Limits...
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

Necking of the nanocrystal.The figure depicts the same nanocrystal shown in Figure 1 (see also Supplementary Movie 3). (a, b) The experimental observations of the cooperative slip between two conjugate {111} planes, leading to the enlargement of the surface steps indicated by the arrowheads. A 10% elastic strain is estimated from the change of the (002) lattice plane spacing. (c) Final fracture of the nanocrystal. The scale bar in each figure represents 3 nm. (d–i) A profile view of the MD simulations of the necking process induced by slip. Atoms are coloured according to the coordination numbers (see Supplementary Materials for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3105591&req=5

f2: Necking of the nanocrystal.The figure depicts the same nanocrystal shown in Figure 1 (see also Supplementary Movie 3). (a, b) The experimental observations of the cooperative slip between two conjugate {111} planes, leading to the enlargement of the surface steps indicated by the arrowheads. A 10% elastic strain is estimated from the change of the (002) lattice plane spacing. (c) Final fracture of the nanocrystal. The scale bar in each figure represents 3 nm. (d–i) A profile view of the MD simulations of the necking process induced by slip. Atoms are coloured according to the coordination numbers (see Supplementary Materials for details).

Mentions: With extensive tensile elongation, necking occurs in the nanocrystal (Fig. 2), which is a result of discrete cooperative slip events on two conjugate {111} planes, giving rise to a number of enlarged surface steps (Fig. 2a–c, see also Supplementary Movie 3). The surface steps are one or two atomic planes apart, exhibiting a saw-tooth morphology. These discrete surface steps could correspond to the quantized plastic deformation observed in tensile-deformed Au nanowires (NWs) conducted by atomic force microscope, wherein the length of the NW was characterized by quantized increment due to the slippage between {111} planes22. The necking process induced by slip in Figure 2a,b is also clearly captured in our MD simulations (Fig. 2d–i). Figure 2f,h specifically shows slip along two sets of {111} planes. When the inhomogeneous deformation occurs in MD simulations, relative slip between two adjacent {111} planes is accompanied by rapid cross-section area reduction, similar to Figure 2a,b. One noticeable difference is the final fracture surface. Fracture in experiments shows a {001} surface enclosed by {111} facets, whereas MD simulations only show {111} facets. The differences could be caused by a number of factors including the stiffness of the loading frame, strain rate effects of MD simulations or the assumed geometry in the MD model.


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)

Necking of the nanocrystal.The figure depicts the same nanocrystal shown in Figure 1 (see also Supplementary Movie 3). (a, b) The experimental observations of the cooperative slip between two conjugate {111} planes, leading to the enlargement of the surface steps indicated by the arrowheads. A 10% elastic strain is estimated from the change of the (002) lattice plane spacing. (c) Final fracture of the nanocrystal. The scale bar in each figure represents 3 nm. (d–i) A profile view of the MD simulations of the necking process induced by slip. Atoms are coloured according to the coordination numbers (see Supplementary Materials for details).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Necking of the nanocrystal.The figure depicts the same nanocrystal shown in Figure 1 (see also Supplementary Movie 3). (a, b) The experimental observations of the cooperative slip between two conjugate {111} planes, leading to the enlargement of the surface steps indicated by the arrowheads. A 10% elastic strain is estimated from the change of the (002) lattice plane spacing. (c) Final fracture of the nanocrystal. The scale bar in each figure represents 3 nm. (d–i) A profile view of the MD simulations of the necking process induced by slip. Atoms are coloured according to the coordination numbers (see Supplementary Materials for details).
Mentions: With extensive tensile elongation, necking occurs in the nanocrystal (Fig. 2), which is a result of discrete cooperative slip events on two conjugate {111} planes, giving rise to a number of enlarged surface steps (Fig. 2a–c, see also Supplementary Movie 3). The surface steps are one or two atomic planes apart, exhibiting a saw-tooth morphology. These discrete surface steps could correspond to the quantized plastic deformation observed in tensile-deformed Au nanowires (NWs) conducted by atomic force microscope, wherein the length of the NW was characterized by quantized increment due to the slippage between {111} planes22. The necking process induced by slip in Figure 2a,b is also clearly captured in our MD simulations (Fig. 2d–i). Figure 2f,h specifically shows slip along two sets of {111} planes. When the inhomogeneous deformation occurs in MD simulations, relative slip between two adjacent {111} planes is accompanied by rapid cross-section area reduction, similar to Figure 2a,b. One noticeable difference is the final fracture surface. Fracture in experiments shows a {001} surface enclosed by {111} facets, whereas MD simulations only show {111} facets. The differences could be caused by a number of factors including the stiffness of the loading frame, strain rate effects of MD simulations or the assumed geometry in the MD model.

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