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Lithium-Sulfur Batteries Overcome Another Limitation: High Temperatures

Lithium-sulfur (Li-S) batteries have been pursued as an alternative to lithium-ion (Li-ion) batteries for powering electric vehicles due to their ability to hold up to four times as much energy per unit mass as Li-ion. However, Li-S batteries don’t come without some problems. For instance, the sulfur in the electrode can become depleted after just a few charge-discharge cycles, or polysulfides can pass through the cathode and foul the electrolyte.

Another issue Li-S batteries face is the difficulty of ensuring that they operate safely at high temperatures due to their low boiling and flash temperatures. Now, researchers at the University of Western Ontario, in collaboration with a team from the Canadian Light Source, have leveraged a relatively new coating technique dubbed molecular layer deposition (MLD) that promises to lead to safe and durable high-temperature Li-S batteries.

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Nanocones Boost Efficiency of Solar-based Water Splitting

The long list of attempts to use the sun to split water, and thus isolate hydrogen, has always had one big issue: energy conversion efficiency. Sure, solar-based water-splitting processes don’t yield carbon dioxide byproducts like those based on natural gas. But their conversion efficiencies are so notoriously low that many have never seen a way for them to make economic sense as a replacement for those based on natural gas. While headlines heralded tenfold increases in solar splitting efficiency, the result was only conversion efficiencies of 2.9 percent.

That is, until now. Researchers at Stanford University have made what they believe to be a significant step in realizing the kind of photovoltaic energy conversion efficiencies that will eventually make solar water-splitting economically competitive with natural gas processes. If they can realize their lofty ambitions for the technique, it could lead to the emission-free hydrogen economy that has for so long been promised.

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Flexible Nanogenerators Offer Dependable Energy Source for Flexible Electronics

Ever since 2012, when Zhong Lin Wang and his colleagues at Georgia Tech developed the first triboelectric nanogenerator (TENG), Wang and his team have been making continual progress in updating the technology so it can better deliver power to small electronic devices. TENGs essentially harvest static electricity from friction.

TENGs consist of two different materials that are rubbed together. In this way, materials that like to give off electrons, such as glass or nylon, will donate them to materials that like to absorb them, such as silicon or teflon. Since rubbing generally results in wear, what Wang and his Georgia Tech colleagues did back in 2012 was arrange the component materials so that they generate electricity when they are pressed together. By corrugating the contact surfaces of the materials, and by pressing them together, the structures enmesh, causing the friction that leads to electricity generation.

Such devices have impressive energy conversion efficiency, but they have thus far been limited to use with rigid electronics. Now Wang and his team have adapted them for use in flexible electronics, thus providing a dependable energy source for bendable, stretchable gadgets that has been sorely lacking.

In research described in the journal Science Advances, the Georgia Tech researchers adapted the TENG device by combining a conductive liquid electrode and a flexible, rubber elastic cover. So successful have the researchers been at making the nanogenerator flexible that they have given it a new name: shape-adaptive TENG, or “saTENG”.

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Ultrahigh Density Data Storage Could Get Faster and Easier to Produce

Data storage density has doubled every three years since magnetic storage was first developed in the mid-1950s. Key technological innovations along the way such as giant magneto resistance (GMR), perpendicular magnetic recording (PMR) and heat-assisted magnetic recording (HAMR) have fueled that enormous growth in capacity. Despite this continually increasing storage density, there is a growing sense that this upward trend is beginning to lose steam.

Now researchers at the Helmholtz Zentrum Berlin (HZB) have developed a new technique with a new kind of material that could move magnetic storage technology beyond the current state-of-the-art HAMR technology and lead to faster and more energy efficient ultrahigh density data storage.

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DNA Structures Coordinate Nanoparticle Self-Assembly

The aim of nanoparticle self-assembly research has been to get the particles to organize themselves into structures arrangment is largely controlled by us. However, the level of control we have sought has sometimes left a little bit to be desired.

Now, researchers at the U.S. Department of Energy's (DOE’s) Brookhaven National Laboratory have demonstrated that polyhedral structures made from DNA can serve as a framework for ensuring that the nanoparticles self-assemble in the exact arrangement their minders intended.  In these DNA structures, the nanoparticles can be assembled into crystalline and open 3-D frameworks that themselves can be interconnected, making possible a wide variety of different structures.

