Beating graphene to push supercapacitors closer to batteries

Scientific Method / Science & Exploration

Adding nitrogen to carbon materials boosts capacitance above that of graphene.

by Shalini Saxena - Dec 30, 2015 11:44am CST

Oak Ridge National Lab

Most people think of batteries when they consider energy storage, but capacitors are an alternative in some use cases. Capacitors are used in almost all electronic devices, often to supply temporary power when batteries are being changed to prevent loss of information. In addition to everyday devices, they are also used in more obscure technologies, including certain types of weapons.

Understanding the supercapacitor

Unlike batteries, capacitors use static electricity to store energy. In their simplest form, they contain two conducting metallic plates with an insulating material (dielectric) placed in between. A typical capacitor charges instantly but usually cannot hold a great deal of charge.
Supercapacitors can at least partly overcome this shortcoming. They differ from the typical capacitor in that their "plates" provide significantly larger surface area and are much closer together. The surface area is increased by coating the metal plates with a porous substance. Instead of having a dielectric material between them, the plates of a supercapacitor are soaked in an electrolyte and separated by an extremely thin insulator.
Carbon supercapacitors offer high electrical power, low weight, and fast charge-discharge cycles. But it's difficult to get carbon to provide a high enough surface area to bring the energy density up to where it could compete directly with batteries.
Though some carbon materials have been made to exhibit a high supercapacitance in theory, they are not able to translate those gains into real-world applications. For example, graphene supercapacitors exhibit a theoretical capacitance of 550 F/g but only reach 300 F/g when used in real-life applications.

Improving one atom at a time

Recently, scientists have focused on altering the surface of carbon-based supercapacitors to increase their potential to store charge. In this case, the supercapacitor system under investigation is composed of carbon plates that contain nano-sized pores (mesoporous carbon) with a polymer insulator. They have altered the surface of the mesoporous carbon plates by the addition of nitrogen. Doping in nitrogen has allowed for reactions between the nitrogen and carbon. These "redox" reactions result in the movement of electrons from one species to another.  
In this study, the scientists demonstrated the ability to produce an electrochemically active substance from layered carbon (similar to graphene) by nitrogen doping.
In order to make the material, they used a sacrificial porous silica template containing self-assembled tubes. This material was then covered with a thin layer of carbon. The silica was then etched away, leaving a self-supported ordered superstructure, with a thickness of only a few atomic layers of carbon.
Since this process was rather involved, they also demonstrated a simplified, template-free method to produce a similar carbon structure with the same overall performance.
These materials were imaged and found to have nanometer-sized tubes that are evenly spaced throughout the material. The tubes themselves were found to be composed of graphene-like sheets with fewer than five total layers. After nitrogen doping, these structural features still remained, but the surface area increased dramatically, as did the total pore volume. The higher surface area should allow it to store more charges.

Performance doping with nitrogen

The scientists tested the capacitance of the nitrogen-doped structure using an aqueous electrolyte. The system was found to have a capacitance of 855 F/g—quite a big step above the graphene-based materials. They also found that the system can be charged and discharged very quickly.
The unusually high capacitance exhibited by this system can be attributed to robust redox reactions. In the course of these reactions, the nitrogen reacts with the carbon on the surface of the plates, forming a variety of compounds. As a result, the layered carbon material is transformed into an electrochemically active substance while maintaining its electrical conductivity. Nitrogen doping also altered other physical properties that are conducive to supercapacitive performance, including resistance, hydrophobicity, and electrostatic charge.
After nitrogen doping, these carbon-based systems can store 41 watt-hours per kilogram. Though that's still not enough to compete with batteries in their energy-storage capabilities, this approach demonstrates that significant improvements in supercapacitor energy storage are still possible.
Science, 2015. DOI: 10.1126/science.aab3798 (About DOIs).

Move over graphene—boron now used to make 2D semi-metals

http://arstechnica.com/

As tough as graphene, with electronic properties that differ based on orientation.

by Shalini Saxena - Dec 23, 2015 11:55am CST

The structure of a borophene cluster.

Wikimedia Commons

Graphene is an exceptionally strong and conductive material composed of a single atomic layer of carbon. Its discovery sparked interest in the development of other two-dimensional (2D) materials, and, over the past decade, scientists have discovered hundreds. These materials boast abilities that could make a noticeable impact in areas such as electronics, thermal management, filtration, medicine, and more.
Now, an unusual atom—boron—has been used to produce a novel 2D material called "borophene."

Boron at the atomic level

Boron is one of the many materials that has been considered for development of 2D materials. Boron is an interesting atom to use as a building block for a number of reasons. First, it is a semi-metal, meaning it exhibits some properties of metals and some properties of nonmetals; as a 2D material, it thus has the potential to exhibit unique behavior.
Additionally, boron has interesting bonding capabilities. It has three valence electrons in the p-orbital, meaning that it can form up to three bonds. Boron can form strong covalent bonds, with two electrons split between two atoms, or stable electron-deficient bonds, with two electrons split between three atoms. As a result, boron can form materials with different three-dimensional patterns.
When it comes to producing 2D boron, however, the majority of boron studies have been theoretical in nature; few experiments were done due to the costly and toxic precursors that seemed necessary. Recently, in an investigation published in Science, scientists have managed to make 2D boron without relying on these precursors. They call their atomically thin film "borophene."

