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'Atomic dance' reveals new insights into performance of 2D materials

Posted By Graphene Council, Monday, February 17, 2020
A team of Northwestern University materials science researchers have developed a new method to view the dynamic motion of atoms in atomically thin 2D materials. The imaging technique, which reveals the underlying cause behind the performance failure of a widely used 2D material, could help researchers develop more stable and reliable materials for future wearables and flexible electronic devices.

These 2D materials - such as graphene and borophene - are a class of single-layer, crystalline materials with widespread potential as semiconductors in advanced ultra-thin, flexible electronics. Yet due to their thin nature, the materials are highly sensitive to external environments, and have struggled to demonstrate long-term stability and reliability when utilized in electronic devices.

"Atomically thin 2D materials offer the potential to dramatically scale down electronic devices, making them an attractive option to power future wearable and flexible electronics," said Vinayak Dravid, Abraham Harris Professor of Materials Science and Engineering at the McCormick School of Engineering.

The study, titled "Direct Visualization of Electric Field induced Structural Dynamics in Monolayer Transition Metal Dichalcogenides," was published on February 11 in the journal ACS Nano. Dravid is the corresponding author on the paper. Chris Wolverton, the Jerome B. Cohen Professor of Materials Science and Engineering, also contributed to the research.

"Unfortunately, electronic devices now operate as a kind of 'black box.' Although device metrics can be measured, the motion of single atoms within the materials responsible for these properties is unknown, which greatly limits efforts to improve performance," added Dravid, who serves as director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center. The research allows a way to move past that limitation with a new understanding of the structural dynamics at play within 2D materials receiving electrical voltage.

Building upon a previous study in which the researchers used a nanoscale imaging technique to observe failure in 2D materials caused by heat, the team used a high-resolution, atomic-scale imaging method called electron microscopy to observe the movement of atoms in molybdenum disulfide (MoS2), a well-studied material originally used as a dry lubricant in greases and friction materials that has recently gained interest for its electronic and optical properties. When the researchers applied an electric current to the material, they observed its highly mobile sulfur atoms move continuously to vacant areas in the crystalline material, a phenomenon they dubbed, "atomic dance."

That movement, in turn, caused the MoS2's grain boundaries -- a natural defect created in the space where two crystallites within the material meet-- to separate, forming narrow channels for the current to travel through.

"As these grain boundaries separate, you are left with only a couple narrow channels, causing the density of the electrical current through these channels to increase," said Akshay Murthy, a PhD student in Dravid's group and the lead author on the study. "This leads to higher power densities and higher temperatures in those regions, which ultimately leads to failure in the material."

"It's powerful to be able to see exactly what's happening on this scale," Murthy continued. "Using traditional techniques, we could apply an electric field to a sample and see changes in the material, but we couldn't see what was causing those changes. If you don't know the cause, it's difficult to eliminate failure mechanisms or prevent the behavior going forward."

With this new way to study 2D materials at the atomic level, the team believes researchers could use this imaging approach to synthesize materials that are less susceptible to failure in electronic devices. In memory devices, for example, researchers could observe how regions where information is stored evolve as electric current is applied and adapt how those materials are designed for better performance.

The technique could also help improve a host of other technologies, from transistors in bioelectronics to light emitting diodes (LEDs) in consumer electronics to photovoltaic cells that comprise solar panels.

"We believe the methodology we have developed to monitor how 2D materials behave under these conditions will help researchers overcome ongoing challenges related to device stability," Murthy said. "This advance brings us one step closer to moving these technologies from the lab to the marketplace."

Tags:  2D materials  Akshay Murthy  Chris Wolverton  Electronics  Graphene  Northwestern University  Vinayak Dravid 

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Crystal with a Twist: Researchers Grow Spiraling New Material

Posted By Graphene Council, Monday, February 17, 2020

With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists have created new inorganic crystals made of stacks of atomically thin sheets. These stacks unexpectedly spiral like a nanoscale card deck. Their surprising structures may yield unique optical, electronic and thermal properties. These properties may even include superconductivity, the ability to conduct electricity without loss. These crystals in the shape of a helix are made of stacked layers of germanium sulfide. This is a semiconductor material that, like graphene, readily forms sheets that are only a few atoms thick. Such “nanosheets” are also called “2D materials.”

