Bacteria as Blacksmiths

A hot bath is a place to relax. For scientists, it is also where molecules or tiny building blocks meet to form materials. Researchers at the Institute of Science and Technology Austria (ISTA) take it to the next level and use the energy of swimming bacteria to forge materials. A recent study in Nature Physics shows us how this works and the potential sustainability benefits that may arise from this innovative approach.

You never know when dazzling ideas will strike you. Sometimes they emerge from the most unexpected places, like a boulder gym in Vienna. Such was the case for ISTA's Daniel Grober, a graduate student in the research group of physicist Jérémie Palacci, who had been working on how to assemble materials leveraging the energy of swimming bacteria, and Mehmet Can Uçar, a postdoc in Edouard Hannezo's group. Fueled by their shared passion for science and climbing, discussions at the gym turned into a paper-pen model of Grober's experiment. Their concept captivated Ivan Palaia, a postdoc in Anđela Šarić's group, who decided to join the task force.

Together, this dynamic all-ISTA trio embarked on a collaborative effort that now reaches its pinnacle with a paper published today in Nature Physics. The study shows a novel experimental strategy to fabricate materials from small building blocks. It translates ideas from metallurgy -- the fine art of blacksmithing, where cycles of high temperature and slow cooling set a material's structure -- into soft materials, using the activity from a bath of swimming bacteria.

What are active baths?

In Jérémie Palacci's research group at the Institute of Science and Technology Austria, it is all about microscopic particles. "Our work revolves around tiny 'Lego'-like building blocks that are a hundred times smaller than a hair. We try to understand how these components come together and form larger structures," he explains. Typically, when these building blocks are suspended in water, they jiggle due to temperature, which provides the energy for the particles to hop back and forth randomly. A phenomenon first rationalized by Einstein in 1905 and known as Brownian motion.

To introduce order amidst the chaos, adding an "active agent" to the water is beneficial. This results in what is known as an "active bath," where the agent acts like a small fire. In principle, with this extra energy, you can hope to control the assembly and properties of materials -- the way the blacksmith forges. However, until now, an approach where for instance bacteria is used to forge, had never been explored.

Bacteria -- the fire

Palacci's student, Daniel Grober, took on this challenge and started to construct such an active bath with characteristics inspired by metallurgy. Grober says, "We used E. coli bacteria as an active agent, as their swimming movement provided energy and some kind of agitation -- 'temperature' for a physicist, equivalent to 2000 °C, similar to the one needed to craft metals. But because it is made by bacteria, and it is not a real oven, it remains gentle enough to be used with gels and soft materials without burning them." The building blocks were microscopic particles in the form of sticky colloids -- round beads that stick together when in contact.

This idea proved to be successful. The swimming bacteria effectively amplified the motion of the beads, resulting in the formation of aggregations and gel-like structures.

Dance to the beat of bacteria

Moreover, the observation of these newly formed clusters showed an intriguing singularity. At all times, the aggregates were spinning clockwise, but very slowly. To shed light on this observation, Grober conducted a statistical analysis of the system's motion. He confirmed a slow and persistent rotation of the aggregates that originates in the clockwise spin (chirality) of the E. coli flagella -- the minuscule appendages that propel the bacteria in their movement. The scientist suspected that the rotational motion played a pivotal role in forming the unconventional structures he observed.

Presenting his work in a weekly lab meeting intrigued his colleague Ivan Palaia, which led to the understanding of the phenomenon. Palaia proposed a minimal computational model, to capture the chirality of the bacterial bath without simulating the swimming bacteria. The computer simulations were first validated by quantitatively reproducing the experimental results before providing a deeper understanding of the mechanism. The model confirmed the salient role of the rotation in shaping gels, by forming remarkable structures with exotic mechanical properties that cannot be achieved conventionally.

More to come in the future

This utilization of bacterial baths to assemble unconventional materials holds great promise. For instance, although the study was limited to 2D structures at the micron scale, the approach was designed for its potential in upscaling. "With this innovative approach, it could theoretically be possible to construct 3D samples, large enough to be held in the palm of my hand!" Palacci adds. This advancement could also enhance the sustainability of material production by harnessing energy from bacteria rather than relying on external energy sources.

Read more at Science Daily

First X-ray of a single atom

A team of scientists from Ohio University, Argonne National Laboratory, the University of Illinois-Chicago, and others, led by Ohio University Professor of Physics, and Argonne National Laboratory scientist, Saw Wai Hla, have taken the world's first X-ray SIGNAL (or SIGNATURE) of just one atom. This groundbreaking achievement was funded by the U.S. Department of Energy, Office of Basic Energy Sciences and could revolutionize the way scientists detect the materials.

Since its discovery by Roentgen in 1895, X-rays have been used everywhere, from medical examinations to security screenings in airports. Even Curiosity, NASA's Mars rover, is equipped with an X-ray device to examine the materials composition of the rocks in Mars. An important usage of X-rays in science is to identify the type of materials in a sample. Over the years, the quantity of materials in a sample required for X-ray detection has been greatly reduced thanks to the development of synchrotron X-rays sources and new instruments. To date, the smallest amount one can X-ray a sample is in attogram, that is about 10,000 atoms or more. This is due to the X-ray signal produced by an atom being extremely weak so that the conventional X-ray detectors cannot be used to detect it. According to Hla, it is a long-standing dream of scientists to X-ray just one atom, which is now being realized by the research team led by him.

"Atoms can be routinely imaged with scanning probe microscopes, but without X-rays one cannot tell what they are made of. We can now detect exactly the type of a particular atom, one atom-at-a-time, and can simultaneously measure its chemical state," explained Hla, who is also the director of the Nanoscale and Quantum Phenomena Institute at Ohio University. "Once we are able to do that, we can trace the materials down to ultimate limit of just one atom. This will have a great impact on environmental and medical sciences and maybe even find a cure that can have a huge impact for humankind. This discovery will transform the world."

Their paper, published in the scientific journal Nature on May 31, 2023, and gracing the cover of the print version of the scientific journal on June 1, 2023, details how Hla and several other physicists and chemists, including Ph.D. students at OHIO, used a purpose-built synchrotron X-ray instrument at the XTIP beamline of Advanced Photon Source and the Center for Nanoscale Materials at Argonne National Laboratory.

For demonstration, the team chose an iron atom and a terbium atom, both inserted in respective molecular hosts. To detect X-ray signal of one atom, the research team supplemented conventional detectors in X-rays with a specialized detector made of a sharp metal tip positioned at extreme proximity to the sample to collect X-ray excited electrons -- a technique known as synchrotron X-ray scanning tunneling microscopy or SX-STM. X-ray spectroscopy in SX-STM is triggered by photoabsorption of core level electrons, which constitutes elemental fingerprints and is effective in identifying the elemental type of the materials directly.

According to Hla, the spectrums are like fingerprints, each one being unique and able to detect exactly what it is.

"The technique used, and concept proven in this study, broke new ground in X-ray science and nanoscale studies," said Tolulope Michael Ajayi, who is the first author of the paper and doing this work as part of his Ph.D. thesis. "More so, using X-rays to detect and characterize individual atoms could revolutionize research and give birth to new technologies in areas such as quantum information and the detection of trace elements in environmental and medical research, to name a few. This achievement also opens the road for advanced materials science instrumentation."

For the last 12 years, Hla has been involved in the development of an SX-STM instrument and its measurement methods together with Volker Rose, a scientist at the Advanced Photon Source at Argonne National Laboratory.

