Last year, researchers in the US caused a big stir when they showed that rotating two stacked graphene layers by a “magical” angle of 1.1 degrees turns graphene superconducting — a striking example of how the combination of atomically thin materials can produce completely new electrical properties.

Precision alignment

Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel have now taken this concept one step further. They placed a layer of graphene between two boron nitride layers, which is often serves to protect the sensitive carbon structure. Doing so, they aligned the layers very precisely with the crystal lattice of the graphene.

The effect observed by the physicists in Professor Christian Schönenberger’s team is commonly known as a moiré pattern: when two regular patterns are superimposed, a new pattern results with a larger periodic lattice.

New three-layer superlattice

Lujun Wang, a member of the SNI PhD School and researcher in Schönenberger’s team, also observed effects of this kind of superlattice when he combined layers of boron nitride and graphene. The atoms are arranged hexagonally in all layers. If they are stacked on top of each other, larger regular patterns emerge, with a size depending on the angle between the layers.

It had already been shown that this works with a two-layer combination of graphene and boron nitride, but the effects due to a second boron nitride layer had not yet been found.

When the physicists from Basel experimented with three layers, two superlattices were formed between the graphene and the upper and the lower boron nitride layer, respectively. The superposition of all three layers created an even larger superstructure than possible with only one layer.

Scientists are very interested in these types of synthetic materials, since the different moiré patterns can be used to change or artificially produce new electronic material properties.

“To put it simply, the atomic patterns determine the behavior of electrons in a material, and we are combining different naturally occurring patterns to create new synthetic materials,” explains Dr. Andreas Baumgartner, who supervised the project. “Now we have discovered effects in these tailor-made electronic devices that are consistent with a three-layer superstructure,” he adds.

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“Most people have experienced that their hearing is impaired and the ear feels numb after listening to loud sounds. After a while hearing returns to normal. We have discovered that a tiny structure in the cochlea known as the tectorial membrane plays an important role in this process, by acting as a storage depot for calcium ions. These calcium ions contribute to regulating the function of the sensory cells,” says Anders Fridberger at the Department of Clinical and Experimental Medicine, who has led the study.

Calcium ions, which are calcium atoms with a positive charge, play a key role in the processes that make hearing possible. The conversion of sound waves to nerve impulses takes place in the inner ear, also known as the cochlea, which looks like the spiral shell that some snails have. The cochlea contains many sensory cells, which detect sounds and generate signals that are passed on to the brain.

Previous research has shown that the fluid that surrounds the sensory cells in the cochlea has a low concentration of calcium ions. There were, however, questions surrounding this, because sensory cells that are placed in fluids with the natural level of calcium no longer work normally. The scientists at LiU have investigated the calcium ion concentration in the inner ear of guinea pigs, which is very similar to the human ear. By fluorescently labelling the calcium ions, the researchers discovered that a membrane that lies on top of the sensory cells, the tectorial membrane, has a much higher concentration of calcium ions than the surrounding fluid. The membrane seems to function as a store, such that the sensory cells are surrounded by higher levels of calcium ions than previously believed.

When the scientists added a substance that mops up calcium ions, the sensory cells ceased to function. In the next step, they exposed the inner ear to noise levels that correspond to those experienced at rock concerts, which had the same effect.

“When we expose isolated inner ears to loud noise in the lab, the level of calcium in the tectorial membrane falls, and the sensory cells cease to function. After a while, however, the calcium ion concentration returns to its previous level, and the sensory cells start to function again,” says Anders Fridberger.

Until now, scientists have thought that the tiny membrane has a mainly mechanical function, but the discovery made by the LiU researchers suggests that the tectorial membrane may play an important role in regulating hearing by storing calcium.

“We knew that the tectorial membrane is necessary for hearing, and that it must be intact and correctly located, but it has been unclear why damage to this membrane contributes to impaired hearing,” says Pierre Hakizimana, one of the researchers behind the study.

The research group is now planning to investigate whether the same mechanism is important in age-related hearing impairment. The research has been financed by, among other contributors, the Swedish Research Council, the Torsten Söderberg Foundation, the Tysta Skolan Foundation and AFA Försäkrings AB.

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This discovery, recently published in Nature Communications, comes as an extension of the development of a polymer ion-gel, which promises to outperform conventional flammable liquid battery electrolytes. Now, equipped with evidence of the double helix structure, the potential for this high-performance material extends well beyond batteries.

“This polymer has been around for 30 years, and no one had figured out that it’s a double helix,” said Associate Professor of Chemistry Lou Madsen, who led this research. “Double helices in synthetic systems are essentially unheard of.”

Madsen led an international collaboration, which included Virginia Tech professors Rui Qiao (mechanical engineering) and Robert Moore (chemistry), as well as Theo Dingemans at the University of North Carolina at Chapel Hill and Bernd Ensing at the University of Amsterdam in the Netherlands. All three Virginia Tech professors are affiliated with the Macromolecules Innovation Institute.

Rigidity could aid new composites

Composites are engineering materials that bond multiple components to create a new set of improved properties.

