Aurelia Butler

Researchers at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, have developed a new, easily manufacturable solid-state thermoelectric refrigeration technology with nano-engineered materials that is twice as efficient as devices made with commercially available bulk thermoelectric materials. As global demand grows for more energy-efficient, reliable and compact cooling solutions, this advancement offers a scalable alternative to traditional compressor-based refrigeration.
In a paper published in Nature Communications on May 21, a team of researchers from APL and refrigeration engineers from Samsung Electronics demonstrated improved heat-pumping efficiency and capacity in refrigeration systems attributable to high-performance nano-engineered thermoelectric materials invented at APL known as controlled hierarchically engineered superlattice structures (CHESS).
The CHESS technology is the result of 10 years of APL research in advanced nano-engineered thermoelectric materials and applications development. Initially developed for national security applications, the material has also been used for noninvasive cooling therapies for prosthetics and won an R&D 100 award in 2023.
“This real-world demonstration of refrigeration using new thermoelectric materials showcases the capabilities of nano-engineered CHESS thin films,” said Rama Venkatasubramanian, principal investigator of the joint project and chief technologist for thermoelectrics at APL. “It marks a significant leap in cooling technology and sets the stage for translating advances in thermoelectric materials into practical, large-scale, energy-efficient refrigeration applications.”
A New Benchmark for Solid-State Cooling
The push for more efficient and compact cooling technologies is fueled by a variety of factors, including population growth, urbanization and an increasing reliance on advanced electronics and data infrastructure. Conventional cooling systems, while effective, are often bulky, energy intensive and reliant on chemical refrigerants that can be harmful to the environment.
Thermoelectric refrigeration is widely regarded as a potential solution. This method cools by using electrons to move heat through specialized semiconductor materials, eliminating the need for moving parts or harmful chemicals, making these next-generation refrigerators quiet, compact, reliable and sustainable. Bulk thermoelectric materials are used in small devices like mini-fridges, but their limited efficiency, low heat-pumping capacity and incompatibility with scalable semiconductor chip fabrication have historically prevented their wider use in high-performance systems.

In the study, researchers compared refrigeration modules using traditional bulk thermoelectric materials with those using CHESS thin-film materials in standardized refrigeration tests, measuring and comparing the electrical power needed to achieve various cooling levels in the same commercial refrigerator test systems. The refrigeration team from Samsung Electronics, led by materials engineer Sungjin Jung, collaborated with APL to validate the results through detailed thermal modeling, quantifying heat loads and thermal resistance parameters to ensure accurate performance evaluation under real-world conditions.
The results were striking: Using CHESS materials, the APL team achieved nearly 100% improvement in efficiency over traditional thermoelectric materials at room temperature (around 80 degrees Fahrenheit, or 25 C). They then translated these material-level gains into a near 75% improvement in efficiency at the device level in thermoelectric modules built with CHESS materials and a 70% improvement in efficiency in a fully integrated refrigeration system, each representing a significant improvement over state-of-the-art bulk thermoelectric devices. These tests were completed under conditions that involved significant amounts of heat pumping to replicate practical operation.
Built to Scale
Beyond improving efficiency, the CHESS thin-film technology uses remarkably less material — just 0.003 cubic centimeters, or about the size of a grain of sand, per refrigeration unit. This reduction in material means APL’s thermoelectric materials could be mass-produced using semiconductor chip production tools, driving cost efficiency and enabling widespread market adoption.
“This thin-film technology has the potential to grow from powering small-scale refrigeration systems to supporting large building HVAC applications, similar to the way that lithium-ion batteries have been scaled to power devices as small as mobile phones and as large as electric vehicles,” Venkatasubramanian said.
Additionally, the CHESS materials were created using a well-established process commonly used to manufacture high-efficiency solar cells that power satellites and commercial LED lights.