This is the first time that scientists have made 2D materials that form a continuously twisting shape in a structure that is thousands layers thick. The spiral structures could hold unique properties that aren’t observed in regularly stacked materials. Scientists could likely use this technique to grow layers of other materials that form atomically thin layers.

Summary

To create the twisted structures, the team took advantage of a crystal defect called a screw dislocation, a “mistake” in the orderly crystal structure that gives it a bit of a twisting force. This “Eshelby Twist”, named after scientist John D. Eshelby, has been used by others to create nanowires that spiral like pine trees. But this study is the first time the Eshelby Twist has been used to make crystals built of stacked 2D layers of an atomically thin semiconductor.

In a major discovery last year, scientists reported that graphene becomes superconductive when two atomically thin sheets of the material are stacked and twisted at what’s called a “magic angle.” While other researchers have since succeeded at stacking two layers at a time, this new work provides a recipe for synthesizing stacked structures that are hundreds of thousands or even millions of layers thick in a continuously twisting fashion.

By adjusting the material synthesis conditions and length, the researchers could change the angle between the layers, creating a twisted structure that is tight, like a spring, or loose, like an uncoiled Slinky.

Scientists performed X-ray analyses for the study at the Advanced Light Source and measured the crystal’s twist angles at the Molecular Foundry, both DOE Office of Science user facilities.

Funding
Y.L. and J.Y. are supported by the Samsung Advanced Institute of Technology. Work at the Molecular Foundry and the Advanced Light Source was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy. H.S. and D.C.C. are supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering. within the Electronic Materials Program (KC1201). This work was performed, in part, at the Center for Nanoscale Materials, a US Department of Energy Office of Science User Facility. We thank C. So, C. Song, X. Wang, S. Yan, K. Bustillo and C. V. Stan for help with the experiments.

Tags:  2D materials  Electronics  Graphene  Samsung Advanced Institute of Technology  Semiconductor 

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The ACS Publishes a Chicken-Sh!T Article About Graphene

Posted By Graphene Council, Friday, February 14, 2020

A joke targeted at graphene research seems driven more by envy than providing a check on its excesses 

Last month, the venerable American Chemical Society (ACS) in its journal ACS Nano decided to take a step off the path of its mandate to promote scientific discovery and thought it might be fun to ridicule it. ("Will Any Crap We Put into Graphene Increase Its Electrocatalytic Effect?" by Lu Wang, Zdenek Sofer and  Martin Pumera*

Of course, the target of the ridicule was graphene, which over the last decade has been taking much of the research funding targeted for advanced materials. Let’s say it was an easy target to malign, especially for those who are not invested in graphene’s development.

The ridicule was formulated in this way: a lot of research papers are published on how to dope graphene (add impurities to it), so what if we published a paper on someone doping graphene with chicken guano. Hysterical, right?

There’s just one problem with this joke, one of the cornerstones of semiconducting engineering for at least the last half-century has been doping. Doping is used to enhance, or just tweak, the conductivity of semiconductors by intentionally introducing impurities into them. 

To forego a long explanation of solid-state physics and band gaps, suffice it to say that digital electronics (the kind of electronics that enables you to read this post) depends on doping of electronic materials to function.

In the decade-and-a-half since graphene was first isolated, researchers have been mesmerized by its extraordinary properties and by logical extension its enormous potential in electronics. However, graphene in its pure state is not a semiconductor, but rather a conductor. In order for it to be useful in electronic applications, especially digital electronics, it needs to behave as a semiconductor: possessing the capability of starting and stopping the flow of electrons through it thereby creating the on/off states for binary digital logic.

