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3D printable 2D materials based inks show promise to improve energy storage devices

Posted By Graphene Council, The Graphene Council, Sunday, August 11, 2019
Updated: Sunday, August 4, 2019
For the first time, a team of researchers, from the School of Materials and the National Graphene Institute at The the University of Manchester have formulated inks using the 2D material MXene, to produce 3D printed interdigitated electrodes.

As published in Advanced Materials, these inks have been used to 3D print electrodes that can be used in energy storages devices such as supercapacitors.

MXene, a ‘clay-like’ two-dimensional material composed of early transition metals (such as titanium) and carbon atoms, was first developed by Drexel University. However, unlike most clays, MXene shows high electrical conductivity upon drying and is hydrophilic, allowing them to be easily dispersed in aqueous suspensions and inks.

Graphene was the world’s first two-dimensional material, more conductive than copper, many more times stronger than steel, flexible, transparent and one million times thinner than the diameter of a human hair.

Since its isolation, graphene has opened the doors for the exploration of other two-dimensional materials, each with a range of different properties. However, in order to make use of these unique properties, 2D materials need to be efficiently integrated into devices and structures. The manufacturing approach and materials formulations are essential to realise this.

Dr Suelen Barg who led the team said: “We demonstrate that large MXene flakes spanning a few atoms thick, and water can be independently used to formulate inks with very specific viscoelastic behaviour for printing. These inks can be directly 3D printed into freestanding architectures over 20 layers tall. Due to the excellent electrical conductivity of MXene, we can employ our inks to directly 3D print current collector-free supercapacitors. The unique rheological properties combined with the sustainability of the approach open many opportunities to explore, especially in energy storage and applications requiring the functional properties of 2D MXene in customized 3D architectures.”

Wenji and Jae, PhD students at the Nano3D Lab at the University, said: “Additive manufacturing offers one possible method of building customised, multi-materials energy devices, demonstrating the capability to capture MXene’s potential for usage in energy applications. We hope this research will open avenues to fully unlock the potential of MXene for use in this field.”

The unique rheological properties combined with the sustainability of the approach open many opportunities to explore, especially in energy storage and applications requiring the functional properties of 2D MXene in customized 3D architectures. Dr Suelen Barg, School of Materials

The performance and application of these devices increasingly rely on the development and scalable manufacturing of innovative materials in order to enhance their performance.

Supercapacitors are devices that are able to produce massive amounts of power while using much less energy than conventional devices. There has been much work carried out on the use of 2D materials in these types of devices due to their excellent conductivity as well as having the potential to reduce the weight of the device.

Potential uses for these devices are for the automotive industry, such as in electric cars as well as for mobile phones and other electronics.

Tags:  2D materials  3D Printing  Drexel University  Graphene  Suelen Barg  Supercapacito  University of Manchester 

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A novel graphene-matrix-assisted stabilization method will help unique 2D materials become a part of quantum computers

Posted By Graphene Council, The Graphene Council, Sunday, August 11, 2019
Updated: Monday, August 5, 2019
The family of 2D materials was recently joined by a new class, the monolayers of oxides and carbides of transition metals, which have been the subject of extensive theoretical and experimental research. These new materials are of great interest to scientists due to their unusual rectangular atomic structure and chemical and physical properties. 

Scientists are particularly interested in a unique 2D rectangular copper oxide cell, which does not exist in crystalline (3D) form, as opposed to most 2D materials, whether well known or discovered recently, which have a lattice similar to that of their crystalline (3D) counterparts. The main hindrance for practical use of monolayers is their low stability.

A group of scientists from MISiS, the Institute of Biochemical Physics of RAS (IBCP), Skoltech, and the National Institute for Materials Science in Japan (NIMS) discovered 2D copper oxide materials with an unusual crystal structure inside a two-layer graphene matrix using experimental methods.

“Finding that a rectangular-lattice copper-oxide monolayer can be stable under given conditions is as important as showing how the binding of copper oxide and a graphene nanopore and formation of a common boundary can lead to the creation of a small, stable 2D copper oxide cluster with a rectangular lattice. In contrast to the monolayer, the small copper oxide cluster’s stability is driven to a large extent by the edge effects (boundaries) that lead to its distortion and, subsequently, destruction of the flat 2D structure. Moreover, we demonstrated that binding bilayered graphene with pure copper, which never exists in the form of a flat cluster, makes the 2D metal layer more stable,” says Skoltech Senior Research Scientist Alexander Kvashnin.

