Tag Archives: graphene

Graphene can now be used to cool your clothes

Researchers have implemented the 2D material graphene into smart textiles that can adapt to lower your temperature in hot climates.

Credits: University of Manchester

When it gets hot, our bodies radiate energy in the form of electromagnetic waves. We can’t see this with the naked eye since it’s in the infrared spectrum (called blackbody radiation). If you want to radiate heat, it’s best to take advantage of the full infrared radiation spectrum, to lower our temperature as much as possible. Conversely, if you’d want to keep the body hot, you’d use something that blocks as much energy as possible.

Emergency blankets — also called space blankets, thermal blankets, or Mylar blankets — are a good example on this: on one side, they trap infrared energy and keep the wearer warm and on the other side, they release energy (although it doesn’t make sense to keep the blanket on you if you want to cool down, because you’d just trap your own heat, and the negative would outweigh the positives).

But regardless of a material’s reflectivity properties, they’re fixed and unchangeable. At least, this was the case until now.

Scientists at Manchester’s National Graphene Institute have developed smart textiles that can change states dynamically, keeping you warmer or cooling you down based on your temperature needs. Professor Coskun Kocabas, who led the research, said:

“Ability to control the thermal radiation is a key necessity for several critical applications such as temperature management of the body in excessive temperature climates. Thermal blankets are a common example used for this purpose. However, maintaining these functionalities as the surroundings heats up or cools down has been an outstanding challenge.”

The technology opens up a world of possibilities, from architecture and space suits to the textile industry. Researchers had previously been able to use graphene for thermal camouflage, fooling infrared cameras. But being able to change from one state to the other dynamically is a completely different beast. The graphene structure can also be embedded into a number of different textile materials, including elastane and cotton.

“We believe that our results are timely showing the possibility of turning the exceptional optical properties of graphene into novel enabling technologies. The demonstrated capabilities cannot be achieved with conventional materials.”

However, while having innovative cooling T-shirts is exciting in itself, researchers have their eyes on a bigger prize: satellites.

“The next step for this area of research is to address the need for dynamic thermal management of earth-orbiting satellites. Satellites in orbit experience excesses of temperature, when they face the sun and they freeze in the earth’s shadow. Our technology could enable dynamic thermal management of satellites by controlling the thermal radiation and regulate the satellite temperature on demand.” concludes Kocabas.

Journal Reference: M. Said Ergoktas et al. Graphene-Enabled Adaptive Infrared Textiles, Nano Letters (2020). DOI: 10.1021/acs.nanolett.0c01694

Flash-baking waste could make for stronger concrete and protect the environment

New research at Rice University describes how bulk quantities of carbon-bearing material can be quickly and cheaply turned into graphene flakes. The secret? Intense bursts of heat.

The process in action.
Image credits Credit: Jeff Fitlow / Rice University.

Waste food, plastics, wood, paper, clothes — carbon is everywhere around us. The new technique developed at Rice aims to reduce the environmental impact related to the production of concrete and other building materials by creating a source of cheap graphene to reinforce these materials.

Cook at high temperature

“This is a big deal,” says James Tour, a chemist at Rice and the lead author of the paper. “The world throws out 30% to 40% of all food, because it goes bad, and plastic waste is of worldwide concern. We’ve already proven that any solid carbon-based matter, including mixed plastic waste and rubber tires, can be turned into graphene.”

“With the present commercial price of graphene being $67,000 to $200,000 per ton, the prospects for this process look superb.”

Tour says that the “flash graphene” method they developed can convert bulk material (such as coal, plastic waste, or discarded food) into graphene for a fraction of the cost of other comparable methods. It takes just 10 milliseconds of extreme heat — 3,000 Kelvin, about 5,000 °F or 2,800 °C — to turn the source material into graphene flakes.

The team christened its new method ‘Flash Joule heating’, and explained that it takes much less effort and costs to produce graphene than previous approaches. The whole process takes place in a custom-designed reactor that quickly heats up the material and removes all non-carbon elements like oxygen and nitrogen from the resulting gas. If applied on an industrial scale, these gases can be captured “because they have value,” Tour explains. He adds that the system produces very little waste heat (meaning it’s energy-efficient) despite the fact that “this is almost three times hotter than the furnaces we formerly used to make graphene”.

The whole process yields “turbostratic” graphene, which has misaligned layers that are easy to separate. This makes it much simpler to work with than stacked graphene layers, which are hard to pull apart. The team hopes that their method will be employed to create stronger building materials and help protect the environment.

“By strengthening concrete with graphene, we could use less concrete for building, and it would cost less to manufacture and less to transport,” Tour said. “Essentially, we’re trapping greenhouse gases like carbon dioxide and methane that waste food would have emitted in landfills.”

‘We are converting those carbons into graphene and adding that graphene to concrete, thereby lowering the amount of carbon dioxide generated in concrete manufacture. It’s a win-win environmental scenario using graphene.”

Tour explains that adding as little as 0.1% flash graphene in the cement used to bind concrete could lessen its massive environmental impact by a third. Production of cement reportedly emits as much as 8% of human-made carbon dioxide every year, the team notes.

“Turning trash to treasure is key to the circular economy,” said co-corresponding author Rouzbeh Shahsavari. “Here, graphene acts both as a 2D template and a reinforcing agent that controls cement hydration and subsequent strength development.”

The paper “Gram-scale bottom-up flash graphene synthesis” has been published in the journal Nature.

Graphene in clothes can stop mosquitoes, study finds

Highly flexible and used to build solar cells, graphene is often praised for its mechanical and electrical properties. A team of researchers has now discovered that graphene is also a powerful mosquito repellent, opening the door to anti-mosquito graphene-lined clothing.

Credit: Flickr

The study, published in the Proceedings of the National Academy of Sciences, found that graphene blocked the chemical signals that draw mosquitoes to other living beings in the first place. It’s not only an effective barrier but also changes the mosquitoes’ behavior.

“With the graphene, the mosquitoes weren’t even landing on the skin patch — they just didn’t seem to care,” said Cintia Castillho, who is the study’s lead author. “We had assumed that graphene would be a physical barrier to biting, through puncture resistance, but when we saw these experiments, we started to think that it was also a chemical barrier.”

Graphene is a 2D material made from a single layer of carbon atoms arranged in a two-dimensional hexagonal lattice. It’s lightweight but 100 times stronger than steel and has been used in everything from wearable blood sugar monitoring patches, bike tires with adaptable grip, and even mind-bending optical illusions.

When coating a thin piece of fabric with the two-dimensional hexagonal lattice, researchers found that mosquitoes couldn’t generate enough force for their proboscis — the needle-like mouthparts that penetrate the skin — to get through. Oddly enough, researchers also observed that graphene blocks the chemical signals that attract mosquitoes in the first place.