Of course, researchers have spent countless hours researching on how to best exploit graphene for electronics—attracted to its extraordinary electronic properties—and have often been funded handsomely to do so. This funding—which has come at the expense of other lines of research (making graphene research an easy target for envy)—has been so strong because of the hope that it would lead to some breakthrough that would stave off the end of Moore’s Law. 

Moore’s Law argued back in 1965 that the number of transistors placed in an integrated circuit (IC) or chip doubles approximately every two years.  It turns out graphene hasn’t saved Moore’s Law as of yet. And Moore’s Law may have seen its road come to a dead end two years ago when chip makers just threw up their hands at a 7-nm node and said, “No more.”

This means for the last decade there has been a pressing need and a fervent hope that graphene could come to the rescue of complimentary metal-oxide-semiconductor (CMOS) digital electronics. To meet this need and interest, graphene research had to devote much of its time to doping of the material.

It is a worthy argument to contest how effective this has all been in bringing graphene closer as a viable alternative in a post-CMOS world. However, it would be silly to argue that such research should never have been undertaken, or even taken on so aggressively and broadly. There was a need and the market pulled for such a use for the material. This was not an idle or wasted effort as the ACS Nano article insinuates.

The gist of the ACS Nano article in the form of a joke was to suggest that all doping of graphene research is nonsense because so much of it is performed and published. “Look how funny it would be to dope graphene with chicken droppings. That will really stick their noses in it.” While this may be funny to some, it’s highly detrimental to the spirit and inspiration for scientific inquiry.

And it certainly doesn’t do justice to the many innovative ways that graphene and a whole class of 2D materials are being applied to solve existing and new engineering challenges. 

Tags:  2D materials  American Chemical Society  Electronics  Graphene  Lu Wang  Martin Pumera  Semiconductors  Zdenek Sofer 

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A novel formulation to explain heat propagation

Posted By Graphene Council, Thursday, February 13, 2020
Researchers at EPFL and MARVEL have developed a novel formulation that describes how heat spreads within crystalline materials. This can explain why and under which conditions heat propagation becomes fluid-like rather than diffusive. Their equations will make it easier to design next-generation electronic devices at the nanoscale, in which these phenomena can become prevalent.

Fourier's well-known heat equation describes how temperatures change over space and time when heat flows in a solid material. The formulation was developed in 1822 by Joseph Fourier, a French mathematician and physicist hired by Napoleon to increase a cannon's rate of fire, which was limited by overheating.

Fourier's equation works well to describe conduction in macroscopic objects (several millimeters in size or larger) and at high temperatures. However, it does not describe hydrodynamic heat propagation, which can appear in electronic devices containing materials such as graphite and graphene.

One of these heat-propagation phenomena is known as Poiseuille heat flow. This is where heat propagates within a material as a viscous-fluid flow. Another phenomenon, called "second sound," takes place when heat propagates in a crystal like a wave, similar to the way in which sound spreads through the air.

Since these phenomena are not described by Fourier's equation, until now researchers have analyzed them using explicit microscopic models, such as the Boltzmann transport equation. However, the complexity of these models means that they cannot be used to design complex electronic devices.

This problem has now been solved by Michele Simoncelli, a PhD student at EPFL, together with Andrea Cepellotti, a former EPFL PhD student now at Harvard, and Nicola Marzari, the chair of Theory and Simulation of Materials in the Institute of Materials at EPFL's School of Engineering and the director of NCCR MARVEL. They showed how heat originating from the atomic vibrations in a solid can be described rigorously by two novel "viscous heat equations", which extend Fourier's law to cover any heat propagation that is not diffusive.

"These viscous heat equations explain why and under which conditions heat propagation becomes fluid-like rather than diffusive. They show that heat conduction is governed not just by thermal conductivity, as described by Fourier's law, but also by a second parameter, thermal viscosity," says Simoncelli.

This breakthrough, published in Physical Review X, will help engineers design next-generation devices, particularly those that feature materials such as graphite or diamond in which hydrodynamic phenomena are prevalent. Overheating is the main limiting factor for the miniaturization and efficiency of electronic devices, and in order to maximize efficiency and predict whether a device will work - or simply melt - it is crucial to have the right model.

