Effect of Eshelby twist on core structure of screw dislocations in molybdenum: atomic structure and electron microscope image simulations

Gröger, Roman; Dudeck, K. J.; Nellist, Peter D.; Vítek, V.; Hirsch, P. B.; Cockayne, D. J. H.

doi:10.1080/14786435.2011.562474

Cited by 18 publications

(6 citation statements)

References 28 publications

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“…Screw dislocations are characterized by equivalent atoms in columns parallel to the screw dislocations being displaced along the screw axis to form a helicoid, which cannot be observed end-on because the displacements are parallel to the viewing direction. Such screw dislocations do however show small rotational displacements in thin foils due to surface stress relaxations known as the Eshelby twist 6 , and these can affect both the contrast and peak positions in high-resolution images 7 8 9 10 . Here we show that the helicoidal displacements around a screw can be imaged directly with the dislocation lying in a plane transverse to the electron beam by optical sectioning using annular dark field (ADF) imaging in a scanning transmission electron microscope (STEM).…”

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Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning

et al. 2015

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Screw dislocations play an important role in materials' mechanical, electrical and optical properties. However, imaging the atomic displacements in screw dislocations remains challenging. Although advanced electron microscopy techniques have allowed atomic-scale characterization of edge dislocations from the conventional end-on view, for screw dislocations, the atoms are predominantly displaced parallel to the dislocation line, and therefore the screw displacements are parallel to the electron beam and become invisible when viewed end-on. Here we show that screw displacements can be imaged directly with the dislocation lying in a plane transverse to the electron beam by optical sectioning using annular dark field imaging in a scanning transmission electron microscope. Applying this technique to a mixed [a+c] dislocation in GaN allows direct imaging of a screw dissociation with a 1.65-nm dissociation distance, thereby demonstrating a new method for characterizing dislocation core structures.

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Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning

et al. 2015

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“…Sears, 1959). Evidence for the Eshelby twist is commonly observed in the TEM since it is responsible for local displacements observable in high-resolution transmission electron microscopy close to the dislocation core where it meets free surfaces (Cosgriff et al, 2010;Gröger et al, 2011). Nanotechnologies provide new evidence for Eshelby twists: for instance, Bierman et al (2008) show a spectacular example of pine tree like nanowires with helically rotating epitaxial branch nanowires.…”

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confidence: 99%

Origin of twist in 'gwindel' quartz crystals from the Alps: a transmission electron microscopy study

Heidelbach

2013

ejm

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Two twisted quartz crystals (gwindels) from the Alps were studied by transmission electron microscopy and large-angle convergent-beam electron diffraction (LACBED) to elucidate the twist mechanism. We found that torsion results from a distribution of straight screw geometrically necessary b ¼ 1 3 2110 dislocations with a dislocation density of the order of 10 10 m À2. This dislocation microstructure induces an Eshelby twist which can account for the observed twist of a few degrees per centimetre. This microstructure suggests that twisted gwindel quartz forms by the spiral growth mechanism which enables crystal growth under small driving forces.

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“…15 ½,111. screw dislocations are well studied experimentally and theoretically in coarse-grained (CG) bcc metals and alloys [9][10][11][12][13][16][17][18][19] , but ½,111. edge dislocations have been rarely studied.…”

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confidence: 99%

Dislocations with edge components in nanocrystalline bcc Mo

Cheng

Jian

et al. 2013

J. Mater. Res.

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We report high-resolution transmission electron microscopy (HRTEM) observation of a high density of dislocations with edge components (;10 16 m À2 ) in nanocrystalline (NC) body-centered cubic (bcc) Mo prepared by high-pressure torsion. We also observed for the first time of the ½,111. and ,001. pure edge dislocations in NC Mo. Crystallographic analysis and image simulations reveal that the best way using HRTEM to study dislocations with edge components in bcc systems is to take images along ,110. zone axis, from which it is possible to identify ½,111. pure edge dislocations, and edge components of ½,111. and ,001. mixed dislocations. The ,001. pure edge dislocations can only be identified from ,100. zone axis. The high density of dislocations with edge components is believed to play a major role in the reduction of strain rate sensitivity in NC bcc metals and alloys.

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Effect of Eshelby twist on core structure of screw dislocations in molybdenum: atomic structure and electron microscope image simulations

Cited by 18 publications

References 28 publications

Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning

Imaging screw dislocations at atomic resolution by aberration-corrected electron optical sectioning

Origin of twist in 'gwindel' quartz crystals from the Alps: a transmission electron microscopy study

Dislocations with edge components in nanocrystalline bcc Mo

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