Aurelia Butler

Adding salt to a road before a winter storm changes when ice will form. Researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have applied this basic concept to develop a new method of heating and cooling. The technique, which they have named “ionocaloric cooling,” is described in a paper published Dec. 23 in the journal Science.
Ionocaloric cooling takes advantage of how energy, or heat, is stored or released when a material changes phase — such as changing from solid ice to liquid water. Melting a material absorbs heat from the surroundings, while solidifying it releases heat. The ionocaloric cycle causes this phase and temperature change through the flow of ions (electrically charged atoms or molecules) which come from a salt.
Researchers hope that the method could one day provide efficient heating and cooling, which accounts for more than half of the energy used in homes, and help phase out current “vapor compression” systems, which use gases with high global warming potential as refrigerants. Ionocaloric refrigeration would eliminate the risk of such gases escaping into the atmosphere by replacing them with solid and liquid components.
“The landscape of refrigerants is an unsolved problem: No one has successfully developed an alternative solution that makes stuff cold, works efficiently, is safe, and doesn’t hurt the environment,” said Drew Lilley, a graduate research assistant at Berkeley Lab and PhD candidate at UC Berkeley who led the study. “We think the ionocaloric cycle has the potential to meet all those goals if realized appropriately.”
Finding a solution that replaces current refrigerants is essential for countries to meet climate change goals, such as those in the Kigali Amendment (accepted by 145 parties, including the United States in October 2022). The agreement commits signatories to reduce production and consumption of hydrofluorocarbons (HFCs) by at least 80% over the next 25 years. HFCs are powerful greenhouse gases commonly found in refrigerators and air conditioning systems, and can trap heat thousands of times as effectively as carbon dioxide.
The new ionocaloric cycle joins several other kinds of “caloric” cooling in development. Those techniques use different methods — including magnetism, pressure, stretching, and electric fields — to manipulate solid materials so that they absorb or release heat. Ionocaloric cooling differs by using ions to drive solid-to-liquid phase changes. Using a liquid has the added benefit of making the material pumpable, making it easier to get heat in or out of the system — something solid-state cooling has struggled with.

Lilley and corresponding author Ravi Prasher, a research affiliate in Berkeley Lab’s Energy Technologies Area and adjunct professor in mechanical engineering at UC Berkeley, laid out the theory underlying the ionocaloric cycle. They calculated that it has the potential to compete with or even exceed the efficiency of gaseous refrigerants found in the majority of systems today.
They also demonstrated the technique experimentally. Lilley used a salt made with iodine and sodium, alongside ethylene carbonate, a common organic solvent used in lithium-ion batteries.
“There’s potential to have refrigerants that are not just GWP [global warming potential]-zero, but GWP-negative,” Lilley said. “Using a material like ethylene carbonate could actually be carbon-negative, because you produce it by using carbon dioxide as an input. This could give us a place to use CO2 from carbon capture.”
Running current through the system moves the ions, changing the material’s melting point. When it melts, the material absorbs heat from the surroundings, and when the ions are removed and the material solidifies, it gives heat back. The first experiment showed a temperature change of 25 degrees Celsius using less than one volt, a greater temperature lift than demonstrated by other caloric technologies.
“There are three things we’re trying to balance: the GWP of the refrigerant, energy efficiency, and the cost of the equipment itself,” Prasher said. “From the first try, our data looks very promising on all three of these aspects.”
While caloric methods are often discussed in terms of their cooling power, the cycles can also be harnessed for applications such as water heating or industrial heating. The ionocaloric team is continuing work on prototypes to determine how the technique might scale to support large amounts of cooling, improve the amount of temperature change the system can support, and improve the efficiency.
“We have this brand-new thermodynamic cycle and framework that brings together elements from different fields, and we’ve shown that it can work,” Prasher said. “Now, it’s time for experimentation to test different combinations of materials and techniques to meet the engineering challenges.”
Lilley and Prasher have received a provisional patent for the ionocaloric refrigeration cycle, and the technology is now available for licensing.
This work was supported by the DOE’s Energy Efficiency and Renewable Energy Building Technologies Program. More

