Columbia physicists see light waves moving through a metal

When we encounter metals in our day-to-day lives, we perceive them as shiny. That’s because common metallic materials are reflective at visible light wavelengths and will bounce back any light that strikes them. While metals are well suited to conducting electricity and heat, they aren’t typically thought of as a means to conduct light.

But in the burgeoning field of quantum materials, researchers are increasingly finding examples that challenge expectations about how things should behave. In new research, Dmitri Basov, Higgins Professor of Physics at Columbia University, describes a metal capable of conducting light through it.

“These results defy our daily experiences and common conceptions,” said Basov.

Whereas graphene is a single, atom-thin layer of carbon, ZrSiSe is a three-dimensional metallic crystal made up of layers that behave differently in the in-plane and out-of-plane directions, a property known as anisotropy.

“It’s sort of like a sandwich: one layer acts like a metal while the next layer acts like an insulator,” explained Yinming Shao, a postdoc at Columbia. “When that happens, light starts to interact unusually with the metal at certain frequencies. Instead of just bouncing off, it can travel inside the material in a zig-zag pattern, which we call hyperbolic propagation.”

In their current work, Shao and his collaborators at Columbia and The University of California, San Diego observed such zig-zag movement of light, so-called hyperbolic waveguide modes, through ZrSiSe samples of varying thicknesses. Such waveguides can guide light through a material and here, result from photons of light mixing with electron oscillations to create hybrid quasiparticles called plasmons.

Although the conditions to generate plasmons that can propagate hyperbolically are met in many layered metals, it is the unique range of electron energy levels, called electronic band structure, of ZrSiSe that allowed the team to observe them in this material.

Plasmons can “magnify” features in a sample, allowing researchers to see beyond the diffraction limit of optical microscopes, which cannot otherwise resolve details smaller than the wavelength of light they use.

“Using hyperbolic plasmons, we could resolve features less than 100 nanometers using infrared light that’s hundreds of times longer,” said Shao.

ZrSiSe can be peeled to different thicknesses, making it an interesting option for nano-optics research that favors ultra-thin materials, said Shao. But, it’s likely not the only material to be valuable—from here, the group wants to explore others that share similarities with ZrSiSe but might have even more favorable waveguiding properties. That could help researchers develop more efficient optical chips, and better nano-optics approaches to explore fundamental questions about quantum materials.

For more information: ScienceAdvances

SkyWater and Lumotive announce qualification and production start for world’s first commercially available optical beamforming chip

SkyWater Technology, Bloomington, Minn., the trusted technology realization partner, and Lumotive, Redmond, Wash., a pioneer in optical semiconductor technology for 3D sensing, announced a collaboration on the production implementation of Lumotive’s groundbreaking solid-state optical beamforming technology in SkyWater’s manufacturing environment.

Continue reading

Penn State, Morgan Advanced Materials partner to improve semiconductor materials

Penn State and Morgan Advanced Materials have signed an MOU to accelerate research and development of silicon carbide (SiC), a semiconductor material that excels at high voltages. This collaborative agreement spans a new five-year, multimillion-dollar initiative. The initiative brings together industry leaders, academic institutions, and government support, aiming to advance SiC crystal research and workforce development.

The agreement also includes a commitment by Morgan to become a founding member of the recently launched Penn State Silicon Carbide Innovation Alliance, as well as to supply the graphite materials and solutions needed for SiC development to Penn State for use by internal and external partners.

The initiative is a coalition of industry leaders, academic institutions and government support led by Joshua Robinson, professor of materials science and engineering and acting associate dean for research in Penn State’s College of Earth and Minerals Sciences.

The MOU outlines how the partners aim to advance carbon research and evaluate how Morgan’s carbon material product impacts SiC wafer fabrication. SiC wafers are a semiconductor material that is increasingly important in the global transition to a greener energy infrastructure and surging demand for semiconductors, as demonstrated by the bipartisan support for the CHIPS for America Act. Traditionally, semiconductor devices have been manufactured from silicon. Silicon carbide is made from tightly arranged silicon and carbon atoms that enable superior performance in a wide range of high-voltage applications, such as high-speed charging stations and power converters in electric vehicles.

Silicon carbide crystals are grown at extreme temperatures — greater than 3,600 degrees Fahrenheit — in a physical vapor transport (PVT) furnace that utilizes a significant amount of carbon to maintain the temperature during the growth process. Similar to insulation in a home, carbon materials made by Morgan act as insulating layers that reduce heat loss and the amount of electricity needed to keep the furnaces running in this weekslong process.

Morgan Advanced Materials is a global company that has been innovating and manufacturing carbon and graphite-based materials essential for growing silicon carbide crystals since the 1990s.

“The new agreement with Penn State seamlessly aligns our goal of establishing Morgan as a key player in the silicon carbide market — we are not only advancing our own graphite competencies but also contributing to the development of high-value products in the market,” said Thomas Connolly, chief technology officer at Morgan Advanced Materials.

