Printing with Ions Additive manufacturing conquers atomic dimensions

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Researchers are now making it possible to produce complex metallic structures in the nanometre range using 3D printing. And this is how it's done.

Chemist Dr Dmitry Momotenko from the University of Oldenburg has now succeeded in producing extremely small metal objects using a new, electrochemical 3D printing technique, according to reports. The products could offer new possibilities for microelectronics, sensor technology or battery technology, Momotenko reported together with a team of researchers from ETH Zurich and Nanyang Technological University in Singapore in the journal Nano Letters. The electrochemical printing process can be used to make objects out of copper with a diameter of 25 billionths of a metre (i.e. 25 nanometres). The participants emphasise that a human hair is about 3000 times thicker than the structures that can be produced.

Additive manufacturing: quasi ion by ion

The printing process is based on the comparatively simple and well-known process of electroplating. For this purpose, positively charged metal ions (here copper ions) are used in a solution. When this solution comes into contact with a negatively charged electrode, the metal ions combine with the electrons present there to form a neutral metal atom, which is deposited on the electrode, the experts explain. In this way, a solid metal layer is gradually formed. The process is also easy to control. The researchers use a pipette to apply the copper ion solution drop by drop through a pressure nozzle to the place where the structure is to be formed. Until now, the hole had a diameter of between 253 and 1.6 nanometres. Only two copper ions could pass through such a tiny hole at the same time, the Oldenburg researchers note. The smallest possible objects that can be printed with the process have a diameter of about 25 nanometres. That corresponds to 195 copper atoms in a row.

Nozzle clogging problem eliminated

The aim was strictly to avoid the growing metal layer blocking the opening of the printing nozzle, which happens quite quickly, they say. The team therefore developed a way to monitor the pressure progress. To do this, they register the electrical current between the negative electrode and an additional positive electrode inside the pipette. Depending on this, the movement of the nozzle can be adjusted to the conditions.

The nozzle also only approaches the electrode for a short time and withdraws as soon as the metal layer exceeds a certain thickness. In this way, the nanostructure can be built up without any problems. By precisely positioning the nozzle, the team also succeeded in printing vertical columns as well as inclined or spiral structures. Even horizontal structures are feasible by simply changing the printing direction, the researchers continue.

According to the scientists, the diameter of the structures can also be controlled: On the one hand, through the size of the printing nozzles, and on the other hand, during the printing process, if the electrochemical parameters are changed accordingly.

Is the next revolution in additive manufacturing on the horizon?

The new electrochemical 3D printing process thus offers the chance to print significantly smaller metal objects than before. The researchers emphasise that only a resolution of about 100 micrometres can be achieved with the currently common powder-based metal printing processes. The smallest conventionally producible printed objects are therefore 4,000 times larger. Although even smaller structures can be produced with other processes, the choice of possible materials is limited.

What can the ‘ion printer’ bring for the future?

3D-printed interfaces could, for example, be used as catalysts for the production of complex chemicals, Momotenko says. And three-dimensionally structured electrodes could store electrical energy more efficiently. This is precisely the task the chemist and his team are currently working on. More precisely, in the ‘Nano-3D-Lion’ project, in which they want to drastically enlarge the surface of electrodes in lithium-ion batteries by 3D printing, thereby speeding up the charging process.

The European Research Council (ERC) has been funding the project since March 2021 with a Starting Grant.

* *Königsreuther, University of Oldenburg, Germany

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