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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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terahertz imaging reveals defects in graphene

Novel Sensing Technique Developed for Graphene Electronics Manufacturing

Researchers at Rice and Osaka universities have developed a method for detecting impurities in graphene using terahertz waves. The joint research team believes that the method could provide a relatively simple way for anyone trying to use graphene for electronic applications to identify problems with the material early in the manufacturing process.

The new technique can identify a single foreign molecule on graphene. This is critically important in electronic applications where a single foreign molecule in graphene can corrupt its electrical properties. Before this work, in order to test those electrical properties you needed to attach contacts to the material, which itself could damage the graphene.

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Silicene's Suicidal Tendencies Can Be Overcome

Early this year, research indicated that silicene—essentially two-dimensional (2-D) silicon—had “suicidal tendencies”. As soon as you tried to layer silicene it would revert back to the crystal structure of silicon instead of maintaining its honeycomb structure.

Now an international team of researchers claims to have proven the stability of silicene under these circumstances,  paving the way for it to compete in the growing world of 2-D materials.

The research, which was published in the journal 2D Materials,  demonstrated for the first time that thick, multilayer silicene films can be stable in air for at least 24 hours. While 24 hours doesn’t seem like a long time, it should give researchers a window of opportunity to perform more tests on the material to reveal its capabilities.

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"Holey" Graphene Boosts Energy Density of Supercapacitors

Image: California NanoSystems Institute/UCLA

A research team at the California NanoSystems Institute (CNSI) at UCLA has developed what they call a “holey graphene framework” that they claim can significantly boost the energy density of supercapacitors.

Graphene has been held out by some as a silver bullet for enabling supercapacitors to combine the quick recharge and large bursts of energy of capacitors with the high storage capacity of electrochemical batteries. But so far using graphene as a replacement for activated carbon on the electrodes of supercapacitors has fallen short of expectations. It seems that graphene-based electrodes don’t enable energy storage much better than activated carbon, but because they can operate a higher frequencies than most supercapacitors they can be applied in novel ways, such as being used as part of filtering circuits in AC rectifiers.

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A microscope slide with a ring of light surrounding a black square surrounding a white rectangle.

Graphene-based Sensor Brings New Wrinkle to Wearables

human os iconThe capabilities of wearable sensors seem to be expanding every day. However, for the most part these sensors have measured just physical attributes, like heart rate.

Now researchers at the University of Michigan have developed a graphene-based wearable sensor capable of detecting airborne chemicals that serve as indicators of medical conditions. For instance, the sensor could detect acetone, which is a biomarker for diabetes. Or it could detect abnormal levels of nitric oxide and oxygen, which would be an indicator of conditions such as high blood pressure, anemia, or lung disease.

"With our platform technology, we can measure a variety of chemicals at the same time, or modify the device to target specific chemicals. There are limitless possibilities," said Zhaohui Zhong, an associate professor at the University of Michigan, in a press release.

The researchers had to take a novel approach to how the nanosensor detect chemicals. In research, which was published in the journal Nature Communications, the Michigan researchers developed a sensing mechanism based on detecting molecular dipoles.

This sensing mechanism stands in contrast to most other nanosensors, which are based on detecting a change in charge density due to a molecule binding to the sensor.

"Nanoelectronic sensors typically depend on detecting charge transfer between the sensor and a molecule in air or in solution," said Girish Kulkarni, a doctoral candidate and one of the researchers, in a press release. "Instead of detecting molecular charge, we use a technique called heterodyne mixing, in which we look at the interaction between the dipoles associated with these molecules and the nanosensor at high frequencies."

The researchers claim that the graphene made this sensing technique possible, resulting in extremely fast response times of tenths of a second as opposed to tens or hundreds of seconds in existing technology. In addition to fast response times the sensors are highly sensitive, capable of detecting molecules with a concentration of a few parts per billion.

With these graphene-based sensors, the researchers have been able to put an entire chromatography system  on a single chip that is able to operate with very little power. With this setup, a badge-side device could be worn on the body to give continuous monitoring of health conditions.

Used Cigarette Filters Could Enable Next Generation of Supercapacitors

A number of lab-engineered nanomaterials have thus far just fallen short of providing a suitable alternative material for supercapacitor electrodes. But the answer may be found in the nearest ashtray. That's right: the much-despised cigarette butt may, in fact, offer the solution.

A group of researchers in South Korea has discovered that the material that makes up used cigarette butts outperforms carbon, graphene and carbon nanotubes in energy storage. 

The researchers, who published their findings in the journal Nanotechnology, took used cigarette filters and found that under a nitrogen-containing atmosphere, they could be transformed into a porous carbon material that by itself has a pore structure that is perfect for energy storage in the electrodes of supercapacitors.

Supercapacitors, also known as ultracapacitors or electrochemical double-layer capacitors (EDLCs), have held out the promise that they could store as much energy as electrochemical batteries such as lithium-ion batteries, but charge up in a matter of seconds and offer high power density for quick bursts of a large amount of energy. Supercapacitors are currently used for this purpose in applications such as powering cranes or buses.

What’s perhaps most attractive about cigarette butts for supercapacitors is that there is a seemingly endless supply of the discarded filters. According to the press release accompanying the research, there are an estimated 5.6 trillion used cigarettes, or 766,571 metric tons, being deposited into the environment every year. And if, on the off chance that it were possible to completely deplete the resource by using the butts to create these supercapacitor electrodes, doing so would still raise cheers at the fact that a way to eliminate the blight of cigarette butts had been found.

"Our study has shown that used-cigarette filters can be transformed into a high-performing carbon-based material using a simple one step process, which simultaneously offers a green solution to meeting the energy demands of society,” said Jongheop Yi, a professor at Seoul National University, and a coauthor of the study, in the press release. "Numerous countries are developing strict regulations to avoid the trillions of toxic and non-biodegradable used-cigarette filters that are disposed of into the environment each year—our method is just one way of achieving this."

The new material possesses the key features that an electrode storage material for supercapacitors would ideally have. It has a large surface area, but perhaps more critically, it has the proper distribution of pore sizes that makes it capable of utilizing a large amount of electrolyte ions and it has quick transfer mobility. It compares favorably to graphene, which has looked very attractive for the electrodes of supercapacitors because of its transfer mobility, but doesn’t really stack up to activated carbon in terms of surface area.

"A high-performing supercapacitor material should have a large surface area, which can be achieved by incorporating a large number of small pores into the material," said Yi in the release. "A combination of different pore sizes ensures that the material has high power densities, which is an essential property in a supercapacitor for the fast charging and discharging."

The bottom line is that in tests, the used-cigarette filters were capable of storing more electrical energy than commercially available carbon. They also beat previously published results for graphene and carbon nanotubes.

Just conjecture, but it would seem that cigarette manufacturers might be wise to invest in this technology since it offers a way to make an extra buck on each cigarette sold.



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
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