The preferability of the copper oxide rectangular lattice forming in a bigraphene nanopore was confirmed by the calculations performed using the USPEX evolutionary algorithm developed by Professor at Skoltech and MIPT, Artem Oganov. The studies of the physical properties of the stable 2D materials indicate that they are good candidates for spintronics applications.

Tags:  2D materials  Alexander Kvashnin  Artem Oganov  Graphene  MIPT  Skoltech 

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New quantum phenomena helps to understand fundamental limits of graphene electronics

Posted By Graphene Council, The Graphene Council, Wednesday, July 31, 2019
Updated: Tuesday, July 30, 2019
A team of researchers from the Universities of Manchester, Nottingham and Loughborough have discovered quantum phenomena that helps to understand the fundamental limits of graphene electronics. As published in Nature Communications, the work describes how electrons in a single atomically-thin sheet of graphene scatter off the vibrating carbon atoms which make up the hexagonal crystal lattice.

By applying a magnetic field perpendicular to the plane of graphene, the current-carrying electrons are forced to move in closed circular “cyclotron” orbits. In pure graphene, the only way in which an electron can escape from this orbit is by bouncing off a “phonon” in a scattering event. These phonons are particle-like bundles of energy and momentum and are the “quanta” of the sound waves associated with the vibrating carbon atom. The phonons are generated in increasing numbers when the graphene crystal is warmed up from very low temperatures.

By passing a small electrical current through the graphene sheet, the team were able to measure precisely the amount of energy and momentum that is transferred between an electron and a phonon during a scattering event.

Their experiment revealed that two types of phonon scatter the electrons: transverse acoustic (TA) phonons in which the carbon atoms vibrate perpendicular to the direction of phonon propagation and wave motion (somewhat analogous to surface waves on water) and longitudinal acoustic (LA) phonons in which the carbon atoms vibrate back and forth along the direction of the phonon and the wave motion; (this motion is somewhat analogous to the motion of sound waves through air).

The measurements provide a very accurate measure of the speed of both types of phonons, a measurement which is otherwise difficult to make for the case of a single atomic layer. An important outcome of the experiments is the discovery that TA phonon scattering dominates over LA phonon scattering.

We were pleasantly surprised to find such prominent magnetophonon oscillations appearing in graphene. We were also puzzled why people had not seen them before, considering the extensive amount of literature on quantum transport in graphene. Laurence Eaves and Roshan Krishna Kumar, The University of Manchester

The observed phenomena, commonly referred to as “magnetophonon oscillations”, was measured in many semiconductors years before the discovery of graphene. It is one of the oldest quantum transport phenomena that has been known for more than fifty years, predating the quantum Hall effect. Whereas graphene possesses a number of novel, exotic electronic properties, this rather fundamental phenomenon has remained hidden.

Laurence Eaves & Roshan Krishna Kumar, co-authors of the work said: “We were pleasantly surprised to find such prominent magnetophonon oscillations appearing in graphene. We were also puzzled why people had not seen them before, considering the extensive amount of literature on quantum transport in graphene.”

Their appearance requires two key ingredients. First, the team had to fabricate high quality graphene transistors with large areas at the National Graphene Institute. If the device dimensions are smaller than a few micrometres the phenomena could not be observed.

Piranavan Kumaravadivel from The University of Manchester, lead author of the paper said: “At the beginning of quantum transport experiments, people used to study macroscopic, millimetre sized crystals. In most of the work on quantum transport on graphene, the studied devices are typically only a few micrometres in size. It seems that making larger graphene devices is not only important for applications but now also for fundamental studies.”

The second ingredient is temperature. Most graphene quantum transport experiments are performed at ultra-cold temperatures in-order to slow down the vibrating carbon atoms and “freeze-out” the phonons that usually break quantum coherence. Therefore, the graphene is warmed up as the phonons need to be active to cause the effect.

Mark Greenaway, from Loughborough University, who worked on the quantum theory of this effect said: “This result is extremely exciting - it opens a new route to probe the properties of phonons in two-dimensional crystals and their heterostructures. This will allow us to better understand electron-phonon interactions in these promising materials, understanding which is vital to develop them for use in new devices and applications.”

Tags:  2D materials  Graphene  Laurence Eaves  Loughborough University  Mark Greenaway  Piranavan Kumaravadivel  Roshan Krishna Kumar  University of Manchester  University of Nottingham 

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Graphene in Electronic Circuits

Posted By Graphene Council, The Graphene Council, Wednesday, July 31, 2019
Updated: Tuesday, July 30, 2019
Ever since graphene was discovered in 2004, researchers around the world have been working to develop commercially scalable applications for this high-performance material.