“We used metal-organic chemical vapor deposition (MOCVD) to produce the CHESS materials, a method well known for its scalability, cost-effectiveness and ability to support large-volume manufacturing,” said Jon Pierce, a senior research engineer who leads the MOCVD growth capability at APL. “MOCVD is already widely used commercially, making it ideal for scaling up CHESS thin-film thermoelectric materials production.”
These materials and devices continue to show promise for a broad range of energy harvesting and electronics applications in addition to the recent advances in refrigeration. APL plans to continue to partner with organizations to refine the CHESS thermoelectric materials with a focus on boosting efficiency to approach that of conventional mechanical systems. Future efforts include demonstrating larger-scale refrigeration systems, including freezers, and integrating artificial intelligence-driven methods to optimize energy efficiency in compartmentalized or distributed cooling in refrigeration and HVAC equipment.
“Beyond refrigeration, CHESS materials are also able to convert temperature differences, like body heat, into usable power,” said Jeff Maranchi, Exploration Program Area manager in APL’s Research and Exploratory Development Mission Area. “In addition to advancing next-generation tactile systems, prosthetics and human-machine interfaces, this opens the door to scalable energy-harvesting technologies for applications ranging from computers to spacecraft — capabilities that weren’t feasible with older bulkier thermoelectric devices.”
“The success of this collaborative effort demonstrates that high-efficiency solid-state refrigeration is not only scientifically viable but manufacturable at scale,” said Susan Ehrlich, an APL technology commercialization manager. “We’re looking forward to continued research and technology transfer opportunities with companies as we work toward translating these innovations into practical, real-world applications.” More

By carefully placing nanostructures on a flat surface, researchers at Linköping University, Sweden, have significantly improved the performance of so-called optical metasurfaces in conductive plastics. This is a major step for controllable flat optics, with future applications such as video holograms, invisibility materials, and sensors, as well as in biomedical imaging. The study has been published in the journal Nature Communications.
To control light, curved lenses are used today, that are often made of glass that is either concave or convex, which refracts the light in different ways. These types of lenses can be found in everything from high-tech equipment such as space telescopes and radar systems to everyday items including camera lenses and spectacles. But the glass lenses take up space and it is difficult to make them smaller without compromising their function.
With flat lenses, however, it may be possible to make very small optics and also find new areas of application. They are known as metalenses and are examples of optical metasurfaces that form a rapidly growing field of research with great potential, though at present the technology has its limitations.
“Metasurfaces work in a way that nanostructures are placed in patterns on a flat surface and become receivers for light. Each receiver, or antenna, captures the light in a certain way and together these nanostructures can allow the light to be controlled as you desire,” says Magnus Jonsson, professor of applied physics at Linköping University.
Today there are optical metasurfaces made of, for example, gold or titanium dioxide. But a major challenge has been that the function of the metasurfaces cannot be adjusted after manufacture. Both researchers and industry have requested features such as being able to turn metasurfaces on and off or dynamically change the focal point of a metalens.
But, in 2019, Magnus Jonsson’s research group at the Laboratory of Organic Electronics showed that conductive plastics (conducting polymers) can crack that nut. They showed that the plastic could function optically as a metal and thus be used as a material for antennas that build a metasurface. Thanks to the ability of the polymers to oxidize and reduce, the nanoantennas were able to be switched on and off. However, the performance of metasurfaces built from conductive polymers has been limited and not comparable to metasurfaces made from traditional materials.
Now, the same research team has managed to improve performance up to tenfold. By precisely controlling the distance between the antennas, these can help each other thanks to a kind of resonance that amplifies the light interaction, called collective lattice resonance.
“We show that metasurfaces made of conducting polymers seem to be able to provide sufficiently high performance to be relevant for practical applications,” says Dongqing Lin who is principal author of the study and postdoc in the research group.
So far, the researchers have been able to manufacture controllable antennas from conducting polymers for infrared light, but not for visible light. The next step is to develop the material to be functional also in the visible light spectrum. More