A new 2D boron sheet

In the new study, scientists grew boron sheets using physical vapor deposition. In this method, boron is evaporated in an ultra-high vacuum. Under vacuum, the evaporated particles travel toward the target surface (in this case, silver) and deposit to form a thin film. Depending on the orientation of the boron to the silver surface and on the deposition conditions, a variety of 2D boron structures will form.
Characterization of the borophene films revealed that certain films displayed similarities to the model “borophene” molecule structure, which consists of 36 boron atoms forming three interconnected, quasi-planar rings around a hexagonal central hole. However, instead of forming individual molecules, the new films were composed of layers of these rings, exhibiting out-of-plane buckling. These fragments orient themselves to form a hexagonal structure with a boron atom sitting in the center, much like a bee resting in a honeycomb within a nest. Other structures were also seen, including a ribbon-like material.
Electronic characterization of the films revealed that they are metallic but that their electronic properties depend on the direction in which the current flows. In other words, electrons moved differently as they crossed the borophene in different directions (the technical term for this is "anisotropic electronic properties").

Borophene vs. other 2D materials

From a fundamental perspective, the 2D borophene layer is truly interesting. It represents the missing link between fully covalently bound 2D materials—such as graphene—and films of semi-metals that are only stable when they're layered on a specific support structure—like silicene (a non-planar, buckled layer of the semi-metal silicon).

Further Reading

First transistor built using two-dimensional silicon

Graphene's big brother finally kept stable long enough to test.

Borophene layers are more stable than silicene due to their strong covalent interactions. Additionally, borophene layers boast similar mechanical properties to graphene. In this case, the borophene layers have different mechanical properties in perpendicular directions. In comparison to graphene, which has a Young's modulus of 340 GPa-nm, borophene layers exhibit a higher Young’s modulus along one axis (398 GPa-nm) and a lower one along the perpendicular axis (170 GPa-nm). The borophene layer films also have considerable toughness.
No other 2D material has the properties of the new borophene layers, which have the capability to interface with metals, semi-metals, and nonmetals. As a result, single and multiple borophene layers offer a broad avenue for development of nano-scale electronic devices and micro-scale mechanical devices. However, future integration into commercial applications hinges on the ability to develop a fabrication method that provides more uniformity, rather than producing multiple versions of the material.

Scientists have developed a way to create diamonds without high heat or pressure

By Ed Oswald December 2, 2015 4:17 PM

A third phase of carbon has been discovered, and from it researchers have been able to produce diamonds at room temperature and standard pressure. Its real-world existence is thought to be rare though, found only at the core of some planets. Researchers at North Carolina State University made the discovery, and call it “Q-Carbon.”
Previously there was thought to only be two solid forms of carbon: graphite and diamond. Graphite is pretty common, although diamonds are found much less often. This is because it takes a substantial amount of pressure and heat to produce a diamond, and the type of conditions for this to happen on Earth haven’t existed for more than a billion years.
Even in the lab, synthetic diamond-makers still must recreate these conditions to get the process to work. That’s a big expense, so the fact that NC State researchers are able to do this without any atmospheric modifications is pretty incredible.

Related: Can you make diamonds faster and cheaper? A Silicon Valley startup says yes

“We can create diamond nanoneedles or microneedles, nanodots, or large-area diamond films, with applications for drug delivery, industrial processes and for creating high-temperature switches and power electronics,” lead research and NC State professor Jay Narayan says.
Narayan noted that Q-Carbon is harder than a diamond, and will glow even when exposed to small amounts of energy. It may show promise for use in new display technologies as well he says, although a lot of research is still needed to understand its properties completely.
Other companies have worked on ways to produce synthetic diamonds on the cheap, such as Santa Clara, Calif.-based Diamond Foundry. However, that company still uses high heat and pressure to produce its gems, which isn’t much different from how diamonds are are produced naturally.
The researchers are still learning how to manipulate Q-Carbon, although in the meantime have filed two provisional patents on both Q-Carbon itself and the diamond production technique used to create it. Researchers did not say when they expect the technique to be ready for commercial use.

Cobalt atoms on graphene a powerful combo

http://nextbigfuture.com/

October 25, 2015

Graphene doped with nitrogen and augmented with cobalt atoms has proven to be an effective, durable catalyst for the production of hydrogen from water, according to scientists at Rice University.

The Rice lab of chemist James Tour and colleagues at the Chinese Academy of Sciences, the University of Texas at San Antonio and the University of Houston have reported the development of a robust, solid-state catalyst that shows promise to replace expensive platinum for hydrogen generation.

A new catalyst just 15 microns thick has proven nearly as effective as platinum-based

 catalysts but at a much lower cost, according to scientists at Rice University. The 

catalyst is made of nitrogen-doped graphene with individual cobalt atoms that activate

 the process. (Credit: Tour Group/Rice University)

Nature Communications - Atomic cobalt on nitrogen-doped graphene for hydrogen generation



Catalysts can split water into its constituent hydrogen and oxygen atoms, a process required for fuel cells. The latest discovery, detailed in Nature Communications, is a significant step toward lower-cost catalysts for energy production, according to the researchers.

“What’s unique about this paper is that we show not the use of metal particles, not the use of metal nanoparticles, but the use of atoms,” Tour said. “The particles doing this chemistry are as small as you can possibly get.”