Graphene is 100 to 300 times stronger than steel at the atomic level and has a maximum electrical current density orders of magnitude greater than that of copper, making it the strongest, thinnest and, by far, the most reliable electrically conductive material on the planet. It is, therefore, an extremely promising material for interconnects, the fundamental components that connect billions of transistors on microchips in computers and other electronic devices in the modern world.

For over two decades, interconnects have been made of copper, but that metal encounters fundamental physical limitations as electrical components that incorporate it shrink to the nanoscale. “As you reduce the dimensions of copper wires, their resistivity shoots up,” said Kaustav Banerjee, a professor in the Department of Electrical and Computer Engineering. “Resistivity is a material property that is not supposed to change, but at the nanoscale, all properties change.”

As the resistivity increases, copper wires generate more heat, reducing their current-carrying capacity. It’s a problem that poses a fundamental threat to the $500 billion semiconductor industry. Graphene has the potential to solve that and other issues. One major obstacle, though, is designing graphene micro-components that can be manufactured on-chip, on a large scale, in a commercial foundry.

“Whatever the component, be it inductors, interconnects, antennas or anything else you want to do with graphene, industry will move forward with it only if you find a way to synthesize graphene directly onto silicon wafers,” Banerjee said. He explained that all manufacturing processes related to the transistors, which are made first, are referred to as the ‘front end.’ To synthesize something at the back-end — that is, after the transistors are fabricated — you face a tight thermal budget that cannot exceed a temperature of about 500 degrees Celsius. If the silicon wafer gets too hot during the back-end processes employed to fabricate the interconnects, other elements that are already on the chip may get damaged, or some impurities may start diffusing, changing the characteristics of the transistors.

Now, after a decade-long quest to achieve graphene interconnects, Banerjee’s lab has developed a method to implement high-conductivity, nanometer-scale doped multilayer graphene (DMG) interconnects that are compatible with high-volume manufacturing of integrated circuits. A paper describing the novel process was named one of the top papers at the 2018 IEEE International Electron Devices Meeting (IEDM),  from more than 230 that were accepted for oral presentations. It also was one of only two papers included in the first annual “IEDM Highlights” section of an issue of the journal Nature Electronics.

Banerjee first proposed the idea of using doped multi-layer graphene at the 2008 IEDM conference and has been working on it ever since. In February 2017 he led the experimental realization of the idea by Chemical Vapor Deposition (CVD) of multilayer graphene at a high temperature, subsequently transferring it to a silicon chip, then patterning the multilayer graphene, followed by doping. Electrical characterization of the conductivity of DMG interconnects down to a width of 20 nanometers established the efficacy of the idea that was proposed in 2008. However, the process was not “CMOS-compatible” (the standard industrial-scale process for making integrated circuits), since the temperature of CVD processes far exceed the thermal budget of back-end processes.

To overcome this bottleneck, Banerjee’s team developed a unique pressure-assisted solid-phase diffusion method for directly synthesizing a large area of high-quality multilayer graphene on a typical dielectric substrate used in the back-end CMOS process. Solid-phase diffusion, well known in the field of metallurgy and often used to form alloys, involves applying pressure and temperature to two different materials that are in close contact so that they diffuse into each other.

Banerjee’s group employed the technique in a novel way. They began by depositing solid-phase carbon in the form of graphite powder onto a deposited layer of nickel metal of optimized thickness. Then they applied heat (300 degrees Celsius) and nominal pressure to the graphite powder to help break down the graphite. The high diffusivity of carbon in nickel allows it to pass rapidly through the metal film.

How much carbon flows through the nickel depends on its thickness and the number of grains it holds. “Grains” refer to the fact that deposited nickel is not a single-crystal metal, but rather a polycrystalline metal, meaning it has areas where two single-crystalline regions meet each other without being perfectly aligned. These areas are called grain boundaries, and external particles — in this case, the carbon atoms — easily diffuse through them. The carbon atoms then recombine on the other surface of the nickel closer to the dielectric substrate, forming multiple graphene layers.

Banerjee’s group is able to control the process conditions to produce graphene of optimal thickness. “For interconnect applications, we know how many layers of graphene are needed,” said Junkai Jiang, a Ph.D. candidate in Banerjee’s lab and lead author of the 2018 IEDM paper. “So we optimized the nickel thickness and other process parameters to obtain precisely the number of graphene layers we want at the dielectric surface. “Subsequently, we simply remove the nickel by etching so that what’s left is only very high-quality graphene — virtually the same quality as graphene grown by CVD at very high temperatures,” he continued. “Because our process involves relatively low temperatures that pose no threat to the other fabricated elements on the chip, including the transistors, we can make the interconnects right on top of them.”

