Developing New High-Performance and Recyclable Materials

Professor Chiyoung Park of the Department of Energy Science and Engineering at DGIST has developed a groundbreaking new material poised to advance high-sensitivity recyclable sensor technology. Working in collaboration with Professor U-hyeok Choi of Inha University, Park’s team created a recyclable high-sensitivity sensor based on the dynamic polymer network. This next-generation material is garnering attention for its ability to combine environmental sustainability with high performance.

Existing high-sensitivity sensors have been limited by performance degradation due to fatigue and repeated use.

However, the dynamic polymer network developed by the research team maintains excellent sensitivity and durability by using vinylogous urethane bonding.

This bonding structure self-heals in response to external stimuli such as temperature, light, and pressure, preventing performance degradation even after repeated use.

The dynamic polymer network is also sensitive to various mechanical movements, heat, and light, and sensors based on the network excel at detecting human body movements.

Researchers have demonstrated that the sensors can accurately detect finger bends, changes in facial expressions, and even swallowing movements in the throat.

One of the biggest strengths of the technology is that it can maintain the same sensitivity after recycling without any degradation.

Addressing the growing issue of e-waste, the team designed the technology to combine recyclability with high performance.

They believe the dynamic polymer network’s versatility supports repeated use and recycling, potentially leading to significant reductions in e-waste.

Their work promises to have far-reaching implications not only in sensor technology but also in next-generation electronics, wearable devices, and medical equipment.

The team continues to work on commercializing the technology for widespread industrial applications.

“Our material offers excellent processability and can be recycled mechanically or chemically,” said DGIST Professor Chiyoung Park.

“The polymer network undergoes a simple recycling process, which we expect will extend the lifespan of electronic devices and wearable sensors, significantly reducing electronic waste.”

For more information: Chemical Engineering Journal

Engineering perovskite materials at the atomic level paves way for new lasers, LEDs

Researchers have developed a technique to engineer layered hybrid perovskites (LHPs) down to the atomic level, precisely controlling how these materials convert electrical charge into light. This advancement paves the way for creating materials tailored for next-generation printed LEDs and lasers, and holds promise for engineering other materials for photovoltaic devices.

Perovskites, known for their crystalline structure, possess desirable optical, electronic, and quantum properties. LHPs are composed of thin sheets of perovskite semiconductor material separated by organic spacer layers, which can be laid down as thin films. These materials are highly efficient at converting electrical charge into light, making them ideal for use in next-generation LEDs, lasers, and photonic integrated circuits. Despite their potential, understanding how to engineer LHPs to control their performance characteristics has been a challenge for researchers until now.

To understand what the researchers discovered, you have to start with quantum wells, which are sheets of semiconductor material sandwiched between spacer layers.

“We knew quantum wells were forming in LHPs – they’re the layers,” says Aram Amassian, corresponding author of a paper on the work and a professor of materials science and engineering at North Carolina State University.

And understanding the size distribution of quantum wells is important because energy flows from high-energy structures to low-energy structures at the molecular level.

“A quantum well that is two atoms thick has higher energy than a quantum well that is five atoms thick,” says Kenan Gundogdu, co-author of the paper and a professor of physics at NC State. “And in order to get energy to flow efficiently, you want to have quantum wells that are three and four atoms thick between the quantum wells that are two and five atoms thick. You basically want to have a gradual slope that the energy can cascade down.”

“But people studying LHPs kept running into an anomaly: the size distribution of quantum wells in an LHP sample that could be detected via X-ray diffraction would be different than the size distribution of quantum wells that could be detected using optical spectroscopy,” Amassian says.

“For example, diffraction might tell you that your quantum wells are two atoms thick, as well as there being a three-dimensional bulk crystal,” Amassian says. “But spectroscopy might tell you that you have quantum wells that are two atoms, three atoms, and four atoms thick, as well as the 3D bulk phase.

“So, the first question we had was: why are we seeing this fundamental disconnect between X-ray diffraction and optical spectroscopy? And our second question was: how can we control the size and distribution of quantum wells in LHPs?”

Through a series of experiments the researchers discovered that there was a key player involved in answering both questions: nanoplatelets.

“Nanoplatelets are individual sheets of the perovskite material that form on the surface of the solution we use to create LHPs,” Amassian says. “We found that these nanoplatelets essentially serve as templates for layered materials that form under them. So, if the nanoplatelet is two atoms thick, the LHP beneath it forms as a series of two-atom-thick quantum wells.

“However, the nanoplatelets themselves aren’t stable, like the rest of the LHP material. Instead, the thickness of nanoplatelets keeps growing, adding new layers of atoms over time. So, when the nanoplatelet is three atoms thick, it forms three-atom quantum wells, and so on. And, eventually, the nanoplatelet grows so thick that it becomes a three-dimensional crystal.”

This finding also resolved the longstanding anomaly about why X-ray diffraction and optical spectroscopy were providing different results. Diffraction detects the stacking of sheets and therefore does not detect nanoplatelets, whereas optical spectroscopy detects isolated sheets.

“What’s exciting is that we found we can essentially stop the growth of nanoplatelets in a controlled way, essentially tuning the size and distribution of quantum wells in LHP films,” Amassian says. “And by controlling the size and arrangement of the quantum wells, we can achieve excellent energy cascades – which means the material is highly efficient and fast at funneling charges and energy for the purposes of laser and LED applications.”

When the researchers found that nanoplatelets played such a critical role in the formation of perovskite layers in LHPs, they decided to see if nanoplatelets could be used to engineer the structure and properties of other perovskite materials – such as the perovskites used to convert light into electricity in solar cells and other photovoltaic technologies.

“We found that the nanoplatelets play a similar role in other perovskite materials and can be used to engineer those materials to enhance the desired structure, improving their photovoltaic performance and stability,” says Milad Abolhasani, co-author of the paper and ALCOA Professor of Chemical and Biomolecular Engineering at NC State.

For more information: Matter

New soft material charges like batteries, can be woven into fabrics, make devices

Scientists from Northwestern University have developed highly energy-efficient, biocompatible materials made of tiny, flexible nano-sized ribbons that can be charged like a battery to store energy or record digital information. These sustainable materials could lead to new types of ultralight electronic devices, reducing the environmental impact of electronic manufacturing and disposal. The study highlights potential applications for these soft materials in low-power, energy-efficient microscopic memory chips, sensors, and energy storage units

Researchers maintain that these materials could also be integrated into woven fibers to create smart fabrics or sticker-like medical implants. In today’s wearable devices, electronics are clunkily strapped to the body with a wristband. But, with the new materials, the wristband itself could have electronic activity.

Northwestern’s Samuel I. Stupp, who led the study, stated that this is a wholly new concept in materials science and soft materials research.
Stupp maintained that researchers imagine a future where you could wear a shirt with air conditioning built into it or rely on soft bioactive implants that feel like tissues and are activated wirelessly to improve heart or brain function.

“Those uses require electrical and biological signals, but we cannot build those applications with classic electroactive materials. It’s not practical to put hard materials into our organs or in shirts that people can wear. We need to bring electrical signals into the world of soft materials. That is exactly what we have done in this study,” added Stupp.

Researchers maintained that the secret behind the new material is peptide amphiphiles, a versatile platform of molecules previously developed in Stupp’s laboratory. These self-assembling structures form filaments in water and have already demonstrated promise in regenerative medicine. The molecules contain peptides and a lipid segment, which drives the molecular self-assembly when placed in water.

In the study, the team replaced the lipid tail with a miniature molecular segment of a plastic called polyvinylidene fluoride (PVDF). But they kept the peptide segment, which contains sequences of amino acids. Commonly used in audio and sonar technologies, PVDF is a plastic with unusual electrical properties.

It can generate electrical signals when pressed or squeezed — a property known as piezoelectricity. It also is a ferroelectric material, which means it has a polar structure that can switch orientation by 180 degrees using an external voltage. The dominant ferroelectrics in technology are hard materials and often include rare or toxic metals, such as lead and niobium.

Stupp stated that PVDF was discovered in the late 1960s and is the first known plastic with ferroelectric properties.

“It has all the robustness of plastic while being useful for electrical devices. That makes it a very high-value material for advanced technologies. However, in pure form, its ferroelectric character is not stable, and, if heated above the so-called Curie temperature, it loses its polarity irreversibly,” said Stupp.

All plastics, including PVDF, contain polymers, which are giant molecules typically composed of thousands of chemical structural units. In the new study, the Stupp laboratory precisely synthesized miniature polymers with only 3 to 7 vinylidene fluoride units. Interestingly, the miniature segments with 4, 5 or 6 units are programmed by nature’s beta-sheet structures, which are present in proteins, to organize into a stable ferroelectric phase, according to the study.

For more information: Nature

Image: This illustration shows a future vision of assemblies of molecules formed by peptides and miniature molecular segments from a plastic material to create ferroelectric structures that switch polarity to store digital information or signal neurons.

Research to use machine learning to ‘reverse-engineer’ new composite materials

Materials science engineers often struggle to design materials that are strong in all directions, as strengthening them for one type of load can create weaknesses for another. To address this, Binghamton University Assistant Professors Mir Jalil Razavi and Dehao Liu are using artificial intelligence and machine learning to develop composite materials with specific mechanical properties. Their project, supported by a $313,087 grant from the National Science Foundation, aims to create a deep-learning model that customizes the microarchitecture of these materials based on physical laws.

“When we look at materials now, we usually tune mechanical properties in one direction,” Razavi said. “For example, they can absorb the shock in ‘x’ direction, but they don’t pay attention to what will happen to the ‘y’ or ‘z’ direction. While we strengthen in one direction, maybe we’ll compromise their mechanical properties in the other directions.”

“Imagine trying to mix two types of materials,” Liu said. “One is very solid and stiff. One is very soft, like if you mix stone and gel and then glue them together. How can you design the distribution of the stone and the gel? They can show different mechanical properties at different directions.”

