Boron Nitride - Page 6

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.

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.

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 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.

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.

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.

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.

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.

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.

Researchers at MIT and Harvard University have found that graphene can be tuned to behave at two electrical extremes: as an insulator, in which electrons are completely blocked from flowing; and as a superconductor, in which electrical current can stream through without resistance.

Researchers in the past, including this team, have been able to synthesize graphene superconductors by placing the material in contact with other superconducting metals — an arrangement that allows graphene to inherit some superconducting behaviors. In this new work, the team found a way to make graphene superconduct on its own, demonstrating that superconductivity can be an intrinsic quality in the purely carbon-based material.

Researchers at The University of Manchester and the NGI have shown how graphene and boron nitride can be used for observing nanomaterials in liquids, by creating a ‘petri-dish’ of sorts.

Scanning / transmission electron microscopy (S/TEM) is one of only few techniques that allows imaging and analysis of individual atoms. However, the S/TEM instrument requires a high vacuum to protect the electron source and to prevent electron scattering from molecular interactions. Several studies have previously revealed that the structure of functional materials at room temperature in a vacuum can significantly different from that in their normal liquid environment. So, it is important to be able to study the structure at the required state.

Researchers from the Pierre Aigrain Laboratory in the ENS Physics department in Paris, France, have discovered a new cooling mechanism for electronic components made of graphene deposited on boron nitride. The efficiency of this mechanism reportedly allowed the team to reach electric intensities at the intrinsic limit of the laws of conduction.

Current-voltage (left) and temperature-voltage (right) characteristics of a graphene on boron nitride transistor. The transistor effect is visible by modulation of the current as a function of the gate voltage in the Zener-Klein tunnel transport regime.

Heat dissipation is vital in order to prevent deterioration or destruction of electronic components. The laws of physics dictate that increasing the density of components on a chipset implies increasing dissipation and thus heat. Nowadays, with the advances in 2D material devices, this question becomes particularly critical since components are required to be one atom thick. By producing a graphene-based transistor deposited on a boron nitride substrate, the team demonstrated a new cooling mechanism 10 times more efficient than basic heat diffusion. This new mechanism, which exploits the two-dimensional nature of the materials opens a "thermal bridge" between the graphene sheet and the substrate.

Researchers from Cambridge University have demonstrated how graphene and other related 2D materials (namely hBN) can be directly printed onto textiles to create fully inkjet-printed dielectrically gated field effect transistors (FETs) with solution processed 2D materials.

According to the team, these devices are washable, flexible, cheap, safe, comfortable to wear and environmentally-friendly, essential requirements for applications in wearable electronics. The team also demonstrated the first reprogrammable memories, inverters and logic gates with solution processed 2D materials by coupling these FETs together to create integrated circuits, the most fundamental components of a modern-day computer.

Scientists from Columbia University have reportedly proven a 30-year-old theory called "the even-denominator fractional quantum Hall state" and established bilayer graphene as a promising platform that could lead to quantum computation.

The team observed an intensely studied anomaly in condensed matter physics—the even-denominator fractional quantum Hall (FQH) state—via transport measurement in bilayer graphene. Observing the 5/2 state in any system is a remarkable scientific opportunity, since it encompasses some of the most perplexing concepts in modern condensed matter physics, such as emergence, quasi-particle formation, quantization, and even superconductivity, the team says. Our observation that, in bilayer graphene, the 5/2 state survives to much higher temperatures than previously thought possible not only allows us to study this phenomenon in new ways, but also shifts our view of the FQH state from being largely a scientific curiosity to now having great potential for real-world applications, particularly in quantum computing.