A new SiC growth facility in Penn State’s Academic Activities Building at University Park, funded via support from Penn State’s Office for the Senior Vice President for Research and the U.S. Air Force Office of Scientific Research, is expected to be fully operational by the beginning of 2025. This will house a pilot-scale facility that will emulate the entire SiC bulk crystal growth supply chain.

“To have the opportunity to continue our partnership with Morgan Advanced Materials will further solidify the University’s reputation as a leader in silicon carbide research and position us to create bigger and more impactful innovations in the future,” said Clive Randall, director of Penn State’s Material Research Institute.

The Corporate Engagement Center played a key role in expanding Morgan’s commitment to Penn State. The center’s leadership has noted that they anticipate that the alliance will attract additional industry partners.

“Partnerships with public and private entities have allowed Penn State to be the first university in decades to house SiC equipment from boule to wafer processing,” said Andrew Read, senior vice president for research at Penn State. We greatly appreciate Morgan’s continued commitment to Penn State and are looking forward to the discoveries we will make together.”

For more information:

Image: Morgan Advanced Materials visited Penn State recently to sign a memorandum of understanding. From left are: Fernando “Nando” Vallejos-Burgos, Global Testing Labs manager at Morgan Advanced Materials; Michael Wade Smith, senior vice president and chief of staff at Penn State; Joe Abrahamson, lead at Morgan Advanced Materials’ Carbon Center of Excellence; Andy Goshe, director of strategy for Morgan Advanced Materials’ Performance Carbon Division; David Fecko, director of industry collaborations in the Materials Research Institute at Penn State; Thomas Connolly, global technology director and chief technology officer for Morgan Advanced Materials’ Performance Carbon Division; Wendy Pryce Lewis, president of Morgan Advanced Materials’ Performance Carbon Division; Neeli Bendapudi, president of Penn State; Andrew Read, senior vice president for research at Penn State; Ashley Chan, director of corporate engagement at Penn State; Josh Robinson, acting associate dean for research in earth and minerals sciences and director of the Silicon Carbide Crystal Center; Aleksandra Slavkovic, associate dean for research and innovation, Eberly College of Science at Penn State; Tonya Peeples, Harold and Inge Marcus Dean of Engineering and professor of chemical engineering at Penn State; Lee Kump, John Leone Dean of College of Earth and Minerals Science and professor of geosciences at Penn State; and David Lieb, interim vice president development and alumni relations at Penn State

New quantum material promises over 190% quantum efficiency in solar cells

The need for sustainable and clean energy sources has never been greater, and solar energy has emerged as a promising solution. To meet the growing demand for efficient and cost-effective solar cells, researchers are constantly exploring emerging and innovative approaches to enhance the performance of solar cells. One exciting development in this field is an emerging material from Lehigh University researchers that has the potential to revolutionize clean energy generation by enabling the efficient conversion of sunlight into electrical energy.

A prototype using the material as the active layer in a solar cell exhibits an average photovoltaic absorption of 80%, a high generation rate of photoexcited carriers, and an external quantum efficiency (EQE) up to an unprecedented 190%—a measure that far exceeds the theoretical Shockley-Queisser efficiency limit for silicon-based materials and pushes the field of quantum materials for photovoltaics to new heights.

“This work represents a significant leap forward in our understanding and development of sustainable energy solutions, highlighting innovative approaches that could redefine solar energy efficiency and accessibility in the near future,” said Chinedu Ekuma, professor of physics.

The material’s efficiency leap is attributable largely to its distinctive “intermediate band states,” specific energy levels that are positioned within the material’s electronic structure in a way that makes them ideal for solar energy conversion.

These states have energy levels within the optimal subband gaps—energy ranges where the material can efficiently absorb sunlight and produce charge carriers—of around 0.78 and 1.26 electron volts.

In addition, the material performs especially well with high levels of absorption in the infrared and visible regions of the electromagnetic spectrum.

In traditional solar cells, the maximum EQE is 100%, representing the generation and collection of one electron for each photon absorbed from sunlight. However, some advanced materials and configurations developed over the past several years have demonstrated the capability of generating and collecting more than one electron from high-energy photons, representing an EQE of over 100%.

While such Multiple Exciton Generation (MEG) materials are yet to be broadly commercialized, they hold the potential to greatly increase the efficiency of solar power systems. In the Lehigh-developed material, the intermediate band states enable the capture of photon energy that is lost by traditional solar cells, including through reflection and the production of heat.

The researchers developed the novel material by taking advantage of “van der Waals gaps,” atomically small gaps between layered two-dimensional materials. These gaps can confine molecules or ions, and materials scientists commonly use them to insert, or “intercalate,” other elements to tune material properties.

To develop their novel material, the Lehigh researchers inserted atoms of zerovalent copper between layers of a two-dimensional material made of germanium selenide (GeSe) and tin sulfide (SnS).

