nanotechnology (78)



Cancer cells are one of the main targets for expanded mRNA-LNP use. Credit: Iliescu Catalin / Alamy

Topics: Biology, Biotechnology, Cancer, COVID-19, Nanotechnology

Note: This is an advertisement on Nature Portfolio discussing that there may be a silver lining in the pandemic we've all experienced.

Lipid nanoparticles (LNPs) transport small molecules into the body. The most well-known LNP cargo is mRNA, the key constituent of some of the early vaccines against COVID-19. But that is just one application: LNPs can carry many different types of payload and have applications beyond vaccines.

Barbara Mui has been working on LNPs (and their predecessors, liposomes) since she was a Ph.D. student in Pieter Cullis’s group in the 1990s. “In those days, LNPs encapsulated anti-cancer drugs,” says Mui, who is currently a senior scientist at Acuitas. This company developed the LNPs used in the Pfizer-BioNTech mRNA vaccine against SARS-CoV-2. She says it soon became clear that LNPs worked even better as carriers of polynucleotides. “The first one that worked really well was encapsulating small RNAs,” Mui recalls.

But it was mRNA where LNPs proved most effective, primarily because LNPs are comprised of positively charged lipid nanoparticles that encapsulate negatively charged mRNA. Once in the body, LNPs enter cells via endocytosis into endosomes and are released into the cytoplasm. “Without the specially designed chemistry, the LNP and mRNA would be degraded in the endosome,” says Kathryn Whitehead, professor in the departments of chemical engineering and biomedical engineering at Carnegie Mellon University.

LNPs are an ideal delivery system for mRNA. “COVID accelerated the acceptance of LNPs, and people are more interested in them,” says Mui. LNP-mRNA vaccines for other infectious diseases, such as HIV or malaria, or for non-communicable diseases, such as cancer, could be next. And the potential doesn’t end with mRNA; there is even more scope to adapt LNPs to carry different types of cargo. But to realize these potential benefits, researchers first need to overcome challenges and decrease toxicity, increase their ability to escape from the endosomes, increase their thermostability, and work out how to effectively target LNPs to organs across the body.

Another potential application for LNPs is immunotherapy. Genetically modifying lymphocytes such as T cells or NK cells with chimeric antibody receptors (CARs) has proven useful in blood cancers. Often this process involves extracting lymphocytes from the blood of the person receiving the treatment, editing the cells in culture to express CARs, and then reintroducing them into the blood. However, LNPs could make it possible to express the desired CAR in vivo by shuttling CAR mRNA to the target lymphocytes. Mui has been involved in vivo studies showing this process works in mouse T cells (Rurik, J.G. et al. Science 375, 91-96, 2022). And Vita Golubovskaya, VP of research and development at ProMab Biotechnologies, presented preliminary data (available here) at the CAR-TCR Summit in September 2022 regarding LNPs that direct CAR-mRNA to NK cells, which can then kill target cells. “The RNA-LNP is a very exciting and novel technology that can be used for delivering CAR and bi-specific antibodies against cancer,” she says.

Beyond COVID vaccines: what’s next for lipid nanoparticles? Nature Portfolio

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Scanning With a Twist...


How it works: illustration of the quantum twisting microscope in action. Electrons tunnel from the probe (inverted pyramid at the top) to the sample (bottom) in several places at once (green vertical lines) in a quantum-coherent manner. (Courtesy: Weizmann Institute of Science)

Topics: Chemistry, Entanglement, Materials Science, Nanotechnology, Quantum Mechanics

When the scanning tunneling microscope debuted in the 1980s, the result was an explosion in nanotechnology and quantum-device research. Since then, other types of scanning probe microscopes have been developed, and together they have helped researchers flesh out theories of electron transport. But these techniques probe electrons at a single point, thereby observing them as particles and only seeing their wave nature indirectly. Now, researchers at the Weizmann Institute of Science in Israel have built a new scanning probe – the quantum twisting microscope – that detects the quantum wave characteristics of electrons directly.

“It’s effectively a scanning probe tip with an interferometer at its apex,” says Shahal Ilani, the team leader. The researchers overlay a scanning probe tip with ultrathin graphite, hexagonal boron nitride, and a van der Waals crystal such as graphene, which conveniently flopped over the tip like a tent with a flat top about 200 nm across. The flat end is key to the device’s interferometer function.  Instead of an electron tunneling between one point in the sample and the tip, the electron wave function can tunnel across multiple points simultaneously.

“Quite surprisingly, we found that the flat end naturally pivots so that it is always parallel with the sample,” says John Birkbeck, the corresponding author of a paper describing this work. This is fortunate because any tilt would alter the tunneling distance and hence strength from one side of the plateau to the other. “It is the interference of these tunneling paths, as identified in the measured current, that gives the device its unique quantum-wave probing function,” says Birkbeck.

