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Computer Model Shows Carbyne is the Strongest Known Material

Researchers at Rice University have developed computer models that reveal that the long-theorized material carbyne is the strongest material in the world.

The research, which was published in the journal ACS Nano (“Carbyne from First Principles: Chain of C Atoms, a Nanorod or a Nanorope”), demonstrated that carbyne should have the greatest tensile strength of any other known material, double that of graphene which itself is 200 times stronger than steel.

Boris Yakobson, a theoretical physicist at Rice who led the research, has previously demonstrated through computer modeling important possibilities for the use of carbon materials, like graphene. In the case of this carbyne research, as with his research into graphene, it remains to be seen whether the computer models can be duplicated in the physical world.

As the press release covering the research describes it: “Carbyne is a chain of carbon atoms held together by either double or alternating single and triple atomic bonds.” It has been encountered in highly compressed graphite. While there have been some demonstrations of the material being synthesized at room temperature,  it’s not clear how it could be produced in bulk.

If such a method could be developed, the Rice researchers believe that the material could be useful in a range of applications.

“You could look at it as an ultimately thin graphene ribbon, reduced to just one atom, or an ultimately thin nanotube,” said Yakobson in the press release. “It could be useful for nanomechanical systems, in spintronic devices, as sensors, as strong and light materials for mechanical applications or for energy storage.”

While the mere fact that carbyne is the strongest possible assembly of atoms is exciting to the Rice researchers, it will take a bit more research to exploit that strength. It wasn’t until recently that the strength of graphene could be fully exploited in a composite material.

The next step for the researchers will be to investigate the possibility of one-dimensional chains of atoms for other elements.

Image: Vasilii Artyukhov/Rice University

There Is No Nanotechnology Equivalent to the Digital Divide

A recent article in the venerable Financial Times proposed a sort of nanotechnology equivalent to the oft-mentioned “digital divide (the idea that the benefits of digital technology appear to accrue to the wealthy while the poor are left out). At issue in the article is whether developed economies and poorer nations are separated in their respective access to nanotechnology.

So, is there a nanotech divide?

The answer probably lies somewhere between “yes” and “no,” depending on the metric you use. But I would argue that nanotechnology has been one of the most egalitarian fields in technology history.

First, you can look at where the money goes. On this count, nanotechnology is basically the same as any other emerging technology: the initial targeted applications are those that can sustain the price premium for using a new and expensive technology.

However, nanomaterials can already be found in inexpensive items ranging from odor-resistant socks to plastic beer bottles.  So as the manufacturing technologies have matured and ramped up, we have seen prices fall and the democratization of nano-enabled products spread.

But I've often argued that analyzing nanotech's impact purely on economic terms can be misleading. It is usually a stretch to try to draw parallels between an emerging technology like nanotech and a developed field like information technology. Nanotech is still in its commercial infancy.

Instead, let's focus just on nanotechnology research, which constitutes the bulk of the activity in the field today. With nanotech, we are probably witnessing the most democratic and open-access research ever in a new technology.

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Silicon and Graphene: Two Great Materials That Stay Great Together

The use of graphene as a transparent conducting film has been hotly pursued of late, in large part because it offers a potentially cheaper alternative to indium tin oxide (ITO) where a bottleneck of supply seems to be looming.

It has not been clear whether photovoltaic manufacturers have taken any interest in graphene as an alternative for transparent conducting films. This lack of interest may in part be the result of there being little research into whether graphene maintains its attractive characteristic of high carrier mobility when used in conjunction with silicon.

Now researchers at the Helmholtz Zentrum Berlin (HZB) Institute in Germany have shown that graphene does not lose its impressive conductivity characteristics even when mated with silicon.

"We examined how graphene's conductive properties change if it is incorporated into a stack of layers similar to a silicon based thin film solar cell and were surprised to find that these properties actually change very little," said Marc Gluba of the HZB Institute for Silicon Photovoltaics in a press release.

The research, which was published in the journal Applied Physics Letters (“Embedded graphene for large-area silicon-based devices”), used the method of growing the graphene by chemical vapor deposition on a copper sheet and then transferring it to a glass substrate. This was then covered with a thin film of silicon.

The researchers experimented with two different forms of silicon commonly used in thin-film technologies: amorphous silicon and polycrystalline silicon. In both cases, despite completely different morphology of the silicon, the graphene was still detectable.

