The smallest lattice in the world is visible under the microscope only. Struts and braces are 0.2 µm in diameter. Total size of the lattice is about 10 µm. Credit: J. Bauer / KIT
Scientists have now presented the smallest human-made lattice structure. 3D lattice with glassy carbon struts and braces of <200 nm in diameter has higher specific strength than most solids. They are smaller than comparable metamaterials by a factor of five. Apps may include electrodes, filters or optical components.
“Lightweight construction materials, such as bones and wood, are found everywhere in nature,” said Dr.-Ing. Jens Bauer of Karlsruhe Institute of Technology (KIT). “They have a high load-bearing capacity and small weight and, hence, serve as models for mechanical metamaterials for technical applications.”
Metamaterials are materials, whose structures of some micrometers possess mechanical or optical properties that cannot be reached by unstructured solids. Examples are invisibility cloaks that guide light, sound or heat around objects, materials that counterintuitively react to pressure and shear (auxetic materials) or lightweight nanomaterials of high specific stability (force per unit area and density).
The smallest stable lattice structure worldwide presented now was produced by the established 3D laser lithography process at first. The desired structure of micrometer size is hardened in a photoresist by laser beams in a computer-controlled manner. However, resolution of this process is limited, such that struts of about 5 – 10 µm length and 1 µm in diameter can be produced only. In a subsequent step, the structure was therefore shrunk and vitrified by pyrolysis. For the first time, pyrolysis was used for manufacturing microstructured lattices. The object is exposed to 900°C in a vacuum furnace. As a result, chemical bonds reorient themselves. Except for carbon, all elements escape from the resist. The unordered carbon remains in the shrunk lattice structure in the form of glassy carbon. The resulting structures were tested for 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,” Prof. Oliver Kraft. “Diamond is the only solid having a higher specific stability.”
Microstructured materials are often used for insulation or shock absorption. Open-pored materials may be used as filters in chemical industry. Metamaterials also have extraordinary optical properties that are applied in telecommunications. Glassy carbon is a high-technology material made of pure carbon. It combines glassy, ceramic properties with graphite properties and is of interest for use in electrodes of batteries or electrolysis systems. http://www.kit.edu/kit/english/pi_2016_015_nature-materials-smallest-lattice-structure-worldwide.php
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