Electron River...

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 can behave like a viscous liquid as they travel through a conducting material, producing a spatial pattern that resembles water flowing through a pipe. So say researchers in Israel and the UK who have succeeded in imaging this hydrodynamic flow pattern for the first time using a novel scanning probe technique. The result will aid developers of future electronic devices, especially those based on 2D materials like graphene in which electron hydrodynamics is important.

We are all familiar with the distinctive patterns formed by water flowing in a river or stream. When the water encounters an obstacle – such as the river bank or a boat – the patterns change. The same should hold true for electron flow in a solid if the interactions between electrons are strong. This rarely occurs under normal conditions, however, since electrons tend to collide with defects and impurities in the material they travel through, rather than with each other.

Making electrons hydrodynamic

Conversely, if a material is made very clean and cooled to low temperatures, it follows that electrons should travel across it unperturbed until they collide with its edges and walls. The resulting ballistic transport allows electrons to flow with a uniform current distribution because they move at the same rate near the walls as at the center of the material.

If the temperature of this material is then increased, the electrons can begin to interact. In principle, they will then scatter off each other more frequently than they collide with the walls. In this highly interacting, hydrodynamic regime, the electrons should flow faster near the center of a channel and slower near its walls – the same way that water behaves when it flows through a pipe.

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

Nanocones...

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

Graphene, buckyballs, and carbon nanotubes now have a new family member, the nanocone, adding to the types of all-carbon nanostructures with remarkable electronic and optical characteristics and bringing its own promising properties. (J. Am. Chem. Soc., 2019, DOI: 10.1021/jacs.9b06617) Such molecules could be useful for developing efficient organic solar cells or as sensor molecules.

Organic chemist Frank Würthner and postdoctoral researcher Kazutaka Shoyama of the University of Würzburg came up with the method for synthesizing the nanocones, which are 1.68 nm in diameter and 0.432 nm tall. A five-atom ring of carbons forms the cone’s tip. The team used a cross-coupling annulation cascade to add hexagons around the edges of the ring until the molecule grew to 80 carbons. The team added five nitrogen atoms around the periphery of the cone, increasing the crystal’s solubility.

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

TBG and Ferromagnets...

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

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

Researchers have found that electrons organize themselves into a new kind of ferromagnet in twisted bilayer graphene (TBG). In this system, which forms when two sheets of graphene are stacked on top of one another with a small twist angle between them, it is the orbital motion of electrons, rather than their spins, that aligns. Such behavior could produce emergent topological states that might be exploited in applications such as low-power magnetic memory in the future.

Graphene is a flat crystal of carbon just one atom thick. When two sheets of the material are placed on top of each other and misaligned by rotating them relative to each other, they form a moiré pattern. Last year, researchers at the Massachusetts Institute of Technology (MIT) found that at a “magic” twist angle of 1.1°, the material becomes a superconductor (that is, it can carry currents with no losses) at 1.7 K. This effect, which occurs thanks to miniband flattening at this angle that strongly enhances interactions between electrons in the material, disappears at slightly larger or smaller angle twists.

A team of researchers led by David Goldhaber-Gordon of Stanford University has now found unambiguous evidence of ferromagnetism – as the giant anomalous Hall (AH) effect – in TBG when its flat conduction miniband is three-quarters filled.

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

Graphene Black Hole Hologram...

An image to illustrate the concept of holographic duality between a graphene flake and a black hole. Physics World

Topics: Black Holes, Einstein, General Relativity, Graphene, Nanotechnology, Quantum Mechanics

Much research on black holes is theoretical since it is difficult to make actual measurements on real black holes. Such experiments also need to be undertaken over decades or longer. Physicists are therefore keen to create laboratory systems that are analogous to these cosmic entities. New theoretical calculations by a team in Canada, the US, UK and Israel have now revealed that a material as simple as a graphene flake with an irregular boundary subjected to an intense external magnetic field can be used to create a quantum hologram that faithfully reproduces some of the signature characteristics of a black hole. This is because the electrons in the carbon material behave according to the Sachdev-Ye-Kitaev model.

Some of the most important unresolved mysteries in modern physics come from the “incompatibility” between Einstein’s theory of general relativity and the theory of quantum mechanics. General relativity describes the physics of the very big (the force of gravity and all that it affects: spacetime, planets, galaxies and the expansion of the Universe). The theory of quantum mechanics is the physics of the very small – and the other three forces, electromagnetism and the two nuclear forces.