"I have been able to successfully supervise four OHIO graduate students for their Ph.D. theses related to SX-STM method development over a 12-year period. We have come a long way to achieve the detection of a single atom X-ray signature," Hla said.

Hla's study is focused on nano and quantum sciences with a particular emphasis on understanding materials' chemical and physical properties at the fundamental level -- on an individual atom basis. In addition to achieving X-ray signature of one atom, the team's key goal was to use this technique to investigate the environmental effect on a single rare-earth atom.

"We have detected the chemical states of individual atoms as well," Hla explained. "By comparing the chemical states of an iron atom and a terbium atom inside respective molecular hosts, we find that the terbium atom, a rare-earth metal, is rather isolated and does not change its chemical state while the iron atom strongly interacts with its surrounding."

Many rare-earth materials are used in everyday devices, such as cell phones, computers and televisions, to name a few, and are extremely important in creating and advancing technology. Through this discovery, scientists can now identify not only the type of element but its chemical state as well, which will allow them to better manipulate the atoms inside different materials hosts to meet the ever-changing needs in various fields. Moreover, they have also developed a new method called "X-ray excited resonance tunneling or X-ERT" that allows them to detect how orbitals of a single molecule orient on a material surface using synchrotron X-rays.

"This achievement connects synchrotron X-rays with quantum tunneling process to detect X-ray signature of an individual atom and opens many exciting research directions including the research on quantum and spin (magnetic) properties of just one atom using synchrotron X-rays," Hla said.

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Searching for life with space dust

Following enormous collisions, such as asteroid impacts, some amount of material from an impacted world may be ejected into space. This material can travel vast distances and for extremely long periods of time. In theory this material could contain direct or indirect signs of life from the host world, such as fossils of microorganisms. And this material could be detectable by humans in the near future, or even now.

When you hear the words vacuum and dust in a sentence, you may groan at the thought of having to do the housework. But in astronomy, these words have different connotations. Vacuum of course refers to the void of space. Dust, however, means diffuse solid material floating through space. It can be an annoyance to some astronomers as it may hinder their views of some distant object. Or dust could be a useful tool to help other astronomers learn about something distant without having to leave the safety of our own planet. Professor Tomonori Totani from the University of Tokyo's Department of Astronomy has an idea for space dust that might sound like science fiction but actually warrants serious consideration.

"I propose we study well-preserved grains ejected from other worlds for potential signs of life," said Totani. "The search for life outside our solar system typically means a search for signs of communication, which would indicate intelligent life but precludes any pre-technological life. Or the search is for atmospheric signatures that might hint at life, but without direct confirmation there could always be an explanation that does not require life. However, if there are signs of life in dust grains, not only could we be certain, but we could also find out soon."

The basic idea is that large asteroid strikes can eject ground material into space. There is a chance that recently deceased or even fossilized microorganisms could be contained in some rocky material in this ejecta. This material will vary in size greatly, with different-sized pieces behaving differently once in space. Some larger pieces might fall back down or enter permanent orbits around a local planet or star. And some much smaller pieces might be too small to contain any verifiable signs of life. But grains in the region of 1 micrometer (one-thousandth of a millimeter) could not only host a specimen of a single-celled organism, but they could also potentially escape their host solar system altogether, and under the right circumstances, maybe even venture to ours.

"My paper explores this idea using available data on the different aspects of this scenario," said Totani. "The distances and times involved can be vast, and both reduce the chance any ejecta containing life signs from another world could even reach us. Add to that the number of phenomena in space that can destroy small objects due to heat or radiation, and the chances get even lower. Despite that, I calculate around 100,000 such grains could be landing on Earth every year. Given there are many unknowns involved, this estimate could be too high or too low, but the means to explore it already exist so it seems like a worthwhile pursuit."

There may be such grains already on Earth, and in plentiful amounts, preserved in places such as the Antarctic ice, or under the seafloor. Space dust in these places could be retrieved relatively easily, but discerning extrasolar material from material originating in our own solar system is still a complex matter. If the search is extended to space itself, however, there are already missions that capture dust in the vacuum using ultralight materials called aerogels.

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New method creates material that could create the next generation of solar cells

Perovskites, a family of materials with unique electric properties, show promise for use in a variety fields, including next-generation solar cells. A Penn State-led team of scientists created a new process to fabricate large perovskite devices that is more cost- and time-effective than previously possible and that they said may accelerate future materials discovery.

"This method we developed allows us to easily create very large bulk samples within several minutes, rather than days or weeks using traditional methods," said Luyao Zheng, a postdoctoral researcher in the Department of Materials Science at Penn State and lead author on the study. "And our materials are high quality -- their properties can compete with single-crystal perovskites."

The researchers used a sintering method called the electrical and mechanical field-assisted sintering technique (EM-FAST) to create the devices. Sintering is a commonly used process to compress fine powders into a solid mass of material using heat and pressure.

A typical process for making perovskites involves wet chemistry -- the materials are liquefied in a solvent solution and then solidified into thin films. These materials have excellent properties, but the approach is expensive and inefficient for creating large perovskites and the solvents used may be toxic, the scientists said.

"Our technique is the best of both worlds," said Bed Poudel, a researcher professor at Penn State and a co-author. "We get single-crystal-like properties, and we don't have to worry about size limitations or any contamination or yield of toxic materials."

Because it uses dry materials, the EM-FAST technique opens the door to include new dopants, ingredients added to tailor device properties, that are not compatible with the wet chemistry used to make thin films, potentially accelerating the discovery of new materials, the scientists said.

"This opens up possibilities to design and develop new classes of materials, including better thermoelectric and solar materials, as well as X- and γ-ray detectors," said Amin Nozariasbmarz, assistant research professor at Penn State and a co-author. "Some of the applications are things we already know, but because this is a new technique to make new halide perovskite materials with controlled properties, structures, and compositions, maybe there is room in the future for new breakthroughs to come from that."

In addition, the new process allows for layered materials -- one powder underneath another -- to create designer compositions. In the future, manufactures could design specific devices and then directly print them from dry powders, the scientists said.

"We anticipate this FAST perovskite would open another dimension for high throughput material synthesis, future manufacturing directly printing devices from powder and accelerating the material discovery of new perovskite compositions," said Kai Wang, an assistant research professor at Penn State and a co-author.

EM-FAST, also known as spark plasma sintering, involves applying electric current and pressure to powders to create new materials. The process has a 100% yield -- all the raw ingredients go into the final device, as opposed to 20 to 30% in solution-based processing.

The technique produced perovskite materials at .2 inch per minute, allowing scientists to create quickly create large devices that maintained high performance in laboratory tests. The team reported their findings in the journal Nature Communications.

Penn State scientists have long used EM-FAST to create thermoelectric devices. This work represents the first attempt to create perovskite materials with the technique, the scientists said.

"Because of the background we have, we were talking and thought we could change some parameters and try this with perovskites," Nozariasbmarz said. "And it just opened a door to a new world. This paper is a link to that door -- to new materials and new properties."

Read more at Science Daily

We need to learn to live with less steel

Steel is one of the most important materials in the world, integral to the cars we drive, the buildings we inhabit, and the infrastructure that allows us to travel from place to place. Steel is also responsible for 7% of global greenhouse gas emissions. In 2021, 45 countries made a commitment to pursue near-zero-emission steel in the next decade. But how possible is it to produce the steel we need in society with zero emissions?

A new study focused on the Japanese steel industry shows that if we are truly committed to reaching zero emissions, we must be prepared for a scenario where the amount of steel we can produce is lower. Japan has set a target for a 46% reduction in emissions from steel by 2030, and zero emissions by 2050. So far, the roadmap for achieving this relies heavily on future innovations in technology. Hope is held out for developments in carbon capture and storage (CCS) and hydrogen-based technologies.