Scanning probe with a twist observes the electron’s wavelike behavior, Anna Demming, Physics World

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Nanowires and Climate Change...


Image Credit: Down to the wire (IMAGE), Yale University

Topics: Biotechnology, Civilization, Climate Change, Nanotechnology

Accelerated climate change is a major and acute threat to life on Earth. Rising temperatures are caused by atmospheric methane, which is 30 times more potent than CO2 at trapping heat. Microbes are responsible for generating half of this methane. Elevated temperatures are also accelerating microbial growth and thus producing more greenhouse gases than can be used by plants, thus weakening the earth’s ability to function as a carbon sink and further raising the global temperature.

A potential solution to this vicious circle could be another kind of microbes that eats up to 80% of methane flux from ocean sediments that protect the Earth. How microbes serve as both the biggest producers and consumers of methane has remained a mystery because they are very difficult to study in the laboratory. In Nature Microbiology, surprising wire-like properties of a protein highly similar to the protein used by methane-eating microbes are reported by the Yale team led by Yangqi Gu and Nikhil Malvankar of Molecular Biophysics and Biochemistry at Microbial Sciences Institute.

The team had previously shown that this protein nanowire shows the highest conductivity known to date,  allowing the generation of the highest electric power by any bacteria. But to date, no one has discovered how bacteria make them and why they show such extremely high conductivity.

An ultra-stable protein nanowire made by bacteria provides clues to combating climate change, Yale University.

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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,

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Pushing Beyond Moore...


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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Cellulose Shoes...


Credit: Tom Mannion

Topics: Additive Manufacturing, Biology, Biotechnology, Environment, Genetics, Nanotechnology

For Hermes, the Greek god of speed, these bacterial sneakers would have been just the ticket. Modern Synthesis co-founders Jen Keane, CEO, and Ben Reeve, CTO, are now setting out to make them available to mere mortals, raising a $4.1 million investment to scale up production. Keane, a graduate from Central Saint Martins School of Art and Design in London, and synthetic biologist Reeve, then at Imperial College London, set up Modern Synthesis in 2020 to pursue ‘microbial weaving’.

Their goal is to produce a new class of material, a hybrid/composite that will replace animal- and petrochemical-made sneakers with a biodegradable, yet durable, alternative. The shoe's upper is made by bacteria that naturally produce nanocellulose—Komagataeibacter rhaeticus—and can be further genetically engineered to also self-dye by producing melanin for color.

The process begins with a two-dimensional yarn scaffold shaped by robotics, which the scientists submerge in a fermentation medium containing the cellulose-producing bacteria. The K. rhaeticus ‘weave’ the sneaker upper by depositing the biomaterial on the scaffold. Once the sheets emerge from their microbial baths, they are shaped on shoe lasts following traditional footwear techniques. “It’s more than the sum of its parts,” Reeves says of the biocomposite. “Initially the scaffold helps the bacteria grow, then the microbial yarn reinforces the material: it holds the scaffold together.” Once the shoe is made, it is sterilized and the bacteria are washed out.

Cellulose shoes made by bacteria, Lisa Melton, Nature Biotechnology

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Nanotubes and Nitro...


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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Quantum Charging...


GIF Source: Sci-Tech Daily

Topics: Alternate Energy, Battery, Green Tech, Nanotechnology, Quantum Mechanics

Note: I'm in the semifinals of the 3-Minute Thesis competition, so I decided to focus on my presentation. Wish me luck. This does, however, relate to our need as a species to get off fossil fuels as soon as possible, so things like Ukraine, Crimea, and the dismemberment of Jamal Khashoggi are not facilitated by our need for energy and our tolerance for tyrants.

Whether it’s photovoltaics or fusion, sooner or later, human civilization must turn to renewable energies. This is deemed inevitable considering the ever-growing energy demands of humanity and the finite nature of fossil fuels. As such, much research has been pursued in order to develop alternative sources of energy, most of which utilize electricity as the main energy carrier. The extensive R&D in renewables has been accompanied by gradual societal changes as the world adopted new products and devices running on renewables. The most striking change as of recently is the rapid adoption of electric vehicles. While they were hardly seen on the roads even 10 years ago, now millions of electric cars are being sold annually. The electric car market is one of the most rapidly growing sectors, and it helped propel Elon Musk to become the wealthiest man in the world.

Unlike traditional cars which derive energy from the combustion of hydrocarbon fuels, electric vehicles rely on batteries as the storage medium for their energy. For a long time, batteries had far lower energy density than those offered by hydrocarbons, which resulted in very low ranges of early electric vehicles. However, gradual improvement in battery technologies eventually allowed the drive ranges of electric cars to be within acceptable levels in comparison to gasoline-burning cars. It is no understatement that the improvement in battery storage technology was one of the main technical bottlenecks which had to be solved in order to kickstart the current electric vehicle revolution.

