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Electricity Makes Mortar for Nanotube Bricks

Each allotrope of carbon—diamond, graphite, graphene, and fullerenes—has its unique set of interesting properties. So finding a way to get carbon to form a hybrid of these allotropes has been an enticing concept. The problem with making such hybrids is that it usually entails extreme chemical, temperature, or pressure conditions, leading to a lack of control over the final product.

Now researchers from Northeastern University, MIT, and the Korea Advanced Institute of Science and Technology (KAIST) have developed a simple, highly-scalable method for creating inter-allotropic transformations and hybridizations of carbon that appear across large-area ​carbon networks. Using alternating pulses of electricity across single-walled carbon nanotubes (SWNTs) they transform them into larger-diameter SWNTs, multi-walled CNTs of varying morphologies, or multi-layered graphene nanoribbons. They reported the details in  the journal Nature Communications.

The key feature of the method is that it produces molecular junctions for the carbon nanotubes that have superior electrical and thermal conductivity compared to carbon nanotubes arrays that are junction-free.

To visualize the difference between a CNT array with molecular junctions and one without, the researchers say that the one without is like a wall of bricks without mortar, while the one with molecular junctions is like a brick wall made using mortar.

“We have filled in the gaps with cement,” said co-​​author Swastik Kar, an assistant pro­fessor of physics at Northeastern, in the press release. “We started with single-​​walled carbon nanotubes,” he added, “and then used this pioneering method to bring them together.”

The researchers believe that CNT arrays using these junctions could be useful for reinforcing composite materials. In the last few years, we have begun to see the use of CNTs in composites that actually improve the strength of the composite as opposed to just replacing a regular resin material. (In research back in 2012, scientists in Switzerland demonstrated how using magnetic forces could orient the carbon nanotubes in the composite to impart even greater strength.)

While stronger composites are indeed an attractive characteristic for these new CNT arrays, their improved electrical and thermal conductivity properties should be attractive for electronic applications as well.

Electronic Skin Made From Nanoparticles Offers Early Breast Cancer Detection

Researchers at the Nebraska Center for Materials and Nanoscience at the University of Nebraska have developed a prototype electronic skin made from nanoparticles that they claim can offer an early detection method for breast cancer.

The researchers, who published their findings in the journal ACS Applied Materials & Interfaces, developed a thin-film tactile device, also known as “electronic skin”, in which the contact pressure that corresponds to the shape of the object can be mapped by measuring the local deformation of the tactile-device film.

The research team built the tactile device layer-by-layer using spin coating of polymers in combination with the deposition of 10-nanometer (nm) gold nanoparticles, which are often used in cancer detection and treatment techniques—along with 3-nm cadmium sulfide nanoparticles. The overall multilayer structure consisted of three layers of gold nanoparticles and two layers of cadmium sulfide nanoparticles separated by nine layers of the polymers. All of this was then deposited onto a indium-tin oxide (ITO) glass substrate. The ITO served as the bottom electrode while aluminum foil was used as the top electrode.

In their tests, the researchers embedded objects that simulated lumps into a piece of silicone and pressed the device against it with the same pressure a clinician would use during a breast exam.

The results were significantly better than what a doctor might be able to detect. With the device, the researchers were able to detect an artificial lump as small as 5 millimeters wide that was embedded 20 mm into the silicone.

This compares favorably to clinical breast exams performed by medical professionals, in which they typically don’t find lumps as large as 21 mm wide. It's estimated that if doctors were able to detect irregularities when they’re half the size of those missed 21-mm lumps, a patient’s chances of survival would improve by more than 94 percent.

This test also offers some benefits over other detection techniques, such as magnetic resonance imaging (MRI), which can be very expensive, and mammography, which is often inadequate for young women or women with dense breast tissue.

The researchers also note that it could be used to screen patients for early signs of melanoma and other cancers.

Is the "Buckydiamondoid" the Future of Molecular Electronics?

What happens when you combine a buckyball with a diamondoid? As it turns out something wonderful for the prospects of molecular electronics. In fact, you get a new kind of material that conducts electricity in just one direction.

This conducting of electricity in one direction is the role of rectifiers, which take the form of diodes in computer chips. By shrinking these diodes down to the size of a nanoparticle it could shrink chip size while making devices faster and more powerful.