The material used in this study was an effective mosquito deterrent only when it was perfectly dry. When it got wet, its force field properties were significantly diminished. To get around this, the researchers found that another form of graphene oxide with a reduced oxygen content was effective against mosquitoes when wet or dry.

Nevertheless, changing the ingredients also meant the material was no longer breathable. So, the next step for the research team is to find a way to stabilize the regular graphene oxide protective layer so that it’s resilient against all conditions—wet or dry—while actually being comfortable to wear.

“Our preferred embodiment of this technology would be to find a way to stabilize GO mechanically so that remains strong when wet. This next step would give us the full benefits of breathability and bite protection,” said Robert Hurt, a professor in Brown’s School of Engineering and senior author of the paper.

Chip combining CRISPR and graphene can detect genetic mutations in minutes

Two of the most promising novel techniques have been used together with remarkable results. US researchers have combined CRISPR with electronic transistors made from graphene to create a new hand-held device that can detect specific genetic mutations in a matter of minutes.

“We have developed the first transistor that uses CRISPR to search your genome for potential mutations,” said Kiana Aran, an assistant professor at KGI who conceived of the technology while a postdoctoral scholar in UC Berkeley bioengineering professor Irina Conboy’s lab. “You just put your purified DNA sample on the chip, allow CRISPR to do the search and the graphene transistor reports the result of this search in minutes.”

The novel system immobilizes the CRISPR complexes on the surface of graphene-based transistors. These complexes search a genome to find their target sequence and, if the search is successful, bind to its DNA. This binding changes the conductivity of the graphene material in the transistor, which picks the change and relays it to a handheld reader. Image credits: Keck Graduate Institute (KGI).

Genetic scissors

Genetic analysis has developed tremendously in recent years. Not only has it become a relatively common scientific and medical practice, but commercial companies are even offering genetic tests readily available to customers. Over 20 million have already reportedly taken at-home genetic tests.

When these tests are looking for genetic mutations, they “amplify” the DNA segment of interest millions of times to have a better look at it. This process (called polymerase chain reaction or PCR) is time and equipment-intensive, which means that samples have to be sent to a lab and subjected to analysis by expensive and delicate equipment. This is where CRISPR and graphene enter the scene.

The CRISPR-Cas9 system brought in an unprecedented precision, allowing researchers to snip threads of DNA at very precise locations — something often called “genetic scissors.”

“CRISPR-Chip has the benefit that it is really point of care, it is one of the few things where you could really do it at the bedside if you had a good DNA sample,” said Niren Murthy, professor of bioengineering at UC Berkeley and co-author of the paper. “Ultimately, you just need to take a person’s cells, extract the DNA and mix it with the CRISPR-Chip and you will be able to tell if a certain DNA sequence is there or not. That could potentially lead to a true bedside assay for DNA.”

But in order for it to work its magic, the Cas9 protein needs to first locate the spots it needs to cut. Graphene, a single atomic layer of carbon, is extremely electrically sensitive and small enough for this type of application. Researchers attached a deactivated Cas9 protein (one which finds the targeted DNA segment, but doesn’t cut it) and tethered it to transistors made of graphene. When the protein finds the spot, it binds to it and triggers a change in the electrical conductance of the graphene. In turn, this changes the characteristics of the transistors, and this change can be detected with a hand-held device. Ultimately, this allows the detection of genetic mutations within minutes, using relatively simple equipment, in less than an hour.

“Graphene’s super-sensitivity enabled us to detect the DNA searching activities of CRISPR,” Aran said. “CRISPR brought the selectivity, graphene transistors brought the sensitivity and, together, we were able to do this PCR-free or amplification-free detection.”

The handheld device. Image credits: Keck Graduate Institute.

To demonstrate the equipment’s potential, researchers analyzed blood samples from patients suffering from Duchenne muscular dystrophy (DMD). DMD is a genetic disorder characterized by progressive muscle degeneration and weakness — one of nine known types of muscular dystrophy. Diseases such as DMD are thought to be caused by mutations throughout the dystrophin gene — but this is one of the longest in the human genome and spotting mutations can be costly and time-consuming using PCR-based genetic testing. This is where the novel CRISPR/graphene technology can make a huge difference.

“As a practice right now, boys who have DMD are typically not screened until we know that something is wrong, and then they undergo a genetic confirmation,” said Conboy, who is also working on CRISPR-based treatments for DMD.

“With a digital device, you could design guide RNAs throughout the whole dystrophin gene, and then you could just screen the entire sequence of the gene in a matter of hours. You could screen parents, or even newborns, for the presence or absence of dystrophin mutations — and then, if the mutation is found, therapy could be started early, before the disease has actually developed.”

Researchers also say that things can be scaled up to the point where a handheld device would scan for multiple genetic disorders at the same time. Rapid genetic testing could also be used to help doctors develop individualized treatment plans for their patients, Murthy said. For example, genetic variations make some people unresponsive to expensive blood thinners, like Plavix.

Rapid genetic testing could also be used to help doctors develop individualized treatment plans for their patients, Murthy said. For example, genetic variations make some people unresponsive to expensive blood thinners, like Plavix.

“If you have certain mutations or certain DNA sequences, that will very accurately predict how you will respond to certain drugs,” Murthy concludes.

The study has been published in nature biomedical engineering

A scanning electron microscope image shows a composite of laser-induced graphene and polystyrene. Credit: Tour Group/Rice University.

Laser-induced graphene foam gains new super powers

A scanning electron microscope image shows a composite of laser-induced graphene and polystyrene. Credit: Tour Group/Rice University.

A scanning electron microscope image shows a composite of laser-induced graphene and polystyrene. Credit: Tour Group/Rice University.

A while back, researchers at Rice University pioneered a novel manufacturing method that produced graphene with a laser. The resulting flaky foam of the atom-thick carbon, however, lacked real-life functionality because of its flimsy nature. Now, the research team has found a way to integrate new materials in a composite that offers more robust properties. The promising graphene composite could be used in electronics, smart clothing, and medicine.

Burned graphene

The team, led by Rice chemist James Tour, first made laser-induced graphene (LIG) in 2014. At the time, they used a commercial laser to burn the surface of a thin sheet of polyimide (a plastic). The concentrated heat turned a narrow piece of the plastic into flakes of interconnected graphene.

Graphene is often called the “wonder material” because of its phenomenal properties. Graphene is 200 times stronger than steel, while at the same time being very thin and elastic. Graphene is also an excellent electrical and thermal conductor thanks to its crystal and band structures.

