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A Nanoscale Peek at Lithium-air Batteries Promises Better Electric Vehicles

Researchers at MIT and Sandia National Laboratory have made some long-awaited progress in lithium-air batteries. The research has provided insight into the electrochemical reactions that occur when they are being charged.

Lithium-air batteries promise five to 10 times greater storage capacity than traditional lithium-ion batteries, leading many to believe that they may hold the key to turning electrical vehicles from a niche market to a much larger segment of the automotive industry.

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Graphene Becomes Magnetic for First Time

Researchers from both the University of Madrid Complutense and Universidad Autonoma working together at the IMDEA-Nanociencia Institute in Spain have for the first time given graphene magnetic properties,opening up the potential that the material can find new applications in future spintronic devices.

Unlike electronics in which an electron’s charge-carrying capabilities are exploited to create circuits, spintronics involves the quantum mechanical property of electrons to spin, which creates a magnetic moment that makes the electrons behave briefly like magnets. When in the presence of a magnetic field the spin of the electrons moves either into a parallel or antiparallel position in relation to the field. This positioning can be translated into a binary signal (1 or 0).

The trials and tribulations trying to make graphene applicable to electronics despite its lack of an inherent band gap have been well documented. However, what many have overlooked in the quest to bring graphene to electronics is that it doesn’t really lend itself very well to spintronics either.

Since 2007, researchers have looked at graphene as the material for channels in spintronic devices. At this function, it appears to excel. In fact, just this year record distances were achieved for carry information using the spin of electrons.

Unfortunately, when two-dimensional graphene is laid out flat, the motion of electrons moving through the material doesn’t influence the spin of other electrons that they pass. Instead the direction and the spin of electrons remain random rather than patterned.

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Defects Have Just the Right Effects for Graphene Sensors

Last year, Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at the University of Illinois at Chicago, discovered that he could make highly sensitive chemical sensors from graphene. He also determined why they were so sensitive: Defects.

The research unveiled not only highly sensitive sensors capable of detecting a single molecule of a chemical, but also that the sensitivity, which was directly tied to defects around the edges of the graphene, would be lost if those defects were to be removed.

When Salehi-Khojin and his colleagues looked a little deeper into the need for defects to maintain sensitivity in graphene nanosensors, they found something remarkable: The graphene could be free from defects and still be a highly sensitive sensor as long as the substrate it was on was a little ragged around edges.

“This was a very surprising result,” Salehi-Khojin said in a press release. “[The results] will open up entirely new possibilities for modulation and control of the chemical sensitivity of these sensors, without compromising the intrinsic electrical and structural properties of graphene.”

The research, which was published in the ACS journal Nano Letters (“The Role of External Defects in Chemical Sensing of Graphene Field-Effect Transistors”), revealed that the poor sensitivity of pristine graphene in terms of electrical conductivity is not necessarily intrinsic to the material but instead can be affected and approved upon by the underlying substrate.

“We could now say that graphene itself is insensitive unless it has defects—internal defects on the graphene surface, or external defects on the substrate surface,”  noted UIC graduate student Poya Yasaei in the press release.

Now that graphene-based field effect transistors (FET) have been with us for a couple of years, this latest research opens up the potential for graphene-based chemFET sensors to be engineered for a number of various applications.

Photo: Roberta Dupuis-Devlin

Silver Nanoparticles Boost Polymer Solar Cells' Commercial Potential

The fate of polymer solar cells in the marketplace has been tied to three main factors: Lifespan in outdoor environments, the cost of materials that make up the modules (namely indium tin oxide, or ITO), and power-conversion efficiency. These three issues remain the keys to unlocking the commercial potential of polymer solar cells to being someday rolled out like plastic tarps to power our homes cheaply and reliably.

Nanotechnology has been trying to address all three of these issues, but perhaps none of them more than improving the power-conversion efficiency, which has lingered at around five to seven percent. Now researchers at the Ulsan National Institute of Science and Technology (UNIST) in Korea have used metal nanoparticles to achieve the highest yet reported power conversion efficiency for plasmonic polymer solar cells, reaching 8.92 percent. While polymer solar cells have been reported as high as 10.6 percent for polymer solar cells with more than one p-n junction, the UNIST researchers believe that their device, which reached nearly 9 percent using a single junction, could exceed 10 percent in commercial products.

