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National Science Foundation awards environmental engineering and advanced manufacturing grants to mechanical engineering department

Posted By Graphene Council, Wednesday, June 17, 2020
The National Science Foundation, or NSF, has granted assistant professors of mechanical engineering, Guoping Xiong and Pradeep Menezes, research awards for their respective projects.

Xiong’s research will be especially useful for cleanup after oil spills into water ecosystems and recovery. In collaboration with the University of Notre Dame, Xiong’s research focuses on understanding the nature of interaction between oil and graphene nanochannels. It will be achieved through experiments designed to explain the mechanisms governing the synergistic effects of the nanochannel geometry and surface functionalization of plasma-nanoengineered, vertically standing graphene petal oil skimmers.

Menezes’ research, titled “Understanding Interfacial Mechanisms to Design and Manufacture High-Performance Biodegradable Ionic Liquid Lubricants.” Many mechanical moving assemblies, or MMAs, require lubrication, and most MMAs use petroleum-based lubricants, which is not environmentally friendly. Menezes’s research will provide new bio-based lubricants that can replace petroleum-based lubricants and reduce the overall carbon footprint of MMAs, positively impacting the environment. Mano Misra, professor of chemical and materials engineering, will be a co-principal investigator.

Tags:  Graphene  Guoping Xiong  Pradeep Menezes  The National Science Foundation 

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Researchers develop new hydrogen-generating photocatalyst design

Posted By Graphene Council, Wednesday, June 17, 2020

Researchers from the Indian Institute of Technology (IIT) Mandi, in collaboration with researchers from Yogi Vemana University, have designed a novel photocatalyst that can remove pollutants from water while simultaneously generating hydrogen using sunlight.

The researchers have designed a series of novel and multifunctional nanocomposite photocatalysts by coupling mesocrystals of calcium titanate with edge sulphur atoms enriched molybdenum disulphide and reduced graphene oxide. A specific and useful example of a photocatalytic reaction is the splitting of water into hydrogen and oxygen. Although this reaction was demonstrated as early as 1972 by Fujishima and Honda, the inefficiency of the process has been a bottleneck in scaling up the technology for practical applications. In addition, the researchers have also used these photocatalysts in the degradation of organic pollutants found in water.

“The performance of a photocatalytic reaction depends upon the efficiency with which the photocatalyst converts light energy into photogenerated charges that drives the reaction of interest,” explains Dr Venkata Krishnan, Associate Professor, School of Basic Sciences, IIT Mandi. Photocatalysts work by generating electron-hole pairs when exposed to light of specific wavelengths, which induces the reaction they are meant to catalyze. Oxide materials such as titania and titanates are commonly studied photocatalysts, but these materials are often inefficient by themselves because the electrons and holes combine before the reaction can be propelled forward.

“Mesocrystals, a new class of ‘superstructures’ made of highly ordered nanoparticles, could limit the recombination of electron-hole pairs because the free electrons that are generated flow between particles before they can recombine with the hole,” says Dr. Venkata Krishnan.

“The performance of a photocatalytic reaction depends upon the efficiency with which the photocatalyst converts light energy into photogenerated charges that drives the reaction of interest,”

“Our combination showed a 33-fold enhanced photocatalytic hydrogen evolution over pure calcium titanate, with apparent light-to-electron conversion efficiencies of 5.4%, 3.0% and 17.7% for light of three different wavelengths, orange light (600 nm wavelength) producing the highest efficiency”, says Dr. Venkata Krishnan. The mesocrystal-semiconductor-graphene combination also degrades many kinds of organic pollutants when exposed to light, which makes it promising for pollution control techniques.

Dr. Venkata Krishnan attributes the enhancement in photocatalytic performance of their material combination, to three factors: (a) the intimate contact between the three components, which leads to better electron transfer; (b) the high surface area that provides more space for the reaction to take place; and (c) specific sites on molybdenum disulphide (MoS2) that act as sticky sites for the positive hydrogen ions that are generated during the reaction, which, in turn, enhances hydrogen production.

It may be known that graphene is the new “wonder-material” in the field of materials science, ever since its isolation earned the Nobel Prize in 2010. The scientists at IIT Mandi found that remarkable enhancement in photocatalytic activity could be achieved with this combination.

Tags:  Environment  Graphene  Indian Institute of Technology Mandi  nanocomposite  Venkata Krishnan  Yogi Vemana University 

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Uwin Chemical Technology Co Sign Distributor Agreement for Taiwan

Posted By Graphene Council, Wednesday, June 17, 2020
Haydale is pleased to announce that it has signed a distributor agreement between Haydale and Uwin chemical Technology Co., Ltd. The Agreement is for a period of 24 months and allows Uwinchem exclusive distributor rights to market Haydale’s products in Taiwan.

Uwinchem is a leading provider of advanced materials and chemical process solutions in Taiwan and the Agreement provides the opportunity for it to promote and supply Haydale’s functionalised graphene and other 2D materials to the Taiwan market.

Of particular interest are the medical, automotive and aerospace markets, where Uwinchem will promote composite materials, inks and sensors for semiconductor, thermal management and mechanical benefits.

