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New design principles for spin-based quantum materials

As our lives become increasingly intertwined with technology — whether supporting communication while working remotely or streaming our favorite show — so too does our reliance on the data these devices create. Data centers supporting these technology ecosystems produce a significant carbon footprint — and consume 200 terawatt hours of energy each year, greater than the annual energy consumption of Iran. To balance ecological concerns yet meet growing demand, advances in microelectronic processors — the backbone of many Internet of Things (IoT) devices and data hubs — must be efficient and environmentally friendly.

Northwestern University materials scientists have developed new design principles that could help spur development of future quantum materials used to advance (IoT) devices and other resource-intensive technologies while limiting ecological damage.

“New path-breaking materials and computing paradigms are required to make data centers more energy-lean in the future,” said James Rondinelli, professor of materials science and engineering and the Morris E. Fine Professor in Materials and Manufacturing at the McCormick School of Engineering, who led the research.

The study marks an important step in Rondinelli’s efforts to create new materials that are non-volatile, energy efficient, and generate less heat — important aspects of future ultrafast, low-power electronics and quantum computers that can help meet the world’s growing demand for data.

Rather than certain classes of semiconductors using the electron’s charge in transistors to power computing, solid-state spin-based materials utilize the electron’s spin and have the potential to support low-energy memory devices. In particular, materials with a high-quality persistent spin texture (PST) can exhibit a long-lived persistent spin helix (PSH), which can be used to track or control the spin-based information in a transistor.

Although many spin-based materials already encode information using spins, that information can be corrupted as the spins propagate in the active portion of the transistor. The researchers’ novel PST protects that spin information in helix form, making it a potential platform where ultralow energy and ultrafast spin-based logic and memory devices operate.

The research team used quantum-mechanical models and computational methods to develop a framework to identify and assess the spin textures in a group of non-centrosymmetric crystalline materials. The ability to control and optimize the spin lifetimes and transport properties in these materials is vital to realizing the future of quantum microelectronic devices that operate with low energy consumption.

“The limiting characteristic of spin-based computing is the difficulty in attaining both long-lived and fully controllable spins from conventional semiconductor and magnetic materials,” Rondinelli said. “Our study will help future theoretical and experimental efforts aimed at controlling spins in otherwise non-magnetic materials to meet future scaling and economic demands.”

Rondinelli’s framework used microscopic effective models and group theory to identify three materials design criteria that would produce useful spin textures: carrier density, the number of electrons propagating through an effective magnetic field, Rashba anisotropy, the ratio between intrinsic spin-orbit coupling parameters of the materials, and momentum space occupation, the PST region active in the electronic band structure. These features were then assessed using quantum-mechanical simulations to discover high-performing PSHs in a range of oxide-based materials.

The researchers used these principles and numerical solutions to a series of differential spin-diffusion equations to assess the spin texture of each material and predict the spin lifetimes for the helix in the strong spin-orbit coupling limit. They also found they could adjust and improve the PST performance using atomic distortions at the picoscale. The group determined an optimal PST material, Sr3Hf2O7, which showed a substantially longer spin lifetime for the helix than in any previously reported material.

“Our approach provides a unique chemistry-agnostic strategy to discover, identify, and assess symmetry-protected persistent spin textures in quantum materials using intrinsic and extrinsic criteria,” Rondinelli said. “We proposed a way to expand the number of space groups hosting a PST, which may serve as a reservoir from which to design future PST materials, and found yet another use for ferroelectric oxides — compounds with a spontaneous electrical polarization. Our work also will help guide experimental efforts aimed at implementing the materials in real device structures.”

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Materials provided by Northwestern University. Original written by Alex Gerage. Note: Content may be edited for style and length.

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Physicists develop basic principles for mini-labs on chips

Colloidal particles have become increasingly important for research as vehicles of biochemical agents. In future, it will be possible to study their behaviour much more efficiently than before by placing them on a magnetised chip. A research team from the University of Bayreuth reports on these new findings in the journal Nature Communications. The scientists have discovered that colloidal rods can be moved on a chip quickly, precisely, and in different directions, almost like chess pieces. A pre-programmed magnetic field even enables these controlled movements to occur simultaneously.