In the study, Dr. Takuma Watari, a researcher at the National Institute for Environmental Studies, Japan, currently working with the University of Cambridge, argues that there is no silver bullet. He says that current plans to cut carbon emissions underestimate how difficult it will be to develop CCS and hydrogen technologies and deploy them widely: "These technologies still face serious technical, economic, and social challenges, and have yet to be implemented at scale. And importantly, it is highly uncertain whether there will be sufficient non-emitting electricity to use these technologies." We need to confront the possibility that technological innovations might not be ready in time to allow us to maintain current levels of steel production whilst cutting emissions to zero.

The research involved mapping the current flows of steel in Japan's industry and using a model to explore how the industry might change if a strict carbon budget were applied in future. Dr. Watari explains that with current practice, the quantity and quality of steel produced would dramatically decrease under a zero-emission carbon budget. This is because of a lack of resources and the practice of downcycling, in which scraps of steel containing impurities are used to make new products. It is difficult to remove these impurities, so the new products have different quality and functionality from the original steel.

According to Dr. Watari, "zero-emission steel production is possible by 2050, but in limited quantity and quality compared to current total production. This is due to the limited availability of zero-emission compatible resources and downcycling practices of scrap steel."

The research indicates that with a carbon budget of zero emissions, the production of steel goods would be dramatically restricted compared to today, reaching about half the current levels at best. In this case, higher-quality steel production (e.g., sheet steel) would be especially hard hit.

The implication is clear. It is not enough to rely on a technological silver bullet materialising to transform the supply of steel. We also need to look seriously at strategies to reduce demand by shifting our culture of steel use and improving our material efficiency. We also need to pursue upcycling to produce high-grade steel from scrap steel.

This will require collaboration from those who use steel as well as those who produce it. Steel products could be made more resource efficient if they are designed to last longer or to be lightweight. Once steel products reach the end of their life, upcycling could be achieved through advanced sorting and shredding to remove impurities from scrap steel. As a society, Japan may also have to become less steel-dependent and shift to a model of 'service use' rather than ownership of products. Unlike today, when steel is abundant and cheap, a net-zero future will require us to use scarcer, more expensive steel resources with greater efficiency. 

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Martian rock-metal composite shows potential of 3D printing on Mars

A small amount of simulated crushed Martian rock mixed with a titanium alloy made a stronger, high-performance material in a 3D-printing process that could one day be used on Mars to make tools or rocket parts. The parts were made by Washington State University researchers with as little as 5% up to 100% Martian regolith, a black powdery substance meant to mimic the rocky, inorganic material found on the surface of the red planet. While the parts with 5% Martian regolith were strong, the 100% regolith parts proved brittle and cracked easily. Still, even high-Martian content materials would be useful in making coatings to protect equipment from rust or radiation damage.

A little Martian dust appears to go a long way. A small amount of simulated crushed Martian rock mixed with a titanium alloy made a stronger, high-performance material in a 3D-printing process that could one day be used on Mars to make tools or rocket parts.

The parts were made by Washington State University researchers with as little as 5% up to 100% Martian regolith, a black powdery substance meant to mimic the rocky, inorganic material found on the surface of the red planet.

While the parts with 5% Martian regolith were strong, the 100% regolith parts proved brittle and cracked easily. Still, even high-Martian content materials would be useful in making coatings to protect equipment from rust or radiation damage, said Amit Bandyopadhyay, corresponding author on the study published in the International Journal of Applied Ceramic Technology.

"In space, 3D printing is something that has to happen if we want to think of a manned mission because we really cannot carry everything from here," said Bandyopadhyay, a professor in WSU's School of Mechanical and Materials Engineering. "And if we forgot something, we cannot come back to get it."

Bringing materials into space can be extremely expensive. For instance, the authors noted it costs about $54,000 for the NASA space shuttle to put just one kilogram of payload (about 2.2 pounds) into Earth orbit. Anything that can be made in space, or on planet, would save weight and money -- not to mention if something breaks, astronauts would need a way to repair it on site.

Bandyopadhyay first demonstrated the feasibility of this idea in 2011 when his team used 3D-printing to manufacture parts from lunar regolith, simulated crushed moon rock, for NASA. Since then, space agencies have embraced the technology, and International Space Station has its own 3D-printers to manufacture needed materials on site and for experiments.

For this study, Bandyopadhyay along with graduate students Ali Afrouzian and Kellen Traxel, used a powder-based 3D printer to mix the simulated Martian rock dust with a titanium alloy, a metal often used in space exploration for its strength and heat-resistant properties. As part of the process, a high-powered laser heated the materials to over 2,000 degrees Celsius (3,632 F). Then, the melted mix of Martian regolith-ceramic and metal material flowed onto a moving platform that allowed the researchers to create different sizes and shapes. After the material cooled down, the researchers tested it for strength and durability.

The ceramic material made from 100% Martian rock dust cracked as it cooled, but as Bandyopadhyay pointed out it could still make good coatings for radiation shields as cracks do not matter in that context. But just a little Martian dust, the mixture with 5% regolith, not only did not crack or bubble but also exhibited better properties than the titanium alloy alone, which meant it could be used to make lighter weight pieces that could still bear heavy loads.

"It gives you a better, higher strength and hardness material, so that can perform significantly better in some applications," he said.

This study is just a start, Bandyopadhyay said, and future research may yield better composites using different metals or 3D-printing techniques.

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Building bricks from waste materials

Firing bricks and making mortar and cement is very costly, but organic chemists at Flinders University are working on more sustainable alternatives -- focusing on building materials made from waste products.

In another move into the circular economy, researchers from the Flinders Chalker Lab have used low-cost feedstocks to make lightweight but durable polymer building blocks which can be bonded together with an adhesive-free chemical reaction.

Their latest study tested the strength of these materials and explored ways they can be reinforced in construction.

Matthew Flinders Professor of Chemistry, Justin Chalker, says the need to develop sustainable building materials is increasingly important, with cement, iron and steel production accounting for more than 15% of global CO2 emissions each year.

"In this study, we tested a new type of brick we can make from waste cooking oil, mixed with sulfur and dicyclopentadiene (DCPD). Both sulfur and DCPD are byproducts of petroleum refining.

"The bricks bond together without mortar upon application of a trace amount of amine catalyst.

"All the starting materials are plentiful and can be classified as industrial waste.

"This research is part of a larger effort to move towards a sustainable built environment," says project leader Professor Chalker.

The Chalker Lab's new polymer research team at Flinders University's College of Science and Engineering is collaborating with Clean Earth Technologies for further development. scale-up and possible commercialisation.

The latest study, published as a cover feature in a special issue on Sustainability in the journal Macromolecular Chemistry and Physics, expanded the research to test the new bricks' mechanical properties and look at ways to reinforce them in construction, including with carbon fibre fillers.

Chalker Lab research associate Dr Maximilian Mann says as well as repurposing waste materials into value-added construction materials, the polymer bricks' sulfur-sulfur bond means they can be bound together without mortar like traditional building method.

"The bonding in this novel catalytic process is very strong, producing a sustainable construction material with its own mortar which will potentially streamline construction," Dr Mann says.

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Shedding new light on controlling material properties

Materials scientists may soon be able to control material properties with light.

A team consisting of researchers at Kyoto University and Kurume Institute of Technology have discovered a scaling law that determines high-order harmonic generation in the solid-layered perovskite material, Ca2RuO4.

