materials science (26)

Nanotubes and Nitro...

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Stored energy: a rendition of a system that combines polymeric nitrogen (blue chain) and carbon nanotube (clear spheres). (Courtesy: Heba Megahd)

Topics: Carbon Nanotubes, Materials Science, Nanotechnology

From TNT to nitro-glycerine, nitrogen-rich compounds are known for packing an explosive punch. When these materials explode, bonds between atoms in the compounds are broken, which gives a chance for two nitrogen atoms to form very strong triple bonds with each other. This releases an enormous amount of chemical energy due to the high strength of the triple bond, which is almost six times stronger than its single-band counterpart. In fact, the strength of nitrogen-nitrogen triple bonds is one of the reasons that the stable nitrogen gas dominates Earth’s atmosphere.

This chemical property of nitrogen is encouraging scientists to develop new nitrogen-rich compounds for use as high-energy-density materials that can be used as explosives or propellants. Polymeric nitrogen exists in the form of chains and tubes of linked nitrogen atoms with a high number of single or double bonds that can break and form triple bonds, releasing a large amount of energy and no dangerous by-products.

Several types of these polymers have been made at high temperatures and pressures, but they have been notoriously difficult to stabilize under ambient conditions. However, the electrochemical pressure inside the confined walls of carbon nanotubes may be the key to realizing these structures under more practical conditions. In a paper, published in Chinese Physics Letters, a team of scientists led by Jian Sun at Nanjing University provides a theoretical map of the process and the resulting compounds.

Carbon nanotubes could stabilize energy-rich nitrogen chains, Heba Megahd, Physics World

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Getting Back Mojo...

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Artist's representation of the circular phonons. (Courtesy: Nadja Haji and Peter Baum, University Konstanz)

Topics: Applied Physics, Lasers, Magnetism, Materials Science, Phonons

When a magnetic material is bombarded with short pulses of laser light, it loses its magnetism within femtoseconds (10–15 seconds). The spin, or angular momentum, of the electrons in the material, thus disappears almost instantly. Yet all that angular momentum cannot simply be lost. It must be conserved – somewhere.

Thanks to new ultrafast electron diffraction experiments, researchers at the University of Konstanz in Germany have now found that this “lost” angular momentum is in fact transferred from the electrons to vibrations of the material’s crystal lattice within a few hundred femtoseconds. The finding could have important implications for magnetic data storage and for developments in spintronics, a technology that exploits electron spins to process information without using much power.

In a ferromagnetic material, magnetism occurs because the magnetic moments of the material’s constituent atoms align parallel to each other. The atoms and their electrons then act as elementary electromagnets, and the magnetic fields are produced mainly by the spin of the electrons.

Because an ultrashort laser pulse can rapidly destroy this alignment, some scientists have proposed using such pulses as an off switch for magnetization, thereby enabling ultra-rapid data processing at frequencies approaching those of light. Understanding this ultrafast demagnetization process is thus crucial for developing such applications as well as for better understanding the foundations of magnetism.

Researchers find ‘lost’ angular momentum, Isabelle Dumé, Physics World

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Fantastic Plastic...

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Plastic fantastic: this perovskite-based device can be reconfigured and could play an important role in artificial intelligence systems. (Courtesy: Purdue University/Rebecca McElhoe)

Topics: Artificial Intelligence, Biology, Computer Science, Materials Science

Researchers in the US have developed a perovskite-based device that could be used to create a high-plasticity architecture for artificial intelligence. The team, led by Shriram Ramanathan at Purdue University, has shown that the material’s electronic properties can be easily reconfigured, allowing the devices to function like artificial neurons and other components. Their results could lead to more flexible artificial-intelligence hardware that could learn much like the brain.

Artificial intelligence systems can be trained to perform a task such as voice recognition using real-world data. Today this is usually done in software, which can adapt when additional training data are provided. However, machine learning systems that are based on hardware are much more efficient and researchers have already created electronic circuits that behave like artificial neurons and synapses.

However, unlike the circuits in our brains, these electronics are not able to reconfigure themselves when presented with new training information. What is needed is a system with high plasticity, which can alter its architecture to respond efficiently to new information.

Device can transform into four components for artificial intelligence systems, Sam Jarman, Physics World

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Quantum AI...