Ekuma, an expert in computational condensed matter physics, developed the prototype as a proof of concept after extensive computer modeling of the system demonstrated theoretical promise.

“Its rapid response and enhanced efficiency strongly indicate the potential of Cu-intercalated GeSe/SnS as a quantum material for use in advanced photovoltaic applications, offering an avenue for efficiency improvements in solar energy conversion,” he said. “It’s a promising candidate for the development of next-generation, high-efficient solar cells, which will play a crucial role in addressing global energy needs.”

Although integrating the newly designed quantum material into current solar energy systems will need further research and development, Ekuma points out that the experimental technique used to create these materials is already highly advanced. Scientists have, over time, mastered a method that precisely inserts atoms, ions, and molecules into materials.

For more information: ScienceAdvances

Image: Schematic of the thin-film solar cell with CuxGeSe/SnS as the active layer.

Inspecting, testing, and measuring SiC

Achieving the auto industry’s stringent zero-defect goals is becoming a big challenge for makers of silicon carbide substrates, which are struggling to achieve sufficient yields and reliability as they migrate from 150 to 200 mm wafers and shift their focus away from pure silicon.

Continue reading

Predictive tool could speed up battery and superconductor research

From lithium-ion batteries to next-generation superconductors, the functionality of many modern, advanced technologies depends on the physical property known as intercalation. Unfortunately, it’s difficult to identify in advance which of the many possible intercalated materials are stable, which necessitates a lot of trial-and-error lab work in product development.

Now, in a new study, researchers from the Institute of Industrial Science, The University of Tokyo, and collaborating partners have devised a straightforward equation that correctly predicts the stability of intercalated materials. The systematic design guidelines enabled by this work will speed up the development of upcoming high-performance electronics and energy-storage devices.

To appreciate the research team’s achievement, we need to understand the context of this research. Intercalation is the reversible insertion of guests (atoms or molecules) into hosts (for example, 2D-layered materials). The purpose of intercalation is commonly to modify the host’s properties or structure for improved device performance, as seen in, for example, commercial lithium-ion batteries. Although many synthetic methods are available for preparing intercalated materials, researchers have had no reliable means of predicting which host-guest combinations are stable. Therefore, much lab work has been needed to devise new intercalated materials for imparting next-generation device functionalities. Minimizing this lab work by proposing a straightforward predictive tool for host-guest stability was the goal of the research team’s study.

“We are the first to develop accurate predictive tools for host-guest intercalation energies, and the stability of intercalated compounds,” explains Naoto Kawaguchi, lead author of the study. “Our analysis, based on a database of 9,000 compounds, uses straightforward principles from undergraduate first-year chemistry.”

A particular highlight of the work is that only two guest properties and eight host-derived descriptors were necessary for the researchers’ energy and stability calculations. In other words, initial “best guesses” weren’t necessary; only the underlying physics of the host-guest systems. Furthermore, the researchers validated their model against nearly 200 sets of regression coefficients.

“We’re excited because our regression model formulation is straightforward and physically reasonable,” says Teruyasu Mizoguchi, PhD, senior author. “Other computational models in the literature lack a physical basis or validation against unknown intercalated compounds.”

NCMS launches nanomanufacturing survey

The National Center for Manufacturing Sciences (NCMS) has partnered with the National Science Foundation under the National Nanotechnology Initiative (NNI) to launch its latest study of commercialization trends in nanotechnology and nanofabrication.

Continue reading

Scientists shine new light on the future of nanoelectronic devices

Artificial intelligence (AI) has the potential to transform technologies as diverse as solar panels, in-body medical sensors and self-driving vehicles. But these applications are already pushing today’s computers to their limits when it comes to speed, memory size and energy use.

Fortunately, scientists in the fields of AI, computing and nanoscience are working to overcome these challenges. And they are using their brains as their models.

That is because the circuits, or neurons, in the human brain have a key advantage over today’s computer circuits: they can store information and process it in the same place. This makes them exceptionally fast and energy efficient. That is why scientists are now exploring how to use materials measured in billionths of a meter — ​“nanomaterials” — to construct circuits that work like our neurons. To do so successfully, however, scientists must understand precisely what is happening within these nanomaterial circuits at the atomic level.

Recently, a team of researchers including scientists from the U.S. Department of Energy’s (DOE) Argonne National Laboratory pioneered a novel way of evaluating exactly that. Specifically, they used the Advanced Photon Source (APS), a DOE Office of Science user facility, to examine the changes that occur in the structure of a specific nanomaterial as it changes from conducting an electrical current to not. This mimics the switching between ​“on” and ​“off” states in a neural circuit.

In these materials, the conducting state, or phase, is controlled by imperfections in the material (or ​“point defects”) at the atomic level. By putting a strain on the nanomaterial, researchers can alter the concentration and change the position of these defects. This changes the pathway of electron flow. However, these defects are constantly moving, which changes the material’s conducting and non-conducting regions. Until now, this motion has been extremely difficult to study.

