Cold welding without direct contact

Welding is widely used in the fabrication of electronic devices and hierarchical systems with desired mechanical and physical properties. Conventional welding generally requires both high temperatures and significant compressive stress to ensure direct contact between the welded parts. Accordingly, traditional welding process may cause deformation of the atomic structure at the joint of the parts, thereby greatly reducing the performance of the device. In this study, the atomic-scale welding two separate platinum nanocrystals into a single crystal was observed in situ. Cold welding was achieved at a relatively low temperature without direct contact between the two platinum nanocrystals, which were separated by a distance of ~ 7.8 Å, more than three times the lattice spacing. The in situ atomic-scale observation revealed that cold welding occurred via forming monatomic chain between the separated nanocrystals by diffusion of atoms, then this monatomic chain grew layer-by-layer into diatomic and triatomic chains. Density functional theory calculations revealed that the adsorption energy of the atoms decreased with the reduction of the separation distance of the two parts, facilitating cold welding. This study demonstrates the feasibility of cold welding without direct contact, thereby facilitating the construction of high-performance nanodevices by atomic engineering.