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Nanostructure of Butterfly Wings Could Lead the Way to Inexpensive Infrared Detectors

The goal of nanotechnology is often just duplicating what nature does. Whether it’s replicating the way that geckos walk on ceilings without falling down, or duplicating plants' use of photosynthesis to design improved solar cells, nature is the source of much inspiration and guidance in nanotech research.

Researchers at GE Global Research have found such inspiration from nature in their recent work in developing better thermal imaging.

The research, published in the journal Nature Photonics, was on “low-thermal-mass resonators inspired by the architectures of iridescent Morpho butterfly scales.”

The experiment involved the doping of Morpho butterfly scales with single-walled carbon nanotubes (SWNTs). When the researchers blew on butterfly wings coated with the SWNTs, the wings detected temperature changes down to a mere 0.02 degrees Celsius within 1/40 of a second.

"The iridescence of Morpho butterflies has inspired our team for yet another technological opportunity. This time we see the potential to develop the next generation of thermal imaging sensors that deliver higher sensitivity and faster response times in a more simplified, cost-effective design,” said Radislav Potyrailo, principal scientist at GE Global Research who leads GE’s bio-inspired photonics programs. “This new class of thermal imaging sensors promises significant improvement over existing detectors in their image quality, speed, sensitivity, size, power requirements, and cost.”

It should be noted that the SWNTs only enhance the heat absorption of the butterfly wings. The phenomenon occurs mainly because the wings are composed of nanoscale structures made of chitin. These structures create the reflections and refractions of light that our eyes perceive as the iridescence associated with this species of butterfly. The light effect is also caused by the expansion of the chitin when it absorbs infrared radiation.

The GE researchers were especially interested in chitin’s ability to expand by actually absorbing the infrared light, and it was this feature that they magnified by doping the wings with SWNTs.

While this is a very promising demonstration, it will likely take some time to convert these observations into any kind of device that could replace today's infrared detectors. However, the researchers are hopeful that the work they are doing with the Morpho butterfly in vapor sensing applications could reach the market as soon as five years.

Some Australians Prefer Skin Cancer to Sunscreens with Nanoparticles

In a survey conducted last month and commissioned by the Australian Department of Industry, Innovation, Science, Research and Tertiary Education, 17 percent of respondents said they would rather risk skin cancer than use sunscreens containing nanoparticles.

This survey—along with three other papers on nanoparticles in sunscreens—was  presented this week at the 2012 International Conference on Nanoscience and Nanotechnology (ICONN) in Perth, Australia.

Of the three other papers, two of them seem to indicate that the risks from using sunscreens containing nanoparticles are no greater than those of traditional sunscreens. The third paper demonstrates that some sunscreens that claim to be “nano-free” sometimes do contain nanoparticles.

Each year, 440,000 Australians receive medical treatment for skin cancers, and more than 1,700 people die from all types of skin cancer annually, according to the Cancer Council of Australia.

So, it’s clear that choosing to avoid sunscreen altogether just because it might contain nanoparticles could threaten your life. This seems an especially grave decision when two of the three reports at ICONN conference indicate that nanoparticle-based sunscreens don’t appear to be any more dangerous than the traditional variety.

Instead of stepping back and reassessing their position on this subject, the Friends of Earth (FoE) remain unconvinced by the mounting evidence that sunscreens containing nanoparticles are not dangerous to our health and have doubled down on their objections to nanoparticles in sunscreens.

The FoE have taken one of the three reports from the ICONN conference that showed that some so-called “nano-free” sunscreens actually contained nanoparticles and used that to call for a government intervention.

"What we see with this research is that in the absence of government regulation, the nanotech industry is able to more or less make up their own rules about what constitutes a nano material," said Elena McMaster, a FoE spokesperson.

That’s one interpretation, I suppose. But it could also be that traditional sunscreens might contain nanoscale particles even though no attempt had been made to manufacture or add them to the mix. Unintentional nanoparticles, if you will, not unlike those created when the tires of your car drive over the pavement.

