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Screw Dislocation Generation by Inclusions in Molecular Crystals
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posted on 2017-12-20, 15:04 authored by Xiaodi Zhong, Alexander G. Shtukenberg, Theodore Hueckel, Bart Kahr, Michael D. WardDislocations
in crystals affect material properties and are essential
for crystal growth near equilibrium, yet their genesis in the absence
of external or internal stresses is unresolved. X-ray topography has
revealed microscopic inclusions as dislocation sources, but the real-time
creation of a dislocation by a particulate inclusion has not been
reported. In situ atomic force microscopy (AFM) was used herein to
visualize dislocation generation in an l-cystine crystal
by a cube-like hematite particle embedded in, and slightly inclined
with respect to, the l-cystine {0001} surface. The particle
produced two pairs of heterochiral screw dislocations with opposing
Burgers vectors. After overgrowth of the particle, dissolution in
undersaturated solutions revealed the dislocations once again until
the detachment of the particle exposed a flat basal plane devoid of
dislocations, thereby corroborating the essential role of the particle.
Hematite particles with their flat faces parallel or at high angle
to the surface, as well as spherical poly(styrene) particles, did
not produce dislocations, suggesting that shape and orientation of
the particle with respect to the step train advancing across the growing
crystal surface are critical features for dislocation generation.