For the recently published study, the research team, led by Prof. Dr. Thomas Fischer, Professor of Experimental Physics at the University of Bayreuth, worked closely with partners at the University of Poznán and the University of Kassel. To begin with, individual spherical colloidal particles constituted the building blocks for rods of different lengths. These particles were assembled in such a way as to allow the rods to move in different directions on a magnetised chip like upright chess figures — as if by magic, but in fact determined by the characteristics of the magnetic field.

In a further step, the scientists succeeded in eliciting individual movements in various directions simultaneously. The critical factor here was the “programming” of the magnetic field with the aid of a mathematical code, which in encrypted form, outlines all the movements to be performed by the figures. When these movements are carried out simultaneously, they take up to one tenth of the time needed if they are carried out one after the other like the moves on a chessboard.

“The simultaneity of differently directed movements makes research into colloidal particles and their dynamics much more efficient,” says Adrian Ernst, doctoral student in the Bayreuth research team and co-author of the publication. “Miniaturised laboratories on small chips measuring just a few centimetres in size are being used more and more in basic physics research to gain insights into the properties and dynamics of materials. Our new research results reinforce this trend. Because colloidal particles are in many cases very well suited as vehicles for active substances, our research results could be of particular benefit to biomedicine and biotechnology,” says Mahla Mirzaee-Kakhki, first author and Bayreuth doctoral student.

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Better material for wearable biosensors

Biosensors that are wearable on human skin or safely used inside the body are increasingly prevalent for both medical applications and everyday health monitoring. Finding the right materials to bind the sensors together and adhere them to surfaces is also an important part of making this technology better. A recent study from Binghamton University, State University of New York offers one possible solution, especially for skin applications.

Matthew S. Brown, a fourth-year PhD student with Assistant Professor Ahyeon Koh’s lab in the Department of Biomedical Engineering, served as the lead author for “Electronic?ECM: A Permeable Microporous Elastomer for an Advanced Bio-Integrated Continuous Sensing Platform,” published in the journal Advanced Materials Technology.

The study utilizes polydimethylsiloxane (PDMS), a silicone material popular for use in biosensors because of its biocompatibility and soft mechanics. It’s generally utilized as a solid film, nonporous material, which can lead to problems in sensor breathability and sweat evaporation.

“In athletic monitoring, if you have a device on your skin, sweat can build up under that device,” Brown said. “That can cause inflammation and also inaccuracies in continuous monitoring applications.

“For instance, one experiment with electrocardiogram (ECG) analysis showed that the porous PDMS allowed for the evaporation of sweat during exercise, capable of maintaining a high-resolution signal. The nonporous PDMS did not provide the ability for the sweat to readily evaporate, leading to a lower signal resolution after exercise.

The team created a porous PDMS material through electrospinning, a production method that makes nanofibers through the use of electric force.

During mechanical testing, the researchers found that this new material acted like the collagen and elastic fibers of the human epidermis. The material was also capable of acting as a dry adhesive for the electronics to strongly laminate on the skin, for adhesive-free monitoring. Biocompatibility and viability testing also showed better results after seven days of use, compared to the nonporous PDMS film.

“You can use this in a wide variety of applications where you need fluids to passively transfer through the material — such as sweat — to readily evaporate through the device,” Brown said.

Because the material’s permeable structure is capable of biofluid, small-molecule and gas diffusion, it can be integrated with soft biological tissue such as skin, neural and cardiac tissue with reduced inflammation at the application site.

Among the applications that Brown sees are electronics for healing long-term, chronic wounds; breathable electronics for oxygen and carbon dioxide respiratory monitoring; devices that integrate human cells within implantable electronic devices; and real-time, in-vitro chemical and biological monitoring.

Koh — whose recent projects include sweat-assisted battery power and biomonitoring — described the porous PDMS study as “a cornerstone of my research.”

“My lab is very interested in developing a biointegrated sensing system beyond wearable electronics,” she said. “At the moment, technologies have advanced to develop durable and flexible devices over the past 10 years. But we always want to go even further, to create sensors that can be used in more nonvisible systems that aren’t just on the skin.

“Koh also sees the possibilities for this porous PDMS material in another line of research she is pursuing with Associate Professor Seokheun Choi from the Department of Electrical and Computer Engineering. She and Choi are combining their strengths to create stretchable papers for soft bioelectronics, enabling us to monitor physiological statuses.

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Materials provided by Binghamton University. Original written by Chris Kocher. Note: Content may be edited for style and length.

