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Atomic-scale analysis of defect dynamics and strain relaxation mechanisms in biaxially strained ultrathin films of face-centered cubic metals
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10.1063/1.2938022
/content/aip/journal/jap/103/12/10.1063/1.2938022
http://aip.metastore.ingenta.com/content/aip/journal/jap/103/12/10.1063/1.2938022
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(a) Evolution of potential energy (per atom), , during biaxial strain relaxation; different evolution curves correspond to different applied biaxial strain levels. The response of the film is elastic up to a strain level of almost 5.5% and the response curves in the elastic deformation regime are not plotted. In the evolution curves shown, the observed oscillatory dynamics corresponds to the initial elastic response to the applied biaxial strain. Also, the energy maximum is higher for higher applied strain level. (b) Dependence on the applied biaxial strain level, , of the strain relaxation time of the thin film and the time for which the thin film exhibits elastic response to applied biaxial strain.

Image of FIG. 2.
FIG. 2.

(a) Top view of the thin-film surface after strain relaxation for different applied biaxial strain levels, . The atoms are shaded (colored online) according to their height in the surface topography; greater shade (color online) contrasts correspond to rougher film surfaces. (b) Evolution of the surface roughness during biaxial strain relaxation; different curves correspond to different applied biaxial strain levels over the range . (c) Dependence on of the surface roughness of the strain-relaxed thin films; corresponds to the steady-state value reached in the evolution shown in (b).

Image of FIG. 3.
FIG. 3.

(a) Evolution of defect atoms with during biaxial strain relaxation; different curves correspond to different applied biaxial strain levels over the range . (b) Dependence on of the percentages of various kinds of atoms (fcc, hcp, and defect atoms) in strain-relaxed thin films. (c) Top view of the thin films after relaxation of the applied biaxial strain, showing the resulting dislocation density; dark and light shaded (blue online) atoms are in local perfect fcc and hcp arrangements, respectively. Atoms with other shades of gray (colors online) correspond to point defects, as well as atoms in the dislocation cores. Surface atoms are not shown for clarity.

Image of FIG. 4.
FIG. 4.

Top views of a section of a strain-relaxed thin film that has been subjected to a high strain , showing the formed nanodomains and their misorientations. Darker shaded (maroon colored online) atoms are surface atoms with ; other atoms mark traces of dislocation activity or locations where point defects are annealed.

Image of FIG. 5.
FIG. 5.

(a) A {111} plane of the Thompson tetrahedron. [(b)–(d)] 3D close view of biaxially strained thin-film material showing the evolution of a threading dislocation from one surface of the film as it extends through the film and intersects with the other film surface. Dark gray (colored dark blue online) atoms are in perfect hcp lattice arrangements. Very light gray (colored light green online) atoms have and light gray (colored light blue online) atoms have . Surface atoms are darker shaded (colored maroon online) and atoms in locally perfect fcc lattice positions are not shown for clarity. The corresponding time in the MD simulation is recorded, starting from the film in its unstrained state.

Image of FIG. 6.
FIG. 6.

[(a)–(d)] A {111} view of biaxially strained thin-film material showing the nucleation and evolution of a dislocation from the bulk of the film as it grows and intersects with one of the film surfaces becoming a threading dislocation loop. Dark gray (colored dark blue online) and light gray (colored light blue online) atoms are in perfect fcc and hcp lattice arrangements, respectively. Lighter gray (colored light green online) atoms have and very light gray (colored yellow online) atoms have . Surface atoms are given a moderately dark gray shade (colored maroon online). [(e)–(h)] 3D close view of the same biaxially strained thin-film material for the same evolution sequence shown in the top row of configurations, (a)–(d), wherein atoms in perfect fcc lattice arrangements are not shown for clarity. The corresponding time in the MD simulation is recorded, starting from the film in its unstrained state.

Image of FIG. 7.
FIG. 7.

(a) Pair correlation function of the thin-film material during application of biaxial tensile strain at a level ; dark and light gray (colored red and green online) curves correspond to the before and after strain relaxation. [(b) and (c)] Top views of the thin-film material during the initial stage of strain relaxation. Dark and light gray (colored dark blue and green online) atoms are in perfect fcc and hcp lattice positions, respectively. Other colored atoms are associated with point defects and dislocations. Surface atoms are not shown for clarity. (d) Same top view as in (b) and (c), where neither surface atoms nor atoms in perfect fcc lattice arrangements are shown for clarity. Light gray (colored light blue online) atoms are in a local hcp lattice arrangement. (b)–(d) are snapshots at a time instant in the MD simulation.

Image of FIG. 8.
FIG. 8.

[(a)–(c)] Top views of a section of a biaxially strained thin film at a level , showing in detail the different stages of dislocation activity in successive atomic planes leading to the formation of two- and three-layer microtwins. Dark and moderately light gray (colored dark blue and light blue online) atoms are in locally perfect fcc and hcp environments, respectively; moderately dark and very light gray (colored red and orange online) atoms have and , respectively; and light gray (colored green online) atoms are those surrounding point and line defects. Surface atoms are removed for clarity. The initial positions of the partial dislocations are labeled as A, B, and C in (a). The glide of dislocations B and C causes the formation of extrinsic stacking faults, while the glide of dislocation A leaves behind an intrinsic stacking fault. Dislocations A and B glide in opposite directions, which causes the unzipping of one layer of hcp atoms, leading to the formation of a two-layer microtwin. The glide of dislocation C also leads to the unzipping of one layer of hcp atoms and leads to the formation of a three-layer microtwin. (d) A view of a single plane of atoms showing the twin and the twin boundary.

Image of FIG. 9.
FIG. 9.

[(a)–(d)] 3D close view of structural evolution in a biaxially strained thin film during the formation of a Lomer–Cottrell junction. Gray (colored blue online) atoms are in perfect hcp lattice positions. Light gray and very light gray (colored green and yellow online) atoms have and , respectively, and these atoms represent the dislocation core. Other atoms correspond to lower coordination defects and atoms on the surface; atoms in locally perfect fcc lattice arrangements are not shown for clarity. The corresponding total time in the MD simulation is recorded, starting from the film in its unstrained state. Two dislocations, and , extend across the film thickness and bind the stacking fault in the plane, while the threading dislocation, , binds the second stacking fault in the plane. Dislocation reacts with dislocation to form a stair-rod dislocation according to the reaction and is represented in (c) and (d) by a straight line of atoms with . This dislocation junction, consisting of mobile Shockley partial dislocations together with the sessile stair-rod dislocation, represents a Lomer–Cottrell lock.

Image of FIG. 10.
FIG. 10.

(a) A {111} view and (b) a 3D close view of a complex immobile stable junction; dark gray and light gray (colored dark blue and light blue online) atoms are in perfect local fcc and hcp environments, respectively, and atoms with other shades of gray (other colors online) have , representing point defects and dislocations. Surface atoms and atoms in a locally perfect fcc lattice arrangement are not shown in (b) for clarity. The two junctions are denoted by A and B. and are a threading dislocation loop and a stair-rod dislocation, respectively, forming junction B.

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/content/aip/journal/jap/103/12/10.1063/1.2938022
2008-06-19
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Atomic-scale analysis of defect dynamics and strain relaxation mechanisms in biaxially strained ultrathin films of face-centered cubic metals
http://aip.metastore.ingenta.com/content/aip/journal/jap/103/12/10.1063/1.2938022
10.1063/1.2938022
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