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ultrafast black phosphorous switch

Black Phosphorus Enables Plasmonic Logic

Much research has been dedicated to exploiting the waves and oscillations of electrons that are produced on the surface of a metallic structure when photons of light strike it. These waves of electrons are called either surface plasmons when referring to the oscillations in charge alone, or surface plasmon polaritons when referring to both the charge oscillations and the electromagnetic wave. The field developed around exploiting this phenomenon has become known as plasmonics.

Plasmonics has made all sorts of interesting things possible, such as confining wavelengths of light to design smaller photonic devices. However, there has been no good way to turn the waves “on” and “off” rapidly.

Now researchers at the University of Regensburg in Germany, in collaboration with colleagues from Istituto Nanoscienze–CNR and Scuola Normale Superiore in Pisa, Italy, have demonstrated the ability to selectively choose between an “on” state, where surface polaritons can be excited and propagate across the sample, and an “off” state, where no polaritons are present.

So what is the trick to achieving these “on/off” states? Don’t use a metal at all. Instead, employ the two-dimensional material du jour: black phosphorus.

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Graphene and silly putty make for a strain sensor

Graphene and Silly Putty Creates a Super-Sensitive Strain Sensor

For all the talk and research that has gone into exploiting graphene’s pliant properties for use in wearable and flexible electronics, most of the polymer composites it has been mixed with to date have been on the hard and inflexible side.

It took a team of researchers in Ireland to combine graphene with the children’s toy Silly Putty to set the nanomaterial community ablaze with excitement. The combination makes a new composite that promises to make a super-sensitive strain sensor with potential medical diagnostic applications.

In research described in the journal Science, scientists at AMBER, the Science Foundation Ireland-funded materials science research center based at Trinity College Dublin, discovered that if you added nanosheets into a low-viscosity material like silly putty, its electromechanical properties dramatically changed. You suddenly have an extremely sensitive strain sensor.

When you apply a voltage to the graphene-infused silly putty, the slightest touch results in a very large change in the current. Voila a strain sensor. 

“If you take the silly putty and stretch it just by one percent, then the current would change by a factor of five: that’s a very small mechanical change with a very big electrical change,” says Jonathan Coleman, the professor at Trinity College Dublin, who led the research.

In tests with the graphene-enabled putty, the researchers placed the composite onto the people’s chests and necks to measure breathing, pulse, and blood pressure. The results demonstrated an unprecedented sensitivity for a strain and pressure sensor, hundreds of times more sensitive than other sensors.

“What we found is that when you put graphene in extremely soft polymers like this, they act as strain sensors that are light years ahead of anything that had been created before,” says Coleman. “And this is intimately linked with the fact that these polymers are so soft.”

What is surprising about this line of research is that there has been so few investigations previously looking at combining graphene with a low-viscosity polymer. Graphene has been put in many different polymers to make composites,  but the vast majority of those polymers are at the harder end of the spectrum. This practice is typically driven by the aim of adding graphene to a strong, hard polymer to make it even stronger and harder.

While there has been some work in putting graphene into soft polymers, no one has put graphene into polymers anywhere near as soft as silly putty. The softest polymer that people had put graphene in previously would be something like rubber, according to Coleman.

Just as there has been a lot of work into adding graphene to polymers, the use of graphene to make a polymer a strain sensor has some history as well. But no one was quite expecting that these softer materials would enhance the effect so profoundly.

“We knew that there had been very little work done in this area,” said Coleman.  “But I have to be completely honest, we didn’t know that the material would have the interesting properties that we saw in the end result.”

While Coleman believes that there is a wide range of medical sensing applications for the material, by far the most clear-cut and important example would be the continuous measurement of pulse and blood pressure.

“We can measure pulse in a relatively straightforward way,” he says. “There are a number of ways to do it. But we can measure blood pressure simply, cheaply and continuously.”

You can see a demonstration of this blood pressure monitoring in the video below:

Coleman is pretty confident that the path to commercialization for this technology is pretty clear with no major obstacles in sight.

