IMOD

Atomic Musical Chairs: How Tiny Nanocrystals Are Informing the Future of Energy-Efficient Electronics

Daniel Morton — Tue, 17 Mar 2026 19:43:33 +0000

Atomic Musical Chairs: How Tiny Nanocrystals Are Informing the Future of Energy-Efficient Electronics Daniel Morton Tue, 03/17/2026 - 13:43

Daniel Morton

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While most people, when asked about energy innovation, think about some of the "large" technologies, such as wind turbines, long transmission lines, or massive power plants, some of the most important advances in how we use energy are happening at a scale so small that millions of the "machines" involved could fit on the head of a pin.

New research from a team led by RASEI Fellow Gordana Dukovic, working in collaboration with RASEI Fellow Sadegh Yazdi and Prof. Dmitri Talapin from the University of Chicago, reveals new insights on a high-speed game of "atomic musical chairs." This collaboration involved two large teams working together. Researchers from two United States National Science Foundation Science and Technology Centers (STCs) including IMOD and STROBE, employed cutting-edge microscopy techniques to directly visualize, for the first time at this scale, how atoms swap places inside tiny semiconductor nanocrystals, which is a crucial step toward understanding the composition, and ultimately the properties, of these materials.

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STROBE STC

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Science and Technology Centers are hubs for collaboration, bringing together multidisciplinary researchers from across the United States to solve large, challenging and complex problems. This article describes a space where two of these large networks worked together. STROBE, or Science and Technology Center on Real-Time Functional Imaging pushes the boundaries of microscopy to observe and understand materials at the atomic and nano-scales. IMOD, or The Center for Integration of Modern Optoelectronic Materials on Demand, focuses on making atomically precise semiconductors and integrating them into applications in VR displays, and devices for quantum communication and computing. This team leverages the expertise from both Centers to create new semiconductors and using cutting-edge microscopes to observe and understand them.

Almost all of our electronic devices are built from semiconductors. Whether it is the screen on your smartphone, the components in your car, or the microchips in your computer, these electronics rely on semiconductors. Traditionally, these materials are "grown" through rigid and often expensive processes. Tuning the properties of a semiconductor using this approach is not straightforward. If you want a specific color of light for a display, or a specific energy absorption profile for a solar panel, you often have to start from scratch with an entirely different material.

This is where semiconductor nanocrystals offer remarkable opportunities. The specific size, shape, and composition of these tiny nanocrystals determine the physical and electronic properties of the overall material. A particularly powerful process with such nanocrystals is called cation exchange. Instead of building a new crystal from scratch, you can take an existing one and swap out its internal atomic components to change its properties.

“This is a project that we have been working on for a long time” explains Ben Hammel, a graduate student in the Dukovic Group, and lead author on this research. “We have been looking at these materials from the Talapin Group for a long time”.

This work, just published in ACS Nano, focuses on what are called III–V nanocrystals, which are tiny, four-sided pyramids, or tetrahedrons, named for the groups of the periodic table their constituent elements come from (Group III includes elements like Indium, Gallium, and Aluminum; Group V includes Phosphorus, Arsenic, and Antimony). In this research, the nanocrystals are made of a mixture of Indium, Phosphorus, and Arsenic. To exert more control over the properties of these nanocrystals, the researchers introduced Gallium. Adding Gallium is like tuning a guitar string: it changes the energy of the crystal, influencing how it interacts with light.

“A lot of people have developed ways to make III-V bulk semiconductors, but the real challenge is making them into nanocrystals, where you have more control over their properties, and the Talapin Group have developed a really neat molten salt process to do this” explains Hammel. The molten salt work was published in Science in 2024.

Imagine the inside of one of these tiny crystals as a perfectly ordered lattice of "seats." There are two types of players: Anions (the Phosphorus and Arsenic atoms) and Cations (the Indium atoms). A key observation from the team was that the "house" never moves. The Anions are like the floor and the chairs, they stay perfectly still, maintaining the overall crystal framework. The Cations, on the other hand, are the players sitting in those chairs.

In this work, the nanocrystals were placed into a "hot bath" of molten Gallium salts, essentially starting the music on the game of atomic musical chairs. Previous work had shown that the atoms exchange, but there was not a lot of evidence for how this process worked. “Understanding how this works is very important, and finding out more about the local elemental composition, and how the Gallium atoms move can inform how we design these systems in the future” explains Hammel.

These nanocrystals are only 5 to 10 nanometers wide. A typical human hair is between 80,000 and 100,000 nanometers wide. These crystals are called "nano" for a reason! To observe this game of atomic musical chairs in action, the team used Scanning Transmission Electron Microscopy (STEM), an instrument that uses a focused beam of electrons to probe and image matter at the atomic scale. “Early on there were some signs that there was heterogeneity within the particles, but it was unclear, a big technical challenge we had to overcome was how we can actually measure the Gallium moving through the nanocrystal” said Hammel.

A key challenge they had to figure out was the sensitivity of the nanocrystals to the very tool being used to study them. The electron beam of the STEM, if used at high intensity, can damage the nanocrystals before a useful image can even be collected. To solve this, the team developed an innovative "statistical" imaging approach. Rather than blasting a single crystal with a high dose of electrons to get a sharp image, the researchers instead took many low-dose, and individually blurry, snapshots of hundreds of different crystals at different stages of the molten salt reaction. “We essentially stacked the data on top of each other” describes Hammel, “If I can add together 10 nanocrystals, I can get 10 times the signal”. Adding these kinds of signals together hadn’t been done before with semiconductor nanocrystals. “A lot of this came together from teamwork, I got a lot of really great suggestions from collaborators on how to collect and analyze this information. I used a suite of open source Python tools, which I was a little lost with until I met the researcher who developed them at a conference (Josh Taillon from NIST), who gave me some great suggestions and ideas” said Hammel. Using these advanced computer algorithms, they aligned and stacked hundreds of images on top of each other. Much like a long-exposure photograph of the night sky reveals stars the naked eye cannot see, this averaged stacked image revealed a detailed map of where the Gallium atoms were moving inside the nanocrystals. To the team’s knowledge, this signal-averaging approach for elemental mapping has not previously been applied to semiconductor nanocrystals.

