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

De-Gang Xie,Zhi-Yu Nie,Evan Ma,Feng-Xian Liu,Ju Li,Shigenobu Ogata,Yue-Qing Yang,Shuhei Shinzato,Zhi-Wei Shan

doi:10.1038/s41467-019-12416-x

Abstract

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.

Highlights

Mass transport driven by temperature gradient is commonly seen in fluids
While grain-boundary (GB) diffusion is similar to surface diffusion and often acts cooperatively to accommodate the thermomigration atomic current, by first transporting along and later depositing/stripping into grain boundary (GB) as the sink/source[7], here, we do want to make a distinction between surface and GB diffusions in that the latter process can be significantly more sluggish than the former depending on T/Tm due to the somewhat lower free volume inside GB than the free surface, so much so that the GB
Three preconditions are required: The first is a hot solid reservoir free of confinement from surface oxide[19], which can be attained by scratching the pulling tip on the hot aluminum substrate to break the native oxide layer and expose fresh metal; The second is the sharp temperature gradient to induce thermomigration, which is achieved by touching a cold nanoscale tip with the hot metal reservoir: this nucleates a small seed that often has a different crystal orientation from the hot metal reservoir beneath; The third one is the mechanical pulling movement to enlarge the seed, and later sustain it as steady-state nanowire growth, with a neck-shaped region bridging the nanowire and the substrate

Summary

Introduction

Mass transport driven by temperature gradient is commonly seen in fluids. 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. 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.

Methods

Results

Conclusion