Titus Huang, President at Uwinchem, said: “Uwinchem welcomes the addition of Haydale’s Graphene and 2D material products and solutions to its portfolio. With Haydale’s products already proven and in use in cutting edge automotive, aeronautical and medical applications, we welcome the opportunity to help clients improve performance significantly.”

Keith Broadbent, Haydale CEO, said: “We are pleased to partner with Uwinchem on its specialist technical areas of expertise. We believe our current range of products and services will provide the next level ground-breaking products in the Taiwanese Market.”

Tags:  2D materials  composites  Graphene  Haydale  Keith Broadbent  Titus Huang  Uwin chemical Technology 

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Newly observed phenomenon could lead to new quantum devices

Posted By Graphene Council, Monday, June 15, 2020
An exotic physical phenomenon known as a Kohn anomaly has been found for the first time in an unexpected type of material by researchers at MIT and elsewhere. They say the finding could provide new insights into certain fundamental processes that help determine why metals and other materials display the complex electronic properties that underlie much of today’s technology.

The way electrons interact with phonons — which are essentially vibrations passing through a crystalline material — determines the physical processes that take place inside many electronic devices. These interactions affect the way metals resist electric current, the temperature at which some materials suddenly become superconductors, and the very low temperature requirements for quantum computers, among many other processes.

But electron-phonon interactions have been difficult to study in detail because they are generally very weak. The new study has found a new, stronger kind of unusual electron-phonon interaction: The researchers induced a Kohn anomaly, which was previously thought to exist only in metals, in an exotic material called a topological Weyl semimetal. The finding could help shed light on important aspects of the complex interplay between electrons and phonons, they say.

The new finding, based on both theoretical predictions and experimental observation, is described this week in the journal Physical Review Letters, in a paper by MIT graduate students Thanh Nguyen and Nina Andrejevic, postdoc Ricardo Pablo-Pedro, Research Scientist Fei Han, Professor Mingda Li, and 14 others at MIT and several other universities and national laboratories.

Kohn anomalies, first discovered in the 1950s by physicist Walter Kohn, reflect a sudden change, sometimes described as a kind of kink or wiggle, in the graph describing a physical parameter called the electron response function. This discontinuity in an otherwise smooth curve reflects a sudden change of the capability of electrons for shielding phonons. This can give rise to instabilities in the propagation of electrons through the material, and can lead to many new electronic properties.

These anomalies have been observed before in certain metals and in other highly electrically conductive materials such as graphene, but had never been seen or predicted before in a “topological material,” whose electrical behaviors are robust against perturbation. In this case, a kind of topological material called a Weyl semimetal, specifically tantalum phosphide, was found to be capable of exhibiting this unusual anomaly. Unlike in conventional metals, where a property called the Fermi surface drives the formation of the Kohn anomaly, in this material, the Weyl points serve as the driving force.

Because electron-phonon couplings are taking place practically everywhere all the time, they can be a major source of disturbance in delicate physical systems such as those used to represent data in quantum computers. Measuring the strength of these interactions, which is key to knowing how to protect such quantum-based technologies, has been very difficult, but this new finding, Li says, provides a way of making such measurements. “The Kohn anomaly can be used to quantify how strong the electron-phonon coupling can be,” he says.

To measure the interactions, the team made use of advanced neutron and X-ray scattering probes at three national laboratories — Argonne National Laboratory, Oak Ridge National Laboratory, and the National Institute of Standards and Technology — to probe the behavior of the tantalum phosphide material. “We predicted that there is a Kohn anomaly in the material just based on pure theory,” Li explains, Using their calculations, “we could guide the experiments to the point where we want to search for the phenomenon, and we see a very good agreement between theory and the experiments.”

Martin Greven, a professor of physics at the University of Minnesota who was not involved in this research, says this work “has impressive breadth and depth, spanning both sophisticated theory and scattering experiments. It breaks new ground in condensed matter physics, in that it establishes a new kind of Kohn anomaly.”

A better understanding of the electron-phonon couplings could help lead the way to developing such materials as better high-temperature superconductors or fault-tolerant quantum computers, the researchers say. This new tool could be used to probe material properties in search of those that remain relatively unaffected at higher temperatures.

Brent Fultz, a professor of materials science and applied physics at Caltech, who was also not involved in this work, adds that “perhaps these effects will help the development of materials with new thermal or electronic properties, but since they are so new, we need time to think about what they can do.”

Nguyen, the paper’s lead author, says he thinks this work helps to demonstrate the sometimes overlooked importance of phonons in the behavior of topological materials. Materials such as these, whose surface electrical properties are different from those of the bulk material, are a hot area of current research. “I think this could lead us to further understand processes that would underlie some of these materials that hold a lot of promise for the future,” says Andrejevic, who along with Han was a co-lead author on the paper.

“Although electron-phonon interaction is long known to exist, the experimental prediction and observation of these interactions is exceedingly rare,” says professor of physics and astronomy Pengcheng Dai at Rice University, who also was not involved in this work. These results, he says, “provide an excellent demonstration of the power of combined theory and experiments as a way to extend our understanding of these exotic materials.”

