Researchers at the California Institute of Technology (Caltech) have developed an innovative fabrication technique for 3D printing metal objects at the nanoscale, with dimensions as small as 150 nanometers (comparable to the size of a flu virus). This innovation builds upon their earlier work of printing microsized metal parts with features as thin as three or four sheets of paper.

What sets this development apart is that the atomic arrangements within these nanosized metal objects are disordered, which, at a larger scale, would typically render them weak and of low quality. However, at the nanoscale, this atomic-level disarray actually makes the parts three to five times stronger than similar structures with more orderly atomic arrangements.

A nanoscale lattice was prepared using a new technique developed by the lab of Julia R. Greer. Credit: Caltech

How Does the Process Happen?

The process begins by creating a photosensitive “cocktail” mainly composed of a hydrogel, a polymer capable of absorbing multiple times its weight in water. This mixture is selectively hardened with a laser to form a 3D scaffold mirroring the desired metal objects’ shapes, such as tiny pillars and nanolattices.

The hydrogel parts are then infused with a solution containing nickel ions, followed by baking to burn out the hydrogel, leaving behind metal ions now oxidized and bound to oxygen atoms. In the final step, the oxygen atoms are chemically removed, converting the metal oxide back into metallic form.

This process creates a messy microstructure full of defects, which, counterintuitively, strengthens the nanoscale parts. In typical metals, defects weaken the material, but in these nanosized structures, defects disrupt the propagation of failure, making them more resilient.

A Diverse Set of Applications

The applications of this nanoscale 3D printing technique are diverse, including catalysts for hydrogen, storage electrodes for chemicals like carbon-free ammonia, and essential components for devices such as sensors and microrobots. It represents one of the first demonstrations of 3D printing metal structures at such a small scale, offering a promising avenue for creating robust and functional nanoscale components.

This innovative approach challenges conventional notions about the relationship between atomic-level structure and material strength, opening up new possibilities for designing and manufacturing advanced materials and devices.

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