The results obtained by EPFL's team are timely. From the 1960s until recently, hydrodynamic heat phenomena had only been observed at cryogenic temperatures (around -260oC) and were therefore thought to be irrelevant for everyday applications. Already in 2015 Marzari and his colleagues predicted that this would be very different in two-dimensional and layered materials - a prediction that was confirmed with the publication in Science of pioneering experiments that found second-sound (or wavelike heat propagation) in graphite at temperatures around -170oC.

The formulation presented by the EPFL researchers yields results that line up closely with those experiments. Most important, they also predict that hydrodynamic heat propagation can also happen at room temperature, depending on the size and type of material.

Through their work, the EPFL researchers are providing new and original insight into heat transport, but also laying the groundwork for an understanding of shape and size effects - not only in next-generation electronic devices but also in "phononic" devices that control cooling and heating through engineered superstructures. Finally, the novel formulation can also be adapted to describe viscous phenomena involving electrons discovered in 2016 by Philip Moll, now a professor at EPFL's Institute of Materials.

Tags:  Andrea Cepellotti  Electronics  EPFL  Graphene  Michele Simoncelli  Nicola Marzari  Philip Moll  photonics 

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NUST MISIS: New Graphene-Based Material to Extend Life of Storage Devices

Posted By Graphene Council, Tuesday, February 11, 2020
International group of Russian and Japanese scientists developed a material that will significantly increase the recording density in data storage devices, such as SSDs and flash drives. Among the main advantages of the material is the absence of rewrite limit, which will allow implementing new devices for Big Data processes. The article on the research is published in Advanced Materials.

The development of compact and reliable memory devices is an increasing need. Today, traditional devices are devices in which information is transferred through electric current. The simplest example is a flash card or SSD. At the same time, users inevitably encounter problems: the file may not be recorded correctly, the computer may stop "seeing" the flash drive, and to record a large amount of information, rather massive devices are required.

A promising alternative to electronics is spintronics. In spintronics, devices operate on the principle of magnetoresistance: there are three layers, the first and third of which are ferromagnetic, and the middle one is nonmagnetic. Passing through such a "sandwich" structure, electrons, depending on their spin, are scattered differently in the magnetized edge layers, which affects the resulting resistance of the device. The control the information using the standard logical bits, 0 and 1, can be performed by detecting an increase or decrease in this resistance.

International group of scientists from National University of Science and Technology MISIS (Russia) and National Institute for Quantum and Radiological Science and Technology (Japan) developed a material that can significantly increase the capacity of magnetic memory by increasing the recording density. The scientists used a combination of graphene and the semi-metallic Heusler alloy Co2FeGaGe.

"Japanese colleagues for the first time grew a single-atom layer of graphene on a layer of semi-metallic ferromagnetic material and measured its properties. The Japanese team, led by Dr. Seiji Sakai, conducts unique experiments, while our group is engaged in a theoretical description of the data obtained. Our teams have been working together for many years and have obtained a number of important results," comments Pavel Sorokin, Sc.D. in Physics and Mathematics, head of the "Theoretical Materials Science of Nanostructures" infrastructure project at the NUST MISIS Laboratory of Inorganic Nanomaterials.

Previously, graphene was not used in magnetic memory devices as carbon atoms reacted with the magnetic layer, which led to changes in its properties. By careful selection of the Heusler alloy composition, as well as the methods of its application, it was possible to create a thinner sample compared to previous analogues. This, in turn, will significantly increase the capacity of magnetic memory devices without increasing their physical size. Next, scientists plan to scale the experimental sample and modify the structure.

Tags:  Electronics  Graphene  nanomaterials  NUST MISIS  Pavel Sorokin  Seiji Sakai 

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Engineers mix and match materials to make new stretchy electronics

Posted By Graphene Council, Saturday, February 8, 2020
At the heart of any electronic device is a cold, hard computer chip, covered in a miniature city of transistors and other semiconducting elements. Because computer chips are rigid, the electronic devices that they power, such as our smartphones, laptops, watches, and televisions, are similarly inflexible.

