High-resolution nanoscale 3D printing gets 1000x speed boost

October 08, 2019 // By Julien Happich
High-resolution nanoscale 3D printing gets 1000x speed boost
Using a new time-based method to control light from an ultrafast laser, researchers have developed a nanoscale 3-D printing technique that can fabricate tiny structures 1000 times faster than conventional two-photon lithography (TPL) techniques, without sacrificing resolution.

The team of researchers from Lawrence Livermore National Laboratory (LLNL) and The Chinese University of Hong Kong paper disclosed their new 3D printing process in a paper titled “Scalable submicrometer additive manufacturing” published in the Science journal.

A millimeter-scale structure with submicron features is
supported on a U.S. penny on top of a reflective surface.
Credit: Vu Nguyen and Sourabh Saha.

To get that 1000x printing speed boost, the authors added a twist to a submicrometer additive manufacturing technique known as two-photon lithography (TPL). Because it use a serial point-by-point writing scheme, TPL is too slow for many applications.

The researchers used an ultrafast laser to implement a projection-based layer-by-layer parallelization through spatial- and temporal- multiplexing. This increased the throughput up to three orders of magnitude while expanding the geometric design space.

Despite the high throughput, the new parallelized technique known as femtosecond projection TPL (FP-TPL) produces depth resolution of 175 nanometers, which is better than established methods, the researchers report. They demonstrated the fabrication of structures with 90-degree overhangs that can't currently be made. The technique could lead to manufacturing-scale production of bioscaffolds, flexible electronics, electrochemical interfaces, micro-optics, mechanical and optical metamaterials, and other functional micro- and nanostructures.

Existing nanoscale additive manufacturing techniques use a single spot of high-intensity light, typically around 700 to 800 nanometres in diameter to convert photopolymer materials from liquids to solids. Because the point must scan through the entire structure being fabricated, the existing TPL technique can require many hours to produce complex 3-D structures, which limits its ability to be scaled up for practical applications.

"Instead of using a single point of light, we project a million points simultaneously," explains Sourabh Saha, the paper's lead and corresponding author. "This scales up the process dramatically because instead of working with a single point that has to be scanned to create the structure, we can use an entire plane of projected light. Instead of focusing a single point, we have an entire focused plane that can be patterned into arbitrary structures."

To create a million points, the researchers used a digital mask similar to those used in projectors to create images and videos. In this case, the mask controls a femtosecond laser to create the desired light pattern in the precursor liquid polymer material. The high-intensity light causes a polymerization reaction that turns the liquid to solid, where desired, to create 3-D structures.

Each layer of the fabricated structure is formed by a 35-femtosecond burst of high-intensity light. The projector and mask are then used to create layer after layer until the entire structure is produced. When the liquid polymer is removed, remains the 3D-printed solid. The FP-TPL technique allowed the researchers to produce in eight minutes a structure that would take several hours to produce using earlier processes.

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