I wonder what kind of government regulations the FoE will request. Will each container of sunscreen have to be opened and its contents examined with a scattering of synchrotron light to determine particle size?

The result of all this has been confusion for the consumer. Unfortunately, it’s the kind of confusion that could mean people risking skin cancer so as to avoid another threat the science increasingly seems to be saying isn’t one.

Super Wear-Resistant AFM Tip Pushes the Boundaries of Nanomanufacturing

In collaborative research among scientists from the University of Pennsylvania, the University of Wisconsin-Madison and IBM Research–Zürich a new ultrasharp silicon carbide tip for an atomic force microscope (AFM) has been fabricated that is thousands of times more wear-resistant at the nanoscale than previous designs.

In their manufacturing of the tip, the researchers took as their inspiration the way in which steel is strengthened through tempering. They exposed the silicon tips typically used in these devices to carbon ions and then annealed them so that a silicon carbide layer was formed while still maintaining the sharpness of the original silicon tip.

This is not the first time this team has pushed the capabilities of AFM tips. Last year the researchers developed silicon oxide-doped diamond-like carbon tips.

At the time, those tips represented the state-of-the-art, with their wear-resistance at the nanoscale being measured as 3000 times greater than silicon. The latest design is 10 000 times more wear resistant at the nanoscale.

IBM's press release quotes University of Pennsylvania professor Robert W. Carpick as saying that "compared to our previous work in silicon, the new carbide tip can slide on a silicon dioxide surface about 10 000 times farther before the same wear volume is reached and 300 times farther than our previous diamond-like carbon tip. This is a significant achievement that will make nanomanufacturing both practical and affordable."

The researchers believe that this new super-hard tip will open up new application areas for probe-based technologies like biosensors for measuring glucose levels. This is due to its ability to resist wear when being slid across the surface of silicon dioxide.

Mark Lantz, manager in storage research at IBM Research-Zurich predicted that the technology will be used in microscopic sensors that monitor "everything from water pollution to patient care."

While biosensors may be the longer range goal of the research, which was published online on 8 February in the journal Advanced Functional Materials, the researchers will initially look to put the tip to work in nanomanufacturing and nanolithography applications.

Nanotechnology Used to Create a "Desalination Battery"

Many places in the world face a shortage of drinkable water, and the situation is getting worse rather than better.

When there's not enough naturally occurring fresh water, various desalination processes become attractive technological solutions. The most recent estimate of desalination prodution that I’ve seen—dating back to 2007—was about 30 billion liters a day.

That number sounds significant, but most of the production is  limited to the oil-producing countries of the Persian Gulf that can afford the huge energy costs of running the multi-stage flash (MSF) process. It generally costs $0.5 to $0.85 per cubic meter of water, with 70% of that cost from energy consumption.

Outside of the Middle East, reverse osmosis (RO) is the most common technique. Even though it is more energy efficient, it still burns up huge amounts of energy. Striking a balance between the needs for freshwater and lower energy consumption remains a struggle. The National Research Council in its Desalination and Water Purification Technology Roadmap (PDF) has set a goal of reducing the cost of desalination by 50-80% in 2020.

Research on nanomaterials has led to several promising ideas for improving desalination. For example, one research group used nanoscale magnetic particles, originally intended for a new memory device, to enable a forward osmosis process that is more energy efficient. Another has used carbon nanotubes to filter out harmful ions from water

Now, German researchers, led by Fabio La Mantia at Center for Electrochemical Sciences at Ruhr-Universität Bochum, have developed what they call a “desalination battery.” (The work was published in the January 23, 2012 online edition Nano Letters A Desalination Battery”)

"By using electric energy, the device is able to capture the salt from a sea water stream, and release it in another sea water stream,” La Mantia explained to Nanowerk. “Our technology is, in this very early stage, very near in efficiency of reverse osmosis, one of the most efficient techniques available today."