Now a process developed by MIT engineers may be the key to manufacturing flexible electronics with multiple functionalities in a cost-effective way.

The process is called  “remote epitaxy” and involves growing thin films of semiconducting material on a large, thick wafer of the same material, which is covered in an intermediate layer of graphene. Once the researchers grow a semiconducting film, they can peel it away from the graphene-covered wafer and then reuse the wafer, which itself can be expensive depending on the type of material it’s made from. In this way, the team can copy and peel away any number of thin, flexible semiconducting films, using the same underlying wafer.

In a paper published today in the journal Nature, the researchers demonstrate that they can use remote epitaxy to produce freestanding films of any functional material. More importantly, they can stack films made from these different materials, to produce flexible, multifunctional electronic devices.

The researchers expect that the process could be used to produce stretchy electronic films for a wide variety of uses, including virtual reality-enabled contact lenses, solar-powered skins that mold to the contours of your car, electronic fabrics that respond to the weather, and other flexible electronics that seemed until now to be the stuff of Marvel movies.

“You can use this technique to mix and match any semiconducting material to have new device functionality, in one flexible chip,” says Jeehwan Kim, an associate professor of mechanical engineering at MIT. “You can make electronics in any shape.”

Buying time

Kim and his colleagues reported their first results using remote epitaxy in 2017. Then, they were able to produce thin, flexible films of semiconducting material by first placing a layer of graphene on a thick, expensive wafer made from a combination of exotic metals. They flowed atoms of each metal over the graphene-covered wafer and found the atoms formed a film on top of the graphene, in the same crystal pattern as the underlying wafer. The graphene provided a nonstick surface from which the researchers could peel away the new film, leaving the graphene-covered wafer, which they could reuse. 

In 2018, the team showed that they could use remote epitaxy to make semiconducting materials from metals in groups 3 and 5 of the periodic table, but not from group 4. The reason, they found, boiled down to polarity, or the respective charges between the atoms flowing over graphene and the atoms in the underlying wafer.

Since this realization, Kim and his colleagues have tried a number of increasingly exotic semiconducting combinations. As reported in this new paper, the team used remote epitaxy to make flexible semiconducting films from complex oxides — chemical compounds made from oxygen and at least two other elements. Complex oxides are known to have a wide range of electrical and magnetic properties, and some combinations can generate a current when physically stretched or exposed to a magnetic field.

Kim says the ability to manufacture flexible films of complex oxides could open the door to new energy-havesting devices, such as sheets or coverings that stretch in response to vibrations and produce electricity as a result. Until now, complex oxide materials have only been manufactured on rigid, millimeter-thick wafers, with limited flexibility and therefore limited energy-generating potential.

The researchers did have to tweak their process to make complex oxide films. They initially found that when they tried to make a complex oxide such as strontium titanate (a compound of strontium, titanium, and three oxygen atoms), the oxygen atoms that they flowed over the graphene tended to bind with the graphene’s carbon atoms, etching away bits of graphene instead of following the underlying wafer’s pattern and binding with strontium and titanium. As a surprisingly simple fix, the researchers added a second layer of graphene.

“We saw that by the time the first layer of graphene is etched off, oxide compounds have already formed, so elemental oxygen, once it forms these desired compounds, does not interact as heavily with graphene,” Kim explains. “So two layers of graphene buys some time for this compound to form.”

Peel and stack

The team used their newly tweaked process to make films from multiple complex oxide materials, peeling off each 100-nanometer-thin layer as it was made. They were also able to stack together layers of different complex oxide materials and effectively glue them together by heating them slightly, producing a flexible, multifunctional device.

“This is the first demonstration of stacking multiple nanometers-thin membranes like LEGO blocks, which has been impossible because all functional electronic materials exist in a thick wafer form,” Kim says.

In one experiment, the team stacked together films of two different complex oxides: cobalt ferrite, known to expand in the presence of a magnetic field, and PMN-PT, a material that generates voltage when stretched. When the researchers exposed the multilayer film to a magnetic field, the two layers worked together to both expand and produce a small electric current. 

