Graphene quantum dots for single electron transistors ~ Application for Future Electronics


The schematic structure of the devices

Scientists from Manchester University, the Ulsan National Institute of Science & Technology and the Korea Institute of Science and Technology have developed a novel technology, which combines the fabrication procedures of planar and vertical heterostructures in order to assemble graphene-based single-electron transistors.

In the study, it was demonstrated that high-quality graphene quantum dots (GQDs), regardless of whether they were ordered or randomly distributed, could be successfully synthesized in a matrix of monolayer hexagonal boron nitride (hBN).

Here, the growth of GQDs within the layer of hBN was shown to be catalytically supported by the platinum (Pt) nanoparticles distributed in-between the hBN and supporting oxidised silicon (SiO2) wafer, when the whole structure was treated by the heat in the methane gas (CH4). It was also shown, that due to the same lattice structure (hexagonal) and small lattice mismatch (~1.5%) of graphene and hBN, graphene islands grow in the hBN with passivated edge states, thereby giving rise to the formation of defect-less quantum dots embedded in the hBN monolayer.

Such planar heterostructures incorporated by means of standard dry-transfer as mid-layers into the regular structure of vertical tunnelling transistors (Si/SiO2/hBN/Gr/hBN/GQDs/hBN/Gr/hBN; here Gr refers to monolayer graphene and GQDs refers to the layer of hBN with the embedded graphene quantum dots) were studied through tunnel spectroscopy at low temperatures (3He, 250mK).

The study demonstrated where the manifestation of well-established phenomena of the Coulomb blockade for each graphene quantum dot as a separate single electron transmission channel occurs.

‘Although the outstanding quality of our single electron transistors could be used for the development of future electronics, “This work is most valuable from a technological standpoint as it suggests a new platform for the investigation of physical properties of various materials through a combination of planar and van der Waals heterostructures.” as explained study co-author Davit Ghazaryan, Associate Professor at the HSE Faculty of Physics, and Research Fellow at the Institute of Solid State Physics (RAS)

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A Conversation with Professor (Sir) Kostya Novoselov, Co-Nobel Prize Winner in Physics 2019 ~ Research into “The Graphene Flagship” and other 2D materials


Talking with SciTech Europa, Professor Novoselov, co-awarded the 2019 Nobel Prize in Physics, for the discovery and isolation of a single atomic layer of carbon for the first time, explores the research into Graphene Flagship and other 2D materials.

At the University of Manchester, UK, in 2004, Professor Sir Kostya Novoselov, along with his colleague Professor Sir Andre Geim, discovered and isolated a single atomic layer of carbon for the first time. The pair received the Nobel Prize in Physics in 2010 in recognition of their breakthrough.

On 28 January 2013, the European Commission announced that, out of the six pilot preparatory actions put forward for the Future and Emerging Technology (FET) Flagships competition, the Graphene Flagship, along with the Human Brain Project, had been selected to receive €1bn in funding over the course of a decade, tasking it with bringing together academic and industrial researchers to take graphene from the realm of academic laboratories into European society, thereby generating economic growth, new jobs, and new opportunities.

In February, SciTech Europa attended the Mobile World Congress in Barcelona, Spain. This event is the world’s largest exhibition for the mobile industry, and where, for the fourth consecutive year, the Graphene Flagship hosted its Graphene Pavilion – this year showcasing over 20 different graphene-based working prototypes and devices that will transform future telecommunications.

At the pavilion, SEQ met with Professor Novoselov to discuss research into graphene and other two dimensional materials, as well as how the Flagship is working to bolster both fundamental research and applications stemming from these advanced materials.

What do you think have been the biggest, and latest, developments in graphene (and other 2D materials) research?

There has been a lot of progress in recent years and, indeed, we are no longer talking only about graphene, but also about many other two dimensional materials as well.

First of all – new applications of graphene is one example of recent developments – we see new applications emerging on an almost monthly basis. Second, there is still a lot of progress being made in fundamental research on graphene and 2D materials. And those fundamental results are being implemented in applications.

In terms of other new 2D materials, there is a lot of activity on ferromagnetic materials.

