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DNA Nanotechnology Takes Two Big Steps Forward in Manufacturing

A fundamental, unproven assumption in the field of DNA nanotechnology was that the nanoscale objects produced through DNA self-assembly achieved atomically precise positional accuracy.

Researchers at Technische Universitaet Muenchen (TUM), led by Hendrik Dietz, have challenged that assumption head on and built a 3-D object using DNA self assembly techniques and found that indeed the object met its design specifications down to the sub-nanometer scale.

For years now, research has shown that DNA could be programmed to take the shape of pre-determined objects. If a five-pointed star was desired, it was possible to program the DNA so that it took a shape that resembled very closely the original design. But no one really knew if the final objects met the original designs at the atomic scale.

To prove this assumption, the TUM researchers designed a test object that was suitable for low-temperature electron microscopy. This object allowed for an electron density map to be generated of the object in which the resolution of the map was sufficient for a pseudo-atomic model that could be flexibly fitted to the entire object. The object, which was comprised of 460 000 atoms, incorporated a variety of designs that should make it useful in further study in the field.

A video describing the object and its model can be seen below along with further information about the research, which was published in the journal Proceedings of the National Academy of Sciences:

Finally having proof of the atomic precision of the DNA manufactured objects is a huge confirmation for the hopes of bottom-up manufacturing.

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Sale of A123 Systems to Chinese-Owned Company Points to Futility of Nationalistic Technology Investments

The continuing saga of A123 Systems Inc. has culminated this past week in most of its assets being sold for US $256.6 million to the Chinese-owned Wanxiang America Corporation, an auto parts conglomerate.

The sale of A123 to Wanxiang had been in the works since this past August. But because of strong opposition from Washington politicians the final sale was delayed.  The main objection to the sale centered on the fact that the US government had floated A123 a “grant” for $250 million as recently as 2009 to expand the company’s production capacity.

Why the US government would give a grant to expand the company’s production capacity when the market problem it faced was that its main customer wasn’t selling any of its own products is probably a worthy discussion. However, combating crony capitalism with more crony capitalism, which some U.S. Senators seemed engaged in with their fight to block the sale, hardly seems to be a solution.

There were concerted efforts by U.S.-based Johnson Controls Inc. to purchase the bulk of A123’s assets. But the prospect of paying Wanxiang back the $75 million the Chinese company had loaned A123 before A123's bankruptcy likely poured cold water on any other plausible deal.

For anyone seeking—from a U.S. nationalistic perspective—some sort of positive takeaway from the deal perhaps comfort can be taken in the news that Navitas Systems, an Illinois battery company, will get all of A123’s defense contracts.

I am sure that this sale is a bitter pill to swallow, especially for those who believe that national nanotechnology investments will translate into new jobs and economic growth.  We have already seen how, after years of government investment in nanotechnology research and commercialization, the benefiting companies can be easily picked up for a song. Not just by shrewd investors, but by other governments.

The last U.S.-based nanotechnology-based Li-ion battery company to go bankrupt (Ener1) ended up being purchased by a Russian interest. Even the former CEO of Ener1 served as an advisor to Wanxiang in its purchase of the A123 assets.

Governments around the world are going to have to come to terms with the notion that investments in technology have a slim chance of producing jobs and economic growth within the region that happens to make those investments. It may in fact be the only the chance, but in the current innovation framework those chances remain slim. A123 beat the odds; it managed to turn a university research project into a commercial product. There just wasn’t any market for the product.

What governments should be doing is reexamining the entire innovation infrastructure. Apparently, they have not done this to date because there has been no pressure to do so. Sure, technology that has been languishing for years in research labs never seems to get to market, but nobody misses what wasn’t there in the first place. But once it leaves the lab for the marketplace there's something to miss: the millions—even billions—being spent without much to show for it.

Nanostructure Material Makes Organic Solar Cells 175 Percent More Efficient in Lab

Organic solar cells have remained a bit of a commercial disappointment. There are a number of reasons for this. Some point to the use of the expensive indium-tin-oxide (ITO) in the electrodes.  Still others believe the use of fullerenes as electron acceptors has kept organic solar cells from achieving wider commercial adoption.

