Great things from small things

Blog Archive

Home
Filter by: Graphene
Page 4

Graphene Water 071115 RTRDE3R1-628x330 This post is part of a series examining the connections between nanotechnology and the top 10 trends facing the world, as described in the Outlook on the Global Agenda 2015. All authors are members of the Global Agenda Council on Nanotechnology.

In the 2015 World Economic Forum’s Global Risks Report survey participants ranked Water Crises as the biggest of all risks, higher than Weapons of Mass Destruction, Interstate Conflict and the Spread of Infectious Diseases (pandemics). Our dependence on the availability of fresh water is well documented, and the United Nations World Water Development Report 2015 highlights a 40% global shortfall between forecast water demand and available supply within the next fifteen years. Agriculture accounts for much of the demand, up to 90% in most of the world’s least-developed countries, and there is a clear relationship between water availability, health, food production and the potential for civil unrest or interstate conflict.

The looming crisis is not limited to water for drinking or agriculture. Heavy metals from urban pollution are finding their way into the aquatic ecosystem, as are drug residues and nitrates from fertilizer use that can result in massive algal blooms. To date, there has been little to stop this accretion of pollutants and in closed systems such as lakes these pollutants are being concentrated with unknown long term effects.

While current solutions such as reverse osmosis exist, and are widely used in the water desalination of seawater, the water they produce is expensive. This is because high pressures are required to force the waster through a membrane and maintaining this pressure requires around 2kWh for every cubic meter of water. While this is less of an issue for countries with cheap energy, it puts the technology beyond the reach of most of the world’s population.

Any new solution for water issues needs to be able to demonstrate precise control over pore sizes, be highly resistant to fouling and significantly reduce energy use, a mere 10% won’t make a difference. Nanotechnology has long been seen as a potential solution. Our ability to manipulate matter on the scale of a few atoms allows scientists to work at the same scale as mot of the materials that need to be removed from water — salts, metal ions, emulsified oil droplets or nitrates. In theory then it should be a simple matter of creating a structure with the correct size nanoscale pores and building a better filter.

Ten years ago, following discussions with former Israeli Prime Minister Shimon Peres, I organised a conference in Amsterdam called Nanowater to look at how nanotechnology could address global water issues. While the meeting raised many interesting points, and many companies proposed potential solutions, there was little subsequent progress.

Rather than a simple mix of one or two contaminants, most real world water can contain hundreds of different materials, and pollutants like heavy metals may be in the form of metal ions that can be removed, but are equally likely to be bound to other larger pieces of organic matter which cannot be simply filtered through nanopores.  In fact the biggest obstacle to using nanotechnology in water treatment is the simple fact that small holes are easily blocked, and susceptibility to fouling means that

Fortunately some recent developments in the ‘wonder material’ graphene may change the economics of water. One of the major challenges in the commercialisation of graphene is the ability to create large areas of defect-free material that would be suitable for displays or electronics, and this is a major research topic in Europe where the European Commission is funding graphene research to the tune of a billion euros. Simultaneously there are vast efforts inside organisations such as Samsung and IBM. While defects are not wanted for electronic applications, recent research by Nobel Prize winner Andrei Geim and Rahul Nair has indicated that in graphene oxide they result in a barrier that is highly impermeable to everything except water vapour. However, precisely controlling the pore size can be difficult.

Another approach taken by researchers at MIT involves bombarding graphene sheets with beams of gallium ions to create weak spots and then etching them to create more precisely controlled pore sizes. A similar approach to water transport through defects has been taken by researchers at Penn State University.

While all of the above show that graphene has prospects for use as a filter medium, what about the usual limiting issue, membrane fouling? Fortunately another property of graphene is that it can be hydrophilic, it repels water, and protein absorption has been reported to have been reduced by over 70% in bioreactor tests. Many other groups are working on the use of graphene oxide and graphene nanoplatelets as an anti-fouling coating.

While the graphene applications discussed so far address one or two of the issues, it seems that thin films of graphene oxide may be able to provide the whole solution. Miao Yu and his team at the University of South Carolina have fabricated membranes that deliver very high flux and do not foul. Fabrication is handled by adding a thin layer of graphene to an existing membrane, as distinct from creating a membrane out of graphene, something which is far harder to do and almost impossible to scale up.

Getting a high flux is crucial to desalination applications where up to 50% of water costs are caused by pressurising water for transmission through a membrane.  Performance tests reveal around 100% membrane recovery simply by surface water flushing and pure water flux rates (the amount of water that the membrane transmits) are two orders of magnitude higher than conventional membranes. This is the result of the spacing between the graphene plates that allows the passage of water molecules via nanoscale capillary action but not contaminants.Graphene Desalinate 0422 water

Non-fouling is crucial for all applications, and especially in oil/water separation as most of what is pumped out of oil wells is water mixed with a little oil.

According to G2O Water, the UK company commercialising Yu’s technology, the increased flux rates are expected to translate directly into energy savings of up to 90% for seawater desalination. Energy savings on that scale have the potential to change the economics of desalination with smaller plants powered by renewable energy and addressing community needs replacing the power hungry desalination behemoths currently under construction such as the Carlsbad Project. This opens the possibility of low-cost water in areas of the world where desalination is currently too expensive or there is insufficient demand to justify large scale infrastructure.

While more work is required to build a robust and cost-effective filtration system, the new ability to align sheets of graphene so that water but nothing else is transmitted may be the simple game-changer that allows the world to finally address the growing water crisis.

Author: Tim Harper is Chief Executive Officer of G2O Water.

Image: The colors of Fall can be seen reflected in a waterfall along the Blackberry River in Canaan, Connecticut REUTERS/Jessica Rinaldi

Super Materials 062015 2D-1 A wave of innovative flat materials is following in the wake of graphene — but the most exciting applications could come from stacking them into 3D devices.

Physicists have used almost every superlative they can think of to describe graphene. This gossamer, one-atom-thick sheet of carbon is flexible, transparent, stronger than steel, more conductive than copper and so thin that it is effectively two-dimensional (2D). No sooner was it isolated in 2004 than it became an obsession for researchers around the world.

