From designing new biomaterials to novel photonic devices, new materials built through a process called bottom-up nanofabrication, or self-assembly, are opening up pathways to new technologies with properties tuned at the nanoscale. However, to fully unlock the potential of these new materials, researchers need to “see” into their tiny creations so that they can control the design and fabrication in order to enable the material’s desired properties.
This has been a complex challenge that researchers from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Columbia University have overcome for the first time, imaging the inside of a novel material self-assembled from nanoparticles with seven nanometer resolution, about 1/100,000 of the width of a human hair. In a new paper published on April 7, 2022, in Science, the researchers showcase the power of their new high-resolution X-ray imaging technique to reveal the inner structure of the nanomaterial.
The team designed the new nanomaterial using DNA as a programmable construction material, which enables them to create novel engineered materials for catalysis, optics, and extreme environments. During the creation process of these materials, the different building blocks made of DNA and nanoparticles shift into place on their own based on a defined “blueprint”—called a template—designed by the researchers. However, to image and exploit these tiny structures with X-rays, they needed to convert them into inorganic materials that could withstand X-rays while providing useful functionality. For the first time, the researchers could see the details, including the imperfections within their newly arranged nanomaterials.
“While our DNA-based assembly of nanomaterials offers a tremendous level of control to fine-tune the properties we desire, they don’t form perfect structures that correspond fully to the blueprint. Thus, without detailed 3D imaging with single-particle resolution, it is impossible to understand how to design effective self-assembled systems, how to tune the assembly process, and to what degree a material’s performance is affected by imperfections,” said corresponding author Oleg Gang, scientist at Brookhaven’s Center for Functional Nanomaterials (CFN) and a professor of chemical engineering and of applied physics and materials science at Columbia Engineering.
As a DOE Office of Science user facility, the CFN offers a wide range of tools for creating and investigating novel nanomaterials. It was at the labs of the CFN and at Columbia Engineering where Gang and his team first built and studied new nanostructures. Using both DNA-based assembly as a new fabrication tool at the nanoscale and precise templating with inorganic materials that can coat DNA and nanoparticles, the researchers were able to demonstrate a novel type of complex 3D architecture.
“When I joined the research team five years ago, we had studied the surface of our assemblies really well, but the surface is only skin deep. If you can’t go further, you’ll never see that there’s a blood system or bones underneath. Since the assembly inside our materials drives their performance, we wanted to go deeper to figure out how it worked,” said Aaron Noam Michelson, first author of the study who was a Ph.D. student with Gang and is now a postdoc at the CFN.
And deeper the team went, collaborating with the researchers at the Hard X-ray Nanoprobe (HXN) beamline at the National Synchrotron Light Source II (NSLS-II), another DOE Office of Science user facility located at Brookhaven Lab. NSLS-II enables researchers to study materials with nanoscale resolution and exquisite sensitivity by providing ultrabright light ranging from infrared to hard X-rays.?
“At NSLS-II, we have many tools that can be used to learn more about a material depending on what you are interested in. What made HXN interesting for Oleg and his work was that you can see the actual spatial relationships between objects within the structure at the nanoscale. But, at that time when we first talked about this research, ‘seeing into’ these tiny structures was already at the limit of what the beamline could do,” said Hanfei Yan, also a corresponding author of the study and a beamline scientist at HXN.
To push through this challenge, the researchers discussed the various hurdles they needed to overcome. At the CFN and Columbia, the team had to figure out how they could build the structures with desired organization and how to convert them into an inorganic replica that can withstand powerful X-ray beams, while at NSLS-II the researchers had to tune the beamline by improving the resolution, data acquisition, and many other technical details.
“I think the best way to describe our progress is in terms of performance. When we first tried to take data at HXN, it took us three days and we got part of a data set. The second time we did this, it took us two days, and we got most of a whole data set, but our sample got destroyed in the process. By the third time it took a little over 24 hours, and we got a full data set. Each of these steps was about six months apart,” said Michelson.
Yan added: “Now we can finish it in a single day. The technique is mature enough that we also offer it to other users who would want to use our beamline to investigate their sample. Seeing into samples on this scale is interesting for fields such as microelectronics and battery research.”
The team leveraged the beamline’s abilities in two ways. They not only measured the phase contrast of the X-rays passing through the samples, but they also collected the X-ray fluorescence—the emitted light—from the sample. By measuring the phase contrast, the researchers could better distinguish the foreground from the background of their sample.