Even particles on the nanoscale work only at the surface, he said. “There are so many atoms inside the nanoparticle that never do anything. But in our process the atoms driving catalysis have no metal atoms next to them. We’re getting away with very little cobalt to make a catalyst that nearly matches the best platinum catalysts.” In comparison tests, he said the new material nearly matched platinum’s efficiency to begin reacting at a low onset voltage, the amount of electricity it needs to begin separating water into hydrogen and oxygen.

The new catalyst is mixed as a solution and can be reduced to a paper-like material or used as a surface coating. Tour said single-atom catalysts have been realized in liquids, but rarely on a surface. “This way we can build electrodes out of it,” he said. “It should be easy to integrate into devices.”

The researchers discovered that heat-treating graphene oxide and small amounts of cobalt salts in a gaseous environment forced individual cobalt atoms to bind to the material.

Electron microscope images showed cobalt atoms widely dispersed throughout the samples.

They tested nitrogen-doped graphene on its own and found it lacked the ability to kick the catalytic process into gear. But adding cobalt in very small amounts significantly increased its ability to split acidic or basic water.

“This is an extremely high-performance material,” Tour said. He noted platinum-carbon catalysts still boast the lowest onset voltage. “No question, they’re the best. But this is very close to it and much easier to produce and hundreds of times less expensive.”

Atom-thick graphene is the ideal substrate, Tour said, because of its high surface area, stability in harsh operating conditions and high conductivity. Samples of the new catalyst showed a negligible decrease in activity after 10 hours of accelerated degradation studies in the lab.

Abstract

Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.

Author: brian wang on 10/25/2015

http://www.gizmag.com/

High-efficiency, semi-transparent perovskite/graphene solar cells created at low cost

• Colin Jeffrey
• September 11, 2015

The semi-transparent, inexpensive solar cells have a claimed
conversion efficiency of around 12 percent
 (Credit: Hong Kong Polytechnic University)

With the continued rise in the uptake of solar cells, consumers are now looking at less obtrusive ways to incorporate these in buildings and vehicles. Transparent or semi-transparent cells provide greater flexibility and visual appeal than standard, opaque silicon solar cells, however their relatively high-cost and poor efficiencies have meant that their adoption has been slow. To help remedy this, researchers working at the Hong Kong Polytechnic University (PolyU) have created semi-transparent, efficient, low-cost perovskite solar cells with graphene electrodes.
First generation silicon solar cells have been the mainstay of photovoltaic (PV) energy conversion for many years now due to their high stability and efficient energy conversion, but their opacity and expense mean that alternatives are now being actively sought for modern building and vehicle applications. Thin film PVs (second generation solar cells) are lightweight and flexible, but are expensive because they are created from rare materials using complex structures requiring high-temperature production processes.
Now, utilizing such materials as thin-film perovskite, the third generation of solar cell is currently being developed for commercial use in the not-too-distant future with the promise of greater power conversion efficiencies, simpler fabrication processes, and lower cost.
In this vein, the PolyU researchers have developed their own version of the third generation solar cell using semitransparent perovskite with graphene used as the electrodes. Being exceptionally thin but with high conductivity and low cost, graphene makes an ideal choice for semitransparent solar cells as it allows light to be absorbed from both sides. As such, the researchers envisage these devices potentially able to be used in windows, louvers, and building roof surfaces, thereby increasing the available surface area for collecting solar energy.

With a claimed power conversion efficiency of around 12 percent, the PolyU solar cells outperform standard transparent and semi-transparent versions hands-down. The potential to be produced at less than HK $0.50 (US $0.06)/Watt also means a greater than 50 percent saving on the cost of conventional silicon solar cells.
While graphene has been around for more than a decade now and is highly-efficient as a conductor in its own right, the PolyU researchers decided to further enhance the conductivity of graphene to meet their specific requirements. To do this, the graphene was coated with a patina of PEDOT:PSS conductive polymer (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) – the same ingredient recently used by KAIST scientists in the production of weavable LED fibers – that also acted as an adhesion layer to the perovskite during the process of lamination.
To promote power conversion efficiency, the researchers found that by multilayering graphene through chemical vapor deposition to create transparent electrodes, the sheet resistance of the electrodes was additionally reduced while the exceptional transparency of the electrodes was retained. Finally, the performance of the device was further improved by enhancing the degree of contact between the top graphene electrodes and the hole transport layer on the perovskite film.
According to the researchers, the exceptional flexibility of graphene and the simplified preparation of the cells means that the PolyU device could be eminently suitable for mass production via direct printing or using a roll-to-roll process. In this way, semitransparent solar cells may well provide a greater uptake of PV panels across markets not currently serviced by traditional, opaque devices.
The results of this research were published in the journal Advanced Materials.
Source: Hong Kong Polytechnic University

http://nextbigfuture.com/

September 29, 2015

Galfenol can convert 70 percent of an applied mechanical energy into magnetic energy

An alloy first made nearly two decades ago by the U. S. Navy could provide an efficient new way to produce electricity. The material, dubbed Galfenol, consists of iron doped with the metal gallium. In new experiments, researchers from UCLA, the University of North Texas (UNT), and the Air Force Research Laboratories have shown that Galfenol can generate as much as 80 megawatts of instantaneous power per square meter under strong impacts.