Tags:  Brent Fultz  Caltech  Graphene  Martin Greven  Massachusetts Institute of Technology  Mingda Li  quantum materials  University of Minnesota 

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Lightning in a (nano)bottle: new supercapacitor opens door to better wearable electronics

Posted By Graphene Council, Friday, June 12, 2020
Researchers from Skoltech, Aalto University and Massachusetts Institute of Technology have designed a high-performance, low-cost, environmentally friendly, and stretchable supercapacitor that can potentially be used in wearable electronics. The paper was published in the Journal of Energy Storage.

Supercapacitors, with their high power density, fast charge-discharge rates, long cycle life, and cost-effectiveness, are a promising power source for everything from mobile and wearable electronics to electric vehicles. However, combining high energy density, safety, and eco-friendliness in one supercapacitor suitable for small devices has been rather challenging.

"Usually, organic solvents are used to increase the energy density. These are hazardous, not environmentally friendly, and they reduce the power density compared to aqueous electrolytes with higher conductivity," says Professor Tanja Kallio from Aalto University, a co-author of the paper.

The researchers proposed a new design for a "green" and simple-to-fabricate supercapacitor. It consists of a solid-state material based on nitrogen-doped graphene flake electrodes distributed in the NaCl-containing hydrogel electrolyte. This structure is sandwiched between two single-walled carbon nanotube film current collectors, which provides stretchability. Hydrogel in the supercapacitor design enables compact packing and high energy density and allows them to use the environmentally friendly electrolyte.

The scientists managed to improve the volumetric capacitive performance, high energy density and power density for the prototype over analogous supercapacitors described in previous research. "We fabricated a prototype with unchanged performance under the 50% strain after a thousand stretching cycles. To ensure lower cost and better environmental performance, we used a NaCl-based electrolyte. Still the fabrication cost can be lowered down by implementation of 3D printing or other advanced fabrication techniques," concluded Skoltech professor Albert Nasibulin.

Tags:  Aalto University  Albert Nasibulin  Electronics  Graphene  Massachusetts Institute of Technology  Supercapacitor  Tanja Kallio 

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New investors for INBRAIN to develop graphene-based implants against brain disorders

Posted By Graphene Council, Friday, June 12, 2020
INBRAIN Neuroelectronics, a spin-off of the Catalan Institute of Nanoscience and Nanotechnology and ICREA, receives funding from Sabadell Asabys and Alta Life Sciences, as well as ICF and Finaves, which will allow the company to speed up the development of novel graphene-based implants to optimise the treatment of brain disorders, such as Parkinson's and epilepsy.

According to a 2010 study commissioned by the European Brain Council, the cost of brain disorders in Europe alone reaches approximately 800 billion euros a year, with more than one-third of the population affected. The high incidence of brain-related diseases worldwide and their huge social cost call for greater investments in basic research in this field, with the aim of developing new and more efficient therapeutic and diagnostic tools.

INBRAIN Neuroelectronics, a spin-off of the Catalan Institute of Nanoscience and Nanotechnology (ICN2) and ICREA, was established in 2019 with the mission to develop brain-implants based on graphene technology for application in patients with epilepsy, Parkinson’s and other neuronal diseases. These smart devices, built around an innovative graphene electrode, will decode with high fidelity neural signals from the brain and produce a therapeutic response adapted to the clinical condition of the specific patient.

Additional resources have been recently injected into this endeavour by new investors — in particular Asabys and Alta Life Sciences, through the Sabadell-Asabys funds, followed by the Institut Català de Finances (ICF) and Finaves (fund promoted and managed by IESE Business School) — and other existing shareholders, such as the ICN2 and ICREA themselves. It will allow INBRAIN to accelerate the development of these novel intracranial implants for patients affected by brain disorders.

The company is designing the least invasive and smartest neural interface on the market that, powered by artificial intelligence and the use of Big Data, will have the ability to read and modulate brain activity, detect specific biomarkers and trigger adaptive responses to deliver optimal results in personalised neurological therapies. So far, the technology has been validated in in-vitro and in-vivo biocompatibility and toxicity tests and it has been successfully used to complete studies on small animals. Recently, INBRAIN has begun tests on large animals with the aim of ensuring that these graphene devices are safe, as well as superior to current solutions based on metals such as platinum and iridium. The company also plans to start soon human studies.

INBRAIN was founded, among others, by ICREA Prof. Jose Garrido, leader of the ICN2 Advanced Electronic Materials and Devices Group, Prof. Kostas Kostarelos, leader of the ICN2 Nanomedicine Group, and Dr Anton Guimerà, a researcher at the Spanish National Centre of Microelectronics (IMB-CNM). "Within the framework of the Graphene Flagship, which is a European macroproject”, explains Prof. Garrido, "we were able to develop this novel graphene-based technology that will allow measuring and stimulating neuronal activity in the brain with a resolution much higher than that of current commercial technologies”. During 2019, the incorporation of INBRAIN was a priority project for the ICN2 Business and Innovation Department, which coordinated the technology transfer process and successfully orchestrated the licensing of this high-potential technology.

“Minimally invasive electronic therapies represent a revolutionary alternative with less potential cost for health systems,” comments Carolina Aguilar, CEO of INBRAIN and a former global executive at Medtronic in the field of neuro-stimulation. "In our case, the application of new 2D materials such as graphene represents a real opportunity to understand how the brain works in order to optimise and personalise the treatment.”