“Measuring the data was only half the battle; now we needed to translate the data into meaningful information about order and imperfection of self-assembled systems. We wanted to understand what type of defects can occur in these systems and what is their origin. Until this point, this information was only available through computation. Now we can really see this experimentally, which is super exciting and, literally, eye-opening for the future development of complex designed nanomaterials,” said Gang.
Together, the researchers developed new software tools to help untangle the large amount of data into chunks that could be processed and understood. One major challenge was being able to validate the resolution they achieved. The iterative process that finally led to the groundbreaking new resolution stretched over several months before the team had verified the resolution through both standard analysis and machine-learning approaches.
“It took my whole Ph.D. to get here but I personally feel very gratified for being part of this collaboration. I was able to get involved in every step of the way from making the samples to running the beamline. All the new skills I have learned on this journey will be useful for everything that lies ahead,” said Michelson.
Even though the team has reached this impressive milestone, they are far from done. They already set their sights on the next steps to further push the boundaries of the possible.
“Now that we have gone through the data analysis process, we plan to make this part easier and faster for future projects, especially when further beamline improvements enable us to collect data even faster. The analysis is currently the bottleneck when doing high-resolution tomography work at HXN,” said Yan.
Gang added, “Aside from continuing to push the performance of the beamline, we also plan to use this new technique to dive deeper into the relationships between defects and properties of our materials. We plan to design more complex nanomaterials using DNA self-assembly that can be studied using HXN. In this way we can see how well the structure is built internally and connect this to the process of the assembly. We are developing a new bottom-up fabrication platform that we would not be able to image without this new capability.“
By understanding this connection between material’s properties and the assembly process, the researchers hope to unlock the path to fine-tuning these materials for future applications in designed nanomaterials for batteries and catalysis, for light manipulation, and for desired mechanical responses.
WHAT IS MAGNONICS?
In a first-of-its-kind discovery, researchers in the University of Chicago’s Pritzker School of Molecular Engineering and Argonne National Laboratory announced they can directly control the interactions between two types of quantum particles called microwave photons and magnons. The approach may become a new way to build quantum technology, including electronic devices with new capabilities.
Scientists have high hopes for quantum technology, which has advanced by leaps and bounds over the past decade and could become the basis of powerful new types of computers, ultra-sensitive detectors, and even “hack-proof” communication. But challenges remain in scaling up the technology, which depends on manipulating the smallest particles in order to harness the strange properties of quantum physics.
Two such quantum particles are microwave photons—elementary particles that form the electromagnetic waves that we already use for wireless communications—and magnons. Magnons are the term for a particle-like entity that forms what scientists call “spin waves” — wave-like disturbances that can occur in magnetic materials, and can be used to move information.
Getting these two types of particles to talk to each other has emerged in recent years as a promising platform for both classical and quantum information processing. But this interaction had proved impossible to manipulate in real time, until now.
“Now, it is more like flying a drone, where we can guide and control its flight electronically.”
“Before our discovery, controlling the photon-magnon interaction was like shooting an arrow into the air,” said Xufeng Zhang, a scientist in the Center for Nanoscale Materials at Argonne National Laboratory and the corresponding author of the study. “One has no control at all over that arrow once in flight.”
The team’s discovery has changed that. “Now, it is more like flying a drone, where we can guide and control its flight electronically,” said Zhang.
Through smart engineering, the team, which published its findings “Floquet Cavity Electromagnonics” in Physical Review Letters, employs an electrical signal to periodically alter the magnon vibrational frequency and thereby induce effective magnon-photon interaction. The result is the first-ever microwave-magnonic device that scientists can “tune” to their wishes.
The team’s device can control the strength of the photon-magnon interaction at any point as information is being transferred between photons and magnons. It can even completely turn the interaction on and off. With this tuning capability, scientists can process and manipulate information in ways that far surpass current versions of hybrid magnonic devices.
“Researchers have been searching for a way to control this interaction for the past few years,” said Zhang.
The team’s discovery opens a new direction for magnon-based signal processing and should lead to electronic devices with new capabilities.
It may also enable important applications for quantum signal processing, where microwave-magnonic interactions are being explored as a promising candidate for transferring information between different quantum systems.
The study’s other authors are Changchun Zhong and Liang Jiang of the University of Chicago, and Jing Xu, Xu Han and Dafei Jin with Argonne National Laboratory.
Funding: U.S. Department of Energy Office of Basic Energy Sciences, U. S. Army Research Laboratory, Army Research Office, Air Force Office of Scientific Research, National Science Foundation, Packard Foundation.
From University of Chicago news site.
Adapted from an article by Joseph Harmon first posted by Argonne National Laboratory.