Tag Archives: material science

Copper foam turns CO2 into useful chemicals

Brown University researchers reported the development of a copper foam which could turn CO2 into useful chemicals such as formic acid – a preservative and antibacterial agent in livestock feed.

Copper1

Copper is the only metal that can reduce CO2 to useful hydrocarbons. A foam of copper offers sponge-like pores and channels, providing more active sites for CO2 reactions than a simple surface. Credit: Palmore lab/Brown University

As CO2 emissions continue to grow, scientists are trying to find potential uses to it. The problem with carbon dioxide is that it is extremely stable, so breaking it and making useful industrial chemicals is no easy feat. The catalyst they made from copper foam has “vastly different properties” from catalysts made with smooth copper in reactions involving carbon dioxide:

“Copper has been studied for a long time as an electrocatalyst for CO2 reduction, and it’s the only metal shown to be able to reduce CO2 to useful hydrocarbons,” said Tayhas Palmore, professor of engineering and senior author of the new research. “There was some indication that if you roughen the surface of planar copper, it would create more active sites for reactions with CO2.”

Copper foam was virtually ignored until a few years ago, when it started receiving the attention it deserves. The foam is created by depositing copper on a surface in the presence of hydrogen and a strong electric current. Hydrogen creates bubbles and the copper is deposited in a sponge-like arrangement of varying sizes.

After the foam was created, researchers set out to experiment, and see which chemicals strongly react to it; lo and behold CO2 was one of the winners. Their experiments showed that the copper foam converted CO2 into formic acid much more efficiently than common copper. The reaction also produced small amounts of propylene, a useful hydrocarbon that’s never been reported before in reactions involving copper.

“The product distribution was unique and very different from what had been reported with planar electrodes, which was a surprise,” Palmore said. “We’ve identified another parameter to consider in the electroreduction of CO2. It’s not just the kind of metal that’s responsible for the direction this chemistry goes, but also the architecture of the catalyst.”

To me, it’s remarkable that a material so common and well studied as copper still yields surprises for us. But it’s clear that we still have much to learn about it.

“People have studied electrocatalysis with copper for a couple decades now,” she said. “It’s remarkable that we can still make alterations to it that affect what’s produced.”

Source: Brown University.

In this photo of the angular-selective sample (the rectangular region), a beam of white light passes through as if the sample was transparent glass. The red beam, coming in at a different angle, is reflected away, as if the sample was a mirror. The other lines are reflections of the beams. (This setup is immersed in liquid filled with light-scattering ­particles to make the rays visible). (credit: Weishun Xu and Yuhao Zhang)

A new method for filtering light coming from a specific direction

Using only material geometry and interference patterns, MIT researchers have devised a novel way of passing light of any colour only if it comes from a specific angle. Light coming from other directions will be reflected, something which can be desirable in certain applications. Those who could benefit immediately from the findings are solar photovoltaics, detectors for telescopes and microscopes, and privacy filters for display screens.

In this photo of the angular-selective sample (the rectangular region), a beam of white light passes through as if the sample was transparent glass. The red beam, coming in at a different angle, is reflected away, as if the sample was a mirror. The other lines are reflections of the beams. (This setup is immersed in liquid filled with light-scattering ­particles to make the rays visible). (credit: Weishun Xu and Yuhao Zhang)

In this photo of the angular-selective sample (the rectangular region), a beam of white light passes through as if the sample was transparent glass. The red beam, coming in at a different angle, is reflected away, as if the sample was a mirror. The other lines are reflections of the beams. (This setup is immersed in liquid filled with light-scattering ­particles to make the rays visible). (credit: Weishun Xu and Yuhao Zhang)

The researchers built a stack of 80 ultrathin layers built out of two materials with different refractive indices (glass and tantalum oxide).  At the interfaces, small amounts of light get reflected, but combining the surrounding layers in a specific fashion, only light coming in from a certain direction and at a specific polarization will become reflected.

“When you have two materials, then generally at the interface between them you will have some reflections,” the researchers explain.

But at these interfaces, “there is this magical angle called the Brewster angle, and when you come in at exactly that angle and the appropriate polarization, there is no reflection at all.”

Previously, researchers demonstrated methods that selectively reflect light for one precise angle, but these involved narrowing down a range of light frequencies (colours). The new system allow all colours in the visible spectrum of light to be reflected from a single direction. A video of the experimental set-up can be viewed below.

A thermophotovoltaic cell that harnesses solar energy to heat a material could employ such a system to radiate light of a particular colour. At the same time, a complementing photovoltaic cell would use all of that colour of light, limiting heat and light lost to reflections, re-emissions and such, thus improving efficiency. Microscopes and telescopes could also potentially benefit from such a system in scenarios where bright cosmic objects interfere and block the view of an object of interest. Using a telescope that only reads light from a certain angle, it’s possible then to observe very faint targets masked by those that are brighter. Display screens or phones could exploit this to only display information when the person is right in front of them, to avoid peeping.

In principle, the angular selectivity can be made narrower simply by adding more layers to the stack, the researchers say. For the experiments performed so far, the angle of selectivity was about 10 degrees; roughly 90 percent of the light coming in within that angle was allowed to pass through.

Findings appeared in the journal Science.

 

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

Synthetic muscle made from nylon is 100 times stronger than human muscle

Sometimes, I come across stories or various research that make me wonder “why the heck hasn’t anyone else thought of this before?” We should be grateful, nevertheless, that researchers from University of Texas at Dallas have found a way to manufacture artificial muscle that is up to 100 times stronger than the flimsy tissue that makes up the human biceps. The material is made out of nylon fibers – the stuff fishnets are made of – that are tensed almost to the upper limit and thermal processed to retain a high energy density.

Like very thin springs, the synthetic muscle is cheap, easy to make and durable. Of course it has some drawbacks, however the researchers envision its introduction in the industry extremely fast considering the facts. Applications include artificial muscles for robots, exoskeleton suits, or automatically heat-regulated window shutters and ventilation systems.

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

Photograph comparing muscles made by coiling (from left to right) 150 μm, 280 μm, 860 μm and 2.45 mm nylon 6 monofilament fibers. Photo: Science

The process through which the synthetic sinew is coiled is quite trivially simple. Basically, it boils down to making sure you apply the right tension and weight to the thread when twisting it. Actually, according to the scientists involved in the work, similar nylon coils like the ones they produced can be made by regular people at home.

Nylon or polyethylene gets twisted under high tension over and over again until it reaches a certain strain threshold. Once the plastic can’t twist any more, it starts to coil up on itself like a curled telephone cord. The coil is then thermally treated so it gets locked in place; along with energy stored in the coil. When the resulting coil is heated, it begins to untwist, but in the process the whole whole material begins to compress.

“At first it seems confusing, but you can think of it kind of like a Chinese finger-trap,” says Ray Baughman, a materials scientist with the team. “Expanding the volume of the finger-trap, or heating the coil, actually makes the device shorten.”

By braiding and twisting different threads together and coiling them in different ways, you can end up with different kinds of variations in muscle strength, depending on the kind of application you’re looking for. Also, by blending in conductive wire or wrapping the muscle with a light-absorbing coating, the researchers can control the muscles’ movements with electricity and light instead of direct heat.

Photo: University of Texas at Dallas.

Photo: University of Texas at Dallas.

