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Dueling Nanowire Lasers Promise Big Changes to Optoelectronics

There appears to be a crush of nanowires laser research. About two weeks ago researchers from the Australian National University (ANU) announced what they claimed to be the first room-temperature lasers made from semiconductor nanowires. And now researchers at the Technische Universitaet Muenchen (TUM) say they too have built semiconductor nanowires that act as lasers at room temperatures.

With the ANU paper being submitted to Nature Photonics (“Optically pumped room-temperature GaAs nanowire lasers”) on 8 July  and then the TUM paper being submitted to Nature Communications one month later (“Lasing from individual GaAs-AlGaAs core-shell nanowires up to room temperature’), the two research projects could understandably both claim to be the first.

But beyond claims of primacy, it appears that the breakthroughs could open up a new avenue for speeding up a range of applications, such as on-chip optical interconnects and integrated optoelectronics for fiber-optic communications.

While these III-V semiconductor nanowires still fall short of the holy grail of getting silicon to act as a laser (though researchers at the University of Pennsylvania did succeed earlier this year in getting a silicon nanowire to emit light through manipulating it with plasmonics), both the ANU and TUM teams are claiming that their nanowires can be grown on silicon. And because of that, they believe the nanowire lasers will win a place in future integrated photonics and optoelectronics.

"The wires and lasers will lead to much faster, much lighter computers because light travels faster than electrons, allowing us to process data much faster," explained Dhruv Saxena from the ANU Research School of Physics & Engineering, in a press release last month.

The leader of the TUM research, Prof. Jonathan Finley, director of TUM's Walter Schottky Institute, more or less echoed this sentiment in a press release this week.

"Nanowire lasers could represent the next step in the development of smaller, faster, more energy-efficient sources of light," said Finley, in the statement.

Both the ANU and TUM teams do face some obstacles that need to be overcome. Both teams acknowledge that the laser emission from the nanowires was simulated by light. To really get to the point of practical applications electrically injected devices, in which the lasers are powered by electricity, will likely be required.

Image: WSI/TU

Viruses Build Piezoelectric Nanogenerator Through Self Assembly

Nanotechnology has opened up the possibility of building things like nature does: on the nanoscale. As such, biomimicry has been a guiding principle of nanomanufacturing.

But unlike natural processes, artificial synthesis of nanoscale structures has often required toxic and expensive conditions. Now researchers at the Korea Advanced Institute of Science and Technology (KAIST) say they've developed a synthesis process that can be done in a more natural way without the costly and extreme environments previously required.

What the researchers came up with uses a harmless, man-made virus, known as the M13 viral gene. The researchers modified it so that it acted as a template for a piezoelectric material, barium titanate (BaTiO3).

The research, which was published in the journal ACS Nano (“Virus-Directed Design of a Flexible BaTiO3 Nanogenerator”), demonstrated that they could build a high-performance, flexible nanogenerator from the piezoelectric material using the M13 viral gene as template for guiding self-assembly of the device.

"This is the first time to introduce a bio-templated inorganic piezoelectric material to a self-powered energy harvesting system, which can be realized through eco-friendly and efficient material syntheses," said Professor Keon Jae Lee from the Department of Material Science and Engineering at KAIST in a press release.

But, of course, using man-made viruses to guide the self-assembly of devices has long been the purview of Angela Belcher at MIT for over a decade. Nonetheless, we can’t quibble that this marks the first time that a virus template was used to create a nanogenerator. And it has a pretty respectable electrical output performance, claimed in the research paper to be about 300 nanoampere and 6 volts.

In fact, the real breakthrough of the research may be that the biosynthetic method that the KAIST researchers developed could open up new possibilities in bio-inspired self-assembly for applications ranging from thermoelectrics to biofuel cells.

Nanorods Enable Regeneration of Damaged or Severed Materials

Sometimes when you combine nanotechnology with biomimetic capabilities you get the somewhat mundane, such as the water-repellant properties of a lotus flower. But other times, you get superhero capabilities, like being able to climb a wall like Spiderman.

Now we have a biomimetic capability enabled by nanotechnology that seems to be really something out of sci-fi—regenerating damaged or severed sections of material, just as some amphibians can grow back amputated limbs.

Although the technology has only been demonstrated in a computer model, it marks the first time that bulk sections of severed materials have been shown to be capable of regenerating.

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Nanomedicines Will Be Big Once They Emerge From Regulatory Troubles

There seems to be a nagging sense among some observers of nanotech—most especially government entities charged with evaluating its progress—that so far it just hasn’t delivered on its promise.

So too seems to be the sentiment with a conference held last week at The New York Academy of Sciences entitled “Nanomedicines: Addressing the Scientific and Regulatory Gap” in which the conference title implies that nanomedicine commercialization has fallen somewhat short of expectations thanks in part to regulatory limitations and uncertainty.

