GNRs

Van der Waals encapsulation of 2D materials in hBN stacks could be a promising way to create ultrahigh-performance electronic devices. However, current approaches for achieving van der Waals encapsulation, which involve artificial layer stacking using mechanical transfer techniques, are difficult to control, prone to contamination and unscalable. 

Researchers at Shanghai Jiao Tong University, Wuhan University, Ulsan National Institute of Science and Technology, National Institute for Materials Science and Tel Aviv University recently reported the transfer-free direct growth of high-quality graphene nanoribbons (GNRs) in hexagonal boron nitride (hBN) stacks. The as-grown embedded GNRs exhibited highly desirable features being ultralong (up to 0.25 mm), ultranarrow (<5 nm) and homochiral with zigzag edges. 

A team of scientists, led by David Serrate, CSIC scientist at the Instituto de Nanociencia y Materiales de Aragón, INMA (a joint institute of the CSIC and the University of Zaragoza), has imaged for the first time the magnetic behavior of a graphene nanostructure. The team has not only revealed the magnetic state of narrow graphene ribbons (~2 nm), but has also shown the method they developed to magnetically characterize any planar nanographene.

Starting with a specifically designed organic precursor, the researchers synthesized the ribbons directly onto a magnetic surface, obtaining atomically precise edges that contain an alternating sequence of zig-zag graphene segments. This geometry strongly confines the graphene electron cloud around the edge, which causes the instability responsible for the intrinsic magnetism of the graphene nanostructure –a remarkable fact taking into account that the ribbon is formed just by non-magnetic carbon and hydrogen atoms.

Researchers from the University of Illinois at Urbana─Champaign and the University of Nebraska─Lincoln have developed a method for "wiring up" graphene nanoribbons (GNRs). Using a direct-write scanning tunneling microscopy (STM) based process, the nanometer-scale metal contacts were fabricated on individual GNRs and could control the electronic character of the GNRs. 

The team says that this is the first demonstration of making metal contacts to specific GNRs with certainty and that those contacts induce device functionality needed for transistor function.

Researchers from Empa and ETH Zurich, in collaboration with partners from Peking University, the University of Warwick and the Max Planck Institute for Polymer Research, have succeeded in attaching electrodes to individual atomically precise graphene nanoribbons, paving the way for precise characterization of the ribbons and their possible use in quantum technology.

Researchers attach carbon nanotube electrodes to individual atomically precise nanoribbons. (Image credit: Empa, from: Nanowerk)

In the coming decades, quantum technology is expected to provide various technological breakthroughs: smaller and more precise sensors, highly secure communication networks, and powerful computers that can help develop new drugs and materials, control financial markets, and predict the weather much faster than current computing technology ever could. To achieve this, there is a need so-called quantum materials: substances that exhibit pronounced quantum physical effects. One such material is graphene. Giving it a ribbon-like shape,  for example, gives rise to a range of controllable quantum effects.

Researchers from Columbia University, Technical University of Denmark, Aarhus University, Université Paris-Saclay and Japan's National Institute for Materials Science have designed a simple fabrication technique that could help study the fundamental properties of twisted layers of graphene and other 2D materials in a more systematic and reproducible way. The team used long “ribbons” of graphene, rather than square flakes, to create devices that offer a new level of predictability and control over both twist angle and strain.

Graphene devices have typically been assembled from atom-thin flakes of graphene that are just a few square millimeters. The resulting twist angle between the sheets is fixed in place, and the flakes can be tricky to layer together smoothly. “Imagine graphene as pieces of saran wrap—when you put two pieces together you get random little wrinkles and bubbles,” says Columbia postdoc Bjarke Jessen, a co-author on the paper. Those bubbles and wrinkles are akin to changes in the twist angle between the sheets and the physical strain that develops in between and can cause the material to buckle, bend, and pinch randomly. All these variations can yield new behaviors, but they have been difficult to control within and between devices.

Researchers from POLYMAT at the University of the Basque Country UPV/EHU, Max Planck Institute for Polymer Research and the University of Aveiro have reported an accelerated iterative approach enabling the synthesis of a series of length-controlled, ultralong atomically precise graphene nanoribbons (GNRs). The longest GNR displays a 920-atoms core with a 35.8-nm long (147 linearly fused rings) backbone that has been obtained in just three synthetic steps from building blocks of ∼2 nm in length. 