At the moment, the nylon artificial muscle isn’t all that efficient. While work is presently underway to solve inefficiency issues, by itself, even in its current form, this research is extremely impressive and will most likely get used in real-world applications real soon. It also is a great example of what you can achieve with readily available materials and technology just by applying novel tricks and strategies.

You can find out more in the paper published just today in the journal Science.

An example of a 4-D structure that morphs in time according to environmental factors. (c) Anna C. Balazs

4D printing may pave way for a new kind of smart materials

A team of scientists, part of a collaborative effort involving multiple Universities from the U.S., are proposing to take 3D printing one step further by adding a new dimension – time. Their work involves building a new class of materials that can morph, change their physical properties and functionality over time based on external stimuli by exploiting the high precision capabilities of 3-D printing.

An example of a 4-D structure that morphs in time according to environmental factors. (c) Anna C. Balazs

An example of a 4-D structure that morphs in time according to environmental factors. (c) Anna C. Balazs

Imagine an automobile coating that changes its structure to adapt to a humid environment or a salt-covered road, better protecting the car from corrosion. Or consider a soldier’s uniform that could alter its camouflage or more effectively protect against poison gas or shrapnel upon contact. The latter example is actually of great importance since the research was recently awarded a $855,000 grant from the United States Army Research Office.

The team includes principal investigator Anna C. Balazs, the Robert v. d. Luft Distinguished Professor of Chemical Engineering in Pitt’s Swanson School of Engineering and a researcher in the computational design of chemo-mechanically responsive gels and composites. Co-investigators are Jennifer A. Lewis, the Hansjo?rg Wyss Professor of Biologically Inspired Engineering at the Harvard School of Engineering and Applied Sciences and an expert in 3D printing of functional materials; and Ralph G. Nuzzo, the G. L. Clark Professor of Chemistry and Professor of Materials Science and Engineering at the University of Illinois, a synthetic chemist who has created novel stimuli-responsive materials.

4D materials

“Rather than construct a static material or one that simply changes its shape, we’re proposing the development of adaptive, biomimetic composites that reprogram their shape, properties, or functionality on demand, based upon external stimuli,” Balazs explained. “By integrating our abilities to print precise, three-dimensional, hierarchically-structured materials; synthesize stimuli-responsive components; and predict the temporal behavior of the system, we expect to build the foundation for the new field of 4D printing.”

The trio of researchers will combine their high-end expertise to manipulate materials at the micro and nano scale using 3-D printing to layer their 4D composites. If you’re not familiar with the tech yet, basically 3D printing involves precision nanoscale depositing of materials, layer by layer, thus crafting high fidelity 3D objects based on a digital model. Since they’re very precise, 3D printers will allow the scientists to build their intricate nano-patterns in specific areas of the structure.

“If you use materials that possess the ability to change their properties or shape multiple times, you don’t have to build for a specific, one-time use,” she explained. “Composites that can be reconfigured in the presence of different stimuli could dramatically extend the reach of 3D printing.”

Since the research will use responsive fillers embedded within a stimuli-responsive hydrogel, Nuzzo says this opens new routes for producing the next generation of smart sensors, coatings, textiles, and structural components.

“The ability to create one fabric that responds to light by changing its color, and to temperature by altering its permeability, and even to an external force by hardening its structure, becomes possible through the creation of responsive materials that are simultaneously adaptive, flexible, lightweight, and strong. It’s this ‘complicated functionality’ that makes true 4D printing a game changer.”

carbon capture tech

Carbon capture of the future might turn CO2 into construction materials

We all know that CO2 dumped in the atmosphere (consequences in the ocean, where the most carbon winds up actually are even dire  – i.e. ocean acidification) causes global warming through what’s commonly referred to as the greenhouse gas effect. Governments and various environmental panels have through out the years issued various policies meant on curbing emissions. Ironically, however, greenhouse gas emissions have only gone up, as year after year there seems to be a new record in how much CO2 gets released into the atmosphere, mainly due to developing countries catching up and becoming industrialized. Only recently, the world passed a frightening threshold after atmospheric CO2 levels reached 400ppm (parts per million) for the first time in 3 million years.

The reason I’m presenting these facts isn’t to inflict panic. Indeed, these are depressing data, however it’s important to build context especially when covering cutting edge research conducted by scientists working effortlessly to battle atmospheric CO2 dumping. One of the most creative solution is the development of carbon trapping technology, and exciting as the tech may be it still bears a grand challenge: what to do with the stored carbon. While more efficient plants and filters significantly cut down emissions, you still windup with excess carbon – sure it’s not in gaseous form as a CO2 compound, so it doesn’t contribute to the greenhouse gas effect, but you still need to get rid of it.

carbon capture tech

(c) carboncapture.us

Some byproducts get pumped into the ground directly, where it seeps though cracks of rock layers deep below the surface, a process that we already know causes huge chemical changes in the rock. Other methods involve dumping the stored carbon by pumping it into the ocean, where pressures below a certain depth will cause it to form a thick slurry that falls to coat the ocean floor – in theory, right at the bottom, it’s harmless. The method is promising when you need to dump a few tons of carbon, but at the massive industrial scale you need a system capable of disposing millions of tones of carbon – hint: it needs to be cheap; dirt cheap!

Researchers at University of Newcastle have come up with a new solution that not only elegantly solves this problem, but offers a practical use. What if instead of dumping the captured carbon you turn it into something useful? This is exactly the reasoning behind the Newcastle researchers project, recently awarded a $9 million grant, inspired by nature, namely the sequestration of CO2 as rocks of neutral carbonate in the Earth itself.

Using CO2 to construct the buildings of the future

Reacting gaseous CO2 with low grade minerals such as magnesium and calcium silicate produces limestone. The scientists’ idea is to exploit the process by combining their captured carbon with cheap minerals and voila! You’ve got some limestone-like material right at your disposal that you can fashion into bricks for construction purposes. You could use it for anything from buildings to paving. Limestone’s pretty resilient and strong, too. Actually, it has been used in everything from the Egyptian Pyramids to the British Parliament buildings.

A multidisciplinary research team, including Professors Bodgan Dlugogorski and Eric Kennedy from the University’s Priority Research Centre for Energy and Orica Senior Research Associate Dr Geoff Brent, have demonstrated the technology in small scale laboratory settings and led the funding bids.

“The key difference between geosequestration and ocean storage and our mineral carbonation model is we permanently transform CO2 into a usable product, not simply store it underground,” Professor Dlugogorski said.

Brilliant, but how come anyone didn’t think of this before? They have, but the problem has always been that the process is highly energy intensive. This means its expensive since you need to produce a lot of energy to funnel the process, then producing this energy typically implies burning fossil fuels, which releases carbon. You can understand how unreasonable the idea becomes. The breakthrough though is that the Newcastle researchers have devised a way of dramatically lowering the energy threshold. This same year, Newcastle  made the production of calcium carbonates “a thousand times cheaper” through the use of nickel nanoparticles. A similar process is employed for the “carbon limestone”.

“The Earth’s natural mineral carbonation system is very slow,” Professor Kennedy said. “Our challenge is to speed up that process to prevent CO2 emissions accumulating in the air in a cost-effective way.”

It might take a while before this process might catch on, however. For now, Newcastle plans on using its grant to built a mineral carbonation research pilot plant, expected to open in 2017. There the researchers can extend the findings in the lab to an environment similar to that found in the industry. If they can manage to produce mineral carbonation at a price that’s under current construction materials then they’ve hit the jackpot!

