Defect-free (Pure) graphene might solve lithium-metal batteries’ dendrite problem – Li metal can store 10X more energy than graphite – BIG Boost Li-Io Battery Based Applications


Defect Free Graphene for LIo Batts id43172_1

Specific energy and specific power of rechargeable batteries. Specific energy is the capacity a battery can hold in watt-hours per kilogram (Wh/kg); specific power is the battery’s ability to deliver power in watts per kilogram (W/kg). (Source: Battery University)

” … a research team from Sichuan University in China and Clarkson University in the U.S. have discovered a key design rule for Li metal batteries: If you want to suppress dendrites, you have to use a defect-free host. More generally, carbon defects catalyze dendrite growth in metal anodes … “

Rechargeable lithium-ion (Li-ion) batteries are the dominant technology not only for portable electronics but it also is becoming the battery of choice for electric-vehicle and electric-grid energy-storage applications.

In a Li-ion battery, the cathode (positive electrode) is a lithium metal oxide while the anode (negative electrode) is graphite. But researchers are looking for ways to replace graphite with lithium metal as the anode to boost the battery’s energy density.
Lithium metal-based batteries such as Li–sulfur and Li–air batteries have received considerable attention because the packing density of lithium atoms is the highest in its metallic form and Li metal can store 10 times more energy than graphite.

However, there are safety and performance concerns for these types of batteries that arise from the formation of dendrites on the metal electrodes; an issue that has been known and investigated since the 1960s.
These dendrites form when metal ions accumulate on the surface of the battery’s electrodes as the electrode degrades during the charging process. Dendrites are often responsible for the highly publicized violent battery failures reported in the news.
When these branch-like filament deposits elongate until they penetrate the barrier between the two halves of the battery, they can cause electrical shorts, overheating and fires. They also cause significant cycling efficiency losses.
To avoid dendrites, researchers are experimenting with new battery electrolyte chemistries, new separator technologies, and new physical hosts for the lithium metal.
Carbon hosts, in particular, are very promising, since they may be added to the anode with little additional cost and minimal modification of the manufacturing process and they are becoming an important way to stabilize Li metal anodes.
However, there are seemingly contradictory findings reported in hundreds of prior publications on the subject: The hosts, which are predominantly made from various nanostructured carbons such as graphene, are in some cases very effective in eliminating dendrites. In other cases, they don’t work at all, or actually make the dendrite problem worse.
Up to now, design of such host systems has been largely Edisonian: researchers use a trial-and-error approach to find an architecture/structure that works better than the rest.
In new work featured on the front cover of Advanced Energy Materials (“Pristine or Highly Defective? Understanding the Role of Graphene Structure for Stable Lithium Metal Plating”), a research team from Sichuan University in China and Clarkson University in the U.S. have discovered a key design rule for Li metal batteries: If you want to suppress dendrites, you have to use a defect-free host. More generally, carbon defects catalyze dendrite growth in metal anodes.
These findings address the major scientific problem of explaining how the structure and chemistry of the carbon per se affects dendrite growth.
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Left half: Defect-free graphene protecting lithium metal anode from the electrolyte. Right half: Defective graphene catalyzing dendrite growth. (Source: Mitlin Research Group, Clarkson University)
“We discovered a critical and unexpected relationship between the host (graphene) chemical/structural defectiveness and its ability to suppress dendrites,” Prof. David Mitlin, who led the work, explains to Nanowerk. “To do this, we created what may be the world’s most pure and ordered graphene and compared it to a standard graphene based on reduced graphene oxide. Using such opposite materials, provided unique and fundamental insight into the way lithium dendrites form and grow.”
“The key finding, which will rationally guide future lithium battery design efforts, is that the carbon defects are themselves catalytic for dendrite growth,” Prof Wei Liu from Sichuan University’s Institute of New Energy and Low Carbon Technology, and the paper’s first author, points out. “Much of the ‘damage’ to the anode ultimately responsible for the dendrites occurs even before the battery is fully charged for the first time. Defects in the carbon host corrode the electrolyte at low voltages, leading to early dendrite formation.”
The team hypothesized that it was the host structure/chemistry that mattered, but needed to create ideal model systems to test the hypothesis.
Prof. Wei Liu’s unique Flow Assisted Sonication (FAS) approach allowed them to create nearly defect-free graphene. Literally, such oxygen-free and structural defect-free graphene has never been synthesized prior by a wet chemistry method.
This graphene is 1-3 atomic layers thick and with only about one and a half percent oxygen. This is much purer than the typical eight percent or more oxygen found in most graphene materials.
“It served as a perfect test bed to explore our hypothesis,” says Liu. “Without such a pristine structure, it would not have been possible to obtain the conclusive answers to the dendrite growth problem.”
He emphasizes that this in itself is a transformative accomplishment for the carbon and energy communities, since prior only vapor deposition could obtain such ideal defect-free structures.
The team then compared their defect-free graphene to a standard highly defective Hummers graphene baseline found in literature.
“A direct one-to-one comparison allowed us to obtain unique insight into the role of carbon defects on Li dendrite growth,” says Mitlin. “A critical new finding is that solid electrolyte interphase (SEI) formation occurring BEFORE metal plating actually dictates dendrites. The fate of the Li metal anode is in effect sealed once the carbon host forms SEI at the initial charge!”
Going forward, the researchers plan to commercialize defect-free graphene host materials for next- generation lithium batteries. They also plan to further understand the complex relationship between carbon defects and metal dendrites by examining carbons with tuned structure/chemistry for lithium, sodium and potassium batteries.
By Michael Berger Copyright © Nanowerk
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University of Manchester – How Can Graphene Help Desalination?(Video+)