Tags:  Carolina Aguilar  Graphene  ICN2  ICREA  IMB-CNM  INBRAIN 

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Smallest cavity for light realized by graphene plasmons

Posted By Graphene Council, Friday, June 12, 2020
Miniaturization has enabled so many unfathomable dreams. Shrinking down electronic circuits has allowed us to access technology like smartphones, health watches, medical probes, nano-satellites, unthinkable a couple decades ago. Just imagine that in the course of 60 years, the transistor has gone from being the size of your hand palm to 14 nanometers in dimension, 1000 times smaller than the diameter of a hair.

Miniaturization has pushed technology to a new era of optical circuitry. But, in parallel, it has also triggered new challenges and obstacles to overcome, for example, on how to deal with controlling and guiding light at the nanometer scale. New techniques have been on the rise searching for ways to confine light into extremely tiny spaces, millions of times smaller than current ones. Researchers had earlier on found that metals can compress light below the wavelength-scale (diffraction limit).

In that aspect, Graphene - a material composed from a single layer of carbon atoms, with exceptional optical and electrical properties, is capable of guiding light in the form of "plasmons", which are oscillations of electrons that are strongly interacting with light. These graphene plasmons have a natural ability to confine light to very small spaces. However, until now it was only possible to confine these plasmons in one direction, while the actual ability of light to interact with small particles, like atoms and molecules, resides in the volume that it can be compressed into. This type of confinement, in all three dimensions, is commonly regarded as an optical cavity.

In a recent study published in Science, ICFO researchers Itai Epstein, David Alcaraz, Varum-Varma Pusapati, Avinash Kumar, Tymofiy Khodkow, led by ICREA Prof. at ICFO Frank Koppens, in collaboration with researchers from MIT, Duke University, Université Paris-Saclay, and Universidad do Minho, have succeeded to build a new type of cavity for graphene plasmons, by integrating metallic cubes of nanometer sizes over a graphene sheet. Their approach enabled to realize the smallest optical cavity ever built for infrared light, which is based on these plasmons.

In their experiment they used silver nanocubes of 50 nanometers in size, which were sprinkled randomly on top of the graphene sheet, with no specific pattern or orientation. This allowed each nanocube, together with graphene, to act as a single cavity. Then they sent infrared light through the device and observed how the plasmons propagated into the space between the metal nanocube and the graphene, being compressed only to that very small volume.

As Itai Epstein, first author of the study, comments, "the main obstacle that we encountered in this experiment resided in the fact that the wavelength of light in the infrared range is very large and the cubes are very small, about 200 times smaller, so it is extremely difficult to make them interact with each other."

In order to overcome this, they used a special phenomenon - when the graphene plasmons interacted with the nanocubes, they were able to generate a special resonance, called a magnetic resonance. As Epstein clarifies, "A unique property of the magnetic resonance is that it can act as a type of antenna that bridges the difference between the small dimensions of the nanocube and the large scale of the light." Thus, the generated resonance maintained the plasmons moving between the cube and graphene in a very small volume, which is ten billion times smaller than the volume of regular infrared light, something never achieved before in optical confinement. Even more so, they were able to see that the single graphene-cube cavity, when interacting with the light, acted as a new type of nano-antenna that is able to scatter the infrared light very efficiently.

The results of the study are extremely promising for the field of molecular and biological sensing, important for medicine, biotechnology, food inspection or even security, since this approach is capable of intensifying the optical field considerably and thus detect molecular materials, which usually respond to infrared light.

As Prof. Koppens states "such achievement is of great importance because it allows us to tune the volume of the plasmon mode to drive their interaction with small particles, like molecules or atoms, and be able to detect and study them. We know that the infrared and Terahertz ranges of the optical spectrum provide valuable information about vibrational resonances of molecules, opening the possibility to interact and detect molecular materials as well as use this as a promising sensing technology".

Tags:  Duke University. Sensors  Frank Koppens  Graphene  ICFO  Itai Epstein 

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Cascade sets the stage for superconductivity in magic-angle twisted bilayer graphene

Posted By Graphene Council, Friday, June 12, 2020
Place a single sheet of carbon atop another at a slight angle and remarkable properties emerge, including the highly prized resistance-free flow of current known as superconductivity.

Now a team of researchers at Princeton University has looked for the origins of this unusual behavior in a material known as magic-angle twisted bilayer graphene, and detected signatures of a cascade of energy transitions that could help explain how superconductivity arises in this material. The study was published June 11 in the journal Nature.

“This study shows that the electrons in magic-angle graphene are in a highly correlated state even before the material becomes superconducting,” said Ali Yazdani, Class of 1909 Professor of Physics, the leader of the team that made the discovery. “The sudden shift of energies when we add or remove an electron in this experiment provides a direct measurement of the strength of the interaction between the electrons.”

This is significant because these energy jumps provide a window into the collective behaviors of electrons, such as superconductivity, that emerge in magic-angle twisted bilayer graphene, a material composed of two layers of graphene in which the top sheet is rotated by a slight angle relative to the other.

In everyday metals, electrons can move freely through the material, but collisions among electrons and from the vibration of atoms give rise to resistance and the loss of some electrical energy as heat – which is why electronic devices get warm during use.