“In recent years, physicists have gleaned important new insights into these questions through the study of the SYK model,” explains Marcel Franz of the University of British Columbia in Canada, who led this research effort. “This model is an illustration of a type of ‘holographic duality’ in which a lower-dimensional system can be represented by a higher dimensional one. In our calculations, the former is N graphene electrons in (0+1) dimensions and the latter the dilation gravity of a black hole in (1+1) dimensional anti-de Sitter (AdS2) space.

Black hole hologram appears in a graphene flake, Belle Dumé, Physics World

Parkinson's and Quantum Dots...

On the dot: Researchers have found that GQDs reduce fibrils in mice with Parkinson's

Topics: Biology, Graphene, Nanotechnology, Quantum Dots

Quantum dots made from the carbon material graphene prevent alpha-synuclein from aggregating into strand-like structures known as fibrils. They also help disaggregate fibrils that have already formed. Alpha-synuclein fibrils are thought to be implicated in Parkinson’s disease because they kill dopamine-generating neurons, so the new findings might help in the development of therapies to treat this disease as well as others in which fibrilization occurs.

Synucleins are a family of proteins typically found in neural tissue. Researchers believe that one type of synuclein, alpha-synuclein, twists into fibrils, which then accumulate in the midbrain of patients with Parkinson’s. Treatments with efficient anti-aggregation agents might thus be one way of fighting the disease.

A team led by Byung Hee Hong of Seoul National University and Han Seok Ko of The Johns Hopkins University in Baltimore have now found that graphene quantum dots (GQDs) bind to alpha-synuclein in vitro. Thanks to fluorescence and turbidity assays, as well as transmission electron microscopy measurements, the researchers found that the dots prevent alpha-synuclein from forming into fibrils. The nanostructures also dissociate already-formed fibrils into short fragments, with the average length of the fragments shortening from 1 micron to 235 nm and 70 nm after 6 and 24 hours respectively. The number of fragments starts to decrease after three days too and cannot be detected at all after seven days, which implies that the fibrils completely disintegrate after this time.

Could graphene quantum dots help treat Parkinson’s disease? Belle Dumé, Physics World

Graphene Mirabilis...

Illustration: Nanotools Bioscience

Topics: Biology, Cancer, Graphene, Nanotechnology, Research

See: "Annus mirabilis" at Wikipedia for the cultural reference.

Shine light on human heart cells cultured on graphene and they beat faster. Shine light on zebrafish embryos with graphene flakes injected in their hearts, and the contraction of that organ speeds up.

That’s what scientists at the University of California San Diego reported today in the journal Science Advances, in a discovery they say has implications for everything from drug testing to pacemakers.

“Sometimes discoveries happen due to serendipity,” says Alex Savchenko, a biophysics researcher at the university, who led the discovery with Elena Molokanova at the San Diego-based startup Nanotools Bioscience. “In this case we were controlling what we wanted to achieve all the way through the experiment.”

Graphene, the wonder material composed of single atom-thick sheets of carbon, has been a focus of excitement and feverish development ever since some of its properties were first demonstrated, in 2004, by Andre Geim and Konstantin Novoselov, both now at the University of Manchester.

One of graphene’s many talents is that it can convert light into electricity. Savchenko and his colleagues hypothesized that the electricity generated by graphene could also stimulate human cells.

After honing the graphene formulation and trying out different types of light, Savchenko’s team managed to do what they set out to do: They built a gentle remote control for cell growth. Call it an opto-graphene stimulator.

Gif: Nanotools Bioscience
This video shows heart cells being manipulated by an optical graphene stimulator.

Graphene Stimulator Paves Way for Optical Pacemakers, Smart Opioids, and Electronic Cancer Killers
Emily Waltz, Spectrum IEEE

Excitons and Bilayer Graphene...