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Researchers at The University of Manchester’s National Graphene Institute in the UK have succeeded in making artificial channels just one atom in size for the first time. The new capillaries, which are very much like natural protein channels such as aquaporins, are small enough to block the flow of smallest ions like Na+ and Cl- but allow water to flow through freely. As well as improving our fundamental understanding of molecular transport at the atomic scale, and especially in biological systems, the structures could be ideal in desalination and filtration technologies.

 

Graphene Man UK 1920_dsc-0640-932465

 

Read More from the University of Manchester

Like …. Scientists develop a new method to revolutionise graphene printed electronics

Next-Gen Lithium-Ion Batteries – Combining Graphene + Silicon Could it be the Key?


Battery

Researchers have long been investigating the use of silicon in lithium-ion batteries, as it has the potential to greatly increase storage capacity compared to graphite, the material used in most conventional lithium-ion batteries. By some estimates, silicon could boast a lithium storage capacity of 4,200 mAh/g—11 times that of graphite.

However, despite its benefits, silicon comes with its own challenges.

“When you store a lot of lithium ion into your silicon you actually physically extend the volume of silicon to about 3 to 3.8 times its original volume—so that is a lot of expansion,” explained Bor Jang, PhD, in an exclusive interview with R&D Magazine. “That by itself is not a big problem, but when you discharge your battery—like when you open your smart phone—the silicon shrinks. Then when you recharge your battery the silicon expands again. This repeated expansion and shrinkage leads to the breakdown of the particles inside of your battery so it loses its capacity.”

Jang offers one solution—graphene, a single layer sheet of carbon atoms tightly bound in a hexagonal honeycomb lattice.

“We have found that graphene plays a critical role in protecting the silicon,” said Jang, the CEO and Chief Scientist of Global Graphene Group. The Ohio-based advanced materials organization has created GCA-II-N, a graphene and silicon composite anode for use in lithium-ion batteries.

The innovation—which was a 2018 R&D 100 Award winner—has the potential to make a significant impact in the energy storage space. Jang shared more about graphene, GCA-II-N and its potential applications in his …

Interview with R&D Magazine:

 

           Photo Credit: Global Graphene Group

 

R&D Magazine: Why is graphene such a good material for energy storage?

Jang: From the early beginning when we invited graphene back in 2002 we realized that graphene has certain very unique properties. For example, it has very high electrical conductivity, very high thermal conductivity, it has very high strength—in fact it is probably the strongest material known to mankind naturally. We thought we would be able to make use of graphene to product the anode material than we can significantly improve not only the strength of the electrode itself, but we are also able to dissipate the heat faster, while also reducing the changes for the battery to catch fire or explode.