In superconducting materials, electrons cooperate. “The electrons are kind of dancing with each other,” said Biao Lian, a postdoctoral research associate in the Princeton Center for Theoretical Science who will become an assistant professor of physics this fall, and one of the co-first authors of the study. “They have to collaborate to go into such a remarkable state.”

By some measures, magic-angle graphene, discovered two years ago by Pablo Jarillo-Herrero and his team at the Massachusetts Institute of Technology (MIT), is one of the strongest superconductors ever discovered. Superconductivity is relatively robust in this system even though it occurs when there are very few freely moving electrons.

The researchers set out to explore how the unique crystal structure of magic-angle graphene enables collective behaviors. Electrons not only have a negative charge, but also two other characteristics: angular momentum or “spin,” and possible movements in the crystal structure known as “valley” states. Combinations of spin and valley make up the various “flavors” of electrons.

The team particularly wanted to know how these flavors affect collective behaviors, so they conducted their experiments at temperatures just slightly above the point at which the electrons become strongly interacting, which the researchers likened to the parent phase of the behaviors.

“We measured the force between the electrons in the material at higher temperatures in the hopes that understanding this force will help us understand the superconductor that it becomes at lower temperatures,” said Dillon Wong, a postdoctoral research fellow in the Princeton Center for Complex Materials and a co-first author.

They used a tool called a scanning tunneling microscope, in which a conductive metal tip can add or remove an electron from magic-angle graphene and detect the resulting energy state of that electron.

Researchers used scanning tunneling microscopy to detect electrons in the material known as magic-angle bilayer graphene. Image by the Yazdani lab at Princeton University. Because strongly interacting electrons resist the addition of a new electron, it costs some energy to add the additional electron. The researchers can measure this energy and from it determine the strength of the interaction force.

“I’m literally putting an electron in and seeing how much energy it costs to shove this electron into the cooperative bath,” said Kevin Nuckolls, a graduate student in the Department of Physics, also a co-first author.

The team found that the addition of each electron caused a jump in the amount of energy needed to add another one – which would not have been the case if the electrons were able to go into the crystal and then move freely among the atoms. The resulting cascade of energy transitions resulted from an energy jump for each of the electrons’ flavors – since electrons need to assume the lowest energy state possible while also not being of the same energy and same flavor as other electrons at the same location in the crystal.

A key question in the field is how the strength of interactions between electrons compares to the energy levels that the electrons would have had in the absence of such interactions. In most common and low-temperature superconductors, this is a small correction, but in rare high-temperature superconductors, the interactions among electrons are believed to change the energy levels of the electrons dramatically. Superconductivity in the presence of such a dramatic influence of interactions among electrons is very poorly understood.

A cascade of changes in the electronic properties of magic-angle graphene are observed by high-resolution scanning tunneling microscopy as a function of applied voltage, which tunes the electron filling between fully occupied (v = 4) and empty (v = -4). Image by the Yazdani lab at Princeton University. Published in Nature. The quantitative measurements of the sudden shifts detected by the researchers confirms the picture that magic-angle graphene belongs to the class of superconductors with strong interaction among the electrons.

Graphene is a single-atom-thin layer of carbon atoms, which, due to the chemical properties of carbon, arrange themselves in a flat honeycomb lattice. The researchers obtain graphene by taking a thin block of graphite – the same pure carbon used in pencils – and removing the top layer using sticky tape.

They then stack two atom-thin layers and rotate the top layer by exactly 1.1 degrees – the magic angle. Doing this causes the material to become superconducting, or attain unusual insulating or magnetic properties.

“If you’re at 1.2 degrees, it’s bad. It’s, it’s just a bland metal. There’s nothing interesting happening. But if you’re at 1.1 degrees, you see all this interesting behavior,” Nuckolls said.

This misalignment creates an arrangement known as a moiré pattern for its resemblance to a French fabric.

To conduct the experiments, the researchers built a scanning tunneling microscope in the basement of Princeton’s physics building, Jadwin Hall. So tall that it occupies two floors, the microscope sits atop a granite slab, which floats on air springs. “We need to isolate the equipment very precisely because it is extremely sensitive to vibrations,” said Myungchul Oh, a postdoctoral research associate and co-first author. Dillon Wong, Kevin Nuckolls, Myungchul Oh, and Biao Lian contributed equally to the work.

Additional contributions were made by Yonglong Xie, who earned his Ph.D. in 2019 and is now a postdoctoral researcher at Harvard University; Sangjun Jeon, who is now an assistant professor at Chung-Ang University in Seoul; Kenji Watanabe and Takashi Taniguchi of the National Institute for Material Science (NIMS) in Japan; and Princeton Professor of Physics B. Andrei Bernevig.

A similar cascade of electronic phase transitions was noted in a paper published simultaneously in Nature on June 11 by a team led by Shahal Ilani at the Weizmann Institute of Science in Israel and featuring Jarillo-Herrero and colleagues at MIT, Takashi Taniguchi and Kenji Watanabe of NIMS Japan, and researchers at the Free University of Berlin.

“The Weizmann team observed the same transitions as we did with a completely different technique,” Yazdani said. “It is nice to see that their data are compatible with both our measurements and our interpretation.”