“There has been a lot of research about the occurrence and nature of defects in nanomaterials,” explained Dillon Fong, a materials scientist at Argonne. ​“But we knew very little about the dynamics of these defects when a material changes phase. We wanted to show that you can use X-rays to examine transitions between conducting and non-conducting phases in nanomaterials under conditions similar to those under which these materials will be used.” The team demonstrated how the APS can help make this possible.

For the experiment, the researchers chose a material, SrCoOx, that easily switches between the conducting and non-conducting, insulating, phases. To see the fluctuation between the conducting phase and the insulating phase at the nanoscale, they used a technique called X-ray photon correlation spectroscopy (XPCS). This is enabled by the highly coherent X-ray beams from the APS. XPCS can directly measure how fast the material fluctuates between different phases at the atomic scale, even when these fluctuations are barely detectable.

“The XPCS measurement would not be possible without the coherent X-ray beam from the APS,” said Qingteng Zhang, an assistant physicist at the APS who led the X-ray measurements. ​“In addition, it is important that we take the measurement under the same conditions that the material will operate under. This allows us to learn how the material will behave while performing its intended function. However, such environmental control usually requires sealing the sample in a chamber or a dome. This is where the highly penetrating X-ray beam from the APS is extremely helpful. Because while the chamber window or the dome shell is opaque to visible light, we can make either one completely transparent to the X-rays.”

The APS upgrade — now underway — will increase the brightness of the APS X-rays by up to 500 times upon its completion in 2024. This will significantly increase the speed of measurement as well as the quality of coherent X-ray techniques, including XPCS. This could create unprecedented scientific opportunities for researchers around the world.

That is an exciting prospect for Panchapakesan Ganesh, a researcher at DOE’s Oak Ridge National Laboratory (ORNL). He led the theoretical work in the study along with his team members Vitalii Starchenko, ORNL, and Guoxiang Hu, now an assistant professor at Georgia Tech.

“High-quality data from experiments like these are critical to our ability to develop theories and build models that can capture what happens in nanoelectronic materials when they go from conducting to non-conducting phases,” Ganesh said. ​“For example, we need to learn how energy dissipates in these systems if we are going to develop nanodevices that approach the energy efficiency of our brains. No single computational approach can solve this type of problem on its own. We need the best inputs from both the experimental and computational science sides to advance this nanoscale understanding. Our integrated approach is a perfect example of that, and we think it will spur more research in this exciting new field.”

For more information: Argonne National Laboratory

Image: This diagram illustrates how the researchers arrayed the APS to examine how the structure of a specific material, SrCoOx, changes when it is conducting an electrical current versus when it is not.

Redefining material science: Scientists have induced polarity in metals

In the field of materials science, the concepts of polarization and polarity are typically linked to insulators. Imagine, though, if we could introduce these properties into metals. This could reduce the power losses associated with semiconductors and enhance the longevity of batteries used in electronic devices. Up to now, despite intensive academic research aimed at inducing polarization and polarity in metals, current technologies have faced significant challenges.

Recent breakthrough by the collaborative efforts of Professor Daesu Lee from the Department of Physics at Pohang University of Science and Technology (POSTECH), Professor Tae Won Noh and Dr. Wei Peng from the Department of Physics and Astronomy at Seoul National University (SNU), and Professor Se Young Park from the Department of Physics at Soongsil University (SSU), have led to the discovery of a method to induce and control polarization and polarity states within metals.

Free electrons within metals, given their name, exhibit unrestricted movement, making it difficult to align them in specific directions to induce polarization or polarity states. Additionally, the symmetric structure of metal crystals at both ends has historically posed challenges in inducing these electrical effects.

However, the research team employed flexoelectric fields to implement polarization and polarity states within metals. This type of field arises when the surface of an object undergoes non-uniform deformation, allowing for the manipulation of charge movement and electrical characteristics by subtly altering the lattice structure of metals.

The team applied external pressure to the widely used strontium ruthenate (SrRuO3) in the field of electronic components and semiconductors, generating a flexoelectric field. This metal oxide, characterized by heteroepitaxy, where crystals of strontium and ruthenium oxide with different shapes grow in the same direction, possesses a centrosymmetric structure.

The flexoelectric field altered the electronic interactions and lattice structure within strontium ruthenate, leading to a successful induction of polarization within the metal, causing a transformation in its electrical and mechanical properties and breaking the previously central symmetric structure. By employing flexoelectric polarizing and control of a ferromagnetic metal, the research team has successfully unraveled the mystery surrounding the implementation of polarization and polarity within metallic substances.

The study’s lead researcher, Professor Daesu Lee from POSTECH, stressed, “We are the first researchers to verify the universal implementation of polarity states within metallic substances. I am hopeful that the findings from this study will prove beneficial in crafting highly efficient devices within the semiconductor and electrical fields.”