UCSB has filed a provisional patent on the process, which overcomes the obstacles that, until now, have prevented graphene from replacing copper. Bottom line: graphene interconnects help to create faster, smaller, lighter, more flexible, more reliable and more cost-effective integrated circuits. Banerjee is currently in talks with industry partners interested in potentially licensing this CMOS-compatible graphene synthesis technology, which could pave the way for what would be the first 2D material to enter the mainstream semiconductor industry.

Tags:  2D materials  CVD  Graphene  Graphite  Junkai Jiang  Kaustav Banerjee  Semiconductor  UC Santa Barbara 

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Unconventional phenomena triggered by acoustic waves in 2D materials

Posted By Graphene Council, The Graphene Council, Tuesday, July 30, 2019
Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea), and colleagues have reported a novel phenomenon, called Valley Acoustoelectric Effect, which takes place in 2D materials, similar to graphene. This research is published in Physical Review Letters and brings new insights to the study of valleytronics.

In acoustoelectronics, surface acoustic waves (SAWs) are employed to generate electric currents. In this study, the team of theoretical physicists modelled the propagation of SAWs in emerging 2D materials, such as single-layer molybdenum disulfide (MoS2). SAWs drag MoS2 electrons (and holes), creating an electric current with conventional and unconventional components. The latter consists of two contributions: a warping-based current and a Hall current. The first is direction-dependent, is related to the so-called valleys -- electrons' local energy minima -- and resembles one of the mechanisms that explains photovoltaic effects of 2D materials exposed to light. The second is due to a specific effect (Berry phase) that affects the velocity of these electrons travelling as a group and resulting in intriguing phenomena, such as anomalous and quantum Hall effects.

The team analyzed the properties of the acoustoelectric current, suggesting a way to run and measure the conventional, warping, and Hall currents independently. This allows the simultaneous use of both optical and acoustic techniques to control the propagation of charge carriers in novel 2D materials, creating new logical devices.

The researchers are interested in controlling the physical properties of these ultra-thin systems, in particular those electrons that are free to move in two dimensions, but tightly confined in the third. By curbing the parameters of the electrons, in particular their momentum, spin, and valley, it will be possible to explore technologies beyond silicon electronics. For example, MoS2 has two district valleys, which could be potentially used in the future for bit storage and processing, making it an ideal material to delve into valleytronics.

"Our theory opens a way to manipulate valley transport by acoustic methods, expanding the applicability of valleytronic effects on acoustoelectronic devices," explains Ivan Savenko, leader of the Light-Matter Interaction in Nanostructures Team at PCS.

Tags:  2D materials  Center for Theoretical Physics of Complex Systems  Electronics  Graphene  Institute for Basic Science  Ivan Savenko 

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Eli and Britt Harari Graphene Enterprise Award 2019 Winners Announced

Posted By Graphene Council, The Graphene Council, Tuesday, July 30, 2019
Two new technology businesses share this year’s £70,000 prize for novel applications of graphene and other 2D materials. The two teams, based at The University of Manchester, are addressing key societal challenges on future energy and food security. They are seeking breakthroughs by using 2D materials to produce hydrogen to generate energy, and by designing polymer hydrogels to increase food production.

The Eli and Britt Harari Enterprise Award, in association with Nobel Laureate Sir Andre Geim, is awarded each year to help the implementation of commercially-viable business proposals from students, post-doctoral researchers and recent graduates of The University of Manchester based on developing the commercial prospects of graphene and other 2D materials.

The first prize of £50,000 was awarded to NanoPlexus and its founding team Jae Jong Byun, Dr. Suelen Barg, Francis Moissinac, Wenji Yang and Thomas Moissinac. Jae and Wenji are undertaking their PhD studies in Dr. Suelen Barg’s research group (Nano3D), with Francis starting in September. Thomas is an aerospace engineering graduate from The University of Manchester. The team has worked under the Nano3D lab in formulating their idea into a marketable product.

NanoPlexus will be developing a range of products using their platform technology; the unique nano-material aerogel technology will offer cost-effective renewable hydrogen production with increased material efficiency for a sustainable green-economy.

Jae said: “Recently, there has been an increased footprint and sense of urgency to transition into renewable energy to tackle climate change. Our concept is ideally positioned to support this transition by acting as a stepping-stone for innovative technology growth into conventional energy systems. Our idea of 2D material-based cells supports the forecasted need of renewable energy implementation, as it uses low to zero carbon energy resources.”

Our commitment to the support of entrepreneurship across the University has never been stronger and is a vital part of our approach to the commercialisation of research. Professor Luke Georghiou, Deputy President and Deputy Vice-Chancellor

Francis added: “We are very grateful to Eli and Britt Harari for their generosity and for the support of the University, which will enable us to develop our novel concept that could one day make a meaningful difference; connecting innovation to convention.”