"That's something we didn't expect to find, but our results demonstrate that graphene remains graphene even if it is coated with silicon," said Norbert Nickel, another researcher on the project, in a press release.

In their measurements, the researchers determined that the carrier mobility of the graphene layer was roughly 30 times greater than that of conventional zinc oxide-based contact layers.

Although the researchers concede that connecting the graphene-based contact layer to external contacts is difficult, it has garnered the interest of their thin-film technology colleagues. "Our thin film technology colleagues are already pricking up their ears and wanting to incorporate it,” Nickel adds.

Illustration: Marc A. Gluba/HZB

High Quality Graphene Could Soon Be Produced in Bulk

Photo: Graphene Frontiers
A Graphene CVD furnace in operation.

Back in September, the National Science Foundation awarded $744,600 to a University of Pennsylvania graphene start-up called Graphene Frontiers. The money is intended to help the young company ramp up a new manufacturing technique for producing graphene in a roll-to-roll process, which could enable large-scale production of high-quality graphene. The company is attempting to be the first to adapt a chemical vapor deposition (CVD) technique, often used to create polycrystalline single layers of graphene, to a roll-to-roll process.

But not all graphene is created equal. While polycrystalline graphene has found use in applications like advanced composites and RF transistors, it's monocrystalline graphene that has the properties worthy of a “wonder material.” Monocrystalline graphene can still only be produced through what are known as mechanical cleavage techniques, in which the graphene is pulled off in single layer flakes from graphite. (One of these became known as the “Scotch Tape” method). These techniques tend to be unscalable for manufacturing large quantities of the material.

Despite this limitation, there are a host of companies like Graphene Frontiers that are already producing graphene. There are several different manufacturing techniques that are suited for producing varying qualities of graphene.

One method is to start with mined graphite and separate out the carbon layers using plasma, mechanical exfoliation, and chemical techniques. This tends to produce lower quality graphene that could eventually be useful in anti-corrosion paints or battery electrodes.

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Researchers Discover Giant Refractive Index in Graphene Oxide

One of the downsides of optical discs is that they are not particularly durable, leading researchers to look at using quartz glass as a replacement for the typical plastic used. The fact that these discs are fragile has also demanded the rather expensive practice of keeping multiple duplicates at large data centers in order to safeguard against loss of data through breakage.

Now researchers at Swinburne University of Technology in Australia have developed a polymer using graphene oxide that makes it possible to retrieve all the information from the disc even in the case of it breaking.

It should be noted that graphene oxide is different from graphene in a couple of ways. First, the manner in which it is produced is fundamentally different. It is made via a chemical reduction process rather than the mechanical or thermal exfoliation processes used to create single layer graphene. Secondly, it differs significantly in its properties. It lacks graphene's unmatched electron mobility, so it's not the great conductor that graphene is. It does, however, have a property that makes it ideal for optical storage applications: a fundamental fluorescence that is useful for multimode optical recording.

The Swinburne researchers took advantage of that fluorescence, demonstrating that when a laser is focused onto a graphene oxide polymer, the beam increases the material's refractive index by 10 to 100 times. All materials have a refractive index, which is essentially a measurement of the speed of light and how much it bends when it passes through a medium.

“The unique feature of the giant refractive-index modulation together with the fluorescent property of the graphene oxide polymer offers a new mechanism for multimode optical recording," said Professor Min Gu, one of the researchers, in a press release.

In their demonstration, which was published in the journal Scientific Reports (“Giant refractive-index modulation by two-photon reduction of fluorescent graphene oxides for multimode optical recording”), the researchers encoded the image of a kangaroo in a computer-generated hologram. The researchers then rendered the hologram as a three-dimensional recording on the graphene oxide polymer.

One other attribute of the recorded hologram is that it lends itself to secure coding. You can’t actually see the encrypted images of the hologram with a microscope, but they can be seen when the images are diffracted.

"The giant refractive index of this material shows promise for merging data storage with holography for security coding," Professor Gu said in the release. "This exciting feature not only boosts the level of storage security, but also helps to reduce the operation costs of big data centers that rely on multiple physical duplicates to avoid data loss."

The researchers believe that optical data storage is only one application that could be impacted by the technology. They believe it could revolutionize flat screen displays and solar cell technology.