[READ ON] Carbon negative: removing CO2 altogether from the atmosphere 

chemical-bond

New anti-fragile plastic becomes stronger every time it’s stressed

Say hello to drop-proof smartphones and whole new generation of plastic products that will be far more durable and strong than their present counterparts. Scientists at Duke University recently unveiled their most recent, stunning work: a new type of polymer that seems to contradict common knowledge and re-arranges its chemical structure each time its under stress, say a mechanical shock. The test of time is in the plastic’s favor as every time the material suffers a mechanical deformation, it becomes stronger.

Plastics are the most widely used class of materials, and there’s no secret why: they’re durable, light, easy to manufacture and they last a long time (they’re lengthy half-life is also an environmental hazard, however) . Their hardness comes in various degrees, however, but what’s certain is that most of us have come to know that plastics aren’t the strongest materials. Bashed house appliances and just about any dropped plastic-based item serve as testament to this claim.

The Duke-made plastic is different. Like most plastics, the polymer is mostly made of carbon. The key difference is that these carbon atoms are arranged in a series of triangles extending down in long chains with two bromine atoms at one point. It’s this unique structure that allows the novel plastic to exhibit its unique, counter-intuitive properties.

chemical-bond

When the plastic is tugged or comes under shock, the polymer chains tear on one side, as opposed to typical plastic polymers who do not experience the same uniform deformation leading to structural failure (breaks, cracks). The shearing force breaks the triangle into a longer chain, which also frees up bonding sites at the bromine locations for a second molecule to come in. That second molecule is a carboxylate that cross-links multiple chains and increases the material’s strength at the site of damage. This happens every time the material comes under deformation.

The material was put to the test on a larger scale after the polymer was introduced into an extruder, which forced the plastic into a mold. Before being placed intro the extruder the material was pliable, but after being molded its hardness increased significantly to the point it become very stiff. Microscopic analysis subsequently showed an increased in hardness 200-fold after the extrusion process.

It’s unclear when the polymer might be introduced in commercial applications, still the prospects are amazing.

Findings appeared in Nature. [via ExtremeTech]

 

Graphene is a perfect 2D crystal of covalently bonded carbon atoms and forms the basis of all graphitic structures. (c) Photo: Costas Galiotis FORTH/ ICE-HT and Dept. Materials Science, University of Patras

Breakthrough could usher away silicon and make way for graphene transistors

Graphene is a perfect 2D crystal of covalently bonded carbon atoms and forms the basis of all graphitic structures. (c) Photo: Costas Galiotis FORTH/ ICE-HT and Dept. Materials Science, University of Patras

Graphene is a perfect 2D crystal of covalently bonded carbon atoms and forms the basis of all graphitic structures. (c) Photo: Costas Galiotis
FORTH/ ICE-HT and Dept. Materials Science, University of Patras

Time and time again we’ve hailed on ZME Science the cultural and scientific advances graphene is about to bring to humanity. It’s the strongest material known so far, while also being the lightest, it can be magnetic and – something of uttermost important to science – it’s the best electrical conductor that we know of.  The latter also comes with a curse; one that electrical engineers have been trying to dispel for years, only to go through arduous sleepless nights. Building working graphene transistors is imperious for technology’s grand design of the future, but the thing with a graphene transistors is that you can’t turn it off. Now, if you know your basic electrical engineering you know that this means graphene’s  useless in this case, despite the numerous and tremendous benefits it could provide.

Yup, it’s that conductive! Scientists at University of Riverside, California (UCR) , however, may have finally developed a work-around after they published a paper in which they demonstrate a graphene transistor circuit that can switch on and off by exploiting a counter-intuitive effect called negative resistance – we’ll get to that in a minute.

 “The obtained results present a conceptual change in graphene research and indicate an alternative route for graphene’s applications in information processing,” the led by Guanxiong Liu  write.

The de facto industry standard for building just about any electronics today is silicon. Now, as faithful and reliable silicon has proven to be along the decades, it’s soon becoming obsolete. Miniaturization has come a long way, but there’s only so much you can squeeze over such a limited surface. Most industry pundits think that the downscaling of silicon chip technology cannot extend much beyond 2026.

Graphene: the transistor

Technically, from there on graphene research should become reliable enough to enter mass manufacturing and replace silicon in the industry. When transistors are concerned, however, graphene has one major flaw – it doesn’t have a bandgap. There’s no energy range in this material where electron states can’t exist or for a transistor to practically function it needs to switch current.

To make this work, you’d need to hoax graphene into working like a semiconductor – electrons cannot flow at low energy and so the material behaves as an insulator. With this in mind, several attempts have been made of creating an artificial graphene band gap using methods such as applying electric fields, doping with atoms or by stretching and squeezing the material. These techniques, however, proved to render only modest results. Practical digital circuits require a band gap on the order of 1 eV at room temperature, but he best efforts with graphene have produced a  few hundred meV at best.

Liu and colleagues however turned to an entirely different approach by exploiting what’s referred to as negative resistance, an effect in which a current entering a material causes the voltage across it to drop.  Various groups, including this one at Riverside, have shown that graphene demonstrates negative resistance in certain circumstances.

Sleepless nights into sweet dreams for graphene scientists

If you exploit these voltage drops you can perform logic and enable switching. Liu and co demonstrate the effectiveness of their approach by designing a graphene-based circuit that can match patterns and show that it has several important advantages over silicon-based versions. For starters, logic gates built from these inverted transistors could be much denser, more efficient at some tasks, and operate at terrifying speeds   over 400GHz.

The only issue that remains now is maybe the most challenging: actually building an inverted graphene transistor circuit. For now, the researchers have demonstrated experimentally that negative resistance occurs in graphene, the rest will remain to be determined. Still, their work is extremely promising and shows off an elegant and creative solution to a pestering problem that has been giving engineers headaches for nearly ten years since graphene has become truly hot.

Even so, graphene is great for electronics. Just a while ago, ZME Science wrote how graphene light sensors are 1,000 more sensitive, can reduce CPU temperature by 25% or multiply light.

Findings were reported in a paper published in the journal Mesoscale and Nanoscale Physics.

Molecules of collagen (top) next to molecules of a crystal of hydroxyapatite (bottom). (c) MIT

Atomic structure of bone deciphered for the first time

Bone is a really awesome material, being hard and flexible at the same time. For something so ubiquitous and studied for so long, it might come as a surprise to some of you to hear that the molecular bone structure of bone has alluded scientists for such a long while. This is because, even though the constituent elements that make up bone have been known for a long time, how they line together to form such an intricate structure has been very difficult to identify, until recently after MIT researchers used supercomputers to reveal with almost atomic precision the precise structure of bone. Their work is a significant step forward in material science, marking a milestone. The researchers hope they can synthesize bone fibers soon enough, while furthering their understanding of how some diseases attack bones.

Molecules of collagen (top) next to molecules of a crystal of hydroxyapatite (bottom).  (c) MIT

Molecules of collagen (top) next to molecules of a crystal of hydroxyapatite (bottom). (c) MIT

Rather curiously, bone is made out of two materials:  a soft, flexible biomolecule called collagen and a hard, brittle form of the mineral apatite (hydroxyapatite). Each substance, taken individually, has nothing to do with bone, but when combined in a very complex manner, they form something that is simultaneously hard, tough and slightly flexible.

