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Molybdenum Disulfide Could Help Memristors Mimic Neurons

The memristor seems to generate fairly polarized debate, especially here on this website in the comments on stories covering the technology. The controversy seems to fall along the lines that the device that HP Labs’ Stan Williams and Greg Snider developed back in 2008 doesn’t exactly line up with the original theory of the memristor proposed by Leon Chua back in 1971.

While this debate will not likely abate, research is continuing in developing two-terminal non-volatile memory devices based on resistance switching.

Along these lines, researchers at Northwestern University have pushed the envelope of the two-terminal device—which can only control one voltage channel—by creating a third terminal. The researchers believe that this will expand the capabilities of memristors into more complex electronics, paving the way for computers to more closely mimic the neurons of the human brain.

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Inexpensive 3-D Imaging Device Integrated Into a Smartphone

Last year we saw confirmation that 3-D printing had emerged into the mainstream. Six years ago, companies like MakerBot were the only ones showing their 3-D wares at CES. Last year, the Consumer Electronics Association dedicated an entire show floor at CES to 3-D printing, only to have it sell out and then sell out again after space was added.

While 3-D printing has been exploding, 3-D imaging of objects so they can be translated into 3-D-printed products has been lagging behind—keeping it an expensive option and outside the reach of most amateur 3-D printing enthusiasts.

Now researchers at CalTech have changed that by developing an inexpensive 3-D imaging device that can be integrated into a smartphone. The imager, they say, can send data to a 3-D printer that will allow it to reproduce a copy accurate to within micrometers of the original object’s dimensions.

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Graphene Finds Its Path in Supercapacitor Commercialization

Researchers at the California NanoSystems Institute (CNSI) at UCLA have been hotly pursuing the ability to apply graphene to the electrodes of supercapacitors. While their efforts have shown progress—improving energy density for a supercapacitor to almost 40 Watt-hours per kilogram from the industry average for a standard supercapacitor of 28 Wh/kg—it apparently hasn’t provided a big enough boost for supercapacitor manufacturers to walk away from the much cheaper activated carbon.

This has not deterred the team at CNSI from continuing to work with graphene and supercapacitors. In fact, they have recently employed the ubiquitous manganese dioxide used in alkaline batteries to create a hybrid material that they believe should boost the commercial prospects for 2-D materials in supercapacitors.

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Will Graphene-based Light Bulbs Be Graphene's Commercial Break Out?

The big story this week in graphene, after taking into account the discovery of “grapene,” has to be the furor that has surrounded news that a graphene-coated light bulb was to be the “first commercially viable consumer product” using graphene.

Since the product is not expected to be on store shelves until next year, “commercially viable” is both a good hedge and somewhat short on meaning. The list of companies with a commercially viable graphene-based product is substantial, graphene-based conductive inks and graphene-based lithium-ion anodes come immediately to mind. Even that list neglects products that are already commercially available, never mind “viable”, like Head’s graphene-based tennis racquets.

So, okay, the BBC got caught up in some PR language promoting what appears to be a UK-developed technology that’s been financed by a Canadian company. That’s nothing outside standard operating procedure. But there were still some issues in the piece that had me scratching my head.

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New 2-D Material Grapene Has Spectacular Properties

Today, 1 April, researchers at the Napa Valley Research Institute announced the discovery of a new two-dimensional material—grapene—that could one-day rival silicon in computers, steel in cars, and chocolate in candybars. (Yes. We know. That’s what they all say.) The new substance exists in flat sheets, connected by strong bonds composed of cellulose and lignin. In bulk form, its natural state, it’s found hanging in chaotically-arranged bunches.

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Molybdenum Disulfide Sees the Light

Roughly two years ago, researchers at MIT started to look at the potential of molybdenum disulfide (MoS2) for photovoltaic applications. The results were somewhat mixed. They saw relatively low conversion efficiency numbers, but were encouraged by the discovery that placing just three sheets of MoS2 into a one-nanometer-thick stack makes it possible to absorb up to 10 percent of incident sunlight. That’s an order of magnitude higher than gallium arsenide and silicon.

While that was indeed an encouraging development, it was far from enough to make anyone start clamoring for MoS2 to replace silicon in photovoltaics or other photonics uses.

Now researchers at Northwestern University have employed plasmonics in combination with MoS2, boosting its ability to absorb light as well as its photolumiscence.

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Silicon Telluride Could Be the Next Big Thing in 2-D Materials

Silicon telluride is a somewhat forgotten silicon-based semiconductor material. After it was identified back in the 1960s, a paper that outlined its general properties was published over 40 years ago.  Not a lot of research has focused on the material since then, despite that fact that you can purchase just about any amount you wish. It is based on silicon after all.