The study, “Cascade of electronic transitions in magic-angle twisted bilayer graphene,” by Dillon Wong, Kevin P. Nuckolls, Myungchul Oh, Biao Lian, Yonglong Xie, Sangjun Jeon, Kenji Watanabe, Takashi Taniguchi, B. Andrei Bernevig, and Ali Yazdani, was published June 11 in the journal Nature. [DOI 10.1038/s41586-020-2339-0]

Tags:  Ali Yazdani  Biao Lian  Graphene  Massachusetts Institute of Technology  Pablo Jarillo-Herrero  Princeton University 

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Applying 'magic angle' twistronics to manipulate the flow of light

Posted By Graphene Council, Friday, June 12, 2020
Monash researchers are part of an international collaboration applying 'twistronics' concepts (the science of layering and twisting 2D materials to control their electrical properties) to manipulate the flow of light in extreme ways.

The findings, published today in the journal Nature, hold the promise for leapfrog advances in a variety of light-driven technologies, including nano-imaging devices; high-speed, low-energy optical computers; and biosensors.

This is the first application of Moire physics and twistronics to the light-based technologies, photonics and polaritonics, opening unique opportunities for extreme photonic dispersion engineering and robust control of polaritons on 2D materials.

APPLYING TWISTRONICS TO PHOTONS

The team took inspiration from the recent discovery of superconductivity in a pair of stacked graphene layers that were rotated to the 'magic twist angle' of 1.1 degrees.

In this stacked, misaligned configuration, electrons flow with no resistance, while separately, each of the two graphene layers shows no special electrical properties.

The discovery has shown how the careful control of rotational symmetries can unveil unexpected material responses.

The research team was led by Andrea Alù at the Advanced Science Research Center at the Graduate Center, CUNY, Cheng-Wei Qiu at National University of Singapore and Qiaoliang Bao formerly at Monash University.

The team discovered that an analogous principle can be applied to manipulate light in highly unusual ways. At a specific rotation angle between two ultrathin layers of molybdenum-trioxide, the researchers were able to prevent optical diffraction and enable robust light propagation in a tightly focused beam at desired wavelengths.

Typically, light radiated from a small emitter placed over a flat surface expands away in circles very much like the waves excited by a stone that falls into a pond. In their experiments, the researchers stacked two thin sheets of molybdenum-trioxide and rotated one of the layers with respect to the other. When the materials were excited by a tiny optical emitter, they observed widely controllable light waves over the surface as the rotation angle was varied. In particular, they showed that at the photonic 'magical twist angle' the configured bilayer supports robust, diffraction-free light propagation in tightly focused channel beams over a wide range of wavelengths.

"While photons - the quanta of light - have very different physical properties than electrons, we have been intrigued by the emerging discovery of twistronics, and have been wondering if twisted two-dimensional materials may also provide unusual transport properties for light, to benefit photon-based technologies," said Andrea Alù.

"To unveil this phenomenon, we used thin layers of molybdenum trioxide. By stacking two of such layers on top of each other and controlling their relative rotation, we have observed dramatic control of the light guiding properties. At the photonic magic angle, light does not diffract, and it propagates very confined along straight lines. This is an ideal feature for nanoscience and photonic technologies."

"Our experiments were far beyond our expectations," said Dr Qingdong Ou, who led the experimental component of the study at Monash University. "By stacking 'with a twist' two thin slabs of a natural 2D material, we can manipulate infrared light propagation, most intriguingly, in a highly collimated style."

"Our study shows that twistronics for photons can open truly exciting opportunities for light-based technologies, and we are excited to continue exploring these opportunities," said National University of Singapore graduate student Guangwei Hu, who led the theoretical component.

"Following our previous discovery published in Nature in 2018, we found that biaxial van der Waals semiconductors like α-MoO3 and V2O5 represent an emerging family of material supporting exotic polaritonic behaviors," said A/Prof Qiaoliang Bao, "These natural-born hyperbolic materials offer an unprecedented platform for controlling the flow of energy at the nanoscale."

DEVELOPMENT OF TWISTRONICS AND MAGIC ANGLES IN GRAPHENE

Novel electronic properties in 'misaligned' graphene sheets was first predicted by National University of Singapore Professor (and FLEET Partner Investigator) Antonio Castro Neto in 2007, and the 'magic angle' of 1.1 degrees was theorised by FLEET PI (University of Texas in Austin) in 2011.

Superconductivity in twisted graphene was experimentally demonstrated by Pablo Jarillo-Herrero (MIT) in 2018.

THE STUDY

Topological polaritons and photonic magic angles in twisted α-MoO3 bi-layers was published in Nature today, 11 June 2020 (DOI 10.1038/s41586-020-2359-9 ).

As well as support from the Australian Research Council, support was also provided by the US Air Force Office of Scientific Research, >Vannevar Bush Fellowship, Office of Naval Research, and National Science Foundation, as well as Singapore's Agency for Science Technology and Research (A*STAR), and China's National Natural Science Foundation.

Layering and twisting of 2D materials was performed at Monash University (Department of Materials Science and Engineering), while the topological polaritons was observed and characterised at the Melbourne Centre for Nanofabrication (MCN), the Victorian Node of the Australian National Fabrication Facility (ANFF).