Razavi and Liu will develop thousands of mechanical computational models to train deep learning algorithms in designing composite materials tailored to specific needs. They will decide which suggestions are most promising, and their collaborator, Associate Professor Yanyu Chen from the University of Louisville (Kentucky), will validate the best combinations through additive manufacturing (3D printing), X-ray imaging and stress testing.

“With this research, the goal would be that you give the material properties you are seeking in that different direction, and I inversely fabricate the material for you,” Razavi said.

The idea for the project originated from Razavi’s research on the human brain. He hopes to chart the formation of brain folds as faster-growing grey matter (the outer layer where higher-level thinking is done) grows on top of white matter (the inner layer that communicates between different gray matter areas and between the gray matter and the rest of the body).

“Because brain tissue has different fiber tracts, it shows different mechanical properties in different directions,” he said. “When we want to fully characterize brain tissue, we need multiple loading cases to analyze that.”

The Binghamton team believes this machine learning research could revolutionize materials design and enable the rapid development of new materials with tailored properties for a wide range of applications, such as designing lighter structures, effective shock absorbers and aerospace components.

“It could be used not just in advanced areas like the brain, but also everyday materials like helmets and shoes,” Liu said. “If your shoes don’t feel comfortable, you can design your own personal pair using materials with different mechanical properties.”

For more information: Binghamton University

INBRAIN Neuroelectronics announces world’s first human graphene-based Brain computer Interface procedure

INBRAIN Neuroelectronics, a company specializing in graphene-based neural technologies, announced the world’s first human procedure using its cortical interface during a brain tumor resection, successfully distinguishing between healthy and cancerous tissue with micrometer precision. This milestone showcases the potential of graphene-based BCI technology not only in decoding brain signals but also as a precise surgical tool for cancer and other neurotechnological applications. The study, sponsored by the University of Manchester and primarily funded by the European Commission’s Graphene Flagship project, marks a significant advancement in the field.

“The world’s first human application of a graphene-based BCI highlights the transformative impact of graphene-based neural technologies in medicine. This clinical milestone opens a new era for BCI technology, paving the way for advancements in both neural decoding and its application as a therapeutic intervention,” said Carolina Aguilar, CEO and Co-Founder of INBRAIN Neuroelectronics.

INBRAIN’s BCI platform leverages the exceptional properties of graphene, a material made of a single layer of carbon atoms. Despite being the thinnest known material to science, graphene is stronger than steel and possesses a unique combination of electronic and mechanical properties that make it ideal for neurotechnology innovation.

“We are capturing brain activity in areas where traditional metals and materials struggle with signal fidelity. Graphene provides ultra-high density for sensing and stimulating, which is critical to conduct high precision resections while preserving the patient’s functional capacities, such as movement, language or cognition,” said Dr. David Coope, the neurosurgeon who performed the procedure.

“After extensive engineering development and pre-clinical trials, INBRAIN’s first-in-human study will involve 8-10 patients, primarily to demonstrate the safety of graphene in direct contact with the human brain,” said Kostas Kostarelos, Ph.D., Co-Founder, INBRAIN Neuroelectronics. “The study will also aim to demonstrate graphene’s superiority over other materials in decoding brain functionality in both awake and asleep states.”

“The integration of graphene and AI with advanced semiconductor technology has allowed INBRAIN to pioneer a new generation of minimally-invasive BCI therapeutics designed for the personalized treatment of neurological disorders,” said Jose A. Garrido, Ph.D., Co-Founder and Chief Scientific Officer of INBRAIN and ICREA Professor at the Catalan Institute of Nanoscience and Nanotechnology.

The study is powered by INBRAIN’s graphene-based Intelligent Network Decoding & Modulation (BCI-Tx) Platform, which has received Breakthrough Device Designation for Parkinson’s disease from the U.S. Food & Drug Administration. INBRAIN’s BCI-Tx platform leverages graphene’s unique properties to deliver ultra-high signal resolution and adaptive neuroelectronic therapy, enabling real-time decoding of biomarkers and precise modulation of cortical and subcortical structures at the micrometer scale for neural network rebalancing.

For more information: INBRAIN Neuroelectronics

‘Writing’ with atoms could transform materials fabrication for Quantum devices

Scientists at the Department of Energy’s Oak Ridge National Laboratory have developed a groundbreaking advanced microscopy tool that can precisely place individual atoms, enabling the creation of new materials with unique properties for quantum computing and communication devices that cannot be produced by conventional methods.

“By working at the atomic scale, we also work at the scale where quantum properties naturally emerge and persist,” said Stephen Jesse, a materials scientist who leads this research and heads the Nanomaterials Characterizations section at ORNL’s Center for Nanophase Materials Sciences, or CNMS. “We aim to use this improved access to quantum behavior as a foundation for future devices that rely on uniquely quantum phenomena, like entanglement, for improving computers, creating more secure communications and enhancing the sensitivity of detectors.”

To accomplish improved control over atoms, the research team created a tool they call a synthescope for combining synthesis with advanced microscopy. The researchers used a scanning transmission electron microscope, or STEM, transformed into an atomic-scale material manipulation platform. The synthescope will advance the state of the art in fabrication down to the level of the individual building blocks of materials. This new approach allows researchers to place different atoms into a material at specific locations; the new atoms and their locations can be selected to give the material new properties.

“Classical computers use bits, which can be either 0 or 1, and do calculations by flipping these bits,” said ORNL’s Ondrej Dyck, a materials scientist contributing to the research. “Quantum computers use qubits, which can be both 0 and 1 at the same time. The qubits can also become entangled, with one qubit connected to the state of another. This entangled system of qubits can be used to solve certain problems much faster than classical computers. The tricky part is keeping these delicate qubits stable and working correctly in the real world.

“One strategy to tackle these challenges is to build and operate at the scale where quantum mechanics exist more naturally—at the atomic scale. We realized that if we have a microscope that can resolve atoms, we may be able to use the same microscope to move atoms or alter materials with atomic precision. We also want to be able to add atoms to the structures we create, so we need a supply of atoms. The idea morphed into an atomic-scale synthesis platform—the synthescope.”

That is important because the ability to tailor materials atom-by-atom can be applied to many future technological applications in quantum information science, and more broadly in microelectronics and catalysis, and for gaining a deeper understanding of materials synthesis processes. This work could facilitate atomic-scale manufacturing, which is notoriously challenging.

“Simply by the fact that we can now start putting atoms where we want, we can think about creating arrays of atoms that are precisely positioned close enough together that they can entangle, and therefore share their quantum properties, which is key to making quantum devices more powerful than conventional ones,” Dyck said.

Such devices might include quantum computers — a proposed next generation of computers that may vastly outpace today’s fastest supercomputers; quantum sensors; and quantum communication devices that require a source of a single photon to create a secure quantum communications system.

By using an electron beam, or e-beam, to remove and deposit the atoms, the ORNL scientists could accomplish a direct writing procedure at the atomic level.

“The process is remarkably intuitive,” said ORNL’s Andrew Lupini, STEM group leader and a member of the research team. “STEMs work by transmitting a high-energy e-beam through a material. The e-beam is focused to a point smaller than the distance between atoms and scans across the material to create an image with atomic resolution. However, STEMs are notorious for damaging the very materials they are imaging.”

The scientists realized they could exploit this destructive “bug” and instead use it as a constructive feature and create holes on purpose. Then, they can put whatever atom they want in that hole, exactly where they made the defect. By purposely damaging the material, they create a new material with different and useful properties.

“We’re exploring methods to create these defects on demand so we can place them where we want to,” Jesse said. “Since STEMs have atomic-scale imaging capabilities, and we work with very thin materials that are only a few atoms in thickness, we can see every atom. So, we are manipulating matter at the atomic scale in real time. That’s the goal, and we are actually achieving it.”

For more information: Nano Letters

Image: This artistic rendering shows a way to make materials atom-by-atom. The electron beam ejects a carbon atom from graphene, and a different atom bonds at the vacancy.

New catalyst material achieves double the DOE fuel cell lifetime target

A UCLA-led team, including Professor Xiangfeng Duan and Dr. Bosi Peng, has developed an ultrafine platinum nanocatalyst embedded with cobalt oxide clusters, significantly enhancing fuel cell efficiency and durability by reducing platinum dissolution. This new catalyst, designed by UCLA materials scientists and chemists, nearly doubles the projected lifetime target set by the U.S. Department of Energy, potentially allowing light-duty vehicles to last beyond 15,000 hours of use, which is 87.5% longer than the department’s goal. This advancement could also benefit heavy-duty vehicles by slightly increasing the use of the embedded-oxide platinum catalyst, making fuel cells a more durable and efficient means of generating electricity with a limited carbon footprint.

Proton-exchange membrane fuel cells that directly convert chemical energy from hydrogen to electricity have been an attractive zero-emission power-generation technology. Inside the cells, the membrane is laced with a catalyst, such as a platinum alloy, which helps spark and speed up the otherwise sluggish chemical reaction that converts the energy stored in hydrogen atoms to electricity. The reaction breaks hydrogen atoms into their constituent protons and electrons, with water vapor being the reaction’s only emission byproduct. This is why adopting fuel-cell vehicles for widespread use offers an attractive option for meeting climate sustainability goals.

However, it has been difficult to find the sweet spot between achieving catalytic efficiency and fuel cell durability because the platinum dissolves over time, dropping the fuel cell’s performance.

“A major challenge in wider fuel cell adoption continues to be making their optimal performance last long enough to be commercially viable,” said Huang, who holds the Traugott and Dorothea Frederking Endowed Chair at UCLA Samueli. “Our research demonstrated an atomic interior scaffold that holds platinum atoms in place in the catalyst so they remain stable over an extended period of time.”

Rather than using a traditional platinum alloy, the researchers embedded clusters of cobalt-oxide molecules inside shells of platinum atoms. The design leverages the strong platinum-oxide interaction, which makes the catalyst more durable structurally and chemically without sacrificing fuel cell activity. The resulting hybrid structure helps the platinum ions stick and stay together despite extended use, reducing catalyst-replacement costs. In their experiments, the researchers saw this design outperformed traditional platinum-cobalt alloys in durability and longevity. The team also verified the nanoscale structure using a suite of microscopic, spectroscopic and simulation techniques.