Also graphene is extremely thin—a single layer graphene is 0.34 nanometer (nm). You can imagine that if you had a fabric that was as thin as 0.34 nanometers in thickness, than you could use this material to wrap around just about anything. So it is a very good protection material in that sense. That is another reason for the flexibility of this graphene material.

 

 

BatteryRead More: Talga’s graphene silicon product extends capacity of Li-ion battery anode

Another interesting feature of graphene is that is a very high specific surface area. For instance if I give you 1.5 grams of single layer graphene it will be enough to cover an entire football stadium. There is a huge amount of surface area per unit weight with this material.

That translates into another interesting property in the storage area. In that field that is a device called supercapacitors or ultracapacitors. The operation of supercapacitors depends upon conducting surface areas, like graphene or activated carbon. These graphene sheets have, to be exact, 2630 meters squared per gram. That would give you, in principle, a very high capacity per unit gram of this material when you use it as an electron material for supercapacitors. There is are so many properties associated with graphene for energy applications, those are just examples, I could talk about this all day!

 

 

R&D Magazine: Where is the team currently with the GCA-II-N and what are the next steps for this project?

Jang: Last year we began to sell the product. In Dayton, OH, where we are situated at the moment we have a small-scale manufacturing facility. It is now about a 50-metric-ton capacity facility and we can easily scale it up. We have been producing mass qualities of this and then delivering them to some of the potential customers for validation. We are basically in the customer validation stage for this business right now.

We will continue to do research and development for this project. We will eventually manufacture the batteries here in the U.S., but at the moment we are doing the anode materials only.

R&D Magazine: What types of customers are showing interest in this technology?

Jang: Electrical vehicles are a big area that is growing rapidly, particularly in areas in Asia such as China. The electrical vehicle industry is taking the driver’s seat and is driving the growth of this business worldwide right now. E-bikes and electronic scooters are another rapidly growing business where this could be used.

Another example is your smart phone. Right now, if you continue to use your phone you may be able to last for half a day or maybe a whole day if you push it. This technology has the ability to double the amount of energy that could be stored in your battery. Electronic devices is another big area for application of this technology. 

A third area is in the energy storage business, it could be utilized to store solar energy or wind energy after it has been captured. Lithium-ion batteries are gaining a lot of ground in this market right now.

Right now, another rapidly growing area is the drone. Drones are used, not only for fun, but for agricultural purposes or for surveillance purposes, such as during natural disasters.  Drones are seeing a lot of applications right now and batteries are very important part of that.

R&D Magazine: Are there any challenges to working with graphene?

Jang: One of the major challenges is that graphene by itself is still a relatively high cost. We are doing second-generation processes right now, and I think in a couple of years we should be able to significantly reduce the cost of graphene. We are also working on a third generation of processes that would allow us to reduce the cost even further. That is a major obstacle to large-scale commercialization of all graphene applications.

The second challenge is the notion of graphene as a so-called ‘nanomaterial’ in thickness that a lot customers find it difficult to disperse in water or disperse in organic solvent or plastic in order to combine graphene with other types of materials, make a composite out of it. Therefor people are resistant to use it. We have found a way to overcome this either real challenge, or perceived challenge. We can do that for a customer and then ship that directly to the customer.

There is also an education challenge. It is sometimes difficult to convince engineers, they want to stick with the materials they are more familiar with, even though the performance is better with graphene. That is a barrier as well. However, I do think it is becoming more well known.

Laura Panjwani
Editor-in-chief R & D Magazine

Graphene research Breakthrough – Graphene produced with unique edge pattern – Crucial step toward using Graphene for ‘Nanoelectronic components’


stablegraphene2-researcherswDifferent patterns are formed at the edges of nanographene. Zigzags are particularly interesting — and particularly unstable. FAU researchers have now succeeded in creating stable layers of carbon with this pattern on their edges. Credit: FAU/Konstantin Amsharov

Bay, fjord, cove, armchair and zigzag—chemists use terms such as these to describe the shapes taken by the edges of nanographene.