The band structure of a bandgap-opened bilayer graphene is shown in the upper left corner, where the trigonal warping effect results in three pockets near the edge of conduction and valence bands. Infrared light illuminates bilayer graphene and creates an exciton (a bound state of an electron and an electron hole), located mostly in the top and bottom layer of carbon atoms respectively. Courtesy: Long Ju and Enrique Sahagún Alonso (Scixel)

Topics: Condensed Matter Physics, Graphene, Particle Physics, Nanotechnology

Researchers in the US have succeeded in observing excitons in bilayer graphene for the first time using photocurrent spectroscopy and modified Fourier transform infrared spectroscopy techniques. The new result could help in the development of next-generation optoelectronics instruments, such as tunable infrared detectors, light-emitting diodes and lasers for molecular spectroscopy, thermal imaging and astronomy applications.

“The excitons we observed can be tuned using an electrical field, have a high quality factor, strongly absorb light and lie in the technologically important mid-infrared to terahertz wavelength range,” explains team member and lead author of the study Long Ju, who is at Cornell University. “No other conventional semiconductor contains such excitons.”

Graphene is a sheet of carbon atoms just one atom thick arranged in a honeycomb lattice. It is a semi-metal and does not contain a bandgap in its pristine state. Bilayer graphene is different, however, in that a large and tunable bandgap can be induced in it using an applied electric field – something that cannot be done for single-layer graphene.

Researchers theorize that bilayer graphene also supports tunable excitons (electron-hole pairs) but these had never been actually observed in an experiment until now.

Excitons seen in bilayer graphene, Belle Dumé, Nanotechweb.org

The Flatness of Being...

A snapshot of silicene (shown in yellow), a 2-D material made up of silicon atoms, as it grows on iridium substrate (shown in red). The image was taken from a molecular dynamics simulation, which Argonne researchers used to predict the growth and evolution of silicene. (Image courtesy of Joseph Insley / Argonne National Laboratory.)

Topics: Computer Science, Graphene, Materials Science, Nanotechnology

Alliteration source: "The Unbearable Lightness of Being," by Milan Kundera.

The remarkable properties of 2-D materials — made up of a single layer of atoms — have made them among the most intensely studied materials of our time. They have the potential to usher in a new generation of improved electronics, batteries and sensory devices, among other applications.

One obstacle to realizing applications of these materials is the cost and time needed for experimental studies. However, computer simulations are helping researchers overcome this challenge in order to accurately characterize material structures and functions at an accelerated pace.

At the U.S. Department of Energy’s (DOE) Argonne National Laboratory, researchers have simulated the growth of silicene, a 2-D material with attractive electronic properties. Their work, published in Nanoscale, delivers new and useful insights on the material’s properties and behavior and offers a predictive model for other researchers studying 2-D materials.

The flat and the curious, Joan Koka, Argonne National Laboratories

Quantum Sensing...

An artistic rendition of the experimental setup for a quantum sensing experiment. The diamond quantum sensor is controlled by lasers. Graphene (a single layer of carbon atoms) sits atop the sensor. Red lines represent the path of the electrons as they move through the graphene. Credit: David A. Broadway/cqc2t.org

Topics: Graphene, Magnetic Resonance Imaging, Nanotechnology, Quantum Mechanics

Graphene, a sheet of carbon just one atom thick, has a number of unique electronic properties, so it is ideal for fundamental studies in condensed matter physics and for making novel electronics and sensing devices. Researchers normally study the electron transport properties of graphene by measuring the material’s resistivity but this approach cannot make out variations in electronic properties caused by local structures, such as defects, which are very important in nanomaterials. Now, a team at the University of Melbourne in Australia has overcome this problem with their new technique based on quantum probes made from nitrogen-vacancy centres to image the flow of electric current in 2D nanomaterials like the carbon sheet - and has found that it is indeed disrupted by minute cracks and defects.

“Our technique is non-invasive, offers high sub-micron spatial resolution and works under ambient conditions,” explains lead author of the new study Jean-Philippe Tetienne. “It could be used to study electron transport in any atomically-thin materials and structures, which are especially vulnerable to imperfections like defects. This is important because it will allow us to see how electric currents are affected by these imperfections and so ultimately help us improve the reliability and performance of existing and emerging technologies.”

The new technique is based on a quantum sensing platform that consists of a diamond chip engineered with an array of atomic defects, known as nitrogen-vacancy (NV) centres. These centres, which form when a nitrogen impurity finds itself next to a missing carbon atom in the diamond lattice, are essentially tiny magnets and can be used as sensors for magnetic resonance imaging (MRI) at the nanoscale. This is because the spin of an electron associated with the NV is relatively insensitive to its environment thanks to the fact that diamond does not have a net nuclear spin.

