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Nanofilm Serves as Artificial Retina

Israel-based Nano Retina made some noise a few years back with its development of so-called “nanoelectrodes” that “interface with the eye’s bipolar neurons” and restart neural stimulation, allowing for messages to go to the brain. The nanoelectrodes served as a kind of artificial retina.

Since then it doesn’t appear that Nano Retina has had much more to report on the development of its implantable device, at least from what its website reveals. But it other Israeli researchers do, in a paper published in the journal Nano Letters. The team from Tel Aviv University, the Hebrew University of Jerusalem Centers for Nanoscience and Nanotechnology and Newcastle University combined semiconductor nanorods and carbon nanotubes to create a wireless, light-sensitive, flexible film that could potentially act in the place of a damaged retina.

The researchers used a plasma polymerized acrylic acid midlayer to make covalent bonds with the semiconductor nanorods directly onto neuro-adhesive, three-dimensional carbon nanotube surfaces.

The researchers have tested the device in a chick’s retina that in normal conditions would not have responded to light. These tests demonstrated that the flexible film absorbed light, which then triggered neuronal activity in the chick.

The researchers claim that this film is more durable, flexible and efficient, as well as better able to stimulate neurons, compared to other competitive devices. While there have been a number of approaches to creating artificial retinas to address diseases of the retina, such as macular degeneration, the stumbling block has largely been getting the device to fit inside the eye itself.

This is why solutions such as Nano Retina’s nanoelectrodes have been so attractive. It would seem, based Nano Retina’s reticence since its initial announcement, that the engineering issues are significant even with a nanoscale solution. Whether this latest research can find a way around them remains to be seen.

Each Nanopore in a Material Serves as a Battery

We have seen batteries get so small that their anodes consist of a single nanowire. In that instance, the research was not really aimed at creating a new battery design but instead at demonstrating that the researchers could use a liquid electrolyte in the vacuum of a transmission electron microscope (TEM).

In contrast, researchers at the University of Maryland have their focus on building a new type of battery that is based on tiny nanopores in a ceramic material. The researchers have developed a method for introducing an electrolyte into the nanopores so that each cavity acts as an individual battery cell and all of them are joined in parallel.

Commenting on their research, published in the journal Nature Nanotechnology, the Maryland researchers note that: “a single nanopore structure that embeds all components of an electrochemical storage device could bring about the ultimate miniaturization in energy storage.”

In the video below, one of the authors of the paper, Chanyuan Liu, explains that the battery they developed in the lab can undergo one thousands charge/discharge cycles. It can be fully charged in 12 minutes, she adds in the press release.

Eleanor Gillette, another member of the group, says in the video that the aim is to develop the manufacturing technology to make larger nanopore  structures possible. Liu says that they have already identified ways to increase the power of the batteries by ten times.

The entire design of the battery involves each of its nanobattery components being composed of an anode, a cathode, and a liquid electrolyte confined within the nanopores of anodic aluminium oxide, which is an advanced ceramic material. Each nanoelectrode includes an outer ruthenium nanotube current collector and an inner nanotube of vanadium pentoxide storage material. These together form a symmetric full nanopore storage cell with anode and cathode separated by an electrolyte region. The vanadium pentoxide is treated with lithium at one end to serve as the anode, with pristine vanadium pentoxide at the other end serving as the cathode.

The researchers believe that the key to the success of the design is the uniformity in shape and size of the nanopores, which allows for a dense packing of the nanopores into the ceramic material.

Graphene-based Supercapacitors Take Another Crack at All-electric Vehicles

Researchers at the Queensland University of Technology (QUT) in Australia have developed a supercapacitor featuring graphene carbon nanotube films. They’re confident that their creation could dramatically boost the power and range of all-electric vehicles that now rely on lithium-ion (Li-ion) batteries for propulsion.

In research that was published in both the Journal of Power Sources and Nanotechnology, the Australian researchers used graphene films as the electrodes and carbon nanotube films as current collectors. The result was devices demonstrating energy densities ranging from  8 to 14 watt-hours per kilogram, and power densities between 250 and 450 kilowatts per kilogram.

