New atomic sensors could lead to a new generation of smart materials

At left, natural diamonds glow under ultraviolet light owing to their various nitrogen-vacancy (NV) centers. At right, a schematic depicting the diamond anvils in action, with NV centers in the bottom anvil. The NV sensors glow a brilliant shade of red when excited with laser light. By probing the brightness of this fluorescence, the researchers were able to see how the sensors responded to small changes in their environment. (Credits: Norman Yao/Berkeley Lab; Ella Marushchenko)

Scientists at Berkeley Lab, UC Berkeley convert diamonds’ atomic flaws into atomic sensors with front-row seats to a quantum world of materials under extreme pressure

Since their invention more than 60 years ago, diamond anvil cells have made it possible for scientists to recreate extreme phenomena – such as the crushing pressures deep inside the Earth’s mantle – or to enable chemical reactions that can only be triggered by intense pressure, all within the confines of a laboratory apparatus that you can safely hold in the palm of your hand.

To develop new, high-performance materials, scientists need to understand how useful properties, such as magnetism and strength, change under such harsh conditions. But often, measuring these properties with enough sensitivity requires a sensor that can withstand the crushing forces inside a diamond anvil cell.

Since 2018, scientists at the Center for Novel Pathways to Quantum Coherence in Materials (NPQC), an Energy Frontier Research Center led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), have sought to understand how the properties of electronic and optical materials can be harnessed to develop ultrasensitive sensors capable of measuring electric and magnetic fields.

Now, a team of scientists led by Berkeley Lab and UC Berkeley, with support from the NPQC, have come up with a clever solution: By turning natural atomic flaws inside the diamond anvils into tiny quantum sensors, the scientists have developed a tool that opens the door to a wide range of experiments inaccessible to conventional sensors. Their findings, which were reported today in the journal Science, have implications for a new generation of smart, designer materials, as well as the synthesis of new chemical compounds, atomically fine-tuned by pressure.

Turning atomic flaws into sensors

At the atomic level, diamonds owe their sturdiness to carbon atoms bound together in a tetrahedral crystal structure. But when diamonds form, some carbon atoms can get bumped out of their “lattice site,” a space in the crystal structure that is like their assigned parking spot. When a nitrogen atom impurity trapped in the crystal sits adjacent to an empty site, a special atomic defect forms: a nitrogen-vacancy (NV) center.

Over the last decade, scientists have used NV centers as tiny sensors to measure the magnetism of a single protein, the electric field from a single electron, and the temperature inside a living cell, explained Norman Yao, faculty scientist in Berkeley Lab’s Materials Sciences Division and assistant professor of physics at UC Berkeley.

To take advantage of the NV centers’ intrinsic sensing properties, Yao and colleagues engineered a thin layer of them directly inside the diamond anvil in order to take a snapshot of the physics within the high-pressure chamber.

Imaging stress inside the diamond anvil cell

After generating a layer of NV center sensors a few hundred atoms in thickness inside one-tenth-carat diamonds, the researchers tested the NV sensors’ ability to measure the diamond anvil cell’s high-pressure chamber.

The sensors glow a brilliant shade of red when excited with laser light; by probing the brightness of this fluorescence, the researchers were able to see how the sensors responded to small changes in their environment.

What they found surprised them: The NV sensors suggested that the once-flat surface of the diamond anvil began to curve in the center under pressure.

Co-author Raymond Jeanloz, professor of earth and planetary science at UC Berkeley, and his team identified the phenomenon as “cupping” – a concentration of the pressure toward the center of the anvil tips.

“They had known about this effect for decades but were accustomed to seeing it at 20 times the pressure, where you can see the curvature by eye,” Yao said. “Remarkably, our diamond anvil sensor was able to detect this tiny curvature at even the lowest pressures.”

There were other surprises, too. When a methanol/ethanol mixture they squeezed underwent a glass transition from a liquid to a solid, the diamond surface turned from a smooth bowl to a jagged, textured surface. Mechanical simulations performed by co-author Valery Levitas of Iowa State University and Ames Laboratory confirmed the result.

