Transistors can now both process and store information

Purdue University engineers have developed a way that the millions of tiny switches used to process information — called transistors — could also store that information as one device. The method, detailed in a paper published in Nature Electronics, accomplishes this by solving another problem: combining a transistor with higher-performing memory technology than is used in most computers, called ferroelectric RAM.

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a, Schematic of a Fe-FET. b, Schematic of a FeS-FET. In the FeS-FET, the conventional semiconductor channel is replaced by a ferroelectric semiconductor, while the gate insulator is still conventional dielectric. c, Polarization bound charge distribution in a FeS-FET in polarization down (after negative gate bias) and polarization up (after positive gate bias) states.

The material, alpha indium selenide, not only has ferroelectric properties, but also addresses the issue of a conventional ferroelectric material usually acting as an insulator rather than a semiconductor due to a so-called wide “band gap,” which means that electricity cannot pass through and no computing happens. Alpha indium selenide has a much smaller band gap, making it possible for the material to be a semiconductor without losing ferroelectric properties.

In the past, researchers hadn’t been able to build a high-performance ferroelectric tunneling junction because its wide band gap made the material too thick for electrical current to pass through. Since alpha indium selenide has a much smaller band gap, the material can be just 10 nanometers thick, allowing more current to flow through it. More current allows a device area to scale down to several nanometers, making chips more dense and energy efficient, Ye said. A thinner material — even down to an atomic layer thick — also means that the electrodes on either side of a tunneling junction can be much smaller, which would be useful for building circuits that mimic networks in the human brain.

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Paper: Mengwei Si, Atanu K. Saha, Shengjie Gao, Gang Qiu, Jingkai Qin, Yuqin Duan, Jie Jian, Chang Niu, Haiyan Wang, Wenzhuo Wu, Sumeet K. Gupta, Peide D. Ye. A ferroelectric semiconductor field-effect transistorNature Electronics, 2019; DOI: 10.1038/s41928-019-0338-7

New method to remove dust on solar panels

Taking a cue from the self-cleaning properties of the lotus leaf, researchers at Ben-Gurion University of the Negev have shed new light on microscopic forces and mechanisms that can be optimized to remove dust from solar panels to maintain efficiency and light absorption. The new technique removed 98% of dust particles. Dust adhesion on solar panels is a major challenge to energy harvesting through photovoltaic cells and solar thermal collectors. New solutions are necessary to maintain maximum collection efficiency in high dust density areas such as the Negev desert in Israel.

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The researchers explored the effect of modifying a silicon substrate (Si), a semiconductor used in photovoltaic cells, to mimic the self-cleaning properties of the lotus leaf, as water rolls down the leaves and removes contamination. It is known that superhydrophobicity reduces the friction between water droplets and the surface, thus allowing water drops to slide clean particles from surfaces. However, the forces that attach and detach particles from surfaces during the self-cleaning mechanism and the effect of nanotextures on these forces are not fully understood.

Particle removal increased from 41% on hydrophilic smooth Si wafers to 98% on superhydrophobic Si-based nanotextured surfaces. The researchers confirmed these results by measuring the adhesion of a micron-sized particle to the flat and nanotextured substrate using an atomic force microscope. They found that the adhesion in water is reduced by a factor of 30.

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Paper: Heckenthaler, T., Sadhujan, S., Morgenstern, Y., Natarajan, P., Bashouti, M. and Kaufman, Y., 2019. Self-Cleaning Mechanism: Why Nanotexture and Hydrophobicity Matter. Langmuir35(48), pp.15526-15534.

Daily exposure to blue light may accelerate aging, even if it doesn’t reach your eyes

Prolonged exposure to blue light, such as that which emanates from your phone, computer and household fixtures, could be affecting your longevity, even if it’s not shining in your eyes. New research at Oregon State University suggests that the blue wavelengths produced by light-emitting diodes damage cells in the brain as well as retinas. The study, involved a widely used organism, Drosophila melanogaster, the common fruit fly, an important model organism because of the cellular and developmental mechanisms it shares with other animals and humans.

young woman using the smart phone on bed before sleep

Jaga Giebultowicz, a researcher in the OSU College of Science who studies biological clocks, led a research collaboration that examined how flies responded to daily 12-hour exposures to blue LED light — similar to the prevalent blue wavelength in devices like phones and tablets — and found that the light accelerated aging. Flies subjected to daily cycles of 12 hours in light and 12 hours in darkness had shorter lives compared to flies kept in total darkness or those kept in light with the blue wavelengths filtered out. The flies exposed to blue light showed damage to their retinal cells and brain neurons and had impaired locomotion — the flies’ ability to climb the walls of their enclosures, a common behavior, was diminished.

Some of the flies in the experiment were mutants that do not develop eyes, and even those eyeless flies displayed brain damage and locomotion impairments, suggesting flies didn’t have to see the light to be harmed by it. “The fact that the light was accelerating aging in the flies was very surprising to us at first,” said Giebultowicz, a professor of integrative biology. “We’d measured expression of some genes in old flies, and found that stress-response, protective genes were expressed if flies were kept in light. We hypothesized that light was regulating those genes. Then we started asking, what is it in the light that is harmful to them, and we looked at the spectrum of light. It was very clear cut that although light without blue slightly shortened their lifespan, just blue light alone shortened their lifespan very dramatically.”

Natural light, Giebultowicz notes, is crucial for the body’s circadian rhythm — the 24-hour cycle of physiological processes such as brain wave activity, hormone production and cell regeneration that are important factors in feeding and sleeping patterns. “But there is evidence suggesting that increased exposure to artificial light is a risk factor for sleep and circadian disorders,” she said. “And with the prevalent use of LED lighting and device displays, humans are subjected to increasing amounts of light in the blue spectrum since commonly used LEDs emit a high fraction of blue light. But this technology, LED lighting, even in most developed countries, has not been used long enough to know its effects across the human lifespan.”

Giebultowicz says that the flies, if given a choice, avoid blue light. In the meantime, there are a few things people can do to help themselves that don’t involve sitting for hours in darkness, the researchers say. Eyeglasses with amber lenses will filter out the blue light and protect your retinas. And phones, laptops and other devices can be set to block blue emissions.

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