Ferromagnetic semiconductors (FMSs) combine the unique properties of semiconductors and magnetism, making them ideal candidates for developing spintronic devices that integrate both semiconductor and magnetic functionalities. However, one of the key challenges in FMSs has been achieving high Curie temperatures (TC) that enable their stable operation at room temperature. Though previous studies achieved a TC of 420 K, which is higher than the room temperature, it was insufficient for effectively operating the spin functional materials, highlighting the demand for an increase in TC among FMSs. This challenge has been featured among the 125 unsolved questions selected by the journal Science in 2005. Materials such as (Ga,Mn)As exhibit low TC, limiting their practical use in spintronic devices. While adding Fe to narrow bandgap semiconductors like GaSb seemed promising, incorporating high concentrations of Fe while maintaining crystallinity proved difficult, restricting the attainable TC.
To overcome these limitations, a team of researchers led by Professor Pham Nam Hai from Institute of Science Tokyo, Japan, developed a high-quality (Ga,Fe)Sb FMS using the step-flow growth method on vicinal GaAs (100) substrates with a high off-angle of 10°. Their findings are published in Volume 126, Issue 16 of Applied Physics Letters on April 24, 2025. Utilization of the step-flow growth approach allowed them to incorporate a high concentration of Fe while maintaining excellent crystallinity, resulting in a TC of up to 530 K — the highest reported so far for FMSs.
The team utilized magnetic circular dichroism spectroscopy measurements to confirm the intrinsic ferromagnetism in the (Ga0.76,Fe0.24)Sb layer based on the spin-polarized band structure of FMS. In addition, the team employed Arrott plots, a standard technique for extrapolating the TC from magnetization data. This method helped identify the magnetic transition points, offering a more precise understanding of the material’s ferromagnetic behavior at varying temperatures.
“In the conventional (Ga,Fe)Sb samples, maintaining crystallinity at high Fe doping levels was a persistent issue. By applying the step-flow growth technique on vicinal substrates, we successfully addressed this challenge and achieved the world’s highest TC in FMSs,” says Prof. Hai.
Furthermore, the researchers also investigated the long-term stability of their sample by measuring the magnetic properties of a thinner (Ga,Fe)Sb (9.8 nm) layer stored in open air for 1.5 years. Despite a slight reduction in TC from 530 K to 470 K, the material retained significant ferromagnetic properties, showing its potential for practical applications. Additionally, the material exhibited a large magnetic moment per Fe atom (4.5 μB/atom), which is close to the ideal value for Fe3+ ions in a zinc blende crystal structure (5 μB/atom). This is twice that of α-Fe metal, highlighting the superior magnetic properties of the material.
“Our results demonstrate the feasibility of fabricating high-TC FMSs that are compatible with room temperature operations, which is a crucial step towards the realization of spintronic devices,” adds Prof. Hai.
Overall, the study highlights the effectiveness of film formation using step-flow growth on vicinal substrates in producing high-quality, high-performance FMSs with higher Fe concentrations. By overcoming the bottleneck of low TC, the study represents a significant step forward toward the realization of spin-functional semi-conductor devices that can operate at room temperature. More