High-order harmonic generation is a nonlinear optical phenomenon where extreme ultraviolet photons are emitted by a material as a result of interactions with high intensity light.

"The phenomenon, which was first observed in atomic gas systems, has since paved the way to attosecond science," says study author Kento Uchida. "But it is slightly more unpredictable in some strongly correlated solids, like Ca2RuO4."

Due to the strong interaction between electrons in these solids, the characteristics of high-order harmonic generation can only be established by understanding how these electrons move in the presence of light.

To tackle this question, which has never been confirmed experimentally, the team set out to observe the relationship between temperature and photon emission in Ca2RuO4. They used a mid-infrared pulse to measure and map out high harmonic generation intensity at temperatures from an extremely low 50 to a moderate 290 Kelvin.

At the low end, the team recorded high-order harmonic generation several hundred times more intense than at room temperature. Photon emissions continued to intensify with increasing gap energy -- the energy required for electrons to conduct electricity -- along with the drop in temperature.

The team found that such emissions occurred in the Mott-insulating phase of the material, where the strong repulsion between electrons and high gap energy transforms the metal from an electrical conductor to an insulator.

"We discovered that high-order harmonics in strongly correlated materials highly depend on the gap energy of the materials," explains Uchida.

This scaling law can direct theoretical studies towards more refined descriptions of non-equilibrium electron dynamics in strongly correlated materials: a central issue in condensed matter physics.

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Artificial muscles made of proteins

Dr. Stefan Schiller and Dr. Matthias Huber from the University of Freiburg's livMatS Cluster of Excellence have succeeded in developing a muscle solely on the basis of natural proteins. The autonomous contractions of the material, which the researchers presented in the journal Advanced Intelligent Systems, can be controlled with the help of pH and temperature changes. The movements are driven by a chemical reaction that consumes molecular energy for this purpose. "Our artificial muscle is still a prototype," says Schiller. "However, the high biocompatibility of the material and the possibility of adjusting its composition to match particular tissue could pave the way for future applications in reconstructive medicine, prosthetics, pharmaceutics, or soft robotics."

In the past, scientists have already taken natural proteins as a basis for developing artificial muscle systems and built them into miniscule molecular machines or into polymers. However, it has not yet been possible to develop synthetic muscle materials that are entirely bio-based and move autonomously with the help of chemical energy.

Material based on the natural protein elastin

The material used by the Freiburg team is based on elastin, a natural fibrous protein that also occurs in humans, for instance giving elasticity to the skin and blood vessels. Following the model of this protein, the researchers developed two elastin-like proteins, one of which responds, for example, to fluctuations in pH, the other to changes in temperature. The scientists combined the two proteins by means of photochemical cross-linking to form a bilayered material. It is possible in this process to flexibly shape the material and set the direction of its movement.

Contractions can be switched on and off with the help of temperature changes

The researchers succeeded in inducing the rhythmic contractions by using a chemical energy source as fuel, in this case sodium sulfite. In an oscillating chemical reaction in which the pH changes in cycles due to a special linkage of several reactions, the added energy was converted into mechanical energy via non-equilibrium states of the material. In this way, the researchers induced the material to contract autonomously in a cyclical manner. They were also able to switch the contractions on and off with the help of temperature changes: The oscillating chemical reaction started at a temperature of around 20 degrees Celsius, and the material began to make rhythmic movements. In the process, it was possible to program certain states for the material to assume and to reset them again with another stimulus. The scientists thus achieved a simple system for implementing learning and forgetting at the material level.

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Templating approach stabilizes 'ideal' material for alternative solar cells

Researchers have developed a method to stabilise a promising material known as perovskite for cheap solar cells, without compromising its near-perfect performance.

The researchers, from the University of Cambridge, used an organic molecule as a 'template' to guide perovskite films into the desired phase as they form. Their results are reported in the journal Science.

Perovskite materials offer a cheaper alternative to silicon for producing optoelectronic devices such as solar cells and LEDs.

There are many different perovskites, resulting from different combinations of elements, but one of the most promising to emerge in recent years is the formamidinium (FA)-based FAPbI3 crystal.

The compound is thermally stable and its inherent 'bandgap' -- the property most closely linked to the energy output of the device -- is not far off ideal for photovoltaic applications.

For these reasons, it has been the focus of efforts to develop commercially available perovskite solar cells. However, the compound can exist in two slightly different phases, with one phase leading to excellent photovoltaic performance, and the other resulting in very little energy output.

"A big problem with FAPbI3 is that the phase that you want is only stable at temperatures above 150 degrees Celsius," said co-author Tiarnan Doherty from Cambridge's Cavendish Laboratory. "At room temperature, it transitions into another phase, which is really bad for photovoltaics."

Recent solutions to keep the material in its desired phase at lower temperatures have involved adding different positive and negative ions into the compound.

"That's been successful and has led to record photovoltaic devices but there are still local power losses that occur," said Doherty. "You end up with local regions in the film that aren't in the right phase."

Little was known about why the additions of these ions improved stability overall, or even what the resulting perovskite structure looked like.

"There was this common consensus that when people stabilise these materials, they're an ideal cubic structure," said Doherty. "But what we've shown is that by adding all these other things, they're not cubic at all, they're very slightly distorted. There's a very subtle structural distortion that gives some inherent stability at room temperature."

The distortion is so minor that it had previously gone undetected, until Doherty and colleagues used sensitive structural measurement techniques that have not been widely used on perovskite materials.

The team used scanning electron diffraction, nano-X-ray diffraction and nuclear magnetic resonance to see, for the first time, what this stable phase really looked like.

"Once we figured out that it was the slight structural distortion giving this stability, we looked for ways to achieve this in the film preparation without adding any other elements into the mix."

Co-author Satyawan Nagane used an organic molecule called Ethylenediaminetetraacetic acid (EDTA) as an additive in the perovskite precursor solution, which acts as a templating agent, guiding the perovskite into the desired phase as it forms. The EDTA binds to the FAPbI3 surface to give a structure-directing effect, but does not incorporate into the FAPbI3 structure itself.

"With this method, we can achieve that desired band gap because we're not adding anything extra into the material, it's just a template to guide the formation of a film with the distorted structure -- and the resulting film is extremely stable," said Nagane.

"In this way, you can create this slightly distorted structure in just the pristine FAPbI3 compound, without modifying the other electronic properties of what is essentially a near-perfect compound for perovskite photovoltaics," said co-author Dominik Kubicki from the Cavendish Laboratory, who is now based at the University of Warwick.

The researchers hope this fundamental study will help improve perovskite stability and performance. Their own future work will involve integrating this approach into prototype devices to explore how this technique may help them achieve the perfect perovskite photovoltaic cells.

"These findings change our optimisation strategy and manufacturing guidelines for these materials," said senior author Dr Sam Stranks from Cambridge's Department of Chemical Engineering & Biotechnology. "Even small pockets that aren't slightly distorted will lead to performance losses, and so manufacturing lines will need to have very precise control of how and where the different components and 'distorting' additives are deposited. This will ensure the small distortion is uniform everywhere -- with no exceptions."

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Earth and Mars were formed from inner Solar System material

Earth and Mars were formed from material that largely originated in the inner Solar System; only a few percent of the building blocks of these two planets originated beyond Jupiter's orbit. A group of researchers led by the University of Münster (Germany) report these findings today in the journal Science Advances. They present the most comprehensive comparison to date of the isotopic composition of Earth, Mars and pristine building material from the inner and outer Solar System. Some of this material is today still found largely unaltered in meteorites. The results of the study have far-reaching consequences for our understanding of the process that formed the planets Mercury, Venus, Earth, and Mars. The theory postulating that the four rocky planets grew to their present size by accumulating millimeter-sized dust pebbles from the outer Solar System is not tenable.