For more information: Nature Catalysis

Scientists find new way to make efficient perovskite LEDs

A research team led by Tae-Woo Lee from Seoul National University’s Department of Materials Science and Engineering, in collaboration with Andrew M. Rappe from the University of Pennsylvania and Omer Yaffe from the Weizmann Institute of Science in Israel, has developed an ultra-high efficiency perovskite nanocrystal LED by strengthening the perovskite lattice and suppressing the material’s inherent low-frequency dynamics. Traditionally used in solar cells due to insufficient luminescence at room temperature, perovskites are composed of weak ionic bonds, and large-amplitude atomic displacements in their crystal lattices can cause dynamic disorder, which interferes with the radiative recombination process, leading to exciton dissociation and reduced luminescence efficiency.

Tae-Woo Lee recognized the potential of perovskite early on and secured several fundamental patents for perovskite light-emitting materials in 2014. Additionally, in 2015, his team published the first research paper demonstrating the enhancement of the efficiency in perovskite LED from 0.1 percent to 8.53 percent, comparable to the level of phosphorescent OLEDs.

In 2022, Lee’s team achieved an external quantum efficiency (EQE) of 28.9 percent (nearly theoretically achievable maximum), a peak brightness of 470,000 nits, and an operational lifetime of up to 30,000 hours. Moving towards commercialization, Lee’s startup company, SN Display, showed TV and tablet display prototypes at the CES (Consumer Electronics Show) in 2022 and 2023.

In this latest work, Lee and colleagues have focused on strategies to improve efficiency by reducing dynamic disorder using a novel mechanism that relies on conjugated molecular multipods (CMMs). When a CMM binds to the surface of the perovskite lattice, the lattice is strengthened, suppressing low-frequency dynamics and reducing dynamic disorder in the perovskite lattice. (Pictured above is a schematic diagram of the fabrication process).

The result is an ultra-high-efficiency LED with an EQE of 26.1 percent. This value is claimed to be among the highest efficiency in perovskite nanocrystal LEDs and is especially significant because the efficiency improvement was achieved by enhancing the intrinsic emission efficiency of the material itself rather than through engineering the device structure that enhances light outcoupling efficiency.

Lee commented: “This research presents a new material-based approach to overcoming the intrinsic limitations of perovskite light emitters. We anticipate that this will significantly contribute to the development of high-efficiency, long-lifetime perovskite light-emitting devices and the commercialization of next-generation displays.”

Rappe agreed, saying: “Together, we have shown the power of molecules in strengthening perovskites and making them better light emitters. By combining the powers of molecular chemistry, physics, mechanics, and optics, we are inventing new materials to lead us into a bright and energy-efficient future.”

For more information: Nature Communications

Image: Novel mechanism enhances luminescence efficiency by suppressing inherent low-frequency dynamics in the perovskite material.

Solar energy breakthrough could reduce need for solar farms

Scientists at Oxford University have developed a groundbreaking approach to generating solar electricity without silicon-based panels. Their innovation involves coating a new, ultra-thin, and flexible light-absorbing material onto everyday objects like rucksacks, cars, and mobile phones. This material uses a multi-junction technique to stack multiple light-absorbing layers into one solar cell, capturing a broader spectrum of light and generating more power from the same amount of sunlight.

This new material has been independently certified to achieve over 27% energy efficiency, matching the performance of traditional silicon photovoltaics for the first time. The certification from Japan’s National Institute of Advanced Industrial Science and Technology (AIST) precedes the publication of the researchers’ study later this year.

“During just five years experimenting with our stacking or multi-junction approach, we have raised power conversion efficiency from around 6% to over 27%, close to the limits of what single-layer photovoltaics can achieve today,” said Dr Shuaifeng Hu, Post Doctoral Fellow at Oxford University Physics. “We believe that, over time, this approach could enable the photovoltaic devices to achieve far greater efficiencies, exceeding 45%.”

This compares with around 22% energy efficiency from solar panels today (meaning they convert around 22% of the energy in sunlight), but the versatility of the new ultra-thin and flexible material is also key. At just over one micron thick, it is almost 150 times thinner than a silicon wafer. Unlike existing photovoltaics, generally applied to silicon panels, this can be applied to almost any surface.

‘By using new materials that can be applied as a coating, we’ve shown we can replicate and out-perform silicon while also gaining flexibility. This is important because it promises more solar power without the need for so many silicon-based panels or specially built solar farms,’ said Dr Junke Wang, Marie Skłodowska Curie Actions Postdoc Fellow at Oxford University Physics.

The researchers believe their approach will continue to reduce solar costs and make it the most sustainable form of renewable energy. Since 2010, the global average cost of solar electricity has fallen by almost 90%, making it almost a third cheaper than that generated from fossil fuels. Innovations promise additional cost savings as new materials, like thin-film perovskite, reduce the need for silicon panels and purpose-built solar farms.

The researchers are among 40 scientists working on photovoltaics led by Professor of Renewable Energy Henry Snaith at Oxford University Physics Department. Their pioneering work in photovoltaics and especially the use of thin-film perovskite began around a decade ago and benefits from a bespoke, robotic laboratory.

Their work has strong commercial potential and has already started to feed through into applications across the utilities, construction, and car manufacturing industries.

For more information: University of Oxford

Image: Dr Shuaifeng Hu, Post Doctoral Fellow at Oxford University Physics, examining the new thin-film perovskite material. Image credit: Martin Small.

Unconventional interface superconductor could benefit quantum computing

A team of scientists, led by physicist Peng Wei at the University of California, Riverside, has developed a new superconductor material with potential applications in quantum computing. This material could be a candidate for a “topological superconductor,” which uses a delocalized state of an electron or hole to robustly carry quantum information and process data.

The researchers combined trigonal tellurium, a chiral and non-magnetic material, with a surface-state superconductor on a thin film of gold. They observed quantum states at the interface with well-defined spin polarization, which could be used to create spin quantum bits (qubits). This breakthrough could significantly advance the field of quantum computing.

“By creating a very clean interface between the chiral material and gold, we developed a two-dimensional interface superconductor,” said Wei, an associate professor of physics and astronomy. “The interface superconductor is unique as it lives in an environment where the energy of the spin is six times more enhanced than those in conventional superconductors.”

The researchers observed that the interface superconductor undergoes a transition under a magnetic field and becomes more robust at a high field compared with the low field, which suggests a transition into a “triplet superconductor,” which is more stable under a magnetic field.

Furthermore, through collaboration with scientists at the National Institute of Standards and Technology, the researchers showed that such a superconductor involving heterostructure gold and niobium thin films naturally suppresses decoherence sources from material defects such as niobium oxides that are a common challenge for niobium superconductors. They showed that the superconductor can be made into high-quality low-loss microwave resonators with a quality factor reaching 1 million.

According to the multinational technology company IBM, the new technology has applications in quantum computing, a field that uses quantum mechanics to solve complex problems that classical computers or supercomputers cannot solve or cannot solve quickly enough.

“We achieved this using materials that are one order of magnitude thinner than those typically used in the quantum computing industry,” Wei said. “The low-loss microwave resonators are critical components of quantum computing and could lead to low-loss superconducting qubits. The biggest challenge in quantum computing is to reduce decoherence or quantum information loss in a qubit system.”

Decoherence occurs when a quantum system interacts with its environment, causing the system’s information to get mixed up with the environment. Decoherence poses a challenge for realizing quantum computers.

Unlike previous methods that require magnetic materials, the researchers’ new approach uses non-magnetic materials for a cleaner interface.

“Our material could be a promising candidate for developing more scalable and reliable quantum computing components,” Wei said.

For more information: Science Advances

Image: Peng Wei

Alfred University awarded NSF grant for ellipsometry equipment acquisition

Alfred University has been awarded a nearly $350,000 grant from the National Science Foundation (NSF) to enhance multi-disciplinary research and education at the Inamori School of Engineering. The grant, led by principal investigator Myungkoo Kang, assistant professor of ceramic engineering, along with co-principal investigators S.K. Sundaram and Mehdi Kabir, will fund the acquisition of an in situ infrared spectroscopic ellipsometry system. This advanced equipment uses polarized light to analyze thin films and bulk materials, providing valuable data on material properties such as complex refractive index dispersion.

The NSF grant will significantly bolster the university’s capabilities in materials science research. The new ellipsometry system will enable detailed characterization of materials, supporting innovative research and educational initiatives within the engineering school.

“A spectroscopic ellipsometer would allow researchers to cross-correlate data with other types of optical, structural, microscopic, and chemical metrology tools to better establish quantitative process-structure-property relationships for a wide variety of optical material systems, thereby truly advancing cutting-edge optical materials research at Alfred University,” Kang said.

The infrared radiation (IR) in-situ IR spectroscopic ellipsometer, when used in tandem with the University’s existing visible near infrared radiation (NIR) spectroscopic ellipsometry system, would enable a first-of-its-kind versatile system for the region. According to Kang, Alfred University will be the only institution in Western New York with such unique versatility in the temperature-wavelength measurement domain, thus becoming a centerpiece in making transformational progress in the University’s research areas of interest.

Kang said the instrument meets a critical need to support multi-disciplinary research and education programs including Ceramic Engineering, Glass Science, Materials Science & Engineering, Biomaterials Engineering, and Mechanical Engineering at Alfred University as well as the greater western New York State region.

The research projects enabled by the instrument have potential major technological impacts on the core interests of faculty and their collaborators, including glass photonics, fundamental glass physics, electro and high-temperature ceramics, biomedical sensors, and additive manufacturing. Incorporating the instrument, data analysis, and interpretation into undergraduate and graduate courses will strengthen educational offerings, thus providing an authentic hands-on experience.

“The acquisition of the instrument would enhance the student learning experience since we plan to actively incorporate a hands-on experimental session on the key optical metrology tool into our coursework,” Kang said, noting the equipment will be utilized by graduate and undergraduate students alike.

