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Researchers develop graphene-nanowire 'sandwich' thermal interface for better electronics

Graphene Info - Scientific and Educational Websites

Researchers from Carnegie Mellon University and MIT have demonstrated a 3D graphene-nanowire “sandwich” thermal interface that enables an ultralow thermal resistance of ∼0.24 mm2·K/W that is about 1 order of magnitude smaller than those of solder...

Feb 16, 2023

MIT Physicists Discover Way To Switch Superconductivity On and Off in “Magic-Angle” Graphene ",plain_text=" MIT physicists have found a new way to switch superconductivity on and off in magic-angle graphene. This figure shows a device with two graphene layers in the middle (in dark gray and in inset). The graphene layers are sandwiched in between boron nitride layers (in blue and purple). The angle and alignment of each layer enables the researchers to turn superconductivity on and off in graphene with a short electric pulse. Credit: Courtesy of the researchers. Edited by MIT NewsApplying a quick electric pulse completely flips the material’s electronic properties, opening a route to ultrafast, brain-inspired, superconducting electronics.MIT physicists have revealed a new and exotic property in “magic-angle” graphene: superconductivity that can be turned on and off with an electric pulse, much like a light switch. To accomplish this, they used some meticulous twisting and stacking of layers of graphene and boron nitride.The discovery could lead to ultrafast, energy-efficient superconducting transistors for neuromorphic devices — electronics designed to operate in a way similar to the rapid on/off firing of neurons in the human brain.Magic-angle graphene refers to a very particular stacking of graphene — an atom-thin material made from carbon atoms that are linked in a hexagonal pattern resembling chicken wire. When one sheet of graphene is stacked atop a second sheet at a precise “magic” angle, the twisted structure creates a slightly offset “moiré” pattern, or superlattice, that is able to support a host of surprising electronic behaviors.In 2018, Pablo Jarillo-Herrero and his group at MIT were the first to demonstrate magic-angle twisted bilayer graphene. They showed that the new bilayer structure could behave as an insulator, much like wood, when they applied a certain continuous electric field. When they upped the field, the insulator suddenly morphed into a superconductor, allowing electrons to flow, friction-free.That discovery was a watershed in the field of “twistronics,” which explores how certain electronic properties emerge from the twisting and layering of two-dimensional materials. Researchers including Jarillo-Herrero have continued to reveal surprising properties in magic-angle graphene, including various ways to switch the material between different electronic states. So far, such “switches” have acted more like dimmers, in that researchers must continuously apply an electric or magnetic field to turn on superconductivity, and keep it on.Now Jarillo-Herrero and his team have shown that superconductivity in magic-angle graphene can be switched on, and kept on, with just a short pulse rather than a continuous electric field. The key, they found, was a combination of twisting and stacking.In a paper published on January 30 in the journal Nature Nanotechnology, the team reports that, by stacking magic-angle graphene between two offset layers of boron nitride — a two-dimensional insulating material — the unique alignment of the sandwich structure enabled the researchers to turn graphene’s superconductivity on and off with a short electric pulse.“For the vast majority of materials, if you remove the electric field, zzzzip, the electric state is gone,” says Jarillo-Herrero, who is the Cecil and Ida Green Professor of Physics at MIT. “This is the first time that a superconducting material has been made that can be electrically switched on and off, abruptly. This could pave the way for a new generation of twisted, graphene-based superconducting electronics.”His MIT co-authors are lead author Dahlia Klein PhD ’21, graduate student Li-Qiao Xia, and former postdoc David MacNeill, along with Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan.Flipping the switchIn 2019, a team at Stanford University discovered that magic-angle graphene could be coerced into a ferromagnetic state. Ferromagnets are materials that retain their magnetic properties, even in the absence of an externally applied magnetic field.The researchers found that magic-angle graphene could exhibit ferromagnetic properties in a way that could be tuned on and off. This happened when the graphene sheets were layered between two sheets of boron nitride such that the crystal structure of the graphene was aligned to one of the boron nitride layers. The arrangement resembled a cheese sandwich in which the top slice of bread and the cheese orientations are aligned, but the bottom slice of bread is rotated at a random angle with respect to the top slice. The result intrigued the MIT group.“We were trying to get a stronger magnet by aligning both slices,” Jarillo-Herrero says. “Instead, we found something completely different.”In their current study, the team fabricated a sandwich of carefully angled and stacked materials. The “cheese” of the sandwich consisted of magic-angle graphene — two graphene sheets, the top rotated slightly at the “magic” angle of 1.1 degrees with respect to the bottom sheet. Above this structure, they placed a layer of boron nitride, exactly aligned with the top graphene sheet. Finally, they placed a second layer of boron nitride below the entire structure and offset it by 30 degrees with respect to the top layer of boron nitride.The team then measured the electrical resistance of the graphene layers as they applied a gate voltage. They found, as others have, that the twisted bilayer graphene switched electronic states, changing between insulating, conducting, and superconducting states at certain known voltages.What the group did not expect was that each electronic state persisted rather than immediately disappearing once the voltage was removed — a property known as bistability. They found that, at a particular voltage, the graphene layers turned into a superconductor, and remained superconducting, even as the researchers removed this voltage.This bistable effect suggests that superconductivity can be turned on and off with short electric pulses rather than a continuous electric field, similar to flicking a light switch. It isn’t clear what enables this switchable superconductivity, though the researchers suspect it has something to do with the special alignment of the twisted graphene to both boron nitride layers, which enables a ferroelectric-like response of the system. (Ferroelectric materials display bistability in their electric properties.)“By paying attention to the stacking, you could add another tuning knob to the growing complexity of magic-angle, superconducting devices,” Klein says.For now, the team sees the new superconducting switch as another tool researchers can consider as they develop materials for faster, smaller, more energy-efficient electronics.“People are trying to build electronic devices that do calculations in a way that’s inspired by the brain,” Jarillo-Herrero says. “In the brain, we have neurons that, beyond a certain threshold, they fire. Similarly, we now have found a way for magic-angle graphene to switch superconductivity abruptly, beyond a certain threshold. This is a key property in realizing neuromorphic computing.”Reference: “Electrical switching of a bistable moiré superconductor” by Dahlia R. Klein, Li-Qiao Xia, David MacNeill, Kenji Watanabe, Takashi Taniguchi and Pablo Jarillo-Herrero, 30 January 2023, Nature Nanotechnology.DOI: 10.1038/s41565-022-01314-xThis research was supported in part by the U.S. Air Force Office of Scientific Research, the U.S. Army Research Office, and the Gordon and Betty Moore Foundation.