Approximately 4.6 billion years ago in the early days of our Solar System, a disk of dust and gases orbited the young Sun. Two theories describe how in the course of millions of years the inner rocky planets formed from this original building material. According to the older theory, the dust in the inner Solar System agglomerated to ever larger chunks gradually reaching approximately the size of our Moon. Collisions of these planetary embryos finally produced the inner planets Mercury, Venus, Earth, and Mars. A newer theory, however, prefers a different growth process: millimeter-sized dust "pebbles" migrated from the outer Solar System towards the Sun. On their way, they were accreted onto the planetary embryos of the inner Solar System, and step by step enlarged them to their present size.

Both theories are based on theoretical models and computer simulations aimed at reconstructing the conditions and dynamics in the early Solar System; both describe a possible path of planet formation. But which one is right? Which process actually took place? To answer these questions, in their current study researchers from the University of Münster (Germany), the Observatoire de la Cote d'Azur (France), the California Institute of Technology (USA), the Natural History Museum Berlin (Germany), and the Free University of Berlin (Germany) determined the exact composition of the rocky planets Earth and Mars. "We wanted to find out whether the building blocks of Earth and Mars originated in the outer or inner Solar System," says Dr. Christoph Burkhardt of the University of Münster, the study's first author. To this end, the isotopes of the rare metals titanium, zirconium and molybdenum found in minute traces in the outer, silicate-rich layers of both planets provide crucial clues. Isotopes are different varieties of the same element, which differ only in the weight of their atomic nucleus.

Meteorites as a reference

Scientists assume that in the early Solar System these and other metal isotopes were not evenly distributed. Rather, their abundance depended on the distance from the Sun. They therefore hold valuable information about where in the early Solar System a certain body's building blocks originated.

As a reference for the original isotopic inventory of the outer and inner Solar System, the researchers used two types of meteorites. These chunks of rock generally found their way to Earth from the asteroid belt, the region between the orbits of Mars and Jupiter. They are considered to be largely pristine material from the beginnings of the Solar System. While so-called carbonaceous chondrites, which can contain up to a few percent carbon, originated beyond Jupiter's orbit and only later relocated to the asteroid belt due to influence of the growing gas giants, their more carbon-depleted cousins, the non-carbonaceous chondrites, are true children of the inner Solar System.

The precise isotopic composition of Earth's accessible outer rock layers and that of both types of meteorites have been studied for some time; however, there have been no comparably comprehensive analyses of Martian rocks. In their current study, the researchers now examined samples from a total of 17 Martian meteorites, which can be assigned to six typical types of Martian rock. In addition, the scientists for the first time investigated the abundances of three different metal isotopes.

The samples of Martian meteorites were first powdered and subjected to complex chemical pretreatment. Using a multicollector plasma mass spectrometer at the Institute of Planetology at the University of Münster, the researchers were then able to detect tiny amounts of titanium, zirconium, and molybdenum isotopes. They then performed computer simulations to calculate the ratio in which building material found today in carbonaceous and non-carbonaceous chondrites must have been incorporated into Earth and Mars in order to reproduce their measured compositions. In doing so, they considered two different phases of accretion to account for the different history of the titanium and zirconium isotopes as well as of the molybdenum isotopes, respectively. Unlike titanium and zirconium, molybdenum accumulates mainly in the metallic planetary core. The tiny amounts still found today in the silicate-rich outer layers can therefore only have been added during the very last phase of the planet's growth.

The researchers' results show that the outer rock layers of Earth and Mars have little in common with the carbonaceous chondrites of the outer Solar System. They account for only about four percent of both planets' original building blocks. "If early Earth and Mars had mainly accreted dust grains from the outer Solar System, this value should be almost ten times higher," says Prof. Dr. Thorsten Kleine of the University of Münster, who is also director at the Max Planck Institute for Solar System Research in Göttingen. "We thus cannot confirm this theory of the formation of the inner planets," he adds.

Lost building material

But the composition of Earth and Mars does not exactly match the material of the non-carbonaceous chondrites either. The computer simulations suggest that another, different kind of building material must also have been in play. "The isotopic composition of this third type of building material as inferred by our computer simulations implies it must have originated in the innermost region of the Solar System," explains Christoph Burkhardt. Since bodies from such close proximity to the Sun were almost never scattered into the asteroid belt, this material was almost completely absorbed into the inner planets and thus does not occur in meteorites. "It is, so to speak, 'lost building material' to which we no longer have direct access today," says Thorsten Kleine.

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Scientists invent ‘smart’ window material that blocks rays without blocking views

An international research team led by scientists from Nanyang Technological University, Singapore (NTU Singapore) has invented a 'smart' window material that controls heat transmission without blocking views, which could help cut the energy required to cool and heat buildings.

Developed by NTU researchers, the new energy-saving material for electrochromic (EC) windows that operates at the flick of a switch is designed to block infrared radiation -- which is the major component of sunlight that emits heat.

The new material has a specifically designed nanostructure and comprises advanced materials like titanium dioxide (TiO2), tungsten trioxide (WO3), neodymium-Niobium (Nd-Nb), and tin (IV) oxide (SnO2). The composite material is intended to be coated onto glass window panels, and when activated by electricity, users would be able to 'switch on and off' the infrared radiation transmission through the window.

The invention, which featured alongside the front cover of the journal ACS Omega, could block up to 70 per cent of infrared radiation according to experimental simulations without compromising views through the window since it allows up to 90 per cent of visible light to pass through.

The material is also about 30 per cent more effective in regulating heat than commercially available electrochromic windows and is cheaper to make due to its durability.

An improvement over current electrochromic (EC) window

Electrochromic windows are a common feature in 'green' buildings today. They work by becoming tinted when in use, reducing light from entering the room.

Commercially available electrochromic windows usually have a layer of tungsten trioxide (WO3) coated on one side of the glass panel, and the other, without. When the window is switched on, an electric current moves lithium ions to the side containing WO3, and the window darkens or turns opaque. Once switched off, the ions migrate away from the coated glass, and the window becomes clear again.

However, current electrochromic windows are only effective in blocking visible light, not the infrared radiation, which means heat continues to pass through the window, warming up the room.

Another drawback of the current technology is its durability, as the performance of the electrochromic component tends to degrade in three to five years. In lab tests, NTU's electrochromic technology was put through rigorous on-off cycles to evaluate its durability Results showed the properties of the window retained excellent stability (blocked more than 65% of infrared radiation) demonstrating its superior performance, feasibility and costs saving potential for long-term use in sustainable buildings.

Lead author of the electrochromic window study, Associate Professor Alfred Tok of the NTU School of Materials Science and Engineering said, "By incorporating the specially designed nanostructure, we enabled the material to react in a 'selective' manner, blocking near infrared radiation while still allowing most of the visible light to pass through whenever our electrochromic window is switched on. The choice of advanced materials also helped improved the performance, stability and durability of the smart window."

The new electrochromic technology may help conserve energy that would be used for the heating and cooling of buildings and could contribute to the future design of sustainable green buildings, say the research team.

The study reflects the university's commitment to address humanity's grand challenges on sustainability as part of the NTU 2025 strategic plan, which seeks to accelerate the translation of research discoveries into innovations that mitigate human impact on the environment.