“This is a fundamentally new way to measure phase transitions in materials at high pressure, and we hope this can complement conventional methods that utilize powerful X-ray radiation from a synchrotron source,” said lead author Satcher Hsieh, a doctoral researcher in Berkeley Lab’s Materials Sciences Division and in the Yao Group at UC Berkeley.

Co-lead authors with Hsieh are graduate student researcher Prabudhya Bhattacharyya and postdoctoral researcher Chong Zu of the Yao Group at UC Berkeley.

Magnetism under pressure

In another experiment, the researchers used their array of NV sensors to capture a magnetic “snapshot” of iron and gadolinium.

Iron and gadolinium are magnetic metals. Scientists have long known that compressing iron and gadolinium can alter them from a magnetic phase to a nonmagnetic phase, an outcome of what scientists call a “pressure-induced phase transition.” In the case of iron, the researchers directly imaged this transition by measuring the depletion of the magnetic field generated by a micron-size (or one millionth of a meter) bead of iron inside the high-pressure chamber.

In the case of gadolinium, the researchers took a different approach. In particular, the electrons inside gadolinium “happily whiz around in random directions,” and this chaotic “mosh pit” of electrons generates a fluctuating magnetic field that the NV sensor can measure, Hsieh said.

The researchers noted that the NV center sensors can flip into different magnetic quantum states in the presence of magnetic fluctuations, much like how a compass needle spins in different directions when you wave a bar magnet near it.

So they postulated that by timing how long it took for the NV centers to flip from one magnetic state to another, they could characterize the gadolinium’s magnetic phase by measuring the magnetic “noise” emanating from the gadolinium electrons’ motion.

They found that when gadolinium is in a non-magnetic phase, its electrons are subdued, and its magnetic field fluctuations hence are weak. Subsequently, the NV sensors stay in a single magnetic quantum state for a long while – nearly a hundred microseconds.

Conversely, when the gadolinium sample changed to a magnetic phase, the electrons moved around rapidly, causing the nearby NV sensor to swiftly flip to another magnetic quantum state.

This sudden change provided clear evidence that gadolinium had entered a different magnetic phase, Hsieh said, adding that their technique allowed them to pinpoint magnetic properties across the sample with submicron precision as opposed to averaging over the entire high-pressure chamber as in previous studies.

The researchers hope that this “noise spectroscopy” technique will provide scientists with a new tool for exploring phases of magnetic matter that can be used as the foundation for smaller, faster, and cheaper ways of storing and processing data through next-generation ultrafast spintronic devices.

Next steps

Now that they’ve demonstrated how to engineer NV centers into diamond anvil cells, the researchers plan to use their device to explore the magnetic behavior of superconducting hydrides – materials that conduct electricity without loss near room temperature at high pressure, which could revolutionize how energy is stored and transferred.

And they would also like to explore science outside of physics. “What’s most exciting to me is that this tool can help so many different scientific communities,” says Hsieh. “It’s sprung up collaborations with groups ranging from high-pressure chemists to Martian paleomagnetists to quantum materials scientists.”

Researchers from Berkeley Lab; UC Berkeley; Ludwig-Maximilian University of Munich, Germany; Iowa State University; Carnegie Institution of Washington, Washington, D.C.; and Ames Laboratory participated in the work.

Learn and see more: Tiny Quantum Sensors Watch Materials Transform Under Pressure



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New material could offer an efficient eco-friendly advance in cooling technology

via University of Maryland

An international research team led by the University of Maryland has developed a novel elastocaloric cooling material that is highly efficient, eco-friendly and easily scaled-up for commercial use.

The researchers new cooling material is a nickel-titanium alloy that was sculpted using additive technology (3-D printing). Their work is published in the November 29 issue of Science.

Cooling technology, used in refrigeration and HVAC systems around the globe, is a multi-billion dollar business. Vapor compression cooling, which has dominated the market for over 150 years, has plateaued in efficiency, and uses chemical refrigerants with high global-warming potential. Solid-state elastocaloric cooling, in which stress is applied to materials to release and absorb (latent) heat, has been under development for the last decade and is a front-runner for alternative cooling technologies. Shape-memory alloys are found to display a significant elastocaloric cooling effect; however,  hysteresis – work lost in each cycle, which causes fatigue and eventual failure of such materials – remains a challenge.