One big challenge that keeps the honeycomb lattice of carbon from becoming mainstream is manufacturing. In this respect, LIG is very promising because it produces graphene flakes in a one-step process, at greater volume and at less cost than traditional chemical vapor deposition.

“LIG is a great material, but it’s not mechanically robust,” Tour said in a statement. “You can bend it and flex it, but you can’t rub your hand across it. It’ll shear off. If you do what’s called a Scotch tape test on it, lots of it gets removed. But when you put it into a composite structure, it really toughens up.”

Since it was first developed, Rice University researchers have refined their technique to make LIG not only with plastic, but also with wood and even food. In their new research, the team combined LIG with other materials to produce composites with intriguing properties. In the video below you can see one such a composite in action with superhydrophobic (water-repelling) properties, which would make it suitable as a deicing coating.

Softer composites of LIG can be used as active electronics in flexible clothing. What’s more, when a voltage is applied to the 20-micron-thick layer of LIG, bacteria present on the surface of the material are destroyed, making it a promising antibacterial application.

Scanning electron microscope image of laser-induced graphene (left) and a composite. Credit: Rice University.

Scanning electron microscope image of laser-induced graphene (left) and a composite. Credit: Rice University.

Potential applications of LIG composites. Credit: Rice University.

Potential applications of LIG composites. Credit: Rice University.

In order to produce the composites, the researchers simply poured or hot-pressed a thin layer of the additive over LIG attached to polyimide. After a while, the liquid hardens, and the polyimide can be stripped off for reuse, leaving connected graphene flakes behind.

“You just pour it in, and now you transfer all the beautiful aspects of LIG into a material that’s highly robust,” Tour said.

The findings were reported in the journal ACS Nano.

GO dough.

GO dough stands poised to bring graphene and its awesome properties into your life

Researchers at Northwestern University wanted to make graphene easier to handle — so they turned it into a toy. Yet this humble plaything might revolutionize how we use the material.

GO dough.

Some shapes and structures the team created out of GO dough by cutting, pinching, molding, and carving.
Image credits Jiaxing Huang / Northwestern University.

The team has turned graphene oxide (GO) into a soft, kneadable, and moldable playdough to make it safer and easier to transport. The material, however, can be shaped and reshaped into a variety of shapes and sizes. The so-called “GO dough”, while undeniably fun to play with, solves several long-standing problems plaguing the graphene manufacturing industry.

GO dough or go home

“Currently graphene oxide is stored as dry solids or powders, which are prone to combustion,” said Jiaxing Huang, the professor of materials science and engineering in Northwestern’s McCormick School of Engineering who led the study. “Or they have to be turned into dilute dispersions, which multiply the material’s mass by hundreds or thousands.”

Huang explains that his most recent shipment of graphene oxide — 5 kilograms / 11 pounds of the substance — came dispersed in 500 liters of liquid. The shipment had to be delivered by truck, he adds, which was very frustrating and impractical. Huang says the same amount of graphene oxide would weigh around 10 kg in dough form and he could “carry it [himself].”

Graphene oxide is the most common precursor used to make graphene, sheets of carbon just one-atom-thick that are remarkably strong and lightweight. Graphene is by far the strongest material ever tested. It’s an efficient conductor of heat and electricity, and it’s nearly transparent. These physical and electrical properties attracted a lot of attention from material scientists aiming to apply graphene to everything from car bodies to advanced electronics and batteries.

However, GO powder is quite explosive, so anyone looking to manufacture graphene on a large scale would have to employ costly methods of transportation and storage — which made the end material too expensive to be viable.

Huang’s team found a simple, and in my eyes, quite elegant, solution to this problem: they mixed a little water into the graphene oxide powder. They didn’t use any binding additives, as these would have to be removed later on to return the graphene oxide to its pure form.

“Adding binders such as plastics could turn anything into a dough state,” Huang explained, “but these additives often significantly alter the material’s properties.”

After being molded into whatever shape is desired, the dough can be converted into a solid form. The resulting items are hardy, electrically-conductive, and chemically stable. The raw dough can also be further processed to make bulk graphene oxide and graphene materials of different forms with tunable microstructures, the team adds. Alternatively, more water can be added to the dough to transform it into a high-concentration GO dispersion.

GO sample transformation.

GO sample converted from a dispersion to a foam, a dough, and back to the a dispersion state. No significant changes in the sizes and morphology of GO sheets are observed during this process. Scale bar = 20 µm for f, g and 10 µm for h, i. Insets in h and i show height profiles of GO sheets in the unit of nanometers.
Image credits

Huang hopes that his GO dough will help graphene reach its much-anticipated potential as a ‘super-material’.

“My dream is to turn graphene-based sheets into a widely accessible, readily usable engineering material, just like plastic, glass and steel,” Huang said.

“I hope GO dough can help inspire new uses of graphene-based materials, just like how play dough can inspire young children’s imagination and creativity.”

I, for one, would definitely play with some GO dough.

The paper “Binder-free graphene oxide doughs” has been published in the journal Nature Communications.

Rubber band.

Rubber band producer adds graphene to its bands — to make them last forever

Hot Springs-based Alliance Rubber Co. teamed up with British researchers to make the humble rubber band eternal — by adding graphene.

Rubber band.

Image via Pixabay.

Graphene really is an incredible material. These atom-thick sheets of pure carbon are ridiculously strong, much stronger than steel and almost every other material we’ve ever discovered. Back in 2008, Columbia University engineer James Hone said that it would take an elephant standing on a pencil to pierce through a sheet of graphene as thick as a regular food wrap. So researchers are trying to mix it into all kinds of materials in an attempt to capitalize on its strength. For example, a recently-published paper details how researchers have been feeding water laced with graphene and carbon nanotubes to spiders so they’re spin ultra-durable silk strands.

Put a band on it

Now, the rubber band manufacturer is looking to bring graphene into the mix and level-up their product. Alliance plans to start a three-year-long partnership with researchers from the University of Sussex, during which they’ll work out the perfect graphene-rubber mix for the bands, says Alliance’s director of business Jason Risner. Too little graphene will result in sub-optimal bands; too much, and they’ll lose elasticity.

Graphene rubber bands aren’t new, however — the two have been mixed before. But what Alliance hopes to do is optimize this design, and get as much strength out of the bands as possible without sacrificing flexibility, allowing them to withstand years of use and abuse. After they figure out the best recipe for the task, the company plans to have virtually unbreakable rubber bands which it can sell to a wide range of industries, from retailers and wholesalers to agribusiness and tech companies, Risner explains.

The mixed-in graphene will address some of the shortcomings of traditional rubber bands. For example, they’ll be anti-static, a critical requirement for companies handling electronic goods — which considered rubber bands anathema up to now, as they easily build up static charges that wreck circuit boards.

