GNRs - Page 2

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.

Researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley have developed a method to stabilize the edges of graphene nanoribbons and directly measure their unique magnetic properties.

The team, co-led by Felix Fischer and Steven Louie from Berkeley Lab’s Materials Sciences Division, found that by substituting some of the carbon atoms along the ribbon’s zigzag edges with nitrogen atoms, they could discretely tune the local electronic structure without disrupting the magnetic properties. This subtle structural change further enabled the development of a scanning probe microscopy technique for measuring the material’s local magnetism at the atomic scale.

Researchers at Shanghai Jiao Tong University, Stanford University, and other US and China institutes have designed a strategy for creating graphene nanoribbons (GNRs) with smooth edges that are below 10 nm in width. This new method is based on the use of squashed carbon nanotubes (CNTs).

The team explained that the idea behind this new work is that if carbon nanotubes (CNTs) can be squashed into GNRs, it would be possible to produce narrow (sub-5-nm wide) GNRs from CNTs that have small diameters. The team said that the GNRs prepared using this method would be much narrower than those obtained by previous methods.

Two recent studies by a collaborative team of scientists from two NCCR MARVEL labs have identified a new type of defect as the most common source of disorder in on-surface synthesized graphene nanoribbons (GNRs).

Combining scanning probe microscopy with first-principles calculations allowed the researchers to identify the atomic structure of these so-called "bite" defects and to investigate their effect on quantum electronic transport in two different types of graphene nanoribbon. They also established guidelines for minimizing the detrimental impact of these defects on electronic transport and proposed defective zigzag-edged nanoribbons as suitable platforms for certain applications in spintronics.

An international research team, led by the University of Cologne, has succeeded in connecting several atomically precise graphene nanoribbons to form complex structures. The scientists have synthesized and spectroscopically characterized nanoribbon heterojunctions, and were able to integrate the heterojunctions into an electronic component. In this way, they have created a novel sensor that is highly sensitive to atoms and molecules.

"The graphene nanoribbon heterojunctions used to make the sensor are each seven and fourteen carbon atoms wide and about 50 nanometres long. What makes them special is that their edges are free of defects. This is why they are called "atomically precise" nanoribbons," explained Dr. Boris Senkovskiy from the Institute for Experimental Physics. The researchers connected several of these nanoribbon heterojunctions at their short ends, thus creating more complex heterostructures that act as tunneling barriers.