Latest news with #TUWien
Yahoo
05-06-2025
- Science
- Yahoo
Single platinum atoms spotted in 2D lattice for first time unlock smarter gas sensors
Austrian scientists have achieved a breakthrough by embedding individual platinum atoms into an ultrathin material and pinpointing their positions within the lattice with atomic precision for the first time ever. The research team from the University of Vienna and the Vienna University of Technology (TU Wien), utilized a new method that combines defect engineering in the host material, the controlled placement of platinum atoms, and a cutting-edge, high-contrast electron imaging technique known as ptychography. Jani Kotakoski, PhD, an expert in the field of physics in nanostructured materials and research group leader, highlighted that the achievement sets the stage for tailoring materials with atomic precision. Active centers, which are tiny sites on the material's surface where chemical reactions occur or gas molecules can specifically bind, are crucial for enhancing the efficiency, selectivity, and overall performance of materials used in catalysis and gas detection. These centers are especially effective when made up of single metal atoms like platinum, which they aimed not only to produce, but also to visualize with atomic-level precision. Known for its highly tunable structure, the host material molybdenum disulfide (MoS₂) is an ultrathin semiconductor. To introduce new active sites, the scientists used helium ion irradiation to deliberately create atomic-scale defects on its surface, such as sulfur vacancies. These vacancy sites were then selectively filled with individual platinum atoms, allowing the team to engineer the material at the atomic level. This precise atomic substitution, known as doping, enables fine-tuning of the material's properties for specific applications, such as catalysis or gas detection. However, previous studies had not provided direct evidence of the exact positions of foreign atoms within the atomic lattice, as conventional electron microscopy lacks the contrast needed to clearly distinguish between defect types such as single and double sulfur vacancies. In a bid to address the challenge, the team has now used a state-of-the-art imaging method known as Single-Sideband Ptychography (SSB), which analyzes electron diffraction patterns to achieve atomic-level resolution. "With our combination of defect engineering, doping, and ptychography, we were able to visualize even subtle differences in the atomic lattice - and clearly determine whether a platinum atom had been incorporated into a vacancy or merely resting loosely on the surface," David Lamprecht, MSc, a student at the University of Vienna's institute for microelectronics, and lead author of the study, said. With the help of computer simulations, the scientists were able to precisely identify the different incorporation sites, such as positions originally occupied by sulfur or molybdenum atoms, marking a key advance toward targeted material design. The team believes that combining targeted atom placement with atomically precise imaging unlocks new possibilities for advanced catalyst design and highly selective gas sensing. While individual platinum atoms placed at precisely defined sites can serve as highly efficient catalysts, like in eco-friendly hydrogen production, the material can also be tailored to respond selectively to specific gas molecules. "With this level of control over atom placement, we can develop selectively functionalized sensors - a significant improvement over existing methods," Kotakoski concluded in a press release. According to the research team, the approach is not limited to platinum and molybdenum disulfide but can also be applied to a wide range of 2D materials and dopant atom combinations. By gaining more precise control over defect creation and incorporating post-treatment steps, the researchers now hope to further refine the technique. Their final goal is to develop functional materials with customized properties, in which every atom is positioned with absolute precision. The study has been published in the journal Nano Letters.
