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Graphene Filter Could Change the Game in Nuclear Power Costs

Ever since Andre Geim and Konstantin Novoselov won the 2010 Nobel Prize in Physics for their production and study of graphene, Geim has dedicated a significant amount of his research efforts to the use of graphene as a filtering medium in various separation technologies such as water desalination and gas separation.

This focus makes sense because graphene possesses qualities such as large surface area, variability of pore size and adhesion properties—traits that have marked it for greatness as a filter medium for years now.

Now Geim and his colleagues at the University of Manchester have found that graphene filters are effective at cleaning up the nuclear waste produced at nuclear power plants.  This application could make one of the most costly and complicated aspects of nuclear power generation ten times less energy intensive and therefore much more cost effective.

In research published in the journal Science, the Manchester researchers used the graphene as a sieve to sort protium, the lightest stable isotope of hydrogen, from deuterium, which, unlike protium, contains a neutron in its nucleus. Deuterium appears in larger amounts in so-called heavy water, which is an essential component of some types of nuclear reactors. Though it’s not radioactive like tritium, the heaviest hydrogen isotope, in high enough concentrations, it can cause cell dysfunction and death. Deuterium is also widely used in analytical and chemical tracing technologies.

The Manchester researchers experimented to see if the nuclei of deuterium, deuterons, could pass through the two-dimensional (2-D) materials graphene and boron nitride. The existing theories seemed to suggest that the deuterons would pass through easily. But to the surprise of the researchers, not only did the 2-D membranes sieve out the deuterons, but the separation was also accomplished with a high degree of efficiency.

“This is really the first membrane shown to distinguish between subatomic particles, all at room temperature,” said Marcelo Lozada-Hidalgo, a post-doctoral researcher at the University of Manchester and first author of the paper, in a press release. “Now that we showed that it is a fully scalable technology, we hope it will quickly find its way to real applications.”

Irina Grigorieva, another member of the research team, added: “It is a really simple set up. We hope to see applications of these filters not only in analytical and chemical tracing technologies but also in helping to clean nuclear waste from radioactive tritium.”

Polymer Embedded With Metallic Nanoparticles Enables Soft Robotics

Nanomaterials are increasingly viewed as important ingredients in artificial muscles meant to power different types of robots. Carbon nanotubes have been proposed as well as graphene

Now researchers at North Carolina State University (NCSU), in Raleigh, have developed a technique for embedding nanoparticles of magnetite—an iron oxide—into a polymer so that when the material comes near a magnetic field the polymer moves. The researchers believe that the nanoparticle-studded polymer could lead to a method of remotely controlling so-called “soft robots” whose flexible components allow them to move around in tight spaces in a manner reminiscent of octopodes.

In research described in a paper published in the journal Nanoscale, the NCSU researchers describe a process that starts with dispersing the nanoparticles in a solvent. Next, a polymer is dissolved into the mixture and the resulting fluid is poured into a mold. Then a magnetic field is applied that arranges the magnetite nanoparticles into parallel chains. Once the solution dries in the mold, the chains of nanoparticles are locked into place.

“Using this technique, we can create large nanocomposites, in many different shapes, which can be manipulated remotely,” said Sumeet Mishra, lead author of the paper, in a press release. “The nanoparticle chains give us an enhanced response, and by controlling the strength and direction of the magnetic field, you can control the extent and direction of the movements of soft robots.”

You can see the movement of the polymer under the influence of a magnetic field in the video below.

The phenomenon that causes the polymer to react so strongly to the magnetic field is something called magnetic anisotropy; it makes the material’s magnetic properties directionally dependent. This is achieved by assembling the nanoparticles into chains.

“The key here is that the nanoparticles in the chains and their magnetic dipoles are arranged head-to-tail, with the positive end of one magnetic nanoparticle lined up with the negative end of the next, all the way down the line,” said Joe Tracy, an associate professor at NCSU and corresponding author of the paper, in the press release. “When a magnetic field is applied in any direction, the chain re-orients itself to become as parallel as possible to the magnetic field, limited only by the constraints of gravity and the elasticity of the polymer.”