Artistic depiction of graphene.

As the graphene-infused bands are expected to last much longer than their rubber-only counterparts, the company is also considering embedding them with radio-frequency identification (RFID) tags or pigments that change color with temperature or time. Alliance says this holds enormous potential for farmers and shops. The tags would allow for much easier and cheaper tracking of products from field to aisle. The pigments would allow stores to track the condition goods are delivered in by showing whether or not produce adhered to temperature standards before delivery.

“They could reject [produce] at the store because [the band] changed colour based on temperature,” Riesler explains.

The RFID-color system would also enable customers to get a lot of information about a product with only a short glance. If a certain item comes normally comes with a blue band, seeing a black band on it would let you know the product’s been improperly handled.

But perhaps the single most satisfying achievement would be to finally have rubber bands that don’t break. That’s why the company plans to eventually mix graphene into every band it produces.

graphene

Scientists devise new, cheaper way to manufacture graphene

Researchers have devised a novel method for manufacturing graphene that uses far less raw materials than conventional methods.

graphene

Credit: Pixabay.

Graphene is an atom-thick sheet of carbon arranged in a honeycomb-shaped lattice. Its properties are remarkable as far as industrial applications go: it’s the strongest material in the world, has a fantastic electrical conductivity, has unlimited heat conductivity, is more sensitive than human skin, and has many other uses. But, for the world to actually get a taste of graphene’s might, we first have to find a way to manufacture it in bulk, cheaply, environmentally-friendly, and without compromising quality. That’s quite a lot to ask from a 2-D material.

Typically, graphene is made by using ultrasound to exfoliate very thin layers from graphite, and then dispersing these layers in large amounts of organic solvent. If there isn’t enough solvent in the solution, the graphene layers will clump together to re-form bulk graphite. Using this method, yielding one kilogram of graphene requires about one ton of organic solvent. This makes the process highly costly and environmentally unfriendly.

A step closer to making graphene mainstream

A team at the National University of Singapore, in collaboration with researchers at Fudan University, has devised a new, much more efficient method that uses up to 50 times less solvent. First, the graphite is pre-treated under highly alkaline conditions. Then, it is exfoliated to trigger flocculation — the process in which graphene layers continuously cluster together to form graphene slurry. Because the method introduces electrostatic repulsive forces between the graphene layers, these are prevented from reattaching themselves into graphite, thus saving the need for so much solvent.

The resulting graphene slurry can then be easily separated into graphene monolayers on the spot or stored away for months. The same slurry can be used to 3D print conductive graphene aerogels, which are very lightweight sponge-like materials that can remove oil spills from the sea.

“We have successfully demonstrated a unique exfoliation strategy for preparing high-quality graphene and its composites,” says study leader Loh Kian Ping, a professor from the chemistry department at the NUS Faculty of Science and head of 2D materials research at the university’s Centre for Advanced 2D Materials.

“Our technique, which produces a high yield of crystalline graphene in the form of a concentrated slurry with a significantly smaller volume of solvent, is an attractive solution for industries to carry out large scale synthesis of this promising material in a cost-effective and sustainable manner,”

The findings were reported in the journal Nature Communications. 

Glass of water.

Novel graphene filter removes 99% of organic waste in water

Australian researchers have developed a filter which promises to revolutionize how we treat drinking water.

Glass of water.

Image via Pixabay.

Graphene has been making many appearances in science lately, owing to its unique physical properties. Today, it’s making headlines in a rather unexpected field of research: water treatment. Researchers from the University of New South Wales (UNSW) Sydney, working together with Sydney Water, have created a world-first graphene filter that can remove 99% of the natural, organic matter left behind by conventional treatment of drinking water. The team is now working on scaling up their technology.

Sydney Water caters to the H2O needs of about 4.8 million people throughout Sydney proper, the Illawarra, and the Blue Mountains. One problem they’re facing is that the source of this water (nature) doesn’t do a very good job at keeping the water pure. For that, Sydney Water employs direct filtration plants, but there’s still a problem — during periods of heavy rains, small-particle organic matter contaminants negatively impact the performance of these plants, reducing their overall capacity.

No organics allowed

The most common working principle these plants rely on is the use of chemical coagulants, which fuse all the organic material together into goop that settles on the bottom. High enough concentrations of these contaminants interfere with the chemical reactions that produce said goop, meaning the plants need to reduce output to ensure the water’s purity.

The team, led by Dr. Rakesh Joshi of the UNSW, decided to skip the chemicals altogether and rely on good old-fashioned mechanical methods:

“Our advance is to use filters based on graphene — an extremely thin form of carbon. No other filtration method has come close to removing 99% of natural organic matter from water at low pressure,” said lead researcher Dr Rakesh Joshi.

“Our results indicate that graphene-based membranes could be converted into an alternative new option that could in the future be retrofitted in conventional water treatment plants.”

The filters are produced by converting natural graphite into membranes of graphite oxide. At high pressures, these membranes become selectively permeable, allowing water to flow through, but not contaminants.

Currently, the filters have only been used in a prototype, small-scale form inside laboratory settings. However, given the exciting results they’ve had thus far, the UNSW team plans to upgrade the experimental rig to a small pilot plant for field testing.

While water filters don’t seem like headline news, it all has to be viewed in the context of our present situation. Pollution, especially plastic pollution, has been plaguing our waterways for decades now. We’re pumping out a lot of waste into the waterways around us, and it’s not going away as we hoped or wanted to think. There’s even cocaine in there. In later years, the situation has taken a dramatic turn for the worst. Plastic particles have found their way into the water we drink, and it also bears the industrial legacy of toxic metal contamination.

Better water filters could help stop the goop before it ever enters the waters — and until it’s clean again, they will help keep the goop (and plastic) out of our bodies.

The paper “Application of graphene oxide membranes for removal of natural organic matter from water” has been published in the journal Carbon.

When rotated at a "magic angle," graphene sheets can form an insulator or a superconductor. Credit: MIT.

‘Magic angle’ allows stacked graphene sheets to work as both insulator and superconductor

When rotated at a "magic angle," graphene sheets can form an insulator or a superconductor. Credit: MIT.

When rotated at a “magic angle,” graphene sheets can form an insulator or a superconductor. Credit: MIT.

Scientists have paradoxically tuned graphene, the so-called ‘wonder material’, to exhibit electrical properties at both extreme ends. According to the findings of researchers at MIT and Harvard University, graphene can operate as an insulator (electrical charge cannot pass through the material) or as a superconductor (electrons can travel through the material without resistance).