“For the graduate-level course, the ellipsometer will be used directly by the students during lab sessions and then later in their dissertation research. We also have highly motivated undergraduate students with a strong interest in characterization, and those students will be given training and permission to use the instrument.”

Kang noted that the equipment will also be beneficial to the Inamori School of Engineering’s outreach initiatives.

For more information: Alfred University

Super-black wood can improve telescopes, optical devices and consumer goods

Researchers at the University of British Columbia, led by Professor Philip Evans and PhD student Kenny Cheng, accidentally discovered a super-black material that absorbs almost all light, potentially useful in fine jewelry, solar cells, and precision optical devices. While experimenting with high-energy plasma to make wood more water-repellent, they found that applying the technique to the cut ends of wood cells turned the surfaces extremely black. Measurements by Texas A&M University’s Department of Physics and Astronomy confirmed that this material reflects less than one percent of visible light, absorbing nearly all the light that strikes it.

Instead of discarding this accidental finding, the team shifted their focus to designing super-black materials, contributing a new approach to the search for the darkest materials on Earth.

“Ultra-black or super-black material can absorb more than 99 percent of the light that strikes it – significantly more so than normal black paint, which absorbs about 97.5 percent of light,” explained Dr. Evans, a professor in the faculty of forestry and BC Leadership Chair in Advanced Forest Products Manufacturing Technology.

Super-black materials are increasingly sought after in astronomy, where ultra-black coatings on devices help reduce stray light and improve image clarity. Super-black coatings can enhance the efficiency of solar cells. They are also used in making art pieces and luxury consumer items like watches.

The researchers have developed prototype commercial products using their super-black wood. They initially focused on watches and jewelry but plan to explore other commercial applications in the future.

The team named and trademarked their discovery Nxylon (niks-uh-lon), after Nyx, the Greek goddess of the night, and xylon, the Greek word for wood.

Most surprisingly, Nxylon remains black even when coated with an alloy, such as the gold coating applied to the wood to make it electrically conductive enough to be viewed and studied using an electron microscope. This is because Nxylon’s structure inherently prevents light from escaping rather than depending on black pigments.

The UBC team have demonstrated that Nxylon can replace expensive and rare black woods like ebony and rosewood for watch faces, and it can be used in jewelry to replace the black gemstone onyx.

“Nxylon’s composition combines the benefits of natural materials with unique structural features, making it lightweight, stiff and easy to cut into intricate shapes,” said Dr. Evans.

Made from basswood, a tree widely found in North America and valued for hand carving, boxes, shutters and musical instruments, Nxylon can also use other types of wood such as European lime wood.

Dr. Evans and his colleagues plan to launch a startup, Nxylon Corporation of Canada, to scale up applications of Nxylon in collaboration with jewellers, artists and tech product designers. They also plan to develop a commercial-scale plasma reactor to produce larger super-black wood samples suitable for non-reflective ceiling and wall tiles.

“Nxylon can be made from sustainable and renewable materials widely found in North America and Europe, leading to new applications for wood. The wood industry in B.C. is often seen as a sunset industry focused on commodity products—our research demonstrates its great untapped potential,” said Dr. Evans.

For more information: The University of British Columbia 

Image: UBC forestry researchers have created a new super-black material that absorbs almost all light. From left, Dengcheng Feng, Kenny Cheng, Dr. Philip Evans and Sara Xu. Credit: UBC Forestry/Ally Penders

A new approach to fine-tuning quantum materials

Quantum materials, which have electronic properties governed by quantum mechanics principles like correlation and entanglement, can display unique behaviors under certain conditions, such as superconductivity, where electricity is transmitted without resistance. To achieve optimal performance, these materials must be finely tuned. A team led by Mingda Li, an associate professor in MIT’s Department of Nuclear Science and Engineering (NSE), has developed an ultra-precise method to adjust the characteristics of quantum materials, using Weyl semimetals as an example.

This new technique isn’t limited to Weyl semimetals; according to NSE postdoc Manasi Mandal, one of the lead authors of the paper detailing the group’s findings, it can be applied to any inorganic bulk material and thin films as well. The experiment described in the paper focused on a specific type of Weyl semimetal, a tantalum phosphide (TaP) crystal.

Materials can be classified by their electrical properties: metals conduct electricity readily, whereas insulators impede the free flow of electrons. A semimetal lies somewhere in between. It can conduct electricity, but only in a narrow frequency band or channel. Weyl semimetals are part of a wider category of so-called topological materials that have certain distinctive features. For instance, they possess curious electronic structures — kinks or “singularities” called Weyl nodes, which are swirling patterns around a single point (configured in either a clockwise or counterclockwise direction) that resemble hair whorls or, more generally, vortices. The presence of Weyl nodes confers unusual, as well as useful, electrical properties. And a key advantage of topological materials is that their sought-after qualities can be preserved, or “topologically protected,” even when the material is disturbed.

“That’s a nice feature to have,” explains Abhijatmedhi Chotrattanapituk, a PhD student in MIT’s Department of Electrical Engineering and Computer Science and the other lead author of the paper. “When you try to fabricate this kind of material, you don’t have to be exact. You can tolerate some imperfections, some level of uncertainty, and the material will still behave as expected.”

The “tuning” that needs to happen relates primarily to the Fermi level, which is the highest energy level occupied by electrons in a given physical system or material. Mandal and Chotrattanapituk suggest the following analogy: Consider a dam that can be filled with varying levels of water. One can raise that level by adding water or lower it by removing water. In the same way, one can adjust the Fermi level of a given material simply by adding or subtracting electrons.

To fine-tune the Fermi level of the Weyl semimetal, Li’s team did something similar, but instead of adding actual electrons, they added negative hydrogen ions (each consisting of a proton and two electrons) to the sample. The process of introducing a foreign particle, or defect, into the TaP crystal — in this case by substituting a hydrogen ion for a tantalum atom — is called doping. And when optimal doping is achieved, the Fermi level will coincide with the energy level of the Weyl nodes. That’s when the material’s desired quantum properties will be most fully realized.

For Weyl semimetals, the Fermi level is especially sensitive to doping. Unless that level is set close to the Weyl nodes, the material’s properties can diverge significantly from the ideal. The reason for this extreme sensitivity owes to the peculiar geometry of the Weyl node. If one were to think of the Fermi level as the water level in a reservoir, the reservoir in a Weyl semimetal is not shaped like a cylinder; it’s shaped like an hourglass, and the Weyl node is located at the narrowest point, or neck, of that hourglass. Adding too much or too little water would miss the neck entirely, just as adding too many or too few electrons to the semimetal would miss the node altogether.

To reach the necessary precision, the researchers utilized MIT’s two-stage “Tandem” ion accelerator — located at the Center for Science and Technology with Accelerators and Radiation (CSTAR) — and buffeted the TaP sample with high-energy ions coming out of the powerful (1.7 million volt) accelerator beam. Hydrogen ions were chosen for this purpose because they are the smallest negative ions available and thus alter the material less than a much larger dopant would. “The use of advanced accelerator techniques allows for greater precision than was ever before possible, setting the Fermi level to milli-electron volt [thousandths of an electron volt] accuracy,” says Kevin Woller, the principal research scientist who leads the CSTAR lab. “Additionally, high-energy beams allow for the doping of bulk crystals beyond the limitations of thin films only a few tens of nanometers thick.”

The procedure, in other words, involves bombarding the sample with hydrogen ions until a sufficient number of electrons are taken in to make the Fermi level just right. The question is: how long do you run the accelerator, and how do you know when enough is enough? The point being that you want to tune the material until the Fermi level is neither too low nor too high.

To streamline the protocol, the team has devised a theoretical model that first predicts how many electrons are needed to increase the Fermi level to the preferred level and translates that to the number of negative hydrogen ions that must be added to the sample. The model can then tell them how long the sample ought to be kept in the accelerator chamber.

The good news, Chotrattanapituk says, is that their simple model agrees within a factor of 2 with trusted conventional models that are much more computationally intensive and may require access to a supercomputer. The group’s main contributions are two-fold, he notes: offering a new, accelerator-based technique for precision doping and providing a theoretical model that can guide the experiment, telling researchers how much hydrogen should be added to the sample depending on the energy of the ion beam, the exposure time, and the size and thickness of the sample.

This could pave the way to a major practical advance, Mandal notes, because their approach can potentially bring the Fermi level of a sample to the requisite value in a matter of minutes — a task that, by conventional methods, has sometimes taken weeks without ever reaching the required degree of milli-eV precision.

For more information: Applied Physics Review

Image: Ion implantation using a tandem accelerator on bulk material. Selected ion species are injected toward the terminal, and ions with specific energies are directed toward the sample. Credits Ella Maru Studio

New 3D reconstruction method aids analysis of property-defining defects

An international research collaboration, including a group from Cornell Engineering, has used a new X-ray-based reconstruction technique to observe topological defects in a nanoscale self-assembly-based cubic network structure of a polymer-metal composite material over a large sample volume for the first time. This technique and the new insights gained could be applied to studying other mesoscale structures with similar defects, which underpin many physical phenomena and can lead to new or enhanced material properties in both natural and synthetic self-assembled materials. Ulrich Wiesner, the Spencer T. Olin Professor in the Department of Materials Science and Engineering, emphasized that this new polymer, structure, and technique allow for unprecedented sample volumes to be reconstructed, enabling detailed examination of defect structures and their frequency.

The question regarding the importance of defects in BCP SA-generated materials has always been elusive, Wiesner said, in part because technologies necessary to measure large-enough sample volumes – with correspondingly larger defect structures – have been slow to develop.

The new technology – hard X-ray ptychography, which was conducted at the Swiss Light Source (SLS), at the Paul Scherrer Institute in Switzerland – is an advanced form of tomography that can penetrate deeper into a material than is possible with beams in electron microscopes. This technique allowed the researchers to reconstruct a very large sample volume of a BCP SA-derived polymer-metal composite material.