“First of all you would have to have a commercial supply of the material; I don’t see that as challenging,” said Coleman. “There are many commercial suppliers of graphene that can produce graphene in large quantities. And, of course, silly putty is commercially available. The procedure of mixing the two components together is fairly straightforward and that could certainly be industrialized. So making the material is not a problem.”

Engineering the sensing device would be a bit more of a challenge. Coleman explains that you would have to make some kind of housing that could be worn on the wrist and would have the sensing material inside of it. Then you would need the electronics to generate the current and measure the changes in it. You would also need some kind of communication system that would send the signal to a mobile phone where you would need an app to collect and analyze the data.

“To be completely honest, all of that stuff is not that far from being off-the-shelf,” he says. “I don’t think there is a great engineering challenge in this work. So really we are actually quite close to the ability to commercialize this material.”

While the strain sensor that Coleman and his colleagues have developed is sensitive, he believes that this research opens up an entirely new way of making composites that will lead to far more sensitive sensing technologies in the future.

“What we really want to do is to go on to the next generation of sensing,” he says. “We have extremely sensitive materials here, but we see an opportunity to make composites in a different way using different polymers that are up to a factor of ten more sensitive than the ones we have created here.”

he researchers’ machine uses a “nanoporous” stamp through which a solution of nanoparticles, or “ink,” can flow uniformly through the stamp and onto whatever surface is to be printed.

Forest of Carbon Nanotubes Stamps Electronic Ink Onto a Surface

About a dozen years ago, I wrote a report on the future of nanomaterials in printing and packaging.  I think copies of it may exist today only on my bookshelf, but it has served over that time to inform my opinion on how nanomaterials can be applied to these areas—most recently contributing to piece on these pages a few years back.  The basic question: How do you get a nanomaterial onto some packaging cheaply enough that it makes sense for what is essentially a throwaway item?

It has not been easy. But MIT researchers believe they have hit upon a low-cost, robust stamping method that manages to get carbon nanotubes onto a flexible surface so that they can serve as a transistor for controlling individual pixels in high-resolution displays.

In research described in the journal Science Advances, the technique developed for getting the carbon nanotubes onto the surface eschews the use of inkjet printing techniques, which have been thought to be way forward in this application space. Instead they turned to a rather old printing technique: the stamp.

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Image of Mona Lisa that appears and disappears

Novel Nanomaterial Enables Rewritable Optical Circuits

Researchers at the University of Texas at Austin have developed a hybrid nanomaterial that enables the writing, erasing and rewriting of optical components. The researchers believe that this nanomaterial and the techniques used in exploiting it could create a new generation of optical chips and circuits.

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Droplets of ‘photonic water’ can change color by using chemical or magnetic forces to adjust the alignment of internal stacks of reflective nanosheet crystals

'Photonic Water' Could Be Boon for Optoelectronic Applications

A two-dimensional metal oxide material called titanate nanosheets has remained pretty much off the radar of flatland materials expected to transform the worlds of electronics and optoelectronics. Its biggest claim to fame has been that it is pretty effective at cleaning up contaminants.

However, it would seem that titanate nanosheets history of being overlooked  in the catalogue of 2D materials may have come to an end thanks to a serendipitous discovery by researchers in Japan.

Researchers at the RIKEN Center for Emergent Matter Science in Japan were experimenting with the material to see if they could get the nanosheets to break into more uniform pieces rather than the varied sizes they typically take. Unfortunately, they weren’t able to solve this problem. But they did discover that when the material was centrifuged in water, it changed from being transparent to taking on a deep purple color.

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TEM image of sulphur-filled PPy-MnO2 coaxial nanotubes.

Novel Electrode Structure Provides New Promise for Lithium-Sulfur Batteries

Lithium-sulfur batteries (Li-S) can hold as much as five times the energy per unit mass that lithium-ion (Li-ion) batteries can. However, Li-S batteries suffer from the propensity for polysulfides to pass through the cathode, foul the electrolyte, then pass through to the other electrode, depleting it of sulfur after just a few charge-discharge cycles. This phenomenon is known as the “shuttle effect.”