Gu adds: "The giant refractive index we discovered shows the promise of graphene to merge electronics and photonics for the platform of the next generation information technologies."

Image: Swinburne University of Technology

Band-Gap Engineering of Nanowires Could Boost Batteries

The reason for replacing graphite in the electrodes of the ubiquitous lithium-ion (Li-ion) battery is clear to anyone who uses a smartphone: The batteries run out of charge in just a few hours under regular use.

One answer has been to replace the graphite with silicon. Unfortunately, the expanding and contracting that occurred as the lithium ions transported in and out of silicon electrodes quickly cracks it.

The next solution was to create “nanostructured silicon” electrodes, sometimes with the help of graphene or good old carbon nanotubes.

Now researchers at the University of California San Diego (UCSD) have brought a new perspective to the issue. They are  taking a page from band-gap engineering, in which heterostructures are used to create energy barriers between electrons and holes, and applied the concept to creating barriers to the ions as they enter into an electrode so they diffuse in a very specific way.

The research, which was published in the journal Nano Letters (“Tailoring Lithiation Behavior by Interface and Bandgap Engineering at the Nanoscale”), describes a method by which the typical surface diffusion of lithium ions into a nanowire electrode is blocked and instead the ions are diffused layer-by-layer along the length of the nanowire.

As the Nano Letters article notes: “These results demonstrate for the first time that interface and band-gap engineering of electrochemical reactions can be utilized to control the nanoscale ionic transport / insertion paths and thus may be a new tool to define the electrochemical reactions in Li-ion batteries.” 

In the video below you can see the different way this impacts the nanowire. Instead of blowing up around its middle, it gradually grows along its axis as the lithium ions transport into the nanowire. The video also demonstrates some new breakthroughs in nanoscale imaging with transmission electron microscopy. It shows lithium-ion reactions in real time at nanoscale precision.

In the press release about his work, Shadi Dayeh, a professor at UCSD, explains that this control of how the ions diffuse could result in “an effective way to tailor volume expansion of lithium ion battery electrodes, which could potentially minimize their cracking, improve their durability, and perhaps influence how one could think about different electrode architectures.”

The new technology starts with germanium nanowires that are then coated with silicon.The research builds on previous work of Dayeh and his colleagues published in the journal Applied Physics Letters and again in Nano Letters in which they demonstrated control over the heterostructuring of germanium-silicon nanowires.

 According to Dayeh, the new electrodes would allow for battery designs in which the expansion of the electrodes would not cause any shorting between the cathode and the anode.

Images: UC San Diego Electrical and Computer Engineering

Previously Unheralded 2-D Material Exhibits High Charge-Storage Capacity

The landscape for two-dimensional materials has been getting a little crowded lately. We, of course, hear stories every day about graphene, but molybdenum disulfide has been getting a lot of interest and perhaps even edging ahead of graphene in transistor applications. Finally hexagonal boron nitride is gaining attention and rounding out this trilogy of 2-D materials that all promise to displace silicon in future electronics.

But another two-dimensional material has been in our midst for years and has largely gone unnoticed.

Researchers at Drexel University developed the 2-D material three years ago to little fanfare. But now they have discovered that the material has extraordinary energy storage capacity and could power flexible devices.

Michel W. Barsoum and Yury Gogotsi, both professors at Drexel’s college of engineering, dubbed the material an “MXene” because of its origin from the process of etching and exfoliating atomically thin layers of aluminum from layered carbides called “MAX phases.” [The M is for transition metal, the A for "A group" metal, and the X for carbon and/or nitrogen.]

Over the last three years, the engineers have been investigating applications for the materials. The research, which was published in the journal Science (“Cation Intercalation and High Volumetric Capacitance of Two-dimensional Titanium Carbide”), shows that MXenes store ions and molecules between layers of the material in a process known as intercalation.

Intercalation is the inclusion of a molecule between two other molecules. The process is sometimes required in order to give two-dimensional materials their unique properties. In the Drexel research, they were able to place lithium ions between MXene sheets, making the materials good candidates for use in lithium-ion batteries.

“Currently, nine MXenes have been reported by our team, but there are likely many more that will be discovered—the MXene-and-ion combinations that have been tested to date are by no means an exhaustive demonstration of the material’s energy storage capabilities,” said Gogotsi, who is also director of the A.J. Drexel Nanotechnology Institute, in a press release. “So even the impressive capacitances that we are seeing here are probably not the highest possible values to be achieved using MXenes. Intercalation of magnesium and aluminum ions that we observed may also pave the way to development of new kinds of metal ion batteries.”