Researchers at North Carolina State University have developed a stretchable strain sensor that has an unprecedented combination of sensitivity and range, allowing it to detect even minor changes in strain with greater range of motion than previous technologies. The researchers demonstrated the sensor’s utility by creating new health monitoring and human-machine interface devices.
Strain is a measurement of how much a material deforms from its original length. For example, if you stretched a rubber band to twice its original length, its strain would be 100%.
“And measuring strain is useful in many applications, such as devices that measure blood pressure and technologies that track physical movement,” says Yong Zhu, corresponding author of a paper on the work and the Andrew A. Adams Distinguished Professor of Mechanical and Aerospace Engineering at NC State.
“But to date there’s been a trade-off. Strain sensors that are sensitive — capable of detecting small deformations — cannot be stretched very far. On the other hand, sensors that can be stretched to greater lengths are typically not very sensitive. The new sensor we’ve developed is both sensitive and capable of withstanding significant deformation,” says Zhu. “An additional feature is that the sensor is highly robust even when over-strained, meaning it is unlikely to break when the applied strain accidently exceeds the sensing range.”
The new sensor consists of a silver nanowire network embedded in an elastic polymer. The polymer features a pattern of parallel cuts of a uniform depth, alternating from either side of the material: one cut from the left, followed by one from the right, followed by one from the left, and so on.
“This feature — the patterned cuts — is what enables a greater range of deformation without sacrificing sensitivity,” says Shuang Wu, who is first author of the paper and a recent Ph.D. graduate at NC State.
The sensor measures strain by measuring changes in electrical resistance. As the material stretches, resistance increases. The cuts in the surface of the sensor are perpendicular to the direction that it is stretched. This does two things. First, the cuts allow the sensor to deform significantly. Because the cuts in the surface pull open, creating a zigzag pattern, the material can withstand substantial deformation without reaching the breaking point. Second, when the cuts pull open, this forces the electrical signal to travel further, traveling up and down the zigzag.
“To demonstrate the sensitivity of the new sensors, we used them to create new wearable blood pressure devices,” Zhu says. “And to demonstrate how far the sensors can be deformed, we created a wearable device for monitoring motion in a person’s back, which has utility for physical therapy.”
“We have also demonstrated a human-machine interface,” Wu says. “Specifically, we used the sensor to create a three-dimensional touch controller that can be used to control a video game.”
“The sensor can be easily incorporated into existing wearable materials such as fabrics and athletic tapes, convenient for practical applications,” Zhu says. “And all of this is just scratching the surface. We think there will be a range of additional applications as we continue working with this technology.”
The work was done with support from the National Science Foundation, under grant number 2122841; the National Institutes of Health, under grant number R01HD108473; and the U.S. Department of Defense, under grant number W81XWH-21-1-0185.
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Materials provided by North Carolina State University. Original written by Matt Shipman. Note: Content may be edited for style and length. More

Creating smart sensors to embed in our everyday objects and environments for the Internet of Things (IoT) would vastly improve daily life — but requires trillions of such small devices. Simon Fraser University professor Vincenzo Pecunia believes that emerging alternative semiconductors that are printable, low-cost and eco-friendly could lead the way to a cheaper and more sustainable IoT.
Leading a multinational team of top experts in various areas of printable electronics, Pecunia has identified key priorities and promising avenues for printable electronics to enable self-powered, eco-friendly smart sensors. His forward-looking insights are outlined in his paper published on Dec. 28 in Nature Electronics.
“Equipping everyday objects and environments with intelligence via smart sensors would allow us to make more informed decisions as we go about in our daily lives,” says Pecunia. “Conventional semiconductor technologies require complex, energy-intensity, and expensive processing, but printable semiconductors can deliver electronics with a much lower carbon footprint and cost, since they can be processed by printing or coating, which require much lower energy and materials consumption.”
Pecunia says making printable electronics that can work using energy harvested from the environment — from ambient light or ubiquitous radiofrequency signals, for example — could be the answer.
“Our analysis reveals that a key priority is to realize printable electronics with as small a material set as possible to streamline their fabrication process, thus ensuring the straightforward scale-up and low cost of the technology,” says Pecunia. The article outlines a vision of printed electronics that could also be powered by ubiquitous mobile signals through innovative low-power approaches — essentially allowing smart sensors to charge out of thin air.
“Based on recent breakthroughs, we anticipate that printable semiconductors could play a key role in realizing the full sustainability potential of the Internet of Things by delivering self-powered sensors for smart homes, smart buildings and smart cities, as well as for manufacturing and industry.”
Pecunia has already achieved numerous breakthroughs towards self-powered printable smart sensors, demonstrating printed electronics with record-low power dissipation and the first-ever printable devices powered by ambient light via tiny printable solar cells.
His research group at SFU’s School of Sustainable Energy Engineering focuses on the development of innovative approaches to eco-friendly, printable solar cells and electronics for use in next-generation smart devices.
Pecunia notes that the semiconductor technologies being developed by his group could potentially allow the seamless integration of electronics, sensors, and energy harvesters at the touch of a ‘print’ button at single production sites — thereby reducing the carbon footprint, supply chain issues and energetic costs associated with long-distance transport in conventional electronics manufacturing.
“Due to their unique manufacturability, printable semiconductors also represent a unique opportunity for Canada,” he says. “Not only to become a global player in next-generation, eco-friendly electronics, but also to overcome its reliance on electronics from faraway countries and the associated supply chain and geo-political issues.
“Our hope is that these semiconductors will deliver eco-friendly technologies for a future of clean energy generation and sustainable living, which are key to achieving Canada’s net-zero goal.”
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Materials provided by Simon Fraser University. Original written by Marianne Meadahl. Note: Content may be edited for style and length. More

