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Category: materials science

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  • Researchers develop a battery cathode material that does it all

    Battery electrode materials need to do a lot of things well. They need to be conductors to get charges to and from the ions that shuttle between the electrodes. They also need to have an open structure that allows the ions to move around before they reach a site where they can be stored. The storage of lots of ions also causes materials to expand, creating mechanical stresses that can cause the structure of the electrode material to gradually decay.

    Because it’s hard to get all of these properties from a single material, many electrodes are composite materials, with one chemical used to allow ions into and out of the electrode, another to store them, and possibly a third that provides high conductivity. Unfortunately, this can create new problems, with breakdowns at the interfaces between materials slowly degrading the battery’s capacity.

    Now, a team of researchers is proposing a material that seemingly does it all. It’s reasonably conductive, it allows lithium ions to move around and find storage sites, and it’s made of cheap and common elements. Perhaps best of all, it undergoes self-healing, smoothing out damage across charge/discharge cycles.

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  • Infrared contact lenses let you see in the dark

    Tired of using bulky night vision goggles for your clandestine nocturnal activities? An interdisciplinary team of Chinese neuroscientists and materials scientists has developed near-infrared contact lenses that enabled both mice and humans to see in the dark, even with their eyes closed, according to a new paper published in the journal Cell.

    Humans and other mammals can only perceive a limited range of the electromagnetic spectrum (light), usually in the 400–700 nm range. There are creatures that can see in infrared (snakes, mosquitoes, bullfrogs) or ultraviolet (bees, birds), and goldfish can perceive both. But humans must augment themselves with technology in order to expand our range of vision.

    Night vision goggles and similar devices have been around since the 1930s, including infrared-visible converters, but these require external energy sources, and the converters have a multilayer structure that makes them opaque and hence challenging to integrate with a human eye. The authors previously were able to confer near-infrared vision to mice by injecting nanoparticles that bind to photoreceptors into their eyes—basically creating a near-infrared nanoantenna—but realized that most people would be averse to the prospect of sticking needles in their eyes. So they looked for a better alternative. Contact lenses seemed the obvious choice.

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  • New material may help us build Predator-style thermal vision specs

    Military-grade infrared vision goggles use detectors made of mercury cadmium telluride, a semiconducting material that’s particularly sensitive to infrared radiation. Unfortunately, you need to keep detectors that use this material extremely cool—roughly at liquid nitrogen temperatures—for them to work. “Their cooling systems are very bulky and very heavy,” says Xinyuan Zhang, an MIT researcher and the lead author of a new study that looked for alternative IR-sensitive materials.

    Added weight was a sacrifice the manufacturers of high-end night-vision systems were mostly willing to make because cooling-free alternatives offered much worse performance. To fix this, the MIT researchers developed a new ultra-thin material that can sense infrared radiation without any cooling and outperforms cooled detectors at the same time. And they want to use it to turn thermal vision goggles into thermal vision spectacles.

    Staying cool

    Cooling-free infrared detectors have been around since before World War II and mostly relied on pyroelectric materials like tourmaline that change their temperature upon absorbing infrared radiation. This temperature change, in turn, generates an electric current that can be measured to get a readout from the detector. Although these materials worked, they had their issues. Operating at room temperature caused a lot of random atomic motion in the pyroelectric material, which introduced electrical noise that made it difficult to detect faint infrared signals.

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  • Scientists made a stretchable lithium battery you can bend, cut, or stab

    The Li-ion batteries that power everything from smartphones to electric cars are usually packed in rigid, sealed enclosures that prevent stresses from damaging their components and keep air from coming into contact with their flammable and toxic electrolytes. It’s hard to use batteries like this in soft robots or wearables, so a team of scientists at the University California, Berkeley built a flexible, non-toxic, jelly-like battery that could survive bending, twisting, and even cutting with a razor.

    While flexible batteries using hydrogel electrolytes have been achieved before, they came with significant drawbacks. “All such batteries could [only] operate [for] a short time, sometimes a few hours, sometimes a few days,” says Liwei Lin, a mechanical engineering professor at UC Berkeley and senior author of the study. The battery built by his team endured 500 complete charge cycles—about as many as the batteries in most smartphones are designed for.

    Power in water

    “Current-day batteries require a rigid package because the electrolyte they use is explosive, and one of the things we wanted to make was a battery that would be safe to operate without this rigid package,” Lin told Ars. Unfortunately, flexible packaging made of polymers or other stretchable materials can be easily penetrated by air or water, which will react with standard electrolytes, generating lots of heat, potentially resulting in fires and explosions. This is why, back in 2017, scientists started to experiment with quasi-solid-state hydrogel electrolytes.

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  • A 32-bit processor made with an atomically thin semiconductor

    On Wednesday, a team of researchers from China used a paper published in Nature to describe a 32-bit RISC-V processor built using molybdenum disulfide instead of silicon as the semiconductor. For those not up on their chemistry, molybdenum disulfide is a bit like graphene: a single molecule of MoS2 is a sheet that is only a bit over a single atom thick, due to the angles between its chemical bonds. But unlike graphene, molybdenum disulfide is a semiconductor.

    The material has been used in a variety of demonstration electronics, including flash storage and image sensors. But we’ve recently figured out how to generate wafer-scale sheets of MoS2 on a sapphire substrate, and the team took advantage of that to build the processor, which they call RV32-WUJI. It can only add single bits at a time and is limited to kilohertz clock speeds, but it is capable of executing the full RISC-V 32-bit instruction set thanks to nearly 6,000 individual transistors.

    Going flat

    We’ve identified a wide range of what are termed 2D materials. These all form repeated chemical bonds in more or less a single plane. In the case of graphene, which consists only of carbon, the bonds are all in the same plane, meaning the molecule is as thick as a carbon atom. Molybdenum disulfide is slightly different, as the angle of the chemical bonds is out of plane, resulting in a zig-zag pattern. This means the sheet is slightly thicker than its component atoms.

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  • Researchers get spiking neural behavior out of a pair of transistors

    The growing energy use of AI has gotten a lot of people working on ways to make it less power hungry. One option is to develop processors that are a better match to the sort of computational needs of neural networks, which require many trips to memory and a lot of communication between artificial neurons that might not necessarily reside on the same processor. Termed “neuromorphic” processors, this alternative approach to hardware tends to have lots of small, dedicated processing units with their own memory and an extensive internal network connecting them.

    Examples like Intel’s Loihi chips tend to get competitive performance out of far lower clock speeds and energy use, but they require a lot of silicon to do so. Other options give up on silicon entirely and perform the relevant computation in a form of phase change memory.

    A paper published in Nature on Wednesday describes a way to get plain-old silicon transistors to behave a lot like an actual neuron. And unlike the dedicated processors made so far, it only requires two transistors to do so.

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