Collective Rotation Mode in Lattice Migration under Electron Irradiation

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.