But not for Andras Kis. As miraculous as graphene was, says Kis, “I felt there had to be more than carbon.” So in 2008, when he got the chance to start his own research group in nanoscale electronics at the Swiss Federal Institute of Technology in Lausanne (EPFL), Kis focused his efforts on a class of super-flat materials that had been languishing in graphene’s shadow.

These materials had an ungainly name — transition-metal dichalcogenides (TMDCs) — but a 2D form that was quite simple. A single sheet of transition-metal atoms such as molybdenum or tungsten was sandwiched between equally thin layers of chalcogens: elements, such as sulfur and selenium, that lie below oxygen in the periodic table. TMDCs were almost as thin, transparent and flexible as graphene, says Kis, but “somehow they got a reputation as not that interesting. I thought they deserved a second chance.”

He was right. Work by his team and a handful of others soon showed that different combinations of the basic ingredients could produce TMDCs with a wide range of electronic and optical properties. Unlike graphene, for example, many TMDCs are semiconductors, meaning that they have the potential to be made into molecular-scale digital processors that are much more energy efficient than anything possible with silicon.

Super Materials 062015 2D-1

Source: H. Terrones et al. Sci. Rep. 3, 1549 (2013)

Stacks of multiple kinds of flat materials can exploit the best properties of each.

Within a few years, laboratories around the world had joined the 2D quest. “At first it was one, then two or three, and suddenly it became whole zoo of 2D materials,” says Kis. From a scattering of publications in 2008, 2D TMDCs alone now generate six publications each day. Physicists think that there may be around 500 2D materials, including not just graphene and TMDCs, but also single layers of metal oxides, and single-element materials such as silicene and phosphorene. “If you want a 2D material with a given set of properties,” says Jonathan Coleman, a physicist at Trinity College Dublin, “you will find one.”

Ironically, one of the most exciting frontiers in 2D materials is stacking them into structures that are still very thin, but definitely 3D. By taking advantage of the vastly different properties of various super-flat materials, it should be possible to build entire digital circuits out of atomically thick components, creating previously unimagined devices. Applications are already being touted in fields from energy harvesting to quantum communications — even though physicists are just beginning to learn the materials’ potential.

“Each one is like a Lego brick,” says Kis. “If you put them together, maybe you can build something completely new.”

Adventures in Flatland

A material that is just a few atoms thick can have very different fundamental properties from a material made of the same molecules in solid form. “Even if the bulk material is an old one, if you can get it into 2D form it opens up new opportunities,” says Yuanbo Zhang, an experimental condensed-matter physicist at Fudan University in Shanghai, China.

Carbon is the classic example, as physicists Andre Geim and Konstantin Novoselov found in 2004 when they first reported isolating graphene1 in their laboratory at the University of Manchester, UK. Their technique was almost absurdly simple. The basic step is to press a strip of sticky tape onto a flake of graphite, then peel it off, bringing with it a few of the atom-thick layers that make up the bulk material. By repeating this process until they had single layers — which many theorists had said could not exist in isolation — Geim and Novoselov were able to start investigating graphene’s remarkable properties. Their work won them the 2010 Nobel Prize in Physics.

Physicists were soon hurrying to exploit those properties for applications ranging from flexible screens to energy storage (see page 268). Unfortunately, graphene proved to be a poor fit for digital electronics. The ideal material for that application is a semiconductor — a material that does not conduct electricity unless its electrons are boosted with a certain amount of energy from heat, light or an external voltage. The amount of energy needed varies with the material, and is known as the band gap. Turning the material’s conductivity on and off creates the 1s and 0s of the digital world. But graphene in its pure form does not have a band gap — it conducts all the time.

Still, Geim and Novoselov’s success in making graphene spurred them, Kis and many others to start investigating alternative 2D materials that could have a band gaps2. They began with TMDCs, which had been studied in bulk form since the 1960s. By 2010, Kis’s team had built its first single-layer transistor3 from the TMDC molybdenum disulfide (MoS2; see ‘Flat-pack assembly’), speculating that such devices could one day offer flexible electronics whose small component size and low voltage requirements would mean that they consumed much less power than conventional silicon transistors. Being semiconducting was not their only advantage. Studies in 2010 showed that MoS2 could both absorb and emit light4, 5 efficiently, making it — and probably other TMDCs — attractive for use in solar cells and photodetectors.

A single layer of TMDCs can capture more than 10% of incoming photons, an incredible figure for a material three atoms thick, says Bernhard Urbaszek, a physicist at the Physics and Chemistry of Nano-Objects Laboratory in Toulouse, France. This also helps them in another task: converting light into electricity. When an incoming photon hits the three-layer crystal, it boosts an electron past the band gap, allowing it to move through an external circuit. Each freed electron leaves behind a kind of empty space in the crystal — a positively charged ‘hole’ where an electron ought to be. Apply a voltage, and these holes and electrons circulate in opposite directions to produce a net flow of electric current.

This process can also be reversed to turn electricity into light. If electrons and holes are injected into the TMDC from an outside circuit; when they meet, they recombine and give up their energy as photons.

This ability to convert light to electricity and vice versa makes TMDCs promising candidates for applications that involve transmitting information using light, as well as for use in tiny, low-power light sources and even lasers. This year, four different teams demonstrated the ultimate control over light emission, showing that the TMDC tungsten diselenide (WSe2) could absorb and release individual photons6, 7, 8, 9. Quantum cryptography and communications, which encode information in one photon at a time, need emitters like this, where you “press a button and get a photon now”, says Urbaszek. Existing single-photon emitters are often made of bulk semiconductors, but 2D materials could prove smaller and easier to integrate with other devices. Their emitters are necessarily on the surface, which could also make them more efficient and easier to control.

Even as researchers were getting to grips with TMDCs, theorists were seeking other materials that could be engineered in two dimensions. One obvious candidate was silicon, which sits right below carbon in the periodic table, forms chemical bonds in a similar way, has a natural band gap and is already widely used in the electronics industry. Calculations suggested that, unlike graphene, a sheet of atomically thick silicon would have a ridged structure that could be squashed and stretched to create a tunable band gap. But like graphene, this ‘silicene’ would be a much faster conductor of electrons than most TMDCs.