Galfenol converts energy with high efficiency; it is able to turn roughly 70 percent of an applied mechanical energy into magnetic energy, and vice versa. (A standard car, by contrast, converts only about 15 to 30 percent of the stored energy in gasoline into useful motion.) Significantly, the magnetoelastic effect can be used to generate electricity. "If we wrap some wires around the material, we can generate an electrical current in the wire due to a change in magnetization," Domann said.

Galfenol in experiments using a device called a Split-Hopkinson Pressure Bar to generate high amounts of compressive stress (e.g., powerful impacts). They found that when subjected to impacts, Galfenol generates as much as 80 megawatts of instantaneous power per cubic meter.

By way of comparison, a device known as an explosively driven ferromagnetic pulse generator produces 500 megawatts of power per cubic meter. However, as their name implies, such generators require an explosion—one that destroys the ferromagnet, even as it produces power.

Among the potential applications, Galfenol-powered devices could be used as wireless impact detectors. "Essentially, we could fabricate small devices that send out a detectable electromagnetic wave when a mechanical pulse moves through it," Domann said. These devices could be embedded in vehicles—military or civilian—to detect collisions. Because electromagnetic waves travel three orders of magnitude faster than mechanical waves, information about the impact could be transmitted ahead of the waves created by the impact.

This picture is of the experimental setup showing the Hopkinson bar

 surrounded by a water-cooled electromagnet. A cylinder of Galfenol

 is inside of the electromagnet, sandwiched between the Hopkinson bars.

 The magnet was used to apply a wide range of static magnetic fields to

 Galfenol while it was mechanically impacted. Credit: John Domann/UCLA

Journal of Applied Physics - High strain-rate magnetoelasticity in Galfen

This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3 ), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3 ). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.

A Kolsky bar was used to generate large constant strain rates in Galfenol, and measure the stress-strain response, as well as the change in magnetic flux density due to magnetoelastic coupling. The experimental results indicate that the average Young's modulus of Galfenol is invariant with increasing strain rates of up to 33/s. The measured voltage was proportional to strain rate, with a more rounded appearance, attributed to dynamic magnetic effects. Furthermore, the measured voltage and change in flux were highly dependent on bias field strength. A lumped parameters model was created that effectively simulates the measured pickup coil voltages in response to an applied stress pulse. The model suggests that magnetoelastic coupling is relatively insensitive to strain rates as high as 33/s. The model also suggests that Galfenol can generate large quantities of instantaneous power, comparable to those created by explosively driven ferromagnetic pulse generators. However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.

SOURCES- UCLA, Phys.org, Journal of Applied Physics 

 http://nextbigfuture.com/

September 29, 2015

Solar Cells Will be Made Obsolete by 3D rectennas aiming at 40-to-90% efficiency

A new kind of nanoscale rectenna (half antenna and half rectifier) can convert solar and infrared into electricity, plus be tuned to nearly any other frequency as a detector.

Right now efficiency is only one percent, but professor Baratunde Cola and colleagues at the Georgia Institute of Technology (Georgia Tech, Atlanta) convincingly argue that they can achieve 40 percent broad spectrum efficiency (double that of silicon and more even than multi-junction gallium arsenide) at a one-tenth of the cost of conventional solar cells (and with an upper limit of 90 percent efficiency for single wavelength conversion).

It is well suited for mass production, according to Cola. It works by growing fields of carbon nanotubes vertically, the length of which roughly matches the wavelength of the energy source (one micron for solar), capping the carbon nanotubes with an insulating dielectric (aluminum oxide on the tethered end of the nanotube bundles), then growing a low-work function metal (calcium/aluminum) on the dielectric and voila--a rectenna with a two electron-volt potential that collects sunlight and converts it to direct current (DC).

"Our process uses three simple steps: grow a large array of nanotube bundles vertically; coat one end with dielectric; then deposit another layer of metal," Cola told EE Times. "In effect we are using one end of the nanotube as a part of a super-fast metal-insulator-metal tunnel diode, making mass production potentially very inexpensive up to 10-times cheaper than crystalline silicon cells."

For commercialization, billions or even trillions of carbon-nanotube bundles could be grown side-by-side, ramping up the power output into the megaWatt range, after optimization for higher efficiency.

"We still have a lot of work to do to lower contact resistance which will improve the impedance match between the antenna and diode, thus raising efficiency," Cola told us."Our proof-of-concept was tuned to the near-infrared. We used infrared-, solar- and green laser-light and got efficiencies of less than one percent, but what was key to our demo was we showed our computer model matched our experimental results, giving us the confidence that we can improve the efficiency up to 40 percent in just a few years."

For the future, Cola's group has a three tiered goal--first develop sensor applications that don't require high efficiencies, second to get the efficiency to 20 percent for harvesting waste heat in the infrared spectrum, then start replacing standard solar cells with 40 percent efficient panels in the visible spectrum. The team is also seeking suitable flexible substrates for applications that require bending.