A University of Minnesota Twin Cities-led team of scientists and engineers has developed a new method for making thin films of perovskite oxide semiconductors, a class of “smart” materials with unique properties that can change in response to stimuli like light, magnetic fields, or electric fields.
The discovery will allow researchers to harness these properties and even combine them with other emerging nano-scale materials to make better devices such as sensors, smart textiles, and flexible electronics.
The paper is published in Science Advances.
Producing materials in thin-film form makes them easier to integrate into smaller components for electronic devices. Many thin films are made using a technique called epitaxy, which consists of placing atoms of a material on a substrate, or a template of sorts, to create a thin sheet of material, one atomic layer at a time. However, most thin films created via epitaxy are “stuck” on their host substrate, limiting their uses. If the thin film is detached from the substrate to become a freestanding membrane, it becomes much more functional.
The University of Minnesota-led team has found a new way to successfully create a membrane of a particular metal oxide — strontium titanate — and their method circumvents several issues that have plagued the synthesis of freestanding metal oxide films in the past.
“We have created a process where we can make a freestanding membrane of virtually any oxide material, exfoliate it, and then transfer it onto any subject of interest we want,” said Bharat Jalan, a senior author on the paper and a professor and Shell Chair in the University of Minnesota Department of Chemical Engineering and Materials Science. “Now, we can benefit from the functionality of these materials by combining them with other nano-scale materials, which would enable a wide range of highly functional, highly efficient devices.”
Making freestanding membranes of “smart” oxide materials is challenging because the atoms are bonded in all three dimensions, unlike in a two-dimensional material, such as graphene. One method of making membranes in oxide materials is using a technique called remote epitaxy, which uses a layer of graphene as an intermediary between the substrate and the thin-film material.

This approach allows the thin-film oxide material to form a thin film and be peeled off, like a piece of tape, from the substrate, creating a freestanding membrane. However, the biggest barrier to using this method with metal oxides is that the oxygen in the material oxidizes the graphene on contact, ruining the sample.
Using hybrid molecular beam epitaxy, a technique pioneered by Jalan’s lab at the University of Minnesota, the researchers were able to get around this issue by using titanium that was already bonded to oxygen. Plus, their method allows for automatic stoichiometric control, meaning they can automatically control the composition.
“We showed for the first time, and conclusively by doing several experiments, that we have a new method which allows us to make complex oxide while ensuring that graphene is not oxidized. That’s a major milestone in synthesis science,” Jalan said. “And, we now have a way to make these complex oxide membranes with an automatic stoichiometric control. No one has been able to do that.”
The materials scientists on Jalan’s team worked closely with engineering researchers in University of Minnesota Department of Electrical and Computer Engineering Professor Steven Koester’s lab, which focuses on making 2D materials.
“These complex oxides are a broad class of materials that have a lot of really important innate functions to them,” said Koester, also a senior author of the study and the director of the Minnesota Nano Center at the University of Minnesota Twin Cities. “Now, we can think about using them to make extremely small transistors for electronic devices, and in a wide array of other applications including flexible sensors, smart textiles, and non-volatile memories.”
The research was funded by the U.S. Department of Energy, the Air Force Office of Scientific Research, and the National Science Foundation.
In addition to Jalan and Koester, the research team included University of Minnesota Department of Chemical Engineering and Materials Science researchers Hyojin Yoon, Tristan Truttmann, Fengdeng Liu, and Sooho Choo; University of Minnesota Department of Electrical and Computer Engineering researcher Qun Su; Pacific Northwest National Laboratory researchers Bethany Matthews, Mark Bowden, Steven Spurgeon, and Scott Chambers; and University of Wisconsin-Madison researchers Vivek Saraswat, Sebastian Manzo, Michael Arnold, and Jason Kawasaki. More