Next generation smart window: Controlling both infrared radiations and conduction heat

Seeking to improve the performance of their smart window technology, the NTU team, in a separate work to that reported in the journal, created a switch system that helps to control conducted heat, which is the heat from the external environment.

The patented NTU switch comprises magnetic carbon-based particles and thin films that are good conductors of heat. When the switch is turned off, conducted heat cannot transfer through the window. When switched on, the heat will be allowed to pass through the glass window.

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Unexpected 'Black Swan' defect discovered in soft matter

In new research, Texas A&M University scientists have for the first time revealed a single microscopic defect called a "twin" in a soft-block copolymer using an advanced electron microscopy technique. This defect may be exploited in the future to create materials with novel acoustic and photonic properties.

"This defect is like a black swan -- something special going on that isn't typical," said Dr. Edwin Thomas, professor in the Department of Materials Science and Engineering. "Although we chose a certain polymer for our study, I think the twin defect will be fairly universal across a bunch of similar soft matter systems, like oils, surfactants, biological materials and natural polymers. Therefore, our findings will be valuable to diverse research across the soft matter field."

The results of the study are detailed in the Proceedings of the National Academy of Sciences (PNAS).

Materials can be broadly classified as hard or soft matter. Hard materials, like metal alloys and ceramics, generally have a very regular and symmetric arrangement of atoms. Further, in hard matter, ordered groups of atoms arrange themselves into nanoscopic building blocks, called unit cells. Typically, these unit cells are comprised of only a few atoms and stack together to form the periodic crystal. Soft matter can also form crystals consisting of unit cells, but now the periodic pattern is not at the atomic level; it occurs at a much larger scale from assemblies of large molecules.

In particular, for an A-B diblock copolymer, a type of soft matter, the periodic molecular motif comprises of two linked chains: one chain of A units and one chain of B units. Each chain, called a block, has thousands of units linked together and a soft crystal forms by selective aggregation of the A units into domains and B units into domains that form huge unit cells compared to hard matter.

Another notable difference between soft and hard crystals is that structural defects have been much more extensively studied in hard matter. These imperfections can occur at a single atomic location within material, called a point defect. For example, point defects in the periodic arrangement of carbon atoms in a diamond due to nitrogen impurities create the exquisite "canary" yellow diamond. In addition, imperfections in crystals can be elongated as a line defect or spread across an area as a surface defect.

By and large, defects within hard materials have been extensively investigated using advanced electron imaging techniques. But in order to be able to locate and identify defects in their block copolymer soft crystals, Thomas and his colleagues used a new technique called slice-and-view scanning electron microscopy. This method allowed the researchers to use a fine ion beam to trim off a very thin slice of the soft material, then they used an electron beam to image the surface below the slice, then slice again, image again, over and over. These slices were then digitally stacked together to get a 3D view.

For their analysis, they investigated a diblock copolymer made of a polystyrene block and a polydimethylsiloxane block. At the microscopic level, a unit cell of this material exhibits a spatial pattern of the so-called "double gyroid" shape, a complex, periodic structure consisting of two intertwined molecular networks of which one has a left-handed rotation and the other, a right-handed rotation.

While the researchers were not actively looking for any particular defect in the material, the advanced imaging technique uncovered a surface defect, called a twin boundary. At either side of the twin juncture, the molecular networks abruptly transformed their handedness.

"I like to call this defect a topological mirror, and it's a really neat effect," said Thomas. "When you have a twin boundary, it's like looking at a reflection into a mirror, as each network crosses the boundary, the networks switch handedness, right becomes left and vice versa."

The researcher added that the consequences of having a twin boundary in a periodic structure that does not by itself have any inherent mirror symmetry could induce novel optical and acoustic properties that open new doors in materials engineering and technology.

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New material to treat wounds can protect against resistant bacteria

Researchers at Chalmers University of Technology, Sweden, have developed a new material that prevents infections in wounds -- a specially designed hydrogel, that works against all types of bacteria, including antibiotic-resistant ones. The new material offers great hope for combating a growing global problem.

The World Health Organization describes antibiotic-resistant bacteria as one of the greatest threats to global health. To deal with the problem, there needs to be a shift in the way we use antibiotics, and new, sustainable medical technologies must be developed.

"After testing our new hydrogel on different types of bacteria, we observed a high level of effectiveness, including against those which have become resistant to antibiotics," says Martin Andersson, research leader for the study and Professor at the Department of Chemistry and Chemical Engineering at Chalmers University of Technology.

Research and development of the material has been ongoing for many years at Martin Andersson's group at Chalmers, growing in scope along the way, with a particular focus on the possibilities for wound care. Now, the important results are published as a scientific article in the journal ACS Biomaterials Science & Engineering.

The main purpose of the studies so far has been to explore new medical technology solutions to help reduce the use of systemic antibiotics. Resistant bacteria cause what is referred to as hospital-acquired infection -- a life-threatening condition and is increasing in incidence worldwide.

Mimicking the natural immune system

The active substance in the new bactericidal material consists of antimicrobial peptides, small proteins which are found naturally in our immune system.

"With these types of peptides, there is a very low risk for bacteria to develop resistance against them, since they only affect the outermost membrane of the bacteria. That is perhaps the foremost reason why they are so interesting to work with," says Martin Andersson.

Researchers have long tried to find ways to use these peptides in medical devices, but so far without much success. The problem is that they break down quickly when they come into contact with bodily fluids such as blood. The current study describes how the researchers managed to overcome the problem through the development of a nanostructured hydrogel, into which the peptides are permanently bound, creating a protective environment.

"The material is very promising. It is harmless to the body's own cells and gentle on the skin. In our measurements, the protective effect of the hydrogel on the antimicrobial peptides is clear -- the peptides degrade much slower when they are bound to it," says Edvin Blomstrand, doctoral student at the Department of Chemistry and Chemical Engineering at Chalmers, and one of the main authors of the article.

"We expected good results, but we were really positively surprised at quite how effective the material has proven," adds Martin Andersson.

According to the researchers, this new material is the first medical device to make successful use of antimicrobial peptides in a clinically and commercially viable manner. There are many varied and promising opportunities for clinical application.

Startup company Amferia takes the research from lab to market

In recent years, foundational research into the antimicrobial peptide hydrogel has run in parallel with commercial development of the innovation through the spin-off company Amferia AB.

The company was founded in 2018 by Martin Andersson together with Saba Atefyekta and Anand Kumar Rajasekharan, who both defended their dissertations at Chalmers' Department of Chemistry and Chemical Engineering.

The material and the idea, which is currently developed as an antibacterial wound patch, has generated interest around the world, attracting significant investment and receiving several awards. The company is working intensively to get the material to market so that it can benefit wider society.

Before the new material can benefit hospitals and patients, clinical studies are needed, which are ongoing. A CE marking of the material is expected to be completed in 2022. Furthermore, the wound patch version of the new material is undergoing trials in veterinary care, for treating pets. The company Amferia AB is already collaborating with a number of veterinary clinics around Europe where the hydrogel is now being tested.

"Amferia has recently entered into a strategic partnership with Sweden's largest distributor of premium medical & diagnostic devices to jointly launch these wound care products for the Swedish veterinary market during 2021" says Martin Andersson.

