materials science (34)

When Water Outpaces Silicon…

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On target: Water is fanned out through a specially developed nozzle, and then a laser pulse is passed through it to create a switch. (Courtesy: Adrian Buchmann)

Topics: Applied Physics, Lasers, Materials Science, Photonics, Semiconductor Technology

A laser-controlled water-based switch that operates twice as fast as existing semiconductor switches has been developed by a trio of physicists in Germany. Adrian Buchmann, Claudius Hoberg, and Fabio Novelli at Ruhr University Bochum used an ultrashort laser pulse to create a temporary metal-like state in a jet of liquid water. This altered the transmission of terahertz pulses over timescales of just tens of femtoseconds.

With the latest semiconductor-based switches approaching fundamental upper limits on how fast they can operate, researchers are searching for faster ways of switching signals. One unexpected place to look for inspiration is the curious behavior of water under extreme conditions – like those deep within ice-giant planets or created by powerful lasers.

Molecular dynamics simulations suggest water enters a metallic state at pressures of 300 GPa and temperatures of 7000 K. While such conditions do not occur on Earth, it is possible that this state contributes to the magnetic fields of Uranus and Neptune. To study this effect closer to home, recent experiments have used powerful, ultrashort laser pulses to trigger photo-ionization in water-based solutions – creating fleeting, metal-like states.

Water-based switch outpaces semiconductor devices, described in APL Photonics.

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Graphullerene...

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Credit: Nicoletta Barolini

Topics: Chemistry, Graphene, Materials Science, Modern Physics, Nanotechnology

Graphullerene, an atom-thin material made of linked fullerene subunits, gives scientists a new form of modular carbon to play with.

Carbon, in its myriad forms, has long captivated the scientific community. Besides being the primary component of all organic life on earth, material forms of carbon have earned their fair share of breakthroughs. In 1996, the Nobel Prize in Chemistry went to the discoverers of fullerene, a superatomic symmetrical structure of 60 carbon atoms shaped like a soccer ball; in 2010, researchers working with an ultra-strong, atom-thin version of carbon, known as graphene, won the Nobel Prize in Physics.

Today in work published in Nature, researchers led by Columbia chemists Xavier Roy, Colin Nuckolls, and Michael Steigerwald, with postdoc and first author Elena Meirzadeh have discovered a new version of carbon that sits somewhere in between fullerene and graphene: graphullerene. It’s a new two-dimensional form of carbon made up of layers of linked fullerenes peeled into ultrathin flakes from a larger graphullerite crystal—just like how graphene is peeled from graphite crystals (the same material found in pencils).

“It is amazing to find a new form of carbon,” said Nuckolls. “It also makes you realize that there is a whole family of materials that can be made in a similar way that will have new and unusual properties as a consequence of the information written into the superatomic building blocks.”

Columbia Chemists Discover a New Form of Carbon: Graphene’s “Superatomic” Cousin, Ellen Neff, Quantum.Columbia.edu

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Serendipitous Quasicrystals...

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Cross-section of a fulgurite sample showing fused sand and melted conductor metal from a downed powerline. Credit: Luca Bindi et al.

Topics: Condensed Matter Physics, Energy, Materials Science

A team of researchers from Università di Firenze, the University of South Florida, California Institute of Technology, and Princeton University has found an incidence of a quasicrystal formed during an accidental electrical discharge.

In their paper published in Proceedings of the National Academy of Sciences, the group describes their study of a quasicrystal found in a sand dune in Nebraska.

Quasicrystals, as their name suggests, are crystal-like substances. They possess characteristics not found in ordinary crystals, such as a non-repeating arrangement of atoms. To date, quasicrystals have been found embedded in meteorites and in the debris from nuclear blasts. In this new effort, the researchers found one embedded in a sand dune in Sand Hills, Nebraska.

A study of the quasicrystal showed it had 12-fold, or dodecagonal, symmetry—something rarely seen in quasicrystals. Curious about how it might have formed and ended up in the sand dune, the researchers did some investigating. They discovered that a power line had fallen on the dune, likely due to a lightning strike. They suggest the electrical surge from either the power line or the lightning could have produced the quasicrystal.

