12 January 2022

For additive manufacturing, 3D laser printing allowing for the best spatial resolution and extremely high printing speed is often the method of choice. In the process, a focussed laser beam is directed toward a light-sensitive liquid. At the focal point, the laser activates special molecules and triggers a chemical reaction, causing local hardening of the material. Any micro- and nanostructures can be produced by moving the focal point. So-called two-photon absorption triggers the reaction. Two photons, i.e. light particles, excite the molecule at the same time, causing the desired chemical change. Yet this requires complex pulsed laser systems, resulting in larger-size laser printers.

In contrast, the two-step process uses more compact and smaller printers. The first photon excites the molecule to an intermediate state, and the second photon brings about the desired end state, thus starting the chemical reaction. The advantage: This does not necessarily need to happen at the same time, like in two-photon absorption. As the study's first author, Vincent Hahn from the Institute of Applied Physics at KIT explains, compact and lower-power continuous-wave laser diodes can be used instead. However, this printing process requires specific photoresists, whose development took several years and was possible only in collaboration with chemists.

“To realise the two-step absorption process, the photochemistry had to be carefully adapted,” explains Junior Professor Dr Eva Blasco, a chemist at the Institute of Organic Chemistry and the Centre for Advanced Materials (CAM) of Heidelberg University. Together with KIT physicists, she developed the photoresist employed in the new printing process. The structure of the woodpiles generated was then analysed with electron microscopy at the CAM. Prof. Dr Rasmus Schröder led the responsible working group. “Our job was to validate the resolution attainable with the new printing process,” states Dr Irene Wacker, a member of Prof. Schröder’s group. One possible application for 3D nanoprinters might be scaffold structures for an artificial retina to be developed in cooperation with biologists at the Cluster of Excellence.

The Heidelberg researchers are convinced that due to its lower cost, this new technology will become accessible to many researchers in future enabling them to print nanostructures for biological and technical applications. Besides the laser itself, now other components of the 3D laser nanoprinter need to be miniaturised, adds Prof. Dr Martin Wegener. The researcher from the Institute of Applied Physics at KIT believes a device the size of a shoebox will be possible in the next few years.

In the “3D Matter Made to Order” Cluster of Excellence, scientists pursue interdisciplinary research into innovative technologies and materials for digital and scalable additive manufacturing processes to enhance the precision, speed, and performance of 3D printing. Work is aimed at completely digitising 3D manufacture and materials processing from the molecule to the macrostructure. In addition to funding as a cluster under the Excellence Strategy competition launched by the federation and the federal states, 3DMM2O is financed by the Carl Zeiss Foundation.