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A Twist and Some Wax Turns Carbon Nanotubes into Super Muscles

Carbon nanotubes have already been demonstrated to be a useful material in the development of artificial muscles. But an international team of researchers led by the University of Texas at Dallas has discovered that if you twist carbon nanotubes into a yarn and infuse them with paraffin wax their capabilities as artificial muscles become staggering.

The researchers claim that the wax-infused muscles can lift 100 000 times their own weight and produce 85 times more mechanical power than natural muscle of equivalent size.

“The artificial muscles that we’ve developed can provide large, ultrafast contractions to lift weights that are 200 times heavier than possible for a natural muscle of the same size,” says Dr. Ray Baughman, team leader, Robert A. Welch Professor of Chemistry and director of the Alan G. MacDiarmid NanoTech Institute at UT Dallas in a press release. “While we are excited about near-term applications possibilities, these artificial muscles are presently unsuitable for directly replacing muscles in the human body.”

You can see Baughman further describe the carbon nanotube-based muscles in the video below:

While Baughman concedes that replacing artificial muscles in humans is out of the application list for this material at the moment, he does believe that it could be used in “robots, catheters for minimally invasive surgery, micromotors, mixers for microfluidic circuits, tunable optical systems, microvalves, positioners, and even toys.”

Baughman further believes that the material can make its way into marketable uses fairly quickly. He notes in the release: “The remarkable performance of our yarn muscle and our present ability to fabricate kilometer-length yarns suggest the feasibility of early commercialization as small actuators comprising centimeter-scale yarn length. The more difficult challenge is in upscaling our single-yarn actuators to large actuators in which hundreds or thousands of individual yarn muscles operate in parallel.”

Whether Baughman can tackle that next challenge remains to be seen, but the research, which was published in the journal Science (“Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles"), is impressive in its elegant simplicity.

The combination of twisting carbon nanotubes into a yarn and infusing them with wax made it possible to simply add a bit of electrical charge to the material to get the wax to expand and then the yarn volume to increase, causing the yarn to shorten. This volume increasing and length decreasing is directly related to the twisting of the carbon nanotube yarn.

In operation, when the wax-filled yarn is heated electrically it untwists, but when the heating is stopped the yarn winds back up. What is remarkable is how fast this twisting and untwisting occurs. The researchers claim that yarn can rotate a paddle that is attached to the yarn at 11 500 revolutions per minute. Perhaps more importantly, it can repeat this cycle more than 2 million times.

Another attractive feature of the material is that fact that it can be treated like a textile. So it could be sewn or woven into clothing to react to outside environmental factors such as heat (a fireman’s coat is given an as an example in the video) and actuate (like a muscle) a change to the textile’s porosity. This change in porosity could provide thermal protection, or chemical protection in the presence of poisonous substances.

Paper and Scissors Key in Latest Development of Nanofluidics

When one recalls that graphene was first produced by placing scotch tape on top of the graphite found in pencils and then pulling the tape off, it may not sound so strange that the next breakthrough in nanofluidic devices may come from using paper and scissors.

Two researchers at Northwestern University have discovered that if you stack up layers of graphene on top of one another it creates a flexible paper-like material that forms tens of thousands of nanoscale channels between the layers.  In keeping with the school supplies theme, the researchers further discovered that they could cut the paper-like material into any shape they wished with a pair of scissors.

“In a way, we were surprised that these nanochannels actually worked, because creating the device was so easy,” said Jiaxing Huang, quoted in a university press release. Huang, a Junior Professor in Materials and Manufacturing, who conducted the research with postdoctoral fellow Kalyan Raidongia, said, “No one had thought about the space between sheet-like materials before. Using the space as a flow channel was a wild idea. We ran our experiment at least 10 times to be sure we were right.”

The material could potentially have applications in batteries, water purification, harvesting energy and DNA sorting. While listing a range of applications for lab technologies is always a fairly easy matter, this material stands out in these application areas because of how cheaply and easily it is produced.

