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Graphene Flakes Make Laser Neuron Superfast

Tiny flakes of graphene may hold the key to building computer chips that can process information similar to the way the human brain does—only far faster—potentially leading to everything from better image recognition to control systems for hypersonic aircraft.

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Nanotech Could Raise Incandescents From The Dead

Love energy-efficient LED lights, but miss the warm glow of incandescent bulbs? A new nanotech-enabled design by MIT researchers just might breathe new life into incandescent lighting. It promises to increase the efficiency of incandescent light sources by twenty times, surpassing that of LED bulbs.

Incandescents are thermal emitters: they heat up a tungsten filament to such high temperatures that it glows. Only a very small fraction of energy is emitted as visible light. Most of it is lost as infrared radiation. So the luminous efficiency of a typical incandescent is a paltry 2.5 percent compared to 5-10 percent for compact fluorescents and 14-15 percent for state-of-the-art compact LED bulbs.

It is possible to tailor the thermal radiation of a light source so that it emits more visible light and less infrared. This involves putting specially designed periodic nanostructures on the emitter’s surface, says Ognjen Ilic, a postdoctoral researcher in physics at MIT. The structures resonate at specific wavelengths of light, allowing only those wavelengths to be emitted.

However, the approach only works for room temperature light sources. The temperature of tungsten filaments reaches up to 3000 K. “Those nanostructures are delicate and would start degrading at those temperatures,” Ilic says.

So Ilic and his colleagues designed a resonating nanostructure that would surround the filament. They used numerical optimization techniques to design the structure, which is a stack of materials of different refractive indices and nanometer thicknesses. The structure lets through visible wavelengths but reflects infrared light back at the tungsten filament to be reabsorbed.

The researchers built a proof-of-principle device based on the scheme. This reincarnated incandescent source, reported in the journal Nature Nanotechnology, doesn’t look much the long coiled tungsten wire in traditional light bulbs. Here, the filament is a flat, wavy 1-square-centimeter piece of tungsten laser-machined from a thin tungsten sheet. The researchers sandwiched it between two 2-cm2 resonators.

In theory, the scheme should allow a luminous efficiency of 40 percent, Ilic says. But the prototype just is 6.6 percent efficient.That would require a complex stack consisting of 300 layers of four different materials: oxides of silicon, aluminum, tantalum, and titanium. For now, the researchers built a simpler resonator containing a 90-layer stack made of silicon dioxide and tantalum pentoxide. 

So, what’s keeping nanotech-enabled incandescents from becoming  the next best thing in efficient lighting? “The materials involved are cheap and abundant and the manufacturing process is scalable,” Ilic says. But the nanolayer production costs will have to be brought down before this reincarnated incandescent could compete with LED light bulbs.

“But beyond lighting, another really interesting avenue to use this would be for energy conversion,” he says. Tailoring thermal emission to match the absorption spectrum of photovoltaic cells, he adds, could boost the efficiency of thermo-photovoltaic systems, which combine solar thermal and photovoltaics to achieve extremely high light-to-electricity efficiencies.

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Little Dripper Builds Better Electrodes for Touch-Screens

The key factors in touch-screen displays are conductivity and transparency. Touch-screen displays need electrodes that are excellent conductors so the electronics react quickly to a touch on the screen. The electrodes also need to be transparent so they they don’t detract from the clarity of the screen image.

The industry standard for producing these transparent electrodes has been indium tin oxide (ITO)—a relatively scarce resource with a price tag commensurate with its scarcity. As a result, a veritable cavalcade of nanomaterials have been experimented with as an alternative, including carbon nanotubes, graphene, and recently a material called correlated metals.

Now researchers at ETH Zurich in Switzerland have not only thrown new materials into the ring in the form of gold or silver nanoparticles, but they’ve also come up with a new way to produce the electrodes on touch-screens with a 3-D printer dubbed the Nanodrip.

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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.”

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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.”

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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.”

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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.”

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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
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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