In addition to lithium, the researchers have been looking at intercalating ions of sodium, magnesium, potassium, ammonium, and aluminum in between the MXene sheets. In each case, the resulting material demonstrated a high capacity for energy storage, they said.

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 F/cm3 due to intercalation of cations between its layers,” Barsoum said. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy”

- See more at: http://www.drexel.edu/now/news-media/releases/archive/2013/September/MXenes-Science/#sthash.PS22z2pL.dpuf

“Two-dimensional, titanium carbide MXene electrodes show excellent volumetric super capacitance of up to 350 [farads per cubic centimeter] due to intercalation of cations between its layers,” Barsoum said in a press release. “This capacity is significantly higher than what is currently possible with porous carbon electrodes. In other words, we can now store more energy in smaller volumes, an important consideration as mobile devices get smaller and require more energy.”

Image: Drexel University

Spray-On Technique Could Bring Carbon Nanotubes to Retailers’ Shelves

Carbon nanotubes appear to be getting back some of their glory—after seemingly being eclipsed by graphene—with the news yesterday that an entire computer could be made from the material.  Now researchers at Technische Universität München (TUM) in Germany are continuing the carbon nanotube comeback with a new, inexpensive process that promises to enable their use in a wide range of applications including electronic skin and sensors integrated into food packaging.

The process, which involves simply spraying the carbon nanotubes onto a flexible, plastic substrate, is described in the journal Carbon (“Fabrication of carbon nanotube thin films on flexible substrates by spray deposition and transfer printing”)

"To us it was important to develop an easily scalable technology platform for manufacturing large-area printed and flexible electronics based on organic semiconductors and nanomaterials," said postdoctoral researcher Alaa Abdellah in a press release. "To that end, spray deposition forms the core of our processing technology."

In the food packaging application, the carbon nanotubes would serve as gas sensors. Nanotubes have long proven themselves to be good sensors. They can be made to bind to certain substances, which changes the electrical properties of the nanotubes in a way that can be measured with a high degree of sensitivity.

In practical applications, the carbon-nanotube-enabled plastic would cover a grocery store product like chicken. If the product contained the chemical indicators of, say, salmonella, the packaging would detect them and alert the consumer.

While this sounds great, the obstacle preventing this from becoming a reality has always been cost. Thin-film sensory packaging may make sense for a high-cost item, but for an inexpensive grocery store product, it’s hard to justify an additional cost that may be as much as the product itself. I made this point nearly a decade ago in report I authored titled, "The Future of Nanotechnology in Printing and Packaging".

This doesn’t even take into account the often biased opinion people have about nanotechnology in relation to food.

For these reasons, I recommend that the researchers focus their attention on high-ticket applications such as electronic skin for robotics and bionics. In those applications, they will likely find greater resistance to the fear mongering practiced by the NGOs. And it just might make more economic sense to adopt their technology for those applications.

Image: Uli Benz/TUM

Plastic OLEDs Just Got a Bump from Silver Nanowires

Polymer-based OLEDs (organic light-emitting devices) have been held out as a kind of Holy Grail in lighting and display applications. Part of their unachievable-quest notoriety stems from the fact that they are expensive in part due to the complex processing involved. Nonetheless, they do possess the magical feature of being flexible.

Researchers at the University of California Los Angeles (UCLA) have developed just such an OLED material that can be twisted and folded and even stretched while remaining lit the entire time and could become the template for all future polymer OLEDs.

"Our new material is the building block for fully stretchable electronics for consumer devices," said Qibing Pei, a UCLA professor of materials science and engineering and principal investigator on the research, in a press release. "Along with the development of stretchable thin-film transistors, we believe that fully stretchable interactive OLED displays that are as thin as wallpaper will be achieved in the near future. And this will give creative electronics designers new dimensions to exploit."

The material, which was described in the journal Nature Photonics ("Elastomeric polymer light-emitting devices and displays"),  owes at least part of its remarkable stretching capabilities to new transparent electrodes the researcher made out of silver nanowires that have been inlaid into the polymer.

