Technical / Research

Researchers from the University of Göttingen, Japan's National Institute for Materials Science and Massachusetts Institute of Technology (MIT) have demonstrated experimentally that electrons in naturally occurring double-layer graphene move like particles without any mass, in the same way that light travels. Furthermore, they have shown that the current can be "switched" on and off, which has potential for developing tiny, energy-efficient transistors. 

Among its many unusual properties, graphene is known for its extraordinarily high electrical conductivity due to the high and constant velocity of electrons travelling through this material. This unique feature has made scientists try to use graphene for faster and more energy-efficient transistors. The challenge has been that to make a transistor, the material needs to be controlled to have a highly insulating state in addition to its highly conductive state. In graphene, however, such a "switch" in the speed of the carrier cannot be easily achieved. In fact, graphene usually has no insulating state, which has limited graphene's potential a transistor.

Researchers from the National University of Singapore (NUS), and Czech Academy of Sciences recently developed a new design concept for creating next-generation carbon-based quantum materials, in the form of a tiny magnetic nanographene with a unique butterfly-shape hosting highly correlated spins. This new design has the potential to accelerate the advancement of quantum materials which are pivotal for the development of quantum computing technologies.

A visual impression of the magnetic “butterfly” hosting four entangled spins on “wings” (left) and its corresponding atomic-scale image obtained using scanning probe microscopy (right). Image credit: NUS

Magnetic nanographene, a tiny structure made of graphene molecules, exhibits remarkable magnetic properties due to the behavior of specific electrons in the carbon atoms’ π-orbitals. By precisely designing the arrangement of these carbon atoms at the nanoscale, control over the behavior of these unique electrons can be achieved. This renders nanographene highly promising for creating extremely small magnets and for fabricating fundamental building blocks needed for quantum computers, called quantum bits or qubits.

Researchers from Princeton University, University of California, Lawrence Berkeley National Laboratory and Japan's National Institute for Materials Science have used a special kind of microscope and two pieces of extremely defect-free graphene to capture the clearest and most direct images of a “Wigner crystal”, a structure made entirely of electrons.

Imaging a “Wigner crystal” is extremely hard. At room temperature, electrons can flow together in electric currents because their kinetic energy overcomes the force that makes particles with the same electric charge repel each other. At very low temperatures, however, repulsive electric forces win out, and the electrons end up arranging themselves into a uniform grid, or a crystal. Physicist Eugene Wigner predicted this phenomenon in 1934, but researchers only recently started to understand how to create Wigner crystals in the lab. 

Researchers from  Purdue University, University of California, Lawrence Berkeley National Laboratory and Japan's National Institute for Materials Science have managed to electrically manipulate a ‘chiral interface state’ in twisted monolayer-bilayer graphene, with potential for energy-efficient microelectronics and quantum computing.

The international research team, led by Lawrence Berkeley National Laboratory (Berkeley Lab), has taken the first atomic-resolution images and demonstrated electrical control of a chiral interface state – an exotic quantum phenomenon that could help researchers advance quantum computing and energy-efficient electronics.

A team from the National Hospital for Paraplegics (SESCAM), in collaboration with the Materials Science Institute of Madrid (ICMM-CSIC), has shown how new cell culture devices based on graphene oxide maintain the anti-inflammatory function of myeloid suppressor cells (MDSCs) once isolated from the donor's body. This function could be crucial for advancing cellular therapy beneficial to people with multiple sclerosis. 

"To exert their inflammation-controlling function in diseases such as multiple sclerosis, myeloid suppressor cells must maintain a very immature state. However, when extracted from the bone marrow and cultured in the laboratory, they begin to mature, losing their immunosuppressive activity, rendering them unsuitable for potential cellular therapy for patients with this type of neurodegenerative disease," explains Diego Clemente, a researcher at the National Hospital for Paraplegics and one of the lead authors of the study.

Researchers from Tohoku University, Tianjin University of Technology, Pohang University of Science and Technology and Johns Hopkins University recently designed a nanocellular graphene (NCG) film through the self-organization of carbon atoms using liquid metal dealloying and employing a defect-free amorphous precursor.

