Understanding atomic migration dynamics is crucial for precise nanostructure synthesis and modification, particularly in beam-assisted phase engineering of nanomaterials. A universal nanoscale rotation mode has been observed during conventional in situ annealing and electron-beam irradiation. However, it remains poorly understood how the rotation mode is activated and drives nanoparticle migration and coalescence, particularly under electron-beam irradiation, where lattice rotation occurs even at room temperature. Here, using in situ transmission electron microscopy, we report a collective rotation mechanism induced by transient thermal spikes under electron irradiation. Our observations reveal that Pt and AuPt nanoparticles coalesce into larger islands with coherent 111 twin structures through nonrandom lattice rotation. We demonstrate that the observed rotation behavior fundamentally originates from asymmetric temperature gradients using molecular dynamics simulations and small-strain theory. These insights advance the understanding of nanocrystal migration dynamics under electron beam irradiation.
Guan et al. (Thu,) studied this question.