GNRs - Page 3

Researchers have fully characterized graphene nanoribbons (GNRs) with a clear route towards upscaling the production. Two-dimensional sheets of graphene in the form of ribbons a few tens of nanometers across have unique properties that are highly interesting for use in future electronics.

The nanoribbons were grown on a template made of silicon carbide under well controlled conditions and thoroughly characterized by a research team from MAX IV Laboratory, Techniche Universität Chemnitz, Leibniz Universität Hannover, and Linköping University. The template has ridges running in two different crystallographic directions to let both the armchair and zig-zag varieties of graphene nanoribbons form. The result is a predictable growth of high-quality graphene nanoribbons which have a homogeneity over a millimeter scale and a well-controlled edge structure.

An international research team, co-led by researchers at the University of California, Riverside, which also included researchers at MIT, Nanyang Technological University, Singapore; Institute of High Performance Computing, Singapore; UC Berkeley; and National Institute for Materials Science, Japan, has found a new mechanism for highly-efficient charge and energy flow in graphene, opening the door to new types of light-harvesting devices.

The researchers made pristine graphene into different geometric shapes, connecting narrow ribbons and crosses to wide open rectangular regions. They found that when light illuminated constricted areas, such as the region where a narrow ribbon connected two wide regions, a large light-induced current, or photocurrent, was detected.

Researchers from the University of California, Santa Barbara, will be presenting a paper focused on CMOS-compatible graphene interconnects next month at the world-renowned semiconductor-technology conference - the IEEE International Electron Devices Meeting (Dec. 1-5 in San Francisco).

The team has shown that integrating graphene into the interconnect scheme holds the promise of increasing performance and limiting power consumption in next-generation CMOS ICs, as graphene offers high conductivity and is not prone to electromigration.

Researchers at EMPA (Swiss Federal Laboratories for Materials Science and Technology), along with colleagues from the Max Planck Institute for Polymer Research in Mainz and other partners, have succeeded in precisely controlling the properties of graphene nano-ribbons (GNRs) by specifically varying their shape. This can be used to generate specific local quantum states, and could in the future be used for precise nano-transistors or possibly even quantum computing.

The team has shown that if the width of a narrow graphene nano-ribbon changes, in this case from seven to nine atoms, a special zone is created at the transition: because the electronic properties of the two areas differ in a special, topological way, a "protected" and thus very robust new quantum state is created in the transition zone. This local electronic quantum state can be used as a basic component to produce tailor-made semiconductors, metals or insulators - and perhaps even as a component in quantum computers.

A team of researchers from the University of Basel, the National Institute for Material Science in Tsukuba in Japan, Kanazawa University, Kwansei Gakuin University in Japan and Aalto University in Finland has succeeded in using atomic force microscopy to obtain images of individual impurity atoms in graphene ribbons. Thanks to the forces measured in the graphene's two-dimensional carbon lattice, they were able to identify boron and nitrogen for the first time.

Using the atomic force microscope's carbon monoxide functionalized tip (red/silver), the forces between the tip and the various atoms in the graphene ribbon can be measured

The team replaced particular carbon atoms in the hexagonal lattice with boron and nitrogen atoms using surface chemistry, by placing suitable organic precursor compounds on a gold surface. Under heat exposure up to 400°C, tiny graphene ribbons formed on the gold surface from the precursors, including impurity atoms at specific sites.

A research team at the U.S. Department of Energy’s (DOE) Argonne National Laboratory has placed armchair-edge graphene nanoribbons (AGNRs) on a gold surface. Since AGNRs become semiconductors at certain widths, this structure may offer advantages in speed, heat dissipation and power consumption in electronic devices and create new research paths in spintronics.

The goal was to use AGNRs to block magnetic interactions on a metal. The team focused on how the AGNRs affect these interactions in a molecule tightly adhered to gold using the phenomenon of Kondo resonance — a well-defined, temperature-dependent effect between a single magnetic atom or molecule and a metal’s free electrons. For this purpose, the team relied on a low-temperature scanning tunneling microscopy tool at Argonne’s Center for Nanoscale Materials.

A collaboration between Spanish research institutes—led by the nanoGUNE Cooperative Research Center (CIC)—has achieved a breakthrough in so-called molecular electronics by devising a way to connect magnetic porphyrin molecules to graphene nanoribbons. These connections may be an example of how graphene could enable the potential of molecular electronics.

Porphyrin is an important molecule that is responsible for making photosynthesis possible in plants and transporting oxygen in the blood. Recently, researchers have been experimenting with "magnetic porphyrins" and discovered that they can form the basis of spintronic devices. Spintronics involves manipulating the spin of electrons and it is this spin that is responsible for magnetism: When a majority of electrons in a material have their spins pointing in the same direction, the material is magnetized. If you can move all the spins up or down and can read that direction, you can create the foundation of the 0 and 1 of digital logic.

Researchers led by the CNR-Nanoscience Institute in Modena, Italy, and the University of Strasbourg in France, have experimentally observed light emission from individual graphene nanoribbons for the first time. They demonstrated that 7-atom-wide nanoribbons emit light at a high intensity that is comparable to bright light-emitting devices made from carbon nanotubes, and that the color can be tuned by adjusting the voltage. These findings may open the door to the development of bright graphene-based light sources.

Experimentally, there have been only a few demonstrations of light emission from graphene nanoribbons, and these have been limited to ensembles of nanoribbons and revealed only weak light emission. So the results of the new study, which show a much brighter light emitted by individual graphene nanoribbons compared to ensembles, hint at the exciting potential of graphene's optical properties.

Researchers from Rice University have discovered that nitrogen-doped carbon nanotubes or modified graphene nanoribbons could potentially replace platinum, one of the most expensive facets in fuel cells, for performing fast oxygen reduction—a crucial reaction that transforms chemical energy into electricity.

The researchers used computer simulations to see how carbon nanomaterials can be improved for fuel-cell cathodes and discovered the atom-level mechanisms by which doped nanomaterials catalyze oxygen reduction reactions. The simulations also revealed why graphene nanoribbons and carbon nanotubes modified with nitrogen and/or boron are so sluggish and how they can be improved.

An international team of researchers from Empa, the Max Planck Institute for Polymer Research in Mainz and the University of California at Berkeley has succeeded in growing graphene ribbons exactly nine atoms wide with a regular armchair edge from precursor molecules. The specially prepared molecules are evaporated in an ultra-high vacuum for this purpose. After several process steps, they are put on a gold base to form the desired nanoribbons of about one nanometer in width and up to 50 nanometers in length.

These structures have a relatively large and, most importantly, precisely defined energy gap. This enabled the researchers to go one step further and integrate the graphene ribbons into nanotransistors. Initially, however, the first attempts were not so successful: Measurements showed that the difference in the current flow between the "ON" state (i.e. with applied voltage) and the "OFF" state (without applied voltage) was far too small. The problem was the dielectric layer of silicon oxide, which connects the semiconducting layers to the electrical switch contact. In order to have the desired properties, it needed to be 50 nanometers thick, which in turn influenced the behavior of the electrons.