Schematic of the components making up the optical rectenna--carbon nanotubes 

 capped with a metal-oxide-metal tunneling diode. (Credit: Thomas Bougher)
(Source: Georgia Tech)

Nature Nanotechnology - A carbon nanotube optical rectenna

An optical rectenna—a device that directly converts free-propagating electromagnetic waves at optical frequencies to direct current—was first proposed over 40 years ago, yet this concept has not been demonstrated experimentally due to fabrication challenges at the nanoscale. Realizing an optical rectenna requires that an antenna be coupled to a diode that operates on the order of 1 pHz (switching speed on the order of 1 fs). Diodes operating at these frequencies are feasible if their capacitance is on the order of a few attofarads but they remain extremely difficult to fabricate and to reliably couple to a nanoscale antenna. Here we demonstrate an optical rectenna by engineering metal–insulator–metal tunnel diodes, with a junction capacitance of ∼2 aF, at the tip of vertically aligned multiwalled carbon nanotubes (∼10 nm in diameter), which act as the antenna. Upon irradiation with visible and infrared light, we measure a d.c. open-circuit voltage and a short-circuit current that appear to be due to a rectification process (we account for a very small but quantifiable contribution from thermal effects). In contrast to recent reports of photodetection based on hot electron decay in a plasmonic nanoscale antenna a coherent optical antenna field appears to be rectified directly in our devices, consistent with rectenna theory. Finally, power rectification is observed under simulated solar illumination, and there is no detectable change in diode performance after numerous current–voltage scans between 5 and 77 °C, indicating a potential for robust operation.

What is Graphene?

Surprise discovery could see graphene used to improve health

http://phys.org/

7 hours ago

(Phys.org) —A chance discovery about the 'wonder material' graphene – already exciting scientists because of its potential uses in electronics, energy storage and energy generation – takes it a step closer to being used in medicine and human health.

Researchers from Monash University have discovered that graphene oxide sheets can change structure to become liquid crystal droplets spontaneously and without any specialist equipment.
With graphene droplets now easy to produce, researchers say this opens up possibilities for its use in drug delivery and disease detection.
The findings, published in the journal ChemComm, build on existing knowledge about graphene. One of the thinnest and strongest materials known to man, graphene is a 2D sheet of carbon just one atom thick. With a 'honeycomb' structure the 'wonder material' is 100 times stronger than steel, highly conductive and flexible.
Dr Mainak Majumder from the Faculty of Engineering said because graphene droplets change their structure in response to the presence of an external magnetic field, it could be used for controlled drug release applications.
"Drug delivery systems tend to use magnetic particles which are very effective but they can't always be used because these particles can be toxic in certain physiological conditions," Dr Majumder said.
"In contrast, graphene doesn't contain any magnetic properties. This combined with the fact that we have proved it can be changed into liquid crystal simply and cheaply, strengthens the prospect that it may one day be used for a new kind of drug delivery system."
Usually atomisers and mechanical equipment are needed to change graphene into a spherical form. In this case all the team did was to put the graphene sheets in a solution to process it for industrial use. Under certain PH conditions they found that graphene behaves like a polymer - changing shape by itself.
First author of the paper, Ms Rachel Tkacz from the Faculty of Engineering, said the surprise discovery happened during routine tests.
"To be able to spontaneously change the structure of graphene from single sheets to a spherical assembly is hugely significant. No one thought that was possible. We've proved it is," Ms Tkacz said.
"Now we know that graphene-based assemblies can spontaneously change shape under certain conditions, we can apply this knowledge to see if it changes when exposed to toxins, potentially paving the way for new methods of disease detection as well."

Commonly used by jewelers, the team used an advanced version of a polarised light microscope based at the Marine Biological Laboratory, USA, to detect minute changes to grapheme.
Dr Majumder said collaborating with researchers internationally and accessing some of the most sophisticated equipment in the world, was instrumental to the breakthrough discovery.
"We used microscopes similar to the ones jewelers use to see the clarity of precious gems. The only difference is the ones we used are much more precise due to a sophisticated system of hardware and software. This provides us with crucial information about the organisation of graphene sheets, enabling us to recognise these unique structures," Dr Majumder said.
Dr Majumder and his team are working with graphite industry partner, Strategic Energy Resources Ltd and an expert in polarized light imaging, Dr. Rudolf Oldenbourg from the Marine Biological Laboratory, USA, to explore how this work can be translated and commercialised.
Mr Mark Muzzin, CEO of Strategic Energy Resources Ltd said the collaboration with Monash was progressing well.
"We are so pleased to be associated with Dr Majumder's team at Monash University. The progress they have made with our joint project has been astonishing," he said.
The research was made possible by an ARC Linkage grant awarded to Strategic Energy Resources Ltd and Monash University and was the first linkage grant for graphene research in Australia.

Boron 'buckyball' discovered

http://phys.org/

Jul 13, 2014

Researchers have shown that clusters of 40 boron atoms form a molecular cage similar to the carbon buckyball. This is the first experimental evidence that such a boron cage structure exists. Credit: Wang lab / Brown University

The discovery 30 years ago of soccer-ball-shaped carbon molecules called buckyballs helped to spur an explosion of nanotechnology research. Now, there appears to be a new ball on the pitch.

