Coalescence behavior of size-selected gold and tantalum nanoclusters under electron beam irradiation: insights into nano-welding mechanisms

The emerging technique of nano-welding (NW) via precisely regulating the fusion of nanoclusters (NCs) in nanotechnology has attracted significant attention for its innovative approach. Employing the gas-phase condensation cluster source with a lateral time-of-flight (TOF) mass-selector, size-selected gold (Au), and tantalum (Ta) NCs were prepared. This study explores the coalescence behavior of size-selected Au and Ta NCs under electron beam irradiation, aiming to investigate the related mechanism governing the welding process. Intrinsically driven by the reduction of excess surface energy, electron beam induces atomic thermal migration, fostering sintering neck growth at cluster interfaces. During this process, atomic diffusion and recrystallization enable NCs to alter shape while retaining stable facet planes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) showcases the formation of single or polycrystalline sintered clusters, during which some lattice distortions can be eliminated. Interestingly, oxidized Ta clusters experience knock-on damage caused by elastic scattering of electron beams, partially deoxidizing them. Additionally, electron–phonon inelastic scattering transforms oxidized Ta clusters from amorphous to crystalline structures. Moreover, the quantum size effect and surface effect of NCs facilitate the surpassing of miscibility limits during Au–Ta heterogeneous welding processes. This investigation bridges the gap between fundamental research on cluster materials and their practical applications.