“If you have a smaller defect such as a line or a point defect, when you perturb the system, often you can ‘correct’ the defect structure,” Wiesner said. “In contrast, topological defects are so large, they are very stable against external perturbations.”

Once the triblock terpolymer was synthesized, researchers in the group of Ulli Steiner at the Adolphe Merkle Institute in Fribourg, Switzerland, a long-time collaborator of Wiesner, generated thin films from it and replaced one of the terpolymer blocks with gold, so the material could withstand repeated exposure to the intense coherent X-ray beams at SLS.

Imaging and image reconstruction at the SLS finally revealed a co-continuous network known as a single-diamond structure, with topological defects that the researchers expect would have substantial effects on mechanical and other properties. Importantly, the defects most closely resemble topological textures found in nematic liquid crystals and in Hydra single-celled organisms, suggesting that self-assembly can be used as a model process to investigate the role of topology in nature.

Wiesner said this collaborative research could pave the way for future studies in an area that his lab has already explored: block copolymer-directed superconductors.

“You would expect that your macroscopic, electronic or transport properties of the superconductor will depend on defects in your materials,” he said. “That’s what I’m really excited about: Now we have a technique that allows us to visualize larger volumes of these materials and to generate defect structure – property correlations.”

For more information: Nature Nanotechnology

Image: Pictured is a two-dimensional, cut-through reconstructed sample volume showing three adjacent crystal grains (red, blue, green) separated by a 100-nanometer-thick grain boundary (yellow) together with the positions of two topological defects (plus and minus signs).

Argonne Lab’s ‘AI-NERD’ predicts material behavior with unprecedented accuracy

Imagine scientific breakthroughs happening without a scientist running every experiment; a new AI development at Argonne National Laboratory, AI-NERD (Artificial Intelligence for Non-Equilibrium Relaxation Dynamics), takes a concrete step toward this vision, marking a significant advancement in autonomous materials discovery. The field of material science faces a challenge as the demand for new, better-performing materials in areas like renewable energy and aerospace outpaces researchers’ ability to discover and characterize them using traditional methods. Traditionally, understanding how materials change at the atomic level has relied on slow, labor-intensive experiments, and observing such microscopic dynamics is challenging. Techniques like X-ray photon correlation spectroscopy (XPCS) offer insights into atomic behavior, but the data generated are incredibly complex. AI-NERD promises to accelerate materials research by addressing these challenges.

This approach leverages unsupervised deep learning, specifically an autoencoder neural network, to analyze complex X-ray data and unveil the hidden “fingerprints” of material behavior. By teaching itself to recognize patterns in XPCS data without expert training, AI-NERD creates condensed material “fingerprints” from intricate X-ray scattering patterns. This breakthrough enables researchers to map and analyze material behavior in previously impossible ways.

“The goal of the AI is just to treat the scattering patterns as regular images or pictures and digest them to figure out what are the repeating patterns. The AI is a pattern recognition expert,” said James (Jay) Horwath Argonne National Laboratory, the first author of the study.

These fingerprints are more than just patterns—they are condensed representations of a material’s structure and behavior, distilling volumes of  of XPCS data into essential features. As Horwath explained, “You can think of it like having the material’s genome, it has all the information necessary to reconstruct the entire picture.”

What sets AI-NERD apart is its ability to learn and identify patterns without expert guidance. This unsupervised learning approach allows the system to discover hidden relationships and trends in material behavior that might elude scientists. By processing and categorizing X-ray scattering images, AI-NERD creates a comprehensive map of material dynamics, offering researchers a new lens for viewing atoms and molecules.

In the research, the scientists used a technique called Uniform Manifold Approximation and Projection (UMAP) to transform their complex dataset into a simple two-dimensional picture, as shown in the visual above. UMAP is similar to another popular method called t-distributed Stochastic Neighbor Embedding (tSNE). Both of these methods try to preserve the relationships between data points when reducing dimensions. For a brief overview of word embeddings, check out the article “What embeddings are and how to explore them in R&D.”

This development in AI-assisted materials research at Argonne National Laboratory is part of a broader trend of artificial intelligence revolutionizing materials science. In recent years, several notable advancements have paved the way for AI-NERD’s development.

In 2023, researchers made significant strides in using AI for materials synthesis and characterization. For instance, one team developed an AI system capable of extracting “recipes” for producing materials from scientific papers. This system could identify correlations between precursor chemicals and resulting crystal structures, streamlining the material discovery process.

Another group created an AI system that recognizes patterns across different materials recipes. This innovation allows the AI to suggest alternative recipes for known materials, potentially opening up new avenues for synthesis.

While machine learning continues to be something of a trending subject, its use in material science is not new. In 2018, researchers at Virginia Tech developed a machine learning framework that trains “on the fly” to accelerate the development of computational models for materials design.

Similarly, AI system called ARTIST from Aalto University and the Technical University of Denmark debuted in 2019 to instantly determine how a molecule will react to light, potentially accelerating the development of flexible electronics and other technologies.

In nuclear materials research, University of Wisconsin-Madison and Oak Ridge National Laboratory unveiled an AI system was trained to detect and analyze microscopic radiation damage in potential nuclear reactor materials in 2018. It outperformed human experts in both accuracy and speed.

In particular, the development of AI-NERD promises to boost the analysis of XPCS data in particular. As the upgraded Advanced Photon Source comes online, generating 500 times brighter X-ray beams than its predecessor, the need for efficient data processing becomes even more critical. “The data we get from the upgraded APS will need the power of AI to sort through it,” Horwath emphasizes. AI-NERD’s ability to create material “fingerprints” and identify patterns in large datasets could advance researchers’ understanding of material dynamics for an array range of applications.

For more information: Nature Communications

Image: The AI-NERD model learns to produce a unique ‘fingerprint’ for each sample of XPCS data enabling the identification of trends and repeating patterns. 

Researchers develop first voxel building blocks for 3D-printed organs

A research team at the University of Virginia School of Engineering and Applied Science, led by Assistant Professor Liheng Cai and his Ph.D. student Jinchang Zhu, has developed biomaterials with controlled mechanical properties that match various human tissues, potentially serving as the first building blocks for human-compatible organs printed on demand. Zhu highlighted this advancement as a significant leap compared to existing bioprinting technologies.

Their unique bioprinting method is called digital assembly of spherical particles. The DASP technique deposits particles of biomaterial in a supporting matrix, both of which are water-based, to build 3D structures that provide a suitable environment for the cells to grow. The assembly process is how “voxels,” the 3D version of pixels, construct 3D objects.

“Our new hydrogel particles represent the first functional voxel we have ever made,” Zhu said. “With precise control over mechanical properties, this voxel may serve as one of the basic building blocks for our future printing constructs.

“For example, with this level of control, we could print organoids, which are 3D cell-based models that function as human tissue, to study disease progression in the search for cures.”

The particles are polymer hydrogels engineered to mimic human tissue by tweaking the arrangement and chemical bonds of single-molecule monomers, which link together in chains to form networks.

Encapsuled within the particles are actual human cells.

Compared to other hydrogel bio-inks, Cai and Zhu’s are less toxic and more biocompatible for cells, they said. Their “double network” hydrogels—formed from two intertwined molecular networks—are mechanically strong, but highly tunable for mimicking the physical characteristics of human tissue.

Cai and Zhu first described their DASP technology in 2021. That work proved the concept of using biomaterial voxels as building blocks and, through lab experiments, demonstrated a DASP-printed material that functioned like a pancreas with glucose-stimulated insulin release.

But DASP 1.0 could only print brittle hydrogels with limited tunability. In their latest paper in Nature Communications, Cai and Zhu present DASP 2.0, which introduces the double-network hydrogel bio-inks formed using a “click chemistry” to rapidly cross-link, or bond, the molecular structures.

Part of what enabled this advancement was improvements to the team’s bioprinter. They designed a multichannel nozzle to mix the hydrogel components on demand. Premixing isn’t possible because the cross-linking occurs so fast, going from liquid droplets to an elastic water-swollen gel within 60 seconds.

In previous studies, the team determined that drop formation and rapid detachment from the nozzle are essential to mimic the mechanical properties—such as elasticity or stiffness—of the target human tissue.

DASP achieves this by depositing large droplets from a narrow and fast-moving nozzle into the matrix, immediately suspending them.

“We’ve now laid the foundation for voxelated bioprinting,” Cai said. “When fully realized, DASP’s applications will include artificial organ transplant, disease and tissue modeling, and screening candidates for new drugs. And it probably won’t stop there.”

For more information: Nature Communications

Image: Reminiscent of a raspberry, this voxelated hollow sphere made of a single layer of droplets was generated using digital assembly of spherical particles, or DASP, a 3D bioprinting process developed in assistant professor of materials science and engineering Liheng Cai’s lab. (Soft Biomatter Lab, UVA Engineering). Credit: University of Virginia School of Engineering and Applied Science/Liheng Cai

Single-crystal cathodes for faster-charging, longer-lasting EVs

A team at Pohang University of Science and Technology has unveiled a groundbreaking single-crystal synthesis technique. This innovation significantly boosts the resilience of cathode materials, a key component in electric vehicle batteries.

Professor Kyu-Young Park from the Graduate Institute of Ferrous & Eco Materials Technology and the Department of Materials Science and Engineering, along with PhD candidate Kyoung Eun Lee and alumna Yura Kim from the same institute at Pohang University of Science and Technology (POSTECH), collaborated with the POSCO Holdings N.EX.T Hub.

Lithium (Li) secondary batteries, widely employed in electric vehicles, function by converting electrical energy into chemical energy during charging and reversing the process to release electrical energy during discharge. This process involves the movement of Li+ ions between a cathode and an anode.

The cathode materials in these batteries typically include nickel (Ni) due to their high lithium-ion storage capacity. However, traditional nickel-based materials exhibit a polycrystalline structure composed of numerous small crystals. This structure is prone to structural degradation during charge and discharge cycles, leading to a considerable reduction in battery lifespan.