What potential is there now to move graphene forwards, and how would you describe the role of the Flagship in this?

The basic technology is in place, and so what is important now is for entrepreneurs and SMEs to convert those developments into commercial applications, and, indeed, we need to help them to do so.

The Flagship, of course, has now reached the half way stage, and we therefore need to carefully balance the amount of effort we place on applications with the effort we place on the development of fundamental science, which remains crucial.

Nevertheless, we also need to ensure we are helping companies and industry to introduce this material into real products, and that is actually much more difficult, not least because of the fact that this has not been done at this scale before, and so nobody knows how to do it yet.

Are you able to utilise EU instruments to help fund commercialisation activities?

It is not necessarily funding that is a problem in in Europe; the challenge comes more in the form of bringing together scientists, entrepreneurs, and funders in the same room, and it is still not clear how to achieve that. There is thus the argument that we need to work more closely with entrepreneurs and we need to grow those entrepreneurs who are working on advanced materials because this is a much more challenging area than, say, ‘.com’ applications.

What do you feel are the biggest barriers here?

It is perhaps the mentality that exists around risk taking that needs to change. Bringing together entrepreneurs, scientists, the technology and the money around the same table is a challenge and, as I have mentioned, it needs to be understood that bringing new materials, especially nanomaterials, to market is much more challenging than it is to bring, for example, new software to consumers.

And, of course, the level of required investment is also much larger. Whether we have enough people in Europe who are ready to take this risk is a good question.

Would you say that Europe is too risk averse when it comes to this type of investment in comparison to, for instance, the USA?

Perhaps; there is certainly a sense that Europe needs to work much harder than the USA or South-East Asia. And the reason for that is not only a lack of those willing to take enhanced risks, but also the level and mobility of the available money and, indeed, how soon financiers expect a return on their investment.

Could 2D materials research spark a ‘revolution’ in real world applications?

I am not sure that we will see a ‘revolution’; the growth in real world applications utilising graphene is, and will continue to be, a gradual introduction. That is not to say, however, that this gradual process won’t speed up a little over time.

And it is great to see that, when it comes to graphene, this introduction, although gradual, is already happening much faster than with any other advanced material that we have seen before. The purpose of the Flagship is to help speed up this process.

The Flagship is now investing in research into the safety of graphene. How important is that?

This is an example of the sort of issue where the Flagship should take the initiative, because it is not only about graphene; we need to realise that many new nanomaterials are going to play an increasing role in the everyday lives of people, and we need to be prepared for that.

There are a great many regulations which have to be passed when bringing such advanced materials to market, including health and safety and toxicology regulations, and very often these are not very well defined because, quite simply, we have never been in this situation before. It can also be quite expensive to run the necessary projects to investigate things like toxicology, and so it is important for projects like the Flagship to take the initiative and help businesses to overcome these barriers.

Where are your own research interests going to lie, moving forwards?

I do indeed conduct my own research, and within that graphene is not the largest part. I go beyond graphene and work on many other 2D materials and heterostructures, but it is nevertheless exciting to remember that it was graphene that made all the other materials possible as we work on those heterostructures towards new discoveries.

Professor Sir Kostya Novoselov
Nobel Laureate 
Director, National Graphene Institute at the University of Manchester
Member, Strategic Advisory Council, Graphene Flagship
Tweet @GrapheneCA @UoMGraphene

www.graphene.manchester.ac.uk/about/ngi
www.graphene-flagship.eu

Directa Plus to provide graphene for textile enhancement project with Loro Piana


It was recently announced that graphene technology developed by Directa Plus will be used to “enrich” textiles made by Italian high-end clothing and fabric maker Loro Piana.

The deal, which is for an initial duration of three years for a minimum value of €0.8 Million, will see Directa’s G+ graphene technology incorporated into some of Loro Piana’s fabrics and garments.

Giulio Cesareo, founder & chief executive of Directa Plus, said:

“The significant innovations in high quality fabrics that can be achieved through the use of Directa Plus’ technology will allow increased comfort and performance for the end users of Loro Piana’s products”.