Researchers at Princeton University, led by electrical engineer Stephen Chou, have developed a nanostructure that promises an economical way to nearly triple the efficiency of organic solar cells and garner them a stronger foothold in the commercial market.

The Princeton research (“Ultrathin, high-efficiency, broad-band, omni-acceptance, organic solar cells enhanced by plasmonic cavity with subwavelength hole array”), which was published in the journal Optics Express, claims to have developed a nansostructured sandwich of metal and plastic that increases the efficiency of the solar cells by 175 percent. The nanostructure manages this feat by reducing the amount of light reflecting off the cell and increasing the amount of light captured by it.

The “sandwich” as it has been dubbed is in fact a subwavelength plasmonic cavity. Plasmonics exploits the phenomenon of "photons striking small, metallic structures to create plasmons, which are oscillations of electron density in the metal." The subwavelength plasmonic cavity--or sandwich—at once dampens the reflection of light and traps light.

The result was a solar cell that reflects a mere 4 percent and absorbs 96 percent of the light that hits it. The researchers claim to have demonstrated a solar cell with this design that produces 52 percent higher efficiency in converting light to electrical energy than conventional solar cells.

These figures are for direct sunlight. On cloudy days, when sunlight hits the solar cells at an angle, the numbers are even more astounding. Efficiency is increased by an additional 81 percent over conventional solar cells, with a total increase of 175 percent.

The breakthrough of the design is the top layer of the sandwich, which is a metal mesh only 30 nanometers thick. The holes in the mesh are only 175 nanometers in diameter and are placed 25 nanometers apart. This first “window” layer means that the ITO typically used in this layer can be omitted, leading to a far cheaper design.

The bottom layer is made of the same metal films found in conventional solar cells. The top and the bottom layers are very close to each other separated only by a thin semiconducting material (silicon, plastic or gallium arsenide can be used). In the Princeton prototype an 85-nanometer-thick layer of plastic was used.

Because the design can use a variety of silicon materials, the researchers believe that it could be used in traditional silicon solar panels and reduce the thickness of the panels by a thousand fold.

Here we have a design that both significantly reduces manufacturing costs and dramatically increases energy efficiency. That’s what we call a win-win in solar cell technology.

Carbon Nanotubes Show Promise in Neural Engineering

Research this summer out of Rice University showed that newly developed nanoparticles could be an effective emergency treatment for traumatic brain injuries.

Now researchers at Duke University have come up with an ultra-pure carbon nanotube—dubbed “few-walled carbon nanotubes” (a reference to the single-walled and multi-walled varieties)—that can regulate excessive levels of chloride in nerve cells.

The research, which was published in the Wiley journal Small (“Highly Conductive Carbon Nanotube Matrix Accelerates Developmental Chloride Extrusion in Central Nervous System Neurons by Increased Expression of Chloride Transporter KCC”), was specifically focused on the impact of carbon nanotubes on neurons.

Carbon nanotubes have been a source of great interest for neuroscientists because of the material’s electrical and mechanical properties. The hope has been that those properties could be exploited in creating devices that could interface with nervous tissue. However, previous experiments with neurons and carbon nanotubes came up with mixed results, largely due to the impurities within the carbon nanotubes.

The Duke team found that by employing the high purity few-walled carbon nanotubes that not only did the nanotubes not harm the nerve cells but they actually seemed to nourish the neurons.

"Previous studies have looked at the behavior of carbon nanotubes on neurons. However, the impurity in the nanotubes significantly affected the results. After we developed pure few-walled carbon nanotubes in our lab, we discovered that nanotubes actually accelerated the growth of the neuronal cells significantly," said Jie Liu, Professor of Chemistry at Duke University and senior author of the study, in a press release.

This accelerated growth of neuronal cells also can regulate chloride levels in the nerve cells. Excessive amounts of chloride can disrupt a neuron's proper function. Epilepsy, chronic pain, and traumatic brain injury all involve this kind of neural circuit damage.