When Jayedi Aman looks at a city, he notices more than just its buildings and streets — he considers how people move through and connect with those spaces. Aman, an assistant professor of architectural studies at the University of Missouri, suggests that the future design of cities may be guided as much by human experience as by physical materials.
In a recent study, Aman and Tim Matisziw, a professor of geography and engineering at Mizzou, took a fresh approach to urban research by using artificial intelligence to explore the emotional side of city life. Their goal was to better understand the link between a city’s physical features and how people feel in those environments.
Using public Instagram posts with location tags, the researchers trained an AI tool to read the emotional tone of the images and text of the posts, identifying whether people were happy, frustrated or relaxed. Then, using Google Street View and a second AI tool, they analyzed what those places looked like in real life and linked those features to how people felt in the moment they posted to social media.
As a result, Aman and Matisziw created a digital “sentiment map” that shows what people are feeling across a city. Next, they plan to use this information to create a digital version of a city — called an urban digital twin — that can show how people are feeling in real time.
This kind of emotional mapping gives city leaders a powerful new tool. Instead of relying solely on surveys — which take time and may not reach everyone — this AI-powered method uses data people already share online.
“For example, if a new park gets lots of happy posts, we can start to understand why,” Aman, who leads the newly established Spatial Intelligence Lab at Mizzou, said. “It might be the green space, the quiet nature or the sense of community. We can now connect those feelings to what people are seeing and experiencing in these places.”
Beyond parks, this tool could help officials improve services, identify areas where people feel unsafe, plan for emergencies or check in on public well-being after disasters.
“AI doesn’t replace human input,” Matisziw said. “But it gives us another way to spot patterns and trends that we might otherwise miss, and that can lead to smarter decisions.”
The researchers believe this information about how people feel could one day be shown next to traffic and weather updates on digital tools used by leaders to make decisions about city operations.
“We envision a future where data on how people feel becomes a core part of city dashboards,” Aman said. “This opens the door to designing cities that not only work well but also feel right to the people who live in them.” More

National Institute for Materials Science, Japan. “Demonstration of spin-torque heat-assisted magnetic recording.” ScienceDaily. ScienceDaily, 21 May 2025. .
National Institute for Materials Science, Japan. (2025, May 21). Demonstration of spin-torque heat-assisted magnetic recording. ScienceDaily. Retrieved June 3, 2025 from www.sciencedaily.com/releases/2025/05/250521124447.htm
National Institute for Materials Science, Japan. “Demonstration of spin-torque heat-assisted magnetic recording.” ScienceDaily. www.sciencedaily.com/releases/2025/05/250521124447.htm (accessed June 3, 2025). More

An international research team, led by Akitoshi Shiotari of the Fritz Haber Institute of the Max Planck Society (Germany), Mariana Rossi of the Max Planck Institute for the Structure and Dynamics of Matter (Germany), and Takashi Kumagai of the Institute for Molecular Science/SOKENDAI (Japan) has successfully achieved single-molecule spectroscopic observation of hydrogen (H2) and deuterium (D2) confined within a picocavity. The picocavity was formed between a silver nanotip and a silver single-crystal substrate under cryogenic and ultrahigh vacuum conditions, using tip-enhanced Raman spectroscopy (TERS).
In recent years, light-matter interactions within atomic-scale volumes, known as picocavities, have attracted growing attention in nanoscience and nanotechnology. The extremely confined electromagnetic field generated by plasmon resonance is now regarded as a promising platform for atomic-scale measurements and quantum photonic technologies.
In this study, the smallest molecule — hydrogen — was confined within a picocavity and investigated using high-resolution TERS. This enabled picometric molecular spectroscopy to resolve its vibrational and rotational modes with unprecedented detail, revealing how the structure and vibrational properties of a single molecule are affected by the extreme spatial confinement of the picocavity. Furthermore, by precisely adjusting the gap distance between the silver tip and the silver substrate, the subtle interaction with the molecule is modified. As a result, it was discovered that only the vibrational mode of H2, and not D2, exhibited a significant change, demonstrating a pronounced isotope-dependent effect — that could not be captured by ensemble-averaged Raman or other conventional vibrational spectroscopies.
To elucidate the origin of this nontrivial isotope effect, the team conducted theoretical simulations using density functional theory (DFT), path-integral molecular dynamics (PIMD), and model Hamiltonians. These calculations revealed that the spectroscopy is exquisitely sensitive to the local interaction potential experienced by the molecules, dominated by van der Waals interactions. Quantum delocalization of the nuclei — a quantum swelling effect at low temperatures — plays a decisive role in the observed differences, favoring distinct equilibrium positions for H2 and D2 in the picocavity, which lead to a substantial difference in their vibrational spectra. Dr. Rossi says, “We were surprised at how vibrational coupling and nuclear quantum effects work hand-in-hand to cause such a large isotope effect.”
Dr. Shiotari says, “This work deepens our understanding of light-molecule interactions and the quantum dynamics of adsorbed molecules in extremely confined spaces, representing a significant step forward in precision molecular spectroscopy.” Prof. Kumagai adds, “Looking ahead, the methods and insights developed here are expected to contribute to the advanced analysis of hydrogen storage materials and catalytic reactions, as well as to the development of quantum control technologies for individual molecules — thereby supporting next-generation nanoscale sensing and quantum photonic technologies.” More

