Study predicts millions of unsellable homes could upend market

Millions of American homes could become unsellable — or could be sold at significant losses to their senior-citizen owners — between now and 2040, according to new research from the University of Arizona.

The study predicts that many baby boomers and members of Generation X will struggle to sell their homes as they become empty nesters and singles. The problem is that millions of millennials and members of Generation Z may not be able to afford those homes, or they may not want them, opting for smaller homes in walkable communities instead of distant suburbs.

Baby boomers are people born between 1946 and 1964, while Gen Xers were born between 1965 and 1980. Millennials were born between 1981 and 1997 and Gen Zers between 1998 and 2015.

The study predicts that the change in home-buying behaviors by younger generations may result in a glut of homes that could grow as high as 15 million by 2040, with homeowners selling for far below what they paid — if they can sell them at all. Most seniors will be able to sell their homes, the study says, but it may become especially difficult in smaller, distant and slow- or non-growing markets.

Arthur C. Nelson, a professor of urban planning and real estate development at the UArizona College of Architecture, Planning and Landscape Architecture, calls his prediction “The Great Senior Short Sale” in a paper published this week in the Journal of Comparative Urban Land and Policy.

An expert in urban studies, public policy and land development, Nelson has spent a large part of his career studying the changing demand for suburban homes, since long before the housing market crash of the Great Recession.

His newest prediction, if it plays out, would undermine one of the “big promises” of homeownership for millions of seniors, Nelson said: that a home, after it’s paid off, can be sold for a retirement nest egg.

“What if you pay off your mortgage over 30 years,” he added, “and nobody buys the home?”

The Mismatch in the Market

Nelson’s prediction comes from synthesizing data from sources such as the U.S. Census Bureau and the Harvard Joint Center for Housing Studies. The Harvard center is a leading source of data for those in academia, government and business to make sense of housing issues to inform policy decisions.

Nelson, using those data, mapped how the ages of homeowners would change between 2018 and 2038. Looking at three age groups — over 65, 35-64 and under 35 — he came to the projection at the center of the study: that there may be fewer homeowners under 65 in 2038 than there were in 2018, even though the vast majority of people over 65 in 2038 will own their homes.

“There’s the mismatch — if those over 65 unload their homes, and those under 65 aren’t buying them, what happens to those homes?” he asks.

Nelson is careful not to overstate his findings; millions of people will buy the homes that older generations are selling, he said.

“But the vast supply is so large and the demand for them is going to be so small, in comparison, that there’s going to be a real problem starting later this decade,” he said.

Nelson said he expects the phenomenon to reveal itself not all at once, but gradually over the next couple decades, at about 500,000 to 1 million homes every year. It’s not likely to have much impact in growing metropolitan areas such as Phoenix or Dallas where “growth will solve all kinds of problems,” he said, but it will matter in thousands of suburban and rural areas — including some parts of Arizona.

“The people who own homes now in thousands of declining communities may simply have to walk away from them,” he said.

Proposed Policy Solutions

Nelson’s study urges action from lawmakers, and he offers some ideas of his own.

Among those is a program in which the federal government would buy back homes that have or may become unsellable. The Federal Emergency Management Agency already does something similar with homes that or have been or are likely to be damaged by natural disasters.

By bearing the cost of buying those homes, Nelson said, the government could help seniors avoid turning to federal social support programs after losing their homes. Those programs are costly to taxpayers, and the cost is even greater when programs need to be administered in rural or suburban areas — where homes are predicted not to sell, Nelson said.

“If you have millions of seniors spread all across the landscape costing a fortune to serve, we might be better off finding ways to induce many to sell their homes,” he said. “And we could actually then save potentially billions in public money that would otherwise be used to serve people in very distant and remove locations.”

Nelson also proposes programs at the state level that would allow younger people to live with older empty nesters, single people and others who live in homes larger than they may need, but who do not want to move.

By sharing homes, Nelson said, older people would not have to sell them, and younger housemates could act as caregivers and property managers.

The idea is already being tested in cities such as Minneapolis and Seattle and across the state of Oregon, Nelson said. There, laws were passed last year that allowed owners of single-family homes to divide them into multiple units.

Nelson completed his study just before the coronavirus outbreak became widespread. But the pandemic, he said, doesn’t make the housing issue any less urgent.

