Nanocrystalline copper films are never flat

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Science  28 Jul 2017:
Vol. 357, Issue 6349, pp. 397-400
DOI: 10.1126/science.aan4797
  • Fig. 1 GBs at ridges and valleys in (111) films of Cu.

    (A) Perspective view of the STM topography of NC Cu film. Tunneling parameters are I = 20 pA and U = 0.2 V. GBs at ridge and valley locations are highlighted by arrows. (B) Close-up view of one GB at valley location. (C) Close-up view of one GB at ridge location. (D) Profile of valley and ridge line cross sections marked by the dashed lines in (B) and (C), respectively. The color of each curve is consistent with that of lines in (B) and (C).

  • Fig. 2 Atomic structure of emergent LAGBs.

    (A) Atomic-resolution STM image of a valley GB segment with ~3° out-of-plane angle. The green path shows a Burgers circuit. The white dotted lines are along Embedded Image and solid lines along Embedded Image. The repeat sequence 3, 4, 4 is shown along Embedded Image. The components of Embedded Image are shown in units of a. The measured boundary misorientation angle θ between the grains is 16.2°. (B) Atomic-resolution STM image of a second valley GB area with a smaller out-of-plane angle. The image contains two dissociated edge dislocations across the GB. (Inset) Plot of the step profile (data points) of the dissociated edge dislocation, which shows the equal and opposite Shockley partials (arrows). (C) Atomic-resolution image of a ridge GB segment.

  • Fig. 3 Relation between in-plane θ and out-of-plane Embedded Image rotations and calculated GB energy.

    (A) Schematic of LAGB-induced film tilting at in-plane angle θ and out-of-plane angle Embedded Image that shows the inclination angle ψ between the dislocation line and the surface normal. (B) Experimentally measured Embedded Image versus θ. (C) Calculated GB energy dependence on ψ for three cases with different θ. Each case exhibits a minimum at ψ = 19.47°.

  • Fig. 4 Molecular statics simulations of LAGBs with θ = 3.89°.

    (A to C) The out-of-plane angles are (A) Embedded Image, (B) 0.79°, and (C) 1.37°. Atoms are colored by central symmetry, and hence, only the atoms located at the defects are visible. Front views show that the density reduction of jogs and increasing separation of the partials as ψ approaches 19.47°. Side views show the inclination of two SFs of one GB. Top view shows the different structures of the GBs emerging at the surface.

Supplementary Materials

  • Nanocrystalline copper films are never flat

    Xiaopu Zhang, Jian Han, John J. Plombon, Adrian P. Sutton, David J. Srolovitz, John J. Boland

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Supplementary Text
    • Figs. S1 and S2
    • Table S1
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