A team of engineers and neuroscientists has demonstrated for the first time that human brain organoids implanted in mice have established functional connectivity to the animals’ cortex and responded to external sensory stimuli. The implanted organoids reacted to visual stimuli in the same way as surrounding tissues, an observation that researchers were able to make in real time over several months thanks to an innovative experimental setup that combines transparent graphene microelectrode arrays and two-photon imaging.
The team, led by Duygu Kuzum, a faculty member in the University of California San Diego Department of Electrical and Computer Engineering, details their findings in the Dec. 26 issue of the journal Nature Communications. Kuzum’s team collaborated with researchers from Anna Devor’s lab at Boston University; Alysson R. Muotri’s lab at UC San Diego; and Fred H. Gage’s lab at the Salk Institute.
Human cortical organoids are derived from human induced pluripotent stem cells, which are usually derived themselves from skin cells. These brain organoids have recently emerged as promising models to study the development of the human brain, as well as a range of neurological conditions.
But until now, no research team had been able to demonstrate that human brain organoids implanted in the mouse cortex were able to share the same functional properties and react to stimuli in the same way. This is because the technologies used to record brain function are limited, and are generally unable to record activity that lasts just a few milliseconds.
The UC San Diego-led team was able to solve this problem by developing experiments that combine microelectrode arrays made from transparent graphene, and two-photon imaging, a microscopy technique that can image living tissue up to one millimeter in thickness.
“No other study has been able to record optically and electrically at the same time,” said Madison Wilson, the paper’s first author and a Ph.D. student in Kuzum’s research group at UC San Diego. “Our experiments reveal that visual stimuli evoke electrophysiological responses in the organoids, matching the responses from the surrounding cortex.”
The researchers hope that this combination of innovative neural recording technologies to study organoids will serve as a unique platform to comprehensively evaluate organoids as models for brain development and disease, and investigate their use as neural prosthetics to restore function to lost, degenerated or damaged brain regions. More

Professor Lee Jong-won’s team of the Department of Energy Science and Engineering at DGIST (President: Kuk Yang), together with Professor Moon Jang-hyeok’s team from the Chung-Ang University, announced the development of solid electrolytes with enhanced atmospheric stability on Wednesday, December 7.
Lithium ion batteries are widely used as energy storage systems for electronic products and electric vehicles. However, since it is vulnerable to ignition as it is manufactured mainly with flammable organic liquid electrolytes, safety issues have been continuously raised as of late.
On the other hand, oxide-based solid electrolytes have the advantage of having high thermal stability and physically preventing the growth of lithium dendrites. Among them, Li7La3Zr2O12 (hereinafter, “LLZO”) electrolyte is considered as a next-generation electrolyte due to its excellent lithium ion conductivity.
Despite these advantages, LLZO electrolyte has a problem — Lithium carbonate forms on the surface due to reaction with moisture and carbon dioxide when exposed to the atmosphere. Lithium carbonate is formed on the surface and then grows along the grain boundaries penetrating into the solid electrolyte and disturb the transfer of lithium ions, which lowers the lithium ion conductivity of the LLZO solid electrolyte.
The research team improved the atmospheric stability of the LLZO electrolyte through the hetero-elemental doping of gallium and tantalum, i.e. by adding gallium and tantalum to pure LLZO electrolytes. In particular, it was verified that ‘LiGaO2,’ a third material formed through the addition of gallium, suppresses the surface adsorption of moisture and carbon dioxide, and promotes the growth of particles during thermal treatment, thus preventing growth of lithium carbonate through grain boundaries and maintaining the lithium ion conduction properties of LLZO electrolytes.
As a result, it was empirically verified that lithium ion conductivity is maintained even when stored for a long time in the air, and stable performance was maintained even after repeated lithium electrodeposition/desorption.
DGIST Department of Energy Science and Engineering Professor Jong-Won Lee said, “I expect the solid electrolyte design concept presented by this research team to be helpful in developing high-performance/high-safety all-solid-state batteries incorporating solid electrolytes, which are stable in the atmosphere and have high lithium ion conductivity.”
Meanwhile, Jung Woo-young in the DGIST Master-Doctor Combined Program participated in this research as the lead author, and the research results were published online on November 2 in Energy Storage Materials, an international journal specializing in energy. In addition, it was carried out with support from the National Research Foundation of Korea’s ‘Nano and Materials Technology Development Project’ and ‘Engineering Research Center Project.’
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Materials provided by DGIST (Daegu Gyeongbuk Institute of Science and Technology). Note: Content may be edited for style and length. More