“We’re going to wake up in 2025 — give or take a few years — to realize that millions of seniors can’t get out of their homes and that it’s going to get worse in to the 2030s,” he said. “We must start doing things now to reduce the coming shock of too many seniors trying to sell their homes to too few younger buyers.”

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Advance in programmable synthetic materials

Artificial molecules could one day form the information unit of a new type of computer or be the basis for programmable substances. The information would be encoded in the spatial arrangement of the individual atoms — similar to how the sequence of base pairs determines the information content of DNA, or sequences of zeros and ones form the memory of computers.

Researchers at the University of California, Berkeley, and Ruhr-Universität Bochum (RUB) have taken a step towards this vision. They showed that atom probe tomography can be used to read a complex spatial arrangement of metal ions in multivariate metal-organic frameworks.

Metal-organic frameworks (MOFs) are crystalline porous networks of multi-metal nodes linked together by organic units to form a well-defined structure. To encode information using a sequence of metals, it is essential to be first able to read the metal arrangement. However, reading the arrangement was extremely challenging. Recently, the interest in characterizing metal sequences is growing because of the extensive information such multivariate structures would be able to offer.

Fundamentally, there was no method to read the metal sequence in MOFs. In the current study, the research team has successfully done so by using atom probe tomography (APT), in which the Bochum-based materials scientist Tong Li is an expert. The researchers chose MOF-74, made by the Yaghi group in 2005, as an object of interest. They designed the MOFs with mixed combinations of cobalt, cadmium, lead, and manganese, and then decrypted their spatial structure using APT.

Li, professor and head of the Atomic-Scale Characterisation research group at the Institute for Materials at RUB, describes the method together with Dr. Zhe Ji and Professor Omar Yaghi from UC Berkeley in the journal Science, published online on August 7, 2020.

Just as sophisticated as biology

In the future, MOFs could form the basis of programmable chemical molecules: for instance, an MOF could be programmed to introduce an active pharmaceutical ingredient into the body to target infected cells and then break down the active ingredient into harmless substances once it is no longer needed. Or MOFs could be programmed to release different drugs at different times.

“This is very powerful, because you are basically coding the behavior of molecules leaving the pores,” Yaghi said.

They could also be used to capture CO2 and, at the same time, convert the CO2 into a useful raw material for the chemical industry.

“In the long term, such structures with programmed atomic sequences can completely change our way of thinking about material synthesis,” write the authors. “The synthetic world could reach a whole new level of precision and sophistication that has previously been reserved for biology.”

The work was supported by the Center of Excellence for Nanomaterials and Clean Energy Applications at King Abdulaziz City for Science and Technology.

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Materials provided by University of California – Berkeley. Original written by Robert Sanders. Note: Content may be edited for style and length.

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Layer of nanoparticles could improve LED performance and lifetime

Adding a layer of nanoparticles to LED designs could help them produce more light for the same energy, and also increase their lifetime.

This is according to a team from Imperial College London and the Indian Institute of Technology (IIT) Guwahati who have found a new way to boost the amount of light LEDs produce. They report their innovation in the journal Light Science & Applications.

Making light-emitting diode (LED) light sources more efficient and longer-lasting will mean they use less energy, reducing the environmental impact of their electricity use. LEDs are used in a wide range of applications, from traffic lights and backlighting for electronic displays, smartphones, large outdoor screens, and general decorative lighting, to sensing, water purification, and decontamination of infected surfaces.

The team modelled the impact of placing a two-dimensional (single layer) of nanoparticles between the LED chip, which produces the light, and the transparent casing that protects the chip. Although the casing is necessary, it can cause unwanted reflections of the light emitted from the LED chip, meaning not all the light escapes.

They found that adding a layer of finely tuned nanoparticles could reduce these reflections, allowing up to 20 percent more light to be emitted. The reflections also increase the heat inside the device, degrading the LED chip faster, so reducing the reflections could also reduce the heat and increase the lifetime of LED chips.

Co-author Dr Debabrata Sikdar from IIT Guwahati, formerly a European Commission Marie Curie-Sklodowska Fellow at Imperial, commented: “While improvements to the casing have been suggested previously, most make the LED bulkier or more difficult to manufacture, diminishing the economic effect of the improvement.