Unfortunately, theory also suggested that a 2D sheet of silicene would be highly reactive and completely unstable in air. Nor could it be ripped from a crystal like other 2D materials: natural silicon exists only in a 3D form analogous to a diamond crystal, with nothing resembling the layered sheets of carbon found in graphite.

“People said it was insane and would never work,” says Guy Le Lay, a physicist at Aix-Marseille University in France. But Le Lay, who had been growing metals on silicon surfaces for years, saw a way to make silicene by doing the reverse — growing atomically thin sheets of silicon on metal. And in 2012 he reported success10: he had grown layers of silicene on silver, which has an atomic structure that matches the 2D material perfectly (see Nature 495, 152153; 2013).

“People said it was insane and would never work.”

Buoyed by that effort, Le Lay and others have since moved down the carbon column of the periodic table. Last year, he demonstrated a similar technique to grow a 2D mesh of germanium atoms — germanene — on a substrate of gold11. His next target is stanene: a 2D lattice of tin atoms. Stanene should have a band gap larger than either silicene and germanene, which would allow its devices to work at higher temperatures and voltages. And it is predicted to carry charges only on its outside edges, so it should conduct with super efficiency. But Le Lay has competition. Although no one has yet reported growing stanene successfully, research groups in China are rumoured to be close.

Elemental shift

Others are exploring different parts of the periodic table. Zhang’s team and another led by Peide Ye at Purdue University in West Lafayette, Indiana, last year described12, 13 stripping 2D layers of phosphorene from black phosphorus, a bulk form of the element that has been studied for a century. Like graphene, phosphorene conducts electrons swiftly. But unlike graphene, it has a natural band gap — and it is more stable than silicene.

Phosphorene has enjoyed a meteoric rise. At the 2013 meeting of the American Physical Society, it was the subject of a single talk by members of Zhang’s group; by 2015, the meeting had three entire sessions devoted to it. But like its fellow pure-element 2D materials, phosphorene reacts very strongly with oxygen and water. If it is to last longer than a few hours, it needs to be sandwiched between layers of other materials. This natural instability makes fabricating devices with the ‘enes’ difficult; Le Lay estimates that around 80% of the papers about them are still theoretical.

Nonetheless, both Zhang and Ye succeeded in making phosphorene transistors. This year, the first transistor from silicene emerged14, although it survived for only a few minutes. Still, Le Lay is optimistic that these issues are not insurmountable. Just two years ago, he points out, Geim and other physicists were saying that a silicene transistor could not be made with current technology. “So it’s always dangerous to predict the future,” laughs Le Lay.

The next dimension

Even as some physicists search for new 2D materials and try to understand their properties, others are already sandwiching them together. “Instead of trying to pick one and say this is the best, maybe the best thing to do is to combine them in such a way that all their different advantages are properly utilized,” says Kis.

This could mean stacking components made of different 2D materials to make tiny, dense 3D circuits. Materials could also be layered inside components — something that chip designers already do when they grow layers of different semiconductors on top of one another to make devices such as the lasers inside DVD players. In standard devices, this is tricky: each layer has to chemically bond with the next, and only certain combinations can be matched. Otherwise, the strain between the different crystal lattices in each layer makes bonding impossible. With 2D materials, that problem goes away: the atoms in each layer bond only very weakly to the neighbouring sheets, so the strain is minimal. Many layers of semiconductors, insulators and conductors can be stacked to form complex devices known generically as van der Waals heterostructures, after the weak bonds that bind the layers.

Already, for example, graphene has been used alongside MoS2 and WSe2 to create the junctions at the heart of solar cells15 and photodetectors16, exploiting the semiconductor’s abilities to absorb photons and graphene’s swift ability to carry the freed electrons away. In February this year, Novoselov and his team reversed the solar-cell concept to make a light-emitting diode17 from MoS2 and other TMDCs between graphene electrodes. By selecting different TMDCs, the team could choose the wavelength of the photons released.

Better still, sandwiching together different 2D layers can allow physicists to fine-tune their devices. Although the bonds between layers are weak, the close proximity of their atoms means that they can affect each other’s properties in subtle ways, says Wang Yao, a physicist at the University of Hong Kong. Stacking order, spacing and orientation all control device behaviour. “Modelling this gives theorists like me a headache, but the new physical properties are definitely there,” says Yao.

Even graphene can get a leg up from other 2D materials, says Marco Polini, a physicist at the National Enterprise for Nanoscience and Nanotechnology (NEST) in Pisa, Italy. His team has been working on devices in which graphene is sandwiched between 2D layers of the insulator boron nitride18. When laser light is focused on the device, it gets compressed and channelled through the graphene layer, much more than in devices that sandwich graphene between bulk materials. In principle, this could provide a way for information to be carried between chips using photons rather than electricity. That, says Polini, could mean faster and more efficient communications within the chips.

Practical predictions

The current buzz around 2D materials is reminiscent of the excitement about graphene in 2005, says physicist Jari Kinaret of Chalmers University of Technology in Gothenburg, Sweden, who heads the European Union’s Graphene Flagship — a programme that also studies other 2D materials. But Kinaret cautions that it could take two decades to really assess the potential of these materials. “The initial studies on 2D materials are focusing a lot on their electronic properties, because these are close to physicists’ hearts,” says Kinaret. “But I think that the applications, if and when they come, are likely to be in a completely unpredicted area.” (See ‘A 2D information highway’.)

A 2D information superhighway

Two-dimensional materials promise to improve more than electronics. Their strange properties also open up entirely new ways of carrying information.

Electronic devices rely on the movement of charged particles: electrons and the positively charged ‘holes’ that they leave behind when they are knocked out of atoms. But as chips get smaller, faster and more complex, engineers’ ability to shift electrons around is approaching a practical limit, and physicists are looking for other ways to encode information.

