GNRs

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.

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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.

University of WisconsinMadison researchers have fabricated graphene into the smallest ribbon structures to date, using a method that is said to make scaling-up simple. In tests with these tiny ribbons, the scientists discovered they were closing in on the properties they needed to move graphene toward usefulness in telecommunications equipment.

Image credit: University of Wisconsin−Madison

Previous research suggested that to be viable for telecommunication technologies, graphene would need to be structured prohibitively small over large areas, (which is) a fabrication nightmare, says Joel Siegel, a UWMadison graduate student in physics professor Victor Brar’s group and co-lead author of the study. In our study, we created a scalable fabrication technique to make the smallest graphene ribbon structures yet and found that with modest further reductions in ribbon width, we can start getting to telecommunications range.

Russian researchers have proposed a new method for synthesizing high-quality graphene nanoribbons. The team's approach to chemical vapor deposition offers a higher yield at a lower cost, compared with the currently used nanoribbon self-assembly on noble metal substrates.

Two nanoribbon edge configurations. The pink network of carbon atoms is a ribbon with zigzag (Z) edges, and the yellow one has so-called armchair (A) edges. Image credit MIPT

Unlike silicon, graphene does not have the ability to switch between a conductive and a nonconductive state. This defining characteristic of semiconductors is crucial for creating transistors, which are the basis for all of electronics. However, once you cut graphene into narrow ribbons, they gain semiconducting properties, provided that the edges have the right geometry and there are no structural defects. Such nanoribbons have already been used in experimental transistors with reasonably good characteristics, and the material’s elasticity means the devices can be made flexible. While it is technologically challenging to integrate 2D materials with 3D electronics, there are no fundamental reasons why nanoribbons could not replace silicon.

University of California researchers, along with teams from other U.S-based institutions like Columbia University, Lawrence Berkeley National Laboratory and University of Washington, have created a metallic wire made entirely of carbon, setting the stage for a ramp-up in research to build carbon-based transistors and, ultimately, computers.

"Staying within the same material, within the realm of carbon-based materials, is what brings this technology together now," said Felix Fischer, UC Berkeley professor of chemistry, noting that the ability to make all circuit elements from the same material makes fabrication easier. "That has been one of the key things that has been missing in the big picture of an all-carbon-based integrated circuit architecture."