The human body typically regulates these chloride levels by producing a protein known as KCC2 (chloride-extruding transporter, potassium chloride cotransporter 2). As nerve cells mature their KCC2 levels increase and their ability to regulate chloride levels becomes more powerful. By exposing the nerve cells to the carbon nanotubes the researchers found that neurons matured faster and the chloride levels in them dropped rapidly.

This research does not appear intended to serve as a treatment in itself but a step towards developing neural engineering devices that employ the carbon nanotubes.

Lead author Wolfgang Liedtke, associate professor of medicine and neurobiology at Duke, adds: "We hope that carbon nanotubes will work as well in injured nerves as they did in our study of developing neurons...The use of carbon nanotubes is just in its infancy, and we are excited to be part of a developing field with so much potential."

Hyperbolic Reporting on Nanotechnology in Food Wreaks Havoc

This past summer Nature published an article outlining some of the causes for the recent bombing attacks on nanotechnology labs. At the time, I suggested on this blog that most of the article scanned about right except for one notable omission: poor reporting on nanotechnology in the mainstream press. 

One of the clearest indications of how this bad journalism has misinformed the public was when the terrorist group “Individuals Tending Toward the Savage,” which attacked a nanotech lab in Mexico, made public its raison d’etre. In it they demonstrated a truly distorted idea of what nanotechnology is and what scientists working on the nansoscale are doing. In their letter they demonstrated the misapprehension that the nanotechnology of today threatens us with the prospect of “grey goo” as tiny nanobots eat the world and leave behind a waste product of goo.

I laid at least part of the blame for this terrorist group confusing science with science fiction at the feet of mainstream journalists, who, not being familiar with the field, mistake Michael Crichton’s Prey with Eric Drexler’s Engines of Creation. It’s probably not fair to say they are confused; it’s more likely the case they have never heard of the latter.

The perfect example of this comes in an article appearing on the website for the local PBS TV station in Los Angeles (KCET). In it the author, explains that Crichton’s Prey is “actually turning out to be more prescient than pessimistic.” The author based his conclusion on article he read in a publication called “E-The Environmental Magazine”.

While that article is filled with a bit more hyperbole and conjecture presented as cold-hard fact than I care for, at least it has an inkling of what a nanoparticle is. But the writer for KCET doesn’t even get that. He believes “nanoparticles” are just another way of saying, “small robots that can move about your body as they please.”

 I am sorry, but nanoparticles are not small robots wandering around in our bodies delivering nutrients, or “attacking from the insides.” Let’s just start there.

Now onto the more reality-based arguments presented in both the E Magazine and KCET articles.  We get this in the E Magazine article: “There is no doubt that nanoparticles are in the food supply and have been for years.” As proof of this statement, the author references research that found carbon nanoparticles in “caramelized sugar, including bread and corn flakes”.

If you have ever heated sugar in a chemistry class you probably recall that carbon, oxygen and hydrogen in the sugar separate. The oxygen and hydrogen burn off leaving carbon behind—probably in nanoscale particles. Is this some deliberate attempt by unscrupulous food company scientists to put nanoparticles (oops, I mean nanobots) into the food supply? Probably not. But if the E Magazine editor wants real proof of nanoparticles in our food, she need only turn to mayonnaise, which is an emulsion of lipids and proteins that are on the nanoscale. I wonder if over 250 years of mankind eating mayonnaise passes the long-term-health-risk test?

Two years ago, the UK government's House of Lords Science and Technology Committee decided they were going to get to the bottom of this nanotechnology-in-food issue. They put together a panel of experts, interviewed experts from all aspects of the issue and concluded that they couldn’t really say to what extent nanotechnology is used in our food.

But I am sure that the author at E Magazine understands the issue better than some UK government committee (it’s likely just some conspiracy anyway to cover up the entire issue) and the reporter can come to conclusions that were not possible for the experts.