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Rutgers researchers and their collaborators have found that learning - a universal feature of intelligence in living beings - can be mimicked in synthetic matter, a discovery that in turn could inspire new algorithms for artificial intelligence (AI). (Courtesy: Rutgers University-New Brunswick)

Topics: Artificial Intelligence, Computer Science, Materials Science, Quantum Mechanics

Quantum materials known as Mott insulators can “learn” to respond to external stimuli in a way that mimics animal behavior, say researchers at Rutgers University in the US. The discovery of behaviors such as habituation and sensitization in these non-living systems could lead to new algorithms for artificial intelligence (AI).

Neuromorphic, or brain-inspired, computers aim to mimic the neural systems of living species at the physical level of neurons (brain nerve cells) and synapses (the connections between neurons). Each of the 100 billion neurons in the human brain, for example, receives electrical inputs from some of its neighbors and then “fires” an electrical output to others when the sum of the inputs exceeds a certain threshold. This process, also known as “spiking”, can be reproduced in nanoscale devices such as spintronic oscillators. As well as being potentially much faster and energy-efficient than conventional computers, devices based on these neuromorphic principles might be able to learn how to perform new tasks without being directly programmed to accomplish them.

Quantum material ‘learns’ like a living creature, Isabelle Dumé, Physics World

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Kilonovas and Gold...

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Artist's impression of a neutron-star merger (Courtesy: NASA)

Topics: Astronomy, Astrophysics, Chemistry, Materials Science, Neutron Stars

The amounts of heavy elements such as gold created when black holes merge with neutron stars have been calculated and compared with the amounts expected when pairs of neutron stars merge. The calculations were done by Hsin-Yu Chen and Salvatore Vitale at the Massachusetts Institute of Technology and Francois Foucart at the University of New Hampshire using advanced simulations and gravitational-wave observations made by the LIGO–Virgo collaboration. Their results suggest that merging pairs of neutron stars are likely to be responsible for more heavy elements in the universe than mergers of black holes with neutron stars.

Today, astrophysicists have an incomplete understanding of how elements heavier than iron are made. In this nucleosynthesis process, lighter nuclei must be able to capture neutrons from their surroundings. Astrophysicists believe this can happen in two ways, each producing about half of the heavy elements in the universe. These are the slow process (s-process) that occurs in large stars and the rapid process (r-process), which is believed to occur in extreme conditions such as the explosion of a star in a supernova. However, exactly where the r-process can take place is hotly debated.

One event that could support the r-process is the merger of a pair of neutron stars, which can result in a huge explosion called a kilonova. Indeed, such an event was seen by LIGO–Virgo in 2017, and simultaneous observations using light-based telescopes suggest that heavy elements were created in that event.

Merging neutron stars create more gold than collisions involving black holes, Sam Jarman, Physics World

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Quantum Exorcism...

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Figure 2. Maxwell’s demon is a hypothetical being that can observe individual molecules in a gas-filled box with a partition in the middle separating chambers A and B. If the demon sees a fast-moving gas molecule, it opens a trapdoor in the partition to let fast-moving molecules into chamber B while leaving slow-moving ones behind. Repeating that action would allow the buildup of a temperature difference between the two sides of the partition. A heat engine could use that temperature difference to perform work, which would contradict the second law of thermodynamics.

Topics: Chemistry, History, Materials Science, Quantum Mechanics, Thermodynamics

Thermodynamics is a strange theory. Although it is fundamental to our understanding of the world, it differs dramatically from other physical theories. For that reason, it has been termed the “village witch” of physics.1 Some of the many oddities of thermodynamics are the bizarre philosophical implications of classical statistical mechanics. Well before relativity theory and quantum mechanics brought the paradoxes of modern physics into the public eye, Ludwig Boltzmann, James Clerk Maxwell, and other pioneers of statistical mechanics wrestled with several thought experiments, or demons, that threatened to undermine thermodynamics.

Despite valiant efforts, Maxwell and Boltzmann were unable to completely vanquish the demons besetting the village witch of physics—largely because they were limited to the classical perspective. Today, experimental and theoretical developments in quantum foundations have granted present-day researchers and philosophers greater insights into thermodynamics and statistical mechanics. They allow us to perform a “quantum exorcism” on the demons haunting thermodynamics and banish them once and for all.