Nanotechweb: NV-quantum probes measure electron flow in graphene, Belle Dumé

PEEM...

Experimental set-up shows an array of graphene-capped liquids. The caps enable the liquids to be studied using an image technique that previously was restricted to studying solid surfaces.

Credit: A. Strelkov/NIST

Topics: Graphene, Electrical Engineering, Materials Science, Nanotechnology, Semiconductor Technology

By capping liquids with graphene, an ultrathin sheet of pure carbon, researchers at the National Institute of Standards and Technology (NIST) and their colleagues have revitalized and extended a powerful technique to image surfaces. The graphene lids enable researchers for the first time to easily and inexpensively image and analyze liquid interfaces and the surface of nanometer-scale objects immersed in liquids. The new capability has the potential to advance the development of batteries, highly charged capacitors for power-grid technology, and new catalysts such as those used in the chemical industry.

In the imaging technique, known as photoemission electron microscopy (PEEM), ultraviolet light or X-rays bombard a sample, stimulating the material to release electrons from a region at or just beneath its surface. Electric fields act as lenses, focusing the emitted electrons to create an image.

NIST: Graphene Lid Revitalizes Imaging Technique, Ben Stein

Micro-Gami...

Image Source: Origami Resource Center

Topics: Graphene, Nanotechnology, NEMS, Robotics

Thirty years ago, a professor in Japan folded an origami crane smaller than a pinhead. Peering through a microscope, he used a sewing needle to carefully crimp the paper.

Now researchers at Cornell University in Ithaca, New York, have gone one step further, creating origami about the size of a red blood cell. Too small for human hands, their origami folds itself. This new take on an old tradition is made not from paper, but from sheets of glass and carbon only a few atoms thick.

“It’s the world’s thinnest origami … comparable in size to a biological microorganism,” said Marc Miskin, a postdoctoral associate in the laboratory of applied physicist Itai Cohen at Cornell. He described the new research in a March 14 talk at an American Physical Society meeting in New Orleans.

The simple shapes formed by the micro-gami, such as cubes and pyramids, lack the grace and sophistication of a bird. But they could be a step toward miniature machines that fold themselves up into packages small enough to be injected into the body.

Inside Science: World's Thinnest Origami Could Build Microscopic Machines
Devin Powell

Graphene and Green Cars...

Simulations by Rice University scientists show that pillared graphene boron nitride may be a suitable storage medium for hydrogen-powered vehicles. Above, the pink (boron) and blue (nitrogen) pillars serve as spacers for carbon graphene sheets (gray). The researchers showed the material worked best when doped with oxygen atoms (red), which enhanced its ability to adsorb and desorb hydrogen (white). Credit: Lei Tao/Rice University

Topics: Climate Change, Graphene, Green Tech, Nanotechnology

Layers of graphene separated by nanotube pillars of boron nitride may be a suitable material to store hydrogen fuel in cars, according to Rice University scientists.

The Department of Energy has set benchmarks for storage materials that would make hydrogen a practical fuel for light-duty vehicles. The Rice lab of materials scientist Rouzbeh Shahsavari determined in a new computational study that pillared boron nitride and graphene could be a candidate.

The study by Shahsavari and Farzaneh Shayeganfar appears in the American Chemical Society journal Langmuir.

Shahsavari's lab had already determined through computer models how tough and resilient pillared graphene structures would be, and later worked boron nitride nanotubes into the mix to model a unique three-dimensional architecture. (Samples of boron nitride nanotubes seamlessly bonded to graphene have been made.)

Just as pillars in a building make space between floors for people, pillars in boron nitride graphene make space for hydrogen atoms. The challenge is to make them enter and stay in sufficient numbers and exit upon demand.

Phys.org:
Scientists say boron nitride-graphene hybrid may be right for next-gen green cars

For The Better...

Illustration: Takashi Takahashi/Tohoku University

Topics: Condensed Matter Physics, Graphene, Materials Science, Nanotechnology, Semiconductor Technology, Superconductors, Solid State Physics, Quantum Mechanics

Graphene is an amazing conductor. The transport of electrons through graphene nanoribbons has even surpassed what scientists thought were the theoretical limits for the material—so much so that electrons moving through it seem to behave almost like photons.

