Controlled growth of single-crystalline metal nanowires via thermomigration across a nanoscale junction

Mass transport driven by temperature gradient is commonly seen in fluids. However, here we demonstrate that when drawing a cold nano-tip off a hot solid substrate, thermomigration can be so rampant that it can be exploited for producing single-crystalline aluminum, copper, silver and tin nanowires. This demonstrates that in nanoscale objects, solids can mimic liquids in rapid morphological changes, by virtue of fast surface diffusion across short distances. During uniform growth, a thin neck-shaped ligament containing a grain boundary (GB) usually forms between the hot and the cold ends, sustaining an extremely high temperature gradient that should have driven even larger mass flux, if not counteracted by the relative sluggishness of plating into the GB and the resulting back stress. This GB-containing ligament is quite robust and can adapt to varying drawing directions and velocities, imparting good controllability to the nanowire growth in a manner akin to Czochralski crystal growth.China. Ministry of Science and Technology. National Key Research and Development Program (Grant 2017YFB0702001)Natural Science Foundation of China (Grant 51701151)Natural Science Foundation of China. 111 Project 2.0 (Grant BP2018008)Shanxi University. Postdoctoral Science Foundation (Grant 2017JQ5110)National Science Foundation (U.S.). Division of Materials Research (Grant DMR-1410636