More about antimicrobial peptides and the new material

The beneficial properties of antimicrobial peptides have been known for some decades, and thousands of different varieties occurring in the natural immune systems of humans, animals and plants have been discovered. Researchers have long tried to mimic and use their natural function to prevent and treat infections without having to use traditional antibiotics. However, because the peptides are broken down as soon as they come in contact with blood or other body fluids, successful clinical usage has proved elusive. The researchers knew that smart new solutions were needed to protect the peptide from degradation. The new material in the study has been shown to work very well, allowing the peptides to be applied directly to wounds and injuries on the body, with the effect of both preventing and treating infection. The material is also non-toxic, so it can be used directly on the skin. The potential of this new material can also be seen in the flexibility that it offers for different types of products.

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Discovery could help lengthen lifespan of electronic devices

Ferroelectric materials are used in many devices, including memories, capacitors, actuators and sensors. These devices are commonly used in both consumer and industrial instruments, such as computers, medical ultrasound equipment and underwater sonars.

Over time, ferroelectric materials are subjected to repeated mechanical and electrical loading, leading to a progressive decrease in their functionality, ultimately resulting in failure. This process is referred to as 'ferroelectric fatigue'.

It is a main cause of the failure of a range of electronic devices, with discarded electronics a leading contributor to e-waste. Globally, tens of millions of tonnes of failed electronic devices go to landfill every year.

Using advanced in-situ electron microscopy, the School of Aerospace, Mechanical and Mechatronic Engineering researchers were able to observe ferroelectric fatigue as it occurred. This technique uses an advanced microscope to 'see', in real-time, down to the nanoscale and atomic levels.

The researchers hope this new observation, described in a paper published in Nature Communications, will help better inform the future design of ferroelectric nanodevices.

"Our discovery is a significant scientific breakthrough as it shows a clear picture of how the ferroelectric degradation process is present at the nanoscale," said co-author Professor Xiaozhou Liao, also from the University of Sydney Nano Institute.

Dr Qianwei Huang, the study's lead researcher, said: "Although it has long been known that ferroelectric fatigue can shorten the lifespan of electronic devices, how it occurs has previously not been well understood, due to a lack of suitable technology to observe it."

Co-author Dr Zibin Chen said: "With this, we hope to better inform the engineering of devices with longer lifespans."

Observational findings spark new debate

Nobel laureate Herbert Kroemer once famously asserted "The interface is the device." The observations by the Sydney researchers could therefore spark a new debate on whether interfaces -- which are physical boundaries separating different regions in materials -- are a viable solution to the unreliability of next-generation devices.

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Less than a nanometer thick, stronger and more versatile than steel

 Scientists create stable nanosheets containing boron and hydrogen atoms with potential applications in nanoelectronics and quantum information technology.

What's thinner than thin? One answer is two-dimensional materials -- exotic materials of science with length and width but only one or two atoms in thickness. They offer the possibility of unprecedented boosts in device performance for electronic devices, solar cells, batteries and medical equipment.

In collaboration with Northwestern University and the University of Florida, scientists from the U.S. Department of Energy's (DOE) Argonne National Laboratory report in Science magazine a breakthrough involving a 2D material called borophane, a sheet of boron and hydrogen a mere two atoms in thickness.

One of the most exciting developments in materials science in recent decades has been a 2D sheet of carbon (graphene), which is one atom thick and 200 times stronger than steel. A similarly promising and newer material is an atom-thick sheet of boron, called borophene -- with an "e." A multi-institutional team, including researchers in Argonne's Center for Nanoscale Materials (a DOE Office of Science User Facility), first synthesized borophene in 2015.

While graphene is simply one atomic layer out of the many same layers in the common material graphite, borophene has no equivalent parent structure and is very difficult to prepare. What's more, the rapid reaction of borophene with air means it is very unstable and changes form readily.

"Borophene by itself has all kinds of problems," said Mark Hersam, Professor of Materials Science and Engineering at Northwestern University. "But when we mix borophene with hydrogen, the product suddenly becomes much more stable and attractive for use in the burgeoning fields of nanoelectronics and quantum information technology."

The research team grew borophene on a silver substrate then exposed it to hydrogen to form the borophane. They then unraveled the complex structure of borophane by combining a scanning tunneling microscope with a computer-vision based algorithm that compares theoretical simulations of structures with experimental measurements. Computer vision is a branch of artificial intelligence that trains high performance computers to interpret and understand the visual world.

Even though the borophane material is only two atoms thick, its structure is quite complex because of the many possible arrangements for the boron and hydrogen atoms. "We have tackled a significant challenge in determining the atomic structures from scanning tunneling microscopy images and computational modeling at the atomic scale with the help of computer vision," said Argonne's Maria Chan, nanoscientist at the Center for Nanoscale Materials. Given the success in unraveling this complex structure, the team's automated analytical technique should be applicable in identifying other complex nanostructures in the future.

"What is really encouraging from our results is that we found a borophane nanosheet on a silver substrate to be quite stable, unlike borophene," said Pierre Darancet, nanoscientist at Argonne's Center for Nanoscale Materials. "This means it should be easily integrated with other materials in the construction of new devices for optoelectronics, devices combining light with electronics." Such light-controlling and light-emitting devices could be incorporated into telecommunications, medical equipment and more.

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From dark to light in a flash: Smart film lets windows switch autonomously

Researchers have developed a new easy-to-use smart optical film technology that allows smart window devices to autonomously switch between transparent and opaque states in response to the surrounding light conditions.

The proposed 3D hybrid nanocomposite film with a highly periodic network structure has empirically demonstrated its high speed and performance, enabling the smart window to quantify and self-regulate its high-contrast optical transmittance. As a proof of concept, a mobile-app-enabled smart window device for Internet of Things (IoT) applications has been realized using the proposed smart optical film with successful expansion to the 3-by-3-inch scale. This energy-efficient and cost-effective technology holds great promise for future use in various applications that require active optical transmission modulation.

Flexible optical transmission modulation technologies for smart applications including privacy-protection windows, zero-energy buildings, and beam projection screens have been in the spotlight in recent years. Conventional technologies that used external stimuli such as electricity, heat, or light to modulate optical transmission had only limited applications due to their slow response speeds, unnecessary color switching, and low durability, stability, and safety.

The optical transmission modulation contrast achieved by controlling the light scattering interfaces on non-periodic 2D surface structures that often have low optical density such as cracks, wrinkles, and pillars is also generally low. In addition, since the light scattering interfaces are exposed and not subject to any passivation, they can be vulnerable to external damage and may lose optical transmission modulation functions. Furthermore, in-plane scattering interfaces that randomly exist on the surface make large-area modulation with uniformity difficult.

Inspired by these limitations, a KAIST research team led by Professor Seokwoo Jeon from the Department of Materials Science and Engineering and Professor Jung-Wuk Hong of the Civil and Environmental Engineering Department used proximity-field nanopatterning (PnP) technology that effectively produces highly periodic 3D hybrid nanostructures, and an atomic layer deposition (ALD) technique that allows the precise control of oxide deposition and the high-quality fabrication of semiconductor devices.

The team then successfully produced a large-scale smart optical film with a size of 3 by 3 inches in which ultrathin alumina nanoshells are inserted between the elastomers in a periodic 3D nanonetwork.

This "mechano-responsive" 3D hybrid nanocomposite film with a highly periodic network structure is the largest smart optical transmission modulation film that exists. The film has been shown to have state-of-the-art optical transmission modulation of up to 74% at visible wavelengths from 90% initial transmission to 16% in the scattering state under strain. Its durability and stability were proved by more than 10,000 tests of harsh mechanical deformation including stretching, releasing, bending, and being placed under high temperatures of up to 70°C. When this film was used, the transmittance of the smart window device was adjusted promptly and automatically within one second in response to the surrounding light conditions. Through these experiments, the underlying physics of optical scattering phenomena occurring in the heterogeneous interfaces were identified. Their findings were reported in the online edition of Advanced Science on April 26. KAIST Professor Jong-Hwa Shin's group and Professor Young-Seok Shim at Silla University also collaborated on this project.

