Until now, mass production of NWs has been hindered by difficulties in maintaining both quality and purity during scaling. Typically, NWs are created by transporting atoms in a gas phase state, but this process has proven particularly challenging for metals, limiting their use in electronic components.
To address this issue, a team led by Yasuhiro Kimura from Nagoya University's Graduate School of Engineering employed a process called atomic diffusion, facilitated in a solid phase state and enhanced by ion beam irradiation, to create aluminum NWs from single crystals.
Atomic diffusion, which involves atoms moving from high concentration areas to low concentration areas due to changes in stress and temperature, was key to this technique. The researchers used ion beams to irradiate crystal grains inside thin aluminum films, causing them to coarsen at the surface. This changed the stress distribution, directing the flow of atoms and creating a feedstock for NW growth. When heat was applied, atoms moved upward from the fine grains at the bottom to the coarser grains at the top, leading to the large-scale production of NWs.
"We increased the density of aluminum NWs from 2x105 NWs per square cm to 180+ 105 per square cm," Kimura explained. "This achievement paves the way for bottom-up metal NW growth methods, which have so far been grown only accidentally and in small quantities. It can also be extended to other metals in principle."
The produced aluminum NWs have several potential applications, particularly as nanocomponents for sensing devices and optoelectronics, due to their large surface area, strong mechanical properties as single crystals, and resistance to natural oxidation.
"We realized mass growth of forest-like metallic NWs using only three key processes: thin film deposition on a substrate, ion beam irradiation, and heating," Kimura added. "Our technique solves the urgent need to establish mass production methods, especially in the production of high-performance nanodevices such as gas sensors, biomarkers, and optoelectronic components."
Research Report:Growth of metal nanowire forests controlled through stress fields induced by grain gradients
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