Visit to Argonne National Laboratory -2/3 -
Commercial Applications of High-Energy Physics:
Nanoscale Additive Manufacturing
Overview
Nearly all materials exhibit different properties at nanoscale; for example, smaller can be stronger or weaker, suppress brittle failure or induce ductility, or create (three dimensional) photonic crystals, negative refraction materials, and activate phonon scattering-driven thermal processes. The development of metal-based AM has revolutionized the production of complex parts for aerospace, automotive and medical applications. Today’s resolution of most commercially available metal AM processes is ~20–50 μm; no established method is currently available for printing 3D features below these dimensions. It has been shown that unique phenomena arise in metals with micro- or nano-dimensions, for example light trapping in optical meta-materials or enhanced mechanical resilience. Accessing these phenomena requires developing a process to fabricate 3D metallic architectures with macroscopic overall dimensions and individual constituents in the sub-micron domain.
Additive manufacturing in the nanoscale regime is the fabrication of 3D structures that contain geometric features smaller than 1 µm. Two photon polymerization (2PP) lithography is one of the very few manufacturing methods that can fabricate true three-dimensional micro/nanostructures of various materials, such as polymer, hybrid materials, or organically modified ceramics. The unprecedented geometrical freedom provided by 2PP allows one to print very complex designs, including overhanging and self-intersecting structures inaccessible by conventional methods. This layer-by-layer printing method can achieve a sub-diffraction-limit resolution (<100 nm). It has thus found widespread applications in making devices and elements in micro-optics, electronics, microfluid devices, MEMs, and metamaterials. (2PP is a photochemical process initiated by focusing a femtosecond laser beam tightly into a volume of photosensitive resin with a high-numerical-aperture (NA) objective. Photo-initiators absorb two photons simultaneously. The cross section of the two-photon absorption is much lower than that for linear one-photon absorption, so an ultra-short pulse laser with high intensity (TW/cm3) is often required. This implies the yield and the speed of printing are slower than one-photon polymerization.)
Figure 1. Schematics of photon polymerization lithography (a) Linear one-photon and non-linear two-photon absorption process (b) laser intensity distribution during two-photon absorption process (c) a typical 2PP setup with 3D linear stage and galvanometer
The major player in the micro-to-nano printing market is currently Nanoscribe GmbH. They have developed a femtosecond laser-driven technology with a tightly integrated design. A different approach, pioneered at Argonne National Labs and at a spin-out company, Robot Nose, is simpler and cheaper to produce, with similar resolution, while printing 3D structures dramatically faster. In 2020, Robot Nose and Argonne began to collaborate on the development of a new additive manufacturing tool with high resolution and unmatched speed. The concept is simple – a photoresist that is driven in the near UV with a single photon can much more efficiently polymerize than a process requiring two IR photons in a two-photon polymerization. No commercial UV printers have the required resolution for the current proposed work. The RN-Argonne design uses unique optics, chemistry and software to allow polymerization at the focus, without any need for confinement and without runaway reaction in the photoresist.
Initial results with the one photon polymerization (1PP) tool show it can achieve at least 10x the volumetric printing rate of the Nanoscribe PP, with equivalent resolution. It is expected that rate will improve further over time. The cost of parts in both time and materials on this new tool will be at least an order of magnitude less than the Nanoscribe, and the level of operator skill required should be reduced as well. Since the polymer CRL is a consumable part, controlling its cost is key to developing the market.
Conclusion
High dimensional accuracy in nanoscale additive manufacturing will be beneficial to the renewable energy industry, the aerospace industry, which manufactures complex parts in relatively low volume production, and can also be used to manufacture medical devices, point-of-care diagnostics and surgical tooling.