One way is to exploit quantum properties such as an electron’s spin, which is analogous to an internal bar magnet that can align either up or down. Spins can be flipped without expending the energy to physically move particles, a property that researchers hope to exploit in ‘spintronic’ devices. In both graphene and a class of 2D materials known as transition-metal dichalcogenides (TMDCs), spins can be controlled in ways that show promise.

These materials also seem well placed to harness electrons’ ‘valley’ state — a quantum property that gets its name from the U-shaped dip in the graph of electrons’ energy against their momentum. In most materials, the graph contains a single valley. But in some TMDCs it has two. This gives the electrons a choice of which valley to occupy, and offers a way to make ‘on’ and ‘off’ states for digital switches.

Although the idea is abstract, valley states are very real. In TMDCs, for example, electrons freed from atoms by laser light will occupy a valley state that depends on the polarization of the light. “You can selectively excite one valley or another,” says Wang Yao, a theoretical physicist at the University of Hong Kong. Graphene is also a potential candidate for ‘valleytronics’, but controlling its valleys often involves a combination of strain and magnetic fields — a more complex task.

Neither spintronics nor valleytronics requires any overall flow of charges. “That means no heating, no power dissipation, and the problems we all know about will disappear — that’s the hope,” says Marco Polini, a physicist at the National Enterprise for Nanoscience and Nanotechnology in Pisa, Italy.

Materials that look good in the lab are not always those that make it out into the real world. One major issue facing all 2D materials is how to produce uniform, defect-free layers cheaply. The sticky-tape method works well for TMDCs and phosphorene, but is too time-consuming to scale up. It is also expensive to make bulk black phosphorus, because it involves subjecting naturally occurring white phosphorus to extreme pressure. No one has yet perfected the process of growing single sheets of 2D materials from scratch, let alone the layered structures that physicists find so promising. “It took a long time to make our heterostructures,” says Xiaodong Xu, a physicist at the University of Washington in Seattle. “How can we speed that up or make it automatic? There is a lot of work to do.”

Such practical considerations could prevent 2D materials from living up to their early promise. “There have been many rushes like this, and some have turned out to be fads,” says Kis. “But I think the sheer number of materials and different properties should make sure something comes out of this.” Meanwhile, the zoo is expanding, says Coleman. Arsenene, a heavier cousin to phosphorene, is already on researcher’s minds.

“As people start to branch out, they are discovering new materials that have these wonderful properties,” says Coleman. “The most exciting 2D material is probably one that hasn’t been made yet.”

Journal name:
Nature
Volume:
522,
Pages:
274–276
Date published:
()

graphenequan 061615 The first graphene quantum dot light-emitting diodes (GQD-LEDs), fabricated by using high-quantum-yield graphene quantum dots through graphite intercalation compounds, exhibit luminance in excess of 1,000 cd/m2.

Graphene is a 2D carbon nanomaterial with many fascinating properties that can enable to creation of next-generation electronics. However, it is known that graphene is not applicable to due to its lack of an electronic band gap. On the other hand, graphene (GQDs), which are merely a few nanometers large in the lateral dimension, are shown to emit light upon excitation in the visible spectral range. The GQDs have attracted a great deal of attention as a next-generation luminescent material for their outstanding properties: tunable luminescence, superior photostability, low toxicity, and chemical resistance.

Recently, Prof. Seokwoo Jeon (Material Science and Engineering), Prof. Yong-Hoon Cho (Physics), and Prof. Seunghyup Yoo (Electrical Engineering) have succeeded in developing LEDs based on . Highly pure GQDs were synthesized by an environmentally-friendly method designed by Prof. Jeon’s group, their light-emitting mechanisms were carefully studied by Prof. Cho’s group with their transient spectroscopic technique, and finally Prof. Yoo’s group brought their OLED expertise to create GQD-based LEDs.

graphenequan 061615

Electroluminescent images of GQD-LEDs (left) and luminescence efficiency of GQD-LEDs (right). Credit: KAIST 

The GQDs with high luminance tunability and efficiency were synthesized by a route based on graphite intercalation compounds (GICs). The proposed method is cost-effective, eco-friendly, and scalable, as it allows direct fabrication of GQDs using water without surfactant or chemical solvent.

GQDs were then used as emitters in (OLEDs) in order to identify the GQD’s key optical properties. After carefully designing the layer configuration so that electron and hole injection could be balanced, the constructed GQD LEDs exhibited luminance of 1,000 cd/m2, which is well over the typical brightness levels of the portable displays used in smartphones. Considering how thin GQDs are, a foldable paper-like display could soon become a reality.

Graphene quantum dot LEDs
A schematic illustration of the preparation method of highly efficient GQDs (left) and an image of GQDs dispersed in water (right). Credit: KAIST

The present work, for the first time, demonstrated that GQDs can be applied to optical devices by fabricating GQD-based LEDs with meaningful brightness. Although, the efficiency of GQD-based LEDs is currently less than those of conventional LEDs, they are expected to improve in the near future with an optimized material process and device structure.

This research was published as a cover article in Advanced Optical Materials (Vol.2, 1016-1023 (2014)), a premier journal that features significant advances in optical materials and devices based upon them.

Explore further: Cheap hybrid outperforms rare metal as fuel-cell catalyst

MIT- Graph RolltoRoll 061015-1

Copper substrate is shown in the process of being coated with graphene. At left, the process begins by treating the copper surface, and, at right, the graphene layer is beginning to form. Upper images are taken using visible light microscopy, and lower images using a scanning electron microscope.

Courtesy of the researchers

New manufacturing process could take exotic material out of the lab and into commercial products.

Graphene is a material with a host of potential applications, including in flexible light sources, solar panels that could be integrated into windows, and membranes to desalinate and purify water. But all these possible uses face the same big hurdle: the need for a scalable and cost-effective method for continuous manufacturing of graphene films.

That could finally change with a new process described this week in the journal Scientific Reports by researchers at MIT and the University of Michigan. MIT mechanical engineering Associate Professor A. John Hart, the paper’s senior author, says the new roll-to-roll manufacturing process described by his team addresses the fact that for many proposed applications of graphene and other 2-D materials to be practical, “you’re going to need to make acres of it, repeatedly and in a cost-effective manner.”