Tires and modern plane fuselages are examples of composites. They require a core material, such as rubber in the tires example, to be mixed with other materials, such as reinforcing fiber fillers, for added strength.

Madsen and his team had already shown in 2016 that PBDT could mix with liquid ions to create a solid battery electrolyte.

“Before we were confident about this double helix, we discovered PBDT could mix with liquid ions and make this electrolyte that has very good conductivity and is also mechanically stiff,” Madsen said. “We made something with PBDT, but we wanted to know why it works so well. We had evidence it was a double helix but hadn’t appreciated most of its features.”

Double helix structures, such as DNA, are well known in nature, and they have high bending stiffness. DNA has a diameter of about 2.5 nanometers and is rigid up to about 50 nanometers in length, where it begins to bend. That creates a “rigidity ratio” of about 20 to 1, similar to a carrot stick.

In comparison, PBDT has a rigidity ratio of 1,000 to 1, making it one of the stiffest molecules yet discovered.

The polymer’s supreme rigidity means that only a fraction of it would be needed to achieve comparable performance to conventional reinforcing fillers. Furthermore, the process for creating it is extremely cheap and easy.

“If you’re using conventional fillers in a composite, you might use 10 percent to get the properties you want,” Madsen said. “But PBDT has this long stiffness length and a tiny diameter. This means you might only have to put in 1 or 2 percent to get a material that’s highly enhanced.”

From X-rays and DNA to computational modeling

Back in 2014, Madsen and his Ph.D. student Ying Wang had thought the polymer was a double helix but didn’t have sturdy evidence. They then began X-ray studies on PBDT, similar to the studies that Rosalind Franklin conducted on DNA in the early 1950s that led to the discovery of the DNA double helix. Sure enough, the PBDT X-ray was similar to Franklin’s DNA X-ray. They further used a technique similar to MRI to bolster their evidence.

Madsen then turned to Ensing in Holland and then to Qiao at Virginia Tech for help in understanding the polymer with computational models.

Qiao said he initially didn’t think the simulation would even work.

“A simulation of a self-assembly to form a double helical structure — I had never heard of it except people had done it for DNA,” Qiao said. “But for this kind of simulation, it’s very difficult. My student tried anyway and miraculously it worked. We tried a bunch of different conditions, different ways of running simulations, but the results were robust, which gave us some confidence that it is a real double helix.”

The confirmation of the double helix structure opens up possibilities for PBDT’s potential application beyond battery electrolytes, such as lightweight aerospace materials.

“The application of this is really going to be limited by our imagination,” Qiao said. “Now we have a new kind of Lego piece. As more people hear about this material, they will come up with their own way of using it. What will really come out of it, we may not envision today.”

An international team led by the TUM chemist Professor Jürgen Hauer has now succeeded in determining the spectral properties of individual molecules. The researchers acquired the absorption and emission spectra of the investigated molecules over a broad spectral range in a single measurement to accurately determine how the molecules interact with their environment, capturing and releasing energy.

Normally, these kinds of measurements are averaged over thousands, even millions, of molecules, sacrificing important detail information. “Previously, emission spectra could be routinely acquired, but absorption measurements on individual molecules were extremely expensive,” explains Hauer. “We have now attained the ultimate limit of detectability.”

Compact apparatus, quick measurement

The new method is based on a compact, merely DIN-A4-sized instrument that the Munich chemists developed in collaboration with colleagues at the Politecnico di Milano.

The key: It generates a double laser pulse with a controlled delay in between. The second pulse modulates the emission spectrum in a specific manner, which in turn provides information about the absorption spectrum. This information is then evaluated using a Fourier transformation.

“The primary advantage is that we can, with little effort, transform a conventional measurement setup for acquiring emission spectra into a device for measuring emission and absorption spectra,” says Hauer. The measurement itself is relatively easy. “At nine o’clock in the morning, we installed the apparatus into the setup at the University of Copenhagen,” says Hauer. “At half past eleven, already, we had our first useful measurement data.”

On the tracks of photosynthesis

Using the new spectroscopy method, chemists hope to now study individual molecules, to understand phenomena such as the energy flow in metal-organic compounds and physical effects in molecules when they come into contact with water and other solvents.

The influence of solvents at the single molecule level is still poorly understood. The chemists also want to display the flow of energy in a time-resolved manner to understand why energy flows faster and more efficiently in certain molecules than in others. “Specifically, we are interested in the transfer of energy in biological systems in which photosynthesis takes place,” says Hauer.

The goal: organic solar cells

The researchers have cast their view on the light collection complex LH2 for future applications. “Once we understand the natural light-harvesting complexes, we can start thinking about artificial systems for deployment in photovoltaics,” says Hauer. The findings could form the basis for future technologies in photovoltaics. The goal is the development of a novel organic solar cell.

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A considerable number of massive stars have a close companion star. Led by researchers at Kyoto University, a team of international researchers observed that some stars exploding as supernovae may release part of their hydrogen layers to their companion stars before the explosion.