Loschmidt’s demon and time reversibility

Boltzmann, a founder of statistical mechanics and thermodynamics, was fascinated by one of the latter field’s seeming paradoxes: How does the irreversible behavior demonstrated by a system reaching thermodynamic equilibrium, such as a cup of coffee cooling down or a gas spreading out, arise from the underlying time-reversible classical mechanics?2 That equilibrating behavior only happens in one direction of time: If you watch a video of a wine glass smashing, you know immediately whether the video was in rewind or not. In contrast, the underlying classical or quantum mechanics are time-reversible: If you were to see a video of lots of billiard balls colliding, you wouldn’t necessarily know whether the video was in rewind or not. Throughout his career, Boltzmann pursued a range of strategies to explain irreversible equilibrating behavior from the underlying reversible dynamics. Boltzmann’s friend Josef Loschmidt famously objected to those attempts. He argued that the underlying classical mechanics allow for the possibility that the momenta are reversed, which would lead to the gas retracing its steps and “anti-equilibrating” to the earlier, lower-entropy state. Boltzmann challenged Loschmidt to try to reverse the momenta, but Loschmidt was unable to do so. Nevertheless, we can envision a demon that could. After all, it is just a matter of practical impossibility—not physical impossibility—that we can’t reach into a box of gas and reverse each molecule’s trajectory.

Technological developments since Loschmidt’s death in 1895 have expanded the horizons of what is practically possible (see figure 1). Although it seemed impossible during his lifetime, Loschmidt’s vision of reversing the momenta was realized by Erwin Hahn in 1950 in the spin-echo experiment, in which atomic spins that have dephased and become disordered are taken back to their earlier state by an RF pulse. If it is practically possible to reverse the momenta, what does that imply about equilibration? Is Loschmidt’s demon triumphant?

The demons haunting thermodynamics, Katie Robertson, Physics Today

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Big Bet on Small...

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Topics: Futurism, Materials Science, Nanotechnology

The National Nanotechnology Initiative promised a lot. It has delivered more.

We’re now more than two decades out from the initial announcement of the National Nanotechnology Initiative (NNI), a federal program from President Bill Clinton founded in 2000 to support nanotechnology research and development in universities, government agencies, and industry laboratories across the United States. It was a significant financial bet on a field that was better known among the general public for science fiction than scientific achievement. Today it’s clear that the NNI did more than influence the direction of research in the U.S. It catalyzed a worldwide effort and spurred an explosion of creativity in the scientific community. And we’re reaping the rewards not just in medicine, but also clean energy, environmental remediation, and beyond.

Before the NNI, there were people who thought nanotechnology was a gimmick. I began my research career in chemistry, but it seemed to me that nanotechnology was a once-in-a-lifetime opportunity: the opening of a new field that crossed scientific disciplines. In the wake of the NNI, my university, Northwestern University, made the strategic decision to establish the International Institute for Nanotechnology, which now represents more than $1 billion in pure nanotechnology research, educational programs, and supporting infrastructure. Other universities across the U.S. made similar investments, creating new institutes and interdisciplinary partnerships.

Moreover, as a new route to inter- or transdisciplinary research, which was at the core of the NNI, nanotechnology has driven a new narrative in STEM: collaboration. Nanotechnology has captured the imagination of a generation of materials scientists, chemists, physicists, and biologists to synthesize and understand new materials; as well as inspiring engineers who are trained to develop tools for making and manipulating such structures; and doctors who can use them in the clinic. Collaborative nanotechnology research at our institute unites faculty members from 32 departments across four schools at Northwestern. This diversity of training and perspective does more than broadening the scope of our research. It enables us to identify, understand and address big problems—and it helps us break down barriers between the lab and the marketplace.

A Big Bet on Nanotechnology Has Paid Off, Chad Mirkin is director of the International Institute for Nanotechnology, George B. Rathmann Professor of Chemistry and a professor of materials science and engineering, medicine, biomedical engineering, and chemical and biological engineering at Northwestern University.

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LCE...