The international team of collaborators led by UMD Materials Science and Engineering (MSE) Professor, Ichiro Takeuchi, has developed an improved elastocaloric cooling material using a blend of nickel (Ni)-titanium (Ti) metals, forged using a 3D printer, that is not only potentially more efficient than current technology, but is completely ‘green.’ Moreover, it can be quickly scaled up for use in larger devices.

“In this field of alternative cooling technologies, it’s very important to work on both the materials end, as well as the systems end – we are fortunate to have a highly-qualified team of experts at the University of Maryland, College Park to work on both ends,” said Professor Takeuchi. “It’s only when these two efforts closely align that you make rapid progress, which our team was able to do.”

Comparatively speaking, there are three classes of caloric cooling technology – magnetocaloric, electrocaloric and elastocaloric – all of which are ‘green’ and vapor-less. Magnetocaloric, the oldest of the three, has been under development for 40 years and is just now on the verge of being commercialized.

“The need for additive technology, otherwise known as 3D printing, in this field is particularly acute because these materials also act as heat exchangers, delivering cooling to a medium such as water,” said Takeuchi.

Takeuchi has been developing this technology for almost a decade – he received the UMD Outstanding Invention of the Year for this research in 2010, and the DOE ranked elastocaloric cooling, also known as thermoelastic cooling, #1 as the ‘most promising’ of alternative cooling technology in 2014 – and it is one step closer to commercialization.

“The key to this innovation that is fundamental, but not often discussed, is that materials fatigue – they wear out,” said Takeuchi. “This is a problem when people expect their refrigerators to last for a decade, or longer. So, we addressed the problem in our study.”

The team tested their creation heavily over a four-month period and still maintained its integrity. “Some known elastocaloric materials start showing degradation in cooling behavior after just hundreds of cycles. To our surprise, the new material we synthesized showed no change after one million cycles,” said, UMD’s Huilong Hou, who is the first author of the work and a post-doctoral researcher  in the Department of Materials Science and Engineering.

The metal additive manufacturing uses a laser to melt, and then mix, metals in powder form. By controlling the powder feed, the team was able to produce nanocomposites which gave rise to the robust mechanical integrity in the material.

The research team also included scientists at the U.S. Department of Energy Ames Laboratory in Ames, Iowa, where the 3D printing was carried out, and researchers from the Colorado School of Mines in Golden, Colorado, who helped investigate the internal structure of the printed materials.

Learn more: UMD-Led Team Creates Novel Material that Potentially Offers an Efficient, Eco-Friendly Advance in Cooling Technology


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Upcycling single-use plastic into high-quality liquid products

via Northwestern University

Catalytic method upcycles single-use plastic into high-quality liquid products

Researchers have developed a new method for upcycling abundant, seemingly low-value plastics into high-quality liquid products, such as motor oils, lubricants, detergents and even cosmetics. The discovery also improves on current recycling methods that result in cheap, low-quality plastic products.

The catalytic method serves a one-two punch by removing plastic pollution from the environment and contributing to a circular economy.

Northwestern University, Argonne National Laboratory and Ames Laboratory led the multi-institutional team.

“Our team is delighted to have discovered this new technology that will help us get ahead of the mounting issue of plastic waste accumulation,” said Northwestern’s Kenneth R. Poeppelmeier, who contributed to the research. “Our findings have broad implications for developing a future in which we can continue to benefit from plastic materials, but do so in a way that is sustainable and less harmful to the environment and potentially human health.”

Poeppelmeier is the Charles E. and Emma H. Morrison Professor of Chemistry at Northwestern’s Weinberg College of Arts and Sciences, director of Northwestern’s Center for Catalysis and Surface Science and member of Northwestern’s Program on Plastics, Ecosystems and Public Health.