Graphene consists of a single-layered carbon structure in which each carbon atom is surrounded by three others. This creates a pattern reminiscent of a honeycomb, with atoms in each of the corners. Nanographene is a promising candidate to bring microelectronics down to the nano-scale and a likely substitute for silicon.

The electronic properties of the material depend greatly on its shape, size and above all, periphery—in other words how the edges are structured. A  periphery is particularly suitable—in this configuration, the electrons, which act as charge carriers, are more mobile than in other edge structures. This means that using pieces of zigzag-shaped graphene in nanoelectronics components may allow higher frequencies for switches.

Materials scientists who want to research only zigzag nanographene confront the problem that this form makes the compounds unstable and difficult to produce in a controlled manner. This is a prerequisite, however, if the  are to be investigated in detail.

Researchers led by Dr. Konstantin Amsharov from the Chair of Organic Chemistry II have now succeeded in doing just that. Their research has now been published in Nature Communications. Not only have they discovered a straightforward method for synthesising zigzag nanographene, their procedure delivers a yield of close to 100 percent and is suitable for large scale production. They have already produced a technically relevant quantity in the laboratory.

Researchers wild about zigzags
The much sought-after zigzag pattern can be found either in staggered rows of honeycombs (blue and purple) or four-limbed stars surrounding a central point of four graphene honeycombs (red and green). Credit: FAU/Konstantin Amsharov

The researchers first produced preliminary molecules, which they then fit together in a honeycomb formation over several cycles in a process known as cyclisation. In the end, graphene fragments are produced from staggered rows of honeycombs or four-limbed stars surrounding a central point of four graphene honeycombs, with the sought-after zigzag pattern at the edges. The product crystallises directly, even during synthesis. In their , the molecules are not in contact with oxygen. In solution, however, oxidation causes the structures to disintegrate quickly.

This approach allows scientists to produce large pieces of graphene, while maintaining control over their shape and periphery. This breakthrough in  research means that scientists should soon be able to produce and research a variety of interesting  structures, a crucial step toward using the material in nanoelectronic components.

 Explore further: Holey graphene as Holy Grail alternative to silicon chips

More information: Dominik Lungerich et al, Dehydrative π-extension to nanographenes with zig-zag edges, Nature Communications (2018). DOI: 10.1038/s41467-018-07095-z

 

Columbia University: Unlocking Graphene’s Superconducting Powers with a ‘Magic Angle’ (a twist) and Compression (a squeeze)


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Pictured: Applying pressure to twisted bilayer graphene pushes the layer together, and transforms the material from a metal to a superconductor. Credit: Ella Maru Studio

A Columbia-led team has discovered a new method to manipulate the electrical conductivity of this game-changing material, the strongest known to man with applications ranging from nano-electronic devices to clean energy.

Graphene has been heralded as a wonder material. Not only is it the strongest, thinnest material ever discovered, its exceptional ability to conduct heat and electricity paves the way for innovation in areas ranging from electronics to energy to medicine.

Now, a Columbia University-led team has developed a new method to finely tune adjacent layers of graphene—lacy, honeycomb-like sheets of carbon atoms—to induce superconductivity. Their research provides new insights into the physics underlying this two-dimensional material’s intriguing characteristics.

The team’s paper is published in the Jan. 24 issue of Science.

“Our work demonstrates new ways to induce superconductivity in twisted , in particular, achieved by applying pressure,” said Cory Dean, assistant professor of physics at Columbia and the study’s principal investigator. “It also provides critical first confirmation of last year’s MIT results—that bilayer graphene can exhibit electronic properties when twisted at an angle—and furthers our understanding of the system, which is extremely important for this new field of research.”

In March 2018 researchers at the Massachusetts Institute of Technology reported a groundbreaking discovery that two graphene layers can conduct electricity without resistance when the twist angle between them is 1.1 degrees, referred to as the “magic angle.”

But hitting that magic angle has proven difficult. “The layers must be twisted to within roughly a tenth of a degree around 1.1, which is experimentally challenging,” Dean said. “We found that very small errors in alignment could give entirely different results.”