Silver nanowires are currently being market by companies like Cambrios Technologies and Blue Nano for use as a replacement to indium tin oxide (ITO) as a transparent conductor to control display pixels.

In this latest application, the UCLA researchers found that when a single layer of an electro-luminescent polymer blend is sandwiched between the silver nanowire electrodes it was possible for the OLED to bend and stretch at room temperature.

As you can see from the video below, the researchers are able to bend and stretch the OLED into every conceivable shape and do it while in normal ambient conditions.

"The lack of suitable elastic transparent electrodes is one of the major obstacles to the fabrication of stretchable display," said Jiajie Liang, a postdoctoral scholar, in a press release. "Our new transparent, elastic composite electrode has high visual transparency, good surface electrical conductivity, high stretchability and high surface smoothness — all features essential to the fabrication of the stretchable OLED."

While the video demonstrates an OLED with just a solid block of light, the researchers have shown that they can create an OLED made up of different pixels, which opens up the possibility of stretch displays as well as new kinds of lighting.

The researchers were able to accomplish this pixel capability by arranging the silver nanowire-based electrodes into a cross-hatched pattern made up of one layer of columns and one layer of rows.

"While we perceive a bright future where information and lighting are provided in various thin, stretchable or conformable form factors, or are invisible when not needed, there are still major technical challenges," Pei conceded in the press release "This includes how to seal these materials that are otherwise sensitive to air. Researchers around the world are racing the clock tackling the obstacles. We are confident that we will get there and introduce a number of cool products along the way."

Graphene Investment Advice Needed, Just Not the Stock Market Variety

With research developments coming daily—if not hourly—in graphene, it really was just a matter of time before investment gurus were going to start giving stock tips. This is not altogether bad. It keeps everything focused on the purpose of pursuing graphene developments to create new and improved products that will enable somebody to make some money.

Unfortunately, the field of nanotechnology has a somewhat checkered past with the stock market and with investment gurus. We’ve been subjected to nanotechnology stock indices that thankfully have (for the most part) withered away. And we’ve seen so-called stock market experts proclaim that a huge company with enormous revenues and cash reserves is the same kind of speculative stock investment as a small start-up. It would seem these “experts” not only don’t know nanotechnology, but also don’t understand simple stock analysis metrics like price-to-earnings ratios.

Now it’s graphene’s turn. There has been a recent flurry of investment reports on graphene, motivating some bloggers to comment on the trend. I was finally nudged into a offering my observations now because of a piece that appeared this week in Forbes (“Graphene Stock Investing: What The Pros Think”) . As these articles go, this is a top-notch effort. But I have to quibble about one point—and it’s a big one—graphene at the moment is not a stock market play.

Here is a list of 39 graphene companies, and I don’t believe that there’s one of them on that list that is at this moment publicly traded. So, after the author asks two investment experts what stocks they would suggest for exploiting all the activity in graphene, we get as a response: Enersys, Tesla Motors, and Johnson Controls without giving any explanation of why these companies constitute  good graphene investments. It’s not even clear how they are involved in graphene.

I suppose in the case of Enersys and Tesla it’s a belief that graphene could enable improved batteries for all-electric vehicles. While I have no idea whether these companies are good stock investments or not, I am pretty certain that their fortunes good or bad are not tied to the fate of graphene one way or the other, especially for a hugely diversified company like Johnson Controls.

I support and would even champion articles that could raise awareness of how crucial it is to invest in companies that are trying to develop products based on graphene. We actually need more of them. Unfortunately, we rarely get those kinds of articles and instead get articles like the one in Forbes that are aimed at those interested to know how they can spend their savings on a “graphene stock market investment,” when, in fact, there is no such thing.

While this is unfortunate, it indicates a perhaps more troubling issue. The kind of early, pre-IPO investment that a company trying to develop products based on graphene needs has become increasingly difficult to source outside of governments as large private capital sources still prefer the fast investment turnarounds offered in complex financial instruments. It’s even got graphene’s co-discoverer, Andre Geim, lamenting society’s current attitude of “throw[ing] a little bit of money at something and expect[ing] it to change the world.

By most estimates products enabled by graphene should really start hitting the market in 2020. With that investment horizon, why are we even talking about the stock market when we should really be discussing how we can support innovation at these early stages. Do that and someday we can actually have publicly traded companies that make products based on graphene.

Image: Erik Vrielink

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
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Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
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