System Bits: Oct. 11

Non-carbon supercapacitors; quantum dot computing; safer perovskite solvents for solar.

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Carbon Is So 2015
Researchers at MIT have created a supercapacitor that relies on a material other than carbon.

This new class of materials, called metal-organic frameworks (MOFs), are a porous and sponge-like, according to MIT, tthereby providing a much larger surface area than carbon. As with most things electrical, more surface area is essential for superconductors.

The problem the research team faced was that MOF materials by nature are not electrically conductive, but they do conduct ions that carry an electric charge. Moreover, they can be manufactured at a much lower temperature than carbon nanotubes or graphene, which are the current favorites in the superconductor world.

“One of our long-term goals was to make these materials electrically conductive,” says Mircea Dincă, an MIT associate professor of chemistry. But doing so “was thought to be extremely difficult, if not impossible.”

What this means for the future of MOFs is uncertain. Work is just beginning in this area. Supercapacitors are just one application. Others include clectrochromic windows and chemoresistive sensors, which can detect trace amounts of chemicals in medical and security applications.

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Fig. 1: To demonstrate the supercapacitor’s ability to store power, researchers modified a hand-crank flashlight (the red parts at each side) by cutting it in half and installing a small supercapacitor in the center using a conventional button battery case. When the crank is turned to provide power to the flashlight the light continues to shine due to stored energy. Source: MIT

Quantum Dot Computing
Using light to carry information rather than electrical signals has been a topic of discussion for years. It requires less power, is less prone to physical effects, is more secure, and signals can travel at the speed of light.

Still, there has been little to show for it. But researchers at the University of Cambridge have made a breakthrough in this field, using ultra-thin quantum LEDs that can emit single photons using only electrical current.

By stacking together different materials that are only a few atoms thick—graphene, boron nitride and transition metal dichalcogenides (TMDs)—holes can be created with electron vacancies. When electrons are pushed into that hole, it emits light, which can be used to carry information inside of quantum networks.

“Ultimately, we need fully integrated devices that we can control by electrical impulses, instead of a laser that focuses on different segments of an integrated circuit,” said Professor Mete Atatüre of Cambridge’s Cavendish Laboratory. “For quantum communication with single photons, and quantum networks between different nodes, we want to be able to just drive current and get light out. There are many emitters that are optically excitable, but only a handful are electrically driven.”

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Fig. 2: Quantum LED device that generates a stream of single photons. Source: University of Cambridge.

Research is underway into other layered materials, as well. This may be just the beginning of research into TMDs, but it’s an interesting step forward in light-based computing because it bridges electrical and photonic research.

Cleaner Renewable Energy

Unless you’ve been hiding deep in the shadows you’ve probably heard about perovskite materials. They’re cheap, relatively easy to work with, and they are almost as good as silicon in capturing solar energy.

A big problem, though, is toxicity. Until now, all of the materials used as solvents have been highly toxic. But scientists at Oxford University say they have made a breakthrough, based on a combination of methylamine and acetonitrile, which can be developed at a low boiling point with low viscosity and still quickly crystalize perovskite films at room temperature. They say this could be used to help coat large solar panels at a much lower cost than vapor deposition, which is the other alternative.

“What is really exciting about this breakthrough is that largely reducing the toxicity of the solvent hasn’t led to a reduction in the efficiency of the material in harnessing solar energy,” said Dr. Nakita Noel of Oxford’s Department of Physics.

Researchers say perovskite-based solar panels are still a few years away, but they note that this will help speed up the market for these devices.