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The microfiber actuators on the metal mesh collector (top left), under SEM (bottom left), under heat activation (top right), and integrated into an artificial arm (bottom right). | Credit: Qiguang He et al./Science Robotics

Topics: Materials Science, Mechanical Engineering, Nanotechnology, Robotics

A new artificial fiber spun from a polymer called liquid crystal elastomer (LCE) using high-voltage electricity replicates the strength, responsiveness, and power density of human muscle fibers, scientists report. When powered by heat or near-infrared light, the fibers pulled upward and downward or oscillated back and forth.

"Our work may open up an avenue to build soft robotics or soft machines using liquid crystal elastomers as the actuator," the authors write in their paper, published in the August 25 issue of Science Robotics.

When applied to a variety of potential applications, the fiber actuators successfully controlled the pinching motion of a micro-tweezer, directed the movement of a microswimmer and a tiny artificial arm, and pumped fluids into a light-powered microfluidic pump.

Inspired by the utility of tiny fibers in nature, scientists sought to create artificial fibers that could also serve as ubiquitous tools in robotics, as sensors or assistive devices, for example. In the past few years, researchers succeeded in constructing fiber actuators driven by heat or light that are as strong and flexible as natural fibers. However, many of these artificial threads respond to their stimulus very slowly, due to their large size or complex actuation processes. When fibers can respond quickly, there's a trade-off in size or quality; for example, micro-yarns made of carbon nanotubes are fast actuators but aren't as strong as other fibers.

"Animal muscle fiber exhibits superior mechanical properties and actuation performance," said senior author Shengqiang Cai, associate professor of mechanical and aerospace engineering at the University of California, San Diego. "Only a few existing materials show similar actuation behaviors as animal muscle, and the fabrication of fibers from those materials with a size and quality comparable to muscle fiber is not easy."

Electrically Spun Artificial Fibers Match Performance of Human Muscle Fibers, Juwon Song, American Association for the Advancement of Science

 

 

 

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Steve Austin's Beads...

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Magnetic prosthetic: A magnetic sensing array enables a new tissue tracking strategy that could offer advanced motion control in artificial limbs. (Courtesy: MIT Media Lab/Cameron Taylor/Vessel Studios)

Topics: Biotechnology, Magnetism, Materials Science, Medicine, Nanotechnology, Robotics

Cultural reference: The Six Million Dollar Man, NBC

In recent years, health and fitness wearables have gained popularity as platforms to wirelessly track daily physical activities, by counting steps, for example, or recording heartbeats directly from the wrist. To achieve this, inertial sensors in contact with the skin capture the relevant motion and physiological signals originating from the body.

As wearable technology evolves, researchers strive to understand not just how to track the body’s dynamic signals, but also how to simulate them to control artificial limbs. This new level of motion control requires a detailed understanding of what is happening beneath the skin, specifically, the motion of the muscles.

Skeletal muscles are responsible for almost all movement of the human body. When muscle fibers contract, the exerted forces travel through the tendons, pull the bones, and ultimately produce motion. To track and use these muscle contractions in real-time and with high signal quality, engineers at the Massachusetts Institute of Technology (MIT) employed low-frequency magnetic fields – which pass undisturbed through body tissues – to provide accurate and real-time transcutaneous sensing of muscle motion. They describe their technique in Science Robotics.

Magnetic beads inside the body could improve control of bionic limbs, Raudel Avila is a student contributor to Physics World

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Exciton Surfing...

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Surfing excitons: Cambridge’s Alexander Sneyd with the transient-absorption microscopy set-up. (Courtesy: Alexander Sneyd)

Topics: Alternate Energy, Applied Physics, Materials Science, Nanotechnology, Solar Power

Organic solar cells (OSCs) are fascinating devices where layers of organic molecules or polymers carry out light absorption and subsequent transport of energy – the tasks that make a solar cell work. Until now, the efficiency of OSCs has been thought to be constrained by the speed at which energy carriers called excitons to move between localized sites in the organic material layer of the device. Now, an international team of scientists led by Akshay Rao at the UK’s University of Cambridge has shown that this is not the case. What is more, they have discovered a new quantum mechanical transport mechanism called transient delocalization, which allows OSCs to reach much higher efficiencies.