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First Graphene-enabled Flexible Display Demonstrated

In the UK’s concerted efforts to become a hub for graphene commercialization, one of the key partnerships between academic research and industry has been the one between the Cambridge Graphene Centre located at the University of Cambridge and a number of companies, including Nokia, Dyson, BaE systems, Philips and Plastic Logic. The last on this list, Plastic Logic, was spun out originally from the University of Cambridge in 2000. However, since its beginnings it has required a $200 million investment from RusNano to keep itself afloat back in 2011 for a time called Mountain View, California, home.

Nonetheless, it seems the connections to the old alma mater are still strong. Plastic Logic has developed in partnership with the Cambridge Graphene Centre for what it claims is the first graphene-based flexible display ever produced.

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Nanowire Circuit Guides Both Electricity and Light on the Same Wire

The field of plasmonics—the use surface plasmons generated when photons hit a metal structure—might enable photonic circuits that could do what electronic ICs do, but do it much faster—at the speed of light.  Without plasmonics, photonic circuits would be too large, because they need to accommodate wavelength of light.

In a step toward that goal, a joint research team from the University of Rochester and the Swiss Federal Institute of Technology in Zurich have developed a primitive circuit consisting of a silver nanowire and single-layer flake of molybdenum disulfide (MoS2). This simple circuit can efficiently guide both electricity and light along the same wire.

In the experiment, which was published in the journal Optica, a laser was used to trigger the plasmons on the surface of the wire. The plasmons coming off the nanowire triggered a photoluminescence in the MoS2, which is a two-dimensional material like graphene but has an inherent band gap. Excitons—basically energized electrons bound to positively charged holes that form when light hits a semiconductor—form in the MoS2, and decay into the nanowire plasmons. So, the international team demonstrated that the nanowire serves the dual purpose of exciting the MoS2 via plasmons and recollecting the decaying exciton as nanowire plasmons.

“We have found that there is pronounced nanoscale light-matter interaction between plasmons and atomically thin material that can be exploited for nanophotonic integrated circuits,” said Nick Vamivakas, assistant professor at the University of Rochester, in the press release.

The combination of subwavelength light guidiance and strong nanoscale light-matter interaction they demonstrated could help lead to compact and efficient on-chip optical processing, the researchers believe.

The next step in their research will be to demonstrate the primitive circuit with light emitting diodes.

Carbon Nanotubes Make a Comeback in Photovoltaics

Carbon nanotubes (CNTs) have had a bit of a hard time of it lately. A few years back the National Institute of Standards and Technology (NIST) reported that CNTs have a major reliability problem when applied to electronics. In photovoltaics the prognosis hasn’t been much better. Despite efforts from some research teams to use CNTs instead of silicon as the basic element for converting light to energy for a solar cell, they simply haven’t proven themselves to be very efficient in energy conversion.

Now researchers at Northwestern University may have turned around the fortunes of CNTs, at least for photovoltaic applications, by demonstrating that they can make solar cells based on CNTs that are twice as efficient at energy conversion than its predecessors.

"The field had been hovering around 1 percent efficiency for about a decade; it had really plateaued," said Mark Hersam, a professor at Northwestern, in a news release. "But we've been able to increase it to over 3 percent. It's a significant jump."

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Nanoparticles Enable New Levels of Holographic Optical Data Storage

By exploiting the same properties of nanoparticles that made the Lycurgus Cup change colors depending on the light hitting it, researchers at the University of Cambridge have used nanoparticles to create holograms that could store twice as much information as today’s digital optical devices.

In research published in the journal Proceedings of the National Academy of Sciences,  the UK team used a thin film of silver nanoparticles to produce multicolor holograms.The nanoparticles create interference that allows the holograms to go beyond the normal limits of diffraction.

The nanoparticles are able to go beyond the normal diffraction limits by exploiting plasmonics, which takes advantage of oscillations in the density of electrons that are generated when photons hit a metal surface. Plasmonics has a number of potential applications, including transmitting data on computer chips and producing high-resolution lithography.

“This technology will lead to a new range of applications in the area of photonics, as conventional optical components simply cannot achieve this kind of functionality,” said Yunuen Montelongo, a PhD student from the Cambridge engineering department, who led the research, in a press release. “The potential of this technology will be realized when they are mass produced and integrated into the next generation of ultra-thin consumer electronics.”

In the device, each nanoparticle scatters light into varying colors depending on its size and shape. The scattered light from all the nanoparticles interacts and combines with each other to produce an image.