For more information: Nature Physics

Bio-inspired materials showcase potential for protective equipment and textiles

Bio-inspired materials (BIM) are synthetic materials whose structure and properties are similar to natural materials or living matter. These materials have the potential to advance structural materials, textiles and protective equipment due to their durability and self-healing properties.

Dr. Vanessa Restrepo, assistant professor in the J. Mike Walker ’66 Department of Mechanical Engineering, and her team at the Bio-Inspired Materials (BIM) Lab aim to create bio-inspired materials with enhanced behaviors by focusing on the nature of proteins to develop the sacrificial bond composites (bonds that break before the main structural link is broken) utilizing non-linear adhesive materials.

This research could significantly impact electrical wired infrastructure in adverse weather conditions. Using these materials, the cables could stretch and extend to bear the additional weight of ice accumulation or sudden tree falls caused by strong winds. This flexibility could prevent cable breakage, meaning less interruptions in electrical service.

“Our commitment remains dedicated to advancing bioinspired materials and their applications in various industries,” said Restrepo. “We’re enthusiastic about these materials’ potential impact and contribution to more resilient and sustainable product development.”

According to Restrepo, non-linear adhesives refer to a force-displacement behavior that deviates from a bilinear path, in contrast to conventional adhesives. Unlike traditional adhesives, the force-displacement relationship of non-linear adhesives does not follow a straightforward, two-stage pattern. Instead, it exhibits a more complex and variable behavior as external forces are applied.

To approach this research, Restrepo is using a cross-scale strategy, integrating non-linear adhesive materials and opposite-facing magnets to form sacrificial bond composites similar to those found in proteins such as the nacre’s interface, which is a multilayered brick-and-mortar natural material 3000 times more resistant to fracture than its constituents.

Their approach involves utilizing sacrificial bond composites that mimic natural biological mechanisms, allowing for energy dissipation and self-healing upon mechanical failure. The external load breaks the sacrificial bonds of sacrificial bond composites, and the opposite-facing magnets bring together the separated interface, allowing the reforming of its sacrificial bonds and the self-repairing of the composite after sustaining large strains.

“This differs significantly from current materials that lack these intrinsic self-repairing abilities, resulting in single-use and disposable products,” she said. “Our proposed research looks at the possibility of creating multiuse self-repairing energy dissipation mechanisms, such as Fall Arresters.”

Incorporating these innovative materials could result in longer-lasting, more cost-effective, and more sustainable products that require less frequent replacement, eventually resulting in the development of self-repairing materials used in various everyday items, such as protective equipment and textiles.

The BIM lab partnered with Dr. Ramses Martinez, associate professor at Purdue University, to conduct this research. This method was recently patented by Restrepo and team.

For more information: Materials & Design

Image: Dr. Vanessa Restrepo showcases prototype of bio-inspired materials. Credit: Texas A&M Engineering

Molecular tape promises seamless transfer and scale up of 2D materials

Materials so thin they are considered two-dimensional are only a couple atoms thick and, at this scale, they behave in surprising ways. Graphene, for example, is ultrathin graphite, the same material used in pencils. But once sliced to a nanosized thickness, it becomes stronger than steel by weight and is among the best materials for conducting electricity.

As with graphene and many other 2D materials, the same attribute that makes them so attractive — their thickness — is also holding back large-scale production. That’s because 2D materials are fragile and prone to damage when researchers attempt to move them or use them in a device.

To overcome this and unlock 2D materials’ potential for commercial production, researchers have recently developed a “molecular tape” that gently adheres to ultrathin materials and selectively releases them exactly where needed using only UV light.

“The variety of 2D materials has vastly increased since the isolation of graphene in 2004, with materials covering the whole range of electronic and magnetic properties,” explained Hiroki Ago, professor at Kyushu University and lead author of the study.

Ago’s lab has spent 10 years developing synthesis techniques for a variety of 2D materials, like high-quality graphene and metal 2D semiconductors. “Many researchers requested our samples, but most of them had problems transferring these 2D materials to their substrates,” he explained. “Due to the thin and delicate nature of 2D materials it is very difficult to transfer them for scientific research and industrial applications,” he said, meaning many promising materials are stuck in the labs where they are produced.

“Therefore, I thought if they can easily transfer 2D materials onto their specific substrates by themselves, 2D materials research and applications will be strongly boosted,” said Ago.

To make the tape user-friendly and simple, Ago and his colleagues devised a material that could selectively stick and un-stick to the 2D materials using UV light. This reduces the chance for damage to occur when the 2D materials are transferred from one surface and to another.

The base of the new tape is a thin layer made from a plastic polymer which gives the tape enough rigidity to be stable and enough flexibility to not damage the materials during transport. Next comes a special blend of polymers — long, chain-like structures made from repeating molecules — that safely attaches to the 2D materials.

“When first adhered to the 2D material, the adhesive layer is soft enough, enabling a uniform contact with the surface and facilitating a full transfer,” Ago said.

