BLOGS

Credit: Nicoletta Barolini

Topics: Chemistry, Graphene, Materials Science, Modern Physics, Nanotechnology

Graphullerene, an atom-thin material made of linked fullerene subunits, gives scientists a new form of modular carbon to play with.

Carbon, in its myriad forms, has long captivated the scientific community. Besides being the primary component of all organic life on earth, material forms of carbon have earned their fair share of breakthroughs. In 1996, the Nobel Prize in Chemistry went to the discoverers of fullerene, a superatomic symmetrical structure of 60 carbon atoms shaped like a soccer ball; in 2010, researchers working with an ultra-strong, atom-thin version of carbon, known as graphene, won the Nobel Prize in Physics.

Today in work published in Nature, researchers led by Columbia chemists Xavier Roy, Colin Nuckolls, and Michael Steigerwald, with postdoc and first author Elena Meirzadeh have discovered a new version of carbon that sits somewhere in between fullerene and graphene: graphullerene. It’s a new two-dimensional form of carbon made up of layers of linked fullerenes peeled into ultrathin flakes from a larger graphullerite crystal—just like how graphene is peeled from graphite crystals (the same material found in pencils).

“It is amazing to find a new form of carbon,” said Nuckolls. “It also makes you realize that there is a whole family of materials that can be made in a similar way that will have new and unusual properties as a consequence of the information written into the superatomic building blocks.”

Columbia Chemists Discover a New Form of Carbon: Graphene’s “Superatomic” Cousin, Ellen Neff, Quantum.Columbia.edu

Splitting up: schematic of the electron beam splitter with the n side on the right and the p side on the left. (Courtesy: M Jo et al/Phys. Rev. Lett.)

Topics: Graphene, Interferometry, Nanotechnology, Quantum Computer

A graphene-based “beam splitter” for electronic currents has been built by researchers in France, South Korea, and Japan. Created by Preden Roulleau at the University of Paris and colleagues, the tunable device’s operation is directly comparable to that of an optical interferometer. The technology could soon enable allow electron interferometry to be used in nanotechnology and quantum computing.

An optical interferometer splits a beam of light in two, sending each beam along a different path before recombining the beams at a detector. The measured interference of the beams at the detector can be used to detect tiny differences in the lengths of the two paths. Recently, physicists have become interested in doing a similar thing with currents of electrons in solid-state devices, taking advantage of the fact that electrons behave like waves in the quantum world.

Graphene is a sheet of carbon just one atom thick and is widely considered to be the best material for realizing such “electron quantum optics”. Indeed, researchers have already used the material to make simple electron interferometers. Now, Roulleau’s team has created a fully adjustable electron beam splitter that could be used to build more sophisticated devices. It exploits the quantum Hall effect, whereby the application of a strong magnetic field perpendicular to a sheet of graphene will cause an electron current to flow around the edge of the sheet.

Graphene beam splitter gives electron quantum optics a boost, Sam Jarman, Physics World

Telltale traces In this doping vs magnetic field conductance map, the magnetic field is varied along the vertical axis. Horizontal yellow streaks show Brown-Zak fermions propagating along straight trajectories with high mobility (low resistance), whereas slanted indigo lines show the cyclotron motion around Brown-Zak fermions. The slope of these lines enabled the researchers to obtain the degeneracy (and find an additional quantum number) of these new quasiparticles. (Courtesy: J Barrier)

Topics: Fermions, Graphene, Nanotechnology, Quantum Mechanics

Researchers at the University of Manchester in the UK have identified a new family of quasiparticles in superlattices made from graphene sandwiched between two slabs of boron nitride. The work is important for fundamental studies of condensed-matter physics and could also lead to the development of improved transistors capable of operating at higher frequencies.

In recent years, physicists and materials scientists have been studying ways to use the weak (van der Waals) coupling between atomically thin layers of different crystals to create new materials in which electronic properties can be manipulated without chemical doping. The most famous example is graphene (a sheet of carbon just one atom thick) encapsulated between another 2D material, hexagonal boron nitride (hBN), which has a similar lattice constant. Since both materials also have similar hexagonal structures, regular moiré patterns (or “superlattices”) form when the two lattices are overlaid.

If the stacked layers of graphene-hBN are then twisted, and the angle between the two materials’ lattices decreases, the size of the superlattice increases. This causes electronic band gaps to develop through the formation of additional Bloch bands in the superlattice’s Brillouin zone (a mathematical construct that describes the fundamental ideas of electronic energy bands). In these Bloch bands, electrons move in a periodic electric potential that matches the lattice and does not interact with one another.

New family of quasiparticles appears in graphene, Isabelle Dumé, Physics World

A river made of graphene with the electrons flowing like water. Courtesy: Ryan Allen and Peter Allen, Second Bay Studios

Topics: Electron Configuration, Graphene, Nanotechnology

Electrons flow like water in ultra-pure graphene, Belle Dumé, Physics World

A carbon nanocone includes nitrogen atoms around the periphery to improve the material’s solubility. Carbon atoms are shown in gray; hydrogen in white; nitrogen in blue; and oxygen in red.

Topics: Applied Physics, Chemistry, Graphene, Nanotechnology

Nanocones extend the graphene toolbox, Neil Savage, Chemical & Engineering News

Magic angle graphene superlattice. Scale=10 nm. Courtesy: P Jarillo-Herrero

Topics: Ferromagnetism, Graphene, Hall Effect, Magnetic Resonance Imaging, Nanotechnology

Ferromagnetism appears in twisted bilayer graphene, Belle Dumé, Physics World