“We think that our innovation, based on fundamental theory and the detailed, balanced optimization analysis we performed, could be introduced into existing manufacturing processes with little disruption or added bulk.”

Co-author Professor Sir John Pendry, from the Department of Physics at Imperial, said: “The simplicity of the proposed scheme and the clear physics underpinning it should make it robust and, hopefully, easily adaptable to the existing LED manufacturing process.

“It is obvious that with larger light extraction efficiency, LEDs will provide greater energy savings as well as longer lifetime of the devices. This will definitely have a global impact on the versatile LED-based applications and their multi-billion-dollar market worldwide.”

Co-author Professor Alexei Kornyshev, from the Department of Chemistry at Imperial, commented: “The predicted effect is a result of development of a systematic theory of various photonic effects related to nanoparticle arrays at interfaces, applied and experimentally tested in the context of earlier reported switchable mirror-windows, tuneable-colour mirrors, and optical filters.”

The next stage for the research will be manufacturing a prototype LED device with a nanoparticle layer, testing the best configurations predicted by the theory — including the size, shape, material and spacing of the nanoparticles, and how far the layer should be from the LED chip.

The authors believe that the principles used can work along with other existing schemes implemented for enhancing light extraction efficiency of LEDs. The same scheme could also apply to other optical devices where the transmission of light across interfaces is crucial, such as in solar cells.

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Materials provided by Imperial College London. Original written by Hayley Dunning. Note: Content may be edited for style and length.

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Surprising number of exoplanets could host life

Our solar system has one habitable planet — Earth. A new study shows other stars could have as many as seven Earth-like planets in the absence of a gas giant like Jupiter.

This is the conclusion of a study led by UC Riverside astrobiologist Stephen Kane published this week in the Astronomical Journal.

The search for life in outer space is typically focused on what scientists call the “habitable zone,” which is the area around a star in which an orbiting planet could have liquid water oceans — a condition for life as we know it.

Kane had been studying a nearby solar system called Trappist-1, which has three Earth-like planets in its habitable zone.

“This made me wonder about the maximum number of habitable planets it’s possible for a star to have, and why our star only has one,” Kane said. “It didn’t seem fair!”

His team created a model system in which they simulated planets of various sizes orbiting their stars. An algorithm accounted for gravitational forces and helped test how the planets interacted with each other over millions of years.

They found it is possible for some stars to support as many as seven, and that a star like our sun could potentially support six planets with liquid water.

“More than seven, and the planets become too close to each other and destabilize each other’s orbits,” Kane said.

Why then does our solar system only have one habitable planet if it is capable of supporting six? It helps if the planets’ movement is circular rather than oval or irregular, minimizing any close contact and maintain stable orbits.

Kane also suspects Jupiter, which has a mass two-and-a-half times that of all the other planets in the solar system combined, limited our system’s habitability.

“It has a big effect on the habitability of our solar system because it’s massive and disturbs other orbits,” Kane said.

Only a handful of stars are known to have multiple planets in their habitable zones. Moving forward, Kane plans to search for additional stars surrounded entirely by smaller planets. These stars will be prime targets for direct imaging with NASA telescopes like the one at Jet Propulsion Laboratory’s Habitable Exoplanet Observatory.

Kane’s study identified one such star, Beta CVn, which is relatively close by at 27 light years away. Because it doesn’t have a Jupiter-like planet, it will be included as one of the stars checked for multiple habitable zone planets.

Future studies will also involve the creation of new models that examine the atmospheric chemistry of habitable zone planets in other star systems.

Projects like these offer more than new avenues in the search for life in outer space. They also offer scientists insight into forces that might change life on our own planet one day.

“Although we know Earth has been habitable for most of its history, many questions remain regarding how these favorable conditions evolved with time, and the specific drivers behind those changes,” Kane said. “By measuring the properties of exoplanets whose evolutionary pathways may be similar to our own, we gain a preview into the past and future of this planet — and what we must do to main its habitability.”

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Materials provided by University of California – Riverside. Original written by Jules Bernstein. Note: Content may be edited for style and length.

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‘Lost’ world’s rediscovery is step towards finding habitable planets

The rediscovery of a lost planet could pave the way for the detection of a world within the habitable ‘Goldilocks zone’ in a distant solar system.

