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Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction.

Qin Q, Yin S, Cheng G, Li X, Chang TH, Richter G, Zhu Y, Gao H - Nat Commun (2015)

Bottom Line: There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices.In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour.More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.

ABSTRACT
There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices. Here we report a dislocation-mediated, time-dependent and fully reversible plastic behaviour in penta-twinned silver nanowires. In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour. Molecular dynamics simulations reveal that the observed behaviour in penta-twinned nanowires originates from the surface nucleation, propagation and retraction of partial dislocations. More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.

No MeSH data available.


Related in: MedlinePlus

Structural characterization of single-crystal and penta-twinned Ag NWs.(a,b) Low-magnification and high-resolution TEM images of single-crystal Ag NW with growth direction of <110>. Scale bar, 200 and 2 nm, respectively. Right and left insets (scale bar, 100 nm) in a show the selected area electron diffraction (SAED) pattern taken from <110> zone axis and the hexagonal cross-sectional shape from SEM observation, respectively. (c) TEM image of Ag NWs showing fivefold twinned structure. Scale bar, 200 nm. Right and left insets (scale bar, 20 nm) in c display the corresponding SAED pattern and the pentagonal cross-sectional shape, respectively. Stacking faults along the boundary between grains IV and V can be clearly seen in the left inset of c. (d) High-angle annular dark-field scanning TEM image of the cross-sectional sample showing the presence of vacancy defects near the boundary between grains IV and V. The yellow star in d indicates the centre of the cross-sectional sample. Scale bar, 2 nm.
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f1: Structural characterization of single-crystal and penta-twinned Ag NWs.(a,b) Low-magnification and high-resolution TEM images of single-crystal Ag NW with growth direction of <110>. Scale bar, 200 and 2 nm, respectively. Right and left insets (scale bar, 100 nm) in a show the selected area electron diffraction (SAED) pattern taken from <110> zone axis and the hexagonal cross-sectional shape from SEM observation, respectively. (c) TEM image of Ag NWs showing fivefold twinned structure. Scale bar, 200 nm. Right and left insets (scale bar, 20 nm) in c display the corresponding SAED pattern and the pentagonal cross-sectional shape, respectively. Stacking faults along the boundary between grains IV and V can be clearly seen in the left inset of c. (d) High-angle annular dark-field scanning TEM image of the cross-sectional sample showing the presence of vacancy defects near the boundary between grains IV and V. The yellow star in d indicates the centre of the cross-sectional sample. Scale bar, 2 nm.

Mentions: Microstructure characterization of single-crystalline and penta-twinned Ag NWs is shown in Fig. 1. Both types of NWs are straight and uniform in diameter, with growth direction of <110>, as shown by transmission electron microscopy (TEM) images and selected area electron diffraction patterns in Fig. 1a,c. The single-crystalline Ag NWs exhibit a hexagonal cross-sectional morphology (inset of Fig. 1a). Figure 1b shows a high-resolution TEM image of a single-crystalline Ag NW, indicating a perfect atomic structure along the longitudinal direction and a uniform atomic arrangement at {002} surface facets. The penta-twinned Ag NWs contain a fivefold twinned nanostructure with five TBs running along {111} planes in parallel to the longitudinal axis of the NWs and five surface facets along {100} planes with a pentagonal cross-sectional morphology (inset of Fig. 1c)1834.


Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction.

Qin Q, Yin S, Cheng G, Li X, Chang TH, Richter G, Zhu Y, Gao H - Nat Commun (2015)

Structural characterization of single-crystal and penta-twinned Ag NWs.(a,b) Low-magnification and high-resolution TEM images of single-crystal Ag NW with growth direction of <110>. Scale bar, 200 and 2 nm, respectively. Right and left insets (scale bar, 100 nm) in a show the selected area electron diffraction (SAED) pattern taken from <110> zone axis and the hexagonal cross-sectional shape from SEM observation, respectively. (c) TEM image of Ag NWs showing fivefold twinned structure. Scale bar, 200 nm. Right and left insets (scale bar, 20 nm) in c display the corresponding SAED pattern and the pentagonal cross-sectional shape, respectively. Stacking faults along the boundary between grains IV and V can be clearly seen in the left inset of c. (d) High-angle annular dark-field scanning TEM image of the cross-sectional sample showing the presence of vacancy defects near the boundary between grains IV and V. The yellow star in d indicates the centre of the cross-sectional sample. Scale bar, 2 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4308715&req=5

f1: Structural characterization of single-crystal and penta-twinned Ag NWs.(a,b) Low-magnification and high-resolution TEM images of single-crystal Ag NW with growth direction of <110>. Scale bar, 200 and 2 nm, respectively. Right and left insets (scale bar, 100 nm) in a show the selected area electron diffraction (SAED) pattern taken from <110> zone axis and the hexagonal cross-sectional shape from SEM observation, respectively. (c) TEM image of Ag NWs showing fivefold twinned structure. Scale bar, 200 nm. Right and left insets (scale bar, 20 nm) in c display the corresponding SAED pattern and the pentagonal cross-sectional shape, respectively. Stacking faults along the boundary between grains IV and V can be clearly seen in the left inset of c. (d) High-angle annular dark-field scanning TEM image of the cross-sectional sample showing the presence of vacancy defects near the boundary between grains IV and V. The yellow star in d indicates the centre of the cross-sectional sample. Scale bar, 2 nm.
Mentions: Microstructure characterization of single-crystalline and penta-twinned Ag NWs is shown in Fig. 1. Both types of NWs are straight and uniform in diameter, with growth direction of <110>, as shown by transmission electron microscopy (TEM) images and selected area electron diffraction patterns in Fig. 1a,c. The single-crystalline Ag NWs exhibit a hexagonal cross-sectional morphology (inset of Fig. 1a). Figure 1b shows a high-resolution TEM image of a single-crystalline Ag NW, indicating a perfect atomic structure along the longitudinal direction and a uniform atomic arrangement at {002} surface facets. The penta-twinned Ag NWs contain a fivefold twinned nanostructure with five TBs running along {111} planes in parallel to the longitudinal axis of the NWs and five surface facets along {100} planes with a pentagonal cross-sectional morphology (inset of Fig. 1c)1834.

Bottom Line: There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices.In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour.More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, North Carolina 27695, USA.

ABSTRACT
There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices. Here we report a dislocation-mediated, time-dependent and fully reversible plastic behaviour in penta-twinned silver nanowires. In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour. Molecular dynamics simulations reveal that the observed behaviour in penta-twinned nanowires originates from the surface nucleation, propagation and retraction of partial dislocations. More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.

No MeSH data available.


Related in: MedlinePlus