Yahoo
15-05-2025
- Science
- Yahoo
A spaceship moving near the speed of light would appear rotated, special relativity experiment proves
When you buy through links on our articles, Future and its syndication partners may earn a commission. In a bizarre repercussion of Albert Einstein's Special Theory of Relativity, objects traveling close to the speed of light appear flipped over. The Special Theory of Relativity, or special relativity for short, describes what happens to objects traveling at close to the speed of light. In particular, it discusses two major repercussions of moving so quickly. One is that time would clearly appear to pass more slowly for the object traveling close to the speed of light relative to slower moving bodies around it. This is rooted in a phenomenon called "time dilation," which also leads to the famous Twin Paradox, has been proven experimentally and is even considered when building certain kinds of technology. Global positioning survey (GPS) satellites in orbit, for instance, have to account for time dilation when providing accurate navigation data. Another consequence is what we call length contraction. "Suppose a rocket whizzes past us at 90% of the speed of light," Peter Schattschneider, a professor of physics at TU Wien, the Vienna University of Technology, said in a statement. "For us, it no longer has the same length as before it took off, but is 2.3 times shorter." This doesn't mean the rocket literally contracts, but rather that it appears contracted to an observer. Astronauts on board the rocket, for example, would still measure their spacecraft to be the same length that it has always been. It's all relative — hence the name of the theory. One consequence of length contraction was proposed in 1959 by physicists James Terrell and Roger Penrose. Known as the Terrell–Penrose effect, it predicted that objects moving at a high fraction of the speed of light should appear rotated. "If you wanted to take a picture of the rocket as it flew past, you would have to take into account that the light from different points took different lengths of time to reach the camera," said Schattschneider. For example, Schattschneider describes trying to take an image of a cube-shaped spacecraft — perhaps a Borg cube! — moving obliquely past us at almost the speed of light. First, we need to state the obvious, which is that light emitted (or reflected) from a corner on the closest side of the cube to us travels a shorter distance than light from the corner of the farthest side of the cube. Two photons departing at the same time from each of those two corners would therefore reach us at slightly different times, because one photon has to travel farther than the other. What this means is in a still image, in which the captured photons have all arrived at a camera lens at the same time, the photon from the far corner must have departed earlier than the one from the near corner in order to arrive synchronously. So far, so logical. However, this cube is not stationary — it's moving extremely fast and covers a lot of ground very quickly. Thus, in our hypothetical still image of this speeding cube, the far corner photon was emitted earlier than the near corner photon as expected — except when the cube was in a different position. And, because the cube is moving at nearly the speed of light, that position was very different indeed. "This makes it look to us as if the cube had been rotated," said Schattschneider. By the time these two photons reach us, the corner on the far side looks like it is at the near corner, and vice versa. However, this effect had not been observed before; accelerating anything other than particles to near the speed of light requires too much energy. However, a team of researchers from TU Wien and the University of Vienna, including Schattschneider, have found a way to simulate the conditions required to rotate the image of a relativistic object. Students Dominik Hornoff and Victoria Helm of TU Wien performed an experiment in which they were able to manufacture a scenario where they could pretend the speed of light was just 6.56 feet (2 meters) per second. This had the effect of slowing the whole process down so they could capture it on a high-speed camera. "We moved a cube and a sphere around the lab and used the high-speed camera to record the laser flashes reflected from different points on these objects at different times," said Hornoff and Helm in a joint statement. "If you get the timing right, you can create a situation that produces the same results as if the speed of light were no more than two meters per second." The cube and the sphere were deformed to mimic length contraction — the cube, simulated to be moving at 80% of the speed of light, was actually a cuboid with an aspect ratio of 0.6, while the sphere was flattened into a disk in accordance with a velocity of 99.9% of the speed of light. Related Stories: — Einstein wins again! Quarks obey relativity laws, Large Hadron Collider finds — Euclid 'dark universe' telescope discovers stunning Einstein ring in warped space-time (image) — Black holes may obey the laws of physics after all, new theory suggests Hornoff and Helm illuminated the cube and the sphere respectively with extremely short pulses from a laser; they also recorded images of the reflected light with camera exposures of just a trillionth of a second (a span of time known as a picosecond). After each image, the cube and the sphere were repositioned as though they were moving at close to the speed of light. The images were then combined to include only those where each object is illuminated by the laser at the moment when light would have been emitted if the speed of light were only two meters per second, rather than the 983,571,056 feet (299,792,458 meters) per second that it actually is. "We combined the still images into short video clips of the ultra-fast objects. The result was exactly what we expected," said Schattschneider. "A cube appears twisted, a sphere remains a sphere but the north pole is in a different place." The Terrell–Penrose effect is just another example of how nature, when pushed to extremes, becomes topsy-turvy, creating phenomena quite alien to our existence. The findings were presented on May 5 in the journal Communications Physics.