So Dean and his colleagues, who include scientists from the National Institute for Materials Science and the University of California, Santa Barbara, set out to test whether magic-angle conditions could be achieved at bigger rotations.

“Rather than trying to precisely control the angle, we asked whether we could instead vary the spacing between the layers,” said Matthew Yankowitz, a postdoctoral research scientist in Columbia’s physics department and first author on the study. “In this way any twist angle could, in principle, be turned into a magic angle.”

They studied a sample with twist angle of 1.3 degrees—only slightly larger than the magic angle but still far enough away to preclude superconductivity.

Applying pressure transformed the material from a metal into either an insulator—in which electricity cannot flow—or a superconductor—where electrical current can pass without resistance—depending on the number of electrons in the material.

“Remarkably, by applying pressure of over 10,000 atmospheres we observe the emergence of the insulating and superconducting phases,” Dean said. Additionally, the superconductivity develops at the highest temperature observed in graphene so far, just over 3 degrees above absolute zero.”

To reach the high pressures needed to induce superconductivity the team worked closely with the National High Magnetic Field user facility, known as the Maglab, in Tallahassee, Florida.

“This effort was a huge technical challenge,” said Dean. “After fabricating one of most unique devices we’ve ever worked with, we then had to combine cryogenic temperatures, high magnetic fields, and high pressure—all while measuring electrical response. Putting this all together was a daunting task and our ability to make it work is really a tribute to the fantastic expertise at the Maglab.”

The researchers believe it may be possible to enhance the critical temperature of the superconductivity further at even higher pressures. The ultimate goal is to one day develop a superconductor which can perform under room temperature conditions, and although this may prove challenging in graphene, it could serve as a roadmap for achieving this goal in other materials.

Andrea Young, assistant professor of physics at UC Santa Barbara, a collaborator on the study, said the work clearly demonstrates that squeezing the layers has same effect as twisting them and offers an alternative paradigm for manipulating the electronic properties in .

“Our findings significantly relax the constraints that make it challenging to study the system and gives us new knobs to control it,” Young said.

Dean and Young are now twisting and squeezing a variety of atomically-thin  in the hopes of finding superconductivity emerging in other two-dimensional systems.

“Understanding ‘why’ any of this is happening is a formidable challenge but critical for eventually harnessing the power of this material—and our work starts unraveling the mystery,'” Dean said.

 Explore further: Twisted electronics open the door to tunable 2-D materials

More information: “Tuning superconductivity in twisted bilayer graphene” Science (2019). science.sciencemag.org/lookup/ … 1126/science.aav1910

 

Atomic-scale capillaries block smallest ions thanks to Graphene – Structures are ideal in Desalination and Filtration Technologies


graphene atomicscalec de sal                                       Credit: University of Manchester

 

** See More About Graphene (YouTube Video) and Desalination at the end of this article **

Researchers at The University of Manchester’s National Graphene Institute in the UK have succeeded in making artificial channels just one atom in size for the first time. The new capillaries, which are very much like natural protein channels such as aquaporins, are small enough to block the flow of smallest ions like Na+ and Cl- but allow water to flow through freely. As well as improving our fundamental understanding of molecular transport at the atomic scale, and especially in biological systems, the structures could be ideal in desalination and filtration technologies.

“Obviously, it is impossible to make capillaries smaller than one atom in size,” explains team leader Sir Andre Geim. “Our feat seemed nigh on impossible, even in hindsight, and it was difficult to imagine such tiny capillaries just a couple of years ago.”

Naturally occurring protein channels, such as aquaporins, allow water to quickly permeate through them but block hydrated ions larger than around 7 A in size thanks to mechanisms like steric (size) exclusion and electrostatic repulsion. Researchers have been trying to make artificial capillaries that work just like their natural counterparts, but despite much progress in creating nanoscale pores and nanotubes, all such structures to date have still been much bigger than biological channels.

Geim and colleagues have now fabricated channels that are around just 3.4 A in height. This is about half the size of the smallest hydrated ions, such as K+ and Cl-, which have a diameter of 6.6 A. These channels behave just like protein channels in that they are small enough to block these ions but are sufficiently big to allow water molecules (with a diameter of around 2.8 A) to freely flow through.

