<Abstrate>

Dislocation mediated alignment processes during gold nanoparticle coalescence

were studied at low and high temperatures using molecular dynamics simulations

and transmission electron microscopy. Particles underwent rigid body rotations

immediately following attachment in both low temperature (500 K) simulated

coalescence events and low temperature (∼315 K) transmission electron microscopy

beam heating experiments. In many low temperature simulations, some degree

of misorientation between particles remained after rigid body rotations, which

was accommodated by grain boundary dislocation nodes. These dislocations were

either sessile and remained at the interface for the duration of the simulation or

dissociated and cross-slipped through the adjacent particles, leading to improved

co-alignment. Minimal rigid body rotations were observed during or immediately

following attachment in high temperature (1100 K) simulations, which is attributed

to enhanced diffusion at the particles' interface. However, rotation was eventually

induced by {111} slip on planes parallel to the neck groove. These deformation

modes led to the formation of single and multi-fold twins whose structures

depended on the initial orientation of the particles. The driving force for {111} slip

is attributed to high surface stresses near the intersection of low energy {111} facets

in the neck region. The details of this twinning process were examined in detail

using simulated trajectories, and the results reveal possible mechanisms for the

nucleation and propagation of Shockley partials on consecutive planes. Deformation

twinning was also observed in-situ using transmission electron microscopy, which

resulted in the co-alignment of a set of the particles' {111} planes across their grain

boundary and an increase in their dihedral angle. This constitutes the first detailed

experimental observation of deformation twinning during nanoparticle coalescence,

validating simulation results presented here and elsewhere.

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