Scientists from Karlsruhe Institute of Technology (KIT) have created a tiny lattice they claim is the world's smallest. Formed with struts and braces measuring less than 10 micrometers in length and less than 200 nanometers in diameter, the 3D lattice has a total size of less than 10 micrometers, but boasts a higher specific strength than most solids.
The KIT team says the lattice achieves new strength to density ratios for metamaterials (man-made materials that have properties not found in nature), thanks to dimensions that are smaller than comparable metamaterials by a factor of five. It is made of glassy carbon, which is a form of pure carbon that boasts both glassy, ceramic properties and graphite properties.
Production of the lattice started with an established 3D lithography process, is which the structure is hardened in a photoresist by computer-controlled lasers. This process is limited to producing struts ranging from around 5 to 10 micrometers in length and 1 micrometer in diameter, so the team then vitrified and further shrunk the lattice through –in what they claim is a first for the manufacture of microstructured lattices – pyrolysis.
Pyrolysis involves exposing material to high temperatures in the absence of oxygen. In this case, the lattice was placed in a vacuum furnace and subjected to temperatures of around 900° C (1,652 °F), causing the chemical bonds to reorient themselves and all elements with the exception of carbon being removed from the lattice. This leaves the unordered carbon, in the form of glassy carbon, forming the shrunk lattice structure.
In subsequent testing, the researchers found this lattice boasted remarkable properties of stability under pressure.
"According to the results, load-bearing capacity of the lattice is very close to the theoretical limit and far above that of unstructured glassy carbon," says Prof. Oliver Kraft, co-author of the study. "Diamond is the only solid having a higher specific stability."
The team believes such microlattices could potentially find applications as electrodes, filters in the chemical industry, or optical components in telecommunications.
The first author of the study was Dr.-Ing. Jens Bauer, who was also involved in previous work at KIT in which a microstructured framework was produced that was less dense than water, but as strong as steel.
The paper detailing the Bauer and the KIT team's latest work appears in the journal Nature Materials.