Poeppelmeier co-led the work with Aaron D. Sadow, a scientist in the Division of Chemical and Biological Sciences at Ames Laboratory, and Massimiliano Delferro, group leader of Argonne National Laboratory’s catalysis program.

The study was published today (Oct. 23) in the journal ACS Central Science.

The plastic problem

Each year, 380 million tons of plastic are created worldwide. And as the plastics market continues to increase, many analysts predict production could quadruple by 2050. More than 75% of these plastic materials are discarded after one use. Many of them end up in our oceans and waterways, harming wildlife and spreading toxins.

“There are certainly things we can do as a society to reduce consumption of plastics in some cases,” Sadow said. “But there will always be instances where plastics are difficult to replace, so we really want to see what we can do to find value in the waste.”

Our findings have broad implications for developing a future in which we can continue to benefit from plastic materials, but do so in a way that is sustainable and less harmful to the environment and potentially human health.”
Kenneth Poeppelmeier

While plastics can be melted and reprocessed, this type of recycling yields lower-value materials that are not as structurally strong as the original material. Examples include down-cycling plastic bottles into a molded park bench.

When left in the wild or in landfills, plastics do not degrade because they have very strong carbon-carbon bonds. Instead, they break up into smaller plastics, known as microplastics. Whereas some people see these strong bonds as a problem, the Northwestern, Argonne National Laboratory and Ames Laboratory team saw this as an opportunity.

“We sought to recoup the high energy that holds those bonds together by catalytically converting the polyethylene molecules into value-added commercial products,” Delferro said.

A catalytic solution

The catalyst consists of platinum nanoparticles — just two nanometers in size — deposited onto a perovskite nanocubes, which are about 50-60 nanometers in size. The team chose perovskite because it is stable under the high temperatures and pressures and an exceptionally good material for energy conversion.

To deposit nanoparticles onto the nanocubes, the team used atomic layer deposition, a technique developed at Argonne that allows precise control of nanoparticles.

Under moderate pressure and temperature, the catalyst cleaved plastic’s carbon-carbon bond to produce high-quality liquid hydrocarbons. These liquids could be used in motor oil, lubricants or waxes or further processed to make ingredients for detergents and cosmetics. This contrasts commercially available catalysts, which generated lower quality products with many short hydrocarbons, limiting the products’ usefulness.

Even better: The catalytic method produced far less waste in the process. Recycling methods that melt plastic or uses conventional catalysts generate greenhouse gases and toxic byproducts.

Learn more: Turning plastic trash into treasure


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Promising new class of super-strong and conducting materials e.g. the world’s strongest silver

Inside a grain of silver, copper atom impurities (in green) have been segregated to a grain boundary (on the left) and into internal defects (long strings, streaming downward.)

Team creates metal that breaks decades-old theoretical limit, promising new class of super-strong and conducting materials.

A team of scientists has made the strongest silver ever—42 percent stronger than the previous world record. But that’s not the important point.

“We’ve discovered a new mechanism at work at the nanoscale that allows us to make metals that are much stronger than anything ever made before—while not losing any electrical conductivity,” says Frederic Sansoz, a materials scientist and mechanical engineering professor at the University of Vermont who co-led the new discovery.

This fundamental breakthrough promises a new category of materials that can overcome a traditional trade-off in industrial and commercial materials between strength and ability to carry electrical current.

The team’s results were published on September 23 in the journal Nature Materials.

Rethinking the defect

All metals have defects. Often these defects lead to undesirable qualities, like brittleness or softening. This has led scientists to create various alloys or heavy mixtures of material to make them stronger. But as they get stronger, they lose electrical conductivity.

“We asked ourselves, how can we make a material with defects but overcome the softening while retaining the electroconductivity,” said Morris Wang, a lead scientist at Lawrence Livermore National Laboratory and co-author of the new study.

By mixing a trace amount of copper into the silver, the team showed it can transform two types of inherent nanoscale defects into a powerful internal structure. “That’s because impurities are directly attracted to these defects,” explains Sansoz. In other words, the team used a copper impurity—a form of doping or “microalloy” as the scientists style it—to control the behavior of defects in silver. Like a kind of atomic-scale jiu-jitsu, the scientists flipped the defects to their advantage, using them to both strengthen the metal and maintain its electrical conductivity.