Donghwi Cho, a PhD candidate in materials science and engineering at KAIST and co-lead author of the study, said, "Our smart optical film technology can better control high-contrast optical transmittance by relatively simple operating principles and with low energy consumption and costs."

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What's Mars made of?

Earth-based experiments on iron-sulfur alloys thought to comprise the core of Mars reveal details about the planet's seismic properties for the first time. This information will be compared to observations made by Martian space probes in the near future. Whether the results between experiment and observation coincide or not will either confirm existing theories about Mars' composition or call into question the story of its origin.

Mars is one of our closest terrestrial neighbors, yet it's still very far away -- between about 55 million and 400 million kilometers depending on where Earth and Mars are relative to the sun. At the time of writing, Mars is around 200 million kilometers away, and in any case, it is extremely difficult, expensive and dangerous to get to. For these reasons, it is sometimes more sensible to investigate the red planet through simulations here on Earth than it is to send an expensive space probe or, perhaps one day, people.

Keisuke Nishida, an Assistant Professor from the University of Tokyo's Department of Earth and Planetary Science at the time of the study, and his team are keen to investigate the inner workings of Mars. They look at seismic data and composition which tell researchers not just about the present state of the planet, but also about its past, including its origins.

"The exploration of the deep interiors of Earth, Mars and other planets is one of the great frontiers of science," said Nishida. "It's fascinating partly because of the daunting scales involved, but also because of how we investigate them safely from the surface of the Earth."

For a long time it has been theorized that the core of Mars probably consists of an iron-sulfur alloy. But given how inaccessible the Earth's core is to us, direct observations of Mars' core will likely have to wait some time. This is why seismic details are so important, as seismic waves, akin to enormously powerful sound waves, can travel through a planet and offer a glimpse inside, albeit with some caveats.

"NASA's Insight probe is already on Mars collecting seismic readings," said Nishida. "However, even with the seismic data there was an important missing piece of information without which the data could not be interpreted. We needed to know the seismic properties of the iron-sulfur alloy thought to make up the core of Mars."

Nishida and team have now measured the velocity for what is known as P-waves (one of two types of seismic wave, the other being S-waves) in molten iron-sulfur alloys.

"Due to technical hurdles, it took more than three years before we could collect the ultrasonic data we needed, so I am very pleased we now have it," said Nishida. "The sample is extremely small, which might surprise some people given the huge scale of the planet we are effectively simulating. But microscale high-pressure experiments help exploration of macroscale structures and long time-scale evolutionary histories of planets."

A molten iron-sulfur alloy just above its melting point of 1,500 degrees Celsius and subject to 13 gigapascals of pressure has a P-Wave velocity of 4,680 meters per second; this is over 13 times faster than the speed of sound in air, which is 343 meters per second. The researchers used a device called a Kawai-type multianvil press to compress the sample to such pressures. They used X-ray beams from two synchrotron facilities, KEK-PF and SPring-8, to help them image the samples in order to then calculate the P-wave values.

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Science reveals improvements in Roman building techniques

The Romans were some of the most sophisticated builders of the ancient world. Over the centuries, they adopted an increasingly advanced set of materials and technologies to create their famous structures. To distinguish the time periods over which these improvements took place, historians and archaeologists typically measure the colours, shapes and consistencies of the bricks and mortar used by the Romans, along with historical sources. In new research published in EPJ Plus, Francesca Rosi and colleagues at the Italian National Research Council improved on these techniques through scientific analysis of the materials used to build the Roman Forum's Atrium Vestae. They found that successive phases of modification to the building saw improvements including higher quality raw materials, higher brick firing temperatures, and better ratios between carbonate and silicate building materials.

The team's analysis could offer important supplements to the techniques currently used by historians and archaeologists. It could also help these academics to end long-standing disputes regarding the time periods of certain building techniques. Since the Atrium Vestae was modified in five distinctive building phases spanning several centuries, the study highlighted technological improvements throughout the Roman age in unprecedented levels of detail.

The techniques employed by Rosi and colleagues included optical and electron microscopy, and measurements of how x-rays were diffracted as they passed through the materials. They also determined the molecular fingerprints, or spectra, of the materials. These are based on the characteristic ways in which their molecules vibrate when illuminated by electromagnetic radiation of specific energies. Using these methods, the team revealed the colours, textures and chemical compositions of Roman building materials on microscopic scales for the first time; clearly revealing technological improvements over the centuries. The findings of Rosi's team are a clear demonstration of the advantages of scientific methods in archaeological analysis. Their techniques could soon be used in future studies to unlock further mysteries concerning the technologies employed by ancient civilisations.

From Science Daily

Researchers revolutionize 3D printed products with data-driven design method

Additive manufacturing (AM), also known as three-dimensional printing, is a process that fabricates parts in a layer-by-layer manner by adding and processing materials. Advancements in AM technology have enabled the processing of a wide range of materials to create products in varying scales which span from medical implants to aircraft engine parts. These products, which can be rich in shape, material, hierarchical and functional complexities, offer high potential to revolutionize existing product development processes.

However, it can be a difficult process to fully realize the potential of AM's unique capabilities for product development as it requires product designers to change their design mindsets.

In conventional manufacturing processes, the main task for designers is tailoring their designs to eliminate manufacturing difficulties and minimize costs. On the contrary, AM has fewer manufacturing constraints while offering designers with much more design freedom to explore. Therefore, designers must search for optimal design solutions out of millions of design alternatives that are different in geometry, topology, structure, and material. This can be a tedious task with current design methods and computer-aided design (CAD) tools due to the lack of ability to rapidly explore and exploit such a high dimensional design space.

To address this issue, researchers from Digital Manufacturing and Design (DManD) Centre from the Singapore University of Technology and Design (SUTD) proposed a holistic approach that applies data-driven methods in design search and optimization at successive stages of a design process for AM products.

First, they used simple and computationally inexpensive surrogate models in the design exploration process to approximate and replace complex high-fidelity engineering analysis models for rapidly narrowing down the high-dimensional design space. Next, they conducted design optimization based on refined surrogate models to obtain a single optimal design. These surrogate models are trained based on an updated dataset using the Markov Chain Monte Carlo resampling method.

This design approach was demonstrated in the design of an AM fabricated ankle brace (refer to image) that has a tunable mechanical performance for facilitating the recovery process of joints. In this design, the researchers selected a metamaterial which has a horseshoe-like structure, where its stiffness can be tailored. The proposed design approach was applied to optimize the orientation and dimensions of the horseshoe-like structure's geometry in different areas to achieve desired stiffness distributions.

Such geometry complexities enabled by AM offer the ankle brace design unique and favorable behaviors. The ankle brace is very soft within the allowable range of motions which provides comfort to patients. However, once the movement is out of the permissible range, it becomes stiff enough to protect the users' joints from extreme load conditions due to its geometrical design.

"Previously, it was hard for designers to imagine a design of such complex geometry due to the limitations in conventional manufacturing, but now this design is easily achievable with AM. Our new approach allows designers to embrace the design freedom in AM that comes with the shift in design paradigm and create more optimal products similar to the ankle brace," said first author Dr. Yi Xiong, Research Fellow from SUTD.

With the design space exploration and exploitation capability developed, the research team is working towards a more ambitious goal -- to develop a next-generation CAD system for AM.

Read more at Science Daily