Researchers have demonstrated that by using a semiconductor with flexible bonds, the material can be moulded into various structures using nano containers, without altering its composition, the discovery could lead to the design of a variety of customised electronic devices using only a single element.
Semiconductors are vital to our daily lives, as they are found in nearly every electronic device. One of the key characteristics of semiconductors is their band gap, which determines how they conduct electric current. The band gap is typically engineered for specific applications by breaking chemical bonds or introducing additional elements into the material. However, these processes can be complex and energy-intensive.
Researchers from the University of Nottingham, the EPSRC SuperSTEM facility, Ulm University in Germany, and BNNT LLC in the USA imaged new forms of selenium using transmission electron microscopy, employing nanotubes as tiny test tubes. The study has been published today in Advanced Materials.
Dr Will Cull, research fellow in School of Chemistry, Univesity of Nottingham, who carried out the experimental work, said, ‘Selenium is an old semiconductor with a rich history, having been used in the first solar cells. In our research, we have revitalised selenium by discovering new forms that can emerge when confined to the nanoscale.’
Selenium can exist as nanowires, with its structure and bonding varying by diameter. Below a certain size, the bonding between selenium atoms changes, increasing bond angles. This causes straightening of the initially helical structure, ultimately constricting it into atomically thin wires.
Dr Will Cull said, ‘We successfully imaged new forms of selenium using transmission electron microscopy, employing nanotubes as tiny test tubes. This approach allowed us to create a new phase diagram that connects the atomic structure of selenium to the diameter of the nanowires.’
The Nottingham group previously reported using nano test tubes to image chemical reactions of individual molecules and to observe phase transitions in semiconductors. This approach enables real-time filming of chemistry at the atomic level.

Dr Will Cull said, ‘To our astonishment, we observed that the nano test tube became thinner as we imaged it! Before our very eyes, we witnessed the selenium nanowire inside the nanotube being squeezed like toothpaste, stretching and thinning. This serendipitous discovery allowed us to establish mechanisms for the transformation of one type of nanowire to another, which have implications for their electronic properties, with near-atomic precision.’
The band gap is a crucial property of semiconductors that significantly impacts their use in various devices, including solar cells, transistors, and photocatalysts. Professor Quentin Ramasse, director of EPSRC SuperSTEM, said, ‘By utilising atomically resolved scanning transmission electron microscopy coupled with electron energy loss spectroscopy, we were able to measure the band gaps of individual chains of selenium. These measurements enabled us to establish a relationship between the diameter of these nanowires and their corresponding band gaps.’
Professor Quentin Ramasse said, ‘Traditionally, carbon nanotubes have been used as nano test tubes; however, their outstanding energy absorption properties can obscure the electronic transitions of the material inside. In contrast, a newer type of nano test tube, boron nitride nanotubes, is transparent, allowing us to observe the band gap transitions in selenium nanowires contained within them.’
The famous Moore’s Law states that the number of transistors on an integrated circuit doubles approximately every two years. As a result, electronic components must become smaller. Professor Andrei Khlobystov, School of Chemistry, University of Nottingham, said, ‘We have investigated the ultimate limit for nanowire size while preserving useful electronic properties. This is possible for selenium because the phenomenon of quantum confinement can be effectively balanced by distortions in the atomic structure, thus allowing the band gap to remain within a useful range.’
The researchers hope that these new materials will be incorporated into electronic devices in the future. Accurately tuning the band gap of selenium by changing the diameter of the nanowire could lead to the design of a variety of customised electronic devices using only a single element. More