The researchers note that the quasicrystal was found inside a tubular piece of fulgurite. They suggest it was also formed during the electrical surge due to the fusing of melted sand and metal from the power line.

Quasicrystal formed during accidental electrical discharge, Bob Yirka, Phys.org

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Pushing Beyond Moore...

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Clean-room technicians at the AIM Photonics NanoTech chip fabrication facility in Albany, New York.  Credit: SUNY Polytechnic Institute

Topics: Computer Science, Electrical Engineering, Materials Science, Nanotechnology, Semiconductor Technology

Over 50 Years of Moore's Law - Intel

GAITHERSBURG, Md. — The U.S. Department of Commerce’s National Institute of Standards and Technology (NIST) has entered into a cooperative research and development agreement with AIM Photonics that will give chip developers a critical new tool for designing faster chips that use both optical and electrical signals to transmit information. Called integrated photonic circuits, these chips are key components in fiber-optic networks and high-performance computing facilities. They are used in laser-guided missiles, medical sensors, and other advanced technologies. 

AIM Photonics, a Manufacturing USA institute, is a public-private partnership that accelerates the commercialization of new technologies for manufacturing photonic chips. The New York-based institute provides small and medium-sized businesses, academics, and government researchers access to expertise and fabrication facilities during all phases of the photonics development cycle, from design to fabrication and packaging.

NIST and AIM Photonics Team Up on High-Frequency Optical/Electronic Chips

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OPVs...

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V. ALTOUNIAN/SCIENCE

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

As ultrathin organic solar cells hit new efficiency records, researchers see green energy potential in surprising places.

In November 2021, while the municipal utility in Marburg, Germany, was performing scheduled maintenance on a hot water storage facility, engineers glued 18 solar panels to the outside of the main 10-meter-high cylindrical tank. It’s not the typical home for solar panels, most of which are flat, rigid silicon and glass rectangles arrayed on rooftops or in solar parks. The Marburg facility’s panels, by contrast, are ultrathin organic films made by Heliatek, a German solar company. In the past few years, Heliatek has mounted its flexible panels on the sides of office towers, the curved roofs of bus stops, and even the cylindrical shaft of an 80-meter-tall windmill. The goal: expanding solar power’s reach beyond flat land. “There is a huge market where classical photovoltaics do not work,” says Jan Birnstock, Heliatek’s chief technical officer.

Organic photovoltaics (OPVs) such as Heliatek’s are more than 10 times lighter than silicon panels and in some cases cost just half as much to produce. Some are even transparent, which has architects envisioning solar panels, not just on rooftops, but incorporated into building facades, windows, and even indoor spaces. “We want to change every building into an electricity-generating building,” Birnstock says.

Heliatek’s panels are among the few OPVs in practical use, and they convert about 9% of the energy in sunlight to electricity. But in recent years, researchers around the globe have come up with new materials and designs that, in small, lab-made prototypes, have reached efficiencies of nearly 20%, approaching silicon and alternative inorganic thin-film solar cells, such as those made from a mix of copper, indium, gallium, and selenium (CIGS). Unlike silicon crystals and CIGS, where researchers are mostly limited to the few chemical options nature gives them, OPVs allow them to tweak bonds, rearrange atoms, and mix in elements from across the periodic table. Those changes represent knobs chemists can adjust to improve their materials’ ability to absorb sunlight, conduct charges, and resist degradation. OPVs still fall short of those measures. But, “There is an enormous white space for exploration,” says Stephen Forrest, an OPV chemist at the University of Michigan, Ann Arbor.

Solar Energy Gets Flexible, Robert F. Service, Science Magazine

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Solar Lilly Pads...

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A floating artificial leaf – which generates clean fuel from sunlight and water – on the River Cam near King's College Chapel in Cambridge, UK. (Courtesy: Virgil Andrei)

Topics: Climate Change, Energy, Environment, Materials Science, Solar Power

Leaf-like devices that are light enough to float on water could be used to generate fuel from solar farms located on open water sources. This avenue hasn’t been explored before, according to researchers from the University of Cambridge in the UK who developed them. The new devices are made from thin, flexible substrates and perovskite-based light-absorbing layers. Tests showed that they can produce either hydrogen or syngas (a mixture of hydrogen and carbon monoxide) while floating on the River Cam.