The structures could, importantly, help in the development of cost-effective, high-flux filters for water desalination and related technologies – a holy grail for researchers in the field.

Credit: University of Manchester

Atomic-scale Lego

Publishing their findings in Science the researchers made their structures using a van der Waals assembly technique, also known as “atomic-scale Lego”, which was invented thanks to research on graphene. “We cleave atomically flat nanocrystals just 50 and 200 nanometre in thickness from bulk graphite and then place strips of monolayer graphene onto the surface of these nanocrystals,” explains Dr. Radha Boya, a co-author of the research paper. “These strips serve as spacers between the two crystals when a similar atomically-flat crystal is subsequently placed on top. The resulting trilayer assembly can be viewed as a pair of edge dislocations connected with a flat void in between. This space can accommodate only one atomic layer of water.”

Using the  monolayers as spacers is a first and this is what makes the new channels different from any previous structures, she says.

The Manchester scientists designed their 2-D capillaries to be 130 nm wide and several microns in length. They assembled them atop a silicon nitride membrane that separated two isolated containers to ensure that the channels were the only pathway through which water and ions could flow.

Until now, researchers had only been able to measure water flowing though capillaries that had much thicker spacers (around 6.7 A high). And while some of their  indicated that smaller 2-D cavities should collapse because of van der Waals attraction between the opposite walls, other calculations pointed to the fact that  inside the slits could actually act as a support and prevent even one-atom-high slits (just 3.4 A tall) from falling down. This is indeed what the Manchester team has now found in its experiments.

Measuring water and ion flow

“We measured water permeation through our channels using a technique known as gravimetry,” says Radha. “Here, we allow water in a small sealed container to evaporate exclusively through the capillaries and we then accurately measure (to microgram precision) how much weight the container loses over a period of several hours.”

To do this, the researchers say they built a large number of channels (over a hundred) in parallel to increase the sensitivity of their measurements. They also used thicker top crystals to prevent sagging, and clipped the top opening of the capillaries (using plasma etching) to remove any potential blockages by thin edges present here.

To measure ion flow, they forced ions to move through the capillaries by applying an electric field and then measured the resulting currents. “If our capillaries were two atoms high, we found that small ions can move freely though them, just like what happens in bulk water,” says Radha. “In contrast, no ions could pass through our ultimately-small one-atom-high channels.

“The exception was protons, which are known to move through water as true subatomic particles, rather than ions dressed up in relatively large hydration shells several angstroms in diameter. Our channels thus block all hydrated ions but allow protons to pass.”

Since these  behave in the same way as protein channels, they will be important for better understanding how water and ions behave on the molecular scale – as in angstrom-scale biological filters. “Our work (both present and previous) shows that atomically-confined water has very different properties from those of bulk ,” explains Geim. “For example, it becomes strongly layered, has a different structure, and exhibits radically dissimilar dielectric properties.”

 Explore further: Devices made from 2-D materials separate salts in seawater

More information: Dorri Halbertal et al. Imaging resonant dissipation from individual atomic defects in graphene, Science (2017). DOI: 10.1126/science.aan0877 , https://arxiv.org/abs/1811.09227

Want to Read More About Cutting Edge Desalination, Energy Storage and Carbon Nanotubes?

opt-cnts-for-water-wang-mutha-nanotubes_0MIT: Optimizing carbon nanotube electrodes for energy storage and water desalination applications

 

 

 

Graphene for Water Desalination

 

Water, one of the world’s most abundant and highly demanded resources for sustaining life, agriculture, and industry, is being contaminated globally or is unsafe for drinking, creating a need for new and better desalination methods. Current desalination methods have high financial, energy, construction, and operating costs, resulting in them contributing to less than 1% of the world’s reserve water supplies. Advances in nanoscale science and engineering suggest that more cost effective and environmentally friendly desalination process using graphene is possible …

MIT: Physicists record ‘lifetime’ of graphene qubits – Foundation for Advancing Quantum Computing


 

Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit

The demonstration, which used a new kind of graphene-based qubit, meaning how long it can maintain a special state that allows it to represent two logical states simultaneously, represents a critical step forward for practical quantum computing, the researchers say.

Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1.

But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks.

Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing. In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials.

These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

“Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT.

“In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

A pristine graphene sandwich

Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum).

In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage.

These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches.

The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

 

When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene.

The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

How voltage helps

The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip.

“Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

Coherent control of a hybrid superconducting circuit made with graphene-based van der Waals heterostructures
Joel I-Jan Wang, Daniel Rodan-Legrain, Landry Bretheau, Daniel L. Campbell, Bharath Kannan, David Kim, Morten Kjaergaard, Philip Krantz, Gabriel O. Samach, Fei Yan, Jonilyn L. Yoder, Kenji Watanabe, Takashi Taniguchi, Terry P. Orlando, Simon Gustavsson, Pablo Jarillo-Herrero & William D. Oliver
Nature Nanotechnology (2018)
DOI: 10.1038_s41565-018-0329-2

Contact information:

William D. Oliver
MIT Physics Professor of the Practice
oliver@ll.mit.edu URL: http://www.rle.mit.edu/

Pablo Jarillo-Herrero
MIT Physics Professor
pjarillo@mit.edu URL: http://jarilloherrero.mit.edu/

Massachusetts Institute of Technology (MIT)

 

Aerospace Potential for Graphene – Provides Superior Mechanical and Thermal Properties – Lower Fuel and Operating Costs


Aernnova, Grupo Antolin-Ingenieria and Airbus – as partners in the Graphene Flagship, the European Union’s largest-ever research initiative with funding of EUR 1 billion – have produced a leading edge for the Airbus A350 horizontal tail plane using graphene-enhanced composites.

“We worked together with Grupo Antolin-Ingenieria and Airbus as part of the Graphene Flagship’s production work package and our collaboration greatly benefitted from the discussions during meetings,” said Ana Reguero of Aernnova.

“Airbus brought us – as the manufacturer of the current leading edge – together with Grupo Antolin-Ingenieria on the project.”

Aernnova, Grupo Antolin-Ingenieria and Airbus produced a leading edge for the Airbus A350 horizontal tail plane using graphene-enhanced composites. © Graphene Flagship

As the first part of the tail plane to contact air, the leading edge is subjected to extreme temperatures caused by compressive heating of the air ahead of the wing. Thus, it must possess excellent mechanical and thermal properties.

“Aernnova supplied the resin to Grupo Antolin-Ingenieria who added graphene directly to the resin and applied milling forces,” said Reguero.

This creates small graphene particles – an important step to get good graphene infiltration within the resin, avoiding unwanted impurities, such as solvents, which can alter the viscosity of the resin.  It is important to maintain the correct viscosity of the resin to ensure the optimal outcome during the resin transfer moulding of the leading edge.”

At a component level the team found that the resin with the added graphene showed increased mechanical and thermal properties, including a decreased fracture speed.

By increasing the resin properties with graphene, it will be possible to make the tail edge thinner, decreasing its weight while maintaining its safety. This will provide a significant saving in fuel and therefore costs and emissions over the aircraft lifetime.

At a component level the team found that the resin with the added graphene showed increased mechanical and thermal properties. © Graphene Flagship

“Our small-scale tests showed an increase in properties. We will next test a one third scale model,” said Reguero.

“This is a great example of the collaborations fostered by the Graphene Flagship,” said Professor Andrea C. Ferrari, its science and technology officer. “Three of our industrial partners came together to address a key problem and found that graphene offers a solution beyond the state of the art.

The development and system integration of graphene-based technologies follows the plans of our innovation and technology, where composite technologies play a prominent role.”

Scientists at the University of Manchester develop revolutionary method for graphene printed electronics – Impact for IoT


graphene post 1This visualisation shows layers of graphene used for membranes. Credit: University of Manchester

 

A team of researchers based at The University of Manchester have found a low cost method for producing graphene printed electronics, which significantly speeds up and reduces the cost of conductive graphene inks.