When light is absorbed by a solar cell, it creates electron-hole pairs called excitons and the motion of these excitons plays a crucial role in the operation of the device. An example of an organic material layer where light absorption and transport of excitons takes place is in a film of well-ordered poly(3-hexylthiophene) nanofibers. To study exciton transport, the team shone laser pulses at such a nanofiber film and observed its response.

Exciton wave functions were thought to be localized due to strong couplings with lattice vibrations (phonons) and electron-hole interactions. This means the excitons would move slowly from one localized site to the next. However, the team observed that the excitons were diffusing at speeds 1000 times greater than what had been shown for similar samples in previous research. These speeds correspond to a ground-breaking diffusion length of about 300 nm for such crystalline films. This means energy can be transported much faster and more efficiently than previously thought.

Exciton ‘surfing’ could boost the efficiency of organic solar cells, Rikke Plougmann, Physics World

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Biggie's Starship...

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Topics: Materials Science, Nanotechnology, Space Exploration, Spaceflight, Star Trek

China is investigating how to build ultra-large spacecraft that are up to 0.6 miles (1 kilometer) long. But how feasible is the idea, and what would be the use of such a massive spacecraft?

The project is part of a wider call for research proposals from the National Natural Science Foundation of China, a funding agency managed by the country’s Ministry of Science and Technology. A research outline posted on the foundation’s website described such enormous spaceships as “major strategic aerospace equipment for the future use of space resources, exploration of the mysteries of the universe, and long-term living in orbit.”

The foundation wants scientists to conduct research into new, lightweight design methods that could limit the amount of construction material that has to be lofted into orbit, and new techniques for safely assembling such massive structures in space. If funded, the feasibility study would run for five years and have a budget of 15 million yuan ($2.3 million).

The project might sound like science fiction, but former NASA chief technologist Mason Peck said the idea isn’t entirely off the wall, and the challenge is more a question of engineering than fundamental science.

“I think it’s entirely feasible,” Peck, now a professor of aerospace engineering at Cornell University, told Live Science. “I would describe the problems here not as insurmountable impediments, but rather problems of scale.”

By far the biggest challenge would be the price tag, noted Peck, due to the huge cost of launching objects and materials into space. The International Space Station (ISS), which is only 361 feet (110 meters) wide at its widest point according to NASA, cost roughly $100 billion to build, Peck said, so constructing something 10 times larger would strain even the most generous national space budget.

China Wants to Build a Mega Spaceship That’s Nearly a Mile Long, Edd Gent, Scientific American

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Cooling Computer Chips...

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An electron microscopy image of a gallium nitride-boron arsenide heterostructure interface at atomic resolution. Courtesy: The H-Lab/UCLA

Topics: Materials Science, Nanotechnology, Semiconductor Technology

A novel semiconducting material with high thermal conductivity can be integrated into high-power computer chips to cool them down and so improve their performance. The material, boron arsenide, is better at removing heat than the best thermal-management devices available today, according to the US-based researchers who developed it.

The size of computer chips has been shrinking over the years and has now reached the nanoscale, meaning that billions of transistors can be squeezed onto a single computer chip. This increased density of chips has enabled faster, more powerful computers, but it also generates localized hot spots on the chips. If this extra heat is not dealt with properly during operation, computer processors begin to overheat. This slows them down and makes them inefficient.

Defect-free boron arsenide

Researchers led by Yongjie Hu at the University of California, Los Angeles, recently developed a new thermal-management material that is much more efficient at drawing out and dissipating heat than other known metals or semiconducting materials such as diamond and silicon carbide. This new material is known as defect-free boron arsenide (BAs), and Hu and colleagues have now succeeded in interfacing it with computer chips containing wide-bandgap high-electron-mobility gallium nitride (GaN) transistors for the first time.

Using thermal transport measurements, the researchers found that processors interfaced with BAs and running at near maximum capacity had much lower hot-spot temperatures than other heat-management materials at the same transistor power density. During the experiment, the temperature of the BAs-containing devices increased from room temperature to roughly 360 K, compared to around 410 K and 440 K, respectively, for diamond and silicon carbide.

New semiconductor cools computer chips, Isabelle Dumé, Physics World

 

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ARPA-E, and Emission-Free Metal...