Typically nanofluidic devices require slow and expensive lithography techniques to carve out the channels. But this technique lends itself to the building of massive arrays of nanochannels simply by staking sheets of graphene oxide (GO) on top of one another. To create more nanochannels, simply stack more layers on top of each other.

The research, which was published in the Journal of the American Chemical Society (“Nanofluidic Ion Transport through Reconstructed Layered Materials’), demonstrated a working device using the material by cutting a piece of the GO paper into a centimeter-long rectangle. Huang and Raidongia covered the paper in a polymer. They then drilled either end of the rectangle to fashion holes in which an electrolyte solution was placed.

In tests, the researchers discovered that the rectangle conducted a higher than normal amount of current, whether it was laid out flat or bent.

The next step is to test the nanoscale properties of papier-mâché. Just kidding—but maybe someone should try it.


Hybrid Nanomaterial Converts Both Light and Heat to Electricity

Nanomaterials are becoming an attractive proposition for realizing the hopes of future thermoelectric devices, which would derive power just from differences in temperature. And, of course, the future of photovoltaics is increasingly dependent on developments in nanomaterials.

What nanomaterials haven’t been used for to date is to combine thermoelectrics with photovoltaics. But now in joint research between Louisiana Tech University and the University of Texas at Arlington that combination has been achieved. The joint research team developed a new hybrid nanomaterial that combines single-walled carbon nanotubes (SWNTs) with copper sulfide (CuS) nanoparticles and is capable of converting both light and thermal radiation into electricity.

The research, which was published in the UK’s Institute of Physics’ journal Nanotechnology (“Optical thermal response of single-walled carbon nanotube-copper sulfide nanoparticle hybrid nanomaterials”), builds on previous work that demonstrated that SWNTs are excellent materials for absorbing both light and thermal energy.

Louisiana Tech University assistant professor Long Que along with UT Arlington associate physics professor Wei Chen took that knowledge one step further by combining the SWNTs with CuS nanoparticles and getting an 80 percent increase in light absorption with the hybrid material versus the pure SWNTs.

In devices that the researchers made from the hybrid material, they measured a clear optical and thermal switching effect. The researchers further discovered that this switching effect could be enhanced by a factor of 10 by using asymmetric illumination in which a polydimethylsiloxane (PDMS) slab covers one of the electrodes so the light source illuminates one of the electrode regions and the other is covered. The difference in temperature between the illuminated electrode and the one in the PDMS shadow creates a thermoelectric effect that increases the electricity generated by the light.

The research team were able to use the material to create a thermoelectric generator that they believe will be able to generate milliwatts of power.  If these nanogenerators could be used in chips it could lead to a range of self-powered devices, according to the researchers.

“If we can convert both light and heat to electricity, the potential is huge for energy production,” Chen says in a press release. “By increasing the number of the micro-devices on a chip, this technology might offer a new and efficient platform to complement or even replace current solar cell technology.”

Water-Splitting Catalyst Revealed

If you wanted to do an imitation—at least an accurate one—you would be well served to carefully observe the original. With artificial photosynthesis being hotly pursued by some of the most renowned nanotechnology researchers, a team at Umeå University in Sweden thought an important step for improving artificial photosynthesis would be to peer deeply into real photosynthesis to reveal the factors that make it work.

The Swedish team examined a manganese complex with spectroscopy in conjunction with the Linac Coherent Light Source (LCLS), a free-electron x-ray laser facility at Stanford University. Manganese is a transitional metal that when combined with calcium and oxygen creates the same water-splitting catalyst found in photosynthesis.

While this may sound like an approximation of photosynthesis, the research group had already used LCLS to perform structural analyses of isolated photosynthesis complexes in plants. The new wrinkle this time was to bring spectroscopy into the imaging process.

To accomplish this imaging, the LCLS emits a laser beam with wavelengths that are the breadth of an atom at pulses that last 50 femtoseconds. When the LCLS was combined with the spectrometer, the x-rays emitted from the manganese complex after being hit with the laser pulses are diffracted by the spectrometer and picked up by a detector array.