Graphene’s amazing properties as a conductor has inspired some researchers to explore whether the single-atom-thick sheets of carbon could also be made into superconductors. Last year, an international research team from Canada and Germany was able to demonstrate that graphene can be made to behave that way when it’s doped with lithium atoms.

Now researchers in Japan (from Tohoku University and the University of Tokyo) have developed a new method for coaxing graphene to behave as a superconductor that has some important and distinctive differences from the previous research by the Canadian and German researchers.

IEEE: Graphene's Role as a Superconductor Just Got Better, Dexter Johnson

Plasmon Laser...

Schematic of the tunable terahertz laser, which is built upon a semiconductor substrate (thick grey slab). The salmon-pink region is the waveguide that is topped by a layer of gold and then graphene. The slits in the gold are shown as a red glow. The graphene is topped with an electrolyte (also shown in gold). (Courtesy: University of Manchester)

Topics: Graphene, Laser, Optical Physics, Quantum Mechanics, Semiconductor Technology

A new type of semiconductor laser has been created using the unique electronic properties of graphene. Designed in the UK by researchers at the University of Manchester, the prototype operates in the terahertz band and can be easily tuned to output radiation at specific wavelengths. The team says that its research could lead to the development of compact devices for a variety of different applications, from security scanning to medical imaging.

Coherent terahertz radiation can be created using quantum-cascade lasers, which were invented in 1994. These devices contain multiple quantum wells with energy bands that are split into subbands and minibands. When a bias voltage is applied to the laser, a periodic cascade of intersubband transitions is established. The population inversion necessary for terahertz lasing is then achieved through electrical injection.

Physics World: Plasmons call the tune in new graphene-based terahertz laser
Tim Wogan

Graphene Superconductor...

Graphene turns into a superconductor when decorated with lithium atoms. (Courtesy: Shutterstock/Inozemtsev Konstantin)

Topics: Condensed Matter Physics, Graphene, Materials Science, Nanotechnology, Phonons, Semiconductor Technology, Superconductors, Solid State Physics, Quantum Mechanics

THIS changes the game! The application to longer life batteries is the first thought that comes to mind. Within semiconductors, we could supplement the physical limitations we're butting up to at the Moore's Law limit with a neat change in the material chemistry used to build the circuitry. A step before and enhancement of carbon nanotubes when they eventually replace them. Exciting times!

The "wonder material" graphene has another significant quality to add to its impressive list of electrical and mechanical properties: superconductivity. Physicists in Canada and Germany have shown that graphene turns into a superconductor when doped with lithium atoms – a result that could lead to a new generation of superconducting nanoscale devices.

Graphene exhibits a range of remarkable properties, thanks to its special structure – a one-atom-thick hexagonal lattice of carbon atoms. It is far stronger than steel while also flexible, and is an excellent conductor of both electricity and heat. In its pristine form, however, it is not a superconductor.

Neither is pure graphite, but in 2005 physicists showed that graphite could be made to superconduct when chemically treated, so as to create bulk materials consisting of graphene alternated with one-atom-thick layers of another element. The best performing material thus created, calcium graphite (CaC₆), has a superconducting transition temperature of 11.5 K. Theorists identified the underlying mechanism for that superconductivity as electron–phonon coupling. Phonons are vibrations in a material's crystal lattice that bind electrons together into "Cooper pairs" that can travel through the lattice without resistance – one of the hallmarks of superconductivity. It was then realized that such electron–phonon coupling might occur not just in bulk graphite compounds but also by depositing atoms of a suitable element on to single layers of graphene.

Physics World: 'Decorated' graphene is a superconductor, Edwin Cartlidge

Supersonic Buckyballs...

Fig 2: a) C60 impinging on Cu (111). b) Excited electronic states visited during a TD-DFT simulation of C20 final configuration after cage breaking on Cu (111) surface at 14 eV (Corresponding to C60 at 42 eV). c) C20 final configuration after cage breaking on Cu (111) surface. d) Total electronic energy of the system during a metadynamics simulation starting from the configuration of a broken C60 cage on Cu (111) surface. e) Final configuration on the metadynamics-DFT simulation.