One clear conclusion we can make from all of this, however, is that the reporter at E Magazine, in an attempt to heighten the fear factor, got another reporter to believe that nanoscale robots were circulating through our body doing some good, but also possibly some unknown harm. Now there is a much wider swath of the general public that believes nanoscientists are producing nanobots that will result in some scenario from the novel Prey.

We’ve already witnessed the damage, maiming and destruction that one small group of people can wreak when they don’t really understand what nanotechnology is. At present that violence far exceeds any harm that nanotechnology has perpetrated upon anyone. Maybe we should be hyping just how careless and misguided the coverage of the subject is and the harm that may be doing.

4-D Nanowire Transistor Takes Shape of a Christmas Tree

Eighteen-months ago, Intel announced with great enthusiasm its three-dimensional (3-D) transistor, dubbed Tri-Gate.  Of course, regular readers of Spectrum have known for years that 3-D transistors were going to be with us sooner or later.

Once you’ve gone from 2-D to 3-D, the next logical step is 4-D, right? Well at least that's the progression that researchers at Purdue and Harvard University want to make. The joint research team has developed a transistor consisting of three nanowires made out of indium-gallium-arsenide instead of silicon. The resulting transistor’s combination of speed and stacking capabilities have led the researchers to refer to it as ‘4-D’.

“It's a preview of things to come in the semiconductor industry," said Peide "Peter" Ye, a professor of electrical and computer engineering at Purdue University, in a press release. "A one-story house can hold so many people, but more floors, more people, and it's the same thing with transistors. Stacking them results in more current and much faster operation for high-speed computing. This adds a whole new dimension, so I call them 4-D."

The advance couldn't be more timely, at least insofar as the transistor is shaped a bit like a Christmas tree—the three nanowires are progressively smaller, resulting in tapered cross section silhouette you'd more likely see at Rockefeller Center than on a chip. (Unfortunately no images of the transistor will be available until 8 December.)

More than the design of the transistor, the real breakthrough for the so-called 4-D transistors was the coating of the nanowires with a new dielectric layer material made from a combination of lanthanum aluminate and aluminum oxide. This new dielectric layer allowed the researchers to use indium-gallium-arsenide, dubbed III-V semiconductor materials, in place of silicon.

Combining elements from group III of the periodic table, including indium and gallium, with those from group V, such as arsenic, has been suggested as a replacement for silicon since the 1960s. The attraction of these hybrid materials is that they can move electrons around much faster than silicon can.

One hiccup in the use of these III-V semiconductors has been reducing the dimensions of the transistor’s gate. The Purdue-Harvard team claims that their indium-gallium-arsenide transistors have 20-nanometer gates, a milestone, according to Ye.

The research will be presented at the IEEE’s International Electron Device Meeting in San Francisco, CA next week in two separate papers.

Innovative Nanopatterning Technique Looks to Anti-Counterfeiting Applications

Earlier this year, researchers at IBM Zurich developed a process in which they used the surface tension of water to manipulate gold nanorods and arrange them into specific patterns.

The technique, which was published in the Wiley journal Advanced Functional Materials ("Self-Assembly: Oriented Assembly of Gold Nanorods on the Single-Particle Level"), allowed the researchers to arrange the nanorods into a pattern resembling the German Ampelmännchen, which is used in Berlin’s crosswalk signals to direct pedestrians when to cross a street.

While that was a nifty demonstration, it didn’t reveal commercial applications. Now, however, the research team led by Dr. Heiko Wolf believes that the technique could be used in anti-counterfeiting efforts.

"In addition to using nanorods, we can also create patterns using florescent spheres which emit red, green and blue,” says Heiko in an IBM press release. “What makes this particularly interesting is that they add another level of security, in that the order of the colors in which they arrange themselves is completely random. So not even I could replicate the pattern. We call it a physically uncloanable function or PUF."

Heiko further describes the technology and its anti-counterfeiting capabilities in the video below:

While I can understand the IBM research team’s enthusiasm for their newly-found application possibilities, there are a couple of issues that may limit commercialization.