Yahoo
06-05-2025
- Science
- Yahoo
Low-cost material conducts electricity with higher stability, 100% efficiency increase
Yahoo is using AI to generate takeaways from this article. This means the info may not always match what's in the article. Reporting mistakes helps us improve the experience. Yahoo is using AI to generate takeaways from this article. This means the info may not always match what's in the article. Reporting mistakes helps us improve the experience. Yahoo is using AI to generate takeaways from this article. This means the info may not always match what's in the article. Reporting mistakes helps us improve the experience. Generate Key Takeaways A team scientists have succeeded in producing new and efficient thermoelectric materials that could compete with state-of-the-art materials, offering greater stability and lower cost. Thermoelectric materials enable the direct conversion of heat into electrical energy. The latest innovation offers new properties through a new combination of materials. Researchers have highlighted that good thermoelectric materials are those that conduct electricity well on the one hand, but transport heat as poorly as possible on the other – an apparent contradiction, as good electrical conductors are generally also good conductors of heat. Scientists try to suppress heat transport through lattice vibrations "In solid matter, heat is transferred both by mobile charge carriers and by vibrations of the atoms in the crystal lattice. In thermoelectric materials, we mainly try to suppress heat transport through the lattice vibrations, as they do not contribute to energy conversion," said first author Fabian Garmroudi, who obtained his doctorate at TU Wien. This makes them particularly attractive for the emerging for the autonomous energy supply of microsensors and other tiny electronic components. In order to make the materials more efficient, at the same time heat transport via the lattice vibrations must be suppressed and the mobility of the electrons increased – a hurdle that has often hindered research until now. Powder of an alloy of iron, vanadium, tantalum and aluminum used Published in the journal Nature Communications, the study demonstrates that by incorporating chemically and structurally distinct archetypal topological insulator Bi1−xSbx at the grain boundaries, charge, and heat transport can be decoupled, "resulting in a reduction of κL, and simultaneously, in an unexpected increase of μW." 'Supported by the Lions Award, I was able to develop new hybrid materials at the National Institute for Materials Science in Japan that exhibit exceptional thermoelectric properties,' recalls Garmroudi of his research stay in Tsukuba (Japan), which he completed as part of his work at TU Wien. Specifically, powder of an alloy of iron, vanadium, tantalum and aluminum (Fe2V0.95Ta0.1Al0.95) was mixed with a powder of bismuth and antimony (Bi0.9Sb0.1) and pressed into a compact material under high pressure and temperature. Due to their different chemical and mechanical properties, however, the two components do not mix at an atomic level. Instead, the BiSb material is preferentially deposited at the micrometer-sized interfaces between the crystals of the FeVTaAl alloy, according to a press release. Researchers highlighted that the lattice structures of the two materials, and therefore also their quantum mechanically permitted lattice vibrations, are so different that thermal vibrations cannot simply be transferred from one crystal to the other. Researchers added that the targeted decoupling of heat and charge transport enabled the team to increase the efficiency of the material by more than 100 %. "This brings us a big step closer to our goal of developing a thermoelectric material that can compete with commercially available compounds based on bismuth telluride," said Garmroudi.
Yahoo
21-04-2025
- Science
- Yahoo
Scientists double thermoelectric efficiency with new hybrid materials
An international research team has developed new, highly efficient thermoelectric materials that have the potential to compete with current state-of-the-art compounds, while offering enhanced stability and significantly lower production costs. Led by Fabian Garmroudi, PhD, a Director's Postdoctoral Fellow at Los Alamos National Laboratory (USA), the research team successfully developed hybrid materials that simultaneously suppress lattice vibrations and enhance charge carrier mobility by employing a novel approach. The innovation, according to Garmroudi, lies in combining two materials with fundamentally different mechanical properties but similar electronic traits. The idea behind the study emerged from the potential of thermoelectric materials to directly convert heat into electrical energy, making them especially appealing for the growing Internet of Things - particularly for powering microsensors and other miniature electronic components autonomously. To improve their efficiency, it is essential to simultaneously suppress heat transport through lattice vibrations and enhance electron mobility, a challenge that has long impeded progress in the field. Efficient thermoelectric materials - solid-state semiconductors that transform heat into electric power- need to conduct electricity efficiently while minimizing heat transfer. This, however, presents a challenge on its own, as materials that conduct electricity well typically also conduct heat effectively. "In solid matter, heat is transferred both by mobile charge carriers and by vibrations of the atoms in the crystal lattice," Garmroudi says, emphasizing that researchers have devised advanced techniques to engineer thermoelectric materials with exceptionally low thermal conductivity over the past few decades. "In thermoelectric materials, we mainly try to suppress heat transport through the lattice vibrations, as they do not contribute to energy conversion," he adds. Garmroudi recalls developing the novel hybrid materials during his research stay in Tsukuba, Japan, supported by the Lions Award and carried out at the National Institute for Materials Science as part of his work at TU Wien (Vienna University of Technology). Under intense heat and pressure, he fused two distinct powders, one made from an iron-based alloy with vanadium, tantalum, and aluminum (Fe2V0.95Ta0.1Al0.95), and the other from a bismuth-antimony mix (Bi0.9Sb0.1). The result was a compact hybrid material with promising thermoelectric potential. Additionally, because of their differing chemical and mechanical characteristics, the two materials did not blend on the atomic scale. Instead the bismuth-antimony component selectively accumulated at the micrometer-sized interfaces between the crystals of the FeVTaAl alloy. According to Garmroudi, the two materials have vastly different lattice structures, which means their allowed quantum lattice vibrations don't align. As a result, thermal vibrations can't easily pass from one crystal to the other, significantly limiting heat transfer at their interfaces. Because the two materials share similar electronic properties, charge carriers not only move freely but also accelerate significantly at the interfaces, the reason being that the BiSb component forms a topological insulator phase, a quantum state that blocks conduction inside while enabling nearly lossless surface transport. "This brings us a big step closer to our goal of developing a thermoelectric material that can compete with commercially available compounds based on bismuth telluride," concludes Garmroudi in a press release, adding that the targeted decoupling of heat and charge transport enabled the team to increase the efficiency of the material by more than 100 percent. Bismuth telluride, introduced in the 1950s, is still regarded as the benchmark for thermoelectric materials today. However, the new hybrid materials offer a major advantage in being significantly more stable and more cost-effective.