Now researchers at the University of Texas at Austin have developed an electrode structure for a Li-S battery that makes use of coaxial polypyrrole-manganese dioxide (PPy-MnO2) nanotubes. This novel electrode combats the shuttle effect by essentially encapsulating the electrodes with the nanotubes.

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Graphene-based NFC antenna is flexible

Graphene-based Antenna Still Looking for Path to Commercialization

Graphene is a pure conductor, just like a metal, which has led researchers to examine applications like antennas to see if graphene could serve as a replacement.

Along this line of inquiry, researchers at the National Research Council Institute for Organic Synthesis and Photoreactivity (CNR-ISOF) in Italy, which is part of Europe’s Graphene Flagship,  have developed a graphene-based near-field communication (NFC) antenna. Unlike today’s NFC antennas their devices are flexibile and have greater durability.

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DGIST's senior researcher Jeong Min-kyung

First Graphene Photodetector To Operate in the Microwave

While graphene may be losing its luster in the field of digital electronics because of its lack of an inherent band gap,  in the world of optoelectronics graphene’s gapless band structure seems to be winning a new set of acolytes. This is seen no more keenly than in photodetectors, where graphene is enabling near-terahertz-speed photodetectors that are more energy efficient.

Now, researchers at the Daegu Gyeongbuk Institute of Science and Technology (DGIST) in South Korea and the University of Basel in Switzerland have developed a new graphene-based photodetector that operates at microwave wavelengths—a departure from graphene photodetectors that detect only optical wavelengths from the near-infrared to ultraviolet light.

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Schematic of the mono- and bilayer crystal structures. Purple and red spheres correspond to indium and selenium atoms, respectively.

Indium Selenide Takes on the Mantle of the New Wonder Material

Is there a research institute with a more distinguished pedigree in graphene research than the University of Manchester? There certainly haven’t been any that have “gone all in” the way Manchester has with its construction of a $71 million graphene research facility near the campus, which is operated under the auspices of the newly established National Graphene Institute (NGI).

This dedication to graphene makes sense considering the fact that Andre Geim and Konstantin Novoselov were at Manchester when they became the first researchers to synthesize graphene—the advance for which they were awarded the 2010 Nobel Prize in Physics.

But now it appears that a new material developed at Manchester, based on indium selenide (InSe), has taken some of graphene’s spotlight at Manchester, at least in terms of meeting the demands of future super-fast electronics.

“Ultra-thin InSe seems to offer the golden middle between silicon and graphene,” said Geim in a press release. “Similar to graphene, InSe offers a naturally thin body, allowing scaling to the true nanometer dimensions. Similar to silicon, InSe is a very good semiconductor.”

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The optical image of a folded graphene oxide film looks like baked filo dough

Graphene Solar Absorber Could Enable Cheap Thermal Desalination

To those uninitiated to the costs of thermal desalination of water, the idea of simply vaporizing water to take out the impurities seems like it would offer a limitless supply of fresh water just by using it on the world’s oceans. However, the energy costs for thermal desalination has been estimated at around 80 megawatt-hours per megaliter of water produced, rendering it too costly for just about everyone except Gulf States rich in oil and desperate for fresh water.

One way around these high-energy costs has been thought to be solar-powered thermal desalination, which can help produce clean water in remote areas and developing countries. However, the solar approach to water desalination is rather limited in the amount of fresh water it can produce and is further hampered by the need for optical concentrators and for thermal insulation, both of which have limited the large-scale use of this approach.

Now researchers at Nanjing University in China have developed a solar absorber material made from graphene oxide that enables a solar approach to desalinating water without the need for solar concentrators and thermal insulation. The result could be a low-cost, portable water desalination solution ideally suited for developing countries and remote areas.

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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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