To make their discovery, the team—including experts from UVM, Lawrence Livermore National Lab, the Ames Laboratory, Los Alamos National Laboratory and UCLA—started with a foundational idea of materials engineering: as the size of a crystal—or grain—of material gets smaller, it gets stronger. Scientists call this the Hall-Petch relation. This general design principle has allowed scientists and engineers to build stronger alloys and advanced ceramics for over 70 years. It works very well.

Until it doesn’t. Eventually, when grains of metal reach an infinitesimally tiny size—under tens of nanometers wide—the boundaries between the grains become unstable and begin to move. Therefore, another known approach to strengthening metals like silver uses nanoscale “coherent twin boundaries,” which are a special type of grain boundary. These structures of paired atoms—forming a symmetrical mirror-like crystalline interface—are exceedingly strong to deformation. Except that these twin boundaries, too, become soft when their interspacing falls under a critical size of a few nanometers, due to imperfections.

Unprecedented properties

Very roughly speaking, nanocrystals are like patches of cloth and nanotwins are like strong but tiny threads in the cloth. Except they’re at the atomic scale. The new research combines both approaches to make what the scientists call a “nanocrystalline-nanotwinned metal,” that has “unprecedented mechanical and physical properties,” the team writes.

That’s because the copper atoms, slightly smaller than the atoms of silver, move into defects in both the grain boundaries and the twin boundaries. This allowed the team—using computer simulations of atoms as a starting point and then moving into real metals with advanced instruments at the National Laboratories—to create the new super-strong form of silver. The tiny copper impurities within the silver inhibit the defects from moving, but are such a small amount of metal—less than one percent of the total—that the rich electrical conductivity of silver is retained. “The copper atom impurities go along each interface and not in between,” Sansoz explains. “So they don’t disrupt the electrons that are propagating through.”

Not only does this metal overcome the softening previously observed as grains and twin boundaries get too small—the so-called “Hall-Petch breakdown”—it even exceeds the long-standing theoretical Hall-Petch limit. The team reports an “ideal maximum strength” can be found in metals with twin boundaries that are under seven nanometers apart, just a few atoms. And a heat-treated version of the team’s copper-laced silver has a hardness measure above what had been thought to be the theoretical maximum.

“We’ve broken the world record, and the Hall-Petch limit too, not just once but several times in the course of this study, with very controlled experiments,” says Sansoz.

Sansoz is confident that the team’s approach to making super-strong and still-conductive silver can be applied to many other metals. “This is a new class of materials and we’re just beginning to understand how they work,” he says. And he anticipates that the basic science revealed in the new study can lead to advances in technologies—from more efficient solar cells to lighter airplanes to safer nuclear power plants. “When you can make material stronger, you can use less of it, and it lasts longer,” he says, “and being electrically conductive is crucial to many applications.”

Learn more: Inventing the World’s Strongest Silver


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    on October 6, 2019 at 11:20 am

    Their work, thus, focused on combining both approaches to make a “nanocrystalline-nanotwinned metal” that has “unprecedented mechanical and physical properties.” What happens is that the copper atoms, ...

  • Inventing the World's Strongest Silver
    on October 3, 2019 at 6:06 am

    Except they're at the atomic scale. The new research combines both approaches to make what the scientists call a "nanocrystalline-nanotwinned metal," that has "unprecedented mechanical and physical ...

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    on October 3, 2019 at 4:53 am

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  • Inventing The World’s Strongest Silver
    on October 2, 2019 at 8:57 pm

    Except they’re at the atomic scale. The new research combines both approaches to make what the scientists call a “nanocrystalline-nanotwinned metal,” that has “unprecedented mechanical and physical ...

  • Inventing the world's strongest silver
    on October 2, 2019 at 3:52 pm

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    on October 2, 2019 at 1:37 pm

    Except they're at the atomic scale. The new research combines both approaches to make what the scientists call a "nanocrystalline-nanotwinned metal," that has "unprecedented mechanical and physical ...