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A titanate nanowire mask that can eliminate pathogens

As part of attempts to curtail the Covid-19 pandemic, paper masks are increasingly being made mandatory. Their relative effectiveness is no longer in question, but their widespread use has a number of drawbacks. These include the environmental impact of disposable masks made from layers of non-woven polypropylene plastic microfibres. Moreover, they merely trap pathogens instead of destroying them. “In a hospital setting, these masks are placed in special bins and handled appropriately,” says László Forró, head of EPFL’s Laboratory of Physics of Complex Matter. “However, their use in the wider world — where they are tossed into open waste bins and even left on the street — can turn them into new sources of contamination.”

Researchers in Forró’s lab are working on a promising solution to this problem: a membrane made of titanium oxide nanowires, similar in appearance to filter paper but with antibacterial and antiviral properties.

Their material works by using the photocatalytic properties of titanium dioxide. When exposed to ultraviolet radiation, the fibers convert resident moisture into oxidizing agents such as hydrogen peroxide, which have the ability to destroy pathogens. “Since our filter is exceptionally good at absorbing moisture, it can trap droplets that carry viruses and bacteria,” says Forró. “This creates a favorable environment for the oxidation process, which is triggered by light.”

The researchers’ work appears today in Advanced Functional Materials, and includes experiments that demonstrate the membrane’s ability to destroy E. coli, the reference bacterium in biomedical research, and DNA strands in a matter of seconds. Based on these results, the researchers assert — although this remains to be demonstrated experimentally — that the process would be equally successful on a wide range of viruses, including SARS-CoV-2.

Their article also states that manufacturing such membranes would be feasible on a large scale: the laboratory’s equipment alone is capable of producing up to 200 m2 of filter paper per week, or enough for up to 80,000 masks per month. Moreover, the masks could be sterilized and reused up a thousand times. This would alleviate shortages and substantially reduce the amount of waste created by disposable surgical masks. Finally, the manufacturing process, which involves calcining the titanite nanowires, makes them stable and prevents the risk of nanoparticles being inhaled by the user.

A start-up named Swoxid is already preparing to move the technology out of the lab. “The membranes could also be used in air treatment applications such as ventilation and air conditioning systems as well as in personal protective equipment,” says Endre Horváth, the article’s lead author and co-founder of Swoxid.

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Materials provided by Ecole Polytechnique Fédérale de Lausanne. Original written by Emmanuel Barraud. Note: Content may be edited for style and length.

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Research could save years of breeding for new Miscanthus hybrids

As climate change becomes increasingly difficult to ignore, scientists are working to diversify and improve alternatives to fossil-fuel-based energy. Renewable bioenergy crops, such as the perennial grass Miscanthus, show promise for cellulosic ethanol production and other uses, but current hybrids are limited by environmental conditions and susceptibility to pests and diseases.

Breeders have been working to develop new Miscanthus hybrids for years, but the clonal crop’s sterility, complex genome, and long time to maturity make conventional breeding difficult. In a new study, University of Illinois researchers mine the crop’s vast genomic potential in an effort to speed up the breeding process and maximize its most desirable traits.

“The method we’re using, genomic selection, can shorten the time it takes to breed a new hybrid by at least half,” says Marcus Olatoye, lead author on the study and postdoctoral researcher in the Department of Crop Sciences at Illinois. “That’s the overall goal.”

In conventional breeding, one typical approach is for researchers to grow individuals from a diverse set of populations and select those with the best traits for mating. But, for Miscanthus, those traits don’t show up until plants are 2-3 years old. Even after plants from this first generation are mated, it takes the offspring another 2-3 years to reveal whether the desired traits were faithfully passed on.

In genomic selection, scientists take genetic samples from seeds or seedlings in a target population. This is the group of plants that would ordinarily have to be grown to maturity before experimental crosses are made. Meanwhile, the researchers compile both genetic and phenotypic data from related populations, known as reference or training sets, into a statistical model. Cross-referencing genetic data from the target population with data in the model allows the researchers to predict the phenotypic outcome of hypothetical crosses within the target population.

This allows breeders to cut to the chase, pursuing only the most promising crosses with further field testing.

“Ideally, this process could allow breeders to make selections based on predicted phenotypic values before plants are even planted,” says Alex Lipka, associate professor of biometry in the Department of Crop Sciences and co-author on the study. “Specifically, we want to make selections to optimize winter hardiness, biomass, disease tolerance, and flowering time in Miscanthus, all of which limit the crop’s performance in various regions of North America.”