Within this adhesive blend, however, are some UV-sensitive polymers which, when exposed to UV light, crosslink, meaning they form a series of repeating, tight bonds throughout the polymer, hardening the adhesive layer. As the tape hardens, it cleanly detaches from and releases the 2D material without the need for destructive manual or chemical processing to remove the tape.

By manipulating the composition of the polymers in the adhesive, the team could fine-tune stickiness and release of the tape for a variety of different 2D materials. “This adaptability ensures the versatility of the UV tapes and their potential in a broad range of applications,” Ago said.

Tests showed the tape greatly reduced the amount of residue and cleaning required after transfer and produced more uniform transfers with fewer cracks when compared to standard methods. “And it allowed for the transfer of larger areas up to the size of 4-inch wafers, which is essential for the adoption of 2D materials at industrial scales,” Ago said.

The tape surprised everyone though when the team tested scenarios beyond their initial designs. It proved successful when transferring 2D materials to fragile or curved surfaces, and the team was able to precisely layer different 2D materials together. Mixing and matching layers and controlling the angles between them, known as twist angles, can significantly boost electrical properties, leading to superconductive states for example.

The team also showed that they could easily cut the tape and transfer different shapes and sizes, enabling researchers to selectively transfer and position custom-sized 2D sheets quite easily. This ability to customize should reduce the amount of adhesive needed and further lower production costs for industry.

The team is now working to improve the composition of the adhesive layer as there is still some wrinkling and bubbling occurring. Efforts are also being made to scale up the sizes, and to one day transfer patterned 2D materials.

For more information: Nature Electronics

Physicists detect elusive ‘Bragg glass’ phase with machine learning tool

Cornell quantum researchers have detected an elusive phase of matter, called the Bragg glass phase, using large volumes of x-ray data and a new machine learning data analysis tool. The discovery settles a long-standing question of whether this almost–but not quite–ordered state of Bragg glass can exist in real materials.

The lead author is Krishnanand Madhukar Mallayya, postdoctoral researcher in the Department of Physics in the College of Arts and Sciences (A&S). Eun-Ah Kim, professor of physics (A&S), is the corresponding author. The research was conducted in collaboration with scientists at Argonne National Laboratory and at Stanford University.

The researchers present the first evidence of a Bragg glass phase as detected from X-ray scattering, which is a probe that accesses the entire bulk of a material, as opposed to just the surface of a material, in a systematically disordered charge density wave (CDW) material, PdxErTe3. They used comprehensive X-ray data and a novel machine learning data analysis tool, X-ray Temperature Clustering (X-TEC).

“Despite its theoretical prediction three decades ago, concrete experimental evidence for CDW Bragg glass in the bulk of the crystal remained missing,” Mallayya said.

Theoretically, there is a sharp distinction between three phases: long-range order, Bragg glass, and disordered state, Kim said. In the disordered state, the CDW correlation decays within a finite distance. In the long-range ordered state, the charge density wave correlation continues indefinitely.

In the Bragg glass phase, Kim went on, the CDW correlation does decay, but so slowly that it will only completely vanish at infinite distances.

“The challenge is detecting these distinctions from experimental data that also reflects real-life issues like noise and finite resolution of the experimental setup,” Kim said.

The researchers overcame key challenges through strategic synergy among materials, data and machine-learning tools. On the materials front, they found, in collaboration with scientists at Stanford, a family of CDW materials that will allow a systematics study with a control over dirt to use in the experiment – PdxErTe3. On the data front, they took massive amounts of data at Argonne National Laboratory in collaboration with Argonne scientists.

On the machine learning front, they used X-TEC, a machine learning tool, to analyze the massive volume of data with a scalable and automated approach.

“An experimental detection of Bragg glass phase through X-ray diffraction has settled the open question regarding the fate of CDW order subject to dirt,” Mallayya said.

Going beyond the specific scientific problem, the paper presents a new mode of research in the age of large data, Kim said: “Using machine learning tools and data-scientific perspectives, we can go after challenging questions and track down subtle signatures through a comprehensive data analysis.”

The researchers wrote that this detection of Bragg glass order and the resulting phase diagram significantly advance our understanding of the complex interplay between disorder and fluctuations. Moreover, using X-TEC to target fluctuations through a high-throughput measure of “peak spread” can revolutionize how the fluctuations are studied in scattering experiments.

For more information: Cornell University

This ultrasound sticker senses changing stiffness of deep internal organs

MIT engineers have developed a small ultrasound sticker that can monitor the stiffness of organs deep inside the body. The sticker, about the size of a postage stamp, can be worn on the skin and is designed to pick up on signs of disease, such as liver and kidney failure and the progression of solid tumors.

The team reports that the sensor can send sound waves through the skin and into the body, where the waves reflect off internal organs and back out to the sticker. The pattern of the reflected waves can be read as a signature of organ rigidity, which the sticker can measure and track.

