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From the Labs: Materials

New publications, experiments and breakthroughs in materials–and what they mean.

Compact Memory
Light-sensitive ­material could hold multiple bits of data in the same area.

Eighteen in one: Each cluster of six images was recorded to a separate layer of a new material, using combinations of three colors and two polarizations of laser light.

Source: “Five-dimensional optical recording mediated by surface plasmons in gold nanorods”
James W. M. Chon et al.
Nature
459: 410-413

Results: Researchers at Swinburne University of Technology in Australia have developed a light-responsive material that can store data at a density of over 1,000 gigabytes per cubic centimeter. It is made up of 10 layers of gold nanoparticles that change shape depending on the color and polarization of light shined on them, a property that makes it possible to store more than one bit of information in a given region of the material.

Why it matters: The material can store far more data than Blu-ray discs, the highest-­density optical storage technology on the market today. Each of those discs can store only 50 gigabytes (about 4.6 gigabytes per square centimeter).

Methods: To store multiple bits of information in a single region, researchers irradiate the region with laser light in different combinations of colors and polarizations. Each combination creates a distinct change in the gold nanoparticles that can be read by shining another laser on the region and measuring the reflected light. The researchers engineered particles that respond to yellow, blue, and green light, exploiting the fact that nanoparticles absorb different colors depending on their size. To ensure that the particles respond to different polarizations, the researchers made them rod-shaped. When the light’s polarization is aligned with the rods’ long axis, they absorb more light, causing the rods to change shape more than if the polarization is not thus aligned. Data can be written separately to different layers of the material, further increasing the amount of data that can be stored in a given area.

Next steps: The researchers will work with Samsung and other companies to engineer data-storage devices based on the new material.

Energy Storage
Nanostructures boost performance of lithium-­sulfur batteries.

Source: “A highly ordered nanostructured carbon-­sulfur cathode for lithium-sulfur batteries”
Linda F. Nazar et al.
Nature Materials
8: 500-506

Results: Researchers at the University of Waterloo in Ontario have demonstrated that a new nanostructured cathode material for rechargeable lithium-sulfur batteries can store three times as much energy as the cathodes in lithium-­ion batteries on the market. The new batteries retained this ability to store energy when repeatedly charged and discharged completely over the course of 10 hours.

Why it matters: Lithium-­sulfur batteries could store a lot of energy, making them attractive for portable electronics and electric cars. But the low electrical conductivity of sulfur has limited how easily they can be charged and discharged without losing much of their energy-storage capacity, and rapid electrochemical degradation has limited their useful lifetime. The new electrode structure largely overcomes these problems, allowing the batteries to be charged and discharged repeatedly at useful rates while retaining about 80 percent of their theoretical storage capacity.

Methods: The researchers created a material made of regularly spaced nanoscale carbon rods. Then they applied molten sulfur, which was sucked in between the closely packed rods by capillary action (picture sucking up liquid with a bundle of straws). Since carbon is more conductive than sulfur, it allows charge to flow more freely to and from the sulfur. The structure also helps prevent the electrochemical degradation that results when lithium and sulfur fail to react completely, forming intermediate reaction products called polysulfides. The incomplete reaction limits the energy storage of the battery, and the polysulfides can accumulate, further degrading the battery’s performance. The tightly packed rods trap polysulfides until the reaction between lithium and sulfur is complete. A polymer coating on the rods helps keep the polysulfides in place.

Next steps: The researchers are developing ways to further improve the stability of the electrode to increase the number of times a battery using it can be recharged. They’re also devising ways to manufacture the necessary nanostructures at large scales.

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