A Lego-like synthesis previously produced record-breaking nanoribbons of 30, then 53 fused rings. Now, a similar ‘accelerated’ modular methodology made a molecular nanoribbon that is triple the longest ever made – in just three simple steps. The resulting graphene nanoribbon is almost 36nm long, with its 147 linearly linked rings and a conjugated core of 920 atoms. The first experiments, although preliminary, envision applications in electronics and optoelectronics, thanks to fluorescence features that reportedly outperform state-of-the-art quantum dots.

Scientists from CiQUS, ICN2, University of Cantabria, Donostia International Physics Center (DIPC), and Technical University of Denmark (DTU) have joined forces to develop a versatile method for building brick by brick carbon nanocircuits with tunable properties. The team sees this as a significant breakthrough in the precise engineering of 2D materials. The proposed fabrication technique opens exciting new possibilities for materials science, and, in particular, for application in advanced electronics and future solutions for sustainable energy.

The team synthesized a new nanoporous graphene structure by connecting ultra-narrow graphene strips, known as “nanoribbons”, by means of flexible “bridges” made of phenylene moieties (which are portions of larger molecules). By modifying in a continuous way the architecture and angle of these bridges, the scientists can control the quantum connectivity between the nanoribbon channels and, ultimately, fine-tune the electronic properties of the graphene nanoarchitecture. The tunability could also be controlled by external stimuli, such as strain or electric fields, providing opportunities for different applications.

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory (ANL) have created a novel testbed to explore the behavior of electrons in a special class of materials called topological insulators, which could see applications in quantum computing.

Left, atomic structure of actual graphene nanoribbon. Middle, CO molecules mapped onto a copper surface to produce graphene structure. Right, scanning tunneling microscope image of the resulting artificial graphene nanoribbon. (Image by Argonne National Laboratory.)
 

in previous work, graphene nanoribbons — small strips of graphene — were shown to exhibit promising topological states. Inspired by this, the Argonne team constructed an artificial graphene testbed with atomic precision in hopes to further explore those topological effects.

An international team, including scientists from DIPC and CFM (CSIC-UPV/EHU) in San Sebastian, CIQUS - Universidade de Santiago de Compostela, Czech Academy of Sciences (Prague), Palacký University (Olomouc), Ikerbasque (Basque Country) and CINN (CSIC-UNIOVI-PA) in El Entrego, have demonstrated two chemical protection/deprotection strategies for the on-surface synthesis of graphene nanostructures.

On-surface synthesis is a synthetic approach that differs from standard wet-chemistry approaches. Instead of the three-dimensional space of solvents in the latter, the environment of the reactants in this approach are well-defined two-dimensional solid surfaces that are typically held under vacuum conditions. These differences have allowed the successful synthesis of a great variety of molecular structures that could not be obtained by conventional means. Among the structures that are raising particular interest are carbon-nanostructures with zigzag-shaped edges, which endow the materials with exciting electronic and even magnetic properties of potential interest for a great variety of applications that include quantum technologies.

A research team, led by Professor Yu Seung-ho of the Department of Chemical and Biological Engineering at Korea University, Seoul National University's Professor Yuanzhe Piao and Sogang University's Professor Back Seo-in, has fabricate nitrogen and sulfur co-doped graphene nanoribbons with stepped edges, elucidating the migration barrier and enhancing the electrochemical performance of potassium batteries.

Potassium has shown promise for large-capacity non-lithium battery cells, because it is affordable, abundant, and has a low redox potential (-2.93V) close to that of lithium ion (-3.04V). Carbon-based nanomaterials, which are chemically stable and lightweight, are popular anode materials used in potassium batteries. However, the high energy barrier between electrochemical intercalation and deintercalation of potassium ions induces adsorption/desorption reactions, resulting in the storage of potassium ions only on the surface of carbon and lowering the energy density during battery assembly. As such, the smooth intercalation/deintercalation of potassium is extremely important in obtaining high-performance potassium batteries.