University of Twente Researchers 3D Print Pure Gold ‘micro jewels’ Using Laser Technique

Dutch researchers at University of Twente has developed a new metal 3D printing technique which allows a laser apparatus to print metal structures drop by drop, including in pure gold, on the few micron scale.

Conventionally, metal structures can be fabricated via lithographic methods, casting, selective laser sintering or melting. However, these new methods are not yet suitable for the 3D printing of metals on a scale with feature sizes of smaller than about 10 μm, which would be interesting for electronics.

Researchers’ new technique, which has been called laser-induced forward transfer (aka ‘LIFT’), uses an ultra-short laser pulse to melt tiny bits of metal from a nano-thickness film. This forms microdroplets of molten metal, which can be ejected to their targets, where they solidify upon landing. Thanks to this technique, the UT researchers are able to build, drop by drop, a helical microstructure with copper and gold microdroplets. The two metals have similar melting points, and in this case the copper acts as a mechanical support ‘box’ on which the gold can form.

The laser printing technique: by printing copper and gold in turn, the gold helix initially is surrounded by a copper box. Etching the copper away, results in a free standing helix of pure gold.

The volumes of the metal droplet were just a few femtolitres (one-trillionth of a litre). The way the droplets are made, is by lighting the metal using an ultrashort pulse of green laser light. This precise generation of droplets allowed for a structure to be carefully constructed that was just tens of microns in height and featured details smaller than 10µm, with minimal surface roughness (about 0.3 to 0.7 microns). A crucial question for the researchers was if the two metals would mix at their interface: this would have consequences for the quality of the product after etching. The researchers, writing in Additive Manufacturing, reported no signs of mixing between the metals.

Once the structure was complete, the researchers used chemical etching in ferric chlorine to entirely remove the copper scaffold. By doing so, they leave behind a free-standing helix composite in pure gold.

Top view (c) of the helix shows that it is threedimensional with a center void. In (b), it is still in the copper box

The ability to create fully free-standing and overhanging structures is crucial for printing complex 3D devices. Using LIFT in combination with chemical etching displays one possibility for creating these types of structures on a small scale.

The LIFT technique is a promising technique for other metals and combinations of metals as well. The researchers expect opportunities for materials used in 3D electronic circuit, micromechanic devices and sensing in, for example, biomedical applications. It therefore is a powerful new production technique on a very small scale: an important step towards ‘functionalisation’ of 3D printing.

The research has been done by the departments of Mechanics of Solids, Surfaces and Systems (MS3) and Design, Production and Management (DPM), both part of the Engineering Technology faculty of the University of Twente. The researchers collaborated with DEMCON corporation, a spinoff company of the University of Twente.

The paper ‘Printing of Complex Free-standing Microstructures via Laser-induced Forward Transfer (LIFT) of Pure Metal Films’ by Matthias Feinaeugle, Ralph Pohl, Ton Bor, Tom Vaneker and Gert-willem Römer is published here.


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