The hope has been that someone could make graphene electrodes for supercapacitors that would boost their energy density into the range of chemical-based batteries. The supercapacitors currently on the market have on average an energy density around 28 Wh/kg, whereas a Li-ion battery holds about 200Wh/kg. That’s a big gap to fill.

The research in the field thus far has indicated that graphene’s achievable surface area in real devices—the factor that determines how many ions a supercapacitor electrode can store, and therefore its energy density—is not any better than traditional activated carbon. In fact, it may not be much better than a used cigarette butt.

Though graphene may not help increase supercapacitors’ energy density, its usefulness in this application may lie in the fact that its natural high conductivity will allow superconductors to operate at higher frequencies than those that are currently on the market. Another likely benefit that graphene will yield comes from the fact that it can be structured and scaled down, unlike other supercapacitor materials.

It is this ability to be molded into various shapes that the Australian researchers hope to exploit; they suggest that the supercapacitor films they have developed could be used to line parts of a car’s chassis to offer a quick energy boost to all-electric vehicles using Li-ion batteries.

"Vehicles need an extra energy spurt for acceleration, and this is where supercapacitors come in. They hold a limited amount of charge, but they are able to deliver it very quickly, making them the perfect complement to mass-storage batteries," said Marco Notarianni, a QUT researcher, in a press release.

Notarianni added: "Supercapacitors offer a high power output in a short time, meaning a faster acceleration rate of the car and a charging time of just a few minutes, compared to several hours for a standard electric car battery."

Graphene-based supercapacitors have been a bit of a disappointment to those who envisioned them completely replacing lithium-ion (Li-ion) batteries for powering all-electric vehicles.  This latest complementary role suggested by the Australian researchers may be a way to see them put to some use.

However, it’s not clear that the energy density numbers achieved during this latest round of research have given us any reason to think that a graphene-based supercapacitor will be the route leading to an all-electric vehicle that operates solely on supercapacitors.

Nanodiamond Production Technique Opens Up Electronic Applications

With news just last week that nanodiamonds could aid in the development of new methods for drug delivery and cancer therapeutics, the prospects for successful cancer treatment got a shot in the arm.

While medical applications for nanodiamonds got a boost, it left the fortunes of nanodiamonds in electronics-related applications a bit out in the cold. The wait was not long, however, with research out of Purdue University that demonstrated a pulsed laser could be used to create synthetic nanodiamond films and patterns on the surface of graphite. This development should have an impact on potential applications for nanodiamonds including biosensors, quantum computing, fuel cells and next-generation computer chips.

"The biggest advantage is that you can selectively deposit nanodiamond on rigid surfaces without the high temperatures and pressures normally needed to produce synthetic diamond," said Gary Cheng, an associate professor of industrial engineering at Purdue University, in a press release. "We do this at room temperature and without a high temperature and pressure chamber, so this process could significantly lower the cost of making diamond. In addition, we realize a direct writing technique that could selectively write nanodiamond in designed patterns."

In research published in the Nature journal Scientific Reports, the Purdue team started with a multilayered film containing a layer of graphite and covered with a glass sheet. They then exposed this layered structure to an ultra-fast pulsing laser that instantaneously transformed the graphite into an ionized plasma that generates a downward pressure. The graphite plasma is prevented from escaping by the glass cover of the multilayered film where, trapped, it quickly solidifies into diamond.

"These are super-small diamonds and the coating is super-strong, so it could be used for high-temperature sensors," Cheng said in the release.

Strength was always the aim of the research. In fact, the technique was originally developed to find a way to strengthen metals. It was only serendipitously that they discovered that it produced this nanodiamond film.

With this development, the researchers believe nanodiamonds could begin to have an impact in electronics. For instance, nanodiamonds have been suggested as a way to get quantum computers to operate at room temperature as opposed to near absolute zero. This would be accomplished by replacing the ions used in some quantum computers with nitrogen-vacancy centers in diamonds.

Nanodiamonds could also lead to next-generation computer chips based on optical transitors in which photons replace electrons. In this scenario, nanodiamonds would replace the special dye molecules that are used in today’s optical transistors. The use of these dyes requires special cooling, which eliminates them from practical use. However, researchers at the Institute of Photonics Sciences (ICFO) in Barcelona demonstrated last year showed that nanodiamond operating at room temperature could be used in an ultrafast optical switch, replacing the dye molecules.