For years scientists have been studying bone at a molecular level, using tools such as atomic force microscopes to probe the material at an atomic level, however using such methods imaging is only possible in 2-D. Bone, taken as a whole, is an intricate molecular 3-D structure that can not be decoded by looking from a 2-D perspective.

“It’s easy to get images of bone, but it’s hard to see exactly where the minerals are located inside the collagen,” says Shu-Wei Chang, a CEE graduate student who was a co-author of the paper.

Using a supercomputer, engineers from MIT, led by civil engineer and materials scientist Markus Buehler, calculated what fibers of collagen, strengthened with hydroxyapatite crystals, look like. To verify their findings, they made a comparative study with laboratory findings. This whole process required several iterations before they could come to a sound conclusion and took several months to complete, something very important to note since the same process would have taken years and years to complete not too long ago. Thankfully supercomputing has evolved exponentially and MIT were quick to update their stock.

What makes up bones

According to their results, the MIT researchers found that the key to the bone’s fantastic molecular structure lies in how the hydroxyapatite crystals align with collagen. Hydroxyapatite grains are tiny, thin platelets just a few nanometers (billionths of a meter) across, and are deeply embedded in the collagen matrix. The two constituents are bound together by electrostatic interactions, which allows them to slip somewhat against each other without breaking. Large pieces of hydroxyapatite are brittle, like chalk, but at such small sizes, the mineral is actually ductile. The researchers also found that under stress tests, the mineral parts of the fibers took on four times as much stress as the collagen portions, whereas bending happened almost exclusively in the collagen.

“In this arrangement of tiny hydroxyapatite grains embedded in the collagen matrix, the two materials can each contribute the best of their properties,” Buehler says. “Hydroxyapatite takes most of the forces in the material, whereas collagen takes most of the stretching.”

Buehler and his team hope they can next create bone fibers in the lab. Also, now with a better understanding of what makes up bone and how its constituent elements are arranged, doctors may find what goes wrong in certain diseases, including osteoporosis and brittle bone disease.

“We can use this model to understand how a bone becomes more brittle,” says Arun Nair, a CEE postdoc who was the first author of the paper. For example, collagen is made up of thousands of amino acids, but “if only one of those amino acids is altered, it changes the way the minerals form” inside the bone, Nair says.

“That’s why this model is so critical,” he adds. Without it, you could observe how bone changes as a result of disease, but “you don’t know why. Now, we can see how a very tiny change … changes the way the mineral grows, or how the forces and deformation are distributed.”

The findings were reported in the journal Nature Communications.

Kawazulite conducts electricity at its surface but not in its bulk. (c) AM. CHEM. SOC.

Topological insulator super-material found in nature too

Researchers have demonstrated for the first time the existence of a naturally occurring topological insulator – an exotic class of materials that possesses the unique ability to conduct electricity and the surface, but not on the inside. Previously, topological insulators have been studied and created in labs only, however now a mineral has been found that acts as one. Moreover, this natural topological insulator is a lot better than synthesized ones since it lacks structural defects typically associated with synthetic materials.

Kawazulite conducts electricity at its surface but not in its bulk. (c) AM. CHEM. SOC.

Kawazulite conducts electricity at its surface but not in its bulk. (c) AM. CHEM. SOC.

Ordinary insulators keep electricity from flowing through out the bulk material since electrons fully occupy energy bands. In topological insulators, however, the spin-orbit interaction is so strong that the insulating energy gap is inverted — the states that should have been at high energy above the gap appear below the gap.  As a result, we have highly conducting metallic states on the surface, while the inside is completely insulated.

First predicted in 2005, scientists have since then rapidly enhanced their understanding and first synthesized a topological insulator in 2008. Just a few weeks ago, researchers demonstrated the first organic topological insulator. What makes this class of materials so exciting is its ability to boost applications of spintronics devices that work with electron spin, rather than voltage. Quantum computers that encode information in electron spin would be primarily first to benefit from the advent of topological insulators.

Pascal Gehring, a solid-state physicist at the Max Planck Institute for Solid State Research in Stuttgart, Germany along with colleagues collected samples of a peculiar mineral called  kawazulite from a gold mine in the Czech Republic. Made out of bismuth, tellurium, selenium and sulphur, the analyzed 0.7 millimetres wide crystalline sheet had electron energy and momentum distribution that matched predictions for a topological insulator.

The analysis was made using photoelectron spectroscopy, which involves measuring the properties of electrons dislodged from a material when ultraviolet light is fired at its surface. Curiously enough kawazulite was synthesized in the past, however its properties are no near as reliable as the natural occurring one, since topological insulators built in the lab always have structural defects that create unwanted conduction in the bulk.

“Surprisingly, the team’s natural sample is cleaner than synthesized samples — even though you would expect it to be more dirty,” says Feng Liu, a materials scientist at the University of Utah in Salt Lake City,. “It may turn out to be cheaper to use a natural supply of topological insulators than it is to make, process and clean them in the lab.”

The findings were reported in the journal Nature Letters.

graphene

Graphene can multiply light, demonstrating new immense energy potential

We’ve never shun away from praising the almost miraculous properties of graphene, the wonder material set to become even more paradigm shifting than plastic. Graphene has found been found to have the potential to revolutionize a myriad of scientific fields, from genetics, to electronics, to nanotech, to security, to just about anything you could think of. The energy sector, however, might be one of the most gifted out of all by graphene’s Midas touch.

grapheneRecent findings by researchers at the Institute of Photonic Science (ICFO), in collaboration with other scientists from Universities in Germany, USA and Spain, have found that graphene is capable of converting a single photon that it absorbs into multiple electrons that could drive electric current. The implications of these findings are enormous, as it would make graphene as the most viable solution for light detection and harvesting applications.

Let’s talk a bit about solar cells, since these are the first to come to mind for most of us. It’s rather unfortunate that solar cells today are so inefficient, where typically the materials employed in their fabrication convert one electron for every absorbed photon. Now with graphene, however, multiple excited electrons can be produced from one single photon, which translates in a significant electrical signal amplification. Solar cells made out of graphene would thus be able to harvest light energy from the full solar spectrum with lower loss.

To reach their conclusions, the researchers devised an experiment in which a known number of photons were emitted with different energies or colors onto a monolayer of graphene.

“We have seen that high energy photons (e.g. violet) are converted into a larger number of excited electrons than low energy photons (e.g. infrared). The observed relation between the photon energy and the number of generated excited electrons shows that graphene converts light into electricity with very high efficiency. Even though it was already speculated that graphene holds potential for light-to-electricity conversion, it now turns out that it is even more suitable than expected!” explains Tielrooij, researcher at ICFO.

There are some issues to tackle before this particular application of graphene can be made truly viable. Scientists have found that graphene has a rather low absorption, which keeps it from being useful for end-user commercial applications – for now, that is. Expect semiconductor technology to be taken afoot by graphene in merely a decade from now. Numerous governments and universities think so, as well, which is why most recently the European Commission awarded  two billion euros ($2.68 billion) in funding – the largest research grant in official, recorded history – for the reserach into the new wondermaterial graphene and the neurochemistry of the human brain.

“It was known that graphene is able to absorb a very large spectrum of light colors. However now we know that once the material has absorbed light, the energy conversion efficiency is very high. Our next challenge will be to find ways of extracting the electrical current and enhance the absorption of graphene. Then we will be able to design graphene devices that detect light more efficiently and could potentially even lead to more efficient solar cells.” concludes Frank Koppens, group leader at ICFO.

