Dynamics and Removal Pathway of Edge Dislocations in Imperfectly Attached PbTe Nanocrystal Pairs: Toward Design Rules for Oriented Attachment

Using in situ high-resolution TEM, we study the
structure and dynamics of well-defined edge dislocations in imperfectly
attached PbTe nanocrystals. We identify that attachment of PbTe nanocrystals
on both {100} and {110} facets gives rise to b = a/2⟨110⟩ edge dislocations. Based on the Burgers
vector of individual dislocations, we can identify the glide plane
of the dislocations. We observe that defects in particles attached
on {100} facets have glide planes that quickly intersect the surface,
and HRTEM movies show that the defects follow the glide plane to the
surface. For {110} attached particles, the glide plane is collinear
with the attachment direction, which does not provide an easy path
for the dislocation to reach the surface. Indeed, HRTEM movies of
dislocations for {110} attached particles show that defect removal
is much slower. Further, we observe conversion from pure edge dislocations
in imperfectly attached particles to dislocations with mixed edge
and screw character, which has important implications for crystal
growth. Finally, we observe that dislocations initially closer to
the surface have a higher speed of removal, consistent with the strong
dislocation free surface attractive force. Our results provide important
design rules for defect-free attachment of preformed nanocrystals
into epitaxial assemblies