New Method for Producing Molybdenum Disulfide Provides Two Potential Applications

Molybdenum disulfide (MoS2) started out as the next big thing after graphene in electronic applications. But that excitement started to wane somewhat when it was revealed that MoS2 contained traps—impurities or dislocations that can trap an electron or hole and hold it until a pair is completed—that limit its electronic properties.

While researchers continue to work on removing those traps in order to improve its electronic properties, others have been looking at uses for MoS2 outside of digital electronics in applications including photovoltaics and wearable electronics.

In this ever-expanding application universe, researchers at Rice University have found a method for manipulating MoS2 so that it could serve both as an improved catalyst for fuel cells and as the electrodes of supercapacitors.

In research published in the journal Advanced Materials, the Rice team, led by James Tour, developed a simple method for producing flexible films made from MoS2 that orients the material on its sides. In other words, they made the material in such a way that the maxiumum amount of its edges are exposed.

The researchers showed that when oriented in this manner, the MoS2 can serve as an effective catalyst in the hydrogen evolution reaction (HER), a process used in fuel cells to pull hydrogen from water.

“So much of chemistry occurs at the edges of materials,” said Tour in a press release. “A two-dimensional material is like a sheet of paper: a large plane with very little edge. But our material is highly porous. What we see in the images are short, 5- to 6-nanometer planes and a lot of edge, as though the material had bore holes drilled all the way through.”

Tour added: “Its performance as a HER generator is as good as any molybdenum disulfide structure that has ever been seen, and it’s really easy to make.”

Other research has attempted to take advantage of MoS2 as a catalyst for fuel cells by standing them up on their sides. The Rice team took a different approach. First, they grew a porous molybdenum oxide film onto a molybdenum substrate through room-temperature anodization, an electrochemical process for thickening metal parts by adding a natural oxide layer.

The researchers then exposed the film to sulfur vapor at 300 °C (572 °F) for one hour. The result was molybdenum disulfide that had a flexible, nano-porous sponge-like structure.

Since the key to catalysts and to the electrodes in supercapacitors is surface area, the researchers immediately realized that the material would fit the bill for both applications. The Rice team developed a supercapacitor using the material and found the device retained 90 percent of its capacity after 10,000 charge-discharge cycles and 83 percent after 20,000 cycles.

Tour believes that this method of exploiting anodization could serve as a platform for a range of applications and devices.

“We see anodization as a route to materials for multiple platforms in the next generation of alternative energy devices,” Tour said. “These could be fuel cells, supercapacitors and batteries. And we’ve demonstrated two of those three are possible with this new material.”

Nanomaterial Promises to Reduce Shutdowns of Concentrating Solar Power Plants

Researchers at the University of California at San Diego have developed a composite nanomaterial that can convert 90 percent of the sunlight it captures into heat, making it an ideal candidate for solar absorption at concentrating solar power (CSP) plants.

"We wanted to create a material that absorbs sunlight [and] doesn't let any of it escape. We want the black hole of sunlight," said Sungho Jin, a professor at UC San Diego, in a press release.

The hybrid material, which is described in the journal Nano Energy,  combines copper oxide nanowires with cobalt oxide nanoparticles to create a multi-scale surface for the material with dimensions ranging from 10 nanometers to micrometers. This multi-scale surface gives the material its extraordinary efficiency at trapping and absorbing light.

Previous research has proposed the use of nanowires for concentrating the sun’s rays into a very small area of solar cells. And copper sulfide nanoparticles in combination with single-walled carbon nanotubes have proven effective in converting both light and thermal radiation into electricity.

In contrast to these other nanomaterials, which were intended for use in photovoltaics that convert light directly into electricity, the hybrid material developed by the UCSD team is being targeted for solar absorption to create heat. The heat is then used to boil water, which in turn creates steam that runs turbines to produce electricity.

The materials that are currently used for solar absorption lack the resistance to high temperatures that the job requires. As a result, they have to be replaced every year. This new hybrid material is unique in that it can withstand temperatures above 700 degrees Celsius.