The magic angle

Since 2004 when graphene was first forged in Manchester, UK, scientists have discovered one astonishing property after the other. It’s the thinnest material known to man, essentially an atom-thick honeycomb sheet of carbon atoms, but also incredibly light and flexible (a 1-square-meter sheet weighs only 0.77 milligrams), while at the same time being hundreds of times stronger than steel. It would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap. Furthermore, graphene is electrically conductive, more so than copper, which is why many look to it as the backbone for the super-electronics of the future.

But there’s even more to it than meets the eye. Most recently, researchers at MIT and Harvard published two papers in the journal Nature that show graphene’s far more curious electrical properties.

Previously, scientists were able to synthesize graphene superconductors by doping it with inherently superconductive metals. This way, graphene would ‘inherit’ the superconductive properties.

Now, researchers led by Pablo Jarillo-Herrero, an associate professor of physics at MIT, found a way to make graphene superconductive on its own.

A material’s ability to conduct electrons is characterized by energy bands, with every single band representing the range of energies that electrons can have. Between bands, there is an energy gap, and to leap over this gap once a band is filled to travel to the next band, electrons need extra energy. An insulator is a material in which the last occupied energy band is completely filled with electrons. Conductors, on the other hand, have partially filled energy bands which electrons can occupy to freely move.

There is, however, one peculiar class of materials which should conduct electricity, judging from their band structure, but don’t actually do, behaving as insulators instead. These are called Mott insulators. The insulating effect is due to strong electrostatic interactions between the electrons.

“This means all the electrons are blocked, so it’s an insulator because of this strong repulsion between the electrons, so nothing can flow,” Jarillo-Herrero explained in a statement. “Why are Mott insulators important? It turns out the parent compound of most high-temperature superconductors is a Mott insulator.”

Jarillo-Herrero and his colleagues experimented with simple stacks of graphene sheets. Eventually, they came across an amazing configuration: two-stack sheet superlattices. Specifically, when rotated at a ‘magic angle’,  two stacks sheets of graphene exhibit nonconducting behavior, similar to an exotic class of materials known as Mott insulators. The graphene sheets don’t sit exactly on top of each other but are instead offset by a magic angle of 1.1 degrees. In this configuration, the graphene superlattice exhibits a flat band structure, similar to a Mott insulator, in which all electrons carry the same energy regardless of their momentum.

“Imagine the momentum for a car is mass times velocity,” Jarillo-Herrero says. “If you’re driving at 30 miles per hour, you have a certain amount of kinetic energy. If you drive at 60 miles per hour, you have much higher energy, and if you crash, you could deform a much bigger object. This thing is saying, no matter if you go 30 or 60 or 100 miles per hour, they would all have the same energy.”

When the researchers then applied voltage, adding small amounts of electrons to the graphene superlattice, they found that, at a certain level, the electrons broke out of the initial insulating state and flowed without resistance, as if through a superconductor.

It’s possible, says Jarillo-Herrero, to tune graphene to either behave as an insulator or a superconductor, as well as any phase in between — all very diverse properties in one single device.

“We can now use graphene as a new platform for investigating unconventional superconductivity,” Jarillo-Herrero says. “One can also imagine making a superconducting transistor out of graphene, which you can switch on and off, from superconducting to insulating. That opens many possibilities for quantum devices.”

Graphene trainers are strong, stretchy, and have an excellent grip

Graphene is already making its mark in real life. Researchers say that the wonder material could pave the way for the next generation of shoes.

The graphene shoe has a better grip and is reportedly stronger than conventional alternatives. Credits: inov-8.

Graphene is already a bit of a show-off, isn’t it? Not only is it extremely strong and light, it has remarkable electrical properties and promises to usher in a new age of material science. As if all that wasn’t enough, researchers have now incorporated it into shoe soles, improving their performance and durability.

The new running shoe was developed in Manchester, UK, where graphene was first produced by Andre Geim and his collaborators. Aravind Vijayaraghavan, a reader in nanomaterials at the University of Manchester, says graphene is an excellent choice for shoes. He and his team mixed the wonder material with rubber, creating a compound with special properties.

“The graphene-enhanced rubber can flex and grip to all surfaces more effectively, without wearing down quickly, providing reliably strong, long-lasting grip.”

“It’s also extraordinarily flexible, and can be bent, twisted, folded and stretched without incurring any damage.”

The problem with shoe rubber is that you always end up having to compromise. If you want to improve the grip, you need to make the rubber softer, so that it deforms easily and grips on to the running surface. But soft rubber tends to wear down more quickly, as you also end up sacrificing some of the material’s strength in the process. Researchers have tried strengthening rubber and enhancing its properties, but in the end, you always end up sacrificing one thing for the other.

This is where graphene steps in. Not only does the material make the rubber stronger, but it also makes it more flexible. So instead of upgrading one aspect and downgrading the other, researchers have managed to upgrade both.

The new shoes are a collaboration between inov-8 and researchers from the University of Manchester. Image credits: inov-8.

“When added to the rubber used in inov-8’s G-Series shoes, graphene imparts all its properties, including its strength. Our unique formulation makes these outsoles 50% stronger, 50% more stretchy and 50% more resistant to wear than the corresponding industry standard rubber without graphene,” Vijayaraghavan adds.

The resulting material can easily be molded into the desired shape, meaning that the technology isn’t limited to shoes, but it could also be applied to surgical gloves, protection gear, and perhaps even tires.

“You mix it until it’s easily dispersed and then you mould your sole,” says Aravind Vijayaraghavan who worked on the project with the fitness brand inov-8.

It’s impressive just how far and how fast graphene has come, from being a lab material and onto the market. The G-series shoes, designed for trail running, cost at around £140 ($187) and will go on sale in 2018. Separate projects have already revealed graphene headphones, sensors, medical devices and a dress.

Scientists combine spider silk with graphene, create incredibly powerful web

Parachutes and many other things could soon be made from spider silk, as two wonder materials combine to achieve remarkable properties.

The spiders produce it

Spider silk is basically a protein fiber spun by spiders to create webs and other similar structures. Different spiders create different types of webs, optimized for their particular needs. But most spider webs are characterized by a unique combination of high tensile strength and extensibility, which allows them to absorb a massive amount of energy before breaking (strength should not be confused with toughness, which is a different property). Meanwhile, graphene is the new wonder material on the block. It’s basically a one-atom thick sheet of carbon which for all purposes can be considered two dimensional. Graphene also exhibits impressive mechanical properties, as well as being a semiconductor.

Now, scientists led by Nicola Pugno at Italy’s University of Trento have managed to combine the two with carbon nanotubes into an innovative material which — amazingly enough — the spiders themselves produce.

“We already know that there are biominerals present in the protein matrices and hard tissues of insects, which gives them high strength and hardness in their jaws, mandibles, and teeth, for example,” Pugno told The Sydney Morning Herald. “So our study looked at whether spider silk’s properties could be ‘enhanced’ by artificially incorporating various different nanomaterials into the silk’s biological protein structures.”