I spoke to one of the conferences organizers and speakers, Dr. Raj Bawa, patent agent at Bawa Biotech LLC, a biotechnology consultancy and patent law firm (he's also an adjunct professor at Rensselaer Polytechnic Institute) on what the limitations were and what the potential fixes might be.

Surprisingly to me, Bawa believes that the issue of definitions for nanotechnology still plays a critical role in hindering its development, at least for nanomedicines and possibly for the entire field of nanotechnology.

Bawa is distressed that many U.S. regulatory bodies and agencies, primarily the Patent & Trademark Office (PTO) and the Food and Drug Administration (FDA), have labored under the strict size guideline laid out by the original definition proposed by the National Nanotechnology Initiative. That guideline does not consider anything to be nanotech unless one or more of its dimensions are under 100nm. Bawa points out that while this somewhat arbitrary size guideline makes sense for advanced materials in which often the novel electrical, conductive or optical properties of a material don’t reveal themselves until they get below 100 nm, it makes little or no sense for nanomedicines, in which the active ingredient that completely changes the drug’s efficacy, safety profile, solubility, or bioavailability can be 1000 nm across or more.

However, Bawa sees signs of hope, especially from the FDA, which in the last couple of years has issued draft guidances related to nanotechnology that he believes represent moves in the right direction.  

“The FDA seems to have said essentially that their investigation of nanotechnology and its regulations needs to be science-based rather than policy based. That’s a positive development for the pharmaceutical industry going forward as they explore nanomedicines as a viable option to some of their formulation woes,” says Bawa.

But Bawa still has reservations about the way the US Patent and Trademark Office is examining and classifying nanopatents. He even suggests a possible open-source licensing solution in some cases where basic nanotechnology patents on upstream "building block" technologies may cause "patent thickets"

The reason nanomedicines are coming into sharp focus is the state of the pharmaceutical industry. We are in the post-blockbuster world now, according to Bawa, and nanomaterials and reformulations via nanotech have offered a way to recoup some of the huge R&D investments that have been made in drugs that failed along the way in the FDA regulatory process.

“Around forty percent of new molecular entities fail during R&D because they are not water soluble,” explains Bawa. “It’s estimated that over $135 billion could be produced in new drugs by tweaking these abandoned entities if this critical solubility issue can be resolved, possibility employing nanoscience.”

With that kind of potential revenue, it is odd that big pharma has not attempted to exploit nanotech more than they have. It would seem Elan Drug Technologies is one of the few examples of a pharma company that has used nanotechnology to create drug products. Its milling technique, called NanoCrystal,  breaks down drug crystal sizes to less than 2000 nanometers.

The company has launched five licensed products using the NanoCrystal technology and achieved sales of nearly $2 billion.

Bawa believes that other big pharma companies are working in this area as well but just haven’t yet engineered the right formulations. But he expects that they will come as more meaningful nano-governance takes shape.

Illustration: iStockphoto

Could Tin be the Two-Dimensional Material of the Future?

For the better part of a decade, researchers have been theorizing and calculating about a mysterious new class of materials called topological insulators. In computer models, scientists have been able to reveal that these topological insulators possess the odd property of insulating on the inside and conducting on the outside. It was even demonstrated last year that topological insulators could be produced from heavy metals like uranium and plutonium that could work at room temperature.

Now researchers at U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University have simulated what would happen if you whittled a topological insulator down to a single atomic layer—a two-dimensional material like graphene. The result is that the edges of the material become conductors and rest behaves as an insulator.

The researchers have dubbed their new material “Stanene”, which is the combining of the Latin word for tin (stannum) with the suffix used in graphene. They believe that it could be a “wonder material” every bit as fascinating as its carbon cousin, graphene. Initial calculations indicate that it could be the world’s first material to conduct electricity with 100 percent efficiency at the temperatures that computer chips operate.

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Nanoparticles Enable Novel Loudspeaker Design

While technological developments in personal computing always seem to be eagerly received, it seems that developments in our personal entertainment—like TVs and stereos—get us most excited.

Along these lines, there is now a completely new way to build loudspeakers thanks in large part to nanoparticles. Researchers at Sweden’s KTH Royal Institute of Technology have found a way to eliminate the need for a permanent magnet in stereo speakers by adding metallic nanoparticles to a speaker's membrane.

“This is, to our knowledge, the first reported magnetic speaker membrane,” said Richard Olsson, a KTH researcher, in a press release.

The design of the speaker, which is detailed in the journal of the Royal Society of Chemistry (“Cellulose nanofibers decorated with magnetic nanoparticles--synthesis, structure and use in magnetized high toughness membranes for a prototype loudspeaker”) employs cellulose nanofibers that have had ferrite nanoparticles dispersed evenly throughout the membrane.

The result is a speaker that does not need a permanent magnet to drive the membrane and yet produces a sound quality the researchers argue is as good as, if not better than, traditional speaker designs because of the even distribution of forces within the membrane.