Findings were reported in the journal Nature Physics. Image source: New Scientist

Rapid actuation of a soft robot (composed of silicone elastomers) was achieved using high-temperature chemical reactions. (c) Nature

Silicon robot hops 30 times its own height using combustion

Researchers at Harvard University in Cambridge, Massachusetts, have developed a three-legged silicon robot that uses chemical reactions to help it leap up to 30 times its own height. Combustion is typically used in hard systems like internal combustion engines where the heat generated by the chemical reaction can be withstood, but this latest demo proves that the material can withstand high working temperatures as well.

Rapid actuation of a soft robot (composed of silicone elastomers) was achieved using high-temperature chemical reactions. (c) Nature

Rapid actuation of a soft robot (composed of silicone elastomers) was achieved using high-temperature chemical reactions. (c) Nature

The key to the robots leaping ability lies in a smart soft valve, positioned at the end of a channel present in each of the three legs. This smart valve allows just the right mix of oxygen and methane to mix – one part methane to two parts oxygen. Then, the same computer that regulates how much gas is let in the channels  controls a high-voltage cable connected to electrodes in each leg. When it deems fit, the electrodes spark which causes the gas mixture to react in combustion, forming CO2 and water, while also releasing a lot of energy.

This energy kick is what allows the silicon robot to hop up to 30 times its own height, but this would have never been possible without destroying the robot were it not, yet again, for the tiny valve.  It closes in response to high pressure, thus making the pressure even higher, and then it opens after the explosion to let the exhaust gases out.


Up until now a similar effect was replicated using compressed air only, as it was thought that the high heat associated with combustion would simply fry it. The Sand Flea, another leaping robot we reported earlier on, uses compressed air to fling itself pass obstacles as high as 10 meters high. Using a smart valve system and a cleverly balanced chemical reaction, the researchers proved that combustion can be made in other soft system as well.

As for some genuine applications for this silicon leaping robot, the researchers envision their device could be used for search-and-rescue operations, leaping and cartwheeling its way over any obstacles that might block its path.

The robot was documented in a paper published in the journal Nature.

The omniphobic material's geometry and close-up structure. (c) Anish Tuteja / University of Michigan

Superomniphobic material can avoid any stain – repels almost any liquid

Scientists have developed a new surface, which they call  “superomniphobic”, that can repel virtually any liquid, even the most troublesome like blood or highly concentrated acids. Their findings brings us a step closer to manufacturing stain-proof, spill-proof clothing, protective garments and other products.

Currently there is a wide range of clothing and garments that are water proof and offer protection against some spills, but even the most expensive and technologically advanced products, be them synthetics to waxed canvas, don’t stand a chance against low-tension liquids like ketchup or oils that soak right up into the fabric.

Superomniphobic surface

Acetic acid and hexylamine droplets bounce off the superomniphobic material.(c) Anish Tuteja / University of Michigan

In a breakthrough, researchers at Scientists at the University of Michigan have developed a superomniphobic surface  that displays extreme repellency to two families of liquids—Newtonian and non-Newtonian liquids.  Newtonian liquids are most common (water) and are basically liquids whose viscosity remains constant no matter the stress they’re subjected too. While surfaces that repel non-Newtonian fluids have been typically the object of research for most scientists, the Michigan scientists decided to tackle non-Newtonian liquids as well, which include blood, yogurt, gravy, various polymer solutions and a range of other liquids.

“Normally when people talk about superhydrophobic or superomniphobic surfaces, they talk about wetting, which is a measure of the shape that droplets make on the surface and their contact angles,’ says Sergiy Minko, who researches smart polymer materials at Clarkson University in Potsdam, US.

The omniphobic material's geometry and close-up structure. (c) Anish Tuteja / University of Michigan

The omniphobic material’s geometry and close-up structure. (c) Anish Tuteja / University of Michigan

Anish Tuteja and colleagues have developed a surface that repels both Newtonian liquids and oily ones – virtually all liquids easily roll off and bounce on the new surfaces, which makes them ideal for protecting other materials from the effects of chemicals. This was achieved by carefully building the surface such that it has a very low wetting hysteresis – contact angles  of the droplet is the same in both front and rear. This causes the droplet to roll over the surface  without leaking through the surface.

The material is based on a fine stainless steel wire mesh. This is coated with a layer of polymer beads, made from a mixture of polydimethylsiloxane (PDMS) and fluorodecyl polyhedral oligomeric silsesquioxane (POSS). Possible applications for this novel superomniphic surface include  stain-free clothing; spill-resistant, breathable protective wear; surfaces that shrug off microbes like bacteria; and corrosion-resistant coatings.




Findings were reported in the Journal of the American Chemical Society.

via Chemistry World

[Via wiki http://en.wikipedia.org/wiki/Mandelbrot_set ]

3D-Printed Fractal structures are ultralight and extrastrong

 

[Via wiki http://en.wikipedia.org/wiki/Mandelbrot_set ]

The pattern seen above is part of the fractal that prof. Benoit Mandelbrot described. He discovered it by exploring the apparent dull 2D space of what are called the imaginary or complex numbers – a relatively simple construct that has been known to mathematics since the 17th century. [Via wiki]

Remember fractals? Those incredible structures that arise from the apparent random variability of both the mathematical and the real universe. A few years after prof. Mandelbrot published his work on what he defined as fractals, swarms of ideas exploded in the minds of scientist: they turned out to be an astonishing revelation in understanding the structure of the universe – from the cosmological scale down to the patterns of biological organisms. The technology applications soon followed. To name a few famous examples: the image and sound compression algorithms that we nowadays use more than we can imagine to applications like fractal antennas used in mobile phones today are just two of the many places where fractals are embedded in our modern world.

Yong Mao, a lecturer at the University of Nottingham, UK and his colleagues have developed new kinds of load bearing structures that use fractal patterns. The advantage of such structures is that they turn out to be both very strong and very light.

 

Above is an example of such a fractal structure (a second generation type) that was created using a 3D printer. Due to manufacturing limitations, the beams recreated here are solid, not hollow. [Via physicsworld.com http://physicsworld.com/cws/article/news/2012/nov/27/ultralight-fractal-structures-could-bear-heavy-loads]

Above is an example of such a fractal structure (a second generation type) that was created using a 3D printer. Due to manufacturing limitations, the beams used here are solid, not hollow. [Via physicsworld.com]

They begin constructing such a structure by building what they call the “generation-0” element – a hollow beam with the right radii and thickness parameters that are optimised for an optimum ratio of strength versus amount of material used. They test this beam by applying loads along two of its axis to see where failures develop and then they optimise the the fractal structure that will sustain these loads accordingly.

Similar to the way a fractal is generated, in the next step, this first segment is replaced by multiple beams according to a specific fractal rule, thus creating a “generation-1” structure. For the “generation-2” element, a further iteration is implemented, by repeating the fractal rule: each individual segment of the first generation is replaced by a smaller scale replica of the generation-1 model. As you can observe in the image below, this is what scientists refer to when speaking about the self-similar nature of fractals.

The iterations can be repeated further as long as the manufacturing limitations permit such a thing – the advantage being, the calculations show, that with each generation, less material is needed to support a given load.