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Australian metals mining wastes (top) and the metal hyperaccumulator plants Alyssum murale and Berkheya coddii (bottom). The former plant can take up 1–3% of its weight in nickel. It has demonstrated yields of up to 400 kg of nickel per hectare annually, worth around $7000 at current prices, excluding processing and production costs. (Images adapted from A. van der Ent, A. Parbhakar-Fox, P. D. Erskine, Sci. Total Environ. 758, 143673, 2021, doi:10.1016/j.scitotenv.2020.143673.)

 

Topics: Climate Change, Green Tech, Materials Science, Research

 

When it comes to making steel greener, “only the laws of physics limit our imagination,” says Christina Chang of the Advanced Research Projects Agency-Energy (ARPA–E). Chang, an ARPA–E fellow, is seeking public input on a potential new agency program titled Steel Made via Emissions-Less Technologies. During her two-year tenure, she will guide program creation, agency strategy, and outreach. Steelmaking currently accounts for about 7% of the world’s carbon dioxide emissions, and demand for steel is expected to double by 2050 as low-income countries’ economies grow, according to the International Energy Agency.

 

Founded in 2009, ARPA–E is a tiny, imaginative office within the Department of Energy. SMELT is one part of a three-pronged thrust by ARPA–E to green up processes involved in producing steel and nonferrous metals, from the mine through to the finished products. Another program seeks ways to make use of the vast volumes of wastes that accumulate from mining operations around the globe—and reduce the amounts generated in the future. The agency is also exploring the feasibility of deploying plants that suck up from soils elements such as cobalt, nickel, and rare earths. Despite being essential ingredients in electric vehicles, batteries, and wind turbines, the US has little or no domestic production of them. (See Physics TodayFebruary 2021, page 20.)

 

Steelmaking

 

The first step in steelmaking is separating iron ore into oxygen and iron metal, which produces CO2 through both the reduction process and the fossil-fuel burning necessary to create high heat. An ARPA–E solicitation for ideas to clean up that process closed on 14 June. The agency is looking to replace the centuries-old blast furnace with greener technology that can work at the scale of 2 gigatons of steel production annually. It may or may not follow up with a request for research proposals to fund.

 

ARPA–E explores paths to emissions-free metal making, Physics Today

 

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Gold Anniversary...

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Images are from the article, link below

Topics: Electrical Engineering, Materials Science, Nanotechnology, Solid-State Physics

It's not exactly a wedding anniversary, but it is significant.

Fifty years ago this month, Intel introduced the first commercial microprocessor, the 4004. Microprocessors are tiny, general-purpose chips that use integrated circuits made up of transistors to process data; they are the core of a modern computer. Intel created the 12 mm2 chip for a printing calculator made by the Japanese company Busicom. The 4004 had 2,300 transistors—a number dwarfed by the billions found in today’s chips. But the 4004 was leaps and bounds ahead of its predecessors, packing the computing power of the room-sized, vacuum tube-based first computers into a chip the size of a fingernail. In the past 50 years, microprocessors have changed our culture and economy in unimaginable ways.

The microprocessor turns 50, Katherine Bourzac, Chemical & Engineering News

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Scrofulous Signaling...

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FIG. 1. Schematics of pulse sequences for spin-locking measurement with (a) two π/2 pulses and (b) two composite pulses. (c) Schematics of a SCROFULOUS composite pulse composed of three pulses. (d) Evolution of the spin state in the Bloch sphere. The spin state is initialized to the |0⟩ state by the first laser pulse. (e) The first π/2 pulse rotates the spin by 90∘ to the (−y)-direction. A y-driving microwave field is applied parallel to the spin in the rotation frame. (f) The second π/2 pulse rotates the spin by 90∘ to the (−z)-direction in the pulse sequence pattern A, or (g) the second −π/2 pulse rotates the spin by −90∘ to the z-direction in the pulse sequence pattern B. Finally, the spin state is read out from the PL by applying the second laser pulse. (h) Schematics of the experimental setup.