Yahoo
07-02-2025
- Science
- Yahoo
Sacred laws of entropy also work in the quantum world, suggests study
According to the second law of thermodynamics, the entropy of an isolated system tends to increase over time. Everything around us follows this law; for instance, the melting of ice, a room becoming messier, hot coffee cooling down, and aging — all are examples of entropy increasing over time. Until now, scientists believed that quantum physics is an exception to this law. This is because about 90 years ago, mathematician John von Neumann published a series of papers in which he mathematically showed that if we have complete knowledge of a system's quantum state, its entropy remains constant over time. However, a new study from researchers at the Vienna University of Technology (TU Wien) challenges this notion. It suggests that the entropy of a closed quantum system also increases over time until it reaches its peak level. 'It depends on what kind of entropy you look at. If you define the concept of entropy in a way that is compatible with the basic ideas of quantum physics, then there is no longer any contradiction between quantum physics and thermodynamics,' the TU Wien team notes. The study authors highlighted an important detail in Neumann's explanation. He stated that entropy for a quantum system doesn't change when we have full information about the system. However, the quantum theory itself tells us that it's impossible to have complete knowledge of a quantum system, as we can only measure certain properties with uncertainty. This means that von Neumann entropy isn't the correct approach to looking at the randomness and chaos in quantum systems. So then, what's the right way? Well, 'instead of calculating the von Neumann entropy for the complete quantum state of the entire system, you could calculate an entropy for a specific observable,' the study authors explain. This can be achieved using Shannon entropy, a concept proposed by mathematician Claude Shannon in 1948 in his paper titled A Mathematical Theory of Communication. Shannon entropy measures the uncertainty in the outcome of a specific measurement. It tells us how much new information we gain when observing a quantum system. "If there is only one possible measurement result that occurs with 100% certainty, then the Shannon entropy is zero. You won't be surprised by the result, you won't learn anything from it. If there are many possible values with similarly large probabilities, then the Shannon entropy is large," Florian Meier, first author of the study and a researcher at TU Wien, said. When we reimagine the entropy of a quantum system through the lens of Claude Shannon, we begin with a quantum system in a state of low Shannon entropy, meaning that the system's behavior is relatively predictable. For example, imagine you have an electron, and you decide to measure its spin (which can be up or down). If you already know the spin is 100% up, the Shannon entropy is zero—we learn nothing new from the measurement. In case the spin is 50% up and 50% down, then Shannon entropy is high because we are equally likely to get either result, and the measurement gives us new information. As more time passes, the entropy increases as you're never sure about the outcome. However, eventually, the entropy reaches a point where it levels off, meaning the system's unpredictability stabilizes. This mirrors what we observe in classical thermodynamics, where entropy increases until it reaches equilibrium and then stays constant. According to the study, this case of entropy also stands valid for quantum systems involving many particles and producing multiple outcomes. "This shows us that the second law of thermodynamics is also true in a quantum system that is completely isolated from its environment. You just have to ask the right questions and use a suitable definition of entropy," Marcus Huber, senior study author and an expert in quantum information science at TU Wien, said. The study is published in the journal PRX Quantum.