The runner-up, receiving £20,000, was AEH Innovative Hydrogel Ltd, founded by Beenish Siddique. Beenish has recently graduated with a PhD from the School of Materials. Her technology aims to provide an eco-friendly hydrogel to farmers that, not only increases crop production but also has potential to grow crops in infertile and water stressed lands, with minimum use of water and fertilisers.

Beenish said: “Many farmers, especially in third world countries with warmer climates, are interested in my product. I have a solution that offers higher crop yield with less water and fertiliser usage, hence, less greenhouse gases emission and a much cleaner environment.”

The quality of the business proposals presented in this year’s finals was exceptionally high. Professor Luke Georghiou, Deputy President and Deputy Vice-Chancellor of The University of Manchester and one of the judges for this year’s competition said: “Our commitment to the support of entrepreneurship across the University has never been stronger and is a vital part of our approach to the commercialisation of research. The support provided by Eli Harari over the last five years has enabled new and exciting ventures to be developed. It provides our winners the early-stage funding that is so vital to creating a significant business, while also contributing to health and social benefit. With support from our world-leading graphene research facilities I am certain that they are on the path to success.”

The winners will also receive support from groups across the University, including the University’s new state-of-the-art R&D facility, the Graphene Engineering Innovation Centre (GEIC); its leading support infrastructure for entrepreneurs, the Masood Enterprise Centre; as well as wider networks to help the winners take the first steps towards commercialising these early stage ideas.

The award is co-funded by the North American Foundation for The University of Manchester through the support of one of the University’s former physics students, Dr Eli Harari, founder of global flash-memory giant, SanDisk, and his wife, Britt. It recognises the role that high-level, flexible, early-stage financial support can play in the successful development of a business targeting the full commercialisation of a product or technology related to research in graphene and 2D materials.

Tags:  2D materials  AEH Innovative Hydrogel Ltd  Andre Geim  Beenish Siddique  Eli Harari  Graphene  Graphene Engineering Innovation Centre  Jae Jong Byun  Luke Georghiou  NanoPlexus  SanDisk  Suelen Barg  Thomas Moissinac  Wenji Yang 

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How to enlarge 2D materials as single crystals?

Posted By Graphene Council, The Graphene Council, Friday, May 31, 2019

What makes something a crystal? When all of its atoms are arranged in accordance with specific mathematical rules, we call the material a single crystal. Like the natural world has its unique symmetry just as snowflakes or honeycombs, the atomic world of crystals is designed by its own structure and symmetry. This material structure has a profound effect on its physical properties as well. Specifically, single crystals play an important role in inducing material's intrinsic properties to its full extent. Faced with the coming end of the miniaturization process that the silicon-based integrated circuit has allowed up to this point, huge efforts have been dedicated to find a single crystalline replacement for silicon.

In search for the transistor of the future, two-dimensional (2D) materials, especially graphene have been the subject of intense research around the world. Being thin and flexible as a result of being only a single layer of atoms, this 2D version of carbon even features unprecedented electricity and heat conductivity. However, the last decade's efforts for graphene transistors have been held up by physical restraints graphene allows no control over electricity flow due to the lack of band gap. Then, what about other 2D materials? A number of interesting 2D materials have been reported to have similar or even superior properties. Still, the lack of understanding in creating ideal experimental conditions for large-area 2D materials has limited their maximum size to just a few mm 2.

Scientists at the Center for Multidimensional Carbon Material (CMCM) within the Institute for Basic Science (IBS) (located in the Ulsan National Institute of Science and Technology (UNIST)) have presented a novel approach to synthesize large-scale of silicon wafer size, single crystalline 2D materials. Prof. Feng Ding and Ms. Leining Zhang in collaboration with their colleagues in Peking University, China and other institutes have found a substrate with a lower order of symmetry than that of a 2D material that facilitates the synthesis of single crystalline 2D materials in a large area. "It was critical to find the right balance of rotational symmetries between a substrate and a 2D material," notes Prof. Feng Ding, one of corresponding authors of this study. The researchers successfully synthesized hBN single crystals of 10*10 cm2 by using a new substrate: a surface nearby Cu (110) that has a lower symmetry of (1) than hBN with (3).