Making such quantities of graphene would represent a big leap from present approaches, where researchers struggle to produce small quantities of graphene — often pulling these sheets from a lump of graphite using adhesive tape, or producing a film the size of a postage stamp using a laboratory furnace. But the new method promises to enable continuous production, using a thin metal foil as a substrate, in an industrial process where the material would be deposited onto the foil as it smoothly moves from one spool to another. The resulting sheets would be limited in size only by the width of the rolls of foil and the size of the chamber where the deposition would take place.

Because a continuous process eliminates the need to stop and start to load and unload materials from a fixed vacuum chamber, as in today’s processing methods, it could lead to significant scale-up of production. That could finally unleash applications for graphene, which has unique electronic and optical properties and is one of the strongest materials known.

The new process is an adaptation of a chemical vapor deposition method already used at MIT and elsewhere to make graphene — using a small vacuum chamber into which a vapor containing carbon reacts on a horizontal substrate, such as a copper foil. The new system uses a similar vapor chemistry, but the chamber is in the form of two concentric tubes, one inside the other, and the substrate is a thin ribbon of copper that slides smoothly over the inner tube.

Gases flow into the tubes and are released through precisely placed holes, allowing for the substrate to be exposed to two mixtures of gases sequentially. The first region is called an annealing region, used to prepare the surface of the substrate; the second region is the growth zone, where the graphene is formed on the ribbon. The chamber is heated to approximately 1,000 degrees Celsius to perform the reaction.

The researchers have designed and built a lab-scale version of the system, and found that when the ribbon is moved through at a rate of 25 millimeters (1 inch) per minute, a very uniform, high-quality single layer of graphene is created. When rolled 20 times faster, it still produces a coating, but the graphene is of lower quality, with more defects.

Some potential applications, such as filtration membranes, may require very high-quality graphene, but other applications, such as thin-film heaters may work well enough with lower-quality sheets, says Hart, who is the Mitsui Career Development Associate Professor in Contemporary Technology at MIT.

So far, the new system produces graphene that is “not quite [equal to] the best that can be done by batch processing,” Hart says — but “to our knowledge, it’s still at least as good” as what’s been produced by other continuous processes. Further work on details such as pretreatment of the substrate to remove unwanted surface defects could lead to improvements in the quality of the resulting graphene sheets, he says.

The team is studying these details, Hart adds, and learning about tradeoffs that can inform the selection of process conditions for specific applications, such as between higher production rate and graphene quality. Then, he says, “The next step is to understand how to push the limits, to get it 10 times faster or more.”

Hart says that while this study focuses on graphene, the machine could be adapted to continuously manufacture other two-dimensional materials, or even to growing arrays of carbon nanotubes, which his group is also studying.

“This is high-quality research that represents significant progress on the path to scalable production methods for large-area graphene,” says Charlie Johnson, a professor of physics and astronomy at the University of Pennsylvania who was not involved in this work. “I think that the concentric tube approach is very creative. It has the potential to lead to significantly lower production costs for graphene, if it can be scaled to larger copper-foil widths.”

The research team also included Erik Polsen and Daniel McNerny of the University of Michigan and postdocs Viswanath Balakrishnan and Sebastian Pattinson of MIT. The work was supported by the National Science Foundation and the Air Force Office of Scientific Research.

Wearable_wireless_devices_Low_cost_radio_frequency_antenna_printed_with_graphene_ink_ml Scientists have moved graphene—the incredibly strong and conductive single-atom-thick sheet of carbon—a significant step along the path from lab bench novelty to commercially viable material for new electronic applications.

Researchers from the University of Manchester, together with BGT Materials Limited, a graphene manufacturer in the United Kingdom, have printed a radio frequency antenna using compressed graphene ink. The antenna performed well enough to make it practical for use in radio-frequency identification (RFID) tags and wireless sensors, the researchers said. Even better, the antenna is flexible, environmentally friendly and could be cheaply mass-produced. The researchers present their results in the journal Applied Physics Letters, from AIP Publishing.

The study demonstrates that printable graphene is now ready for commercial use in low-cost radio frequency applications, said Zhirun Hu, a researcher in the School of Electrical and Electronic Engineering at the University of Manchester.

“The point is that graphene is no longer just a scientific wonder. It will bring many new applications to our daily life very soon,” added Kostya S. Novoselov, from the School of Physics and Astronomy at the University of Manchester, who coordinated the project.

Graphene Gets Inked

Since graphene was first isolated and tested in 2004, researchers have striven to make practical use of its amazing electrical and mechanical properties. One of the first commercial products manufactured from graphene was conductive ink, which can be used to print circuits and other electronic components.

Graphene ink is generally low cost and mechanically flexible, advantages it has over other types of conductive ink, such as solutions made from metal nanoparticles.

To make the ink, graphene flakes are mixed with a solvent, and sometimes a binder like ethyl cellulose is added to help the ink stick. Graphene ink with binders usually conducts electricity better than binder-free ink, but only after the binder material, which is an insulator, is broken down in a high-heat process called annealing. Annealing, however, limits the surfaces onto which graphene ink can be printed because the high temperatures destroy materials like paper or plastic.

The University of Manchester research team, together with BGT Materials Limited, found a way to increase the conductivity of graphene ink without resorting to a binder. They accomplished this by first printing and drying the ink, and then compressing it with a roller, similar to the way new pavement is compressed with a road roller.

Compressing the ink increased its conductivity by more than 50 times, and the resulting “graphene laminate” was also almost two times more conductive than previous graphene ink made with a binder.

The high conductivity of the compressed ink, which enabled efficient radio frequency radiation, was one of the most exciting aspects of the experiment, Hu said.

Paving the Way to Antennas, Wireless Sensors, and More

The researchers tested their compressed graphene laminate by printing a graphene antenna onto a piece of paper. The antenna measured approximately 14 centimeters long, and 3.5 millimeter across and radiated radio frequency power effectively, said Xianjun Huang, who is the first author of the paper and a PhD candidate in the Microwave and Communcations Group in the School of Electrical and Electronic Engineering.