The IBM press release presents this work as a first for anti-counterfeiting with nanotechnology, but there are already existing techniques with similar applications. SingularID, (now part of Bilcare Research) use nanomagnets to create a suite of tools that can be used for detecting counterfeits. The patterns generated with Bilcare’s technique are also completely random and can’t be reproduced. What makes that technology stand out is that it’s not just a material but an entire product that can be bought to combat counterfeiting. There's always room for another player in the market, but IBM will have to prove that their method has additional advantages. 

Secondly, when I heard Heiko explain, “All you need is an optical microscope to see the pattern,” I immediately thought that it sounded impractical. While a nanoscientist might think analyzing a product with an optical microscope is no big deal, it’s hard to picture a port authority official sitting down with one to check and see if the Swiss watches are what they claim to be.

The IBM Zurich team have found a very good way to create nanopatterns with nanoparticles using a directed self-assembly technique, but it may still be in search of a worthy application outside of anti-counterfeiting.

Innovative Nanofabrication Technique Produces Semiconductors without a Substrate

If you stepped up and suggested that eliminating the substrate was the future of semiconductor manufacturing, nine times out of 10 (or 10 out of 10) you would be dismissed with a wave of the hand. That’s not too different than the initial reactions Lars Samuelson of Lund University in Sweden received when he presented that possibility to his colleagues.

“When I first suggested the idea of getting rid of the substrate, people around me said ‘you’re out of your mind, Lars; that would never work,'” Samuelson relates in a release describing his latest research. But it did work and the process for doing it, which was published in the journal Nature ("Continuous gas-phase synthesis of nanowires with tunable properties"),  looks like it could reach the commercial stage in applications for solar cells in as little as two to four years.

The process consists of putting freely suspended gold nanoparticles in a gas flow. These gold nanoparticles serve as a substrate on which semiconductor nanowires can grow.

Research in the area of growing nanowires with “seed” particles (metal nanoparticles) in a gas flow has already enjoyed some breakthroughs this year. In February, researchers at MIT demonstrated that by controlling the amount of gas you could actually change the properties of the resulting nanowires.

However, the Lund University research team still saw that the field of fabricating semiconductor nanowires lacked a method by which nanowires could be mass-produced “with perfect crystallinity, reproducible and controlled dimensions and material composition, and low cost.”

So Samuelson and his colleagues experimented with a process they dubbed “aerotaxy”--a name based on the process known as epitaxy, in which a crystal layer is grown on crystal substrate. Aerotaxy is essentially an aerosol-based growth method that proved successful in continuously producing nanowires with controlled dimensions. The trick to getting it to work properly was carefully controlling the temperature, the timing of the process, along with the dimensions of the seed particles—in this case, the gold nanoparticles.

“In addition, the process is not only extremely quick, it is also continuous. Traditional manufacture of substrates is batch-based and is therefore much more time-consuming,” adds Samuelson in the release.

The research team has gone so far as to actually build a prototype manufacturing system consisting of a series of ovens that will cure the nanowires to create variants such as p-n diodes. With this focus on engineering the fabrication techniques, the researchers seem to be really pushing for a solar cell prototype in two years.

Collodial Semiconductors Challenge Amorphous Silicon

Amorphous silicon has been the “king of the hill” when it comes to thin, fast, and flexible semiconductors, but researchers at the University of Pennsylvania believe they have knocked the king off his throne and maybe right into the past.

The U Penn research team, led by doctoral students David Kim and Yuming Lai along with Professor Cherie Kagan, have used cadmium selenide nanocrystals (which are proving themselves useful in a number of areas)  to deliver devices that can move electrons 22 times faster than in amorphous silicon.

Cadmium selenide nanocrystals are within a class of colloidal semiconductor nanocrystals that have been found effective for making thin-film field-effect transistors. Essentially taking the form of ink, these colloidal nanocrystals have tantalized researchers looking to create inexpensive thin-film electronics. But until this most recent research they had not been demonstrated for use in the high-performance field-effect transistors needed in large-area integrated circuits.