PHOTONICS AT FLEET

Experimental physicist Dr Qingdong Ou is a research fellow now working with Prof Michael Fuhrer at Monash University to study nano-device fabrication based on 2D materials, within FLEET's Enabling technology B.

Qingdong seeks to minimise energy losses in light-matter interactions, aiming to realise ultra-low energy consumption in 2D-material-based photonic and optoelectronic devices. He also studies highly-confined low-loss polaritons in 2D materials using near-field optical nano-imaging within FLEET's Research theme 2.

FLEET is an Australian Research Council Centre of Excellence developing a new generation of ultra-low energy electronics.

Tags:  2D materials  Andrea Alù  CUNY  Electronics  Graphene  Monash University  photonics  Qingdong Ou 

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UT Projects Win $23.6M in R&D Funds as Part of Portuguese Government Technology Program

Posted By Graphene Council, Wednesday, June 10, 2020
The UT Austin Portugal program, a 13-year-old innovation partnership between the university and the Portuguese government, received $23.6 million in funding to pursue 11 R&D projects as part of a major technology initiative from Portugal’s Ministry of Science, Technology and Higher Education.

The projects fall under four major categories: nanomaterials, earth-space interactions, medical physics and advanced computing. The teams will spend the next three years developing their projects, which could transform industries like automotive, space, health care and data science.

“Ranging from electromagnetic interference shielding nanomaterials, to in-beam time-of-flight positron emission tomography for proton radiation therapy, all the way to an ocean and climate change monitoring constellation based on radar altimeter data combined with gravity and ocean temperature and salinity measurements, the spread, number, and quality of the UT Austin Portugal joint strategic projects selected for funding within the recent competitive solicitation set forth by the Foundation for Science and Technology and National Innovation Agency are truly outstanding,” said Manuel Heitor, Portugal’s Minister of Science, Technology and Higher Education. “I look forward to witnessing the results of such collaborative research between Portuguese and UT researchers.”

The call for proposals included just three universities: The University of Texas at Austin, Carnegie Mellon University and the Massachusetts Institute of Technology. UT won the majority of the investment dollars, about 40% of the funding, and saw the most projects funded among the three engineering powerhouses.

“We had anticipated four to five projects would be selected for strategic grant awards and were astounded when we learned 11 had been selected by the evaluation panel in Portugal,” said John Ekerdt, Cockrell School associate dean for research and principal investigator for UT Austin Portugal. “This is a testament to the outstanding faculty and quality projects they proposed with collaborators in Portugal and to the close ties that have been forged between UT researchers and faculty and counterparts in Portugal.”

“The performance of the UT Austin Portugal program in the 2019 call for strategic projects has been remarkable,” said Marco Bravo, executive director of the UT Austin Portugal program. “Eleven of 14 project proposals submitted by the UT Austin Portugal research consortia were approved for funding through an independent assessment process. Overall, UT Austin Portugal saw 11 of its groundbreaking, industry-led proposals approved out of a total of 25 projects approved at this solicitation that included proposals from two other international partnerships, corresponding to nearly $24 million over three years. That’s 40% of total funding to UT Austin Portugal projects, the largest share of research dollars available. UT Austin researchers are to be congratulated on this effort.”

The UT Austin Portugal program dates back to 2007, and it is one of several partnerships between the Portuguese government and research institutions. The goal is to elevate science and technology in Portugal while fostering strong partnerships to help universities continue to innovate. The partnership with UT was extended in 2018, continuing the alliance until at least 2030.

“Of the three international partnerships with American universities sponsored by the Portuguese Foundation for Science and Technology in Portugal, the partnership with UT Austin had the best performance in this call, which was designed and launched on the Portuguese side,” said José Manuel Mendonça, national director of the program. “The 11 approved projects represent a proposal success rate of almost 80% for the UT Austin Portugal Program. The approved projects will, undoubtedly, contribute to promoting and strengthening collaborations with UT Austin in high-level R&D matters with immediate transposition to various sectors of economic activity, several of which are critical to Portugal's competitive position at an international level.”

About a third of the funds for UT’s projects come from the university, with the rest coming from a combination of public and private Portuguese entities. Each project team in Portugal is led by a Portuguese company. The UT side includes 21 faculty members and one from the MD Anderson Cancer Center.

Here is a look at the UT projects:

Shielding electronic devices from electromagnetic interference
This project proposes to use the “wonder material” graphene to improve on methods to combat electromagnetic interference, which can disrupt circuits and cause devices to fail. The team plans to create two composites with electromagnetic interference shielding capabilities and fabricate a solution to protect electric wires used in the automotive industry.

UT Austin Faculty: Deji Akinwande, Cockrell School of Engineering, Department of Electrical and Computer Engineering; Brian Korgel, Cockrell School of Engineering, McKetta Department of Chemical Engineering

New lasers for next-generation biomedical imaging
The use of multiphoton microscopy to examine cell behavior in live tissue over time has become an important research tool for learning more about brains and tumors. This project aims to increase the speed and depth of this form of imaging and diagnostics through the development and application of ultrashort laser pulses.