[Via physicsworld.com http://physicsworld.com/cws/article/news/2012/nov/27/ultralight-fractal-structures-could-bear-heavy-loads]

On the left side is an example of a “generation-1” element – the fractal rule, and on the right, after a further iteration, the “generation-2” type structure. [Via physicsworld.com]

Trying to quantify the advantages of this type of structures, the team calculated that if they were to replace for example a beam made from solid steel from a crane boom with a generation-1 model, the fractal pattern would turn out to be 100 times lighter than the initial simple beam. The amazing thing is that with each further generation, such a fractal design gains another two orders of magnitude in the strength versus mass ratio, making the range of possibilities really interesting.

Then, you might ask yourself – if these structures are so efficient, why haven’t we seen more of its applications in the world around ? Well..it’s because the resources used in manufacturing such intricate patterns outweigh the potential benefits..at least that was the case until high quality 3D printing came along. And because 3D printing is just beginning to improve itself, we might find very soon that printing such strong and lightweight objects would turn out to be quite useful and efficient. As Yong Mao puts it, “we could just upload our different designs to a program and people could download and print off the structures at home.”

 

 

A Giant Blue Morpho butterfly.

Butterfly wings inspire high-tech self-cleaning surfaces

Common to Central and South America, the Blue Morpho is an iconic butterfly, prized for its brilliant blue color and iridescence. Beyond its beauty, however, scientists have discovered that its wings have a certain microscopic texture that could benefit a wide range of applications from self-cleaning instruments, to more efficient piping.

For example, the researchers were able to clean up to 85 percent of dust off a coated plastic surface that mimicked the texture of a butterfly wing, compared to only 70 percent off a flat surface. The Blue Morpho is a highly fragile, light weight insect, so even a few specs of dust or drops of moisture can overburden it and cause a huge energy consumption. Upon inspection by electron microscope, the scientists found that the butterfly’s wings are far from being smooth like they might seem with the naked eye; instead, the surface texture resembles a clapboard roof with rows of overlapping shingles radiating out from the butterfly’s body, suggesting that water and dirt roll off the wings “like water off a roof,” the authors say.  Check out these electron microscope images zoom by zoom.

A Giant Blue Morpho butterfly.

A Giant Blue Morpho butterfly. (c) Ohio State University

Zooming in, texture becomes visible on the wing.

Zooming in, texture becomes visible on the wing. (c) Ohio State University

Wing texture in more detail.

Wing texture in more detail. (c) Ohio State University

Electron microscope image reveals the texture on the micrometer scale.

Electron microscope image reveals the texture on the micrometer scale. (c) Ohio State University

Closeup of micrometer-length 'shingles.' (c) Ohio State University

Closeup of micrometer-length ‘shingles.’ (c) Ohio State University

Nanometer-scale grooves on the surface of the shingles.

Nanometer-scale grooves on the surface of the shingles. (c) Ohio State University

 

“Nature has evolved many surfaces that are self-cleaning or reduce drag,” said Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor ofmechanical engineering at Ohio State. “Reduced drag is desirable for industry, whether you’re trying to move a few drops of blood through a nano-channel or millions of gallons of crude oil through a pipeline. And self-cleaning surfaces would be useful for medical equipment – catheters, or anything that might harbor bacteria.”

In addition to the Blue Morpho, the Ohio State researchers also analyzed leaves of the rice plant Oriza sativa, which also exhibits an interesting self-cleaning texture – rows of micrometer- (millionths of a meter) sized grooves, each covered with even smaller, nanometer- (billionths of a meter) sized bumps; this construction directs raindrops to the stem and down to the base of the plant. Plastic replicas of both microscopic textures were cast and compared in their ability to repel dirt and water to replicas of fish scales, shark skin, and plain flat surfaces.

To test the capabilities of these textures, with respect to other known industry useful texture or simple control texture (smooth), the researchers devised plastic pipes the sized of a cocktail straw with the different coated textures and pushed water through them. The resulting water pressure drop in the pipe was an indication of fluid flow.

A thin lining of shark skin texture coated with nanoparticles reduced water pressure drop by 29 percent compared to the non-coated surface. The coated rice leaf came in second, with 26 percent, and the butterfly wing came in third with around 15 percent.

That was the easy part. Next, the scientists simulated applications where environmental contaminants like dirt are present. So, the dusted each of the textures with  silicon carbide powder, an industrial powder that resembles dirt, and tested them out. They held the samples at a 45-degree angle and dripped water over them from a syringe for two minutes, so that about two tablespoons of water washed over them in total and then, using software, they counted the number of silicon carbide particles on each texture before and after washing.

The shark skin came out the cleanest, with 98 percent of the particles washing off during the test. Next came the rice leaf, with 95 percent, and the butterfly wing with about 85 percent washing off. By comparison, only 70 percent washed off of the flat surface.

The authors believe the rice leaf texture might be especially suited to helping fluid move more efficiently through pipes, such as channels in micro-devices or oil pipelines, while  the Blue Morpho’s clapboard roof texture might suit medical equipment, where it could prevent the growth of bacteria.

Findings were published in the journal Soft Matter.

source

A small car is supported on one of its wheels by a thin block of polymer aerogel. Were this have been silica aerogel, it would have surely crumbled within moments. (c) NASA

New polymer aerogels might become the wonder insulating material

Since they were first invented in 1931, aerogels have become widely used in the industry, mostly for insulation purposes, thanks to their low thermal conductivity and light weight. Traditional silica aerogels, however, are brittle and obtuse, typically unsuited for applications where flexing of the material would occur. A novel class of polymer aerogels seeks to fix most of these inconveniences, after scientists at NASA have shown that the polymer version is up to 500 times stronger and has a thermal resistance up to 10 times higher than typical silica aerosols. If proven commercially cost effective in the future, a whole super-insulation revamp might commence – from refrigeration, to clothing, to heating systems and so on.

Aerogels are basically gels where the liquid component has been replaced by a gas, through the process of supercritical drying. The resulting gel, an aerogel, has a low heat transfer and low density, since it retains its pre-treatment volume even after the water has been replaced. This makes them ideal for insulating applications, but they’ve also been used from particle physics to biomedical fields.

Their only draw back is that they’re extremely brittle, and crumble easily. Until now that is, since researchers at  NASA’s Glenn Research Center in Ohio managed to create a full polymer aerogel which is just as potent as its silica counterpart, but only much more stronger. Best of all, it can be produced into thin stripes which don’t break down, allowing for insulation of sensitive parts.

“The new aerogels are up to 500 times stronger than their silica counterparts,” says Meador. “A thick piece actually can support the weight of a car. And they can be produced in a thin form, a film so flexible that a wide variety of commercial and industrial uses are possible.”

A small car is supported on one of its wheels by a thin block of polymer aerogel. Were this have been silica aerogel, it would have surely crumbled within moments. (c) NASA

A small car is supported on one of its wheels by a rather thick block of polymer aerogel. Were this have been silica aerogel, it would have surely crumbled within moments. (c) NASA

The scientists worked up from previous attempts which coated silica aerogels with polymers by chemical vapor deposition. However, most of the polymers that could be deposited in this manner have rather low melting temperatures, unfit for most applications. So the scientists took a more direct route – they formed polymer aerogels directly, without any coating. The resulting material has a resistance to temperatures of 400 Celsius degrees and higher.

