posted on 2020-02-06, 22:44authored byHarshal Agrawal, Biplab K. Patra, Thomas Altantzis, Annick De Backer, Erik C. Garnett
Nanoparticle
self-assembly and epitaxy are utilized extensively
to make 1D and 2D structures with complex shapes. High-resolution
transmission electron microscopy (HRTEM) has shown that single-crystalline
interfaces can form, but little is known about the strain and dislocations
at these interfaces. Such information is critically important for
applications: drastically reducing dislocation density was the key
breakthrough enabling widespread implementation of light-emitting
diodes, while strain engineering has been fundamental to modern high-performance
transistors, solar cells, and thermoelectrics. In this work, the interfacial
defect and strain formation after self-assembly and room temperature
epitaxy of 7 nm Pd nanocubes capped with polyvinylpyrrolidone (PVP)
is examined. It is observed that, during ligand removal, the cubes
move over large distances on the substrate, leading to both spontaneous
self-assembly and epitaxy to form single crystals. Subsequently, atomically
resolved images are used to quantify the strain and dislocation density
at the epitaxial interfaces between cubes with different lateral and
angular misorientations. It is shown that dislocation- and strain-free
interfaces form when the nanocubes align parallel to each other. Angular
misalignment between adjacent cubes does not necessarily lead to grain
boundaries but does cause dislocations, with higher densities associated
with larger rotations.