In recent years, 3D printing, also known as additive manufacturing, has emerged as a promising new manufacturing process for a wide variety of components. Dr Dmitry Momotenko, a chemist at the University of Oldenburg, has now successfully fabricated ultra-small metal objects using a new 3D printing technique. In an article published with a team of researchers from ETH Zurich (Switzerland) and Nanyang Technological University (Singapore) in the scientific journal Nano letters, he reports that the technique has potential applications in microelectronics, sensor technology and battery technology. The team has developed an electrochemical technique that can be used to make copper objects that are only 25 billionths of a meter (equivalent to 25 nanometers) in diameter. For comparison, a human hair is about 3000 times thicker than filigree nanostructures.
The new printing technique is based on the relatively simple and well-known process of electroplating. In electroplating, positively charged metal ions are suspended in a solution. When the liquid comes in contact with a negatively charged electrode, the metal ions combine with the electrons in the electrode to form neutral metal atoms which then settle on the electrode and gradually form a solid metal layer. âIn this process, a solid metal is made from a liquid salt solution – a process that we electrochemists can control very effectively,â says Momotenko. For his nanoprinting technique, he uses a solution of positively charged copper ions in a tiny pipette. The liquid exits the tip of the pipette through a printing nozzle. In the team’s experiments, the nozzle opening had a diameter of between 253 and 1.6 nanometers. Only two copper ions can pass through such a small opening simultaneously.
Monitoring the progress of the printing process
The biggest challenge for scientists was that as the metal layer grew, the printing nozzle opening tended to become blocked. To avoid this, the team developed a technique to monitor the progress of the printing process. They recorded the electric current between the negatively charged substrate electrode and a positive electrode inside the pipette, then the movement of the nozzle was adjusted accordingly in a fully automated process: the nozzle approached the negative electrode for a very short period then retracted as soon as the metal layer had exceeded a certain thickness. Using this technique, the researchers gradually applied one layer of copper after another to the surface of the electrode. Thanks to the extremely precise positioning of the nozzle, they were able to print both vertical columns and tilted or spiral nanostructures, and even managed to produce horizontal structures by simply changing the printing direction.
They were also able to control the diameter of the structures very precisely – on the one hand by the choice of the size of the printing nozzle and on the other hand during the printing process itself on the basis of electrochemical parameters. According to the team, the smallest possible objects that can be printed using this method are around 25 nanometers in diameter, which is equivalent to 195 copper atoms in a row.
Combining metal printing and precision at the nanoscale
This means that with the new electrochemical technique it is possible to print much smaller metal objects than ever before. 3D printing using metal powders, for example – a typical method for 3D printing metals – can currently achieve a resolution of around 100 micrometers. The smallest objects that can be produced by this method are therefore 4000 times larger than those in the present study. Although even smaller structures can be produced using other techniques, the choice of potential materials is limited. âThe technology we are working on combines both worlds: metal printing and nano-scale precision,â Momotenko explains. Just as 3D printing has sparked a revolution in the production of larger, complex components, additive manufacturing at the micro and nanoscale could make it possible to manufacture functional structures and even devices of very small dimensions, he explains. -he.
â3D printed catalysts with a large specific surface area and a special geometry to allow special reactivity could be prepared for the production of complex chemicals,â explains Momotenko. Three-dimensional electrodes could make electrical energy storage more efficient, he adds. The chemist and his team are currently working towards the same objective: in their NANO-3D-LION project, they aim to drastically increase the surface area of ââthe electrodes and to reduce the distances between the cathode and the anode of lithium-ion batteries thanks to the 3D printing, in order to speed up the charging process. The project has been funded by a start-up grant from the European Research Council since March 2021.