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Researchers from the Georgia Institute of Technology have found a way to accelerate the additive manufacturing of nanometer scale structures by using a small, high-energy supersonic jet of inert gas to energize precursor molecules. The novel approach is also enabling the production of nanoscale structures with high aspect ratios.

The technique, which could lead to new applications in nanoscale 3D printing, is based on a focused electron beam deposition process that enables structures to be produced from gas-phase precursors at speeds comparable to those of liquid phase without the need to heat the substrates. According to the research team, the method’s print rates make the process suitable for applications in magnetic memory, high-frequency antennas, quantum communication devices, spintronics and atomic-scale resonators.

“We are controlling matter on the atomic scale to bring about new modes of additive manufacturing,” said Andrei Fedorov, a professor in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “This new science could bring about additive manufacturing applications that might otherwise be impossible. The resulting new technology will open up new dimensions for additive manufacturing at the atomic scale.”

Adding energy

The research team behind the nanoscale printing process was inspired to develop the technology after trying and failing to produce structures measuring just a few nanometers in size using electron beams (which themselves measure just a few nanometers in diameter.)

Fedorov explained: ”When we went to the lab to use nanofabrication with focused electron beams, which are the size of a few nanometers, we could not grow structures that were just a few nanometers. They grew to be 50 or 100 nanometers. And it also took a long time to produce the structures, which meant that, without improvements, we’d never be able to produce them at high volume.”

Along with his fellow researchers Matthew Henry and Songkil Kim, Fedorov realized that the challenges with the electron beam process were in part due to slow reactions in the print process, which was related to the thermodynamic state of the substrate.

By adding energy to the process—by way of a high-energy supersonic jet of inert gas—the team found it was able to speed the process up dramatically, as much as a hundred times.

The work ultimately resulted in a micro-capillary injector measuring just a few micrometers in diameter which can introduce tiny jets of gaseous molecules into the deposition chamber, activating the precursors for nanoscale structures. Because the jet is introduced in a vacuum chamber, the gas is actually accelerates to supersonic speeds, which energizes the precursor molecules that are adsorbed to the substrate.

“This energetic thermal state allows the electrons from the beam to much more easily break chemical bonds, and as a result, structures grow much faster,” Fedorov said. “All of this amplification, both the molecule transport and the rate of reaction, are exponential, meaning a small change can lead to a dramatic increase in outcome.”

Creating a theory

To better understand the new process and to learn how to control it, the research team set about creating a theory for the additive approach. This phase of the project involved using nanoscale thermometric techniques to measure the temperature of the adsorbed atoms subjected to the jet. This information enabled the researchers to understand the basic physics of the technique, which in turn could lead to new applications.

“Once we have a model, it essentially becomes a design tool,” Fedorov added. “With this understanding and the capabilities we have demonstrated, we can expand them to other fields such as directed self-assembly, epitaxial growth and other areas. This could enable a whole host of new capabilities to use this kind of direct-write nanofabrication.

“With this, you can have almost the same order of magnitude growth rate as you’d have with liquid phase precursors, but still have access to the richness of possible precursors, the ability to manipulate alloying, and all the experience that has been developed over the years with gas phase deposition. This technology will allow us to do things at a scale that is meaningful from a practical standpoint and cost-effective.”

The researchers have also created hybrid jets which are said to contain high-energy inert gas and precursor gases, which could allow not only for heightened print rates but also precise control of the material composition throughout the process. Going forward, the team plans to leverage the hybrid approach to produce nanostructures with phase and topology that would be impossible to manufacture using other nanofabrication techniques.

The study was recently published in the journal Physical Chemistry Chemical Physics.