Then, why does symmetry matters? Symmetry, in particular rotational symmetry, describes how many times a certain shape fits on to itself during a full rotation of 360 degrees. The most efficient method to synthesize large-area and single crystals of 2D materials is to arrange layers over layers of small single crystals and grow them upon a substrate. In this epitaxial growth, it is quite challenging to ensure all of the single crystals are aligned in a single direction. Orientation of the crystals is often affected by the underlying substrate. By theoretical analysis, the IBS scientists found that an hBN island (or a group of hBN atoms forming a single triangle shape) has two equivalent alignments on the Cu(111) surface that has a very high symmetry of (6). "It was a common view that a substrate with high symmetry may lead to the growth of materials with a high symmetry. It seemed to make sense intuitively, but this study found it is incorrect," says Ms. Leining Zhang, the first author of the study.

Previously, various substrates such as Cu(111) have been used to synthesize single crystalline hBN in a large area, but none of them were successful. Every effort ended with hBN islands aligning along in several different directions on the surfaces. Convinced by the fact that the key to achieve unidirectional alignment is to reduce the symmetry of the substrate, the researchers made tremendous efforts to obtain vicinal surfaces of a Cu(110) orientation; a surface obtained by cutting a Cu(110) with a small tilt angle. It is like forming physical steps on Cu. As a hBN island tends to place in parallel to the edge of each step, it gets only one preferred alignment. The small tilt angle lowers the symmetry of the surface as well.

They eventually found that a class of vicinal surfaces of Cu (110) can be used to support the growth of hBN with perfect alignment. On a carefully selected substrate with the lowest symmetry or the surface will repeat itself only after a 360degree rotation, hBN has only one preferred direction of alignment. The research team of Prof. Kaihui Liu in Peking University, has developed a unique method to anneal a large Cu foil, up to 10*10 cm2, into a single crystal with the vicinal Cu (110) surface and, with it, they have achieved the synthesis of hBN single crystals of same size.

Besides flexibility and ultrathin thickness, emerging 2D materials can present extraordinary properties when they get enlarged as single crystals. "This study provides a general guideline for the experimental synthesis of various 2D materials. Besides the hBN, many other 2D materials could be synthesized with the large area single crystalline substrates with low symmetry," says Prof. Feng Ding. Notably, hBN is the most representative 2D insulator, which is different from the conductive 2D materials, such as graphene, and 2D semiconductors, such as molybdenum disulfide (MoS2). The vertical stacking of various types of 2D materials, such as hBN, graphene and MoS2, would lead to a large number of new materials with exceptional properties and can be used for numerous applications, such as high-performance electronics, sensors, or wearable electronics."

Tags:  2D materials  Center for Multidimensional Carbon Material  Feng Ding  Graphene  Kaihui Liu  Peking University  Semiconductors 

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Manipulating atoms one at a time with an electron beam

Posted By Graphene Council, The Graphene Council, Thursday, May 30, 2019
Updated: Friday, May 24, 2019

The ultimate degree of control for engineering would be the ability to create and manipulate materials at the most basic level, fabricating devices atom by atom with precise control.

Now, scientists at MIT, the University of Vienna, and several other institutions have taken a step in that direction, developing a method that can reposition atoms with a highly focused electron beam and control their exact location and bonding orientation. The finding could ultimately lead to new ways of making quantum computing devices or sensors, and usher in a new age of “atomic engineering,” they say.

The advance is described in the journal Science Advances, in a paper by MIT professor of nuclear science and engineering Ju Li, graduate student Cong Su, Professor Toma Susi of the University of Vienna, and 13 others at MIT, the University of Vienna, Oak Ridge National Laboratory, and in China, Ecuador, and Denmark.

“We’re using a lot of the tools of nanotechnology,” explains Li, who holds a joint appointment in materials science and engineering. But in the new research, those tools are being used to control processes that are yet an order of magnitude smaller. “The goal is to control one to a few hundred atoms, to control their positions, control their charge state, and control their electronic and nuclear spin states,” he says.

While others have previously manipulated the positions of individual atoms, even creating a neat circle of atoms on a surface, that process involved picking up individual atoms on the needle-like tip of a scanning tunneling microscope and then dropping them in position, a relatively slow mechanical process. The new process manipulates atoms using a relativistic electron beam in a scanning transmission electron microscope (STEM), so it can be fully electronically controlled by magnetic lenses and requires no mechanical moving parts. That makes the process potentially much faster, and thus could lead to practical applications.

Using electronic controls and artificial intelligence, “we think we can eventually manipulate atoms at microsecond timescales,” Li says. “That’s many orders of magnitude faster than we can manipulate them now with mechanical probes. Also, it should be possible to have many electron beams working simultaneously on the same piece of material.”

“This is an exciting new paradigm for atom manipulation,” Susi says.