The results demonstrate that remote epitaxy can be used to make flexible electronics from a combination of materials with different functionalities, which previously were difficult to combine into one device. In the case of cobalt ferrite and PMN-PT, each material has a different crystalline pattern. Kim says that traditional epitaxy techniques, which grow materials at high temperatures on one wafer, can only combine materials if their crystalline patterns match. He says that with remote epitaxy, researchers can make any number of different films, using different, reusable wafers, and then stack them together, regardless of their crystalline pattern.

“The big picture of this work is, you can combine totally different materials in one place together,” Kim says. “Now you can imagine a thin, flexible device made from layers that include a sensor, computing system, a battery, a solar cell, so you could have a flexible, self-powering, internet-of-things stacked chip.”

The team is exploring various combinations of semiconducting films and is working on developing prototype devices, such as something Kim is calling an “electronic tattoo” — a flexible, transparent chip that can attach and conform to a person’s body to sense and wirelessly relay vital signs such as temperature and pulse. “We can now make thin, flexible, wearable electronics with the highest functionality,” Kim says. “Just peel off and stack up.”

Tags:  Electronics  Graphene  Jeehwan Kim  MIT  Semiconductor 

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Versarien plc US graphene operations update

Posted By Graphene Council, Tuesday, January 21, 2020
Versarien plc is pleased to provide an update on its US graphene operations. The Company continues to make progress with current and potential partners in the US.  As announced on 27 June 2019, the Company appointed Brian Berney as President of North American Operations at Versarien Graphene Inc., reporting to Neill Ricketts, CEO of Versarien.  Since then the Company has continued to enter into confidentiality agreements with potential partners to examine collaborations and develop trials in the region, including in particular, with a global tyre manufacturer.

Versarien has strengthened its US profile by attending two trade missions in Q4 2019, supported by the UK government.  In October 2019, Versarien attended the UK Supplier Showcase in Wichita, in conjunction with Spirit AeroSystems, and in December 2019 the Company was part of Innovate UK's Global Business Innovation Programme to Boston, which focused on graphene applications and technology in the electronics, composites and energy sectors.

Versarien Graphene, Inc. has a serviced office location.  Brian Berney, who is the only full-time employee in the US, is supported by the UK Company team, including from within the Company's laboratory facilities at the Graphene Engineering Innovation Centre in the UK. The Company also has access to third party laboratory facilities in Texas, which are utilised on a flexible basis and only as required.  This strategy is in line with the Group's approach to keep cost to a minimum and utilise customer's R&D facilities, where possible, as well as the Company's R&D expertise and available facilities in the UK.

Tags:  Brian Berney  composites  Electronics  Graphene  Graphene Engineering Innovation Centre  Neill Ricketts  Versarien  Versarien Graphene 

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'Superdiamond' carbon-boron cages can trap and tap into different properties

Posted By Graphene Council, Monday, January 13, 2020
A long-sought-after class of "superdiamond" carbon-based materials with tunable mechanical and electronic properties was predicted and synthesized by Carnegie's Li Zhu and Timothy Strobel. Their work is published by Science Advances.

Carbon is the fourth-most-abundant element in the universe and is fundamental to life as we know it. It is unrivaled in its ability to form stable structures, both alone and with other elements.

A material's properties are determined by how its atoms are bonded and the structural arrangements that these bonds create. For carbon-based materials, the type of bonding makes the difference between the hardness of diamond, which has three-dimensional "sp3" bonds, and the softness of graphite, which has two-dimensional "sp2" bonds, for example.

Despite the enormous diversity of carbon compounds, only a handful of three-dimensionally, sp3-bonded carbon-based materials are known, including diamond. The three-dimensional bonding structure makes these materials very attractive for many practical applications due to a range of properties including strength, hardness, and thermal conductivity.