Although it’s not a simple process in the best of times, genomic selection in Miscanthus is orders of magnitude more challenging than in other crops. The hybrid of interest, Miscanthus × giganteus, is the product of two separate species, Miscanthus sinensis and Miscanthus sacchariflorus, each of which have different numbers of chromosomes and contain a great deal of variation within and across natural populations.

“As far as we know, no one has tried to train genomic selection models from two separate species before. We decided to go totally nuts here,” Lipka says. “Unfortunately, we found the two parent species do not do a very good job of predicting biofuel traits in Miscanthus × giganteus.”

The problem was twofold. First, the statistical model simply revealed too much genetic variation among parental subpopulations to capture the impact of genes controlling biofuel traits. This meant the parental populations chosen for the reference set were too diverse to reliably predict traits in the hybrid Miscanthus × giganteus. And second, the genes controlling a particular trait — like those related to biofuel potential — seemed to be different in the two parent species.

In other words, the genomes contributing to Miscanthus × giganteus are highly complex, explaining why the statistical approach had a hard time predicting traits in offspring from the two parents.

Still, the research team kept trying. In a simulation study, Olatoye created 50 Miscanthus × giganteus families, each derived from parents randomly selected from both species. He selectively dialed genetic contributions of each parent up and down, and these contributions formed the genetic basis of simulated phenotypes. The intention of the study was to provide a better view of which individuals and populations might be most valuable for crosses in real life.

“The results suggest the best strategy for utilizing diversity in the parents is to fit genomic selection models within each parental species separately, and then add the predicted Miscanthus × giganteus trait values from the two models separately,” Olatoye says.

Although the researchers have more work to do, the simulation study proved genomic selection can work for Miscanthus × giganteus. The next step is further refining which populations are used to train the statistical model and evaluating crosses in the field.

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Discovery offers new avenue for next-generation data storage

The demands for data storage and processing have grown exponentially as the world becomes increasingly connected, emphasizing the need for new materials capable of more efficient data storage and data processing.

An international team of researchers, led by physicist Paul Ching-Wu Chu, founding director of the Texas Center for Superconductivity at the University of Houston, is reporting a new compound capable of maintaining its skyrmion properties at room temperature through the use of high pressure. The results also suggest the potential for using chemical pressure to maintain the properties at ambient pressure, offering promise for commercial applications.

The work is described in the Proceedings of the National Academy of Sciences.

A skyrmion is the smallest possible perturbation to a uniform magnet, a point-like region of reversed magnetization surrounded by a whirling twist of spins. These extremely small regions, along with the possibility of moving them using very little electrical current, make the materials hosting them promising candidates for high-density information storage. But the skyrmion state normally exists only at a very low and narrow temperature range. For example, in the compound Chu and colleagues studied, the skyrmion state normally exists only within a narrow temperature range of about 3 Kelvin degrees, between 55 K and 58.5 K (between -360.7 Fahrenheit and -354.4 Fahrenheit). That makes it impractical for most applications.

Working with a copper oxyselenide compound, Chu said the researchers were able to dramatically expand the temperature range at which the skyrmion state exists, up to to 300 degrees Kelvin, or about 80 degrees Fahrenheit, near room temperature. First author Liangzi Deng said they successfully detected the state at room temperature for the first time under 8 gigapascals, or GPa, of pressure, using a special technique he and colleagues developed. Deng is a researcher with the Texas Center for Superconductivity at UH (TcSUH).

Chu, the corresponding author for the work, said researchers also found that the copper oxyselenide compound undergoes different structural-phase transitions with increasing pressure, suggesting the possibility that the skyrmion state is more ubiquitous than previously thought.

“Our results suggest the insensitivity of the skyrmions to the underlying crystal lattices. More skyrmion material may be found in other compounds, as well,” Chu said.

The work suggests the pressure required to maintain the skyrmion state in the copper oxyselenide compound could be replicated chemically, allowing it to work under ambient pressure, another important requirement for potential commercial applications. That has some analogies to work Chu and his colleagues did with high-temperature superconductivity, announcing in 1987 that they had stabilized high-temperature superconductivity in YBCO (yttrium, barium, copper, and oxygen) by replacing ions in the compound with smaller isovalent ions.

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Materials provided by University of Houston. Original written by Jeannie Kever. Note: Content may be edited for style and length.