The Penn research, which was published in the journal Nature Communications (“Flexible and low-voltage integrated circuits constructed from high-performance nanocrystal transistors”), may have found a way to achieve these high-performance large-area integrated circuits.

The researchers started with a flexible polymer on which they used a masking technique to stencil one level of electrodes for the circuit. Another area on the polymer was stenciled off for a conducting gold that would later serve as the electrical connection to the upper levels of the circuit. After putting down an insulating aluminum oxide layer, a spincoating deposition technique was used to deposit a 30-nanometer layer of nanocrystals on top.

What might be the main distinguishing factor between this technique and previous methods using colloidal semiconductor nanocrystals  was the use of a new ligand. These ligands extend out from the surface of the nanocrystals and aid conductivity of the nanocrystals as they are packed tightly together.

“There have been a lot of electron transport studies on cadmium selenide, but until recently we haven’t been able to get good performance out of them,” says Kim in a press release. “The new aspect of our research was that we used ligands that we can translate very easily onto the flexible plastic; other ligands are so caustic that the plastic actually melts.”

While the nanocrystal-based devices that the researchers developed are giving amorphous silicon a run for the money in terms of electron mobility, it doesn’t seem that the researchers are targeting amorphous silicon’s main application of flat-panel displays. Instead they envision these flexible and easy-to-produce circuits in pervasive sensors used in either security or biomedical applications.

Newly Developed Live Nanoscale Imaging Technique Promises Improvement in Li-ion Batteries

Much of the nanotechnology-related work going on today for improving Lithium-ion (Li-ion) batteries has focused on developing nanostructured silicon to replace graphite in the anodes of the next generation Li-ion batteries.

While this work has been encouraging, another line of research has taken a different tack. Instead of just replacing the graphite in the anodes, researchers have sought to determine why the degradation of Li-ion batteries’ storage capacity occurs in the first place.

Two years ago, I covered work conducted at Ohio State University in conjunction with both Oak Ridge National Laboratory and the National Institute of Standards and Technology that employed every microscopy tool researchers could get their hands on in the search for nanoscale phenomena that would cause this degradation. The results showed that the material from which the electrodes in Li-ion batteries are made coarsen over time; the lithium ions that need to go between the positively and negatively charged electrodes become increasingly unavailable for charge transfer.

Now researchers at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a new imaging technique that allows them to observe lithium-ion reactions in real time with at the nanoscale precision.

Critical to the new imaging technique is transmission electron microscopy (TEM), which has been used to fabricate the “world’s smallest” battery. In the Brookhaven work, which was published in the journal Nature Communications (“Tracking lithium transport and electrochemical reactions in nanoparticles”), the TEM is modified with an in-situ electrochemical cell that can operate inside the TEM. This novel design gives researchers the combination of live imaging found with in-situ techniques and the spatial resolution and nanoscale precision of TEM.

The design of the modified TEM may be novel, but it’s not overly complex. “The entire setup for the in-situ TEM measurements was assembled from commercially available parts and was simple to implement," said Brookhaven Lab physicist and lead author Feng Wang in a press release. "We expect to see a widespread use of this technique to study a variety of high-energy electrodes in the near future,” says Wang.

The new imaging technique allowed the researchers to observe the lithium ion reaction that occurs across iron fluoride (FeF2) nanoparticles. They watched the lithium ions move quickly across the surface of the nanoparticles and then observed the compounds being broken down into different regions in a layer-by-layer process—all in real time. The Brookhaven team saw that the lithium-ion reaction leaves in its wake a trail of new molecules.

“Although many questions remain regarding the true mechanisms behind this conversion reaction, we now have a much more detailed understanding of electron and lithium transport in lithium-ion batteries,” said Brookhaven physicist and study coauthor Jason Graetz in the release. “Future studies will focus on the charge reaction in an attempt to gain new insights into the degradation over time that plagues most electrodes, allowing for longer lifetimes in the next generation of energy storage devices.”

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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.

 
Editor
Dexter Johnson
Madrid, Spain
 
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Rachel Courtland
Associate Editor, IEEE Spectrum
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