Also Read About Nanotechnology in Smart Textiles and Wearables

The company said the hypoallergenic, non-toxic and sustainably produced nature of Loro Piana’s product range fitted “perfectly” with Directa’s own culture and values.

Breakthrough in the search for graphene-based electronics


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A team of researchers from Denmark has solved one of the biggest challenges in making effective nanoelectronics based on graphene. The new results have just been published in Nature Nanotechnology.

For 15 years, scientists have tried to exploit the “miracle material” graphene to produce nanoscale electronics. On paper, graphene should be great for just that: it is ultra-thin – only one atom thick and therefore two-dimensional, it is excellent for conducting electrical current, and holds great promise for future forms of electronics that are faster and more energy efficient. In addition, graphene consists of carbon atoms – of which we have an unlimited supply.

In theory, graphene can be altered to perform many different tasks within e.g. electronics, photonics or sensors simply by cutting tiny patterns in it, as this fundamentally alters its quantum properties. One “simple” task, which has turned out to be surprisingly difficult, is to induce a band gap – which is crucial for making transistors and optoelectronic devices. However, since graphene is only an atom thick all of the atoms are important and even tiny irregularities in the pattern can destroy its properties.

“Graphene is a fantastic material, which I think will play a crucial role in making new nanoscale electronics. The problem is that it is extremely difficult to engineer the electrical properties,” says Peter Bøggild, professor at DTU Physics.

The Center for Nanostructured Graphene at DTU and Aalborg University was established in 2012 specifically to study how the electrical properties of graphene can be tailored by changing its shape on an extremely small scale. When actually patterning graphene, the team of researchers from DTU and Aalborg experienced the same as other researchers worldwide: it didn’t work.

“When you make patterns in a material like graphene, you do so in order to change its properties in a controlled way – to match your design. However, what we have seen throughout the years is that we can make the holes, but not without introducing so much disorder and contamination that it no longer behaves like graphene. It is a bit similar to making a water pipe that is partly blocked because of poor manufacturing. On the outside, it might look fine, but water cannot flow freely. For electronics, that is obviously disastrous,” says Peter Bøggild.

Now, the team of scientists have solved the problem. The results are published in Nature Nanotechnology. Two postdocs from DTU Physics, Bjarke Jessen and Lene Gammelgaard, first encapsulated graphene inside another two-dimensional material – hexagonal boron nitride, a non-conductive material that is often used for protecting graphene’s properties.

Next, they used a technique called electron beam lithography to carefully pattern the protective layer of boron nitride and graphene below with a dense array of ultra small holes. The holes have a diameter of approx. 20 nanometers, with just 12 nanometers between them – however, the roughness at the edge of the holes is less than 1 nanometer, or a billionth of a meter. This allows 1000 times more electrical current to flow than had been reported in such small graphene structures. And not just that.

“We have shown that we can control graphene’s band structure and design how it should behave. When we control the band structure, we have access to all of graphene’s properties – and we found to our surprise that some of the most subtle quantum electronic effects survive the dense patterning – that is extremely encouraging. Our work suggests that we can sit in front of the computer and design components and devices – or dream up something entirely new – and then go to the laboratory and realise them in practice,” says Peter Bøggild. He continues:

“Many scientists had long since abandoned attempting nanolithography in graphene on this scale, and it is quite a pity, since nanostructuring is a crucial tool for exploiting the most exciting features of graphene electronics and photonics. Now we have figured out how it can be done; one could say that the curse is lifted. There are other challenges, but the fact that we can tailor electronic properties of graphene is a big step towards creating new electronics with extremely small dimensions,” says Peter Bøggild.

About the Center for Nanostructured Graphene

• Funded by the Danish National Research Foundation with a total budget of 100 million DKK for the ten-year period 2012 – 2022. It focuses on basic research, but all its research projects have long-term perspectives for applications.

• the team is also part of the Graphene Flagship, which with a budget of €1 billion represents a new form of joint, coordinated research on an unprecedented scale, and is Europe’s biggest ever research initiative. It is tasked with bringing together academic and industrial partners to take graphene from the realm of academic laboratories into society in the space of 10 years, thus generating economic growth, new jobs and new opportunities for Europe.

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

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 …