The dispute over the origins of terahertz photoresponse in graphene results in a draw

Researchers at the Russia-based MIPT, MSPU and the University of Manchester revealed the mechanisms leading to photocurrent in graphene under terahertz radiation. The paper is said to put an end to a long-lasting debate about the origins of direct current in graphene illuminated by high-frequency radiation, and also sets the stage for the development of high-sensitivity terahertz detectors. Such detectors have applications in medical diagnostics, wireless communications and security systems.

Wiring diagram of a graphene-based terahertz detector image

In 2005, MIPT alumni Andre Geim and Konstantin Novoselov experimentally studied the behavior of electrons in graphene and found that electrons in graphene respond to electromagnetic radiation with an energy of quantum, whereas the common semiconductors have an energy threshold below which the material does not respond to light at all. However, the direction of electron motion in graphene exposed to radiation has long remained a point of controversy, as there is an abundance of factors pulling it in different directions. The controversy was especially stark in the case of the photocurrent caused by terahertz radiation.

Flagship team uses graphene to squeeze light into one atom

Researchers at the Institute of Photonic Sciences (ICFO) in Spain, along with other members of the Graphene Flagship, have reached what they consider to be the ultimate level of light confinement - being able to confine light down to a space of one atom. This may pave the way to ultra-small optical switches, detectors and sensors.

Graphene Flagship team uses graphene to confine light to one atom image

“Graphene keeps surprising us: nobody thought that confining light to the one-atom limit would be possible. It will open a completely new set of applications, such as optical communications and sensing at a scale below one nanometer,” said ICREA Professor Frank Koppens at ICFO, who led the research.

Researchers design a method for detecting individual impurities in graphene

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.

Researchers design a method to detect individual impurities in graphene image 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.

Graphene and hBN used to create unique 2D quantum bits

Two novel 2D materials, graphene and hexagonal boron nitride, and the tip of a scanning tunneling microscope – these were the ingredients used to create a novel kind of a so-called “quantum dot”. These extremely small nanostructures allow delicate control of individual electrons by fine-tuning their energy levels directly. Such devices can be key for modern quantum technologies.

Graphene and hBN 2D quantum bits image

The theoretical simulations for the new technology were performed at TU Wien. The experiment involved RWTH Aachen and the team around Nobel-prize laureates Andre Geim and Kostya Novoselov from Manchester who prepared the samples.

U.S collaboration grows large single-crystal graphene that could advance graphene research and commercialization

A team led by the Department of Energy’s Oak Ridge National Laboratory, that also included scientists from University of Tennessee, Rice University and New Mexico State University, has developed a new method to produce large, monolayer single-crystal-like graphene films more than a foot long. The novel technique may open new opportunities for producing high-quality graphene of unlimited size and in a way that is suitable for roll-to-roll production.

Method to grow large single-crystal graphene could advance scalable 2D materials image

The ORNL team used a CVD method — but with a twist. They explained in this work how localized control of the CVD process allows evolutionary, or self-selecting, growth under optimal conditions, yielding a large, single-crystal-like sheet of graphene. “Large single crystals are more mechanically robust and may have higher conductivity,” ORNL lead coauthor Ivan Vlassiouk said. “This is because weaknesses arising from interconnections between individual domains in polycrystalline graphene are eliminated”. “Our method could be the key not only to improving large-scale production of single-crystal graphene but to other 2D materials as well, which is necessary for their large-scale applications,” he added.

XFNANO: Graphene and graphene-like materials since 2009XFNANO: Graphene and graphene-like materials since 2009