This should make a significant difference for CSP plants that, as it stands now, have to shut down once a year to remove the degraded sunlight-absorbing material and apply a new coating. Because this means that there is no power generation occurring during this reapplication, the U.S. Department of Energy’s SunShot program was keen to support this most recent research to find a material that would have a significantly longer life span.

With CSP plants already producing approximately 3.5 gigawatts of power globally, the prospect of eliminating an annual shutdown and extending the maintenance interval to several years would make a big difference to the amount of electricity they produce and the confidence people have in this source of electricity.

Nanodiamonds Could Become Mankind's Best Friend

Researchers at Cardiff University in Wales have developed a new method for taking readings of processes going on inside living cells. The technique, which relies on nanodiamonds, could eventually aid in developing new modes of drug delivery and cancer therapeutics.

The traditional method for imaging cellular processes has depended on fluorophores, which are a fluorescent chemical compound that can re-emit light upon light excitation. But they degrade under the light used to illuminate them. This renders them ineffective as visualization targets after a short period of time. Furthermore, fluorophores have been shown to become toxic over time, sometimes killing nearby cells.

Nanodiamonds have been proposed as a one-to-one replacement for fluorophores for sometime now. But getting them to fluoresce required designing small defects into them. Manufacturing these defects into the diamonds proved to be costly and time consuming.

In research published in the journal Nature Nanotechnology, the Cardiff researchers developed a new method wherein the nanodiamonds are used differently, thus eliminating the need for this difficult trick of producing them with specific defects.

Instead, the Cardiff team demonstrated that nanodiamonds without defects can be imaged optically through the interaction between the illuminating light and the vibration of the chemical bonds inside the diamond lattice structure. These vibrations cause the light to scatter in such a way that they produce a different color.

To get this effect, the researchers used two laser beams pulsing at a specific frequency so that laser light triggers the chemical bonds inside the nanodiamonds to vibrate in sync. The researchers then focus one of two lasers at these vibrations, which produces a light known as, coherent anti-Stokes Raman scattering (CARS).

The researchers were then able to use a microscope to measure the intensity of the CARS light on a series of nanodiamonds of varying sizes. After using electron microscopy and other optical contrast methods developed by the researchers, the team was able to accurately measure the sizes of the diamonds. This then made it possible to quantify the relationship between the size of the nanodiamonds and the intensity of light that they produce.

The end result was a method that allowed the researchers to measure the size and number of nanodiamonds that had been delivered into the living cells.

“This new imaging modality opens the exciting prospect of following complex cellular trafficking pathways quantitatively with important applications in drug delivery,” said Paola Borri from the School of Biosciences, who led the study, in a press release. “The next step for us will be to push the technique to detect nanodiamonds of even smaller sizes than what we have shown so far and to demonstrate a specific application in drug delivery.”

DNA Can Carry Current, a Promising Step Toward Molecular Electronics

The promise of molecular electronics gets hoisted up the flagpole periodically, but now an international team of researchers based out of the Hebrew University of Jerusalem claim to have made a breakthrough with DNA molecules that they believe may be the most significant development in the last decade of molecular electronics research.

In research published in the journal Nature Nanotechnology,  a international group of researchers hailing from Cyprus, Denmark, Italy, Spain, and the United States has demonstrated that electric current can be transmitted through long DNA molecules. They believe that this demonstration could lead to the development of DNA-based electronic circuits.

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Super-Black Nanotube Coating Could Reveal Space Obscured by the Sun's Glare

When astronomers want to see objects that are extremely faint, they call on powerful and sensitive instruments to make them clear. The problem is that these instruments are so sensitive, the slightest bit of stray light can simply overwhelm them, making it impossible to resolve the faint object over the other light.

To overcome this problem, telescopes and other deep-space imaging devices use something called a coronagraph, a telescope attachment that blocks out stray light coming into the telescope as the instrument attempts to resolve dimmer objects that may be washed out by the light.

This fall, NASA researchers on the International Space Station will test a new super-black carbon nanotube coating that promises to make these coronagraphs even more effective.