Among some of the unusual effects that can be produced by this device is its ability to display different images when illuminated with different color light and its ability to produce a multi-color image when multiple light sources are focused on it.

“This hologram may find a wide range of applications in the area of displays, optical data storage, and sensors,” said PhD student Calum Williams, a co-author of the paper. “However, scalable approaches are needed to fulfill the potential of this technology.”

Graphene Drumheads Could Lead to New Sensors for Mobile Phones

Just over two years ago, we reported on research out of the National Institute of Standards and Technology (NIST) and the University of Maryland that discovered graphene could be manipulated to act like a drumhead giving it electromechanical properties.

Following along this line of research, a team of scientists at the TU Delft’s Kavli Institute of Nanoscience in the Netherlands has demonstrated that using this drumhead principal for graphene could lead to new types of sensors for mobile phones, or even quantum memory used in quantum computing.

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Nanoscale Material Enables Cheap, Emission-free Hydrogen Production

When it comes to separating hydrogen from the water molecule, it’s like the old Neil Sedaka song said: “Breaking up is hard to do.” It is so difficult, in fact, that the production of hydrogen gas has been one of the main obstacles in the deployment of fuel cellbased vehicles.

Now researchers at Stanford University have developed a nanoscale material that makes it possible to split water cheaply using just a 1.5-volt "AAA" battery, and they claim it can be done without producing any emissions. 

We've previously reported on the work done by Hongjie Dai, who has spent years working on developing better catalysts for fuel cells, including some employing carbon nanotubes. But this time, instead of focusing on the fuel cell itself, Dai has turned his eye towards ways of generating the hydrogen to feed the fuel cells.

Dai’s previous work, which examined how carbon nanotubes could replace more expensive catalysts used in oxidizing the hydrogen at the anode within the fuel cell, indirectly came into play here. Since the process inside the fuel cell is the mirror opposite of what is needed to split water, this latest work, which was published in the journal Nature Communications, is somewhat along the same lines. It involves using an inexpensive nanomaterial made from nickel and iron in place of platinum as the catalyst in the water-splitting reaction.

“Using nickel and iron, which are cheap materials, we were able to make the electrocatalysts active enough to split water at room temperature with a single 1.5-volt battery," said Dai, in a press release. "This is the first time anyone has used non-precious metal catalysts to split water at a voltage that low. It's quite remarkable, because normally you need expensive metals, like platinum or iridium, to achieve that voltage."

Dai further describes the water-splitting device and its implications in the video below.

While there has been much research into using nanomaterials for hydrogen separation, previous efforts to produce hydrogen gas on an industrial scale without first generating hot steam in an energy-intensive process with carbon dioxide as a byproduct were unsuccessful.

"It's been a constant pursuit for decades to make low-cost electrocatalysts with high activity and long durability," Dai says. "When we found out that a nickel-based catalyst is as effective as platinum, it came as a complete surprise."

A surprise indeed. In fact, the Stanford researchers don’t even understand the science that makes the novel nickel-metal/nickel-oxide nanomaterial perform the way it does.

However, the researchers do know that it works.

One area where continued research might yield improvement is durability. The material, say the Stanford engineers, doesn’t last as long as hoped, and certainly not long enough for an industrial application.

"The electrodes are fairly stable, but they do slowly decay over time," said Ming Gong, the graduate student who discovered the material, in a press release. "The current device would probably run for days, but weeks or months would be preferable. That goal is achievable based on my most recent results"

Dai added: "We're very glad that we were able to make a catalyst that's very active and low cost. This shows that through nanoscale engineering of materials we can really make a difference in how we make fuels and consume energy."

A close up look at a pile of multicolor rubber bands of many sizes.

Graphene and Rubber Bands Could Revolutionize Health Monitoring

One of graphene’s most attractive properties is its flexibility. It’s this property that has led researchers to consider using it to replace for indium tin oxide (ITO) in the electrodes of organic solar cells. Researchers at the University of Surrey and Trinity College may have found another use for that flexibility—adding graphene to rubber bands to give elastics electronic properties and using the combination for health monitoring.

In research published in the journal ACS Nano,  the researchers explain a simple process for infusing graphene into elastic bands such that they become extremely sensitive strain sensors.

The researchers claim that the sensors are extremely cheap to produce and could be used as wearable sensors for monitoring a patient's breathing, heart rate, or irregular movements.

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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
New York City
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