The new class of aerogel however couldn’t be manufactured by conventional methods used thus far. The team of researchers tried a cross-linking approach, where linear polyamides were reacted with a bridging compound to form a three-dimensional covalent polymer. The resulting density of the polymer aerogel was 0.14 g/cc, with 90% porosity. Silica gels were made with much better specs, but the polymer more than makes up for scale in strength.

Silica aerogels have been shown to of a similar density have a resistance to comperession and tensile limit more than 100 times smaller than the new polymer aerogels.

Nanocellular structure of the aerogel shows pores averaging about ten nanometers in size. A quarter-inch (6 mm) sheet of this aerogel would provide as much insulation as three inches of fiberglass. (c) NASA Glenn

Nanocellular structure of the aerogel shows pores averaging about ten nanometers in size. A quarter-inch (6 mm) sheet of this aerogel would provide as much insulation as three inches of fiberglass. (c) NASA Glenn

Polymer aerogels show a resistance to compression and tensile stress more than 100 times higher than silica aerogels. Mechanically, the new class is very similar to synthetic rubber, but at a mere 10% of its weight. One can imagine the virtually broad range of applications this new material could have impact upon. Imagine super-insulated clothing at the fraction of the weight currently employed, higher efficiency for thermal based systems, and so on. The only problem that remains to be settled is cost, and if not now, in the near future expect this kind of technology to become commercially viable.

source: NASA report via Gizmag

 

 

(c) University of Manchester

Graphene layered in 3D crystal structure might allow for electronics revolution

Graphene is an atomic-scale honeycomb lattice made of carbon atoms.

Graphene is an atomic-scale honeycomb lattice made of carbon atoms.

It seems scientists have yet to draw the line on where graphene, man’s greatest material ever discovered, ceases to amazes with its new abilities, since apparently new properties and uses for the carbon allotrope are found constantly. Most of the contributions come from University of Manchester, where the material has been recognized for its true history-shaping potential and where a state-of-the-art National Graphene Institute is currently being built. The latest discovery, indeed, hails from the same Manchester University where scientists were baffled themselves to find that graphene, a 2D structured material, can be used as basic building block for creating 3D crystal structures which are not confined by what nature can produce. The potential impact this could have on the electronics industry development is significant, by increasing efficiency.

This method may well open up a new aspect of physics research. The research shows that a new side-view imaging technique is able to be used to visualize the individual atomic layers of graphene inside the devices they have built. They discovered that the structures were nearly perfect, even when in excess of 10 different layers were used to build the stack, resulting in multilayer heterostructures and devices with designed electronic properties.

(c) University of Manchester

(c) University of Manchester

The side view imaging approach works by extracting a thin slice from the centre of the device. The researchers used a beam of ions to cut into the surface of the graphene and dig a trench on either side of the section they wanted to isolate.

“The difference is that our slices are only around 100 atoms thick and this allows us to visualise the individual atomic layers of graphene in projection,” commented Dr Sarah Haigh at the University of Manchester’s school of materials. “We have found that the observed roughness of the graphene is correlated with their conductivity.”

This result indicates that the latest techniques of isolating graphene could be a big step forward for engineering at the atomic level as well as giving more weight to graphene’s suitability for next gen computer chips.

The scientists’ results suggest a leap forward for atomic-level engineering, and add more weight to the possibilitiy of seeing graphene as a sustainable solution for next-generation’s computer chips. Here’s how I described in short graphene’s properties a while back, when we found out that graphene can actually repair its structure automatically simply by substituting carbon atoms from its environment.

“It’s so thin, it can be molded into sheets just 1 atom thick, yet despite this, it’s so strong that you can actually pick it up. It has the highest current density (a million times that of copper) at room temperature, the highest intrinsic mobility (100 times more than in silicon), and conducts electricity in the limit of no electrons. Also, graphene now holds the record for conducting heat — it’s better than any other known material. But wait, there’s more – graphene is the most impermeable material ever discovered – so neatly packed together, that not even helium atoms can squeeze through.”

Yes, we’re pretty excited about graphene. If you understand what graphene can do for technology and human kind in the following decades, you’d be as well.  Demonstrating graphene’s remarkable properties won Professor Andre Geim and Professor Kostya Novoselov the Nobel prize for Physics in 2010.

Professor Novoselov said: “Although the exciting physics which we have found in this particular experiment may have an immediate implementation in practical electronic devices, the further understanding of the electronic properties of this material will bring us a step closer to the development of graphene electronics.”

Professor Geim added: “The progress have been possible due to quantum leap in improvement of the sample quality which could be produced at The University of Manchester.”

Findings were published in the journal Nature.

Graphene, probably the most fascinating material discovered thus far, is capable of self-repair, as carbon atoms naturally attach themselves to free spots in the lattice, new study finds.

Graphene sheets can repair themselves naturally

Graphene is one of the most phenomenal materials discovered in science. It’s so thin, it can be molded into sheets just 1 atom thick, yet despite this, it’s so strong that you can actually pick it up. It has the highest current density (a million times that of copper) at room temperature, the highest intrinsic mobility (100 times more than in silicon), and conducts electricity in the limit of no electrons. Also, graphene now holds the record for conducting heat — it’s better than any other known material. But wait, there’s more – graphene is the most impermeable material ever discovered – so neatly packed together, that not even helium atoms can squeeze through.

Graphene, probably the most fascinating material discovered thus far, is capable of self-repair, as carbon atoms naturally attach themselves to free spots in the lattice, new study finds.

Graphene, probably the most fascinating material discovered thus far, is capable of self-repair, as carbon atoms naturally attach themselves to free spots in the lattice, new study finds.

Are you impressed yet? Well, add self-repair to the list. Yes, a team of researchers at University of Manchester, UK, including Konstantin Novoselov the co-discoverer of graphene and Nobel Prize laureate, have found that this amazing material can actually perfectly fill gaps within its sheets simply by bombarding it with pure carbon. I think I’m in love!

The researchers initially set out to study the effects of adding metal contacts to strips of graphene, the only way to exploit its phenomenal electronic properties. This typically leads to forming holes in the graphene sheet, a curious fact which scientists set out to study more in depth. After firing electron beams through graphene sheets and studying the damage with an electron microscope, the researchers were surprised to find that the carbon atoms in the metal molecules snapped to the graphene sheet.

When damaged sheets were bombarded with pure carbon atoms, not only did the carbon wash away any metal molecules from the surface of the graphene, but they also perfectly aligned in the gaps, forming an uninterrupted lattice of hexagons – the shape of graphene.

“If you can drill a hole and control that ‘carbon reservoir’, and let them in in small amounts, you could think about tailoring edges of graphene or repairing holes that have been created inadvertently,” Dr Ramasse said.

“We know how to connect small strips of graphene, to drill it, to tailor it, to sculpt it, and it now seems we might be able to grow it back in a reasonably controlled way.”

The findings were reported in the journal Mesoscale and Nanoscale Physics.

No, this is not a DJ spinning your favorite groove, although there's a laser show. The photo depicts Brown University physicist Cuong Dang directing a green laser onto a film of colloidal quantum dots, which reemit RGB light. All using a single laser.

First single RGB laser devised using quantum dots

No, this is not a DJ spinning your favorite groove, although there's a laser show. The photo depicts Brown University physicist Cuong Dang directing a green laser onto a film of colloidal quantum dots, which reemit RGB light. All using a single laser.

No, this is not a DJ spinning your favorite groove, although there's a laser show. The photo depicts Brown University physicist Cuong Dang directing a green laser onto a film of colloidal quantum dots, which reemit RGB light. All using a single laser.