The planet, the size and mass of Saturn with an orbit of thirty-five days, is among hundreds of ‘lost’ worlds that University of Warwick astronomers are pioneering a new method to track down and characterise in the hope of finding cooler planets like those in our solar system, and even potentially habitable planets.

Reported in Astrophysical Journal Letters, the planet named NGTS-11b orbits a star 620 light years away and is located five times closer to its sun than Earth is to our own.

The planet was originally found in a search for planets in 2018 by the Warwick-led team using data from NASA’s TESS telescope. This uses the transit method to spot planets, scanning for the telltale dip in light from the star that indicates that an object has passed between the telescope and the star. However, TESS only scans most sections of the sky for 27 days. This means many of the longer period planets only transit once in the TESS data. And without a second observation the planet is effectively lost. The University of Warwick led team followed up one of these ‘lost’ planets using the telescopes at the Next-Generation Transit Survey (NGTS) in Chile and observed the star for seventy-nine nights, eventually catching the planet transiting for a second time nearly a year after the first detected transit.

Dr Samuel Gill from the Department of Physics at the University of Warwick said: “By chasing that second transit down we’ve found a longer period planet. It’s the first of hopefully many such finds pushing to longer periods.

“These discoveries are rare but important, since they allow us to find longer period planets than other astronomers are finding. Longer period planets are cooler, more like the planets in our own Solar System.

“NGTS-11b has a temperature of only 160°C — cooler than Mercury and Venus. Although this is still too hot to support life as we know it, it is closer to the Goldilocks zone than many previously discovered planets which typically have temperatures above 1000°C.”

The Goldilocks zone refers to a range of orbits that would allow a planet or moon to support liquid water: too close to its star and it will be too hot, but too far away and it will be too cold.

Co-author Dr Daniel Bayliss from the University of Warwick said: “This planet is out at a thirty-five days orbit, which is a much longer period than we usually find them. It is exciting to see the Goldilocks zone within our sights.”

Co-author Professor Pete Wheatley from the University of Warwick said: “The original transit appeared just once in the TESS data, and it was our team’s painstaking detective work that allowed us to find it again a year later with NGTS.

“NGTS has twelve state-of-the-art telescopes, which means that we can monitor multiple stars for months on end, searching for lost planets. The dip in light from the transit is only 1% deep and occurs only once every 35 days, putting it out of reach of other telescopes. “

Dr Gill adds: “There are hundreds of single transits detected by TESS that we will be monitoring using this method. This will allow us to discover cooler exoplanets of all sizes, including planets more like those in our own Solar System. Some of these will be small rocky planets in the Goldilocks zone that are cool enough to host liquid water oceans and potentially extraterrestrial life.”

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Twisting magnetic fields for extreme plasma compression

A new spin on the magnetic compression of plasmas could improve materials science, nuclear fusion research, X-ray generation and laboratory astrophysics, research led by the University of Michigan suggests.

The study shows that a spring-shaped magnetic field reduces the amount of plasma that slips out between the magnetic field lines.

Known as the fourth state of matter, plasma is a gas so hot that electrons rip free of their atoms. Researchers use magnetic compression to study extreme plasma states in which the density is high enough for quantum mechanical effects to become important. Such states occur naturally inside stars and gas giant planets due to compression from gravity.

The research group led by Ryan McBride, an associate professor of nuclear engineering and radiological sciences at U-M, tests ways to achieve states like this by imploding plasma cylinders with magnetic fields. These cylinders have a tendency to break up in a “sausage link” fashion when the magnetic field finds tiny divots in the cylinder’s surface and cuts into them. (The technical term is “sausage instability.”)

“It’s like trying to squeeze a stick of soft butter with your hands,” said McBride. “The butter squishes out between your fingers.”

The butter in McBride’s analogy is plasma and the fingers are magnetic field lines. His group looked for a way to keep the magnetic field from digging into the imperfections in the cylinder, instead causing the field to press more uniformly on the cylinder’s outer surface. They did this by twisting the magnetic field into a helix, that spring-like shape, and varying the angle at which the helix pressed on the plasma cylinder. This made it harder for the magnetic field to slice in — the field moved across many divots rather than pressing into any one divot for too long.