Entangling Different Kinds of Atoms Could Be the Way Forward for Quantum Computers

Last week two research groups, one at the National Institute of Standards and Technology (NIST) in Boulder, Col., and one at the University of Oxford reported experiments in which particles of different species were entangled for the first time.

Entangled particles—whose quantum properties remain linked, even if separated (in principle) by intergalactic distances—will form the building blocks of future quantum computers. Up to now scientists have entangled photons, electrons, and ions of the same species.  The NIST group reported in the journal Nature that they successfully entangled magnesium ions and beryllium ions, and used the entangled pair to demonstrate two key quantum logic operations—CNOT and SWAP gates. The scientists at Oxford obtained a similar result with ions of calcium-40 and calcium-43, and also performed tests proving that showed that the pair were properly entangled. They, too, reported their results in Nature.

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Electron Beam 3-D Nanofabrication Made 5000 Times Faster

All the various permutations of electron beam induced processing  have provided fairly effective nanofabrication techniques for either etching or depositing material. As important as these processes have been for nanofabrication, there has been one big problem with them: they don’t lend themselves to being scaled up.

Now researchers at Georgia Tech have developed a technique using a liquid precursor that provides fabrication at rates up to 5000 times faster than previous methods.

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Laser Printing a Nanoscale Mona Lisa Could Revolutionize Reproduction Technology

The field of plasmonics has offered some pretty exciting technologies over the past few years, including improved photovoltaics, LEDs, and a host of other optoelectronic applications—most notably photonic circuits that duplicate what electronic ICs can do.

Now researchers at the Technical University of Denmark (DTU) have leveraged plasmonics in a way that may completely revolutionize laser printing by creating a laser printer capable of producing images with 120,000 dots-per-inch resolution. Just to demonstrate how revolutionary the technology is, the DTU researchers reproduced a color image of the Mona Lisa in a space smaller than the footprint taken up by a single pixel on an iPhone Retina display.

In the research, which was published in the journal Nature Nanotechnology,  the Denmark researchers were able to achieve this remarkable resolution using plasmonic nanostructures in place of dyes. However, the researchers added a bit of a twist to traditional techniques for doing this that could make the process far more scalable.

Instead of using methods such as e-beam lithography (EBL) or focused ion beam (FIB), neither of which can be scaled to pre-design and print the plasmonic nanostructures, the researchers went with a process known as laser post-writing. The process starts with a surface that has been prepped by adding rows and columns of nanoscale structures, each with a diameter of 100 nanometers. This nanostructured surface is then covered by a 20-nm-thick sheet of aluminum.  At this point, the laser post-writing is introduced. A laser pulse is aimed at each column, heating it up locally and causing it to melt and deform.

The intensity of the laser pulse determines the level of deformation, and consequently, the colors that the column reflects. A low-intensity laser pulse causes little deformation; the colors of blue and purple are reflected. When the laser pulses are more intense and the deformation more extreme, the deformed structure reflects orange and yellow colors.

“Every time you make a slight change to the column geometry, you change the way it absorbs light,” explained N. Asger Mortensen, a professor at DTU, in a press release. “The light which is not absorbed is the color that our eyes see. If the column absorbs all the blue light, for example, the red light will remain, making the surface appear red.”

While printing images of the Mona Lisa on a single pixel may not seem like a practical use of the technology, it could be useful in applications where presenting images that are undetectable by the naked eye could be quite valuable.

“It will be possible to save data invisible to the naked eye,” said Anders Kristensen, a DTU professor, in a press release. “This includes serial numbers or bar codes of products and other information. The technology can also be used to combat fraud and forgery, as the products will be labeled in way that makes them very difficult to reproduce. It will be easier to determine whether the product is an original or a copy.”

Could Borophene Rival Graphene?

Future electronic devices and batteries could become faster and more energy efficient by harnessing new 2-D sheets of electrically-conductive materials. The latest example of such materials comes in the form of newly-created sheets of boron atoms, called borophene, that could outperform even graphene as an electrical conductor in 2-D form.

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Thin Films of Correlated Metals Could Replace ITO

It’s become somewhat of a rite of passage: Any new nanomaterial is eventually offered as an alternative to indium tin oxide (ITO) in displays. We’ve seen the standard offerings of carbon nanotubes and graphene trotted out fairly regularly, and we’ve even seen some pretty exotic offerings like those based on inorganic materials patterned by man-made viruses.