To tackle this issue, one proposed solution involves producing the cathode material in a “single-crystal” form. This approach aims to enhance the structural, chemical stability, and durability of nickel-based cathode materials by synthesizing them into large, single particles or “single crystals.”

Single-crystal materials are typically synthesized at high temperatures, where they undergo a process of becoming rigid. However, the precise mechanisms of this hardening process during synthesis and the specific conditions under which it occurs are still not fully understood.

To enhance the durability of nickel cathode materials for electric vehicles, the researchers concentrated on identifying a critical temperature threshold conducive to synthesizing high-quality single-crystal materials. They conducted experiments across different synthesis temperatures to pinpoint the optimal conditions for producing single crystals in the synthesis of a specific nickel-based cathode material (N884). The team systematically evaluated how varying temperatures affected the material’s capacity and long-term performance.

The researchers found that conventional polycrystalline materials synthesized below a specific critical temperature degrade over time when used in secondary batteries. In contrast, synthesizing these materials above this critical temperature enables the production of high-quality single crystals through a process known as “densification.”

During densification, the internal grain size of the material increases, and empty spaces within the structure are densely filled. This transformation results in single crystals that are exceptionally hard and resistant to degradation over prolonged periods, significantly enhancing their durability.

Based on these insights, the team confirmed that synthesizing single crystals above the critical temperature represents a more advantageous strategy for material design. They also proposed an effective method for synthesizing high-quality single crystal materials.

For more information: POSTECH

Into another dimension: Nanoscale trilayer exhibits ultrafast charge transfer in semiconductor materials

Advancements in optoelectronic semiconductor technology are heavily reliant on the controlled movement of charges and excitons—pairs of electrons and holes—towards specific directions to generate fuel or electricity. Mirroring the mechanism of photosynthesis, where pigments capture solar energy and funnel it to a reaction center for conversion and utilization, photons in this process create electron-hole pairs. These pairs must be parted to kick-start chemical reactions.

Deriving inspiration from the natural process of photosynthesis, National Renewable Energy Laboratory (NREL) researchers developed a mixed-dimensionality (2D/1D/2D) trilayer of semiconductors to enable exciton dissociation. This exciton dissociation step, a splitting and spatial separation of excited electron–hole pairs, is a microscopic process that is fundamental to the performance of photovoltaic systems.

As the clean energy transition progresses, advances in photovoltaic systems, which convert sunlight into electricity, are crucial. Photovoltaics rely on the light-activated creation of separated electron-hole pairs to drive an external circuit.

“In this study, we were able to create light-activated electron hole pairs and separate them for a long time, longer than previously reported similar systems,” said NREL’s Alexis Myers, a graduate student researcher.

The diverse and tunable electronic and optical properties of quantum-confined low-dimensional materials such as two-dimensional (2D) transition metal dichalcogenides (TMDCs) and one-dimensional (1D) single-walled carbon nanotubes (SWCNTs) make them prime candidates for fundamental studies on charge and exciton transfer. These types of materials have enhanced electron-hole Coulomb interactions, where the electrostatic force causes the attraction between an electron and an electron hole to form an exciton. To separate the charges, researchers must overcome the attraction, made more difficult by the large binding energies.

These materials exhibit large exciton binding energies—the energy needed for exciton dissociation—which can inhibit generation of electrical currents for photovoltaics, photodetectors, and sensors or chemical bonds in solar fuel schemes. So, NREL researchers sought to develop a hetero-trilayer that would address this challenge.

“Extending charge separation lifetimes is necessary to increase the chance of charge extraction,” Myers said. “The creation of bilayers and trilayers comes from this desire to increase the distance between separated charges. However, it’s unclear in the literature whether the ‘separated’ charges are still electrostatically bound across the interface. So, though separated, the Coulomb interaction is still present, which can decrease charge separation lifetimes. In the trilayer, we were able to track the movements of electrons and holes sequentially through each layer, confirming they are indeed no longer bound to each other.”

Complex, low-dimensional heterostructures—like TMDCs—exhibit longer lifetimes, initiating important photochemical reactions, which are critical to generating electricity in photovoltaics. Alexis Myers and team developed a mixed-dimensionality hetero-trilayer of SWCNTs between two semiconductors that enables a photoinduced charge transfer cascade where electrons (negative charge carriers) move in one direction while holes (positive charge carriers) move in the other direction.

The hetero-trilayer mimics the natural charge transfer cascade observed in plant photosynthesis, which inspired its development. A key part of the heterostructure is the one-dimensional middle layer, which helps the charge carriers diffuse efficiently from one 2D layer to the other.

The study also looked at the mechanics of carrier diffusion in TMDCs. Using transient absorption spectroscopy, researchers tracked exciton dissociation and charge diffusion across the hetero-trilayer, observing ultrafast electron transfer to one layer and hole transfer to the another. The trilayer architecture appears to facilitate ultrafast hole transfer and exciton dissociation, resulting in a long-lived charge separation.

The charge transfer cascade enables an excited state—where electrons and holes reside in separate places within the trilayer—where photochemical reactions could be initiated. Longer charge separation lifetimes could mean greater electric current generation because more electrons and holes have not recombined.

The trilayer produced double the carrier yield compared with a 2D/1D bilayer. It also empowered the separated charges to overcome the interlayer exciton binding energies of unbound separated charges, a key challenge with such materials.

“These materials have high electrostatic interaction between the electron and hole, yet we have shown that we can successfully separate them through efficient diffusion along the SWCNT mesh,” said NREL’s Alejandra Hermosilla Palacios, a materials science postdoctoral researcher. “Kinetic analysis of the different steps is necessary to understand the efficiency in these systems. We have mostly focused on the diffusion of charges thanks to the SWCNTs. We would like to understand how charges diffuse or move in the TMDC layer to better propose new systems that could lead to higher efficiencies—more electrons and holes generated—and even longer-lived charges (chance for higher electric current generation).”

In previous charge transfer cascades, the mechanism for charge transfer is unclear or does not proceed as expected.

“Our results suggest that well-defined charge transfer cascades can result in longer charge separated lifetimes and higher charge yield (or efficient transfer), paving the way for better understanding of how charges are moving through these systems and how we can continue to optimize them,” Myers said.

“Our results show promising implications for the development of nanoscale optoelectronic devices like solar cells and solar fuel architectures,” Hermosilla Palacios said. “Mixed-dimensionality heterostructures demonstrate photophysics and technological advantages that may enhance and accelerate innovation in optoelectronics.”

For more information: ACS Nano

Image: Charge movement in a mixed-dimensionality hetero-trilayer material: Photoexcited electrons and holes travel from the transition metal dichalcogenide layer (top) through single-walled carbon nanotubes (middle), resulting in a long charge recombination lifetime of 1.2 microseconds, which has potential applications in optoelectronics and energy harvesting. Image by Alexis Myers, NREL.

New technique enables ultrafast imaging of light-matter interactions

Scientists at the SLAC National Accelerator Laboratory, part of the Department of Energy, have uncovered novel properties in an ultrathin material that could revolutionize the way we handle light. This breakthrough is anticipated to benefit optoelectronic devices—those that sense, modulate, or produce light—as well as advance our understanding of light polarization within substances.

These insights emerged during sessions with the laboratory’s rapid “electron camera.” A wide array of common applications, including medical imaging systems, fiber optics, and light-emitting diodes (LEDs), rely on the capabilities of optoelectronic devices.

The team, led by SLAC and Stanford Professor Aaron Lindenberg, discovered that an ultrathin film of tungsten ditelluride, which has desirable properties for polarizing light used in optical devices, will polarize incoming light in a circular pattern when oriented in a particular direction and exposed to linear terahertz radiation.

Terahertz radiation falls between the microwave and infrared regions in the electromagnetic spectrum. It offers new possibilities for material property management and characterization. Scientists want to figure out how to harness light to create optoelectronic devices.

The MeV-UED, the world-leading instrument for ultrafast electron diffraction at the Linac Coherent Radiation Source (LCLS) at SLAC, can capture interactions at ultrafast speeds, which is precisely what is needed to capture a material’s activity under terahertz radiation.

This new work used the femtosecond electron pulses to visualize the electric and magnetic fields of the incoming terahertz pulses, which caused the electrons to wiggle back and forth. Normally, the MeV-UED is used to visualize the motion of atoms by measuring how they scatter electrons after hitting a sample with an electron beam.

Images of the electrons in the investigation that displayed a circular pattern rather than a straight line indicated circular polarization.

The substance was so thin, just 50 nm thick.

Scientists are eager to use these incredibly thin materials, sometimes referred to as two-dimensional (2D) materials, to reduce the size and increase the functionality of optoelectronic devices. According to Lindenberg, they see themselves building devices out of layers of 2D structures, much like Legos.

A distinct material would make up each 2D structure, which would be perfectly aligned to provide a particular kind of optical response. These many shapes and functionalities can be combined to create small devices with potential uses, such as optoelectronic devices or medical imaging.

For more information: SLAC National Accelerator Laboratory

Image: Snapshot taken by SLAC’s high-speed electron camera, an instrument for ultrafast electron diffraction (MeV-UED), showing evidence of circular polarization of terahertz light by an ultrathin sample of tungsten ditelluride. Image Credit: Sie et al., Nano Letters

 

Soft, stretchy electrode simulates touch sensations using electrical signals

Researchers at the University of California San Diego have developed a soft, stretchy electronic device that simulates pressure or vibration sensations when worn on the skin. This innovative device represents a step toward creating haptic technologies capable of reproducing a more varied and realistic range of touch sensations

The device consists of a soft, stretchable electrode attached to a silicone patch. It can be worn like a sticker on either the fingertip or forearm. The electrode, in direct contact with the skin, is connected to an external power source via wires. By sending a mild electrical current through the skin, the device can produce sensations of either pressure or vibration depending on the signal’s frequency.

“Our goal is to create a wearable system that can deliver a wide gamut of touch sensations using electrical signals—without causing pain for the wearer,” said study co-first author Rachel Blau, a nano engineering postdoctoral researcher at the UC San Diego Jacobs School of Engineering.