The most twisted magnetic configurations tested in these experiments reduced the length of the escaping plasma tentacles by about 70%. The research was done in collaboration with Sandia National Laboratories and the Laboratory of Plasma Studies at Cornell University.

The team changed the shape of the magnetic field by changing the way that the electrical current — over 1 million amperes — ran through the compression device. The electrical current typically runs up through the central cylinder that is to be compressed and then back down through straight “return current” columns that surround the central cylinder. This produces a cylindrical magnetic field that surrounds the central cylinder. To transform the cylindrical field into a helix, the team twisted the return-current columns around the central cylinder. The central cylinder starts out as a metal foil, but the huge electrical current quickly transforms the metal into a plasma. They ran the experiments on the Cornell Beam Research Accelerator.

“Designing the return current structures was an interesting balancing act,” said Paul Campbell, first author on the paper and a Ph.D. student in nuclear engineering and radiological sciences at U-M. “We weren’t sure we could even get these structures machined, but fortunately, metal 3D printing has advanced far enough that we were able to get them printed instead.”

Campbell explained that when the structures are more twisted, less current runs through them, so the columns had to be placed closer to the imploding plasma to compensate. At the same time, they needed gaps in the structure so that they could see what was going on with the implosion.

In line with replicating the conditions inside stars, magnetic compression is a method for compressing nuclear fusion fuel — typically variants of hydrogen — to study the processes that power stars. The technique can also generate powerful X-ray bursts and simulate astrophysical phenomena such as plasma jets near black holes.

A paper on this research, “Stabilization of liner implosions via a dynamic screw pinch,” is accepted by the journal Physical Review Letters. The research will also be featured in an invited talk at the annual conference of the American Physical Society’s Division of Plasma Physics in November 2020.

The study was funded by the National Science Foundation and the Department of Energy. The opinions, findings and conclusions or recommendations expressed are those of the authors and do not necessarily reflect the views of the National Science Foundation or the U.S. Department of Energy.

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Materials provided by University of Michigan. Original written by Kate McAlpine. Note: Content may be edited for style and length.

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The new tattoo: Drawing electronics on skin

One day, people could monitor their own health conditions by simply picking up a pencil and drawing a bioelectronic device on their skin. In a new study, University of Missouri engineers demonstrated that the simple combination of pencils and paper could be used to create devices that might be used to monitor personal health.

Their findings are published in the journal Proceedings of the National Academy of Sciences.

Zheng Yan, an assistant professor in the College of Engineering, said many existing commercial on-skin biomedical devices often contain two major components — a biomedical tracking component and a surrounding flexible material, such as plastic, to provide a supportive structure for the component to maintain an on-skin connection with a person’s body.

“The conventional approach for developing an on-skin biomedical electronic device is usually complex and often expensive to produce,” he said. “In contrast, our approach is low-cost and very simple. We can make a similar device using widely available pencils and paper.”

Since its invention, pencils — made of lead including various levels of graphite, clay and wax — have often been used for writing and drawing. In the study, the researchers discovered that pencils containing more than 90% graphite are able to conduct a high amount of energy created from the friction between paper and pencil caused by drawing or writing. Specifically, the researchers found pencils with 93% graphite were the best for creating a variety of on-skin bioelectronic devices drawn on commercial office copy paper. Yan said a biocompatible spray-on adhesive could also be applied to the paper to help it stick better to a person’s skin.

The researchers said their discovery could have broad future applications in home-based, personalized health care, education and remote scientific research such as during the COVID-19 pandemic. Yan said the group’s next step would be to further develop and test the use of the biomedical components, including electrophysiological, temperature and biochemical sensors.

“For example, if a person has a sleep issue, we could draw a biomedical device that could help monitor that person’s sleep levels,” he said. “Or in the classroom, a teacher could engage students by incorporating the creation of a wearable device using pencils and paper into a lesson plan. Furthermore, this low-cost, easily customizable approach could allow scientists to conduct research at home, such as during a pandemic.”

An additional benefit to their approach, Yan said, is that paper can decompose in about a week, compared to many commercial devices that contain components that are not easily broken down.

