3D printing approaches atomic dimensions
3D printing – aka additive manufacturing – has established itself in recent years as a promising new manufacturing process for a wide range of components. Chemist Dr Dmitry Momotenko from the University of Oldenburg (Germany) has now succeeded in creating extremely small metal objects using a new 3D printing technique. Possible applications could be in microelectronics, sensor technology or battery technology, Momotenko reports together with a team of researchers from ETH Zurich (Switzerland) and Nanyang Technological University in Singapore in the journal Nano Letters. The team developed an electrochemical process that can be used to produce objects made of copper with a diameter of 25 nanometres.
The printing method is based on the well-known process of electroplating. This process, in which a solid metal is produced from a liquid salt solution, can be controlled very well. For the nanoprinting process of the Oldenburg scientists, a solution with positively charged copper ions is used, which are located in a tiny pipette. The liquid emerges at the end of the pipette drop by drop through a pressure nozzle. In the team’s experiments, this orifice had a diameter between 253 and 1.6 nm. Only two copper ions fit through such a tiny hole at a time.
The biggest challenge for the research team was that the growing metal layer could block the opening of the pressure nozzle very quickly. The group therefore developed a technique to monitor the progress of the pressure. Towards this end, they monitored the electrical current between the negative electrode and a positive electrode inside the pipette and automatically adjusted the movement of the nozzle accordingly: The nozzle only approached the electrode for a short time and retracted as soon as the metal layer had exceeded a certain thickness. In this way, the researchers gradually applied new copper layers to the electrode surface. By precisely positioning the nozzle, they succeeded in printing both vertical columns and inclined or spiral-shaped structures.
The diameter of the structures could also be controlled – on the one hand by the size of the printing nozzles, and on the other hand even during the printing process using electrochemical parameters. According to the team, the smallest possible objects that can be printed with the method have a diameter of about 25 nm. That corresponds to 195 copper atoms in a row.
This means that the new electrochemical process makes it possible to print significantly smaller metal objects than was previously possible. By processing metal powders, a typical method for 3D printing metals, a resolution of about 100 micrometres can currently be achieved, for example – that is 4,000 times larger than those of the Momotenko team. Although there are already processes that can produce even smaller structures, the choice of possible materials is limited, the researchers say. “The technology we are working on combines both worlds – metal printing and nanoscale precision,” Momotenko says. Just as 3D printing has sparked a revolution in the production of complex larger components, additive manufacturing at the micro and nano scales could make it possible to produce completely new kinds of objects in very small dimensions.
The potential applications are numerous: 3D-printed boundary layers could, for example, be used as catalysts for the production of complex chemicals. Three-dimensionally structured electrodes could help store electrical energy more efficiently. Momotenko and his team are currently working on this task: In the NANO-3D-LION project, the researchers want to drastically enlarge the surface of electrodes in lithium-ion batteries using 3D printing in order to speed up the charging process.
The European Research Council (ERC) has been funding the project with a “Starting Grant” since March 2021.
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