The Gallium atoms rush in to claim “seats”, but not randomly. Gallium grabs the seats near the surface first. Because of the high surface-to-volume ratio of these tiny particles, this surface exchange causes a dramatic and rapid change in overall composition: within the first 15 minutes in the molten salt bath, the outside of the nanocrystals is substantially transformed. However, as the game goes on, it gets progressively harder. The Indium atoms sitting in the seats at the center of the nanocrystal are crowded in, and for a Gallium atom to reach the core, an Indium atom must fight its way out through an increasingly Gallium-rich lattice. This sets up a compositional gradient, essentially a smooth transition from a Gallium-rich exterior to an Indium-rich core, that persists even after 16 hours of reaction.

This new methodology, combining STEM with advanced computational image processing, is sensitive enough to detect and map the movement of atoms through individual nanocrystals. Applying it here directly revealed that the cation exchange process (Indium being replaced by Gallium) creates a graded composition rather than a simple sharp boundary between materials. The team also used computer simulations (finite element analysis in COMSOL) to model this exchange as a diffusion-limited process, finding that the rate of exchange slows dramatically as more Gallium enters the lattice, likely because the smaller Gallium atoms cause the lattice to contract, making it progressively harder for further exchange to occur.

Importantly, the methods developed in this work are broadly applicable and could be used to determine the elemental composition of many other types of nanocrystals that have previously been difficult to study due to their sensitivity to electron beams.

Daniel Morton — Thu, 24 Oct 2024 19:50:17 +0000

RASEI Researchers unlock a 'new synthetic frontier' for quantum dots Daniel Morton Thu, 10/24/2024 - 13:50

Lauren Scholz

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University of Chicago Press Release

In a breakthrough for nanotechnology, researchers have discovered a new way to synthesize quantum dot nanocrystals using molten salt as a medium. Traditional methods to create these materials required organic solvents, which cannot withstand the high temperatures needed for certain semiconductor materials, particularly those combining elements from groups III and V on the periodic table. By using superheated molten sodium chloride, scientists were able to synthesize these semiconductor nanocrystals, paving the way for improved applications in fields like quantum computing, LED lighting, and solar technology.

Led by a team from the University of Chicago and collaborating institutions, including RASEI Fellows Sadegh Yazdi and Gordana Dukovic, this novel method also opens new avenues for materials science by enabling the synthesis of previously inaccessible nanocrystal compositions. The technique addresses long-standing challenges by providing a high-temperature environment without degrading the materials. Researchers hope this advance will contribute to new types of devices and materials, marking a significant expansion in the range of accessible quantum dot technologies.

For a more information, please see the press release from The University of Chicago.

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Colossal Core/Shell CdSe/CdS Quantum Dot Emitters

Anonymous — Fri, 26 Jul 2024 06:00:00 +0000

Colossal Core/Shell CdSe/CdS Quantum Dot Emitters Anonymous (not verified) Fri, 07/26/2024 - 00:00

ACS NANO, 2024, 18, 31, 20726-20739

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RASEI Fellows Collaborating Partners in two new NSF PREM Awards

Daniel Morton — Thu, 25 Jul 2024 22:13:17 +0000

RASEI Fellows Collaborating Partners in two new NSF PREM Awards Daniel Morton Thu, 07/25/2024 - 16:13

Daniel Morton

NSF Press Release

UC Merced VISION Press Release

PEAQS PREM Page

VISION PREM Page

Several RASEI Fellows and members of the NSF Science and Technology Center for Integration of Modern Optoelectronic Materials on Demand (IMOD) were involved in the development of successful proposals for NSF Partnerships for Research and Education in Materials (PREM) grants.

These grants will enable RASEI members to form closer partnerships with researchers at Fort Lewis College (Durango, CO), Norfolk State University (Norfolk, VA), and UC Merced (Merced, CA). These projects will expand participation, provide access to materials and facilities and provide support for training, research exchanges, meetings and workshops.

Two proposals were funded. The Venture for Innovation in Self-Assembly and Integration of Optoelectronic Nanostructures (VISION) focuses on a partnership between IMOD (which includes RASEI Fellows Seth Marder, Mike Toney, Gordana Dukovic, David Jonas and Matt Beard), and UC Merced. The Partnership for Education and Advancement of Quantum and nano-Sciences (PEAQS) brings together the IMOD team with researchers from Fort Lewis College and Norfolk State University.

While their scientific and technical foci are different, these collaborations have shared missions of developing programs that cultivate student potential in STEM, offering enriched research opportunities, interdisciplinary scientific collaborations, pedagogical development and inclusive mentoring.

Check out more about each the programs by reading their abstract and checking out their websites.

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Ligand Equilibrium Influences Photoluminescence Blinking in CsPbBr3: A Change Point Analysis of Widefield Imaging Data

Anonymous — Tue, 09 Jul 2024 06:00:00 +0000

Ligand Equilibrium Influences Photoluminescence Blinking in CsPbBr3: A Change Point Analysis of Widefield Imaging Data Anonymous (not verified) Tue, 07/09/2024 - 00:00

ACS NANO, 2024, 18, 29, 19208-19219

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