Topics: Applied Physics, Electrical Engineering, Materials Science, Optics

We present results of near-field radio-frequency (RF) imaging at micrometer resolution using an ensemble of nitrogen-vacancy (NV) centers in diamond. The spatial resolution of RF imaging is set by the resolution of an optical microscope, which is markedly higher than the existing RF imaging methods. High sensitivity RF field detection is demonstrated through spin locking. SCROFULOUS composite pulse sequence is used for manipulation of the spins in the NV centers for reduced sensitivity to possible microwave pulse amplitude error in the field of view. We present procedures for acquiring an RF field image under spatially inhomogeneous microwave field distribution and demonstrate a near-field RF imaging of an RF field emitted from a photolithographically defined metal wire. The obtained RF field image indicates that the RF field intensity has maxima in the vicinity of the edges of the wire, in accord with a calculated result by a finite-difference time-domain method. Our method is expected to be applied in a broad variety of application areas, such as material characterizations, characterization of RF devices, and medical fields.</em>

Near-field radio-frequency imaging by spin-locking with a nitrogen-vacancy spin sensor, Shintaro Nomura1,a), Koki Kaida1, Hideyuki Watanabe2, and Satoshi Kashiwaya3, Journal of Applied Physics

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Smart Foam...

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A robotic hand with the AiFoam artificially innervated smart foam, which enables it to sense objects in proximity by detecting their electrical fields and also self-heals if it gets cut, is pictured at National University Singapore's Materials Sciences and Engineering lab in Singapore June 30, 2021. REUTERS/Travis Teo

Topics: Biology, Biotechnology, Materials Science, Polymer Science, Robotics

SINGAPORE, July 6 (Reuters) - Singapore researchers have developed a smart foam material that allows robots to sense nearby objects, and repairs itself when damaged, just like human skin.

Artificially innervated foam, or AiFoam, is a highly elastic polymer created by mixing fluoropolymer with a compound that lowers surface tension.

This allows the spongy material to fuse easily into one piece when cut, according to researchers at the National University of Singapore.

"There are many applications for such a material, especially in robotics and prosthetic devices, where robots need to be a lot more intelligent when working around humans," explained lead researcher Benjamin Tee.

To replicate the human sense of touch, the researchers infused the material with microscopic metal particles and added tiny electrodes underneath the surface of the foam.

Smart foam material gives robotic hand the ability to self-repair, Travis Teo, Lee Ying Shan, Reuters Science

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Kagome Metal...

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The normalized resistance under magnetic fields and anisotropic upper critical magnetic fields of the CsV3Sb5 single crystal. Credit: Chinese Physics Letters

Topics: Condensed Matter Physics, Materials Science, Superconductors

Researchers at the Chinese Academy of Sciences have found evidence for an unusual superconducting state in CsV3Sb5, a so-called Kagome metal that exhibits exotic electronic properties. The finding could shed new light on how superconductivity emerges in materials where phenomena such as frustrated magnetism and intertwined orders play a major role.

Kagome metals are named after a traditional Japanese basket-weaving technique that produces a lattice of interlaced symmetrical triangles. Physicists are interested in this configuration (known as a Kagome pattern) because when the atoms of metal or other conductors are arranged in this fashion, their electrons behave in unusual ways.

An example is [frustrated] magnetism, which occurs when electrons are “not happy to live together”, observes Ludovic Jaubert, a condensed-matter physicist at the University of Bordeaux in France who was not involved in the present work. In frustrated materials, not all interactions between electron spins can be satisfied at the same time, which prevents the spins from ordering themselves on long-length scales. This failure has significant consequences for the material’s properties: if water behaved like this, for example, it would never freeze.

Unusual superconductivity appears in a Kagome metal, Isabelle Dumé, Physics World

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MIT engineers have developed self-cooling fabrics from polyethylene, commonly used in plastic bags. They estimate that the new fabric may be more sustainable than cotton and other common textiles. (Courtesy: Svetlana Boriskina)

Topics: Ecology, Environment, Green Tech, Materials Science

Polyethylene is one of the most common plastics in the world, but it is seldom found in clothing because it cannot absorb or carry away water. (Imagine wearing a plastic bag – you would feel very uncomfortable very quickly.) Now, however, researchers in the US have developed a new material spun from polyethylene that not only “breathes” better than cotton, nylon, or polyester, but also has a smaller ecological footprint due to the ease with which it can be manufactured, dyed, cleaned and used.