Researchers from Brown University, Shanxi University and Tsinghua University in China have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball. It's the first experimental evidence that a boron cage structure—previously only a matter of speculation—does indeed exist.
"This is the first time that a boron cage has been observed experimentally," said Lai-Sheng Wang, a professor of chemistry at Brown who led the team that made the discovery. "As a chemist, finding new molecules and structures is always exciting. The fact that boron has the capacity to form this kind of structure is very interesting."
Wang and his colleagues describe the molecule, which they've dubbed borospherene, in the journal Nature Chemistry.
Carbon buckyballs are made of 60 carbon atoms arranged in pentagons and hexagons to form a sphere—like a soccer ball. Their discovery in 1985 was soon followed by discoveries of other hollow carbon structures including carbon nanotubes. Another famous carbon nanomaterial—a one-atom-thick sheet called graphene—followed shortly after.
After buckyballs, scientists wondered if other elements might form these odd hollow structures. One candidate was boron, carbon's neighbor on the periodic table. But because boron has one less electron than carbon, it can't form the same 60-atom structure found in the buckyball. The missing electrons would cause the cluster to collapse on itself. If a boron cage existed, it would have to have a different number of atoms.
Wang and his research group have been studying boron chemistry for years. In a paper published earlier this year, Wang and his colleagues showed that clusters of 36 boron atoms form one-atom-thick disks, which might be stitched together to form an analog to graphene, dubbed borophene. Wang's preliminary work suggested that there was also something special about boron clusters with 40 atoms. They seemed to be abnormally stable compared to other boron clusters. Figuring out what that 40-atom cluster actually looks like required a combination of experimental work and modeling using high-powered supercomputers.

On the computer, Wang's colleagues modeled over 10,000 possible arrangements of 40 boron atoms bonded to each other. The computer simulations estimate not only the shapes of the structures, but also estimate the electron binding energy for each structure—a measure of how tightly a molecule holds its electrons. The spectrum of binding energies serves as a unique fingerprint of each potential structure.
The next step is to test the actual binding energies of boron clusters in the lab to see if they match any of the theoretical structures generated by the computer. To do that, Wang and his colleagues used a technique called photoelectron spectroscopy.
Chunks of bulk boron are zapped with a laser to create vapor of boron atoms. A jet of helium then freezes the vapor into tiny clusters of atoms. The clusters of 40 atoms were isolated by weight then zapped with a second laser, which knocks an electron out of the cluster. The ejected electron flies down a long tube Wang calls his "electron racetrack." The speed at which the electrons fly down the racetrack is used to determine the cluster's electron binding energy spectrum—its structural fingerprint.
The experiments showed that 40-atom-clusters form two structures with distinct binding spectra. Those spectra turned out to be a dead-on match with the spectra for two structures generated by the computer models. One was a semi-flat molecule and the other was the buckyball-like spherical cage.
"The experimental sighting of a binding spectrum that matched our models was of paramount importance," Wang said. "The experiment gives us these very specific signatures, and those signatures fit our models."
The borospherene molecule isn't quite as spherical as its carbon cousin. Rather than a series of five- and six-membered rings formed by carbon, borospherene consists of 48 triangles, four seven-sided rings and two six-membered rings. Several atoms stick out a bit from the others, making the surface of borospherene somewhat less smooth than a buckyball.
As for possible uses for borospherene, it's a little too early to tell, Wang says. One possibility, he points out, could be hydrogen storage. Because of the electron deficiency of boron, borospherene would likely bond well with hydrogen. So tiny boron cages could serve as safe houses for hydrogen molecules.
But for now, Wang is enjoying the discovery.
"For us, just to be the first to have observed this, that's a pretty big deal," Wang said. "Of course if it turns out to be useful that would be great, but we don't know yet. Hopefully this initial finding will stimulate further interest in boron clusters and new ideas to synthesize them in bulk quantities."

Explore further: Graphene-like material made of boron a possibility, experiments suggest

Company says it's created the world's blackest black with carbon nanotubes

http://www.theverge.com/

By Adi Robertson on July 14, 2014 11:52 am Email @thedextriarchy 34Comments

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(NASA Goddard / Stephanie Getty)

 

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Black may not be, it turns out, the darkest shade — at least not black as we know it. British tech company Surrey Nanosystems says it's developed the world's blackest material: made of carbon nanotubes, it can absorb 99.96 percent of light that hits it. Its developers say that to the human eye, the material — called Vantablack — completely erases any features on a surface, becoming simply a void. "It's like black, like a hole, like there's nothing there. It just looks so strange," chief technical officer Ben Jensen tells The Independent. That's because the dense coating of carbon nanotubes, rolled sheets of carbon atoms like the one seen above, are used to create a lattice that absorbs virtually all light as it's refracted around the tubes.

(Surrey Nanosystems / The Independent)

Super-black carbon nanotube coatings are used in telescopes and other instruments that need to operate without any kind of noise from reflected light. Back in 2010, NASA announced that it was assessing whether its own carbon nanotubes should be used to coat the Ocean Radiometer for Carbon Assessment, which measured ocean color and had to be covered in black paint to prevent contaminating the results. The explanatory video below introduces the concepts that underlie it and Surrey Nanosystems' technology.

Besides the color, one of the most important issues is how well the material can stick to the objects it's trying to blacken, and how versatile it is. Surrey Nanosystems says this is one of the major differences between Vantablack and similar coatings: unlike many others, which have to be heated at several hundred degrees Celsius, it can be applied at low temperatures. This makes it possible to use the nanotubes on objects that might melt with a traditional process. The company is also claiming that it's set a new record for light absorption. To people looking at the coating, though, it might not be a completely new experience. NASA's super-black surfaces absorbed 99.5 percent of light, and in 2011, researchers used nanotubes to make an object virtually invisible against a black background.