With this set-up the researchers observed detailed information about the compound’s electronic structure before the laser beam destroyed it.

"Having both structural information and spectroscopic information means that we can much better understand how the structural changes of the whole complex and the chemical changes on the active surface of the catalysts work together to enable the enzymes to perform complex chemical reactions at room temperature,” says Johannes Messinger, professor at the Department of Chemistry at Umeå University, in a university press release.

This detailed imaging of how photosynthesis splits water into its constituent parts has been held out as a way to help engineers more cheaply synthesize hydrogen gas to power hydrogen fuel cells—and possibly the automobiles powered by them. Research efforts to split water molecules into hydrogen gas have been taken on both by commercial entities and the academics. Perhaps this new information on the electronic structure of the water-splitting process of photosynthesis can further inform both these lines of research.

How Far Can IT Take Material Science?

Last year the White House announced an oddly entitled plan called the “Materials Genome Initiative”. The aim of the initiative—and thus the title—was to apply the same kind of data crunching fire power that was used on the mapping of DNA in the so-called Genome Project to the field of material science.

While one could argue that the White House dubbing this project the Materials Genome Initiative was more a metaphorical flourish than a scientific aim, it does raise the question of whether we can map all of material science in a way that will improve manufacturing as the plan has set out to do.

To answer that question, Richard Jones has penned a piece on his blog Soft Machines, which starts by posing the rhetorical question, "Do materials even have genomes?"

Jones raises many of the questions and problems that result from depending on—or expecting—computer simulation to help us design materials to perform tasks we have designed for them. Some of the points he makes remind me of a piece I wrote five years ago: Materials By Design: Future Science or Science Fiction?

At the time, I noted that “Any useful software modeling would need to be able to reveal how an alteration in a material’s structure—for example, a change in a crystal’s lattice structure—affect its properties and functions. Such a program would also need to be able to do that in a range of scales, because we also don’t know whether we must look at the atomic or particle level to find out where effects are taking place.”

This concern about problems of scale is reflected in Jones’ piece but he also raises the question of on what time scale this kind of endeavor would proceed:

"Even with the fastest computers, you can’t simulate the behavior of a piece of metal by modelling what the atoms are doing in it—there’s just too big a spread of relevant length and timescales. If you wanted to study the way different atoms cluster together as you cast an alloy, you need to be concerned with picosecond times and nanometer lengths, but then if you want to see what happens to a turbine blade made of it in an operating jet engine, you’re interested in meter lengths and timescales of days and years (it is the slow changes in dimension and shape of materials in use—their creep—that often limits their lifetime in high temperature situations)."

Jones points out that developing multi-scale modeling like this is nothing new; he refers to Masao Doi’s Octa project as an example. But such projects remain problematic. There are so many variables involved with material science, he says, that it is not clear how generic you can make the processes seem, at least for computer modeling. He further argues that researchers would quickly turn to physical experiments outside of the computer models.

He notes: “I’m skeptical that anyone trying to test out how to shape and weld big structures out of an oxide dispersion strengthened steel (these steels, reinforced with 2 nm nanoparticles of yttrium oxide, are candidate materials for fusion and fourth-generation fission reactors, due to their creep resistance and resistance to radiation damage) without getting someone to make a big enough batch to try it out.”

There is no doubt that computer modeling is a fantastic tool--a view Jones seems to support in the piece--but it should be clear we had better not be expecting material science to reveal itself the way the DNA molecule was mapped by the Genome Project. Whether the Materials Genome Initiative will prove beneficial to US manufacturing is something that can only be determined over the scale of time.

Plasmonic Nanolasers Shrink Down to Size of a Virus

When lasers start getting down to the nanoscale, they run up against the diffraction limit where the size of the laser cannot be smaller than the wavelength of light it emits. But researchers have shown that nanoscale plasmonic lasers can reach an optical mode well below this limit by confining light of very short wavelengths through the use of surface plasmons—oscillations of electrons that occur at the junction of a metal and an insulator. This has revitalized the hope that chips populated with these plasmonic nanolasers could make possible computer processors run by light rather than electrons.