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Excitation of robust materials

In physics, they are currently the subject of intensive research; in electronics, they could enable completely new functions. So-called topological materials are characterised by special electronic properties, which are also very robust against external perturbations. This material group also includes tungsten ditelluride. In this material, such a topologically protected state can be “broken up” using special laser pulses within a few trillionths of a second (“picoseconds”) and thus change its properties. This could be a key requirement for realising extremely fast, optoelectronic switches. For the first time physicists at Kiel University (CAU), in cooperation with researchers at the Max Planck Institute for Chemical Physics of Solids (MPI-CPfS) in Dresden, Tsinghua University in Beijing and Shanghai Tech University, have been able to observe changes to the electronic properties of this material in experiments in real-time. Using laser pulses, they put the atoms in a sample of tungsten ditelluride into a state of controlled excitation, and were able to follow the resulting changes in the electronic properties “live” with high-precision measurements. They published their results recently in the scientific journal Nature Communications.

“If these laser-induced changes can be reversed again, we essentially have a switch that can be activated optically, and which can change between different electronic states,” explained Michael Bauer, professor of solid state physics at the CAU. Such a switching process has already been predicted by another study, in which researchers from the USA were recently able to directly observe the atomic movements in tungsten ditelluride. In their study, the physicists from the Institute of Experimental and Applied Physics at the CAU now focused on the behaviour of the electrons, and how the electronic properties in the same material can be altered using laser pulses.

Weyl semimetals with unusual electronic properties

“Some of the electrons in tungsten ditelluride are highly mobile, so they are excellent information carriers for electronic applications. This is due to the fact that they behave like so-called Weyl fermions,” said doctoral researcher Petra Hein to explain the unusual properties of the material, also known as a Weyl semimetal. Weyl fermions are massless particles with special properties and have previously only been observed indirectly as “quasi-particles” in solids like tungsten ditelluride. “For the first time, we were now able to make the changes in the areas of the electronic structure visible, in which these Weyl properties are exhibited.”

Excitations of the material changes its electronic properties

To capture the barely-visible changes in the electronic properties a highly-sensitive experimental design, extremely precise measurements and an extensive analysis of the data obtained were required. During the past years the Kiel research team was able to develop such an experiment with the necessary long-term stability. With the generated laser pulses they put the atoms inside a sample of tungsten ditelluride into a state of vibrational excitation. Different overlapping vibrational excitations arose, which in turn changed the electronic properties of the material. “One of these atomic vibrations was known to change the electronic Weyl properties. We wanted to find out exactly what this change looks like,” said Hein to describe one of the key goals of the study.

Series of snapshots shows how properties change

In order to observe this specific process, the research team irradiated the material with a second laser pulse after a few picoseconds. This released electrons from the sample, which allowed drawing conclusions about the electronic structure of the material — the method is known as “time-resolved photoelectron spectroscopy.” “Due to the short exposure time of only 0.1 picoseconds, we get a snapshot of the electronic state of the material. We can combine many of these individual images into a film and thereby observe how the material reacts to the excitation by the first laser pulse,” said Dr Stephan Jauernik to explain the measurement method.

Recording a single data set on the extremely short modification process typically took one week. The Kiel research team evaluated a large number of such data sets using a newly developed analytical approach and was thus able to visualize the changes in the electronic Weyl properties of tungsten ditelluride.

Extremely short switching processes conceivable

“Our results demonstrate the sensitive and highly-selective interplay between the vibrations of the atoms of the solid and the unusual electronic properties of tungsten ditelluride,” summarised Bauer. Follow-up research aims at investigating whether such electronic switching processes can be triggered even faster — directly by the irradiating laser pulse — as has already been theoretically predicted for other topological materials.

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Microscopic structures could improve perovskite solar cells

Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these electron highways could make perovskite solar cells even more powerful.

When solar cells convert sunlight into electricity, the electrons of the material inside the cell absorb the energy of the light. Traditionally, this light-absorbing material is silicon, but perovskites could prove to be a cheaper alternative. The electrons excited by the sunlight are collected by special contacts on the top and bottom of the cell. However, if the electrons remain in the material for too long, they can lose their energy again. To minimize losses, they should therefore reach the contacts as quickly as possible.