Computer chips are typically made by “doping” a silicon crystal with other atoms needed to confer specific electrical properties, thus creating “defects’ in the material — regions that do not preserve the perfectly orderly crystalline structure of the silicon. But that process is scattershot, Li explains, so there’s no way of controlling with atomic precision where those dopant atoms go. The new system allows for exact positioning, he says.

The same electron beam can be used for knocking an atom both out of one position and into another, and then “reading” the new position to verify that the atom ended up where it was meant to, Li says. While the positioning is essentially determined by probabilities and is not 100 percent accurate, the ability to determine the actual position makes it possible to select out only those that ended up in the right configuration.

Atomic soccer

The power of the very narrowly focused electron beam, about as wide as an atom, knocks an atom out of its position, and by selecting the exact angle of the beam, the researchers can determine where it is most likely to end up. “We want to use the beam to knock out atoms and essentially to play atomic soccer,” dribbling the atoms across the graphene field to their intended “goal” position, he says.

“Like soccer, it’s not deterministic, but you can control the probabilities,” he says. “Like soccer, you’re always trying to move toward the goal.”

In the team’s experiments, they primarily used phosphorus atoms, a commonly used dopant, in a sheet of graphene, a two-dimensional sheet of carbon atoms arranged in a honeycomb pattern. The phosphorus atoms end up substituting for carbon atoms in parts of that pattern, thus altering the material’s electronic, optical, and other properties in ways that can be predicted if the positions of those atoms are known.

Ultimately, the goal is to move multiple atoms in complex ways. “We hope to use the electron beam to basically move these dopants, so we could make a pyramid, or some defect complex, where we can state precisely where each atom sits,” Li says.

This is the first time electronically distinct dopant atoms have been manipulated in graphene. “Although we’ve worked with silicon impurities before, phosphorus is both potentially more interesting for its electrical and magnetic properties, but as we’ve now discovered, also behaves in surprisingly different ways. Each element may hold new surprises and possibilities,” Susi adds.

The system requires precise control of the beam angle and energy. “Sometimes we have unwanted outcomes if we’re not careful,” he says. For example, sometimes a carbon atom that was intended to stay in position “just leaves,” and sometimes the phosphorus atom gets locked into position in the lattice, and “then no matter how we change the beam angle, we cannot affect its position. We have to find another ball.”

Theoretical framework
In addition to detailed experimental testing and observation of the effects of different angles and positions of the beams and graphene, the team also devised a theoretical basis to predict the effects, called primary knock-on space formalism, that tracks the momentum of the “soccer ball.” “We did these experiments and also gave a theoretical framework on how to control this process,” Li says.

The cascade of effects that results from the initial beam takes place over multiple time scales, Li says, which made the observations and analysis tricky to carry out. The actual initial collision of the relativistic electron (moving at about 45 percent of the speed of light) with an atom takes place on a scale of zeptoseconds — trillionths of a billionth of a second — but the resulting movement and collisions of atoms in the lattice unfolds over time scales of picoseconds or longer — billions of times longer.

Dopant atoms such as phosphorus have a nonzero nuclear spin, which is a key property needed for quantum-based devices because that spin state is easily affected by elements of its environment such as magnetic fields. So the ability to place these atoms precisely, in terms of both position and bonding, could be a key step toward developing quantum information processing or sensing devices, Li says.

“This is an important advance in the field,” says Alex Zettl, a professor of physics at the University of California at Berkeley, who was not involved in this research. “Impurity atoms and defects in a crystal lattice are at the heart of the electronics industry. As solid-state devices get smaller, down to the nanometer size scale, it becomes increasingly important to know precisely where a single impurity atom or defect is located, and what are its atomic surroundings. An extremely challenging goal is having a scalable method to controllably manipulate or place individual atoms in desired locations, as well as predicting accurately what effect that placement will have on device performance.”

Zettl says that these researchers “have made a significant advance toward this goal. They use a moderate energy focused electron beam to coax a desirable rearrangement of atoms, and observe in real-time, at the atomic scale, what they are doing. An elegant theoretical treatise, with impressive predictive power, complements the experiments.”

Besides the leading MIT team, the international collaboration included researchers from the University of Vienna, the University of Chinese Academy of Sciences, Aarhus University in Denmark, National Polytechnical School in Ecuador, Oak Ridge National Laboratory, and Sichuan University in China. The work was supported by the National Science Foundation, the U.S. Army Research Office through MIT’s Institute for Soldier Nanotechnologies, the Austrian Science Fund, the European Research Council, the Danish Council for Independent Research, the Chinese Academy of Sciences, and the U.S. Department of Energy.