The flexible freestanding nanocellular graphene film. Image credit: Advanced Materials
 

Nanocellular graphene is a specialized form of graphene that achieves a large specific surface area by stacking multiple layers of graphene and controlling its internal structure with a nanoscale cellular morphology. NCG is attractive thanks to its potential to improve the performance of electronic devices, energy devices and sensors. However, its development has been hindered by defects that occur during the manufacturing process. Cracks often appear when forming NCG, and scientists are looking for new processing technologies that can fabricate homogeneous, crack-free and seamless NCGs at appropriate scales.

It is a known fact that animals require the integration of cues collected from multiple sensory organs to enhance the overall perceptual experience and thereby facilitate better decision-making in most aspects of life. However, despite the importance of multisensory integration in animals, the field of artificial intelligence (AI) and neuromorphic computing has primarily focused on processing unisensory information. This lack of emphasis on multisensory integration can be attributed to the absence of a miniaturized hardware platform capable of co-locating multiple sensing modalities and enabling in-sensor and near-sensor processing. 

a) A simplified abstraction of visual and chemical stimuli from male butterflies and visuo-chemical integration pathway in female butterflies. b) Butterfly-inspired neuromorphic hardware comprising of monolayer MoS₂ memtransistor-based visual afferent neuron, graphene-based chemoreceptor neuron, and MoS₂ memtransistor-based neuro-mimetic mating circuits. Image credit: Advanced Materials

In their recent study, researchers at Penn State University addressed this limitation by utilizing the chemo-sensing properties of graphene and the photo-sensing capability of monolayer molybdenum disulfide (MoS₂) to create a multisensory platform for visuochemical integration. 

Researchers at AIST, Osaka University, Tokyo Polytechnic University, Kyushu University, and National Tsing Hua University, have developed a technique to insert alkali metals (AMs) into the interlayers of graphene. They them used low-voltage scanning transmission electron microscopy (LV-STEM) to visualize the atomic structure of the intercalated AMs (potassium, rubidium, and cesium) in the bilayer graphene (BLG). The team's findings revealed that the intercalated AMs adopt bilayer structures with hcp stacking, and specifically a C₆M₂C₆ composition. 

The performance of rechargeable batteries is a key factor influencing the driving distance of electric vehicles and the usage time of smartphones. Improving the performance of these electronic devices is possible if rechargeable batteries can accumulate greater electrical capacities. Graphite, the electrode material used in batteries, is composed of multilayers of graphene, with alkali metals placed between the layers to facilitate the flow of electrons during charging and discharging. Achieving a high density of alkali metals storage between graphene layers could increase the electric capacity.

Researchers from Pohang University of Science and Technology (POSTECH), Korea Institute of Industrial Technology and Konkuk University have fabricated highly deformable graphene-based micro supercapacitors (MSCs) using liquid metal current collectors on an elastic polymer substrate.

a Illustration of an integrated system comprising soft-electronics and deformable energy storage component. b The fabrication process of EGaIn-based MSC. c UV-vis spectra of SEBS, EGaIn, and graphene. FE-SEM images of laser ablated d Graphene/EGaIn and e EGaIn (Scale bar = 200 µm). Photographs of f institute logos, g deformed logos, and h an LED connected to the MSC circuit (Scale bar = 1 cm). (Image from npj Flexible Electronics)

The team used eutectic gallium-indium (EGaIn), a liquid metal alloy, as the current collector since a deformable current collector is needed in order to create a deformable MSC. Commonly used current collectors made of brittle materials like gold (Au) are not suitable in this case, so the team turned to 'liquid metal' that inherently possesses the properties of a liquid and metallic conductivity.

Researchers from China's Zhengzhou University, Ningbo University and Jilin University have used nanodiamonds as precursors to make centimeter-sized diamond/graphene composites under moderate pressure and temperature conditions (12 GPa and 1,300 to 1,500 °C). The composite is reportedly able to conduct electricity while maintaining its ultra-hardness.

This work could pave the way for realizing large-sized diamond-based materials with ultrahigh electrical conductivity and superior mechanical properties under moderate synthesis conditions, which will facilitate their large-scale applications in a variety of fields.