“When some organs undergo disease, they can stiffen over time,” says the senior author of the paper, Xuanhe Zhao, professor of mechanical engineering at MIT. “With this wearable sticker, we can continuously monitor changes in rigidity over long periods of time, which is crucially important for early diagnosis of internal organ failure.”

The team has demonstrated that the sticker can continuously monitor the stiffness of organs over 48 hours and detect subtle changes that could signal the progression of disease. In preliminary experiments, the researchers found that the sticky sensor can detect early signs of acute liver failure in rats.

The engineers are working to adapt the design for use in humans. They envision that the sticker could be used in intensive care units (ICUs), where the low-profile sensors could continuously monitor patients who are recovering from organ transplants.

“We imagine that, just after a liver or kidney transplant, we could adhere this sticker to a patient and observe how the rigidity of the organ changes over days,” lead author Hsiao-Chuan Liu says. “If there is any early diagnosis of acute liver failure, doctors can immediately take action instead of waiting until the condition becomes severe.” Liu was a visiting scientist at MIT at the time of the study and is currently an assistant professor at the University of Southern California.

The study’s MIT co-authors include Xiaoyu Chen and Chonghe Wang, along with collaborators at USC.

Like our muscles, the tissues and organs in our body stiffen as we age. With certain diseases, stiffening organs can become more pronounced, signaling a potentially precipitous health decline. Clinicians currently have ways to measure the stiffness of organs such as the kidneys and liver using ultrasound elastography — a technique similar to ultrasound imaging, in which a technician manipulates a handheld probe or wand over the skin. The probe sends sound waves through the body, which cause internal organs to vibrate slightly and send waves out in return. The probe senses an organ’s induced vibrations, and the pattern of the vibrations can be translated into how wobbly or stiff the organ must be.

Ultrasound elastography is typically used in the ICU to monitor patients who have recently undergone an organ transplant. Technicians periodically check in on a patient shortly after surgery to quickly probe the new organ and look for signs of stiffening and potential acute failure or rejection.

“After organ transplantation, the first 72 hours is most crucial in the ICU,” says another senior author, Qifa Zhou, a professor at USC. “With traditional ultrasound, you need to hold a probe to the body. But you can’t do this continuously over the long term. Doctors might miss a crucial moment and realize too late that the organ is failing.”

The team realized that they might be able to provide a more continuous, wearable alternative. Their solution expands on an ultrasound sticker they previously developed to image deep tissues and organs.

“Our imaging sticker picked up on longitudinal waves, whereas this time we wanted to pick up shear waves, which will tell you the rigidity of the organ,” Zhao explains.

Existing ultrasound elastrography probes measure shear waves, or an organ’s vibration in response to sonic impulses. The faster a shear wave travels in the organ, the stiffer the organ is interpreted to be. (Think of the bounce-back of a water balloon compared to a soccer ball.)

The team looked to miniaturize ultrasound elastography to fit on a stamp-sized sticker. They also aimed to retain the same sensitivity of commercial hand-held probes, which typically incorporate about 128 piezoelectric transducers, each of which transforms an incoming electric field into outgoing sound waves.

“We used advanced fabrication techniques to cut small transducers from high-quality piezoelectric materials that allowed us to design miniaturized ultrasound stickers,” Zhou says.

The researchers precisely fabricated 128 miniature transducers that they incorporated onto a 25-millimeter-square chip. They lined the chip’s underside with an adhesive made from hydrogel — a sticky and stretchy material that is a mixture of water and polymer, which allows sound waves to travel into and out of the device almost without loss.

In preliminary experiments, the team tested the stiffness-sensing sticker in rats. They found that the stickers were able to take continuous measurements of liver stiffness over 48 hours. From the sticker’s collected data, the researchers observed clear and early signs of acute liver failure, which they later confirmed with tissue samples.

“Once liver goes into failure, the organ will increase in rigidity by multiple times,” Liu notes.

“You can go from a healthy liver as wobbly as a soft-boiled egg, to a diseased liver that is more like a hard-boiled egg,” Zhao adds. “And this sticker can pick up on those differences deep inside the body and provide an alert when organ failure occurs.”

The team is working with clinicians to adapt the sticker for use in patients recovering from organ transplants in the ICU. In that scenario, they don’t anticipate much change to the sticker’s current design, as it can be stuck to a patient’s skin, and any sound waves that it sends and receives can be delivered and collected by electronics that connect to the sticker, similar to electrodes and EKG machines in a doctor’s office.

“The real beauty of this system is that since it is now wearable, it would allow low-weight, conformable, and sustained monitoring over time,” says Shrike Zhang, an associate professor of medicine at Harvard Medical School and associate bioengineer at Brigham and Women’s Hospital, who was not involved with the study. “This would likely not only allow patients to suffer less while achieving prolonged, almost real-time monitoring of their disease progression, but also free trained hospital personnel to other important tasks.”

