Dutch researchers at University of Twente have invented a new form of metal additive manufacturing that allows a laser apparatus to print pure gold particles. The new technique, which they’ve dubbed LIFT (laser-induced forward transfer), uses ultra-short green laser pulses to melt tiny bits of metal from a nano-thickness film. Gold is an essential metal in many electronics and communications devices, so the method may prove very important. Even aside from gold itself, metal microstructures are also heavily relevant to the fields of photonics, plasmonics, micromechanics and biomedical technology.
Aside from being an important means of printing pure gold, the process also allows for immense resolution. The researchers deposited metal droplets that were mere femtolitres (one-trillionth of a litre). This ability to process precise droplets allows for the careful construction of materials just tens of microns in height. It can thus deliver detailed prints of smaller than 10µm while minimising surface roughness. Moreover, the researchers reported no signs of mixing between the metals.
Laser-Induced Forward Transfer
Schematic of the setup used for the LIFT experiments.
During the LIFT process, the green laser pulses melt tiny bits of metal from a nano-thickness film. This forms microdroplets of molten metal, which when ejected to their targets, solidify upon landing. This helps in forming the pure gold particles at such controllable volumes and high resolutions. The researchers managed to build a helical microstructure using copper and gold. Since they have similar melting points, the metals are quite compatible for the process. The copper served as a mechanical support ‘box’ on which the gold can form. These steps complete the LIFT process, however, the researchers were not done yet.
Upon completing the structure, they began chemical etching it in ferric chlorine to entirely remove the copper scaffold. By doing so, they leave behind a free-standing helix composite in pure gold. The helix shape is quite complex, so its interesting to see the level of complexity in this form of printing especially considering the overhangs. Using LIFT along with chemical etching displays one possibility for creating these micro-structures.
This combination of processes allows for some novel possibilities in electronics and communication devices. It’s especially notable due to how it can use separate metals simultaneously, while avoiding mixing them together. This multi-material application could be very useful on an industrial level.
Featured image courtesy of the University of Twente. The full study is available on Additive Manufacturing.
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