Ultrathin Gold Nanowire Cold Welding Induced by the\nCollapse of Carbon Nanotube Walls

The\ncold welding of two Au nanowires (AuNWs) encapsulated in carbon\nnanotubes (CNTs) is observed <i>in situ</i> using a transmission\nelectron microscope (TEM) at room temperature. It is observed that\nunder electron irradiation, the radial shrinkage and collapse of CNT\nwalls lead to the squeezing of the two AuNWs encapsulated within CNTs,\nbringing their ends closer to each other. Upon further irradiation,\nthe ends of the two AuNWs make contact and fuse together. However,\ninstances of failed welding are observed, with the distance between\nthe two AuNWs identified as a significant factor determining a successful\nwelding. Specifically, when the tip-to-tip distance is too large,\nthe amorphous carbon generated from the amorphization of CNT walls\ncannot provide sufficient squeezing force. Additionally, the acceleration\nvoltage of the TEM is identified as another critical factor affecting\nthe welding, as the acceleration voltage decreases, the welding is\ndifficult to carry out. The compressive stresses generated by the\ncollapse of CNT walls on AuNWs are calculated using gold’s\ncompressive stress–strain curve and strain in the diameter\nof AuNWs. It is estimated that a stress of at least 539 MPa is required\nfor the successful cold welding of AuNWs. Furthermore, it is also\ncalculated for the first time that the force generated by amorphous\ncarbon resulting from CNT amorphization is approximately over 384\nMPa.