Their work ingeniously takes advantage of the metabolic processes already happening inside the spiders. The researchers fed spiders water containing the nanotubes. The spiders then produced an improved silk which was five times stronger than the regular one, putting it on par with the strongest materials on Earth (ie Kevlar).

Applications for this are far reaching. For now, researchers have their eyes set on parachutes, but Pugno says that this approach could be extended to other animals as well. Basically, a similar mixture could be fed to different animals, giving birth to a completely new class of materials.

“This process of the natural integration of reinforcements in biological structural materials could also be applied to other animals and plants, leading to a new class of ‘bionicomposites’ for innovative applications,” he asserted.

Still, this is only in early stages of testing — only a small quantity of silk has been harvested and analyzed, it remains to be seen whether the process can be scaled

Journal Reference: Emiliano Lepore et al. Spider silk reinforced by graphene or carbon nanotubes.

graphene-based salt sieve

Graphene-based sieve makes drinking water out of seawater

In many places on Earth, we’re using more water than can be replenished and with climate change looming, more and more communities are set to suffer water shortages. Drinking water shortages, that is, because if there’s anything this planet isn’t lacking in, it’s water. The problem is most of it lies in the oceans which are salty and desalinization can be extremely expensive and energy intensive. If you could filter the salts out of the ocean as easily as you’d separate common impurities with a sieve, that’d be a real breakthrough.

graphene-based salt sieve

Credit: The University of Manchester

Researchers from the University of Manchester, UK, are close to making this idea into a practical, working solution in the real world. Their solution is based on graphene-oxide membranes which had already previously proven highly effective at filtering out small nanoparticles and even large salts.

Common salts dissolved in water form a sort of ‘shell’ of water molecules around the salts. Tiny capillaries etched inside the graphene-oxide membranes can block these salts from flowing along with the water. Water molecules then pass through the sieve at a flow rate that’s anomalously fast, which is highly desirable for desalination applications.

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the described approach and mass produce graphene-based membranes with required sieve sizes,” said Professor Rahul Nair from the University of Manchester.

Previously at Manchester, the birthplace of graphene more than 15 years ago, the same team found graphene-oxide membranes get swollen after prolonged used and smaller salts get through the membrane along with the water. This time around, membrane swelling was avoided by controlling pore size. Pore sizes as small as 9.8 Å to 6.4 Å were demonstrated where one Å is equal to 0.1 nanometers.

“Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” Nair said.

These membranes are not only useful for desalination. The same atomic-scale tunability of the pore sizes can be used to manufacture membranes that filter a variety of ions.

According to the U.N., 14 percent of the world’s population could encounter water scarcity by 2025. Off-grid, small-scale solutions like these graphene-oxide membranes have their place and will help lessen the strain in those areas of the world where there’s not enough capital to support large desalination plants.

Scientific reference: Tunable sieving of ions using graphene oxide membranes, Nature Nanotechnology, nature.com/articles/doi:10.1038/nnano.2017.21

This graphene nanoribbon is only seven carbon atoms in width. Credit: Chuanxu Ma and An-Ping Li

Nanoribbons pave the way for switching graphene ‘on-off’

Among its many stellar properties, graphene is an amazing electrical conductor. However, if graphene is to reach its full potential in the field of electronics, it needs to coaxed to turn current on or off like silicon transistors. Physicists at the Department of Energy’s Oak Ridge National Laboratory (ONRL) present a recent breakthrough that may enable graphene to act like a semiconductor. The catch is to grow graphene in curled nanoribbons rather than in flat 2-D sheets.

This graphene nanoribbon is only seven carbon atoms in width. Credit: Chuanxu Ma and An-Ping Li

This graphene nanoribbon is only seven carbon atoms in width. Credit: Chuanxu Ma and An-Ping Li

When arranged in wide sheets, the hexagon-linked graphene doesn’t have a band gap, which means you can’t use it in modern electronics like computer chips or solar panels. It’s a great electrical wire but useless as a transistor. That’s speaking about its traditional configuration because graphene can work as a semiconductor in other arrangements. Doping graphene with various impurities can enable the material to switch on or off, for instance, DNA and copper ions as demonstrated previously by another team. 

The team from ONRL, however, made semiconductive graphene with no other additional material by fashioning it in ribbons because when graphene becomes very narrow, it creates an energy gap. The narrower the ribbon is, the wider the energy gap and the ribbons made at ONRL are definitely narrow. One nanoribbon has a width of only one nanometer or less.

Besides narrowness, another important factor is the shape of the edge. When graphene’s hexagon is cut along the side, its shapes resembles an armchair — this shape enables the material to act like a semiconductor.

Previously, scientists made graphene nanoribbons by growing them on a metal substrate. This was necessary but undesirable because the metal hinders some of the ribbons’ useful electrical properties.

The scanning tunneling microscope injects charge carriers called “holes” into a polymer precursor. . Credit: Oak Ridge National Laboratory, U.S. Dept. of Energy

The scanning tunneling microscope injects charge carriers called “holes” into a polymer precursor. . Credit: Oak Ridge National Laboratory, U.S. Dept. of Energy

ONRL took a different route to get rid of the metal substrate altogether. To trigger chemical reactions that control the width and edge structure from polymer precursors, the team used the tip of a scanning tunneling microscope to inject positive charge carriers called ‘holes’. The reaction could be triggered at any point of the polymer chain by moving the tip in the right direction. This method rendered ribbons that were only seven carbon atoms wide whose edges were neatly wrapped in the armchair configuration.

“We figured out the fundamental mechanism, that is, how charge injection can lower the reaction barrier to promote this chemical reaction,” said An-Ping Li, a physicist at the Department of Energy’s Oak Ridge National Laboratory.

Moving forward, the researchers plan on making the heterojunctions with different precursor molecules. One exciting possibility is conducting photons in a new electronic device with graphene semiconductors where current could be carried with virtual no resistance even at room temperature — a life-long dream in solid state physics.

“It’s a way to tailor physical properties for energy applications,” Li said. “This is an excellent example of direct writing. You can direct the transformation process at the molecular or atomic level.”

Scientific reference: Chuanxu Ma et al, Controllable conversion of quasi-freestanding polymer chains to graphene nanoribbons, Nature Communications (2017). DOI: 10.1038/ncomms14815.

Czech researchers turn graphene sheets into the first stable non-metallic magnets

Researchers have created the first stable non-metal magnet ever by treating graphene layers with non-metallic elements.

Image credits Wikimedia / AlexanderAlUS.