Printed electronics offer a breakthrough in the penetration of information technology into everyday life. The possibility of printing  will further promote the spread of Internet of Things (IoT) .

The development of printed conductive inks for electronic applications has grown rapidly, widening applications in transistors, sensors, antennas RFID tags and wearable electronics.

Current conductive inks traditionally use metal nanoparticles for their high electrical conductivity. However, these  can be expensive or easily oxidised, making them far from ideal for low cost IoT applications.

The team have found that using a material called dihydro-levo-gucosenone known as Cyrene is not only non-toxic but is environmentally- friendly and sustainable but can also provide higher concentrations and conductivity of  ink.

Professor Zhiurn Hu said: “This work demonstrates that printed graphene technology can be low cost, sustainable, and environmentally friendly for ubiquitous wireless connectivity in IoT era as well as provide RF energy harvesting for low power electronics”.

Professor Sir Kostya Novoselov said: “Graphene is swiftly moving from research to application domain. Development of production methods relevant to the end-user in terms of their flexibility, cost and compatibility with existing technologies are extremely important. This work will ensure that implementation of graphene into day-to-day products and technologies will be even faster”.

Kewen Pan, the lead author on the paper said: “This perhaps is a significant step towards commercialisation of printed graphene technology. I believe it would be an evolution in printed electronics industry because the material is such low cost, stable and environmental friendly”.

The National Physical Laboratory (NPL), who were involved in measurements for this work, have partnered with the National Graphene Institute at The University of Manchester to provide a materials characterisation service to provide the missing link for the industrialisation of graphene and 2-D materials. They have also published a joint NPL and NGI a good practice guide which aims to tackle the ambiguity surrounding how to measure graphene’s characteristics.

Professor Ling Hao said: “Materials characterisation is crucial to be able to ensure performance reproducibility and scale up for commercial applications of graphene and 2-D materials. The results of this collaboration between the University and NPL is mutually beneficial, as well as providing measurement training for Ph.D. students in a metrology institute environment.”

Graphene has the potential to create the next generation of electronics currently limited to science fiction: faster transistors, semiconductors, bendable phones and flexible wearable electronics.

 Explore further: Fully integrated circuits printed directly onto fabric

 

Holey graphene as ‘Holy Grail’ alternative to silicon chips – turning graphene into a semiconductor


3D Graphene

Graphene, in its regular form, does not offer an alternative to silicon chips for applications in nanoelectronics. It is known for its energy band structure, which leaves no energy gap and no magnetic effects.

Graphene antidot lattices, however, are a new type of graphene device that contain a periodic array of holes—missing several atoms in the otherwise regular single layer of carbon atoms. This causes an energy band gap to open up around the baseline energy level of the material, effectively turning graphene into a semiconductor.

 

In a new study published in EPJ B, Iranian physicists investigate the effect of antidot size on the electronic structure and magnetic properties of triangular antidots in graphene. Zahra Talebi Esfahani from Payame Noor University in Tehran, Iran, and colleagues have confirmed the existence of a band gap opening in such antidot graphene lattices, which depends on the electron’s spin degree of freedom, and which could be exploited for applications like spin transistors. The authors perform simulations using holes that are shaped like right and equilateral triangles, to explore the effects of both the armchair-shaped and zigzag-shaped edges of graphene holes on the material’s characteristics.

In this study, the values of the  and the total magnetisation, the authors find, depend on the size, shape and spacing of the antidots. These may actually increase with the number of zigzag edges around the holes. The induced  are mainly localised on the edge atoms, with a maximum value at the centre of each side of the equilateral triangle. By contrast, armchair edges display no local magnetic moment.

Thanks to the energy band gap created, such periodic arrays of triangular antidot lattices can be used as magnetic semiconductors. And because the  band gap depends on the electron spins in the material, magnetic antidot lattices are ideal candidates for spintronic applications.

 Explore further: Artificial magnetic field produces exotic behavior in graphene sheets

More information: Zahra Talebi Esfahani et al, A DFT study on the electronic and magnetic properties of triangular graphene antidot lattices, The European Physical Journal B (2018). DOI: 10.1140/epjb/e2018-90517-6