Now researchers at Northwestern University have developed a new design for plasmonic nanolasers that are the size of a virus particle and capable of operating at room temperature. They described the discovery in the journal Nano Letters, (“Plasmonic Bowtie Nanolaser Arrays”).

"The reason we can fabricate nano-lasers with sizes smaller than that allowed by diffraction is because we made the lasing cavity out of metal nanoparticle dimers -- structures with a 3-D 'bowtie' shape," says Teri Odom, the leader of the research and professor of Chemistry at Northwestern, in a press release.

The bowtie geometry allowed the nanoparticles to achieve an antenna effect and suffer only minimal metal “losses”. Typically, plasmon nanolaser cavities have suffered from both metal and radiation losses that required them to be operated at cryogenic temperatures.

Odom also explains that the antenna effect  allows for lasing to occur from an "electromagnetic hot spot"—a capability not demonstrated previously. "Surprisingly, we also found that when arranged in an array, the 3-D bowtie resonators could emit light at specific angles according to the lattice parameters," Odom adds in the release.

Of course, nanolasers that are capable of operating at room temperature are not unique. Researchers at the University of California, San Diego reported earlier this year on a room temperature nanolaser design that requires less power to generate a coherent beam than other designs. The key difference between the two plasmonic nanolasers seems to be the bowtie geometry the Northwestern team developed.

At least one of the aims of both lines of research seems to be to integrate these nanolasers with CMOS electronics.  Whether they can reach this lofty goal remains to be seen, but these nanolasers are a key step in their realization.

Carbon Nanotube Memory Thrown a Lifeline from Nanoelectronics Powerhouse

Massachusetts-based Nantero has faced some challenges over the last decade in getting its carbon nanotube-based non-volatile memory to market. My colleague Philip Ross did a good job characterizing perhaps the biggest obstacle here in the pages of Spectrum over four years ago: “That instant-on computer that Nantero sketched out more than six years ago? You can buy one right now for just $400; it's called the iPhone.”

My contribution to that Spectrum article was to ask whether the tiny start-up really expected the big multinationals that are today’s flash memory manufacturers to just step aside and relinquish the market by letting Nantero essentially eliminate it.

Despite these challenges the company has remained steadfast in its conviction that its carbon nanotube memory would change computing, even in the face of having to sell off part of its company four years ago to Lockheed Martin. At the time, observers were really beginning to question the wisdom of Nantero taking on the role of David to the flash memory producers' Goliath, especially since Nantero was playing the role without a slingshot.

All of this may have changed significantly yesterday with the announcement of a joint development agreement with Belgium-based nanoelectronics powerhouse Imec to develop Nantero’s carbon-nanotube-based memory. Imec may very well be the needed slingshot.

“After review of the progress to date by Nantero and its manufacturing partners, we decided that this CNT-based non-volatile memory has multiple very attractive characteristics for next-generation highly scaled memory,” said Luc Van den hove, CEO of Imec in a press release. “By taking a leadership position in this area of development, in partnership with Nantero, we will be able to bring substantial benefit to our member companies.”

On its own Nantero had managed to bring its NRAM technology to the point where it was producing high-yielding 4 megabit arrays within CMOS production environments. Now with the NRAM arrays being manufactured, tested and characterized in Imec’s facilities, the aim will be to use the memory for applications below 20 nm, such as terabit-scale memory arrays and ultra-fast gigabit-scale nonvolatile cache memories, according to Jo de Boeck, CTO of Imec.

This is the kind of development that would have been welcomed by Nantero supporters many years ago. Even at this late date, it is still hopeful news for the fortunes of the company. But while flash memory has been the company’s great rival up until now, perhaps there are new ones in the shape of graphene-based flash memory that will form the competition in the future.

