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

ABSTRACT 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.