"Aside from diamond and some of its analogs that incorporate additional elements, almost no other extended sp3 carbon materials have been created, despite numerous predictions of potentially synthesizable structures with this kind of bonding," Strobel explained. "Following a chemical principle that indicates adding boron into the structure will enhance its stability, we examined another 3D-bonded class of carbon materials called clathrates, which have a lattice structure of cages that trap other types of atoms or molecules."

Clathrates comprised of other elements and molecules are common and have been synthesized or found in nature. However, carbon-based clathrates have not been synthesized until now, despite long-standing predictions of their existence. Researchers attempted to create them for more than 50 years.

Strobel, Zhu, and their team -- Carnegie's Gustav M. Borstad, Hanyu Liu, Piotr A. Guńka, Michael Guerette, Juli-Anna Dolyniuk, Yue Meng, and Ronald Cohen, as well as Eran Greenberg and Vitali Prakapenka from the University of Chicago and Brian L. Chaloux and Albert Epshteyn from the U.S. Naval Research Laboratory -- approached the problem through a combined computational and experimental approach.

"We used advanced structure searching tools to predict the first thermodynamically stable carbon-based clathrate and then synthesized the clathrate structure, which is comprised of carbon-boron cages that trap strontium atoms, under high-pressure and high-temperature conditions," Zhu said.

The result is a 3D, carbon-based framework with diamond-like bonding that is recoverable to ambient conditions. But unlike diamond, the strontium atoms trapped in the cages make the material metallic -- meaning it conducts electricity -- with potential for superconductivity at notably high temperature.

What's more, the properties of the clathrate can change depending on the types of guest atoms within the cages.

"The trapped guest atoms interact strongly with the host cages," Strobel remarked. "Depending on the specific guest atoms present, the clathrate can be tuned from a semiconductor to a superconductor, all while maintaining robust, diamond-like bonds. Given the large number of possible substitutions, we envision an entirely new class of carbon-based materials with highly tunable properties."

"For anyone who is into -- or whose kids are into -- Pokémon, this carbon-based clathrate structure is like the Eevee of materials," joked Zhu. "Depending which element it captures, it has different abilities."

Tags:  2D materials  Carnegie Institution for Science  Electronics  Graphene  Graphite  Li Zhu  Timothy Strobel  University of Chicago 

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Layered heterostructures put a spin on magnetic memory devices

Posted By Graphene Council, Thursday, January 9, 2020
Graphene is a unique material with great potential for the long-distance transportation of spin information. However, spin-to-charge interconversion (SCI) in graphene and graphene-based heterostructures to date could not be performed at room temperature. But now, researchers at Graphene Flagship partners ICN2 and Universitat Autònoma de Barcelona, Spain, and the University of Groningen, the Netherlands, have achieved efficient room temperature SCI in graphene-based structures, and devised a way to make this process tuneable using an external electric field. The findings, published in Nature Materials and Nano Letters, could allow scientists to use layered heterostructures for ultra-compact, low-power consumption magnetic memory devices.

Spintronics is a branch of electronics which uses electrons' spin to store, manipulate and transfer information. Spintronics could benefit many emerging markets, like motion sensing and next-generation memory devices. Developing efficient and versatile spin-based technologies requires both high-quality materials for long-distance spin transfer, and suitable engineering methods to generate and manipulate spin currents, to ensure electrons move in a controlled way with their spins oriented along a given direction.

Generally, spin currents are generated and detected using ferromagnetic contacts. But as an alternative, spin-orbit interactions could enable spin currents to be controlled entirely by an electric field, resulting in a far more versatile tool to be implemented in large-scale spin devices. Now, Graphene Flagship researchers ICREA Prof. Sergio O. Valenzuela, ICREA Prof. Stephan Roche, and colleagues have exploited the unique spin properties of graphene to transport spin information across long distances in large-scale SCI electronics. Additionally, by interfacing graphene with transition metal dichalcogenides (TMDs), another family of layered materials with strong spin-orbit coupling, they were able to precisely control spin transport in these devices. "Thanks to this research, the Graphene Flagship's Spintronics Work Package has made a major step towards the engineering of SCI in quantum devices, with genuine potential for spintronics applications," explains Roche.