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Unique material could unlock new functionality in semiconductors

If new and promising semiconductor materials are to make it into our phones, computers, and other increasingly capable electronics, researchers must obtain greater control over how those materials function.

In an article published today in Science Advances, Rensselaer Polytechnic Institute researchers detailed how they designed and synthesized a unique material with controllable capabilities that make it very promising for future electronics.

The researchers synthesized the material — an organic-inorganic hybrid crystal made up of carbon, iodine, and lead — and then demonstrated that it was capable of two material properties previously unseen in a single material. It exhibited spontaneous electric polarization that can be reversed when exposed to an electric field, a property known as ferroelectricity. It simultaneously displayed a type of asymmetry known as chirality — a property that makes two distinct objects, like right and left hands, mirror images of one another but not able to be superimposed.

According to Jian Shi, an associate professor of materials science and engineering at Rensselaer, this unique combination of ferroelectricity and chirality is advantageous. When combined with the material’s conductivity, both of these characteristics can enable other electrical, magnetic, or optical properties.

“What we have done here is equip a ferroelectric material with extra functionality, allowing it to be manipulated in previously impossible ways,” Shi said.

The experimental discovery of this material was inspired by theoretical predictions by Ravishankar Sundararaman, an assistant professor of materials science and engineering at Rensselaer. A ferroelectric material with chirality, Sundararaman said, can be manipulated to respond differently to left- and right-handed light so that it produces specific electric and magnetic properties. This type of light-matter interaction is particularly promising for future communication and computing technologies.

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Materials provided by Rensselaer Polytechnic Institute. Original written by Torie Wells. Note: Content may be edited for style and length.

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Instrument may enable mail-in testing to detect heavy metals in water

Lead, arsenic, and other heavy metals are increasingly present in water systems around the world due to human activities, such as pesticide use and, more recently, the inadequate disposal of electronic waste. Chronic exposure to even trace levels of these contaminants, at concentrations of parts per billion, can cause debilitating health conditions in pregnant women, children, and other vulnerable populations.

Monitoring water for heavy metals is a formidable task, however, particularly for resource-constrained regions where workers must collect many liters of water and chemically preserve samples before transporting them to distant laboratories for analysis.

To simplify the monitoring process, MIT researchers have developed an approach called SEPSTAT, for solid-phase extraction, preservation, storage, transportation, and analysis of trace contaminants. The method is based on a small, user-friendly device the team developed, which absorbs trace contaminants in water and preserves them in a dry state so the samples can be easily dropped in the mail and shipped to a laboratory for further analysis.

The device resembles a small, flexible propeller, or whisk, which fits inside a typical sampling bottle. When twirled inside the bottle for several minutes, the instrument can absorb most of the trace contaminants in the water sample. A user can either air-dry the device or blot it with a piece of paper, then flatten it and mail it in an envelope to a laboratory, where scientists can dip it in a solution of acid to remove the contaminants and collect them for further analysis in the lab.

“We initially designed this for use in India, but it’s taught me a lot about our own water issues and trace contaminants in the United States,” says device designer Emily Hanhauser, a graduate student in MIT’s Department of Mechanical Engineering. “For instance, someone who has heard about the water crisis in Flint, Michigan, who now wants to know what’s in their water, might one day order something like this online, do the test themselves, and send it to a lab.”

Hanhauser and her colleagues recently published their results in the journal Environmental Science and Technology. Her MIT co-authors are Chintan Vaishnav of the Tata Center for Technology and Design and the MIT Sloan School of Management; John Hart, associate professor of mechanical engineering; and Rohit Karnik, professor of mechanical engineering and associate department head for education, along with Michael Bono of Boston University.

From teabags to whisks

The team originally set out to understand the water monitoring infrastructure in India. Millions of water samples are collected by workers at local laboratories all around the country, which are equipped to perform basic water quality analysis. However, to analyze trace contaminants, workers at these local labs need to chemically preserve large numbers of water samples and transport the vessels, often over hundreds of kilometers, to state capitals, where centralized labs have facilities to properly analyze trace contaminants.

“If you’re collecting a lot of these samples and trying to bring them to a lab, it’s pretty onerous work, and there is a significant transportation barrier,” Hanhauser says.

In looking to streamline the logistics of water monitoring, she and her colleagues wondered whether they could bypass the need to transport the water, and instead transport the contaminants by themselves, in a dry state.