The research, which was published in the ACS journal Nanoletters (“Multipositional Silica-Coated Silver Nanoparticles for High-Performance Polymer Solar Cells”) focused on polymer solar cells enhanced by plasmonics. Plasmonics exploits the phenomenon of "photons striking small, metallic structures to create plasmons, which are oscillations of electron density in the metal," as Neil Savage explained here on the pages of Spectrum.

The Korean researchers were able achieve high light absorption despite thinning out the films that make up the active layer of the solar cell by using silver nanoparticles. These nanoparticles provided the metal in the material that allowed for the exploitation of the surface plasmon resonance effect.

“This is the first report introducing metal NPs between the hole transport layer and active layer for enhancing device performance,” says Jin Young Kim, associate professor at UNIST and a leader of the research, in a press release. “The multi-positional and solutions-processable properties of our surface plasmon resonance (SPR) materials offer the possibility to use multiple plasmonic effects by introducing various metal nanoparticles into different spatial location for high-performance optoelectronic device via mass production techniques.”

While conversion efficiency seems to have been improved in the lab with this research, it will need to be demonstrated this new material will not deteriorate in the environment as some nanomaterial-enabled polymer solar cells have in the past. However, if it can exhibit this kind of robustness and is coupled with a suitable material to replace the expensive ITO, it may indeed be an important commercial step in the polymer solar cells.

Photo: Ken Fields/Creative Commons

Yet Another Nanomaterial Does a Good Job at Oil Spill Remediation

This blog has chronicled many nanomaterials suggested for cleaning up oil spills over the years, with the most recent being an aerogel developed in China that the researchers claim to be the lightest ever produced and capable of soaking up a rather astounding 900 times its own weight in oil. This compares favorably to the current mainstay for oil spill remediation, hay, which only absorbs 3 to 15 times its weight in oil.

Now researchers at Deakin University in Australia have developed a nanosheet made of a porous boron nitride that can soak up 33 times its own weight in oil. While this weight-to-oil-ratio figure doesn’t seem to stack up favorably to some other technologies, like the aerogel above, it does have some side benefits that are lacking in some of the other solutions.

Notable among them is that once the nanosheets have soaked up their share of oil, they can be cleaned and ready to be used again by merely letting them heat in ambient air for two hours. They also are hydrophobic, meaning they repel water, which allows them to float on the surface of the water and be available for easy retrieval during a clean up.

The nanosheets, which are fully described in the journal Nature Communications (“Porous boron nitride nanosheets for effective water cleaning”),  were fabricated by mixing boron oxide powder and guanidine hydrochloride with methane and then heated at 1100 C for several hours in nitrogen gas. In this process, the guanidine hydrochloride decomposes to release several gasses that tunnel out, which results in the formation of the holes in the nanosheets.

So it sounds like a solution to oil spills is at hand—in fact, the Deakin University nanosheets have attractive characteristics for not just oil spill remediation but water purification in general. In fact, there are a variety of nanomaterials for these applications—so many of them that there are catalogues to guide you through them.  But not so fast. As yet, no one is bothering to commercialize them so that they are available for the next oil spill.

Today is three years to the day since I first highlighted this critical point that the nanotechnologies exist but not the commercial interest in making them available for the next oil spill, not much has changed. Perhaps the only way to ensure that these superior technologies are available to clean up the next inevitable oil spill is to institute government regulations requiring them, as IEEE Spectrum editor, Steven Cherry, suggested on his podcast, also nearly three years ago. Sometimes you have to force markets to adopt technologies when doing so may not help the bottom line, but keeps our planet habitable.

Image: Weiwei Lei

IBM Makes Smallest Movie Ever

If there were a Nanoscale category in the Academy Awards, the 2013 winner would surely be a movie made by IBM Research that has carbon and oxygen atoms of carbon monoxide molecules being moved around on a copper surface with a scanning tunneling microscope. The 250-frame stop-motion film, entitled “A Boy and His Atom” (which you can see below), uses discrete atoms to draw a stick-figure-like boy that bounces on a trampoline and plays catch with an individual atom "ball."

The breakthrough here seems to be the use of a stop-motion film that has garnered IBM the Guinness Book of World Records for World’s Smallest Movie.

