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Detergent Triggers Self Assembly of Two-Dimensional Zinc Oxide

There is a fairly large number of materials that might have some pretty attractive properties if they could be made into monolayer, two-dimensional (2-D) sheets. Unfortunately, unlike graphene, which is fabricated by peeling away layers from bulk graphite, these other materials don’t have a multi-layered source. But now the fabrication of these materials has become a possibility through a novel “bottom-up” production technique whose development may have just changed the future of 2-D materials in electronics.

Researchers at the University of Wisconsin-Madison (UW-Madison) have developed a technique in which a zinc oxide monolayer self assembles in a liquid with the help of a surfactant.  After six years of trial-and-error testing with different surfacants, the UW-Madison researchers believe they have found the right mix.

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Nanoscale Thermal Interfaces Eliminate Overheating in Future Photonic Circuits

For years the prospects of photonic circuits—those that use photons instead of the electrons—were mired in a lack-of-space problem: A photonic system couldn’t get any smaller than a wavelength of light, about 1000 nanometers for infrared, while some dimensions of today’s transistors are one one-hundedth that size.

Enter plasmonics in which devices exploit the oscillating waves of electrons that are generated when photons hit a metal surface. Plasmonic-based approaches confine the size of the wavelength and makes it possible to fabricate smaller devices. But plasmonics for photonic circuits has some drawbacks too, namely surface-of-the-sun type heat.

Now researchers at Moscow Institute of Physics and Technology's (MIPT) Laboratory of Nanooptics and Plasmonics have found a solution to the problem of overheating of active plasmonic components using industry-standard heatsinks. If this solution proves successful, the prospects for photonic circuits will have brightened significantly.

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Graphene Offers Emission Tunability for Terahertz Lasers

Despite the myriad uses we have for lasers, once the wavelengths of light have been set for a laser, it’s usually fixed for that device.

Now researchers at the University of Manchester in the UK have demonstrated that they can tune a terahertz laser so that there is reversible control over its emission. They’ve done so by combining a graphene sheet with a terahertz quantum cascade laser. The key to this control over the laser’s emission is manipulating the doping of the graphene layer to change the concentration of charge carriers.

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Laser-Driven "Bubble Pen" Patterns Nanoparticles

Lasers have been used inside microscopes for many years to trap and move objects floating around in solution. 

Now Linhan Lin, a postdoctoral researcher in Yuebing Zheng’s group at the University of Texas in Austin and colleagues have developed a new strategy for drawing those particles down to the surface, where they can be arranged at will.

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Flexible Nanocomposite Film Could Yield Handheld Cancer Detector

This past September, we reported on research out of Vanderbilt University, in Nashville, in which nanowires were used to create the first integrated circularly polarized light (CPL) detector on a silicon chip that could ultimately lead to portable sensors for drug screening—or even enable quantum computers.

Now, researchers at the University of Michigan, in Ann Arbor, have continued this miniaturization of CPL detectors by developing a flexible nanocomposite circularly polarized-light detector that they claim could lead to the development of a cellphone-size cancer detector.

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Stable Superoxide Could Usher in New Class of Lithium-Air Batteries

Researchers at the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory have added a twist to lithium-oxygen batteries (Li–O2) by successfully demonstrating for the first time the ability to stabilize crystalline lithium-superoxide (LiO2) which could usher in an entirely new class of batteries.

In research published in the journal Nature,  the Argonne researchers were able to produce the stable lithium-superoxide by using a graphene-based cathode. This approach avoids the presence of lithium peroxide (Li2O2), a solid precipitate that clogs the pores of the electrode in lithium-oxygen (aka lithium-air) batteries.

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Potential of Graphene Nanoribbons in Electronics Gets a Boost

If graphene is going to make a splash in electronics, it more than likely is going to be in the form of nanoribbons.  What makes them attractive is that their width determines their electronic properties: Narrow ones are semiconductors, while wider ones act as conductors. This essentially provides a simple way to engineer a band gap into graphene.

Last summer, this blog reported on news that a bottom-up approach to manufacturing graphene nanoribbons (GNRs) had been developed that is both compatible with current semiconductor manufacturing methods and can be scaled up.

Okay, so, GNRs have the properties you need for electronics and you can manufacture the material in bulk. But what can you do with it once you’ve made it? An international team of researchers at Tohoku University's Advanced Institute of Materials Research (AIMR) in Japan has demonstrated the ability to interconnect GNRs end to end using molecular assembly that forms elbow structures which are essentially interconnection points. The researchers believe that this development provides the key to unlocking GNRs’ potential in high-performance and low-power-consumption electronics.

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"Printing Press" Method Stamps Out Gold Nanoparticles With New Properties

Gold nanoparticles have become a de facto do-it-all substance, with applications including cancer treatment and a number of electronics applications. If gold nanoparticles have become the go-to nanomaterial for myriad applications, then DNA has to be considered a key tool for generating patterns upon which effective nanomaterial designs are based. 

Now researchers at McGill University, in Montreal, Canada, have brought gold nanoparticles and DNA together in a new process that serves as a kind of printing press that makes it easier to replicate such designs.

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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.



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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