This work builds on the work done with Yi Cui and his team at Stanford last year in developing manganese-dioxide nanorod that makes up an electrode for a battery that exploits the difference in salinity between freshwater and saltwater.

The new research runs the Stanford team's process in reverse. Instead of generating electricity from the difference in salinity, the desalination battery introduces electrical energy to extract sodium and chloride ions from seawater. The result? Desalination.

"In the first step, the fully charged electrodes, which do not contain mobile sodium or chloride ions when charged, are immersed in seawater,” explains La Mantia to Nanowerk. “A constant current is then applied in order to remove the ions from the solution. In the second step, the fresh water solution in the cell is extracted and then replaced with additional seawater. The electrodes are then recharged in this solution, releasing ions and creating brine. In the final, fourth step, the brine solution is replaced with new seawater, and the desalination battery is ready for the next cycle."

The attractive feature of the desalination battery is that it can run on low voltages, which means that a solar power source could run the battery. Perhaps it will some day be powered by nanotech-enabled  photovoltaics.

via Nanowerk

UK Reveals Plans for Becoming “Graphene Hub”

The University of Manchester in the UK has been at the forefront of graphene research ever since Andre Geim and Konstantin Novoselov fabricated the single atom-thick sheets of carbon back in 2004 and were awarded the Nobel Prize for Physics in 2010 for it.

Since then researchers across the globe have been exploring the possibilities of this wonder material, especially in the field of electronics despite it not possessing an inherent band gap. The research has not only been geographically spread out but also in terms of both commercial and government research institutions being involved in it. In short, it seems like just about any lab doing work in nanomaterials has at least one researcher working on graphene.

But the UK government was intent on not relinquishing their lead in graphene, or so it seems. So they promised £50 million ($79 million) in additional funding specifically targeted at graphene research and yesterday they announced the details of how that money is to be used.

The press release emphasizes how “The graphene hub will build on this by taking this research through to commercial success." So I was wondering if there would be any discussion of how they intended to build up an electronics industry that it never really had in the first place to exploit the material.

But the whole “commercialization” idea is left pretty vague. Instead, we get what we typically get whenever governments decide to support nanotechnology research: a building.

Nanotechnology really must be one of the biggest boons for the construction industry over the last 10 years. It certainly is putting a smile on the face of cement contractors in and around Manchester with a £45 million ($71 million) to be spent on building a new graphene institute.

The “commercial”aspect? Well, both researchers and businesses will have access to the facility.

I have heard it argued that the UK’s nanotechnology initiative might have benefited from focusing its funds and resources on a few large research institutes rather than spreading them out among a much larger number of labs. That may be true and this announcement seems to be following that line of logic.

Nonetheless, I can’t help but think that funding the construction of one large institute is an overly simplified way of maintaining your perceived leadership in graphene research and later commercialization.

While it would certainly have been more complicated to plan out how you would take all the research that already exists in the field and see how government funds could help bring the fruits of that research to market, it might have had a greater impact on the commercial aspect of keeping the UK as a leader in the field of graphene.

Salmon DNA Embedded with Nanoparticles Leads to a Novel Memory Device

Researchers from Germany and Taiwan have combined expertise to create a “write-once-read-many-times” (WORM) memory device made from embedding silver nanoparticles into a biopolymer film of salmon DNA.

The collaboration began a little over a year ago. Researchers from the DFG-Center for Functional Nanostructures (CFN) at the Karlsruhe Institute of Technology (KIT) in Germany, led by Dr. Ljiljana Fruk, had been working on producing nanoparticles through DNA templates, which has been a fertile area of research of late. Meanwhile, the team at the National Tsing Hua University, led by Dr. Yu-Chueh Hung, worked on optimizing the process and actually designed the memory device.

The device they came up with is a DNA-based biopolymer nanocomposite that is sandwiched between two electrodes. When UV light shines on it, the silver atoms group into nano-sized particles. By creating these particles, the researchers were able to encode data. This device is able to store data through the phenomenon known as bistability, in which a device exhibits two states of different conductivities at the same applied voltage.

