3,000 times thinner than a hair: Using an innovative printing process, researchers can now produce incredibly small and surprisingly complex metallic objects. The ultra-fine motions of the nano-absorbent motor and electrochemical effects ensure that the rock structures made of copper atoms are built. In addition to the many possible applications in microelectronics, the technology could also be used to develop more efficient energy storage systems, the scientists say.
Additive manufacturing is the technical term: Techniques for producing 3D objects in the printing process in the meantime have become well established in many areas of application and process development is continuing. More and more materials can be used and methods are being improved. A team of scientists from the Swiss Federal Institute of Technology in Zurich and the University of Oldenburg are also dedicated to this challenge. You are pushing the miniaturization of complex metal objects even further. Now they are reporting on their newly developed process, which clearly exceeds previous manufacturing capabilities.
Nano pipettes allow small metallic objects to grow
As the developers explain, the concept is mainly based on the well-known principle of electroplating – the process of painting objects with metallic paint. In conventional methods, positively charged metal ions are present in a solution in which the workpieces connected to the negative electrode are immersed. “In this process, a solid metal is formed from a liquid salt solution – a well-controlled process,” says senior author Dmitriy Momotenko of the University of Oldenburg. Specifically, during electroplating, metal ions combine with electrons to form neutral metal atoms, which are then deposited on the electrode – the workpiece. Then a metallic layer gradually forms on the body.
For their 3D nanoprinting technique, the scientists now take this process to an extreme: The solution using positively charged copper ions is in tiny pipettes, with holes between 1.6 and 253 nanometers in diameter at their tip. The liquid can be dispensed there drop by drop on the electrode surface. Complex structures can be built by making precise movements of the pipette. Scientists say that only two copper ions pass through the hole at the same time with the smallest hole size. As they explained, one of the main challenges in the process was to prevent the openings from becoming clogged. They achieve this by actively monitoring the progress of the print and the function of the nozzle.
Miniaturization with technical capabilities
By precisely positioning the nozzle, electrochemists have finally succeeded in building complex copper nanostructures: In addition to vertical shafts, they can also print inclined or spiral staircase-like structures by changing the direction of motion. The diameter can be adjusted by setting the size of the printing nozzle and can also be affected by changes in electrochemical parameters during the printing process. According to the team, the smallest objects that can be printed using this process are about 3,000 times thinner than a human hair: 25 nanometers wide — the equivalent of 195 copper atoms, respectively. The researchers stress that these lower values overshadow all previous options for 3D printing of metals. “This technology now combines metallic printing with nano-resolution,” Momotenko says.
He and his colleagues see great potential in their process: Similar to the way 3D printing has revolutionized the production of complex and larger components, additive manufacturing at the micro- and nano-scale could make it possible to fabricate entirely new types of objects in very small dimensions. Possible applications could be in microelectronics, sensor technology, or battery technology. “For example, 3D-printed interfaces can be used as catalysts for the production of complex chemicals,” Momotenko says.
However, the developers particularly stress that the 3D electrodes can help store electrical energy more efficiently. As part of a project, it is also now working to improve its process for this field of application: Scientists are trying to dramatically expand the surface of the electrodes in lithium-ion batteries using 3D printing in order to speed up the charging process.
Source: Karl von Ossetsky University of Oldenburg, specialized article: Nano Letters, doi: 10.1021/acs.nanolett.1c02847
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