Printing electronics onto cheap, flexible materials like paper and plastic could mean that wireless technology, like RFID tags that currently transmit identifying info on everything from cattle to car parts, could become even more ubiquitous.

Most commercial RFID tags are made from metals like aluminium and copper, Huang said, expensive materials with complicated fabrication processes that increase the cost.

“Graphene based RFID tags can significantly reduce the cost thanks to a much simpler process and lower material cost,” Huang said. The University of Manchester and BGT Materials Limited team has plans to further develop graphene enabled RFID tags, as well as sensors and wearable electronics.

SOURCE: American Institute of Physics

graphene Nose -grain-bounderyEver since single-layer graphene burst onto the science scene in 2004, the possibilities for the promising material have seemed nearly endless.

 

 

With its high electrical conductivity, ability to store energy, and ultra-strong and lightweight structure, graphene has potential for many applications in electronics, energy, the environment, and even medicine.

Now a team of Northwestern University researchers has found a way to print three-dimensional structures with graphene nanoflakes. The fast and efficient method could open up new opportunities for using graphene printed scaffolds regenerative engineering and other electronic or medical applications.

Led by Ramille Shah, assistant professor of materials science and engineering at Northwestern’s McCormick School of Engineering and of surgery in the Feinberg School of Medicine, and her postdoctoral fellow Adam Jakus, the team developed a novel graphene-based ink that can be used to print large, robust 3-D structures.

“People have tried to print graphene before,” Shah said. “But it’s been a mostly polymer composite with graphene making up less than 20 percent of the volume.”

With a volume so meager, those inks are unable to maintain many of graphene’s celebrated properties. But adding higher volumes of graphene flakes to the mix in these ink systems typically results in printed structures too brittle and fragile to manipulate. Shah’s ink is the best of both worlds. At 60-70 percent graphene, it preserves the material’s unique properties, including its electrical conductivity. And it’s flexible and robust enough to print robust macroscopic structures. The ink’s secret lies in its formulation: the graphene flakes are mixed with a biocompatible elastomer and quickly evaporating solvents.

“It’s a liquid ink,” Shah explained. “After the ink is extruded, one of the solvents in the system evaporates right away, causing the structure to solidify nearly instantly. The presence of the other solvents and the interaction with the specific polymer binder chosen also has a significant contribution to its resulting flexibility and properties. Because it holds its shape, we are able to build larger, well-defined objects.”

Supported by a Google Gift and a McCormick Research Catalyst Award, the research is described in the paper “Three-dimensional printing of high-content graphene scaffolds for electronic and biomedical applications,” published in the April 2015 issue of ACS Nano. Jakus is the paper’s first author. Mark Hersam, the Bette and Neison Harris Chair in Teaching Excellence, professor of materials science and engineering at McCormick, served as coauthor.

An expert in biomaterials, Shah said 3-D printed graphene scaffolds could play a role in tissue engineering and regenerative medicine as well as in electronic devices. Her team populated one of the scaffolds with stem cells to surprising results. Not only did the cells survive, they divided, proliferated, and morphed into neuron-like cells.

“That’s without any additional growth factors or signaling that people usually have to use to induce differentiation into neuron-like cells,” Shah said. “If we could just use a material without needing to incorporate other more expensive or complex agents, that would be ideal.”

The printed graphene structure is also flexible and strong enough to be easily sutured to existing tissues, so it could be used for biodegradable sensors and medical implants. Shah said the biocompatible elastomer and graphene’s electrical conductivity most likely contributed to the scaffold’s biological success.

“Cells conduct electricity inherently — especially neurons,” Shah said. “So if they’re on a substrate that can help conduct that signal, they’re able to communicate over wider distances.”

The graphene-based ink directly follows work that Shah and her graduate student Alexandra Rutz completed earlier in the year to develop more cell-compatible, water-based, printable gels. As chronicled in a paper published in the January 2015 issue of Advanced Materials, Shah’s team developed 30 printable bioink formulations, all of which are compatible materials for tissues and organs. These inks can print 3-D structures that could potentially act as the starting point for more complex organs.

“There are many different tissue types, so we need many types of inks,” Shah said. “We’ve expanded that biomaterial tool box to be able to optimize more mimetic engineered tissue constructs using 3-D printing.”


Story Source:

The above story is based on materials provided by Northwestern University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Adam E. Jakus, Ethan B. Secor, Alexandra L. Rutz, Sumanas W. Jordan, Mark C. Hersam, Ramille N. Shah. Three-Dimensional Printing of High-Content Graphene Scaffolds for Electronic and Biomedical Applications. ACS Nano, 2015; 9 (4): 4636 DOI: 10.1021/acsnano.5b01179

MIT scientists couple graphene with BN to manipulate light image

MIT researchers managed to use graphene, deposited on top of a similar 2D material called hexagonal boron nitride (hBN), to couple the properties of the different 2D materials to provide a high degree of control over light waves. They state this has the potential to lead to new kinds of light detection, thermal-management systems, and high-resolution imaging devices.

Both materials are structurally alike (in that they’re both composed of hexagonal arrays of atoms that form 2D sheets), but they react to light differently. These different reactions, though, were found by the researchers to be complementary, and assist in gaining control over the behavior of light. The hybrid material blocks light upon applying a particular voltage to the graphene, while allowing a special kind of emission and propagation, called “hyperbolicity,” when a different voltage is applied. This means that an extremely thin sheet of material can interact strongly with light, allowing beams to be guided, funneled, and controlled by voltages applied to the sheet. This poses a phenomenon previously unobserved in optical systems. 

Light’s interaction with graphene produces particles called plasmons, while light interacting with hBN produces phonons. The scientists found that when the materials are combined in a certain way, the plasmons and phonons can couple, producing a strong resonance. Also, the properties of the graphene allow precise control over light, while hBN provides very strong confinement and guidance of the light. Combining the two makes it possible to create new “metamaterials” that marry the advantages of both. The combined materials create a system that can be adjusted to allow light only of certain specific wavelengths or directions to propagate, and to selectively pick which frequencies to let through and which to reject.