A team from the Regional Center of Advanced Technologies and Materials at the Palacky University, Olomouc, Czech Republic, announced that they have created the first non-metal magnet that can maintain its properties at room temperature. The process requires no metals — the team created their magnet by treating graphene layers with non-metallic elements such as fluorine, hydrogen, or oxygen.

“For several years, we have suspected that the path to magnetic carbon could involve graphene — a single two-dimensional layer of carbon atoms,” lead researcher Radek Zbořil, director of the RCATM, in a press release.

“[Through the process] we were able to create a new source of magnetic moments that communicate with each other even at room temperature. This discovery is seen as a huge advancement in the capabilities of organic magnets.”

They’ve also developed the theoretical framework to explain why their unique chemical treatment creates magnets without any metal.

“In metallic systems, magnetic phenomena result from the behavior of electrons in the atomic structure of metals,” explained co-author Michal Otyepka.

“In the organic magnets [i.e. the graphene ones] that we have developed, the magnetic features emerge from the behavior of non-metallic chemical radicals that carry free electrons.”

Graphene is already getting a lot of attention for its unique electrical and physical properties as well as electrical conductivity. Adding magnetism to the list of it can do opens up a whole new range of possibilities for a material that is in essence sheet carbon you can cook make from soy.

“Such magnetic graphene-based materials have potential applications in the fields of spintronics and electronics, but also in medicine for targeted drug delivery and for separating molecules using external magnetic fields,” the team adds.

The full paper “Room temperature organic magnets derived from sp3 functionalized graphene” has been published in the journal Nature.

Dr Zhao Jun Han holds a thin film of graphene he made from soybean oil. Credit: CSIRO.

How to cook graphene using only soybean oil. Seriously, these scientists did it

 Dr Zhao Jun Han holds a thin film of graphene he made from soybean oil. Credit: CSIRO.

Dr Zhao Jun Han holds a thin film of graphene he made from soybean oil. Credit: CSIRO.

Since it was first forged in the labs of the University of Manchester in the UK, graphene has been touted as the miracle material of the 21st century. For good reason, too. It’s 200 times stronger than steel, has a fantastic electrical conductivity, unlimited heat conductivity, it’s more sensitive than human skin, and has many other uses. It could revolutionize everything from commercial electronics to space flight.

It’s been 13 years, however, since graphene was first synthesized by Andre Geim and Konstantin Novoselov (the two would later win a Nobel Prize for their wok) and we’re still far from living in the graphene age.

Graphene’s desirable properties are attainable as long as it stays in its 2-D, one-atom thick configuration. In reality, that’s impractical and graphene applications will typically use materials made from multiple sheets. The more sheets you add, the worse graphene’s performance and creating high-quality graphene in bulk is still a big challenge.

Australian researchers from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) might not have made the best graphene in the world, but it sure is cheap and fast to make.

Dr Zhao Jun Han and colleagues made their sheets of graphene starting from a common household item: soybean oil.

Firstly, the team heated the soybean oil in a furnace for about 30 minutes. The heat decomposed the oil into carbon building blocks which became deposited on a nickel foil. Once the foil is put out of the oven, it is then rapidly cooled. What you get is a thin rectangle of graphene film about one nanometer thick or 80,000 times thinner than a human hair.

The whole process takes place at ambient air, unlike other methods that grow graphene in vacuum.

The graphene sheet. Credit: CSIRO

The graphene sheet. Credit: CSIRO

Jun Han claims his team’s technique is faster, cheaper, and more efficient than any other graphene manufacturing process before it. Moreover, costs could be brought down ten-fold, as reported in a paper published in  Nature Communications.

“We believe that this process can significantly reduce the cost of producing graphene film,” he said.

“It can then accommodate many applications that were previously limited by the high price of producing these films.”

Using soybean oil as a source of carbon for graphene production is definitely unheard of but the resulting material should be just as good as those made using other methods. It’s still graphene. Dr Han says their graphene films could be used straight away in batteries and supercapacitors. However, it’s still unclear whether this process can be scaled to industrial size. The film made at CSIRO is a small rectangle only 5x2cm across. Producing thousands of square meters of sheets, as it would be desirable, is a whole different ball game.

 

Colemans

Mixing Silly Putty with graphene creates incredibly sensitive pressure sensors, scientists find

Trinity College Dublin researchers working together with University of Manchester’s National Graphene Institute (NGI) have found that mixing graphene with polysilicone (Silly Putty) produces incredibly sensitive pressure and strain sensors — they can even pick up on the footsteps of small spiders.

Colemans

Johnny Coleman investigates G-Putty with his son Oisin.
Image credits AMBER, Trinity College Dublin.

Graphene can be used to make some pretty sweet sensors. Previously, researchers from the Nanyang Technological University in China developed highly efficient light sensors using the stuff. Now, Trinity’s School of Physics Professor Jonathan Coleman along with postdoctoral researcher Conor Boland found that putty mixed with graphene (which they call G-putty) has a surprising property: its electrical resistance is extremely sensitive to the slightest deformation or impact. The discovery could potentially open the way for inexpensive devices with a wide range of applications, such as diagnostics in healthcare.

Adding graphene to plastics is a pretty common practice. Usually, it improves the materials’ electrical, mechanical, thermal, or barrier properties, but the results can generally be predicted without too much surprise. The behavior of G-putty is unique, however, and Coleman believes it will “open up major possibilities in sensor manufacturing worldwide.”

“What we are excited about is the unexpected behaviour we found when we added graphene to the polymer, a cross-linked polysilicone,” Coleman said.

“It caused [the putty] to conduct electricity, but in a very unusual way. The electrical resistance of the G-putty was very sensitive to deformation with the resistance increasing sharply on even the slightest strain or impact.”

“Unusually, the resistance slowly returned close to its original value as the putty self-healed over time.”

The two first tested the G-putty by placing it on the chest and neck of subjects, then using it to measure breathing, pulse, even blood pressure. The material proved to be hundreds of times more sensitive than current pressure and strain sensors. It can even pick up on impacts as light as a small spider’s footstep.

Following initial development at Trinity, University of Manchester NGI scientists analyzed the material to determine its structure. From this, they developed a mathematical model of how G-putty deforms, explaining how the material’s structure dictates its mechanical and electrical properties.

“These phenomena are associated with the mobility of the [graphene] nanosheets in the low-viscosity polymer matrix,” the paper reads.

“By considering both the connectivity and mobility of the nanosheets, we developed a quantitative model that completely describes the electromechanical properties.”

The full paper “Sensitive electromechanical sensors using viscoelastic graphene-polymer nanocomposites” has been published in the journal Science.

Graphene elastomer is more sensitive than human skin

Researchers have developed a new graphene-based elastomer that can revolutionize prosthetic skin. The sponge-like material is highly sensitive to pressure and vibrations, even more so than the human skin.