By fabricating a high-quality device and using very sensitive detection techniques to evaluate the spin Hall and inverse spin Galvanic effects – focusing in particular on spin precession and non-local measurements – they demonstrated experimentally that the SCI in graphene–TMD heterostructures is in good agreement with theoretical models. Furthermore, using these techniques, Graphene Flagship researchers not only demonstrated the spin-related character of the signals, but also tailored the efficiency of their SCI and sign using electrostatic gating. This important feature directly showcases their ability to manipulate spin information in the heterostructures with an electric field, and this could soon lead to new applications in magnetic memory devices. Most notably, they found that the room temperature SCI efficiencies were just as high as the best results using other materials.

"We're very excited to report the first unambiguous evidence of large and tuneable SCI in van der Waals heterostructures at room temperature," comments Valenzuela, from Graphene Flagship partner ICN2. "This is a significant step forward towards the long sought-after goal of electrostatic control of spin information," he continues. Additionally, Prof. Bart van Wees, from Graphene Flagship partner the University of Groningen, elaborates: "It is difficult to imagine how complex it is to fabricate spin devices combining various types of magnetic and non-magnetic materials, graphene, boron nitride, and strong spin-orbit coupling materials such as TMDs. Thanks to this work, the Spintronics Work Package has developed a unique expertise in realizing operational spin devices which really show the full potential of layered materials."

Kevin Garello, Graphene Flagship Work Package Leader for Spintronics, comments: "Devices involving the spin–orbit torque phenomenon, such as the spin Hall effect and the spin Galvanic effect, are great candidates for future spintronics applications as they require low power input and are capable of ultra-fast performance. It is great to see that spin-orbit torques can be electrically manipulated and improved by the smart engineering of layered materials, which has now been unequivocally confirmed independently by two experimental teams in Work Package Spintronics. This opens the door for new and exciting perspectives and strategies to manipulate spin information and further advance applications in spintronics based on layered materials."

The success of these studies is the result of the joint effort between experimental and theoretical researchers working closely together in the EU-funded Graphene Flagship framework. The results provide valuable insights for the spintronics and layered materials communities, and the researchers hope that their findings will enable scientists to explore new theoretical models and further experiments in the future.

Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel, adds: "The Graphene Flagship has invested in spintronics research since the very beginning. The great potential of graphene and related materials in this area has been showcased by world-leading work done in the Flagship. These results indicate that we are getting close to the point where the fundamental work can be translated into useful applications, as foreseen in our science and technology and innovation roadmaps."

Tags:  Andrea C. Ferrari  Electronics  Graphene  Graphene Flagship  ICN2  ICREA  Kevin Garello  Sergio O. Valenzuela  Stephan Roche  Universitat Autònoma de Barcelona  University of Groningen 

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U.S. Army seeks a graphene-based composite EMI shielding material.

Posted By Terrance Barkan, Tuesday, January 7, 2020

OBJECTIVE: Develop a graphene-based composite EMI shielding material capable of replacing metal shielding in IC packages and printed circuit board components.

DESCRIPTION: As soldier electronics and their components operate at faster speeds, smaller size, and in closer confinements a substantial increase in Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) can lead to system failures. This effort supports the FREEDOM ERP as it enables enhanced technologies to protect next generation of highly mobile RF communications for battlefield dominance in the broad bandwidth frequencies X-band (8-12 GHz) to the Ku-band (12-18 GHz). Metal EMI shields in IC packages and printed circuit board components have limitations in poor chemical resistance, oxidation in long term harsh environments, high density, flexibility, and form factor. Current strategies to obtain the desired EMI shields mainly rely on increasing the material's thickness to prolong the EM wave absorption routes or loading large amounts of fillers in order to increase its electrical conductivity [1]. However, these factors inevitably increase the production cost and limit scalability.

Click to read the rest of the SBIR project description and to reach the Technical Points of Contact. 

Tags:  Composite  Electronics  EMI Shield  Graphene  RF Shield  SBIR 

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