Topics: Buckminsterfullerene, C60, Condensed Matter Physics, Graphene, Electrical Engineering, Materials Science, Nanotechnology

TECHNOLOGY REVIEW: Graphene is one of the wonder materials of our age. It is some 200 times stronger than steel, it is an extraordinary conductor of heat and electricity, and it is almost transparent. And yet making graphene is still tricky, particularly when it needs to sit on a substrate for applications such as electronics.

Today, Simone Taioli at the Trento Institute for Fundamental Physics and Applications in Italy and a few pals say they’ve worked out how to do it starting with the famous football-shaped molecule buckminsterfullerene.

Their idea is remarkably simple: bombard the substrate with buckyballs travelling at supersonic speeds. That’s fast enough to crack them open when they hit, and the resulting unzipped cages then bond together to form a graphene film.

Researchers have long thought of using buckyballs as a precursor for graphene. But the only way to get them to unzip and bind together is to heat them to temperatures in excess of around 600 °C.

Physics arXiv:
Towards room-temperature single-layer graphene synthesis by C60 Supersonic Molecular Beam Epitaxy
Roberta Tatti, Lucrezia Aversa, Roberto Verucchi, Emanuele Cavaliere, Giovanni Garberoglio, Nicola M. Pugno, Giorgio Speranza, Simone Taioli

Hype Material...

Fig 1. Graphene and its descendants: top left: graphene; top right: graphite = stacked graphene; bottom left: nanotube=rolled graphene; bottom right: fullerene=wrapped graphene (adapted from ref.[1]).2
National University of Singapore

Topics: Graphene, Materials Science, Nanotechnology, Semiconductor Technology, STEM

Though the article tends to reset expectations, I think there is still a lot of good research to do with graphene in the foreseeable future. The statement of being "decades" out shouldn't discourage anyone. There's room for a few more scientists; a few more Nobel's that are either currently in grad school, in kindergarten or might not have even been born yet. We just have to have the foresight to build the education infrastructure to develop the young people that will do it in this country or elsewhere (likely Singapore). Somewhat irritatingly, the microwave and the Internet have given us a sense of instantaneous expectations in research and especially politics. May we never get to the point where we can walk up to a 3-D printer (the Heisenberg Uncertainty Principle pretty much kills all hope of a replicator) and say: Tea, Earl Grey: Hot. Instead of the Star Trek post-apocalyptic utopia, we may be insufferable to the point of obsessive compulsive, if - like our conundrums with our mobile devices and microwaves - such a device quits working...

The wonder material. It’s just one atom thick but 200 times stronger than steel; extremely conductive but see-through and flexible. Graphene has shot to fame since its discovery in 2004 by UK-based researchers Andre Geim and Konstantin Novoselov, for which the University of Manchester pair were awarded the 2010 Nobel prize in physics.

We’ve heard the facts. We’ve read about how graphene could push the boundaries of today’s technology in almost unlimited ways. We’ve even pictured an elephant balanced on a pencil. But looking past the headlines, it’s clear that a lot of the most exciting areas of graphene science are still in the early stages. It will be years, decades perhaps, before we see the first graphene-enhanced smartphones, aeroplanes or bulletproof vests. But beyond these pie-in-the-sky promises, the underlying research is gathering pace.

Scientific American: Graphene: Looking beyond the Hype, Emma Stoye and ChemistryWorld

Graphene Ice Sandwich...

Square ice between two graphene sheets as seen in a transmission electron microscope. High-contrast dark spots are oxygen atoms that indicate positions of water molecules. Hydrogen atoms yield too little contrast to be resolved even by the state-of-the-art TEM. The top right inset shows a magnified image of a small area in the centre of the ice crystal. Credit: University of Ulm, Germany

Topics: Carbon Nanotubes, Graphene, Nanotechnology, Nanostructures

Researchers in the UK, Germany and China say they have observed a new type of frozen water in the form of square ice sandwiched between sheets of graphene. The ice films, which are less than 1 nm thick, have a completely different symmetry to that of normal ice – which has a hexagonal structure. This ice should also exist inside certain other types of nanostructures, such as carbon nanotubes, and could help explain why water moves unusually in these materials – a result that could have implications for developing more efficient filtration, desalination and distillation technologies.