The researchers are also hoping to work the sticker into a more portable, self-enclosed version, where all its accompanying electronics and processing is miniaturized to fit into a slightly larger patch. Then, they envision that the sticker could be worn by patients at home, to continuously monitor conditions over longer periods, such as the progression of solid tumors, which are known to harden with severity.

“We believe this is a life-saving technology platform,” Zhao says. “In the future, we think that people can adhere a few stickers to their body to measure many vital signals, and image and track the health of major organs in the body.”

For more information: Science Advances

Image: A small ultrasound sticker, worn on the skin, can monitor the stiffness of organs deep inside the body. The MIT-developed sensor could detect signs of disease such as liver and kidney failure, and the progression of solid tumors.

Combining materials may support unique superconductivity for quantum computing

A new fusion of materials, each with special electrical properties, has all the components required for a unique type of superconductivity that could provide the basis for more robust quantum computing. The new combination of materials, created by a team led by researchers at Penn State, could also provide a platform to explore physical behaviors similar to those of mysterious, theoretical particles known as chiral Majoranas, which could be another promising component for quantum computing.
The new study describes how the researchers combined the two magnetic materials in what they called a critical step toward realizing the emergent interfacial superconductivity, which they are currently working toward.

Superconductors—materials with no electrical resistance—are widely used in digital circuits, the powerful magnets in magnetic resonance imaging (MRI) and particle accelerators, and other technology where maximizing the flow of electricity is crucial.

When superconductors are combined with materials called magnetic topological insulators—thin films only a few atoms thick that have been made magnetic and restrict the movement of electrons to their edges—the novel electrical properties of each component work together to produce “chiral topological superconductors.”

The topology, or specialized geometries and symmetries of matter, generates unique electrical phenomena in the superconductor, which could facilitate the construction of topological quantum computers.

Quantum computers have the potential to perform complex calculations in a fraction of the time it takes traditional computers because, unlike traditional computers which store data as a one or a zero, the quantum bits of quantum computers store data simultaneously in a range of possible states.
Topological quantum computers further improve upon quantum computing by taking advantage of how electrical properties are organized to make the computers robust to decoherence, or the loss of information that happens when a quantum system is not perfectly isolated.

“Creating chiral topological superconductors is an important step toward topological quantum computation that could be scaled up for broad use,” said Cui-Zu Chang, Henry W. Knerr Early Career Professor and associate professor of physics at Penn State and co-corresponding author of the paper.

“Chiral topological superconductivity requires three ingredients: superconductivity, ferromagnetism and a property called topological order. In this study, we produced a system with all three of these properties.”

The researchers used a technique called molecular beam epitaxy to stack together a topological insulator that has been made magnetic and an iron chalcogenide (FeTe), a promising transition metal for harnessing superconductivity. The topological insulator is a ferromagnet—a type of magnet whose electrons spin the same way—while FeTe is an antiferromagnet, whose electrons spin in alternating directions.

The researchers used a variety of imaging techniques and other methods to characterize the structure and electrical properties of the resulting combined material and confirmed the presence of all three critical components of chiral topological superconductivity at the interface between the materials.

Prior work in the field has focused on combining superconductors and nonmagnetic topological insulators. According to the researchers, adding in the ferromagnet has been particularly challenging.

“Normally, superconductivity and ferromagnetism compete with each other, so it is rare to find robust superconductivity in a ferromagnetic material system,” said Chao-Xing Liu, professor of physics at Penn State and co-corresponding author of the paper.

“But the superconductivity in this system is actually very robust against the ferromagnetism. You would need a very strong magnetic field to remove the superconductivity.”

The research team is still exploring why superconductivity and ferromagnetism coexist in this system.

“It’s actually quite interesting because we have two magnetic materials that are non-superconducting, but we put them together and the interface between these two compounds produces very robust superconductivity,” Chang said.

“Iron chalcogenide is antiferromagnetic, and we anticipate its antiferromagnetic property is weakened around the interface to give rise to the emergent superconductivity, but we need more experiments and theoretical work to verify if this is true and to clarify the superconducting mechanism.”

The researchers said they believe this system will be useful in the search for material systems that exhibit similar behaviors as Majorana particles—theoretical subatomic particles first hypothesized in 1937. Majorana particles act as their own antiparticle, a unique property that could potentially allow them to be used as quantum bits in quantum computers.

“Providing experimental evidence for the existence of chiral Majorana will be a critical step in the creation of a topological quantum computer,” Chang said. “Our field has had a rocky past in trying to find these elusive particles, but we think this is a promising platform for exploring Majorana physics.”

For more information: Science

RoodMicrotec and SGA enter into cooperation for ASIC testing

RoodMicrotec, Netherlands, a leading independent company for semiconductors supply and quality services, and Svenska Grindmatriser AB, Sweden, a well-established fabless IDM for the development and supply of customized mixed-signal ASICs, started a cooperation for high-volume production testing of SGA’s ASIC products.

Continue reading