Source: newsoffice.mit

KAIST-emissive-graphene-quantum-dots-img_assist-400x257 From Scopii News

Ground-breaking research has successfully created the world’s first truly electronic textile, using the wonder material Graphene. An international team of scientists, including Professor Monica Craciun from the University of Exeter, have pioneered a new technique to embed transparent, flexible graphene electrodes into fibers commonly associated with the textile industry.

The discovery could revolutionize the creation of wearable electronic devices, such as clothing containing computers, phones and MP3 players, which are lightweight, durable and easily transportable.
Graphene Exeter 051115 1431364300347

The international collaborative research, which includes experts from the Centre for Graphene Science at the University of Exeter, the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel), is published in the leading scientific journal Scientific Reports.
Professor Craciun, co-author of the research said: “This is a pivotal point in the future of wearable electronic devices. The potential has been there for a number of years, and transparent and flexible electrodes are already widely used in plastics and glass, for example. But this is the first example of a textile electrode being truly embedded in a yarn. The possibilities for its use are endless, including textile GPS systems, to biomedical monitoring, personal security or even communication tools for those who are sensory impaired.  The only limits are really within our own imagination.”

At just one atom thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for the use in wearable electronic devices in recent years.
This new research has identified that ‘monolayer graphene’, which has exceptional electrical, mechanical and optical properties, make it a highly attractive proposition as a transparent electrode for applications in wearable electronics. In this work graphene was created by a growth method called chemical vapor deposition (CVD) onto copper foil, using a state-of-the-art nanoCVD system recently developed by Moorfield.

The collaborative team established a technique to transfer graphene from the copper foils to a polypropylene fibre already commonly used in the textile industry.
Dr Helena Alves who led the research team from INESC-MN and the University of Aveiro said: “The concept of wearable technology is emerging, but so far having fully textile-embedded transparent and flexible technology is currently non-existing. Therefore, the development of processes and engineering for the integration of graphene in textiles would give rise to a new universe of commercial applications. “
Dr Ana Neves, Associate Research Fellow in Prof Craciun’s team from Exeter’s Engineering Department and former postdoctoral researcher at INESC added: “We are surrounded by fabrics, the carpet floors in our homes or offices, the seats in our cars, and obviously all our garments and clothing accessories. The incorporation of electronic devices on fabrics would certainly be a game-changer in modern technology.

“All electronic devices need wiring, so the first issue to be address in this strategy is the development of conducting textile fibers while keeping the same aspect, comfort and lightness. The methodology that we have developed to prepare transparent and conductive textile fibers by coating them with graphene will now open way to the integration of electronic devices on these textile fibers.”

Dr Isabel De Schrijver,an expert of smart textiles fromCenTexBel said: “Successful manufacturing of wearable electronics has the potential for a disruptive technology with a wide array of potential new applications. We are very excited about the potential of this breakthrough and look forward to seeing where it can take the electronics industry in the future.”

Professor Saverio Russo, co-author and also from the University of Exeter, added: “This breakthrough will also nurture the birth of novel and transformative research directions benefitting a wide range of sectors ranging from defense to health care. “
In 2012 Professor Craciun and Professor Russo, from the University of Exeter’s Centre for Graphene Science, discovered GraphExeter – sandwiched molecules of ferric chloride between two graphene layers which makes a whole new system that is the best known transparent material able to conduct electricity.  The same team recently discovered that GraphExeter is also more stable than many transparent conductors commonly used by, for example, the display industry.

Source: University of Exeter

Graphene Mem 050815 3-anewapproach Massachusetts Institute of Technology

 Summary: For faster, longer-lasting water filters, some scientists are looking to graphene –thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.

 

Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak. Now engineers have devised a process to repair these leaks.

 

Graphene Mem 050815 3-anewapproach

Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.

Now engineers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.

Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.

In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.

Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.

“We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”

Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.

A delicate transfer

“The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”

O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.

However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.

Plugging graphene’s leaks

To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.

The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.

Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.

In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.

Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.

The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.

“Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”


Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Sean C. O’Hern, Doojoon Jang, Suman Bose, Juan-Carlos Idrobo, Yi Song, Tahar Laoui, Jing Kong, Rohit Karnik. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene. Nano Letters, 2015; 150427124208006 DOI: 10.1021/acs.nanolett.5b00456

Difference engine

Graphene’s lightbulb moment

Can the “wonder material” live up to all the hype?

PHYSICISTS Andre Geim and Kostya Novoselev have been rightly feted for their isolation, in 2003, of graphene—sheets of pure carbon a single atom thick—whose existence had been pondered for decades, but which theory suggested was too unstable to survive. The two Soviet-born researchers won the Nobel physics prize in 2010 for their groundbreaking work, carried out at Manchester University, which involved peeling layers of graphene from blocks of graphite. Both men, now British citizens, were knighted in 2012 for their contribution to science. Their work has won generous support from the British government and the European Union—in particular, the construction, at a cost of £61m ($92m), of the National Graphene Institute, which was opened by George Osborne, Chancellor of the Exchequer, in March.

The researchers now have another distinction to their credit: their discovery is about to become a commercial product. A graphene-based lightbulb, said to be longer-lasting, more efficient and cheaper to make than today’s domestic LED lamps, will go on sale in a few months’ time. Though graphene flakes have already been incorporated into tennis racquets, skis and conductive ink, the new lightbulb is claimed by its manufacturer—Graphene Lighting Plc, a spin-out from the National Graphene Institute and Manchester University—to be the first commercially viable consumer product based on the material.

That may be splitting hairs. Even so, going from discovery to commercialisation in little more than a decade is quick. Many entrepreneurial companies find turning an invention into a successful innovation can take 20 years or more.

Graphene is composed of a single layer of carbon atoms arranged in the form of a hexagonal lattice. This means there is a world of difference between it and a three-dimensional crystalline structure like graphite. The electrons associated with carbon atoms in graphite can interact with other carbon atoms in the layers above and below them. In a sheet, this electron-coupling effect disappears, and the electrons are free to behave in entirely different ways.