Synthesizing graphene without damaging its electric and mechanical properties is one of the most significant breakthroughs in graphene research in history and will accelerate many commercialization applications

http://nextbigfuture.com/

April 05, 2014

Working with Sungkyungkwan University’s School of Advanced Materials Science and Engineering, Samsung's Advanced Institute of Technology (SAIT) has uncovered a new method of synthesising graphene without damaging its electric and mechanical properties.

In the past, researchers have found that multi-crystal synthesis – the process of synthesising small graphene particles to produce large-area graphene – deteriorated the electric and mechanical properties of the material, limiting its application range and making it difficult to commercialise.

The new method involves synthesising large-area graphene into a single crystal on a semiconductor, while maintaining its electric and mechanical properties. By developing a method for growing a single crystal graphene into a large area, the researchers claim they could displace the tech industry’s reliance on silicon.

"This is one of the most significant breakthroughs in graphene research in history,” said the laboratory leaders at SAIT’s Lab. “We expect this discovery to accelerate the commercialisation of graphene, which could unlock the next era of consumer electronic technology."

Science - Wafer-Scale Growth of Single-Crystal Monolayer Graphene on Reusable Hydrogen-Terminated Germanium

ABSTRACT

The uniform growth of single-crystal graphene over wafer-scale areas remains a challenge in the commercial-level manufacturability of various electronic, photonic, mechanical, and other devices based on graphene. Here, we describe wafer-scale growth of wrinkle-free single-crystal monolayer graphene on silicon wafer using a hydrogen-terminated germanium buffer layer. The anisotropic twofold symmetry of the germanium (110) surface allowed unidirectional alignment of multiple seeds, which were merged to uniform single-crystal graphene with predefined orientation. Furthermore, the weak interaction between graphene and underlying hydrogen-terminated germanium surface enabled the facile etch-free dry transfer of graphene and the recycling of the germanium substrate for continual graphene growth.

21 pages of supplemental material

Tom Billings • 4 hours ago

So, we now have had at least 3 teams in the last 12 months announce solutions to the grain boundary problems of graphene CVD sheets. There is the Columbia Engineering group last May 31, IIRC, who said they'd found an etchant for removing the copper substrate that left the sheet of graphene 90% as strong in tension as a single crystalline grain is, at 180 times the tensile strength of Steel, instead of 200 times. There is the group that found they could anneal the copper substrate for graphene deposition so that the crystal sizes of the copper substrate were much larger, giving larger far larger graphene crystals. Now, we have a Samsung group saying that they can use thermal release tape to remove the substrates.
I am awaiting the combination of one or more of these methods with the work by Dr. Greer's Caltech group and their 3d nano-architectured materials.
http://www.jrgreer.caltech.edu...
We already have heard that a graphene sheet can be a base from which to grow vertically aligned 3d carbon nanotubes. It seems the nano-lattices the Greer Group is making should be doable with graphene, even using copper substrates deposited on their original plastic lattice. Lastly, there are recent reports of starting with multilayered graphene sheets, adding excess hydrogen to the atmosphere in which they grow, and seeing those multiple sheets transform into well-ordered diamond crystalline sheets, without high pressures. If this can be added to the above, then a composite graphene/diamond 3d nano-architectured material could have the toughness of high tensile strength graphene reinforcement inside a stiff diamond matrix, ...all as the basic material for the nano-lattice structured materials the Greer Group has been speaking about.
This would allow many good things to be built, such as SSTO vehicles light enough that when they re-enter they could float in the lower atmosphere until they compress enough air for ballast to bring them to ground, and figurative "cloud-castles" in the sky, to live in. However, it would also make the use of in situ resources in Space more economical more quickly. We could haul in 10s of thousands of tons of asteroid material in the next several decades.
Still, with the above technology combinations we could build structures equal to what we would build here today with 100s of thousands of tons of materials, using a few hundred tons of raw asteroid material. It is not at all impossible that the atmospheres it holds in Space would be the majority of the mass of a habitat. This would seem to shift the emphasis at the start of asteroid mining from finding huge amounts of asteroid materials to processing smaller amounts of them to make the easily obtained small amounts into what we want for the first several decades. Far lower capital costs that way!

Superstrong graphene metal composite created that hundreds of times stronger than pure metal

August 26, 2013

New metamaterial has been developed exhibiting hundreds of times greater strength than pure metals. Professor Seung Min, Han and Yoo Sung, Jeong,Professor Seok Woo, Jeon have developed a composite nanomaterial. The nanomaterial consists of graphene inserted in copper and nickel and exhibits strengths 500 times and 180 times, respectively, greater than that of pure metals.

Schematic of metal–graphene multilayer system synthesis.

In separate research announced in May, 2013, Columbia Engineering researchers demonstrated that graphene, even if stitched together from many small crystalline grains, is almost as strong as graphene in its perfect crystalline form. This work resolves a contradiction between theoretical simulations, which predicted that grain boundaries can be strong, and earlier experiments, which indicated that they were much weaker than the perfect lattice. Scientists can grow sheets of graphene as large as a television screen by using chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. One of the first applications of graphene may be as a conducting layer in flexible displays. The graphene has a strength of 95 gigapascals. It has 90% of the strength of perfect molecular graphene and is stronger than molecular carbon nanotubes.