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    on October 2, 2019 at 1:05 pm

    Except they're at the atomic scale. The new research combines both approaches to make what the scientists call a "nanocrystalline-nanotwinned metal," that has "unprecedented mechanical and physical ...

  • Inventing the world's strongest silver
    on October 2, 2019 at 1:05 pm

    Except they’re at the atomic scale. The new research combines both approaches to make what the scientists call a “nanocrystalline-nanotwinned metal,” that has “unprecedented mechanical and physical ...

  • Ideal maximum strengths and defect-induced softening in nanocrystalline-nanotwinned metals
    on September 22, 2019 at 5:00 pm

    Different softening mechanisms are considered to occur for nanocrystalline and nanotwinned materials. Here, we report nanocrystalline-nanotwinned Ag materials that exhibit two strength transitions ...

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Printing flexible electronics on almost anything using a new heat-free technique

Martin Thuo and his research group have developed heat-free technology that can print conductive, metallic lines and traces on just about anything, including a rose petal. Photo courtesy of Martin Thuo.

Martin Thuo of Iowa State University and the Ames Laboratory clicked through the photo gallery for one of his research projects.

How about this one? There was a rose with metal traces printed on a delicate petal.

Or this? A curled sheet of paper with a flexible, programmable LED display.

Maybe this? A gelatin cylinder with metal traces printed across the top.

All those photos showed the latest application of undercooled metal technology developed by Thuo and his research group. The technology features liquid metal (in this case Field’s metal, an alloy of bismuth, indium and tin) trapped below its melting point in polished, oxide shells, creating particles about 10 millionths of a meter across.

When the shells are broken – with mechanical pressure or chemical dissolving – the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials, everything from a concrete wall to a leaf.

That could have all kinds of applications, including sensors to measure the structural integrity of a building or the growth of crops. The technology was also tested in paper-based remote controls that read changes in electrical currents when the paper is curved. Engineers also tested the technology by making electrical contacts for solar cells and by screen printing conductive lines on gelatin, a model for soft biological tissues, including the brain.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” Thuo and a team of researchers wrote in a paper describing the technology recently published online by the journal Advanced Functional Materials.

Thuo – an assistant professor of materials science and engineering at Iowa State, an associate of the U.S. Department of Energy’s Ames Laboratory and a co-founder of the Ames startup SAFI-Tech Inc. that’s commercializing the liquid-metal particles – is the lead author. Co-authors are Andrew Martin, a former undergraduate in Thuo’s lab and now an Iowa State doctoral student in materials science and engineering; Boyce Chang, a postdoctoral fellow at the University of California, Berkeley, who earned his doctoral degree at Iowa State; Zachariah Martin, Dipak Paramanik and Ian Tevis, of SAFI-Tech; Christophe Frankiewicz, a co-founder of Sep-All in Ames and a former Iowa State postdoctoral research associate; and Souvik Kundu, an Iowa State graduate student in electrical and computer engineering.

The project was supported by university startup funds to establish Thuo’s research lab at Iowa State, Thuo’s Black & Veatch faculty fellowship and a National Science Foundation Small Business Innovation Research grant.

Thuo said he launched the project three years ago as a teaching exercise.

“I started this with undergraduate students,” he said. “I thought it would be fun to get students to make something like this. It’s a really beneficial teaching tool because you don’t need to solve 2 million equations to do sophisticated science.”

And once students learned to use a few metal-processing tools, they started solving some of the technical challenges of flexible, metal electronics.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

And so the researchers have learned how to effectively bond metal traces to everything from water-repelling rose petals to watery gelatin. Based on what they now know, Thuo said it would be easy for them to print metallic traces on ice cubes or biological tissue.

All the experiments “highlight the versatility of this approach,” the researchers wrote in their paper, “allowing a multitude of conductive products to be fabricated without damaging the base material.”

Learn more: Self-sterilizing polymer proves effective against drug-resistant pathogens


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