Metal–Insulator–Graphene diodes enable terahertz rectennas on flexible substrates

Researchers from AMO GmbH, RWTH Aachen University, Chalmers University and the University of Wuppertal have recently developed a novel type of graphene-based flexible energy harvester, which reportedly shows good prospects for powering wearable and conformal devices.

A terahertz rectenna on polyimide image

The device is a 'rectenna' - an antenna directly coupled to a diode, which is able to detect radiation and to transform it into a DC output. Rectennas working in the microwave region have been well established since the sixties, thanks to the availability of Schottky diodes with a sufficiently short response time. The challenge is to extend the working principle of rectennas to higher frequency ranges – in particular terahertz (THz) and optical frequencies.

Moiré graphene may assist in harnessing Bloch oscillations

For many years, scientists have been trying to harness Bloch oscillations, an exotic kind of behavior by electrons that could introduce a new field of physics and important new technologies. Now, MIT physicists report on a new approach to achieving Bloch oscillations in recently introduced graphene superlattices. Graphene's electronic properties undergo an interesting transformation in the presence of an “electric mesh” (a periodic potential), resulting in new types of electron behavior not seen in pristine materials. In their recent work, the scientists show why graphene superlattices may be game changers in the pursuit of Bloch oscillations.

Normally, electrons exposed to a constant electric field accelerate in a straight line. However, Quantum Mechanics predicts that electrons in a crystal, or material composed of atoms arranged in an orderly fashion, can behave differently. Upon exposure to an electric field, they can oscillate in tiny waves—Bloch oscillations. “This surprising behavior is an iconic example of coherent dynamics in quantum many-body systems,” says Leonid Levitov, an MIT professor of physics and leader of the current work. Levitov is also affiliated with MIT’s Materials Research Laboratory.

New method creates sub-10-nm GNRs from squashed carbon nanotubes

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.

Researchers take a closer look at a mysterious graphene oxide phenomenon

A team of researchers at UNSW has observed a unique phenomenon in graphene oxide (GO). The oxygen atoms in GO are normally attached in a rather chaotic way. At elevated temperatures, however, the oxygen atoms form more organized structures – by themselves. This process of ‘self-organization’ was found to drastically improve various properties of GO – for example, its electrical conductivity.

UNSW scientists solve decade-old graphene oxide puzzle image

For years, researchers have been aware that this phenomenon existed, but they could only demonstrate it using computational simulations. The new research, led by Dr. Rakesh Joshi at UNSW, successfully observed it for the first time in real life, using cutting-edge electron microscopy. While common microscopes use light to create a magnified image, electron microscopes use electrons. With this type of microscope, it is possible to observe single atoms, by magnifying what you’re looking at by a factor of 1,000,000.

Researchers discover a correlated electron-hole state in double-bilayer graphene

A team of researchers, led by Klaus Ensslin and Thomas Ihn at the Laboratory for Solid State Physics at ETH Zurich, together with colleagues at the University of Texas in Austin (USA), has observed a novel state in twisted bi-layer graphene. In that state, negatively charged electrons and positively charged (so-called) holes, which are missing electrons in the material, are correlated so strongly with each other that the material no longer conducts electric current.

An insulator made of two conductors imageImage by Peter Rickhaus / ETH Zurich (taken from Nanowerk)

“In conventional experiments, in which graphene layers are twisted by about one degree with respect to each other, the mobility of the electrons is influenced by quantum mechanical tunneling between the layers”, explains Peter Rickhaus, a post-doc and lead author of the study. “In our new experiment, by contrast, we twist two double layers of graphene by more than two degrees relative to each other, so that electrons can essentially no longer tunnel between the double layers.”