High Density Carbon Nanotubes Show Way Forward for Smaller and Faster Transistors

Researchers at IBM’s T. J. Watson Research Center in Yorktown Heights, New York are reporting success in precisely locating a high density of carbon nanotubes on a substrate that should lead to high-speed and power-efficient chips and could show a way forward after silicon.

The IBM team was able to successfully place over 10,000 working transistors on the surface of a silicon wafer. Some anticipate that this research will not only allow the building of smaller transistors but also improve the clock speed of the transistors.

The research, which was published in Nature Nanotechnology (“High-density integration of carbon nanotubes via chemical self-assembly”), was hinted at last year during the IEEE International Electron Devices Meeting (IEDM).

At the IEDM meeting last year there was a lot of noise about IBM demonstrating the first transistor with sub-10nm channel lengths. The tie into that line of research and this latest work is that the IBM team built those sub-10nm nanostructures out of carbon nanotubes and grew them through self- assembly on standard 200-millimeter diameter wafers.

The latest research used ion-exchange chemistry to trigger a chemical self-assembly process for the nanostructures. The researchers place the carbon nanotubes in a solution that makes them water-soluble. Then the carbon nanotubes chemically self assemble onto the substrate in patterned arrays.

The process made it possible to place the carbon-nanotube transistors in a density high enough that the resulting material outperformed any other switches from any other material, according to Supratik Guha, director of physical sciences at IBM’s Yorktown Heights research center in a New York Times article covering the research.   “We had suspected this all along, and our device physicists had simulated this, and they showed that we would see a factor of five or more performance improvement over conventional silicon devices,” says Guha in the article.

What might be the most impressive aspect about the results is that the researchers were able to electrically test the 10,000 transistors. Being able to characterize this large a number of nanotube devices is critical for analyzing transistor performance and yield.

This step will also prove crucial in what remains to be the biggest obstacle for the technology in replacing silicon: achieving carbon nanotube purity. At the moment, the carbon nanotubes the researchers have access to contain enough metal in them that they don’t make ideal semiconductors. The IBM team are confident that they can reach a 99.99 percent pure form of carbon nanotubes that will make the devices operate even better than their current prototypes.

Image courtesy of Nature Publishing

Nanostructured Silicon Li-ion Batteries’ Capacity Figures Are In

Seven months ago I covered a small start-up called California Lithium Battery Inc. (CalBattery) that had entered into a Work for Others (WFO) agreement with Argonne National Laboratory (ANL) to develop and commercialize what they dubbed as the “GEN3” lithium-ion battery.

The GEN3 battery is largely based on ANL’s silicon-graphene battery anode process. Basically the ANL approach is to sandwich silicon between graphene sheets in the anode of the battery to allow more lithium atoms in the electrode.

This line of research was motivated by the hope of improving the charge life of Li-ion batteries. First, researchers showed that if you replaced the graphite of the anodes with silicon, the charge could be increased by a factor of ten.  There was one big drawback though. After a few charge-discharge cycles the silicon would crack and become inoperable from the expansion and contraction of the material. The solution seemed to be nanostructured silicon anodes that could last longer than the pure silicon variety, but just barely. 

The ANL silicon-graphene anode is supposed to overcome this problem and achieve comparable charge-discharge cycles of graphite, but with the charge significantly increased like you would achieve with pure silicon in the anode.

So, what’s been happening in the last seven months? Well, CalBattery has released a press announcement revealing the results of their last eight months of testing. According to the press release, the Li-ion batteries they have been testing have an energy density of 525WH/Kg and specific anode capacity of 1,250mAh/g. To offer a comparison, the company press release explains that Li-ion batteries currently on the market have an energy density of between 100-180WH/kg and a specific anode capacity of 325mAh/g.

“This equates to more than a 300% improvement in LIB (Li-ion battery) capacity and an estimated 70% reduction in lifetime cost for batteries used in consumer electronics, EVs, and grid-scale energy storage,” says CalBattery CEO Phil Roberts in the company press release.