Tags:  2D materials  Alex Zettl  Electronics  Graphene  Ju Li  MIT  Toma Susi  University of California at Berkeley  University of Vienna 

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NovoCarbon Enters Collaboration Agreement with Versarien Graphene

Posted By Graphene Council, The Graphene Council, Monday, May 13, 2019
Updated: Tuesday, May 14, 2019

Great Lakes Graphite Inc., doing business as NovoCarbon Corporation, announced that the Company and Versarien Graphene have executed a collaboration agreement.


  • Versarien will qualify NovoCarbon as a supply chain partner.
  • The Companies will develop a robust graphene supply chain with processing in the USA.
  • The Companies will work to enable a number of applications for a variety of industries.
  • The collaboration between Companies will afford opportunities to create a strong market presence and an improved ability to target significant technology opportunities.

Neill Ricketts, CEO of Versarien plc said, “We are very pleased to have our dedicated facility in Houston up and running. This has enabled us to more efficiently progress a number of new and existing relationships and accelerate our traction in the US. We now have relationships with over 25 companies in North America, encompassing sectors as diverse as automotive, aerospace, consumer goods, oil and gas, sports equipment and specialty plastics."

“We continue to receive a high number of enquiries for the supply of our graphene and other 2D materials from leading US companies and others globally. Versarien is now truly operating on a global basis and I look forward to providing further updates on our activities with our multiple collaboration partners in due course.”

NovoCarbon CEO Paul Ferguson said, “NovoCarbon’s mission is to enhance the ability of companies such as Versarien to serve their customers and markets with consistent, high quality materials.  We are excited to be working with Versarien and their highly capable team.”

Tags:  2D materials  Great Lakes Graphite  Neill Ricketts  NovoCarbon  Patrick Abbott  Paul Ferguson  Versarien 

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New graphene-based material developed for medical implants

Posted By Graphene Council, The Graphene Council, Thursday, May 2, 2019
Updated: Wednesday, May 1, 2019
A group of scientists have developed a new material for biomedical applications by combining a graphene-based nanomaterial with Hydroxyapatite (HAp), a commonly used bioceramic in implants.

In recent years, biometallic implants have become popular as a means to repair, restructure or replace damaged or diseased parts in orthopaedic and dental procedures. Metal parts also find use in devices such as pacemakers.

However, metallic implants face several limitations and are not a permanent solution. They react with body fluids and corrode, release wear and tear debris resulting in toxins and inflammation. They also have high thermal expansion and low compressive strength causing pain and are dense and may cause reactions.

On the other hand, bioceramics do not have these limitations. HAp specifically is osteoconductive, with a bone-like porous structure offering the required scaffold for tissue re-growth. However, it is brittle and lacks the mechanical strength of metals. The problem is overcome by combining it with nanoparticles of materials such as Zirconia.

In the new research, scientists have combined HAp with graphene nanoplatelets. “Previously reported studies have focused on only structural properties of such composites without throwing light on their biological properties. We have found that combining HAp with graphene nanomaterial enhances mechanical strength, provides better in-vivo imaging and biocompatibility without changing its basic bone-like properties,” explained Dr Gautam Chandkiram, the principal investigator at University of Lucknow, while speaking to India Science Wire.

Purification of the base ceramic material is a significant primary challenge in fabricating composites. According to scientists, in the current study, highly efficient biocompatible Hydroxyapatite was successfully prepared via a microwave irradiation technique and the consequent composites was synthesised using a simple solid-state reaction method.

The process involved mixing different concentrations of graphene nanoplatelet powders and drying, crushing, sieving and ball-milling the resulting slurry. The fine composite powder was further cold-compressed and sintered at 1200 degrees Celsius to achieve the desired density.

The scientists found that the composite had adequate interfacial area between the nanoparticles, with the graphene nanoplatelets well distributed into the hydroxyapatite matrix, while exhibiting high fracture resistance. Further, structural characterization, mechanical and load bearing tests showed that the 2D nature of graphene improves the load transfer efficiency significantly.

Researchers also examined cell viability of the composite by observing metabolic activity in specific cells using a procedure known as MTT assay. They used gut tissues of Drosophila larvae and primary osteoblast cells of a rat. “The overall cell viability studies demonstrated that there is no cytotoxic effect of the composites on any cell type,” explained Dr. Gautam.

Biomaterials also find use in drug delivery and bioimaging diagnosis. “Our research on the composite found that it displays a better fluorescence behaviour as compared to pure hydroxyapatite, indicating it has a great potential in bone engineering and bioimaging bio-imaging applications as well,” he added.

Tags:  2D Materials  Gautam Chandkiram  Graphene  Medical  nanomaterials  University of Lucknow 

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