Microscopically small structures in the perovskites — so-called ferroelastic twin domains — could be helpful in this respect: They can influence how fast the electrons move. An international research group led by Stefan Weber at the Max Planck Institute for Polymer Research in Mainz discovered this phenomenon. The stripe-shaped structures that the scientists investigated form spontaneously during the fabrication of the perovskite by mechanical stress in the material. By combining two microscopy methods, the researchers were able to show that electrons move much faster parallel to the stripes than perpendicular to them. “The domains act as tiny highways for electrons,” compares Stefan Weber.

Possible applications in light-emitting diodes and radiation detectors

For their experiments, the researchers first had to visualize the stripe-shaped domains. They succeeded in doing this with a piezo force microscope (PFM). Five years ago, Weber and his colleagues discovered the domains for the first time in a perovskite crystal using this method. “Back then, we already wondered whether the structures had an influence on the operation of a perovskite solar cell,” Weber explains. “Our latest results now show that this is the case.”

The breakthrough came when the researchers compared their PFM images with data obtained from another method called photoluminescence microscopy. “Our photoluminescence detector works like a speed trap,” explains Ilka Hermes, researcher in Weber’s group and first author of the study. “We use it to measure the speed of electrons in different directions at the microscopic level.” Hermes discovered that along the stripes the electrons moved about 50 to 60 percent faster than perpendicular to them. “If we were able to make the stripes point directly to the electrodes, a perovskite solar cell could become much more efficient,” concludes Hermes.

With the new results, not only solar cells could be improved. Other optoelectronic applications such as light-emitting diodes or radiation detectors could also benefit from directed charge transport. “In general, it is an advantage if we can direct the electrons in the right direction,” explains Stefan Weber. The researchers’ idea: to put perovskite crystals under mechanical stress during their production. This so-called strain engineering would enable an optimized orientation of the electron highways.

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Implants: Can special coatings reduce complications after implant surgery?

New coatings on implants could help make them more compatible. Researchers at the Martin Luther University Halle-Wittenberg (MLU) have developed a new method of applying anti-inflammatory substances to implants in order to inhibit undesirable inflammatory reactions in the body. Their study was recently published in the International Journal of Molecular Sciences.

Implants, such as pacemakers or insulin pumps, are a regular part of modern medicine. However, it is not uncommon for complications to arise after implantation. The immune system identifies the implant as a foreign body and attempts to remove it. “This is actually a completely natural and useful reaction by the immune system,” says Professor Thomas Groth, a biophysicist at MLU. It helps to heal wounds and kills harmful pathogens. If this reaction does not subside on its own after a few weeks, it can lead to chronic inflammation and more serious complications. “The immune system attracts various cells that try to isolate or remove the foreign entity. These include macrophages, a type of phagocyte, and other types of white blood cells and connective tissue cells,” explains Groth. Implants can become encapsulated by connective tissue, which can be very painful for those affected. In addition, the implant is no longer able to function properly. Drugs that suppress the immune response in a systemic manner are often used to treat chronic inflammation, but may have undesired side effects.

Thomas Groth’s team was looking for a simple way to modify the immune system’s response to an implant in advance. “This is kind of tricky, because we obviously do not want to completely turn off the immune system as its processes are vital for healing wounds and killing pathogens. So, in fact we only wanted to modulate it,” says the researcher. To do this, his team developed a new coating for implants that contains anti-inflammatory substances. For their new study, the team used two substances that are already known to have an anti-inflammatory effect: heparin and hyaluronic acid.

In the laboratory, the scientists treated a surface with the two substances by applying a layer that was only a few nanometres thick. “The layer is so thin that it does not affect how the implant functions. However, it must contain enough active substance to control the reaction of the immune system until the inflammatory reaction has subsided,” adds Groth. In cell experiments, the researchers observed how the two substances were absorbed by the macrophages, thereby reducing inflammation in the cell cultures. The untreated cells showed clear signs of a pronounced inflammatory reaction. This is because the active substances inside the macrophages interfere with a specific signalling pathway that is crucial for the immune response and cell death. “Both heparin and hyaluronic acid prevent the release of certain pro-inflammatory messenger substances. Heparin is even more effective because it can be absorbed by macrophage cells,” Groth concludes.

So far, the researchers have only tested the method on model surfaces and in cell cultures. Further studies on real implants and in model organisms are to follow.

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