The 3-D printed graphene scaffold appeared on the cover of ACS Nano.

The team from Northwestern University found a way to develop three-dimensional structures with graphene nanoflakes. The key was that they incorporate only a part of graphene in the structures – high enough to retain some of its praised properties, but low enough so that it can create robust macroscopic 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.”

The result is an ink-like material with the best properties of both worlds – it retains graphene’s electrical conductivity, and is very stable and sturdy to be used as a prosthetic.

“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.”

It works so well that even some of its creators were surprised. Professor Dan Li and Dr Ling Qiu from the Monash Centre for Atomically Thin Materials (MCATM) praised the results:

“This graphene elastomer is a flexible, ultra-light material which can detect pressures and vibrations across a broad bandwidth of frequencies. It far exceeds the response range of our skin, and it also has a very fast response time, much faster than conventional polymer elastomer.”

“Although we often take it for granted, the pressure sensors in our skin allow us to do things like hold a cup without dropping it, crushing it, or spilling the contents. The sensitivity and response time of G-elastomer could allow a prosthetic hand or a robot to be even more dexterous than a human, while the flexibility could allow us to create next generation flexible electronic devices,” he said.

The applications for this type of technology are limitless. Not only can it lead to developing better, softer robots which can for example aid in healthcare or take care of the elders, but it can create a new generation of skin prosthetics. Right now, despite the great advancement in prosthetics provided by 3D printing, skin prosthetics still remain a challenge due to their lack of sensitivity.

graphene

Growing graphene nanoribbons jut got a lot easier, spelling great news for electronics

University of Wisconsin-Madison engineers devised a new method that grows graphene nanoribbons directly on a germanium wafer. The ribbons are of excellent quality and the technique is compatible with current manufacturing methods. These sort of ribbons have been heralded by industry experts as the component of the future which will make electronics faster and more efficient. The only thing that’s been missing until now was a sound way to make them.

graphene

Image: extremetech

Graphene – the one atom thick carbon allotrope spaced in a hexagonal lattice – is a wonder material with fantastic electrical conductivity and heat dissipation. These properties makes it an ideal component in electronics, but graphene on its own is rather useless for semiconductor applications. For graphene to work as a semiconductor, it needs to be able to switch currents on and off. In more technical terms, previously scientists calculated that an optimal design would be a 10nm wide graphene with a well-defined edge where carbon-carbon bonds are parallel to the edge (the ‘armchair’ edge).

These sort of requirements are by no means easy to deliver. So far, two distinct approaches have been used to make the ribbons. One is “top-down” and involves cutting ribbons from a lithographically layered sheet of graphene. However, this method leads to ribbons with rough edges and variable size – a level of imprecision that is unpractical for use in high-grade electronics. The “bottom-up” method involves making the ribbons through chemical means from the ground up. Typically, various molecules react on a substrate surface where they polymerize into the ribbons. The quality of the ribbons is great, but the downside of the “bottom-up” method is that it only works on metal surfaces and the resulting ribbons are too short.

Zoom in of graphene nanoribbon on germanium. Image: Arnold Research Group

Zoom in of graphene nanoribbon on germanium. Image: Arnold Research Group

The UW-Madison researchers also used a “bottom-up” technique, with some key differences. Using chemical vapor deposition, the researchers carefully sprayed a germanium wafer with methane. Th methane gets adsorbed by the germanium wafer and eventually decomposes into graphene. Now, they key is to use methane in very small concentration to slow down the growth rate. At a low growth rate, the graphene crystals naturally grow into the ribbons.
“What we’ve discovered is that when graphene grows on germanium, it naturally forms nanoribbons with these very smooth, armchair edges,” said research leader Michael Arnold. “The widths can be very, very narrow and the lengths of the ribbons can be very long, so all the desirable features we want in graphene nanoribbons are happening automatically with this technique.”
“Graphene nanoribbons that can be grown directly on the surface of a semiconductor like germanium are more compatible with planar processing that’s used in the semiconductor industry, and so there would be less of a barrier to integrating these really excellent materials into electronics in the future,” Arnold said in a statement.
Besides fast electronics, the graphene nanoribbons can also be used to fashion chemical sensors which are very tiny and sensitive (very useful for detecting drugs or explosives). For the moment, Arnold and colleagues are concentrating on refining their method. For instance, they’ve yet to find a way to control the growth of the ribbons, i.e. choose where the ribbons start growing and in what direction.
Findings appeared in Nature Communications
stanene

Introducing stanene: just like graphene, except it’s a 2D tin honeycomb

After graphene proved to be one of the greatest discovery of the century, material scientists became inspired to see if other 2D meshes (just one atom thick layer of material) could be made from other elements. In time, we’ve heared about silicenephosphorene or germanene. Now, a group from China reports for the first time stanene: a honeycomb 2D arrangement of tin (Sn) atoms, with a a bismuth telluride support that buckles the whole structure. Stanene is extremely exciting because it’s been previously theorized that it could transfer electricity without heat loss, implying huge energy savings and increased performance for semiconductor applications.

stanene

Microscope images like the one the left pick out only the upper ridges of the stanene sheet. Image: Nature

The zero energy loss of stanene was predicted by Stanford researchers in 2011. That’s because stanene is a topological insulator: it can’t conduct electricity inside the bulk material, but it can at the edge.

When electrons travel through a material they bump into atoms, transferring some of the energy to the atoms that causes them to jiggle. This extra vibration gives off energy we know as heat. But in order for the electron (quantum particle) to collide with an atom, it needs to fill an unoccupied quantum state with the correct spin, energy and momentum. Because there are fewer collisions in an topological insulator, such a material used as a conductor could save a lot of energy. However, Shou-Cheng Zhang, a physicist at Stanford University in California and co-author of the present study, says that his team was yet to prove that stanene can conduct electricity without generating any waste heat.

What they have, for now, is prove that stanene can exist in this state. The researchers made the mesh by vaporizing tin in a vacuum and allowing the atoms to waft onto a supporting surface made of bismuth telluride. This allowed 2D crystals to form, but the bismuth telluride also interacts with the mesh causing the material to lose its topological insulating properties. There’s another possible shortcoming. Theory says stanene should like a buckled honeycomb, but the researchers could only see see the upper ridge of atoms with their scanning tunnelling microscope, as reported in Nature Materials. To be sure of its properties, the researchers should make pure stanene, and not some other tin arrangement.

Still, efforts so far with graphene and its cousins have proven to be extremely lucrative and, most of all, promising. “It’s like going to the Moon,” says And Guy Le Lay, a physicist at Aix-Marseille University in France. “The first step is the crucial step.”