The DNA-based biopolymer nanocomposite was used because of its affinity with metal ions and its effectiveness as a template for metal polymer nanoparticle systems.

The memory device is fully described in the journal Applied Physics Letters under the title “Photoinduced write-once read-many-times memory device based on DNA biopolymer nanocomposite”,.

In working with the device, the Taiwanese researchers soon discovered that once it had been turned on it would stay turned on, and that variations in voltage across the electrodes did not alter the device’s conductivity. In other words, once information is written onto the device it cannot be written over, and the information appears to persist indefinitely.

The researchers have indicated that the technique for making the device could provide new design techniques for making optical storage devices, as wall as having applications in plasmonics.

Take Nanocrystals, Add Boiling Water, and Get a 400-Fold Increase in Luminescence

Just when you were about to throw out those old nanocrystals, a last minute shine from an ultraviolet light reveals previously non-existent luminescence. Is there a word for something that is even more serendipitous than serendipity?

Perhaps we will have to invent one after Prashant Jain, out of habit, put some nanocrystals that he was about to throw out under an ultraviolet light and discovered a significant increase in their luminescence.

Jain, now a chemist with the University of Illinois, was part of a team of researchers led by chemist Paul Alivisatos at the U.S. Department of Energy's Lawrence Berkeley National Laboratory. The team was looking at the "cation-exchange" technique for creating core/shell nanocrystals, in which one type of semiconductor is enclosed within another.

While this type of nanocrystal and technique for making them added a new contestant to compete with quantum dots and nanorods synthesized from colloids, they weren’t really impressing with their luminescence.

"While holding promise for the simple and inexpensive fabrication of multi-component nanocrystals, the cation-exchange technique has yielded quantum dots and nanorods that perform poorly in optical and electronic devices," explains Alivisatos in a press release.

But you put those same crystals on the shelf for six months and things change. Upon discovering the change, Jain thought that maybe he could make them change faster by heating the crystals…and it did.

"It was an accidental finding and very exciting," Jain says, "but since no one wants to wait six months for their samples to become high quality I decided to heat the nanocrystals to speed up whatever process was causing their luminescence to increase."

"By heating these nanocrystals to 100 degrees Celsius, we were able to remove the impurities and increase their luminescence by 400-fold within 30 hours," says Jain. "When the impurities were removed the optoelectronic properties of nanocrystals made through cation-exchange were comparable in quality to dots and nanorods conventionally synthesized. "Jain and his colleagues have published their work in the journal Angewandte Chemie under the title "Highly Luminescent Nanocrystals From Removal of Impurity Atoms Residual From Ion Exchange Synthesis".

Why Ener1 Went Bankrupt

It’s hard to deny that when Ener1 announced that it had built “a pilot nanotechnology-based manufacturing facility to fabricate electrodes for high discharge rate, lithium-ion batteries” that it sounded like we were about to witness a new successful nanotechnology company.

The fate of the company might have been foreseen, however, if one examined the use of this technology for this particular application area—namely Li-ion batteries for electric vehicles (EVs).

What was likely whispered among some battery experts became a bit more public when the US Secretary of Energy, Stephen Chu, implied over a year ago that the Li-ion battery might not be the best solution for powering EVs.

Just to be clear, I would like to see some technology replace the internal combustion engine for powering automobiles. I just don’t think it’s clear that the Li-ion battery is the best alternative.

It would seem that the marketplace agreed. In announcing its Chapter 11 bankruptcy yesterday, Ener1’s CEO, Alex Sorkin, acknowledged, “Our business plan was impacted when demand for lithium-ion batteries slowed due to lower-than-expected adoption for electric passenger vehicles."

If I may turn Mr. Sorkin’s assessment around somewhat, it might be that there are customers for electric passenger vehicles but those vehicles need to have the same level of functionality as the fossil-fuel-powered variety and come in at the same, or at least competitive, price. So, come up with a power source that does that and the demand for electric vehicles is there, especially at the current price for gasoline. It may be that the demand for EVs exists, just not for Li-ion-battery-powered EVs.