They eventually found inspiration in dry blood spotting, a simple technique that involves pricking a person’s finger and collecting a drop of blood on a card of cellulose. When dried, the chemicals in the blood are stable and preserved, and the cards can be mailed off for further analysis, avoiding the need to preserve and ship large volumes of blood.

The team started thinking of a similar collection system for heavy metals, and looked through the literature for materials that could both absorb trace contaminants from water and keep them stable when dry.

They eventually settled on ion-exchange resins, a class of material that comes in the form of small polymer beads, several hundreds of microns wide. These beads contain groups of molecules bound to a hydrogen ion. When dipped in water, the hydrogen comes off and can be exchanged with another ion, such as a heavy metal cation, that takes hydrogen’s place on the bead. In this way, the beads can absorb heavy metals and other trace contaminants from water.

The researchers then looked for ways to immerse the beads in water, and first considered a teabag-like design. They filled a mesh-like pocket with beads and dunked it in water they spiked with heavy metals. They found, though, that it took days for the beads to adequately absorb the contaminants if they simply left the teabag in the water. When they stirred the teabag around, turbulence sped the process somewhat, but it still took far too long for the beads, packed into one large teabag, to absorb the contaminants.

Ultimately, Hanhauser found that a handheld stirring design worked best to take up metal contaminants in water within a reasonable amount of time. The device is made from a polymer mesh cut into several propeller-like panels. Within each panel, Hanhauser hand-stitched small pockets, which she filled with polymer beads. She then stitched each panel around a polymer stick to resemble a sort of egg beater or whisk.

Testing the waters

The researchers fabricated several of the devices, then tested them on samples of natural water collected around Boston, including the Charles and Mystic rivers. They spiked the samples with various heavy metal contaminants, such as lead, copper, nickel, and cadmium, then stuck a device in the bottle of each sample, and twirled it around by hand to catch and absorb the contaminants. They then placed the devices on a counter to dry overnight.

To recover the contaminants from the device, they dipped the device in hydrochloric acid. The hydrogen in the solution effectively knocks away any ions attached to the polymer beads, including heavy metals, which can then be collected and analyzed with instruments such as mass spectrometers.

The researchers found that by stirring the device in the water sample, the device was able to absorb and preserve about 94 percent of the metal contaminants in each sample. In their recent trials, they found they could still detect the contaminants and predict their concentrations in the original water samples, with an accuracy range of 10 to 20 percent, even after storing the device in a dry state for up to two years.

With a cost of less than $2, the researchers believe that the device could facilitate transport of samples to centralized laboratories, collection and preservation of samples for future analysis, and acquisition of water quality data in a centralized manner, which, in turn, could help to identify sources of contamination, guide policies, and enable improved water quality management.

The researchers have now partnered with a company in India, in hopes of commercializing the device. Together, their project was recently chosen as one of 26 proposals out of more than 950 to be funded by the Indian government under its Atal New India Challenge program.

This research was funded, in part, by the Abdul Latif Jameel Water and Food Systems Lab, the MIT Tata Center, and the National Science Foundation.

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Oblique electrostatic inject-deposited TiO2 film for efficient perovskite solar cells

The need to efficiently harvest solar energy for a more sustainable future is increasingly becoming accepted across the globe. A new family of solar cells based on perovskites — materials with a particular crystal structure — is now competing with conventional silicon materials to satisfy the demand in this area. Perovskite solar cells (PSCs) are continually being optimized to fulfill their commercial potential, and a team led by researchers from Kanazawa University has now reported a new and simple oblique electrostatic inkjet (OEI) approach to deposit a titanium oxide (TiO2) compact layer on FTO-pattern substrates without the need for a vacuum environment as an electron transport layer (ETL) for enhancing the efficiency of PSCs. The findings are published in Scientific Reports.

The PSCs comprise a stack of different component layers that all have a specific role. The ETL, which is often composed of TiO2, enables the transport of electrons — which carry charge — to the electrodes, while blocking the transport of holes — which can recombine with electrons to prevent their flow. Establishing a complete TiO2 layer with the correct thickness, which is uniform and free of flaws, is therefore critical to producing efficient solar cells.

Many of the numerous TiO2 deposition techniques reported to date have associated limitations, such as poor coverage or reproducibility, or being unsuitable for scale-up. They can also require challenging preparation conditions such as a vacuum. The researchers report a simple, low-cost OEI-method that achieves a compact layer without requiring a vacuum.