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On-Chip Supercapacitors Dump Carbon in Favor of Silicon

Tiny supercapacitors that can fit right on a chip have been hotly pursued for at least the last half decade. We’ve seen the usual suspects—graphene, titanium carbide and porous carbon—proposed for making the electrode material for these on-chip supercapacitors.

Now researchers at the VTT Technical Research Centre of Finland have turned to an unlikely material for producing these pint-sized energy storage devices: porous silicon.  What have the researchers done to turn this notoriously weak electrode material into a powerhouse? They have found that topcoating it with a nanometer-thick layer of titanium nitride makes all the difference.

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Serving as guides to the eye, the inner dashed triangles in the image depict the graphitic nitrogen nearest neighbors and the corners of the outer triangles are terminated at the locations of the enhanced electron density among second and third nearest

Now Graphene Can Have a Tunable, Stable Bandgap

The knock against using graphene in digital electronics has been that it lacks an inherent band gap. However, over the years there have been a number of approaches that have been able to engineer a band gap into the material.

One of the most promising methods has been nitrogen doping, which actually increases the material’s conductivity rather than reduces it.

Now researchers at the U.S. Naval Research Laboratory (NRL) have developed a new technique for nitrogen doping of graphene that can control exactly where the dopants are placed in the graphene lattice. This precise localizing of the dopants reduces defects and provides greater material stability.

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Breaking Up Comes With Some Unexpected Benefits

In polymer manufacturing, a technique known as cold drawing is used to imbue polyester and nylon fibers with high tensile strength. It involves pulling the fiber so that its diameter is reduced and the polymer chains are aligned. Nobody ever really considered doing this with composite materials because no one imagined that it would lead to anything useful.

But researchers at the University of Central Florida (UCF), in Orlando, believed that seeing what would happen was worth an experiment. In a paper published in the journal Nature, the researchers recall that what they discovered was not at all what they were expecting. And the result could change nanomanufacturing by enabling the production of new kinds of materials.

The unexpected development, said Ayman Abouraddy, an associate professor and co-author of the research, in a press release: 

While we thought [that when they performed the cold drawing on the composite fiber, which consisted of a brittle core and ductile outer coating] the core material would snap into two large pieces, instead it broke into many equal-sized pieces.

Though a surprise to Abouraddy, Robert S. Hoy, a University of South Florida physicist who specializes in the properties of materials like glass and plastic, wasn’t shocked by the UCF professor’s the initial findings. Hoy recognized this behavior as something familiar to those in the polymer business—a phenomenon called “necking,” which occurs when cold drawing causes non-uniform strain in a material.

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Brighter Displays Come From the Wings of a Butterfly

Biomimetics, in which nature serves as a model for devising technologies, has been a key inspiration for scientists working in nanotechnology. For instance, we’ve seen researchers mimic the bioluminescent light of fireflies for improved organic light emitting diodes (OLEDs). But one of the favorite insects for nanotech researchers is the butterfly. By attempting to duplicate the wing structures of butterflies, researchers have come up with an anti-counterfeiting technique and inexpensive infrared detectors.

Now researchers at the Swinburne University of Technology in Australia have again turned to the wings of a butterfly—this time, to help develop nanostructures that could lead to more compact light-based electronics that would yield brighter displays.

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Molecules that alight on a surface used to test nanocars look more like obstacles, according to researchers at Rice University and North Carolina State University testing the mobility of single-molecule cars in open air.

It's a Bumpy Ride for Nanocars in Air

So-called “nanocars” have been a fixture on the nanotechnology landscape for at least the last decade.  And, no, these will not be cars that we humans will be shrunk down to fit into like in the sixties sci-fi movie “Fantastic Voyage.”  Instead nanocars are molecular-scale devices that can be directed to move around with light or other means and ferry around payloads not unlike the way a macroscale vehicle might.

Now researchers at Rice University, who developed the first nanocars, have teamed up with researchers at North Carolina State University to make it possible for nanocars to move around in ambient environments instead of being restricted to vacuums.

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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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