Existing technologies that recreate a sense of touch through electrical stimulation often induce pain due to the use of rigid metal electrodes, which do not conform well to the skin. The air gaps between these electrodes and the skin can result in painful electrical currents.

To address these issues, Blau and a team of researchers led by Darren Lipomi, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at UC San Diego, developed a soft, stretchy electrode that seamlessly conforms to the skin.

The electrode is made of a new polymer material constructed from the building blocks of two existing polymers: a conductive, rigid polymer known as PEDOT:PSS, and a soft, stretchy polymer known as PPEGMEA. “By optimizing the ratio of these [polymer building blocks], we molecularly engineered a material that is both conductive and stretchable,” said Blau.

The polymer electrode is laser-cut into a spring-shaped, concentric design and attached to a silicone substrate. “This design enhances the electrode’s stretchability and ensures that the electrical current targets a specific location on the skin, thus providing localized stimulation to prevent any pain,” said Abdulhameed Abdal, a Ph.D. student in the Department of Mechanical and Aerospace Engineering at UC San Diego and the study’s other co-first author. Abdal and Blau worked on the synthesis and fabrication of the electrode with UC San Diego nano engineering undergraduate students Yi Qie, Anthony Navarro and Jason Chin.

In tests, the electrode device was worn on the forearm by 10 participants. In collaboration with behavioral scientists and psychologists at the University of Amsterdam, the researchers first identified the lowest level of electrical current detectable. They then adjusted the frequency of the electrical stimulation, allowing participants to experience sensations categorized as either pressure or vibration.

“We found that by increasing the frequency, participants felt more vibration rather than pressure,” said Abdal. “This is interesting because biophysically, it was never known exactly how current is perceived by the skin.”

The new insights could pave the way for the development of advanced haptic devices for applications such as virtual reality, medical prosthetics and wearable technology.

For more information: Science Robotics

Image: Soft, stretchable electrode recreates sensations of vibration or pressure on the skin through electrical stimulation. Photos by Liezel Labios/UC San Diego Jacobs School of Engineering

Scientists develop the next generation of highly efficient memory materials with atom-level control

Similar to the butterfly effect, tiny adjustments can yield significant outcomes. Researchers at Pohang University of Science and Technology (POSTECH) achieved a breakthrough by modifying a material called ‘spin-orbit torque (SOT).’ This material is now a key focus in next-generation DRAM memory.

This research team, led by Professor Daesu Lee and Yongjoo Jo, a Ph.D. candidate, from the Department of Physics and Professor Si-Young Choi from the Department of Materials Science and Engineering at POSTECH, achieved highly efficient field-free SOT magnetization switching through atom-level control of composite oxides.

SOT arises from the interaction between the spin (magnetic property) and motion (electrical property) of electrons. This phenomenon controls the magnetic state through the movement of spin when current flows. By utilizing magnetic information instead of electrical information, memory power consumption is reduced, making it advantageous for non-volatile memory which retains information even when powered off.

Researchers have been actively exploring various materials including semiconductors and metals for these applications. Particularly, there is significant interest in discovering materials that exhibit both magnetism and the “spin-Hall effect.”

The study of efficient magnetization switching via SOTs has garnered much attention. However, a challenge remains: opposite spin currents generated within a single layer tend to cancel each other out.

In this study, Professors Daesu Lee and Si-Young Choi from POSTECH addressed the problem by systematically modifying the material’s seemingly insignificant structure. Strontium ruthenate (SrRuO3), a complex oxide known for exhibiting both magnetism and spin-Hall effects, has been widely used in SOT research.

The team synthesized SrRuO3 with asymmetric spin-Hall effects on the top and bottom surface layers by minutely adjusting the atomic lattice structure of these layers. By creating an imbalance in the spin-Hall effect with a strategically designed asymmetric surface structure, they were able to control the magnetization in a specific direction.

Building on this approach, the team successfully achieved efficient magnetization switching without the need for a magnetic field. By incorporating SOT into a device based on SrRuO3, they could reorient the magnetic domain using only an electric current to write and read data.

The resulting memory device demonstrated the highest efficiency (2 to 130 times greater) and lowest power consumption (2 to 30 times lower) compared to any known single-layer, field-free system to date. This magnetization switching was accomplished without a magnetic field while preserving the conventional properties of SrRuO3 used in previous studies.

Professor Daesu Lee of POSTECH says, “The asymmetric SrRuO3 synthesized by the team is a crucial platform for studying the interaction between ferromagnetism and the spin-Hall effect.” He added, “We look forward to further research to uncover new SOT mechanisms and develop highly efficient, room-temperature, single-phase SOT materials.”

For more information: Nano Letters

Image: Atomic structure of asymmetric SrRuO3 thin films and spin-orbit torque magnetization switching results controlled at the atomic layer level. Credit: POSTECH

Recent advances in twisted bilayer graphene

Graphene, a widely studied 2D material, exhibits exceptional physical and electronic properties. Twisting two graphene monolayers at a small angle creates twisted bilayer graphene (tBLG), which forms a superlattice. The moiré pattern resulting from relative layer orientation has driven significant progress in graphene research, enhancing its optical and electrical properties, including superconductivity.

The mechanical, optical, and electronic properties of multilayer graphene structures can be tailored by altering the stacking order, interlayer spacing, and relative twisting angle (θ). Similarly, tBLG is fabricated by stacking two single-layer graphene sheets, synthesized by chemical vapor deposition (CVD), at a specific twisting angle.

The unusual stacking imparts various angle-dependent properties to tBLG.

Moiré patterns are generated by graphene-graphene interactions resulting from the relative layer orientations. These highly periodic patterns are responsible for the extraordinary optical and electronic properties of tBLG. Additionally, tBLG exhibits twisting angle-dependent Dirac spectra (similar to chirality dependence in carbon nanotubes), Fermi velocity, magnetoresistance oscillations, and quantum Hall effect.

Innovative methods are being explored to fabricate tBLG with small twist angles. For example, hexagonal boron nitride is utilized to obtain graphene layers with rotationally aligned crystal axes. tBLG is also prepared by cutting, rotating, and stacking a graphene layer through femtosecond laser micromachining and precise transfer.

Other methods for preparing tBLG films include controlled hydrophilic and hydrophobic boundary folding of single-layer graphene and vertical stacking.

Easy twisting and stacking of two graphene layers can result in a uniform and ordered moiré superlattice capable of exhibiting unusual superconductivity and correlations in tBLG. However, the twist angle becomes rigid after interlayer stacking. Alternatively, mechanical elastic strain can help control the electronic structure of tBLG by regulating the lattice spacing and symmetry.

A recent study reviewed various innovations in straining tBLG by in-plane and out-of-plane modes. It included the characterizations and calculations performed to quantitatively tune the strain-engineered electronic structures.

Another study demonstrated a topological superconducting state in tBLG depending only on the moiré minibands instead of the twist angle tuning. The method involved subjecting tBLG to induced Rashba spin-orbit coupling, s-wave superconductivity, and exchange field and is valid for 1.3 to 3 degrees twist angles. This approach could be feasible for developing a tBLG-based quantum computer.

Despite several research advances and potential applications, significant challenges remain in achieving controlled twisting of two graphene layers to fabricate and characterize tBLG. Additionally, precise stacking of bilayer graphene at the first magic angle of 1.1 degrees to observe superconductivity is tedious due to the intrinsic disruptions caused by strain and angular disorder.

Modifications in the twist angle significantly alter the spatial wavefunction distribution. While this allows engineering bandgaps in tBLG for electronic applications, the localized wavefunction at certain twist angles leads to a sudden reduction in carrier mobility. This can negatively influence the tBLG-based device performance. Hence, careful considerations are required to obtain preferred electronic characteristics and carrier mobility for ideal device functioning.

The ultrathin nature of tBLG leads to localized stretching or compression due to substrate deformation or thermal stresses during fabrication. Despite the positive impact of these localized strains on the physical properties of the material, their non-uniformity hinders practical device applications of the material.

The constant improvements in the synthesis, characterization, and electronic structure determination techniques are anticipated to accelerate the tBLG-related advances and applications. This, in turn, may lead to the advancement of “twistronics,” the fusion of “twist” and “electronics,” which exploits the electronic properties of layered materials like graphene changing with the twist angle.

The strain engineering of twisted 2D materials like tBLG can further expand “twistronics” and “straintronics” into the realm of “strain-twistronics.” Consequently, novel ferroelectric and optoelectronic devices with tunable characteristics and regulated performance may become a reality in the future.

For more information: AZO Nano

AI chips could get a sense of time

Researchers have developed the first memristor with a tunable ‘relaxation time,’ potentially enabling artificial neural networks to process time-dependent data more efficiently. The study was led by the University of Michigan.

Memristors, electrical components that store information in their electrical resistance, could reduce AI’s energy needs by about a factor of 90 compared to today’s graphical processing units. Already, AI is projected to account for about half a percent of the world’s total electricity consumption in 2027, which has the potential to balloon as more companies sell and use AI tools.

“Right now, there’s a lot of interest in AI, but to process bigger and more interesting data, the approach is to increase the network size. That’s not very efficient,” said Wei Lu, the James R. Mellor Professor of Engineering at U-M and co-corresponding author of the study with John Heron, U-M associate professor of materials science and engineering.

The problem is that GPUs operate very differently from the artificial neural networks that run the AI algorithms—the whole network and all its interactions must be sequentially loaded from the external memory, which consumes both time and energy. In contrast, memristors offer energy savings because they mimic key aspects of the way that both artificial and biological neural networks function without external memory. To an extent, the memristor network can embody the artificial neural network.

“We anticipate that our brand-new material system could improve the energy efficiency of AI chips six times over the state-of-the-art material without varying time constants,” said Sieun Chae, a recent U-M Ph.D. graduate in materials science and engineering and co-first-author of the study with Sangmin Yoo, a recent U-M PhD graduate in electrical and computer engineering.