Researchers at Brown University have pulled silicon telluride out of obscurity and have placed it solidly into the growing universe of two-dimensional (2-D) materials.  The result may be that it yields advances including improved electrodes in batteries and better LEDs.

“My guess as to why there is very little literature on 2-D silicon telluride is that it was simply forgotten among the class of 2-D materials,” said Kristie Koski, assistant professor of chemistry at Brown, who led the work, in an e-mail interview with IEEE Spectrum.

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"Robogerms" Spawned by Combo of Graphene and Bacterial Spores

Researchers at the University of Illinois Chicago (UIC) have combined graphene quantum dots (GQCs) with a single bacterial spore to create bio-electromechanical devices. This so-called “robotic germ” functions an electromechanical humidity sensor.

Recently, James Tours’ group at Rice University, who were the first to develop GQCs in 2013, created an improved way to manufacture them that promised to open them up to a new range of applications in optics.

However, they may not have considered the possibility of joining them to a living organism for the kind of machine the UIC researchers created. The Chicago-based team have dubbed their hybrid device NERD, standing for Nano-Electro-Robotic Device.

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Graphene Supercharges 3-D Hybrid Supercapacitor

By combining sheets of graphene with a traditional battery material, scientists have created hybrid supercapacitors that can store as much charge as lead acid batteries but can be recharged in seconds compared with hours for conventional batteries.

Supercapacitors now play an important role in hybrid and electric vehicles, consumer electronics, and military and space applications. However, they are often limited in terms of how much energy they can store.

Now researchers at the University of California, Los Angeles, have developed a hybrid supercapacitor that is based on graphene, which is made of single layers of carbon atoms. Graphene is flexible, transparent, strong and electrically and thermally conductive, qualities that have led to research worldwide into whether the material could find use in advanced circuitry and other devices.

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For First Time, Researchers Demonstrate Heat and Sound Are Magnetic

Earlier this month, we reported on research demonstrating that heat propagates as a wave through graphene rather than as vibrations of atoms the way it does in 3-D materials.  In 3-D materials, the collective state of those vibrating atoms is known as phonons.

For the first time, researchers at Ohio State University (OSU) have demonstrated that acoustic phonons, which can carry both heat and sound, have magnetic properties that allow them to be manipulated with magnetism. 

In research published in the journal Nature Materials, the OSU researchers applied a magnetic field equivalent to that inside a magnetic resonance imaging (MRI) device (in this case, the magnet was reported to be fairly powerful at seven Tesla). They discovered that they could reduce the amount of heat flowing through a semiconductor by 12 percent.

“This adds a new dimension to our understanding of acoustic waves,” said Joseph Heremans, professor of mechanical engineering at Ohio State, in a press release. “We’ve shown that we can steer heat magnetically. With a strong enough magnetic field, we should be able to steer sound waves, too.”

Before anyone starts thinking about the discovery’s applicability to heat management in computers, they should keep in mind that the semiconductor had to be kept at temperatures very close to absolute zero (specifically, -268 degrees Celsius) in order for the researchers to measure the movements of the phonons.

In fact, it was the complexity of taking the measurements that had prevented researchers from recognizing the magnetic properties of phonons previously. In order to take thermal measurements at such a low temperature, Hyungyu Jin, a postdoctoral researcher and lead author of the study, used the semiconductor indium antimonide and shaped it into a lopsided tuning fork in which one arm was 4 millimeters wide and the other was 1 mm wide. Then he placed a heater at the base of each arm.

At normal temperatures, the ability of the material to transfer heat would be solely dependent on the kind of atoms in the material. But near absolute zero, the ability of the material to transfer heat can be determined by the physical size of the material. In this case, the difference in the sizes of the fork arms was significant. Phonons more easily filled the wider arm.

“Imagine that the tuning fork is a track, and the phonons flowing up from the base are runners on the track,” explained Heremans in the press release. “The runners who take the narrow side of the fork barely have enough room to squeeze through, and they keep bumping into the walls of the track, which slows them down. The runners who take the wider track can run faster, because they have lots of room.”

Eventually they all end up at their respective finish lines. But the track’s geometry determines just how quickly. 

With this understanding, Jin was able to compare the temperature changes in the two fork arms. He first took the measurements without a magnet and then with one. With the magnet on, the heat flow through the larger arm slowed down by 12 percent.

Now that the researchers have measured magnetism’s effect on heat, they want to move on to see if they can use it to deflect sound waves.



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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