SciTechDaily - Scientific News Websites

Applying a quick electric pulse completely flips the material’s electronic properties, opening a route to ultrafast, brain-inspired, superconducting electronics. MIT physicists have revealed a new...

Feb 15, 2023

Stretchy Devices Spin Electricity from Body Heat ",plain_text=" Phones, appliances, and humans all generate heat that usually escapes into the environment as waste energy. Thermoelectric generators, which convert temperature differences into electricity, are a way to capture that wasted heat for power.Researchers have now made a thermoelectric generator (TEG) that is soft and stretchy and that biodegrades completely when exposed to the environment. Unlike conventional rigid thermoelectric devices, this one, reported in the journal Science Advances, could be easily integrated into fabrics, allowing for body-heat-powered wearable sensors or temperature-detecting disposable face masks.Researchers used a pattern inspired by the stripes of a zebra to create hot and cold regions next to each other to yield temperature differences great enough to produce electricity.Korea UniversityIn TEGs, the flow of charge between hot and cold regions creates a voltage difference, leading to electricity. Thermoelectric generators are made in various ways using different materials. They typically consist of one side that stays cold, while the other is in touch with the heat-generating component, be it an electric motor or the body. Because they are solid-state devices with no moving parts, TEGs are low maintenance and long lasting. So far, they have relied on expensive or toxic semiconductor materials such as bismuth telluride and lead telluride, and mainly found use in niche applications like spacecraft and satellites. Researchers have been pushing to bring down the cost and improve the efficiency of TEGs. Recently, a team devised a way to create thermoelectricity by coupling the sun’s warmth with the coldness of space by putting a material that radiates heat into outer space on top of one that absorbs warmth from the surrounding air.However, the materials and designs used to make TEGs so far “can result in a complex and inefficient TEG that is bulky and difficult to fit in with other components,” says Young Min Song, a professor of electrical engineering and computer science at Gwangju Institute of Science and Technology, in Korea. Song and colleagues decided to ditch the conventional top-down stacked approach. Instead, using a pattern inspired by the stripes of a zebra, they create hot and cold regions next to each other on a surface to create an in-plane temperature difference large enough to produce electricity. They start with a white sheet made of a stretchable and biodegradable polymer called caprolactone that is commonly used for surgical-implant and drug-delivery devices. The material reflects sunlight and is a strong emitter of infrared heat. The researchers coat the sheet with regularly spaced strips of a black polymer that absorbs sunlight and reflects infrared radiation. The alternating black and white strips create hot and cold regions on the stretchable material.The researchers put the striped sheet on top of what they call a silicon nanomembrane. This nanoscale membrane is an array of several n- and p-doped silicon wires, which the researchers grow in a serpentine pattern on a silicon wafer and then transfer to a sheet made of the estercaprolactone. The wires’ wavy structure helps them stretch without breaking.When the researchers placed this device outdoors for testing, the white parts became up to 8 °C cooler than the ambient temperature, while the temperature of the black parts rose up to 14 °C above ambient air, creating a maximum temperature difference of 22 °C. The silicon wires converted this temperature difference into electrical energy, generating a maximum power of about 6 microwatts per square meter (µW/m²). That is enough to operate low-power sensors, Song says, but he admits it is lower than ideal for commercial applications. Using more thermoelectrically efficient materials like bismuth telluride would boost the power output, but the advantage here is that the device is low cost, stretchable, and completely biodegradable. “Even when the sample was stretched by about 1.3 times, the generation performance was maintained,” Song says.In the lab, the device dissolved completely into harmless by-products in 35 days when placed in a saline solution. That degradation would take longer in natural environments, Song says.

