Artificial Intelligence Used to Facilitate Self-Assembly of New Nanostructures

The team demonstrated that Artificial Intelligence (AI) can be used to facilitate the self-assembly of new nanostructures. The new autonomous methods have led to the discovery of three new nanostructures, including a first-of-its-kind nanoscale ‘ladder’, the journal Science Advances reported.

Self-assembly is the process where a material’s molecules organise themselves into unique patterns. Scientists at Brookhaven’s Center for Functional Nanomaterials (CFN) are experts at directing the self-assembly process and have created templates for materials to form desirable arrangements for applications in microelectronics and catalysis. The newly discovered structures further widen the scope of self-assembly’s applications.

“Self-assembly can be used as a technique for nanopatterning, which is a driver for advances in microelectronics and computer hardware,” said CFN scientist and co-author Gregory Doerk.

“These technologies are always pushing for higher resolution using smaller nanopatterns. You can get really small and tightly controlled features from self-assembling materials, but they do not necessarily obey the kind of rules that we lay out for circuits, for example. By directing self-assembly using a template, we can form patterns that are more useful.”

The team aims to build a library of self-assembled nanopattern types to broaden their applications. In previous studies, they demonstrated that new types of patterns are made possible by blending two self-assembling materials together.

“The fact that we can now create a ladder structure, which no one has ever dreamed of before, is amazing,” said CFN group leader and co-author Kevin Yager.

“Traditional self-assembly can only form relatively simple structures like cylinders, sheets, and spheres. But by blending two materials together and using just the right chemical grating, we’ve found that entirely new structures are possible.”

Blending self-assembling materials together has allowed for unique structures to be discovered, but has also generated new challenges. With many more factors to control in the self-assembly process, finding the right combination of parameters to create new and useful structures is a battle against time. To accelerate their research, the team used a new AI capability – autonomous experimentation.

Brookhaven scientists at CFN and the National Synchrotron Light Source II (NSLS-II) have been collaborating with the Center for Advanced Mathematics for Energy Research Applications (CAMERA) at DOE’s Lawrence Berkeley National Laboratory to develop an AI framework that can autonomously define and perform all the steps of an experiment.

CAMERA’s gpCAM algorithm drives the framework’s autonomous decision-making. The latest research is the team’s first successful demonstration of the algorithm’s ability to discover new materials.

“gpCAM is a flexible algorithm and software for autonomous experimentation,” said Berkeley Lab scientist and co-author Marcus Noack. “It was used particularly ingeniously in this study to autonomously explore different features of the model.”

“With help from our colleagues at Berkeley Lab, we had this software and methodology ready to go, and now we’ve successfully used it to discover new materials,” Yager said. “We’ve now learned enough about autonomous science that we can take a materials problem and convert it into an autonomous problem pretty easily.”

First, the team developed a complex sample with a spectrum of properties for analysis. The sample was then fabricated using the CFN nanofabrication facility and carried out the self-assembly in the CFN material synthesis facility.

“An old school way of doing material science is to synthesise a sample, measure it, learn from it, and then go back and make a different sample and keep iterating that process,” Yager said. “Instead, we made a sample that has a gradient of every parameter we’re interested in. That single sample is thus a vast collection of many distinct material structures.”

The team then brought the samples to NSLS-II, which generates ultrabright X-rays for studying the structure of materials.

“One of the SMI beamline’s strengths is its ability to focus the X-ray beam on the sample down to microns,” said NSLS-II scientist and co-author Masa Fukuto.

“By analysing how these microbeam X-rays get scattered by the material, we learn about the material’s local structure at the illuminated spot. Measurements at many different spots can then reveal how the local structure varies across the gradient sample. In this work, we let the AI algorithm pick, on the fly, which spots to measure next to maximise the value of each measurement.”

As the sample was measured at the SMI beamline, the algorithm created a model of the material’s numerous and diverse set of structures, without human intervention. With each subsequent X-ray measurement, the model updated itself, making every measurement more accurate.

In just a few hours, the algorithm identified three key areas for researchers to study in more detail. These key areas were imaged with the CFN electron microscopy facility, which uncovered the rails and rungs of a nanoscale ladder, among other new features.

It is estimated that the researchers would have needed a month to make this discovery using traditional methods, compared to the six hours taken for the experiment.

“Autonomous methods can tremendously accelerate discovery,” Yager said. “It’s essentially ‘tightening’ the usual discovery loop of science so that we cycle between hypotheses and measurements more quickly. Beyond just speed, however, autonomous methods increase the scope of what we can study, meaning we can tackle more challenging science problems.”

“Moving forward, we want to investigate the complex interplay among multiple parameters. We conducted simulations using the CFN computer cluster that verified our experimental results, but they also suggested how other parameters, such as film thickness, can also play an important role,” Doerk said.

Now, the team is applying its autonomous research method to more challenging material discovery problems in self-assembly. Autonomous discovery methods are adaptable and can be applied to nearly any research problem.

“We are now deploying these methods to the broad community of users who come to CFN and NSLS-II to conduct experiments,” Yager said. “Anyone can work with us to accelerate the exploration of their materials research. We foresee this empowering a host of new discoveries in the coming years, including in national priority areas like clean energy and microelectronics.”

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