Grain-Boundary-Free Fusion of Non-Oriented Nanocrystals via Transient Amorphization

Conventional paradigms of nanocrystal coalescence often posit that crystallographic alignment is a prerequisite for coherent interface formation, imposing constraints on the structural design of nanoscale materials. Departing from this assumption, we demonstrate that significantly misaligned nanoclusters can fuse directly into a grain-boundary-free structure without requiring rotational alignment, thereby bypassing the need for precise crystallographic registry. Using in situ atomic-scale transmission electron microscopy, we identify two distinct non-oriented integration pathways under conditions of restricted rotational freedom: (i) interface-driven amorphization, where localized 2D structural reordering at the interface enables layer-by-layer incorporation-dominant when at least one nanocluster exceeds a critical size threshold, and (ii) bulk-mediated amorphization, where global 3D reordering facilitates the nucleation and growth of a metastable crystalline phase, ultimately resulting in single-crystal fusion when both clusters are below the size threshold. Complementary atomistic simulations elucidate that nanocluster size and substrate interactions govern pathway selection: larger clusters favor interfacial reconfiguration, while smaller clusters undergo bulk restructuring. These insights establish amorphization-mediated coalescence as a viable mechanism for assembling nanostructures, expanding the design space for creating defect-free materials at the nanoscale.