after the twin formation. Likewise, the open circles are drawn to represent the twinning partials. (g) A quantitative strain analysis, performed using the LADIA software, of the black-box region in e and f, showing data before (green curve) and after twinning (red curve). All images are taken along the [11̄0] zone axis. The surface steps indicated by the arrowheads are caused by partial dislocation slip and the double arrowheads show the deformation twins.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Dislocation slip and deformation twinning with their quantitative strain analysis.(a, b) In a, individual slip dominates the plastic deformation for a [001] loading, whereas in b twinning is the main deformation mode for [110] loading, see also Supplementary Movies 1, 2 and 3. (c, d) Sequential images captured before and after the twinning partials are emitted; the double arrowheads indicate the location of the deformation twins. The scale bar in each figure represents 4 nm. (e, f) The strain mapping of the HRTEM images of c and d, respectively, showing a strain relaxation immediately after the twin formation. Likewise, the open circles are drawn to represent the twinning partials. (g) A quantitative strain analysis, performed using the LADIA software, of the black-box region in e and f, showing data before (green curve) and after twinning (red curve). All images are taken along the [11̄0] zone axis. The surface steps indicated by the arrowheads are caused by partial dislocation slip and the double arrowheads show the deformation twins.
Mentions: We also found that the tensile loading direction affects the deformation mechanisms of sub-10-nm Au significantly. Figure 4a,b (see Supplementary Movies 4 and 5) shows that slip and twinning are favoured under 〈001〉 and 〈110〉 tensile loading directions, respectively, which confirms theoretical predictions5. The dominant effect is the Schmid law, which indicates that the slip system with highest Schmid factor is preferred on the deformation modes in small-scale materials. For the 〈001〉 orientation, the Schmid factor for the trailing partial is higher than the leading partial, which suggests that slip is preferred. However, for the 〈110〉 direction, the Schmid factor for leading partial is higher, which therefore enhances the propensity of twinning5.

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