Artificial leaves like these are a type of photoelectrochemical cell (PEC) that transforms sunlight into electrical energy or fuel by mimicking some aspects of photosynthesis, such as splitting water into its constituent oxygen and hydrogen. This differs from conventional photovoltaic cells, which convert light directly into electricity.

Because PEC artificial leaves contain both light harvesting and catalysis components in one compact device, they could, in principle, be used to produce fuel from sunlight cheaply and simply. The problem is that current techniques for making them can’t be scaled up. What is more, they are often composed of fragile and heavy bulk materials, which limits their use.

In 2019 a team of researchers led by Erwin Reisner developed an artificial leaf that produced syngas from sunlight, carbon dioxide, and water. This device contained two light absorbers and catalysts, but it also incorporated a thick glass substrate and coatings to protect against moisture, which made it cumbersome.

Floating artificial leaves could produce solar-generated fuel, Isabelle Dumé, Physics World

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Solid-State Cooling...

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Cool stuff: the diagram shows how the temperature of the caloric material was measured. The plot in the center shows the temperature change in the sample when exposed to a magnetic field. The plot on the right shows the change in temperature when the sample is strained. (Courtesy: Peng Wu et al/Acta Materialia 237 118154)

Topics: Global Warming, Green Tech, Materials Science, Solid-State Physics, Thermodynamics

Researchers in China have shown that applying strain to a composite material using an electric field induces a large and reversible caloric effect. This novel way of enhancing the caloric effect without a magnetic field could open new avenues of solid-state cooling and lead to more energy-efficient and lighter refrigerators.

The International Institute of Refrigeration estimates that 20% of all electricity used globally is expended on vapor-compression refrigeration – which is the technology used in conventional refrigerators and air conditioners. What is more, the refrigerants used in these systems are powerful greenhouse gases that contribute significantly to global warming. As a result, scientists are trying to develop more environmentally friendly refrigeration systems.

Cooling systems can also be made from completely solid-state systems, but these cannot currently compete with vapor compression for most mainstream applications. Today, most commercial solid-state cooling systems use the Peltier effect, which is a thermoelectric process that suffers from high cost and low efficiency.

Solid-state cooling is achieved via electric field-induced strain, Hardepinder Singh, Physics World

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Mirror, Mirror...

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Various views of a 3D-printed object are captured by a single camera using a dome-shaped array of mirrors. Left: The raw image. Right: closeups of some of the individual views. (Image: Sanha Cheong, SLAC National Accelerator Laboratory)

Topics: Applied Physics, Atomic-Scale Microscopy, Materials Science, Optics

(Nanowerk News) When it goes online, the MAGIS-100 experiment at the Fermi National Accelerator Laboratory and its successors will explore the nature of gravitational waves and search for certain kinds of wavelike dark matter. But first, researchers need to figure out something pretty basic: how to get good photographs of the clouds of atoms at the heart of their experiment.

Researchers at the Department of Energy's SLAC National Accelerator Laboratory realized that task would be perhaps the ultimate exercise in ultra-low light photography.

But a SLAC team that included Stanford graduate students Sanha Cheong and Murtaza Safdari, SLAC Professor Ariel Schwartzman, and SLAC scientists Michael Kagan, Sean Gasiorowski, Maxime Vandegar, and Joseph Frish found a simple way to do it: mirrors. By arranging mirrors in a dome-like configuration around an object, they can reflect more light towards the camera and image multiple sides of an object simultaneously.

And, the team reports in the Journal of Instrumentation ("Novel light field imaging device with an enhanced light collection for cold atom clouds"), that there's an additional benefit. Because the camera now gathers views of an object taken from many different angles, the system is an example of “light-field imaging”, which captures not just the intensity of light but also which direction light rays travel. As a result, the mirror system can help researchers build a three-dimensional model of an object, such as an atom cloud.

How do you take a better image of atom clouds? Mirrors - lots of mirrors, SLAC National Accelerator Laboratory

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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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