New Quantum Technology To Make Charging Electric Cars As Fast as Pumping Gas, Institute for Basic Science, Sci-Tech Daily

Reference: “Quantum Charging Advantage Cannot Be Extensive Without Global Operations” 21 March 2022, Physical Review Letters.

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Wearable Pressure Sensor...


Hybrid device: A diagram of the layers in the new soft pressure sensor. (Courtesy: the University of Texas at Austin)

Topics: Applied Physics, Biotechnology, Nanotechnology

Wearable pressure sensors are commonly used in medicine to track vital signs, and in robotics to help mechanical fingers handle delicate objects. Conventional soft capacitive pressure sensors only work at pressures below 3 kPa, however, meaning that something as simple as tight-fitting clothing can hinder their performance. A team of researchers at the University of Texas has now made a hybrid sensor that remains highly sensitive over a much wider range of pressures. The new device could find use in robotics and biomedicine.

The most common types of pressure sensors rely on piezoresistive, piezoelectric, capacitive, and/or optical mechanisms to operate. When such devices are compressed, their electrical resistance, voltage, capacitance, or light transmittance (respectively) changes in a well-characterized way that can be translated into a pressure reading.

The high sensitivity and long-term stability of capacitive pressure sensors make them one of the most popular types, and they are often incorporated into soft, flexible sensors that can be wrapped around curved surfaces. Such sensors are popular in fields such as prosthetics, robotics, and biometrics, where they are used to calibrate the strength of a robot’s grip, monitor pulse rates, and blood pressure, and measure footstep pressure. However, these different applications involve a relatively wide range of pressures: below 1 kPa for robotic electronic skin (e-skin) and pulse monitoring; between 1 and 10 kPa for manipulating objects; and more than 10 kPa for blood pressure and footstep pressure.

Wearable pressure sensors extend their range, Isabelle Dumé, Physics World

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Vortex Beams...


This calculated diffraction image shows how forked diffraction gratings shape the atoms' wave function into a vortex. (Courtesy: Science/AAAS)

Topics: Bose-Einstein Condensate, Nanotechnology, Particle Physics, Quantum Optics

A wave-like property previously only seen in beams of light and electrons has been observed for the first time in atoms and molecules. By passing beams of helium and neon through a grid of specially shaped nanoslits, researchers led by Edvardas Narevicius of Israel’s Weizmann Institute of Science succeeded in giving the beams a non-zero orbital angular momentum (OAM). The resulting structures are known vortex beams, and they could be used for fundamental physics studies such as probing the internal structure of protons.

Many natural systems contain vortices – think of tornadoes and ocean eddies on Earth, the red spot on Jupiter, and gravitational vortices around black holes. On all scales, such vortices are characterized by the circulation of a flux around an axis. In the quantum world, these swirling structures are found in ensembles of particles that can be described by a wavefunction, including superfluids and Bose-Einstein condensates.

Atoms and molecules make vortex beams, Isabelle Dumé, Physics World

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Big Bet on Small...


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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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...


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...


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...


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...


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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Stop-Motion Efficiency...


A team of researchers created a new method to capture ultrafast atomic motions inside the tiny switches that control the flow of current in electronic circuits. Pictured here are Aditya Sood (left) and Aaron Lindenberg (right). Courtesy: Greg Stewart/SLAC National Accelerator Laboratory

Topics: Applied Physics, Electrical Engineering, Nanotechnology, Semiconductor Technology

A new ultrafast imaging technique that captures the motion of atoms in nanoscale electronic devices has revealed the existence of a short-lived electronic state that could make it possible to develop faster and more energy-efficient computers. The imaging technique, which involves switching the devices on and off while taking snapshots of them with an electron diffraction camera, could also help researchers probe the limits of electronic switching.

“In general, we know very little about the intermediate phases materials pass through during electronic switching operations,” explains Aditya Sood, a postdoctoral researcher at the US Department of Energy’s SLAC National Accelerator Laboratory and lead author of a paper in Science about the new method. “Our technique allows for a new way to visualize this process and therefore address what is arguably one of the most important questions at the heart of computing – that is, what are the fundamental limits of electronic switches in terms of speed and energy consumption?”

Ultrafast electron diffraction camera

Sood and colleagues at SLACStanford UniversityHewlett Packard LabsPennsylvania State University, and Purdue University chose to study devices made from vanadium dioxide (VO2) because the material is known to transition between insulating and electrically conducting states near room temperature. It thus shows promise as a switch, but the exact pathway underlying electric field-induced switching in VOhas long been a mystery, Sood tells Physics World.