Curiously, I didn’t see anything in the press release that talks about what numbers they were able to achieve in charge/discharge cycles with the material. And that really is the crux of the matter. Everyone has understood for the last few years that nanostructured silicon anodes have a high capacity. The problem is that it has only been slightly better than regular silicon when it comes to charge/discharge cycles.

Let’s look at Energy Secretary’s threshold numbers for making Li-ion battery-powered competitive to petrol-powered vehicles:

  • A rechargeable battery that can last for 5000 deep discharges
  • 6–7 x higher storage capacity (3.6 Mj/kg = 1000 Wh) at [a] 3x lower price

Well, we don’t know what the deep discharge figures are for this GEN3 battery. But improving the capacity 300% seems to be a little short of factor of 6 or 7. But as it was pointed out to me in the comments a 70% reduction in lifetime cost does seem to meet the criteria of a 3x lower price.

Maybe EVs don’t really need to be competitive with petrol-powered vehicles, and Secretary Chu’s figures are not pertinent, but if the dwindling sales of EVs are any indication, maybe those figures are relevant and EVs actually do need to be competitive with petrol-powered vehicles…for now.

Nanotechnology Won't Be Delivering a Utopia Anytime Soon

Dr. Michio Kaku, a theoretical physicist at the City University of New York, and regular contributor to numerous TV documentaries on subjects within physics, has offered up an intriguingly titled video on the website Big Think that’s spreading like wildfire through social media: Can Nanotechnology Create Utopia? You can watch the video (5+ minutes long) below.

Kaku starts off by discussing the quest for utopias that fueled the early settlers of the New World. Oddly, his main example is the Shakers. A little background is in order here: The Shakers took a monastic pledge of celibacy. That sort of lifestyle inevitably dwindles your numbers. In fact, the sect probably would have died out in the 19th century, but for the Civil War, during which they took in large numbers of orphans. However, Kaku cites as one of the main causes of Shakers disappearing (they haven’t by the way, there are still a few Shakers) the issue of scarce resources. You see, in the cold winters they couldn’t get enough seeds and this created scarcity, which in turn led to conflict, or so Kaku seems to believe or wants us to believe. In point of fact, the Shakers were among the first organizations to create a business through mail order, and one of the main things they sold were seeds.

But Kaku’s expertise is not the history of religions in the colonial United States, rather, it's theoretical physics. I think based on his next example of utopias we can safely say that the emphasis should be on “theoretical” because what we get is a discussion of a Star Trek replicator.

In the video Kaku draws a comparison between a Star Trek replicator and the molecular manufacturing  of table-top factories and universal assemblers. He explains that with these universal assemblers we become “like gods” able to turn wood into glass. If I had these god-like powers, I doubt my first feat would be turn wood into glass, but I guess he was just illustrating a point.

And what is his point? Well, when we get these universal assemblers and can make anything we want just by pressing the button “Ferrari,” we will be in a world of such abundance that it will seem like a kind of utopia.

However, Kaku cautions that this utopia has interesting philosophical repercussions, which he illustrates by describing a near-entire episode of Star Trek. I won’t bother you with the plot here, but the question it raises are along the lines of: Will we lose the will to work with all this abundance?

This kind of handwringing over a nanotechnology future is really the bailiwick of the Center for Responsible Nanotechnology. They could devote great tomes to concerns over a possible outcome that is so far away that not only can nobody predict when it might come (with the exception of an exceptional futurist like Ray Kurzweil) but some believe may never come.

These naysayers who question the physics of universal assemblers do not deter Kaku because we already have a replicator as proof: Ribosomes. Kaku explains that ribosomes turn your cheeseburger into the DNA that makes for the next generations of humans.

Of course, it took nature a few billion years to come up with this feat of molecular manufacturing. With that time frame in mind, should we really be worrying ourselves about the ironic hardships delivered upon us by a utopia that was created by a reproductive technology for which there is little indication will happen anytime soon?



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

Dexter Johnson
Madrid, Spain
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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