The Chapter 11 debt restructuring will allow the company to recapitalize itself to the tune of $81 million, but one has to wonder what $81 million will accomplish that a matching grant of $118 million from the US government couldn’t.

It seems accepted wisdom that technologies currently exist for eliminating a fossil-fuel economy and that just acts of will—including capital investment—will simply make this happen. But perhaps we’re not as far along as we imagine in the technological struggle or in the strategic application of capital to bring those technologies to market.

Carbon Nanotubes Bend and Stretch and Still Conduct

It seems the most desirable characteristic for electronics at the moment is flexibility, at least as far as nanotechnology research is concerned. Somehow—and I am not sure why—being able to bend electronic devices into various shapes seemed to take hold as a much sought-after quality with Nokia's conceptual introduction of the Morph phone four years ago based on joint research with Cambridge University.

I for one have always felt that a longer lasting battery was a more attractive feature in a phone than being able to wrap it around my wrist. But artificial skin has been raised as a possible application for flexible electronics recently and that sounds a good deal more like market pull than technology push.

Whatever the future holds for flexible electronics, the one thing we can say for certain is that nanotechnology, specifically carbon nanotubes, are pretty good at enabling it.

The most recent research in this vein comes from researchers at North Carolina State University who have developed a method for using carbon nanotubes as elastic conductors.

"We're optimistic that this new approach could lead to large-scale production of stretchable conductors, which would then expedite research and development of elastic electronic devices," says Dr. Yong Zhu, an assistant professor of mechanical and aerospace engineering at NC State, and lead author of a paper describing the new technique.

The approach, which was published online Jan. 23 in Advanced Materials, involves placing carbon nanotubes in parallel lines onto an elastic substrate. When the substrate material is stretched, the nanotubes are separated and maintain their parallel alignment. When the substrate is relaxed, the carbon nanotubes do not fall back into their previous positions but instead form into squiggly shapes and are now elastic and flexible while still retaining their excellent electrical properties.

The proposed list of applications includes “implantable medical devices, and sensors that can be stretched over unmanned aerial vehicles.” A bit of a new twist for flexible electronics.

Is this a quality of carbon nanotubes that simply works or is it truly useful? We’ll see if industry comes knocking.

Quantum Dots with Built-in Charge Could Lead to Highly Efficient Solar Cells

When you see 45 percent energy conversion efficiency for solar cells, you stop and take notice.

The story of nanotechnology in solar cells over the last decade has often been about pushing energy conversion efficiency higher and higher while dragging prices lower and lower. It hasn’t always been easy to sustain that dual-pronged attack.

Certainly, quantum dots have been looked at by researchers in this area as a possibility for achieving high conversion efficiency at a lower cost.

But I had no reason to expect that the use of quantum dots in solar cells would yield 45 percent conversion efficiency. Nonetheless that’s the figure I saw when University of Buffalo, in collaboration with both the Army Research Laboratory and the Air Force Office of Scientific Research,  announced a way of embedding charged quantum dots into solar cells that allows the cells to harvest infrared light.

The research, which was originally published in the ACS journal Nano Letters last May, used selective doping of some of the quantum dots so they have a built-in charge that repels incoming electrons. This in turn forces the electrons to travel around the quantum dots.

As the abstract explains: “We found that the quantum dots with built-in charge (Q-BIC) enhance electron intersubband quantum dot transitions, suppress fast electron capture processes, and preclude deterioration of the open circuit voltage in the n-doped structures. These factors lead to enhanced harvesting and efficient conversion of IR energy in the Q-BIC solar cells.”

The three University of Buffalo researchers behind this work—Vladimir Mitin, Andrei Sergeev and Nizami Vagidov—have spun-out a company called Optoelectronic Nanodevices LLC that presumably will attempt to commercialize this technology.

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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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