“Our technique can produce uniform electron transport layers whose thickness can be varied by controlling the deposition time.” Study lead author Assistant Professor Dr. Md. Shahiduzzaman explains. “Solar cells made using our approach had power-conversion efficiencies of up to 13.19%, which, given the other advantages of our technique, is very promising for scale-up and commercialization.”

The technique is based on the deposition of positively charged droplets that are attracted to a negatively charged surface. Previous reports using the same electrostatic approach achieved lower power-conversion efficiencies because the droplets formed a stack on the surface as a result of gravity. Introducing an oblique angle into the process — spraying the TiO2 precursor at 45° to the surface — eliminated the effect of gravity, leading to the deposition of a more uniform layer.

“An optimum ETL deposition method must offer a number of properties to result in a high efficiency solar cell,” Dr. Shahiduzzaman explains. “The ability to control the layer thickness and achieve a uniform, reproducible layer at low cost, without the need for a vacuum, provides a unique package of advantages that has not been reported to date. We hope that these properties will lead to effective and commercially relevant scale-up that will contribute to the drive towards cleaner energy worldwide.”

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Urban health scare: E-scooters show alarming spike in injuries

Electric scooters are increasingly part of the crowded urban landscape, but a UC San Francisco study has found a major surge of injuries related to scooters, particularly among young adults.

The number of scooter-related injuries and hospital admissions in the United States grew by 222 percent between 2014 and 2018 to more than 39,000 injuries, while the number of hospital admissions soared by 365 percent to a total of nearly 3,300, according to the study.

Nearly a third of the patients suffered head trauma — more than twice the rate of head injuries to bicyclists. About a third of the e-scooter injuries were to women, and people between the ages of 18 and 34 were the most often injured for the first time in 2018.

The study appears Jan. 8, 2020 in JAMA Surgery.

“E scooters are a fast and convenient form of transportation and help to lessen traffic congestion, especially in dense, high-traffic areas,” said senior and corresponding author Benjamin N. Breyer, MD, a UCSF Health urologist. “But we’re very concerned about the significant increase in injuries and hospital admissions that we documented, particularly during the last year, and especially with young people, where the proportion of hospital admissions increased 354 percent.”

The UCSF team had previously looked at bicycle injuries using the same data set and found scooter riders had a higher proportion of head injuries, which was also identified in this study.

“There was a high proportion of people with head injuries, which can be very dangerous,” said Breyer, an associate professor of urology and chief of urology at UCSF partner hospital Zuckerberg San Francisco General Hospital and Trauma Center. “Altogether, the near doubling of e-scooter trauma from 2017 to 2018 indicates that there should be better rider safety measures and regulation.”

As motorized scooters have become more ubiquitous in the last few years, particularly within the country’s biggest cities and suburbs, health officials and medical experts across the country grew increasingly alarmed by the number of fractures, dislocations and head injuries appearing in trauma centers. Regulatory oversight is largely absent about where people can ride scooters and whether helmets are mandatory: Previous research showed that only a fraction of injured e-scooter riders (ranging from 2 to about 5 percent) wore helmets when they were hurt.

In the new study, the UCSF researchers used data from the National Electronic Injury Surveillance System on national estimates of injuries related to emergency room visits.

They found that a total of nearly 40,000 injuries occurred from powered scooters in the U.S. between 2014 and 2018. The study found that the rate of scooter accidents also increased, from 6 per 100,000 people in 2014 to 19 per 100,000 in 2018. The most common injuries were fractures (27 percent), contusions and abrasions (23 percent), and lacerations (14 percent).

Over the study period, urban hospitals received the highest proportion of patients (78 percent) compared to rural (20 percent) and children’s hospitals (2 percent).

The authors note that the actual incidence of e-scooter trauma may be underestimated because cases with unclear scooter types were excluded from the study, and some riders likely did not go to the emergency department despite their injuries. Future research into pedestrian and cyclist trauma associated with e-scooter use is needed, the authors said.

“It’s been shown that helmet use is associated with a lower risk of head injury,” said first author Nikan K. Namiri, medical student at the UCSF School of Medicine. “We strongly believe that helmets should be worn, and e-scooter manufacturers should encourage helmet use by making them more easily accessible.”

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Materials provided by University of California – San Francisco. Original written by Elizabeth Fernandez. Note: Content may be edited for style and length.

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