In traditional speaker designs, a voice coil is wrapped around a permanent magnet. The voice coil drives the speaker cone’s movements, which produces the sounds that we hear.

In the speaker design resulting from this latest advance, there is still a voice coil but it is obviously not wrapped around a permanent magnet nor is it directly attached to the cone. Instead, sound is produced solely by the movement of air.

This isn't the first time that nanotechnology has been offered as a possible solution to loudspeaker design.  Five years ago, researchers in China demonstrated how carbon nanotubes could be used to create a transparent loudspeaker film. I have not heard whether anything ultimately ever came of that research.

But if KTH's new speaker technology doesn’t get off the ground, the researchers believe that it has alternative applications in sound cancellation and in one of our other favorite technologies: the automobile.

“We want to look at applications for the material that are driven by magnetic fields. It may, for example, be a form of active damping for cars and trains,” says Olsson in the press release.

Photo: Richard Anderssson

Graphene Comes to Nanopore Gene Sequencing

Nanopore sequencing—the ability to sequence a strand of DNA by reading its electronic signature as it slithers through a nanoscale pore in a membrane— has always held great promise, but it has been frustratingly difficult to realize its full potential. There have been attempts to boost the faint signal produced as the DNA passes through the nanopore. Other research has aimed to slow the speed at which the DNA passes through the nanopore to improve the measurement. Some researchers have even created a molecular motor that doesn’t just slow the DNA down but controls it’s movement through the nanopore.

Now researchers at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have turned to the wonder material graphene as the membrane.

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New Path to Big Crystals of Graphene

While stock market mavens try to find an angle for making a buck on graphene,  researchers are just trying to find a way to manufacture the material in a way that could work at industrial scale while maintaining high quality. It’s proving much more difficult than expected.

Now researchers at the University of Texas at Austin have developed a new method by which very large flakes of single-crystal graphene can be produced that exhibit excellent electrical properties. The Austin engineers claim that these graphene crystals are 10 000 times larger than the largest crystals they could produce only four years ago.

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Nanowires and Viruses Combine to Create High-Capacity Batteries

While lithium-ion (Li-ion) batteries have managed to elevate hybrid vehicles into a significant segment of the automotive market, all-electric vehicles using that same battery technology have languished as a niche product. Li-ion batteries just don’t have the long charge life or short recharging capabilities that would make all-electric vehicles a good fit for most people’s driving habits. (It also doesn’t help the marketing image of automakers when these all-electric vehicles burst into flames.)

Marketing considerations aside, the recent demise of a few high-profile nanotech companies that tried to make Li-ion batteries for all-electric vehicles may indicate fundamental problems with the current approach. Maybe we need a different battery technology to make all-electric vehicles mainstream.

This realization already began to sink in with the research communities a few years back, and I started noticing more research into Lithium-air batteries.  Lithium-air batteries use the oxidation of lithium at the anode and the reduction of oxygen at the cathode to create a current. This battery design has promised up to 10 times as much energy as a lithium-ion battery at the same weight, giving them an energy density equal to that of gasoline.

Greater storage capacity certainly helps solve one EV limitation, but if a battery technology is going to displace fossil fuels, it also needs to recharge as quickly as—or on par with—filling up a car at gas station. Earlier this year, researchers at Massachusetts Institute of Technology (MIT) and Sandia National Laboratory peered into the lithium oxidation process of Li-air batteries and saw a possible way to speed up battery recharging.

Now researchers—again from MIT—have made progress on both fronts. They took nanowires made of manganese oxide (which is often used as the material for the cathode of Li-air batteries) and coated them with man-made viruses. These viruses create a larger surface area that improves the reaction between the lithium and oxygen, resulting in a greater storage capacity and a faster rate of recharging. A video describing the technology can be seen below.

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Flexible Mobile Devices Get a Flexible Battery Made From Nanotubes

After years of promises that mobile phones were going to become flexible, Samsung announced plans last month to release its flexible phone.

While the Samsung Galaxy Round is not flexible to the extent you can bend it to your heart’s content, it does offer a display that is flexible enough for the manufacturer to curve it. The move has also spurred other mobile device manufacturers to announce their intentions to market similar devices.

With the age of flexible devices seemingly upon us, one of the primary challenges for their development has been the power source. Samsung’s new phone is more or less powered by a standard rigid battery. But both LG and Samsung acknowledged that they are on a quest to develop a flexible battery that will enable a truly flexible phone.

Researchers, who anticipated that the launch of flexible mobile devices would require a flexible power source, have steadily pursued the flexible battery. There have been a few commercial efforts using printed electronics, and some thin-film technologies that have made a splash.

Now researchers at the New Jersey Institute of Technology (NJIT) have developed a flexible battery made from carbon nanotubes that is aimed at powering flexible 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
New York, NY
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