The NASA researchers were compelled to look for a new coating for coronagraphs to deal with the special challenges brought on by a new, compact coronagraph NASA had developed that is roughly half the mass, volume, and cost of today’s coronagraphs. But with this smaller size come greater demands on the instrument.

"Compact coronagraphs make greater demands on controlling stray light and diffraction," said Doug Rabin, a Goddard heliophysicist who studies diffraction and stray light in coronagraphs, in a press release. Rabin expects that the nanotube coating should be better at preventing stray light from reaching the focal plane of the instrument than the black paint currently used.

While space-based testing, meant to see how the coating responds to the environment of space is taking place, researchers at NASA’s Goddard Space Flight Center in Greenbelt, MD, will use the material to coat a cylindrically shaped coronagraph.

If both tests prove successful, the carbon nanotube coating would replace the black paint that is currently used on coronagraphs.  The enhanced coronagraph would not be limited to just the International Space Station, will likely also be used on commercial satellites that make critical space-weather-related measurements.

"We've made great progress on the coating," said Goddard optics engineer John Hagopian, in a press release. "The fact the coatings have survived the trip to the space station already has raised the maturity of the technology to a level that qualifies them for flight use. In many ways the external exposure of the samples on the space station subjects them to a much harsher environment than components will ever see inside of an instrument."

Skyrmions: Communication With Magnetic Swirls Instead of Electrons

A year ago, a team at the University of Hamburg showed that one could use skyrmions—tiny, swirling magnetic spin patterns in thin films—to store and erase data on magnetic media.

Because these patterns are much smaller than the magnetic domains in magnetic media such as today’s hard disks, this would raise the limit on data storage density. However, the team only proved that this could be done at a temperature of 4 K, and would require the application of a magnetic field to stabilize the patterns.

Now, Hamburg researchers have reported in Nature Nanotechnology how they created molecular magnets in a skyrmionic lattice without the need of an external magnetic field. These skyrmions, they say, also survive at room temperature. To form the skyrmion lattice, they used a single atomic layer of iron deposited on an iridium substrate. This layer has some interesting magnetic properties resembling antiferromagnetism. Looking at a small area of an antiferromagnetic lattice, you can observe two spins pointing up and two spins pointing down, and no net magnetic moment, explains Jens Brede, a physicist at the University of Hamburg and co-author of the paper.

“It is more complicated in a skyrmion lattice because the spins rotate, but roughly in a one-by-one-nanometer area you have as many spins pointing in one direction as the other, and therefore you have no net magnetic moment, and it does not react to an external magnetic field,” says Brede.

Now the researchers have found a way to create small magnetic islands on the skyrmion lattice by depositing single hydrocarbon molecules comprising six benzene rings atop the iron. “These molecules form a new way for the iron atoms directly below them to couple, and locally destroy the skyrmion, resulting in a tiny magnet in the skyrmion lattice,” says Brede.

These magnets, formally known as organic-ferromagnetic units, can have their magnetization switched up or down by an external magnetic field. “You can store information in them, but what is more interesting is that when you switch one of these little magnets, the skyrmion around it reacts,” says Brede. This has an interesting consequence: if you switch the magnetic field in one tiny magnet, the magnetization of another magnet at a distance of several nanometers will flip as well.

The skyrmion lattice is comparable to a compass array: a board carrying many magnetic needles that interact with each other like spins do. If you turn one needle, the other needles react by rotating to reestablish a lower energy level of the array. “This way you can transfer information from one magnetic molecule, through the skyrmion lattice, to the next one,” says Brede. “We saw this process of transferring information in this way for a distance of more than 10 nanometers; for magnetic interactions, this is a very long distance,” says Brede.

These magnetic interactions open the door for using the organic-ferromagnetic units in logic devices and information processing, says Brede. It is unlikely that these magnetic molecules could become qubits in quantum computers, but skyrmion lattices could still play a role in quantum computing.

“The system that we have now is absolutely flat. But we have a third dimension available. So we can imagine that instead of the particular molecule that we use, we use another molecule that contains a qubit. Then you have the skyrmion lattice to couple this qubit to another qubit in some part far away. You can imagine using that for parallel processing in quantum computing.” says Brede.

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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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Rachel Courtland
Associate Editor, IEEE Spectrum
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