In Situ Tracking of Long-Range Surface Diffusion of Gold Clusters Mediating Amorphous Si Crystallization

Understanding the migration of metal clusters within amorphous matrices and crystallization dynamics is fundamental to tailoring interface reactions and designing material functionalities. Despite extensive advances in metal-induced crystallization, the atomistic dynamic pathways and microscopic mechanisms of metal long-range diffusion on disordered matter remain elusive. Here, we employ atomic-resolution in situ heating transmission electron microscopy, integrated with density functional theory calculations, to systematically investigate the Au cluster long-range diffusion on amorphous silicon (a-Si) and the simultaneous resulting crystallization mechanism at the atomic scale. Amorphous Au clusters follow Arrhenius-type diffusion kinetics with an activation energy barrier of approximately 0.69 eV, notably without the formation of any intermediate metal silicide. Our dynamic observations reveal two synergistic diffusion modes: linear homogeneous diffusion and nonlinear aggregation-spreading, fundamentally driven by the higher diffusion barrier on the amorphous surface compared to its crystalline counterpart. These results offer atomic-scale evidence for Au surface diffusion and its role in mediating crystallization, thereby providing a pathway for exploring surface diffusion dynamics at amorphous-amorphous/crystalline interfaces.