The most striking consequence of this is that those electrons are thus able to move great distances at close to the speed of light, resulting in a material that has exceptionally low resistance. Because graphene can transport electricity 200 times faster than silicon, it seems a good candidate to replace that element as the semiconductor material used in computer chips.

Hype aside, graphene has not been called a “wonder material” for nothing. Apart from its remarkable electrical properties (and also, thermal and acoustical properties), it is the thinnest and lightest substance known, as well as being the strongest (more than 100 times stronger than high-strength steel). As if all that were not enough, graphene is also extremely flexible and almost totally transparent, absorbing only a minuscule amount of the light falling on it.

As such, potential applications of graphene appear myriad. Some of the more obvious ones include rapid-charging lithium-ion batteries, better solar cells, compact supercapacitors, printable electronics, foldable LED touchscreens, tunable sensors, ultrafast molecular sieves, improved DNA sequencers, corrosion-resistant coatings, a replacement for Kevlar, terahertz wave generators for extremely fast wireless communication, and, of course, more efficient lightbulbs. The list of proposals for future graphene products goes on and on, as researchers cozy up to potential sponsors.

There is little, save lack of money and consumer interest, to stop a good number of these suggestions reaching the market in the not-too-distant future. But the one graphene application that could turn the whole of electronics on its head—a replacement for silicon-based semiconductors—remains tantalisingly over the horizon.

Big computer, wireless and electronics firms—including such research powerhouses as IBM, Intel and Samsung—have been racing to create a field-effect transistor that uses graphene instead of silicon. They have a big incentive to do so. After 50 years of success, Moore’s Law (that the processing power of semiconductor devices doubles every 18 months or so) appears to be coming to an end, at least as far as silicon is concerned. Another material is needed to take its place.

Despite the billions poured into finding an alternative, attempts to make graphene work as a semiconductor have been disappointing. The problem is that the material has no “band gap”—the property that makes a solid an insulator (large band gap), a conductor (tiny or no band gap) or something in between—ie, a semiconductor (small band gap). Having no band gap at all is why graphene is such an excellent conductor. Making it into a semiconductor is tricky.

That is not all. A transistor works by flipping between two states—one insulating and the other conductive—in the presence of an electric field. These two states (off and on) represent the digital zeros and ones of computerspeak. By its nature, a graphene gate (switch) is on all the time. Getting it to turn off, let alone flip on and off billions of times a second, is the stumbling block.

There have been various attempts to open a band gap in graphene. One approach has been to dope it with compounds like silicon carbide or boron nitride that have matching crystalline lattice structures. Unfortunately, creating a band gap big enough to turn graphene into a usable semiconductor destroys the very properties—especially the high electron mobility—that made the material so attractive in the first place.

Older and wiser, researchers have turned to building hybrid chips that are fabricated, layer by layer, using conventional silicon epitaxy for everything except the final graphene transistor channels on the top of the device. These delicate structures are added at the end, so as not to get damaged during fabrication. So far, only analogue chips have been built this way. Even IBM has failed to create a band gap in graphene that would result in a digital device capable of challenging silicon’s preeminence. Transistors made entirely from graphene appear to be decades away.

So, where does that leave graphene’s prospects? While a replacement for silicon may be a long shot, many applications that do not rely on a band gap have a better chance of success. That said, not all graphene proposals being hyped at present can expect to survive the inevitable shake-out.

Had Gartner, an information-technology consultancy in Connecticut, included graphene-based processes as a stand-alone entry in its latest Emerging Technologies Hype Cycle, such processes would be over two-thirds the way up the slope to its “peak of inflated expectations”,which comes before the tip-over into the “trough of disillusionment” (see “Divining reality from hype”, August 27th 2014). Experience suggests that only those innovations which show genuine commercial value manage to crawl out of the trough and up the subsequent slope of enlightenment towards the plateau of productivity and market acceptance. Venture capitalists reckon no more than one in seven, at this stage of development, manages such a feat. It is too early to say whether graphene lightbulbs will be among them.

Readers with long memories may have noticed how the trajectory graphene is following resembles the one blazed by carbon fibre back in the 1960s. Then, as now, the new material was seen as a wonder product that would have numerous applications. Then, as now also, the British government felt it had a sacred duty to protect and promote what it perceived to be a home-grown invention—with the promise of jobs and exports.

If truth be told, the first hank of pyrolysed nylon (a carbon-fibre precursor) was snaffled from a Japanese textile factory and flown back to Britain in a diplomatic bag. At the time, British officials involved considered the super-strength material ideal for making gas centrifuges for enriching uranium. But samples that landed up at the Royal Aircraft Establishment in Farnborough led to the first carbon-fibre composite (Hyfil) being made available to select industrial partners, including the aeroengine manufacturer Rolls-Royce.

Of the many applications touted for carbon fibre, its promise to revolutionise air travel captured the most attention. With stronger, lighter fan blades, made from Hyfil instead of aluminium alloy or titanium, in a fan-jet’s first compressor stage, Rolls-Royce’s latest aircraft engine at the time, the RB211, would have had a significant weight-saving advantage—and thus better fuel economy—over rivals from General Electric and Pratt & Whitney.

The outcome was rather different. While turbine blades made from Hyfil had all the tensile strength, and more, to withstand the centrifugal forces of a big fan engine at full power, their shear strength left much to be desired. The story of how compressor blades shattered when a frozen chicken was fired at them to simulate bird impact contributed to carbon fibre’s fall from grace.

Meanwhile, the cost and delay involved in replacing the RB211’s Hyfil blades with titanium ones plunged Rolls-Royce into bankruptcy. Britain’s proudest engineering firm then had to be rescued at taxpayer expense. So much for governments picking winners. Hopefully, graphene is spared a similar fate.


Recent Posts

Categories

Search

Nano Enabled Super Capacitors and Batteries for the Future of Energy Storage

Follow Us on Twitter @Genesisnanotech


Could not authenticate you.