Strain-release mechanisms in bimetallic core-shell nanoparticles as revealed by Cs-corrected STEM

Area of Science:

• Materials Science
• Nanotechnology
• Surface Science

Background:

• Lattice mismatch in core-shell nanoparticles induces strain in the epitaxial shell.
• Exceeding critical layer thickness results in misfit dislocations, altering nanoparticle properties.

Purpose of the Study:

• To observe and track the evolution of dislocations in gold-palladium (AuPd) core-shell nanoparticles.
• To investigate the impact of shell growth on strain and defect formation.

Main Methods:

• Aberration-corrected scanning transmission electron microscopy (STEM) was employed.
• Direct observation and in-situ analysis of dislocation evolution within AuPd nanoparticles.

Main Results:

• Shockley partial dislocations (SPDs) and stacking faults (SFs) initially formed at the palladium (Pd) layer.
• As shell growth progressed, SPDs and SFs merged with misfit dislocations at the interface.
• Alloying of gold (Au) into the Pd shell facilitated dislocation diffusion to free surfaces.
• The critical layer thickness for defect formation was at least 50% greater in nanoparticles compared to thin films.

Conclusions:

• Nanoparticle shells can accommodate significantly higher strain than thin films due to their three-dimensional geometry.
• Dislocation dynamics and alloying play crucial roles in strain relaxation in core-shell nanoparticles.
• Understanding these defect mechanisms is key to controlling the properties of nanomaterials.