IEEE Spectrum - Scientific and Educational Websites

Phones, appliances, and humans all generate heat that usually escapes into the environment as waste energy. Thermoelectric generators, which convert temperature differences into electricity, are a way to capture that wasted heat for power.Researc...

Feb 15, 2023

Engineers discover a new way to control atomic nuclei as 'qubits': Using lasers, researchers can directly control a property of nuclei called spin, that can encode quantum information.

ScienceDaily - General News Websites

Researchers propose a new approach to making qubits, the basic units in quantum computing, and controlling them to read and write data. The method is based on measuring and controlling the spins of atomic nuclei, using beams of light from two lase...

Feb 15, 2023

Proposed quantum device may succinctly realize emergent particles such as the Fibonacci anyon

ScienceDaily - General News Websites

Tenacity has taken a roadblock and turned it into a possible route to the development of quantum computing.

Feb 15, 2023

Food coloring and anti-caking nanoparticles may affect the human gut

Phys.org - Scientific News Websites

Metal oxide nanoparticles—ubiquitous in nature, and commonly used as food coloring and anti-caking agents in the commercial ingredients industry—may damage and disturb parts of the human intestine, according to new research conducted by Cornell an...

Feb 15, 2023

New approach for Majorana research in short nanowires

Phys.org - Scientific News Websites

Researchers and engineers from QuTech and Eindhoven University of Technology have created Majorana particles and measured their properties with great control.

Feb 15, 2023

Nanotechnology Now - Press Release: Scientists boost quantum signals while reducing noise: �Squeezing� noise over a broad frequency bandwidth in a quantum system could lead to faster and more accurate quantum measurements

Nanotechnology Now - Nanotechnology Websites

A certain amount of noise is inherent in any quantum system. For instance, when researchers want to read information from a quantum computer, which harnesses quantum mechanical phenomena to solve cert...

Feb 15, 2023

Nanotechnology Now - Press Release: Fiber sensing scientists invent 3D printed fiber microprobe for measuring in vivo biomechanical properties of tissue and even single cell

Nanotechnology Now - Nanotechnology Websites

Fiber sensing scientists at Shenzhen University have developed a compact fiber optical nanomechanical probe (FONP) for measuring in vivo biomechanical properties of tissue and even single cell.

Feb 15, 2023

Nanotechnology Now - Press Release: Graphene Flagship start-up Bedimensional closes a second �10 million investment round

Nanotechnology Now - Nanotechnology Websites

Spin-off of the Graphene Flagship Partner Italian Institute of Technology (IIT), BeDimensional S.p.A. has announced its second 10 million Series B investment round, which was led by CDP Venture Capit...

Feb 15, 2023