Most digital devices today, like displays or blue-ray disks, use lasers which emit the colors red, green and blue, which when combined can render any color in the visible spectrum of light. However, current technology requires a separate laser for each color, since they produce monochromatic light. A team of researchers at Brown University has successfully managed to produce a RGB laser which emits visible light of varied colors using a single device, by employing nanoscale single crystals called colloidal  quantum dots.

“Today in order to create a laser display with arbitrary colors, from white to shades of pink or teal, you’d need these three separate material systems to come together in the form of three distinct lasers that in no way shape or form would have anything in common,” said Arto Nurmikko, professor of engineering at Brown University and senior author of a paper describing the innovation in the journal Nature Nanotechnology. “Now enter a class of materials called semiconductor quantum dots.”

Colloidal quantum dots (CQDs) produce light by quantum excitation, which allow for precise control and whose size determine the emitted color. By overlaying many thin quantum dots films of variable size, the researchers researchers observed broad-spectrum emission.

The idea of leveraging the properties of the thin film isn’t new, but past attempts to use CQDs in semiconductor lasers have failed because the necessary energy tends to wind up as heat instead of light. The Brown University researchers chose to use a different semi-conducting alloy, made of of zinc, cadmium, sulfur and proprietary organic molecular glue. The latter element is highly important because it reduces an excited electronic state requirement for lasing and protects the nanocrystals from a kind of crosstalk that makes it hard to produce laser light.

This alloy coating allowed the researchers to build a device which directed the excitations within the material to make light rather than heat the primary output. Thus, the scientists concluded the coated pyramids require 10 times less pulsed energy or 1,000 times less power to produce laser light than previous attempts at the technology.

The team of researchers demonstrated their setup in an experiment which used a monochromatic laser directed onto the thin coated layers. The short laser pulses stimulated the three different CQDs to re-emit light of red, green, and blue wavelengths, after applied filtering.

“We have managed to show that it’s possible to create not only light, but laser light,” Nurmikko said. “In principle, we now have some benefits: using the same chemistry for all colors, producing lasers in a very inexpensive way, relatively speaking, and the ability to apply them to all kinds of surfaces regardless of shape. That makes possible all kinds of device configurations for the future.”

The team’s prototypes are the first lasers of their kind, however the researchers warrant that the solution is far from practical for use in commercial products. The findings, described in a paper published in the journal Nature Nanotechnology, represent a milestone in the march towards a single-material multi-wavelength laser, which might provide important technological advances. Full color holograms? Well just have to wait and see…

source: Ars Technica 

Physics Professor Michael Weinert and engineering graduate student Haihui Pu display the atomic structure on GMO. (Photos by Alan Magayne-Roshak)

Scientists manage to derive semiconductor from graphene – huge implications for electronics industry

Graphene has been countless times hailed as the material at the forefront of the coming technological leaps ahead in the future, thanks to its extraordinary properties and countless applications. Electronics is where graphene shines the most, though, and now scientists at University of Wisconsin-Milwaukee have managed to synthesize a semiconductor variant of graphene which might lead to a whole new generation of faster and more reliable electronics.

Physics Professor Michael Weinert and engineering graduate student Haihui Pu display the atomic structure on GMO. (Photos by Alan Magayne-Roshak)

Physics Professor Michael Weinert and engineering graduate student Haihui Pu display the atomic structure on GMO. (Photos by Alan Magayne-Roshak)

What makes graphene so remarkable is that the one-atom thick layer of carbon has a much better conductivity than copper wires and even gold. Silicon, the material used in 99.99% of today’s working transistors, has nearly reached the limit at which it can be shrinked without drastically loosing its electrical properties. Naturally, the next step for technology is using materials from the graphene family.

The main building block of the future’s electronics might be a variant called  “graphene monoxide (GMO),” which is easier to scale up than graphene, and also exhibits semiconducting properties. Until recently, graphene only presented insulating and conducting properties.

“Now all three characteristics of electrical conductivity – conducting, insulating and semiconducting – are found in the carbon family, offering needed compatibility for use in future electronics,” says the team.

Like all great discoveries, the researchers discovered GMO by accident. The team was studying a hybrid nanomaterial comprising carbon nanotubes with attached tin-oxide nanoparticles for use as a sensor.

The team discovered GMO while researching the behavior of a hybrid nanomaterial comprising carbon nanotubes with attached tin-oxide nanoparticles that was being investigated for use as a sensor. During one experiment when scientists attempted to synthesize graphene from graphene oxide (GO), a multilayer insulator, the researchers found that layers of GO became aligned and formed GMO.

The next step is more science. The team will need to find out what triggered the reorganization of the material, and also what conditions would ruin the GMO’s formation.

“In the reduction process, you expect to lose oxygen,” says Michael Weinert, professor of physics and director of UWM’s Laboratory for Surface Studies. “But we actually gained more oxygen content. So we’re at a point where we’re still learning more about it.”

Some gas giants have metallic hydrogen in their centers, which explains why Jupiter, for instance, has such a powerful magnetic field. (c) Wikimedia

Scientists turn hydrogen into metal

For years and years scientists have tried to make hydrogen exhibit metal properties, by experimentally proving what’s already been more or less acknowledged in theory. Hydrogen is an alkali metal, and under the right circumstances it can be fooled  into becoming a metal. These “right” circumstances have yet to be found, until recently when a pair of scientists from the Max-Planck Institute  in Germany has released a bold claim that they’ve indeed managed to achieve this extraordinary feat.

Some gas giants have metallic hydrogen in their centers, which explains why Jupiter, for instance, has such a powerful magnetic field. (c) Wikimedia

Some gas giants have metallic hydrogen in their centers, which explains why Jupiter, for instance, has such a powerful magnetic field. (c) Wikimedia

When you think of metal, one tends to image some kind of solid, shiny, electropositive material, generally a good conductor of electricity or heat, and of a certain malleability. How can you possibly make hydrogen act like anything stated earlier? Well, scientists have been slaving away trying to find the right pressure and temperature at which hydrogen should exhibit some kind of metallic quality, but so far  Mikhail Erements and Ivan Troyan are the first to have reached them, according to a recently published paper in the journal Nature Materials.

Their procedure was the following: a sample of hydrogen in a alumina-epoxy gasket that they put inside of a diamond anvil cell, which they first compressed at a pressure of 220GPa (incredibly huge!). A highly calibrated laser then tested the material, which helped the researchers observed that the hydrogen sample began to cloud to the point of becoming opaque and that it could conduct electricity. They then increased the pressure to 260GPa, and also lowered the temperature at 30K, roughly -240 °C (the temperature at which most material become superconductors), and observed an electrical resistance increase of 20 percent. This is where they wrapped it up and concluded that in these circumstances hydrogen exhibits metal properties.

This claim hasn’t been left without echoes in the scientific community, however. Peer review will certainly soon enough jump at this and come with their own mind at what constitutes a metal. Then there’s also the issue of other researchers having to replicate Erements and Troyan’s experiment, and only after they also reach the same results, will their claim be considered as fact. What’s important, however, is that the two, peer reviewal and credits aside, have managed to make hydrogen conduct electricity at room temperature. Nevermind turning into a full pledged metal, this is enough to prove that the most aboundant element in the Universe might be the best superconductor scientists have been looking for all this while.

source