UT Austin Faculty: Andrew Dunn, Cockrell School of Engineering, Department of Biomedical Engineering; Adela Ben-Yakar, Cockrell School of Engineering, Walker Department of Mechanical Engineering

Nano-satellites for gravitational field assessment
Researchers propose to develop a nano-satellite prototype for studying gravitational fields. The project will also develop a platform for future nano-satellite capabilities, including Earth observation, communications and exploration missions.

UT Austin Faculty: Byron Tapley, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Center for Space Research; Brandon Jones, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Texas Spacecraft Laboratory

Software to match big data with high-performance computing
The advancement of technology has generated huge troves of data, which requires stronger computing power to process and analyze all that information. This project aims to create a software bundle to help companies pair their big data operations with high-performance computing, which includes tools for managing challenges such as computing and research storage.

UT Austin Faculty: Vijay Chidambaram, College of Nature Sciences, Department of Computer Science; Todd Evans, Texas Advanced Computing Center

Sensors for monitoring cancer patients
This project will develop a biosensor that can be injected into prostate cancer patients after surgery. The minimally invasive sensor would allow medical personnel to monitor high-risk patients remotely and look for the development of early tumors, with the potential to increase the predictive value of cancer screenings.

UT Austin Faculty: Thomas Milner, Cockrell School of Engineering, Department of Biomedical Engineering; James Tunnell, Cockrell School of Engineering, Department of Biomedical Engineering

Wearable rehabilitation devices
Researchers will develop a series of nano-sensors embedded into clothing that administer electrostimulation to people suffering from a lack of mobility and motor deficiency. The sensors could be monitored remotely by health professionals, creating a mobile rehabilitation option for people who have trouble getting to a doctor’s office consistently or want greater freedom to complete treatment anywhere. The team envisions its project as a tool mostly for elderly people, but it has applications for training high-level athletes as well.

UT Austin Faculty: George Biros, Cockrell School of Engineering, Walker Department of Mechanical Engineering, and the Oden Institute for Computational Engineering and Sciences; Michael Cullinan, Cockrell School of Engineering, Walker Department of Mechanical Engineering

Software for gathering better data on manufacturing
Getting reliable data on manufacturing processes proves challenging due to issues with placing sensors in the right spots and retaining strong connectivity. Thin films loaded with small sensors that can be applied directly to the equipment represent a promising solution; however, installation has proved difficult. This project proposes a new set of software to make it easier to layer these films on top of equipment by providing necessary data to avoid mechanical problems during installation.

UT Austin Faculty: Rui Huang, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, Center for Mechanics of Solids, Structures and Materials; Kenneth M. Liechti, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, Center for Mechanics of Solids, Structures and Materials

A new way to measure next-generation cancer therapy
Proton radiation therapy, the use of protons rather than X-rays to treat cancer patients, is on the rise, but measuring the distance protons travel proves problematic. Typically, it takes a ring of detectors surrounding the patient to get accurate measurements, but that poses geometric challenges. This project proposes to develop a new type of Positron Emission Tomography scan, which shows how tissues and organs are functioning to better understand the range of protons and whether they are traveling to the right spots to attack the cancer.

UT Faculty: Karol Lang, College of Natural Sciences, Department of Physics; Narayan Sahoo, University of Texas MD Anderson Cancer Center, Department of Radiation Physics

Satellite constellations for monitoring climate change
This project aims to develop the next generation of radar altimeter instruments — which measure the distance between an aircraft and the terrain below it — and a series of small satellites that can understand long-term variability in local, regional and global climate created by changes in sea levels due to water temperature. The project also includes a data processing and visualization system using advanced modeling, estimation techniques, statistical and scientific machine learning methods and error analysis.

UT Austin Faculty: Byron Tapley, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics Department, and the Center for Space Research; Patrick Heimbach, Jackson School of Geosciences, Department of Geological Sciences, and the Oden Institute for Computational Engineering and Sciences

Improving cutting tools for airline and automotive components
Fabricating parts of cars and planes is hard on cutting tools and tends to ware them down. This project aims to develop coatings that better protect and extend the lifespan of these crucial pieces of equipment. The team also plans to develop simulation programs to improve cutting tools’ performance.

UT Austin Faculty: Gregory J. Rodin, Cockrell School of Engineering, Department of Aerospace Engineering and Engineering Mechanics, and the Oden Institute for Computational Engineering and Sciences; Filippo Mangolini, Cockrell School of Engineering, Walker Department of Mechanical Engineering

An alternative to traditional water treatment options
Traditional water treatment tech struggles to efficiently remove high amounts of pollutants from some types of surface and groundwater. This team is looking to use metallic nanoparticles to clean water by improving a process called catalytic hydrogenation, which involves adding hydrogen via a metallic catalyst.

UT Austin Faculty: Charles J. Werth, Cockrell School of Engineering, Department of Civil, Architectural, and Environmental Engineering; Simon M. Humphrey, College of Natural Sciences, Department of Chemistry

Tags:  Biomedical  Carnegie Mellon University  Electronics  Environment  Graphene  Healthcare  John Ekerdt  Marco Bravo  Massachusetts Institute of Technology  nanomaterials  Sensors  The University of Texas at Austin  Water Purification 

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