DGIST (President: Kuk Yang) Department of Electrical Engineering and Computer Science Professor Hwang Jae-yoon’s team developed a ‘deep learning-based ultrasound hologram generation framework’ technology that can freely configure the form of focused ultrasound in real time based on holograms. It is expected to be used as a basic technology in the field of brain stimulation and treatment that requires precision in the future.
Ultrasound is a safe technology even used for prenatal examination. Since it can stimulate deep areas without surgery, ultrasound methods for brain stimulation and treatment have recently been studied, and results that ultrasound brain stimulation have actually improved diseases, such as Alzheimer’s disease, depression, and pain, have been published.
However, the problem is that it is difficult to selectively stimulate related areas of the brain in which several areas interact with each other at the same time because the current technology focuses ultrasound into a single small point or a large circle for stimulation. To solve this problem, a technology capable of freely focusing ultrasound on a desired area using the hologram principle had been proposed, but has limitations, such as low accuracy and long calculation time to generate a hologram.
DGIST Professor Hwang Jae-yoon’s team proposed a deep learning-based learning framework that can embody free and accurate ultrasound focusing in real time by learning to generate ultrasound holograms to overcome the limitations. As a result, Professor Hwang’s team demonstrated that it was possible to focus ultrasound into the desired form more accurately in a hologram creation time close to real time, and maximum 400 times faster than the existing ultrasound hologram generation algorithm method.
The deep learning-based learning framework proposed by the research team learns to generate ultrasonic holograms through self-supervised learning. Self-supervised learning is a method of learning to find the answer by finding a rule on its own for data with no answer. The research team proposed a methodology for learning to generate ultrasonic hologram, a deep learning network optimized for ultrasonic hologram generation, and a new loss function, while proving the validity and excellence of each component through simulations and actual experiments.
DGIST Department of Electrical Engineering and Computer Science Professor Hwang Jae-yoon said, “We applied deep learning technology to ultrasound holograms proposed relatively recently. As a result, we developed a technology that can freely, quickly and accurately generate and change the form of ultrasound beams,” and added, “We hope that the results of this research are used in patient-specific precision brain stimulation technology and general ultrasound fields (ultrasound imaging, thermal therapy, etc.).”
Meanwhile, this research was carried out with the Ministry of Science and ICT’s Four Major Institutes of Science and Technology Support Program. Researcher Lee Moon-hwan of DGIST Information and Communication Engineering Research Center, Ph.D. students Ryu Ha-min and Yoon Sang-yeon of the Department of Electrical Engineering and Computer Science, and GIST Professor Kim Tae’s team. The research results were published as a cover paper in the December edition of IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, an international academic journal in the related field. More

Biofilms form when microorganisms such as certain types of bacteria adhere to the surface of objects in a moist environment and begin to reproduce resulting in the excretion of a slimy glue-like substance.
These biofilms aren’t just unpleasant and unappealing however, they can be seriously troublesome. For example, in the medical field, the formation of biofilm can reduce the effectiveness of antibiotic treatments. The key to understanding biomass formation lies in understanding how bacteria behave en masse.
A new paper in EPJE by Heinrich-Heine-Universität, Düsseldorf, Germany, researcher Davide Breoni and his co-authors presents a mathematical model for the motion of bacteria that includes cell division and death, the basic ingredients of the cell cycle.
The team developed a mathematical model of bacterial movement in process creating a link between statistical physics and biophysics.
“Our new model belongs to a class of models for ‘active matter’ that currently encounter a lot of interest in statistical physics,” Breoni says. “This field studies the collective properties of particle systems that have their own energy source — bacteria are an exemplary case.”
The model devised by the team delivered a surprise by suggesting that when it comes to movement bacteria can act as a unit.
“In the course of our investigation, we found out that the model predicts that the formation of bacterial colonies can occur through the build-up of travelling waves, concentrated ‘packages’ of bacteria,” Breoni adds. “We did not expect this to arise from such a simple model as ours.”
He believes that the results should be interesting to the general public who may be aware of bacterial colonies, but not know how they move in a collective way.
Breoni concludes by pointing out this is a very simple model suggesting how the research could proceed from here. “We could try to make the model more realistic and confront the results to experiment to test its predictions,” he says. “On the other hand, this research is very much curiosity-driven and results from intense discussions among the researchers — an approach we’d like to maintain so we can continue to surprise ourselves with our findings.”
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