Researchers at the University of California (UC) -Riverside have used electromagnetic fields to direct the shapes formed by vaporized metal nanoparticles.
Metallic nano materials could be the key to the development of transformative new electronic and energy devices.
However, for these nano materials to have the correct mechanical and electrical properties, they must be formed with consistent shapes and surfaces. To take advantage of their properties, they must be produced using scalable techniques.
Nano materials – which are made of nanoscale particles between one and 100 nm – are usually made in a liquid matrix; not only is this extremely expensive to scale, but it cannot be used to make pure metals such as aluminum or magnesium.
Alternative techniques, usually creating a cloud of particles from a condensing vapor, are very difficult to master. Engineers at UC-Riverside approached this challenge by vaporizing metals in a magnetic field to direct the reassembly of atoms into predictable shapes.
The researchers made nano materials from iron, copper and nickel in a gas phase. They placed solid metal in a powerful electromagnetic levitation coil to heat the metal above its melting point, causing it to evaporate.
The droplets of metal vapor floated in the gas and moved under the influence of the forces exerted by the magnetic field. This allowed the droplets to adhere in an orderly manner that could be predicted based on the type of metal and how the magnetic fields were applied.
While iron and nickel nanoparticles (which are ferromagnetic) form cord-like structures, copper nanoparticles form clusters of spheres. Iron and nickel aggregates produced a porous surface when deposited on a carbon film, while the copper produced a more compact and rigid surface.
The properties of these surfaces reflected on a larger scale the properties of the types of nanoparticles. According to the researchers, the magnetic field can be considered an “add-on”, meaning that this technique can be applied to create predictable structures from all vapor phase nanoparticles.
This could allow greater control over the electrical and mechanical properties of nano materials.
“This” field-oriented “approach allowed one to manipulate the assembly process and change the architecture of the resulting particles from objects of high fractal size to string-like structures of lower size,” said Professor Michael Zachariah, an expert in the field.
of chemical engineering at UC-Riverside. “The field strength can be used to manipulate the size of this setup.”