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Scientists Learn to Control the Twist of Carbon Nanotubes

Graphene has been holding the spotlight for so long in nanomaterial research now that we are beginning to forget that carbon nanotubes were once the rock star of nanomaterials for a post-silicon world.

Now researchers at Aalto University in Finland, the A.M. Prokhorov General Physics Institute RAS in Russia and the Technical University of Denmark (DTU) have put single-walled carbon nanotubes (SWNTs) back center stage by devising a method to control their chirality in a chemical vapor deposition (CVD) growth process.  Since the chirality of carbon nanotubes (CNTs)—the angle its 2-D carbon lattice makes around its circumference—defines both their optical and electrical properties, gaining more control over it addresses an issue of primary concern in their practical application to electronics.

Along with the promise of CNTs—especially SWNTs—have come some pretty big obstacles. Researchers are still struggling to get the tangled rats nest of CNTs oriented and connected in electronic devices. Producing CNTs with some kind of predictability—either semiconducting or metallic—has nearly been abandoned in favor of just finding a way to separate them afterwards.

While many methods have been developed for separating CNTs, they don’t really lend themselves to the scalability of creating the type you want in first place. But the international team of researchers found that their process produced greater uniformity among the nanotubes.

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Nanosponges Soak Up Antibiotic-resistant Bacteria and Toxins

Researchers at the University of California, San Diego, have developed a nanoparticle that mimics a human blood cell so that it can circulate through our bloodstream soaking up bacterial infections and toxins. These so-called ‘nanosponges’ are expected to be particularly effective in treating bacterial infections that have developed an immunity to antibiotic treatments—and also for treating venoms from snake bites.

The nanosponges are made up of a biocompatible polymer core and covered by an outer layer of red blood cell membrane. With a diameter of 85 nanometers, the nanosponges are 3000 times smaller than a human blood cell, so in a single infusion of nanosponges into the blood stream they would easily outnumber the red blood cells, and thus intercept most of the attacking toxins before they damaged the actual blood cells.

A video containing a description of the nanoparticles, along with an animation of how the particles would circulate through our bloodstream soaking up toxins can be seen below.

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Researchers Discover New Structure Inside Nanowires

Nanowires made from III-V semiconductors like indium gallium arsenide are having a bit of run of late. Yesterday, I reported on a new method for growing them on graphene.

Now researchers at the University of Cincinnati have discovered that a newly developed architecture for semiconductor nanowires has a hidden nook in which to find electrons and holes. The discovery opens up a new understanding of the fundamental physics of nanowires.

The research, which was published in the journal Nano Letters (“Optical, Structural, and Numerical Investigations of GaAs/AlGaAs Core–Multishell Nanowire Quantum Well Tubes”), involved a host of characterization and measurement techniques.

University of Cincinnati physics professors Howard Jackson and Leigh Smith, who together led the research, believe that applications of this new structure could range from solar cells to environmental sensors.

“This kind of structure in the gallium arsenide/aluminum gallium arsenide system had not been achieved before,” Jackson said in a press release. “It’s new in terms of where you find the electrons and holes, and spatially it’s a new structure.”

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Nanowires Grow Better on Graphene

In an attempt to grow nanowires on a graphene substrate, researchers at the University of Illinois may have stumbled upon a new paradigm for epitaxy (the growth of crystals on a susbstrate).

Some believe that developing new manufacturing methods for nanoscale devices—like epitaxy—may be more crucial to meeting the demands of next generation chips than creating new materials, especially when feature sizes start falling below three nanometers. So, the Illinois researchers' development of a new method of epitaxy may ultimately be more significant than creating a new material.

The research, which was published in the journal Nano Letters (“InxGa1–xAs Nanowire Growth on Graphene: van der Waals Epitaxy Induced Phase Segregation”), produced nanowires made from III-V compound semiconductors. Generally, III-V semiconductors like gallium arsenide don't integrate well with silicon, but  recently  it was discovered that when these materials were brought down to the nanoscale that they were compatible.

Researchers have previously combined two of these semiconductors in gaseous form so that they deposit themselves on a graphene substrate (a process known as metalorganic chemical vapor deposition, or MOCVD) and self assemble into ordered crystalline form. However, the Illinois research marks the first time three of the semiconductors have been mixed together in this way.

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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
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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