The nanoscale heat dissipation (Joule heating) and mass transport during electromigration (EM) have attracted considerable attention in recent years. Here, the EM-driven movement of voids in gold (Au) nanowires of different shapes (width range: 50–300 nm) was directly observed by performing atomic force microscopy. Using the data, we determined the average mass transport rate to be 105 to 106 atoms/s. We investigated the heat dissipation in L-shaped, straight-shaped, and bowtie-shaped nanowires. The maximum Joule heating power of the straight-shaped nanowires was three times that of the bowtie-shaped nanowires, indicating that EM in the latter can be triggered by lower power. Based on the power dissipated by the nanowires, the local temperature during EM was estimated. Both the local temperature and junction voltage of the bowtie-shaped nanowires increased with the decrease in the Joule heating power and current, while the current density remained in the order of 108 A/cm2. The straight-shaped nanowires exhibited the same tendency. The local temperature at each feedback point could be simply estimated using the diffusive heat transport relationship. These results suggest that the EM-driven mass transport can be controlled at temperatures much lower than the melting point of Au
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