The textile industry produces about 62 million tons of fabric each year. In the process, it consumes huge quantities of water, generates millions of tons of waste, and accounts for 5–10% of global greenhouse gas emissions, making it one of the world’s most polluting industries. Later stages of the textile use cycle also contribute to the industry’s environmental impact. Textiles made from natural fibers such as wool, cotton, silk, or linen require considerable amounts of energy and water to recycle, while textiles that are colored or made of composite materials are hard to recycle at all.

Hydrophilic and wicking

Researchers led by Svetlana Boriskina of the Massachusetts Institute of Technology (MIT) set out to produce an alternative. They began by melting powdered low-density polyethylene and then extruding it into thin fibers roughly 18.5 μm in diameter (as measured using scanning electron microscopy and micro-computed tomography imaging techniques). This process slightly oxidizes the material’s surface so that it becomes hydrophilic – that is, it attracts water molecules – without the need for a separate chemical treatment.

Recycled plastic bags make sustainable fabrics, Isabelle Dumé, Physics World

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Colloidal Quantum Dots...

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FIG. 1. (a) Schematic of La Mer and Dinegar's model for the synthesis of monodispersed CQDs. (b) Representation of the apparatus employed for CQD synthesis. Reproduced with permission from Murray et al., Annu. Rev. Mater Res. 30(1), 545–610 (2000). Copyright 2000 Annual Reviews.

Topics: Energy, Materials Science, Nanotechnology, Quantum Mechanics, Solar Power

ABSTRACT
Solution-processed colloidal quantum dot (CQD) solar cells are lightweight, flexible, inexpensive, and can be spray-coated on various substrates. However, their power conversion efficiency is still insufficient for commercial applications. To further boost CQD solar cell efficiency, researchers need to better understand and control how charge carriers and excitons transport in CQD thin films, i.e., the CQD solar cell electrical parameters including carrier lifetime, diffusion length, diffusivity, mobility, drift length, trap state density, and doping density. These parameters play key roles in determining CQD thin film thickness and surface passivation ligands in CQD solar cell fabrication processes. To characterize these CQD solar cell parameters, researchers have mostly used transient techniques, such as short-circuit current/open-circuit voltage decay, photoconductance decay, and time-resolved photoluminescence. These transient techniques based on the time-dependent excess carrier density decay generally exhibit an exponential profile, but they differ in the signal collection physics and can only be used in some particular scenarios. Furthermore, photovoltaic characterization techniques are moving from contact to non-contact, from steady-state to dynamic, and from small-spot testing to large-area imaging; what are the challenges, limitations, and prospects? To answer these questions, this Tutorial, in the context of CQD thin film and solar cell characterization, looks at trends in characterization technique development by comparing various conventional techniques in meeting research and/or industrial demands. For a good physical understanding of material properties, the basic physics of CQD materials and devices are reviewed first, followed by a detailed discussion of various characterization techniques and their suitability for CQD photovoltaic devices.

Advanced characterization methods of carrier transport in quantum dot photovoltaic solar cells, Lilei Hu, Andreas Mandelis, Journal of Applied Physics

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Snapping Polymer Discs...

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Thin polymer discs self-propel by repeated "snapping" motions. Credit: Yongjin Kim, UMass Amherst

Topics: Chemistry, Polymer Science, Materials Science, Research

A polymer-based gel made by researchers in the US and inspired by the Venus flytrap plant can snap, jump and “reset” itself autonomously. The new self-propelled material might have applications in micron-sized robots and other devices that operate without batteries or motors.

“Many plants and animals, especially small ones, use special parts that act like springs and latches to help them move really fast, much faster than animals with muscles alone,” explains team leader Alfred Crosby, a professor of polymer science and engineering in the College of Natural Sciences at UMass Amherst. “The Venus flytraps are good examples of this kind of movement, as are grasshoppers and trap-jaw ants in the animal world.”

Snapping instabilities
The Venus flytrap plant works by regulating the way its turgor pressure – that is, the swelling produced as stored water pushes against a plant cell wall – is distributed through its leaves. Beyond a certain point, this swelling leads to a condition known as snapping instability, where the tiny additional pressure of a fly’s footsteps is enough to cause the plant to snap shut. The plant then automatically regenerates its internal structures in readiness for its next meal.

Polymer gels snap and jump on their own, Isabelle Dumé, Physics World

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