This effort to replace ITO makes sense because it is a relatively scarce resource. And with the explosion of handheld electronic devices, the demand for ITO as a transparent conductor for controlling display pixels has become increasingly acute.

Now there’s a new pretender to ITO’s throne: correlated metals. Researchers at the Penn State Materials Research Institute believe that by using 10-nanometer-thick films of these materials, it’s possible to make large screen displays, touch screens, and even photovoltaics more affordable and efficient.

In this new class of materials, which includes strontium vanadate and calcium vanadate, electrons flow like a liquid rather than like a gas as they do in conventional metals. The Penn State researchers wanted to see if they could make these correlated metals demonstrate a high optical transparency despite possessing metal-like conductivity.

“We are trying to make metals transparent by changing the effective mass of their electrons,” said Roman Engel-Herbert, assistant professor at Penn State, in a press release. Engel-Herbert explains that the team has chosen materials in which the electrostatic interaction between electrons is very large compared with their kinetic energy.  The result, he says, is that:

Electrons ‘feel’ each other and behave like a liquid rather than a gas of non-interacting particles. This electron liquid is still highly conductive, but when you shine light on it, it becomes less reflective, thus much more transparent.”

Even while they were conducting the correlated metals research—which is explained in a paper published in the journal Nature MaterialsLei Zhang, the paper’s lead of author, knew that the team had struck upon something significant.

“I came from Silicon Valley, where I worked for two years as an engineer before I joined the group,” said Zhang, who is a graduate student in Engel-Herbert’s group.  “I was aware that there were many companies trying hard to optimize those ITO materials and looking for other possible replacements, but they had been studied for many decades and there just wasn’t much room for improvement,” said Zhang in the press release. “When we made the electrical measurements on our correlated metals, I knew we had something that looked really good compared to standard ITO.”

With ITO selling for about $750 per kilogram, while vanadium goes for only around $25/kg (and strontium for even less), it’s pretty clear that the correlated metals will make for much cheaper transparent conductors. The question is whether it will be possible to integrate these materials into existing large-scale manufacturing processes for displays.

Engel-Herbert added: “Our correlated metals work really well compared to ITO...From what we understand right now, there is no reason that strontium vanadate could not replace ITO in the same equipment currently used in industry.”

Nanopillars Are Becoming the New Black in Photovoltaics

Less than two weeks ago, we reported on research out of Stanford University in which a process was developed for creating nanopillars on the metallic surface of a solar cell. These nanopillars would negate the reflective properties of the metal wires needed for shunting power to and from the device, thus allowing more photons to pass through the surface.

Now, a collaboration among researchers at the University of Illinois at Urbana Champaign and the University of Massachusetts at Lowell has yielded another approach to producing nanopillars on the surface of solar cells that promises to allow more photons through so more electricity is generated.

The Stanford researchers presented a one-step chemical process in which silicon and a perforated gold film are placed together in a solution of hydrofluoric acid and hydrogen peroxide. The Illinois and Massachusetts-based researchers employ a metal-assisted chemical etch process (MacEtch) to produce their pillars.

In a paper published in the journal Advanced Materials, the latter team explains how the MacEtch process, which is a patented method developed at the University of Illinois, was used to create tiny nanopillars that rise above the metal film.

“The nanopillars enhance the optical transmission while the metal film offers electrical contact. Remarkably, we can improve our optical transmission and electrical access simultaneously,” said Runyu Liu, a graduate researcher at Illinois and a coauthor of the paper, in a press release.

The sudden popularity of these nanopillars is explained somewhat in the press release. Coauthor Viktor Podolskiy, a professor at the University of Massachusetts at Lowell, says the aim has been to develop nanostructures with holes that can find a way around the model known as Fresnel’s equations, which describe the reflection and transmission of light at the interface between two materials.

“It has been long known that structuring the surface of a material can increase light transmission,” said Podolskiy in the press release. “Among such structures, one of the more interesting is similar to structures found in nature, and is referred to as a ‘moth-eye’ pattern: tiny nanopillars which can ‘beat’ the Fresnel equations at certain wavelengths and angles.”

