Picture: Songyun Gu
Researchers at Lawrence Livermore National Laboratory (LLNL) and Stanford University have presented a new platform for two-photon lithography (TPL) that scales 3D printing in the nano- and submicrometer range to larger areas. The work was published in Nature and aims to break TPL out of the bottleneck of classical laboratory setups without sacrificing the typical precision of nonlinear polymerization.
TPL has been considered a method for fine 3D architectures for years, but it is usually tied to microscope objectives. This limits the print field to a few hundred micrometers; larger structures have to be assembled from many tiles, which takes time and increases the risk of alignment errors. The team replaces the optics with tiled arrays of high-numerical-aperture metalenses that split a femtosecond laser into more than 120,000 coordinated focal points. In this way, the system writes in parallel over centimeter-scale areas. The authors cite a minimum feature size of 113 nanometers, while throughput is said to increase by more than a factor of 1,000 compared to commercial systems.
“When the 3D printing system started to work at one-centimeter scale and then three-centimeter scale for the first time, it was really amazing to see the idea that was developed for three to four years at that time come true,” said Xiaoxing Xia, an LLNL materials engineer and principal investigator. “To see a print being done accurately at speed hundreds to thousands of times faster than our commercial printer, we realized a breakthrough has happened.”“It means TPL finally has the potential for industry adoption,” said Songyun Gu, a postdoctoral researcher at LLNL and the first author on the paper. “Previously it was purely an experimental tool for researchers. With wafer-scale nanomanufacturing, we have the potential to make nanomaterials and microdevices the same way we make computer chips, which are highly complex but can be made in volume at very low unit cost. And meta-optics is exactly the solution.”
For nonperiodic geometries, a spatial light modulator complements the optics: it regulates the intensity of each focal point in real time, can switch spots on and off, and varies line widths via grayscale control.
“During the project, we realized that by dynamically switching the focal spots on and off and carefully planning the printing trajectory, we can actually print fully stochastic structures with a high degree of parallelization,” Xia said. “Songyun [Gu] and [co-author] Sarvesh [Sadana] printed 16 different microscopic chess openings in one process.” The team named the method Adaptive Meta-Lithography to acknowledge extensive support from LLNL’s Advanced Manufacturing Laboratory.Xia sees the convergence of optics and additive manufacturing as a defining step for the field. “Light is the finest chisel on earth to craft functional materials and micro-architectures,” he said. “New ways to control light will revolutionize how to make materials.”