To take snapshots of VO2’s atomic structure, the team used periodic voltage pulses to switch an electronic device made from the material on and off. The researchers synchronized the timing of these voltage pulses with the high-energy electron pulses produced by SLAC’s ultrafast electron diffraction (UED) camera. “Each time a voltage pulse excited the sample, it was followed by an electron pulse with a delay that we could tune,” Sood explains. “By repeating this process many times and changing the delay each time, we created a stop-motion movie of the atoms moving in response to the voltage pulse.”

This is the first time that anyone has used UED, which detects tiny atomic movements in a material by scattering a high-energy beam of electrons off a sample, to observe an electronic device during operation. “We started thinking about this subject three years ago and soon realized that existing techniques were simply not fast enough,” says Aaron Lindenberg, a professor of materials science and engineering at Stanford and the study’s senior author. “So we decided to construct our own.”

‘Stop-motion movie of atoms’ reveals short-lived state in nanoscale switch, Isabelle Dumé, Physics World

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Gold Anniversary...


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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Nano Laser...


In their experiments, the researchers used ultrathin crystals consisting of a single layer of atoms. These sheets were sandwiched between two layers of mirror-like materials. The whole structure acts as a cage for light and is called a microcavity.

Topics: Applied Physics, Bose-Einstein Condensate, Lasers, Nanotechnology, Optics

Physicists have taken a step towards realizing the smallest-ever solid-state laser by generating an exotic quantum state known as a Bose-Einstein condensate (BEC) in quasiparticles consisting of both matter and light. Although the effect has so far only been observed at ultracold temperatures in atomically thin crystals of molybdenum diselenide (MoSe2), it might also be produced at room temperature in other materials.

When particles are cooled down to temperatures just above absolute zero, they form a BEC – a state of matter in which all the particles occupy the same quantum state and act in unison, like a superfluid. A BEC made up of tens of thousands of particles behaves as if it were just one giant quantum particle.

An international team of researchers led by Carlos Anton-Solanas and Christian Schneider from the University of Oldenburg, GermanySven Höfling of the University of Würzburg, GermanySefaattin Tongay at Arizona State University, US; and Alexey Kavokin of Westlake University in China, has now generated a BEC from quasiparticles known as exciton-polaritons in atomically thin crystals. These quasiparticles form when excited electrons in solids couple strongly with photons.

“Devices that can control these novel light-matter states hold the promise of a technological leap in comparison with current electronic circuits,” explains Anton-Solanas, who is in the quantum materials group at Oldenburg’s Institute of Physics. “Such optoelectronic circuits, which operate using light instead of electric current, could be better and faster at processing information than today’s processors.”

Anton-Solanas, Schneider, and colleagues studied crystals of MoSe2 that were just a single atomic layer thick. MoSe2belongs to a family of materials known as transition-metal dichalcogenides (TMDCs). In their bulk form, these materials act as indirect band-gap semiconductors. Still, when scaled down to a monolayer thickness, they behave as direct band-gap semiconductors, capable of efficiently absorbing and emitting light.

In their experiments, the researchers assembled sheets of MoSe2 less than a nanometer thick and sandwiched them between alternating layers of silicon dioxide and titanium dioxide (SiO2/TiO2), which reflect light like a mirror. The resulting structure is known as a microcavity and acts as a cage for light. “It’s like trapping the light-emitting material in a room filled with mirrors and mirrors only,” Tongay tells Physics World. “The light gets reflected these mirrors and is absorbed by the material back and forth.”

Exotic quantum state could make smallest-ever laser, Isabelle Dumé, Physics World

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Graphene Beam Splitter...


Splitting up: schematic of the electron beam splitter with the n side on the right and the p side on the left. (Courtesy: M Jo et al/Phys. Rev. Lett.)

Topics: Graphene, Interferometry, Nanotechnology, Quantum Computer

A graphene-based “beam splitter” for electronic currents has been built by researchers in France, South Korea, and Japan. Created by Preden Roulleau at the University of Paris and colleagues, the tunable device’s operation is directly comparable to that of an optical interferometer. The technology could soon enable allow electron interferometry to be used in nanotechnology and quantum computing.

An optical interferometer splits a beam of light in two, sending each beam along a different path before recombining the beams at a detector. The measured interference of the beams at the detector can be used to detect tiny differences in the lengths of the two paths. Recently, physicists have become interested in doing a similar thing with currents of electrons in solid-state devices, taking advantage of the fact that electrons behave like waves in the quantum world.

Graphene is a sheet of carbon just one atom thick and is widely considered to be the best material for realizing such “electron quantum optics”. Indeed, researchers have already used the material to make simple electron interferometers. Now, Roulleau’s team has created a fully adjustable electron beam splitter that could be used to build more sophisticated devices. It exploits the quantum Hall effect, whereby the application of a strong magnetic field perpendicular to a sheet of graphene will cause an electron current to flow around the edge of the sheet.

Graphene beam splitter gives electron quantum optics a boost, Sam Jarman, Physics World

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