While the two research groups created their nanopillars using different processes, both groups claim to have achieved largely similar improvements to the solar cells’ light-absorbing efficiency. Both the Stanford and the Illinois-Massachusetts teams reported that even when more than half of a solar cell’s surface is covered in metal, 90 percent of the incident light can make it past that layer.

For both of these research projects, the challenge will be to build a silicon-based solar cell with a greater energy conversion ratio than what is currently state-of-the-art, or even currently available on the market.

Daniel Wasserman, a professor at University of Illinois, added: “We are looking to integrate these nanostructured films with optoelectronic devices to demonstrate that we can simultaneously improve both the optical and electronic properties of devices operating at wavelengths from the visible all the way to the far infrared.”

A New, Bottom-up Process for Tunable Nanostructured Germanium

Researchers at the Technische Universität München (TUM) and the Ludwig Maximilian University of Munich have developed a new type of porous germanium with 200-nanometer pores giving it a large active surface area compared to its volume. This property is important for the exchange of electrical charges via a conducting surface in applications such as photovoltaic cells and batteries. The researchers, led by Thomas Fässler, a chemist researching novel materials at TUM, published their research in Angewandte Chemie Online earlier this month. 

Currently, scientists use etching techniques to create nanostructured surfaces in germanium or silicon—a top down approach. The Munich researchers however used a bottom-up method based on the use of so-called Zintl clusters—charged structures of identical atoms discovered by the German chemist Eduard Zintl in the 1930s. 

The germanium Zintl clusters, consisting of nine germanium atoms, were dissolved in a solution, and because they are charged, they repelled each other. Next, the researchers poured the solution over a template comprising a layer of closely packed polymer beads, 50 to 200 nm in diameter. The solution filled the spaces between the beads; when the solution was subsequently evaporated by heating, the germanium atoms merged and formed pure germanium—but studded with the beads. By dissolving the polymer beads, a pure germanium, spongy and lightweight, was left—with pores where the polymer beads had been.

Fässler notes that this is the first time such a porous material that is entirely inorganic has been created in this fashion. Further, he says, this porous semiconductor matrix can be doped by conventional means or by introducing dopants in the porous network, making it easy to tune its electrical properties.

Highly porous materials have been studied for their capability to transport charge carriers more efficiently in photovoltaic cells and batteries. Says Fässler:

Our overall goal is the creation of a hybrid solar cell; this means, the combination of an organic conductive polymer and a classical material—in our case, germanium. If you fill the pores with a conductive polymer, you can produce charge separation with sunlight, where the polymer produces a hole and the germanium uptakes an electron. 

There are still hurdles. “The specific size of the pores is now 200 nm,” says Fässler. “In the long term we want to make those pores smaller. We built a first prototype, but the performance is low." He adds that he expects it to take a year to get a prototype with a new material to work.

Still, the German team’s research is on a fast track with a lithium-ion battery featuring a porous semiconductor electrode. Fässler explains that while other groups have used nanosize silicon or germanium particles, his group uses the inverse approach: producing nanoporous germanium instead of nanoparticles. 

Currently, for the prototype, we use a germanium half cell on one side, and a pure lithium cell on the other side. This is our benchmark. The lithium will react with the walls of the pores and we have a much higher surface exposed to the lithium. Generally, if you use silicon or germanium in an anode,  you need additional carbon with a high surface area to get a better conductivity.  In our case, we can make a half cell without using any carbon. 

Fässler reports that he and his collaborators are now doing cycling with this battery.  

Silicon is the next major step in their research, but there are tradeoffs. “Actually, germanium is a better conductor,” says Fässler, “but silicon is much cheaper.” And although Zintl clusters for silicon exist, they are more difficult to make and to manipulate.

Spy Agency Bets on IBM for Universal Quantum Computing

A real-life U.S. version of “Q Branch” from the James Bond films has greater ambitions than creating personal spy gadgets such as exploding watches or weaponized Aston Martins. It’s betting on an IBM team to develop the first logical qubits as crucial building blocks for universal quantum computers capable of outperforming today’s classical computers.

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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
Associate Editor, IEEE Spectrum
New York, NY
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