“In a binary star system, the star can interact with the companion during its evolution. When a massive star evolves, it swells to become a red supergiant star, and the presence of a companion star may disrupt the outer layers of this supergiant star, which is rich in hydrogen. Therefore, binary interaction may remove the hydrogen layer of the evolved star either partially or completely,” says Postdoctoral Researcher Hanindyo Kuncarayakti from the Department of Physics and Astronomy at the University of Turku in Finland and the Finnish Centre for Astronomy with ESO. Kuncarayakti is a member of the researcher team that made the observations.

As the star has released a significant part of its hydrogen layer due to the close companion star, its explosion can be observed as a type Ib or IIb supernova.

A star more massive explodes as a type Ic supernova after having lost its helium layer, too, due to the so-called stellar winds. Stellar winds are massive streams of energetic particles from the surface of the star that may remove the helium layer below the hydrogen layer.

“However, the companion star does not have a significant role in what happens to the exploding star’s helium layer. Instead, stellar winds play a key role in the process as their intensity is dependent on the star’s own initial mass. According to theoretical models and our observations, the effects of stellar winds on the mass loss of the exploding star are significant only for stars above a certain mass range,” says Kuncarayakti.

The research group’s observations show that the so-called hybrid mechanism is a potential model in describing the evolution of massive stars. The hybrid mechanism indicates that during its lifespan, the star may gradually lose part of its mass both to its companion star as a result of interaction as well as due to stellar winds.

“By observing stars dying as supernovae and the phenomena within, we can improve our understanding on massive star evolution. However, our understanding of massive star evolution is still far from complete,” states Professor Seppo Mattila from the Department of Physics and Astronomy at the University of Turku.

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The Milky Way weighs in at about 1.5 trillion solar masses (one solar mass is the mass of our Sun), according to the latest measurements. Only a few percent of this is contributed by the approximately 200 billion stars in the Milky Way and includes a 4-million-solar-mass supermassive black hole at the center. Most of the rest of the mass is locked up in dark matter, an invisible and mysterious substance that acts like scaffolding throughout the universe and keeps the stars in their galaxies.

Earlier research dating back several decades used a variety of observational techniques that provided estimates for our galaxy’s mass ranging between 500 billion to 3 trillion solar masses. The improved measurement is near the middle of this range.

“We want to know the mass of the Milky Way more accurately so that we can put it into a cosmological context and compare it to simulations of galaxies in the evolving universe,” said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “Not knowing the precise mass of the Milky Way presents a problem for a lot of cosmological questions.”

The new mass estimate puts our galaxy on the beefier side, compared to other galaxies in the universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.

Astronomers used Hubble and Gaia to measure the three-dimensional movement of globular star clusters — isolated spherical islands each containing hundreds of thousands of stars each that orbit the center of our galaxy.

Although we cannot see it, dark matter is the dominant form of matter in the universe, and it can be weighed through its influence on visible objects like the globular clusters. The more massive a galaxy, the faster its globular clusters move under the pull of gravity. Most previous measurements have been along the line of sight to globular clusters, so astronomers know the speed at which a globular cluster is approaching or receding from Earth. However, Hubble and Gaia record the sideways motion of the globular clusters, from which a more reliable speed (and therefore gravitational acceleration) can be calculated.

The Hubble and Gaia observations are complementary. Gaia was exclusively designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and track their motions. It made exacting all-sky measurements that include many globular clusters. Hubble has a smaller field of view, but it can measure fainter stars and therefore reach more distant clusters. The new study augmented Gaia measurements for 34 globular clusters out to 65,000 light-years, with Hubble measurements of 12 clusters out to 130,000 light-years that were obtained from images taken over a 10-year period.

When the Gaia and Hubble measurements are combined as anchor points, like pins on a map, astronomers can estimate the distribution of the Milky Way’s mass out to nearly 1 million light-years from Earth.

“We know from cosmological simulations what the distribution of mass in the galaxies should look like, so we can calculate how accurate this extrapolation is for the Milky Way,” said Laura Watkins of the European Southern Observatory in Garching, Germany, lead author of the combined Hubble and Gaia study, to be published in The Astrophysical Journal. These calculations based on the precise measurements of globular cluster motion from Gaia and Hubble enabled the researchers to pin down the mass of the entire Milky Way.

The earliest homesteaders of the Milky Way, globular clusters contain the oldest known stars, dating back to a few hundred million years after the big bang, the event that created the universe. They formed prior to the construction of the Milky Way’s spiral disk, where our Sun and solar system reside.

“Because of their great distances, globular star clusters are some of the best tracers astronomers have to measure the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk of stars,” said Tony Sohn of STScI, who led the Hubble measurements.

The international team of astronomers in this study are Laura Watkins (European Southern Observatory, Garching, Germany), Roeland van der Marel (Space Telescope Science Institute, and Johns Hopkins University Center for Astrophysical Sciences, Baltimore, Maryland), Sangmo Tony Sohn (Space Telescope Science Institute, Baltimore, Maryland), and N. Wyn Evans (University of Cambridge, Cambridge, United Kingdom).

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.