"The new phase of ice forms at room temperature, well above the 'normal' freezing temperature of water," explain team leaders Irina Grigorieva and Andre Geim of the University of Manchester in the UK. "Apart from finding this new phase – not something that happens every day – our result will allow us to better understand the counterintuitive behaviour of water inside nanochannels, such as ultrafast permeation though graphene oxide membranes."

Nanotech Web: Square ice forms in graphene sandwich, Belle Dumé, contributing editor at nanotechweb.org

On The Dot...

Physicists in Finland and Russia have shown how graphene quantum dots can be used to split Cooper pairs. (Courtesy: Shutterstock/Mopic)

Topics: Cooper Pairs, Graphene, Modern Physics, Superconductivity, Quantum Computers, Quantum Mechanics

Superconducting "Cooper pairs" of electrons have been split to create entangled pairs of electrons in a new device built by physicists in Finland and Russia. The device employs two quantum dots made of graphene. Although other types of quantum dots have been used for this purpose, the latest research suggests that graphene quantum dots should deliver long-lived entangled electron pairs that could be used in quantum computers.

Entanglement is a quantum-mechanical phenomenon in which properties of fundamental particles are correlated so that making a measurement on one particle can instantaneously affect another particle – even across very large distances. In principle, a quantum computer can use this connectedness to perform certain calculations much faster than a conventional computer. Although practical quantum computers do not exist today, some potential designs involve using the intrinsic angular momenta, or "spin", of electrons as quantum bits (qubits) of information that can be entangled.

Superconductors provide a ready source of entangled electrons because the Cooper pairs that allow these materials to conduct electricity with little or no resistance are in fact entangled pairs of electrons with opposite spin. Splitting the pairs while preserving the electrons' entanglement can be done simply by connecting ordinary metal wires to either end of the superconductor. If the set-up is just right, each wire will carry away one electron from a pair. However, it is more often the case that both electrons will end up going down the same wire.

Physics World: Graphene quantum dots split Cooper pairs, Edwin Cartlidge

Silicene Transistor...

Image: University of Texas at Austin, Source: IEEE link below

Topics: Graphene, Nanotechnology, Semiconductor Technology, STEM

TECHNOLOGY REVIEW: An exotic but tricky-to-use new form of silicon is being eyed as a way to build much faster computer chips. And now, those who see its potential can claim a minor victory by making the first transistors out of the stuff.

The material in question, called silicene, comes in layers of silicon just one-atom thick. This structure gives the material fantastic electrical properties, but it also means it’s devilishly tricky to produce and work with. Even testing its basic properties in the lab has proved difficult.

Now Deji Akinwande, a computer engineer at the University of Texas at Austin, has figured out how to work with the stubborn material well enough to make the first silicene transistors. His first-of-their-kind devices are described today in the journal Nature Nanotechnology, and they live up to silicene’s promise by switching with extraordinary speed.

Another atom-thick material, graphene, which is made from carbon, has gained attention in recent years for its own electrical properties. The appeal of silicene, says Akinwande, is that it’s made from the stuff Silicon Valley was built on. In theory, it should be easier for chipmakers to work with than some new material. “If we can get good properties out of it, it can be translated immediately by the semiconductor industry,” Akinwande says.

Deji received a B.S/M.S. combined degree in Electrical Engineering and Applied Physics from Case Western Reserve University, Cleveland, Ohio. His master’s research involved the development and characterization of evanescent microwave probes for non-destructive imaging of materials. Afterwards, he gained experience designing and testing a variety of analog circuits from MHz to 110 GHz for network analyzer and signal generator instruments at Agilent Technologies in northern California.

He subsequently worked at XtremeSpectrum, Freescale and Motorola on the modeling, design and testing of the first commercial 100 Mb/s ultra-wideband receiver chip.

He received the Ph.D. degree from Stanford University in December 2009. His thesis focused on the physics, chemistry, materials and electronic properties of carbon materials. He has published widely on carbon nanomaterials in a variety of disciplines including physics, chemistry, materials, and electrical engineering journals.

Professor Akinwande joined UT Austin starting from January 2010, and he is a member of IEEE, APS, ACS, and MRS societies.

Extreme Tech:
Silicene could help create create an alternative to graphene with many of its benefits, Joel Hruska
Nature: Graphene's cousin silicene makes transistor debut, Mark Peplow
Spectrum IEEE: Transistor Made From Silicene for the First Time,
Dexter Johnston