In a biological neural network, timekeeping is achieved through relaxation. Each neuron receives electrical signals and sends them on, but it isn’t a guarantee that a signal will move forward. Some threshold of incoming signals must be reached before the neuron will send its own, and it has to be met in a certain amount of time. If too much time passes, the neuron is said to relax as the electrical energy seeps out of it. Having neurons with different relaxation times in our neural networks helps us understand sequences of events.

Memristors operate a little differently. Rather than the total presence or absence of a signal, what changes is how much of the electrical signal gets through. Exposure to a signal reduces the resistance of the memristor, allowing more of the next signal to pass. In memristors, relaxation means that the resistance rises again over time.

While Lu’s group had explored building relaxation time into memristors in the past, it was not something that could be systematically controlled. But now, Lu and Heron’s team have shown that variations on a base material can provide different relaxation times, enabling memristor networks to mimic this timekeeping mechanism.

The team built the materials on the superconductor YBCO, made of yttrium, barium, carbon and oxygen. It has no electrical resistance at temperatures below -292 Fahrenheit, but they wanted it for its crystal structure. It guided the organization of the magnesium, cobalt, nickel, copper and zinc oxides in the memristor material.

Heron calls this type of oxide, an entropy-stabilized oxide, the “kitchen sink of the atomic world”—the more elements they add, the more stable it becomes. By changing the ratios of these oxides, the team achieved time constants ranging from 159 to 278 nanoseconds, or trillionths of a second. The simple memristor network they built learned to recognize the sounds of the numbers zero to nine. Once trained, it could identify each number before the audio input was complete.

These memristors were made through an energy-intensive process because the team needed perfect crystals to precisely measure their properties, but they anticipate that a simpler process would work for mass manufacturing.

“So far, it’s a vision, but I think there are pathways to making these materials scalable and affordable,” Heron said. “These materials are earth-abundant, nontoxic, cheap and you can almost spray them on.”

For more information: Nature Electronics

Image: The entropy-stabilized oxide is sandwiched between the superconductor YBCO, on which it was grown, and a titanium and platinum electrode. The many colors represent the different components of the entropy-stabilized oxide. By tweaking the ratios of the components, the team could create memristors that relaxed at different rates after exposure to an electrical current, mimicking the way that neurons sense time. Credit: Sieun Chae and Sangmin Yoo, University of Michigan.

Kentucky Junior wins international science fair

Grace Sun, a junior at Paul Laurence Dunbar High School in Kentucky, earned the top prize at the 2024 Regeneron International Science & Engineering Fair (ISEF) in the Materials Science category. Her entry, “Novel Chemical Doping Strategy to Enhance N-Type Organic Electrochemical Transistors,”researches building a better organic electrochemical transistor that she hopes will be used to develop new electronic devices that could help detect and treat serious illnesses like diabetes, epilepsy, and organ failure.

ISEF drew nearly 2,000 students from all over the world. Capping this year’s competition in Los Angeles, Regeneron and Society for Science presented Grace the $75,000 honor for the George D. Yancopoulos Innovator Award, which goes to the best first-place project based on outstanding and innovative research as well as the potential impact of her work.

Dunbar High School also had two other students to place in their respective divisions at ISEF. Alex Thuringer was fourth in Engineering Technology for “An Improved Color Filter Array Design Using Metafilters,” and Joseph Vulakh placed fourth in Mathematics for “Twisted Homogeneous Racks over the Alternating Groups.”

For more information: Fayette County Public Schools

Image: Grace Sun at the Los Angeles competition.

Organic semiconductors doped with air to increase conductivity in new study

Researchers have discovered that doping organic semiconductors with air can significantly enhance their electrical conductivity. This breakthrough could lead to more efficient organic electronic devices, such as flexible displays and sensors

Semiconductors are the foundation of all modern electronics. Now, researchers at Linköping University have developed a new method where organic semiconductors can become more conductive with the help of air as a dopant. The study is a significant step towards future cheap and sustainable organic semiconductors.

“We believe this method could significantly influence the way we dope organic semiconductors. All components are affordable, easily accessible, and potentially environmentally friendly, which is a prerequisite for future sustainable electronics,” says Simone Fabiano, associate professor at Linköping University.

Semiconductors based on conductive plastics instead of silicon have many potential applications. Among other things, organic semiconductors can be used in digital displays, solar cells, LEDs, sensors, implants, and for energy storage.

To enhance conductivity and modify semiconductor properties, so-called dopants are typically introduced.

These additives facilitate the movement of electrical charges within the semiconductor material and can be tailored to induce positive (p-doping) or negative (n-doping) charges. The most common dopants used today are often either very reactive (unstable), expensive, challenging to manufacture, or all three.

Now, researchers at Linköping University have developed a doping method that can be performed at room temperature, where inefficient dopants such as oxygen are the primary dopant, and light activates the doping process.

“Our approach was inspired by nature, as it shares many analogies with photosynthesis, for example. In our method, light activates a photocatalyst, which then facilitates electron transfer from a typically inefficient dopant to the organic semiconductor material,” says Simone Fabiano.

The new method involves dipping the conductive plastic into a special salt solution – a photocatalyst – and then illuminating it with light for a short time. The duration of illumination determines the degree to which the material is doped. Afterwards, the solution is recovered for future use, leaving behind a p-doped conductive plastic in which the only consumed substance is oxygen in the air.

This is possible because the photocatalyst acts as an “electron shuttle”, taking electrons or donating them to material in the presence of sacrificial weak oxidants or reductants. This is common in chemistry but has not been used in organic electronics before.

“It’s also possible to combine p-doping and n-doping in the same reaction, which is quite unique. This simplifies the production of electronic devices, particularly those where both p-doped and n-doped semiconductors are required, such as thermoelectric generators. All parts can be manufactured at once and doped simultaneously instead of one by one, making the process more scalable,” says Simone Fabiano.

The doped organic semiconductor has better conductivity than traditional semiconductors, and the process can be scaled up. Simone Fabiano and his research group at the Laboratory of Organic Electronics showed earlier in 2024 how conductive plastics could be processed from environmentally friendly solvents like water; this is their next step.

“We are at the beginning of trying to fully understand the mechanism behind it and what other potential application areas exist. But it’s a very promising approach showing that photocatalytic doping is a new cornerstone in organic electronics,” says Simone Fabiano, a Wallenberg Academy Fellow.

For more information: Nature

‘Surprising’ hidden activity of semiconductor material spotted by researchers

New research suggests that materials commonly overlooked in computer chip design actually play an important role in information processing, a discovery which could lead to faster and more efficient electronics.

Using advanced imaging techniques, an international team led by Penn State researchers found that the material that a semiconductor chip device is built on, called the substrate, responds to changes in electricity much like the semiconductor on top of it.

The researchers worked with the semiconductor material, vanadium dioxide, which they said shows great potential as an electronic switch. They also studied how vanadium dioxide interacts with the substrate material titanium dioxide and said they were surprised to discover that there seems to be an active layer in the substrate that behaves similarly to the semiconductor material on top of it when the semiconductor switches between an insulator — not letting electricity flow — and a metal — letting electricity flow. The revelation that substrates can play an active role in semiconductor processes is significant for designing future materials and devices, said study lead Venkatraman Gopalan, professor of materials science and engineering and of physics at Penn State.

The potential of vanadium dioxide as a metal-to-insulator transistor is well-documented and the material is considered promising for semiconductor technology due to its low energy consumption, Gopalan said. However, the material’s properties are still not fully understood, and until now, it has usually been observed in isolation rather than while functioning in a real device.

Vanadium dioxide has strongly correlated electronic effects, meaning the repulsion between electrons interferes with the device, so cannot be ignored as is currently done in silicon-based electronics. This characteristic can result in materials with novel functionalities such as high-temperature superconductivity and enhanced magnetic properties.

The team investigated vanadium dioxide in a device rather than in isolation, applying a voltage to it to make it switch from an insulating to a conducting state. They used the Advanced Photon Source (APS) at Argonne National Laboratory, which uses powerful X-ray beams to study the behavior and structure of materials on the atomic level. When mapping the spatial and temporal response of the material to the switching event, the researchers observed unexpected changes to the structure of the material and substrate.

“What we found was that as the vanadium dioxide film changes to a metal, the whole film channel bulges, which is very surprising,” Gopalan said. “Normally it is supposed to shrink. So clearly something else was going on in the film geometry that was missed before.”

The APS X-ray penetrated through the vanadium dioxide film and into the titanium dioxide (TiO2) substrate — which is normally considered an electrically and mechanically passive material — that the thin film was grown on.

To understand these findings, the theory and simulation effort — led by Long-Qing Chen, Hamer Professor of Materials Science and Engineering, professor of engineering science and mechanics and of mathematics at Penn State — developed a theoretical framework to explain the entire process of the film and the substrate bulging instead of shrinking. When their model incorporated naturally occurring missing oxygen atoms in this material of two types, charged and uncharged, the experimental results could be satisfactorily explained.

Gopalan credited the multidisciplinary team’s combined expertise in material growth, synthesis, structure analysis and synchrotron beamline operation with the new understanding. Using a collaborative approach led by Greg Stone, a physical scientist with the U.S. Army and the lead experimental author, and Yin Chi, postdoctoral scholar at Penn State and the lead theory author, the researchers disentangled the material’s responses and observed them individually using phase field simulations, a simulation that helps scientists understand material changes over time by depicting various states of matter in a virtual setting.

The responses themselves require further investigation, researchers said, but they believe that understanding them will assist in identifying previously unknown capabilities of vanadium dioxide, including potential yet-to-be discovered phenomena in the TiO2 substrate that was considered passive before this study. The study itself unfolded over 10 years, Gopalan noted, including validating the results.

“This is what it takes to go from interesting science to a working device you can hold in the palm of your hand,” Gopalan said. “Experiments and theory are complex and require large-scale collaborative teams working closely together over an extended period of time to solve difficult problems that could have a large impact. We hope and expect that this will accelerate the progress towards a new generation of electronic devices.”

For more information: AdvancedMaterials

Image: Venkatraman Gopalan, professor of materials science and engineering and of physics, in his optical lab