The copper-graphene multilayer material with an interplanar distance of 70nm exhibited 500 times greater (1.5GPa) strength than pure copper and nickel-graphene multilayer material with an interplanar distance of 100nm showed 180 times greater (4.0GPa) strength than pure nickel. It was found that there is a clear relationship between the interplanar distance and the strength of the multilayer material. A smaller interplanar distance made dislocation movement more difficult and therefore increased the strength of the material. Professor Han, who led the research effort, commented "the result is astounding as 0.00004% in weight of graphene increased the strength of the materials by hundreds of times" and that "improvements based on this success, especially enabling mass production with roll-to -roll process or metal sintering process, in the production of automobile and spacecraft lightweight, ultra-high strength parts may become possible. "In addition Professor Han mentioned that" the new material can be applied to coating material for nuclear reactor construction or other structural materials requiring high reliability.

Nature Communications - Strengthening effect of single-atomic-layer graphene in metal–graphene nanolayered composites

The US Army Armaments Research, Development and Engineering Center developed a graphene-metal nanomaterial but failed to drastically improve the strength of the material. To maximize the increase in strength imparted by the addition of graphene, the KAIST research team created a layered structure of metal and graphene. Using CVD (Chemical Vapor Deposition) the team grew a single layer of graphene on a metal deposited substrate then deposited another metal layer and repeated the process to produce a metal-graphene multilayer composite material that, achieving a world first in doing so, utilized single layer of graphene. Micro-compression tests within Transmission Electronic Microscope and Molecular Dynamics simulation effectively showed the strength enhancing effect and the dislocation movement on an atomic level. The mechanical characteristics of the graphene layer within the metal-graphene composite material successfully blocked the dislocations and cracks from external damage from traveling inwards. Therefore the composite material displayed strength beyond conventional metal-metal multilayer materials.

ABSTRACT -
Graphene is a single-atomic-layer material with excellent mechanical properties and has the potential to enhance the strength of composites. Its two-dimensional geometry, high intrinsic strength and modulus can effectively constrain dislocation motion, resulting in the significant strengthening of metals. Here we demonstrate a new material design in the form of a nanolayered composite consisting of alternating layers of metal (copper or nickel) and monolayer graphene that has ultra-high strengths of 1.5 and 4.0 GPa for copper–graphene with 70-nm repeat layer spacing and nickel–graphene with 100-nm repeat layer spacing, respectively. The ultra-high strengths of these metal–graphene nanolayered structures indicate the effectiveness of graphene in blocking dislocation propagation across the metal–graphene interface. Ex situ and in situ transmission electron microscopy compression tests and molecular dynamics simulations confirm a build-up of dislocations at the graphene interface.

6 pages of supplemental material.
 

Single layer tin could Conduct Electricity with 100 Percent Efficiency at Room Temperature

November 24, 2013

A single layer of tin atoms could be the world’s first material to conduct electricity with 100 percent efficiency at the temperatures that computer chips operate, according to a team of theoretical physicists led by researchers from the U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University.

Researchers call the new material "stanene," combining the Latin name for tin (stannum) with the suffix used in graphene, another single-layer material whose novel electrical properties hold promise for a wide range of applications.

"Stanene could increase the speed and lower the power needs of future generations of computer chips, if our prediction is confirmed by experiments that are underway in several laboratories around the world," said the team leader, Shoucheng Zhan



For the past decade, Zhang and colleagues have been calculating and predicting the electronic properties of a special class of materials known as topological insulators, which conduct electricity only on their outside edges or surfaces and not through their interiors. When topological insulators are just one atom thick, their edges conduct electricity with 100 percent efficiency. These unusual properties result from complex interactions between the electrons and nuclei of heavy atoms in the materials.

“The magic of topological insulators is that by their very nature, they force electrons to move in defined lanes without any speed limit, like the German autobahn,” Zhang said. “As long as they’re on the freeway – the edges or surfaces – the electrons will travel without resistance.”

In 2006 and 2009, Zhang’s group predicted that mercury telluride and several combinations of bismuth, antimony, selenium and tellurium should be topological insulators, and they were soon proven right in experiments performed by others. But none of those materials is a perfect conductor of electricity at room temperature, limiting their potential for commercial applications.

Earlier this year, visiting scientist Yong Xu, who is now at Tsinghua University in Beijing, collaborated with Zhang’s group to consider the properties of a single layer of pure tin.

“We knew we should be looking at elements in the lower-right portion of the periodic table,” Xu said. “All previous topological insulators have involved the heavy and electron-rich elements located there.”

Their calculations indicated that a single layer of tin would be a topological insulator at and above room temperature, and that adding fluorine atoms to the tin would extend its operating range to at least 100 degrees Celsius (212 degrees Fahrenheit).

Ultimately a Substitute for Silicon?

Zhang said the first application for this stanene-fluorine combination could be in wiring that connects the many sections of a microprocessor, allowing electrons to flow as freely as cars on a highway. Traffic congestion would still occur at on- and off-ramps made of conventional conductors, he said. But stanene wiring should significantly reduce the power consumption and heat production of microprocessors.

Manufacturing challenges include ensuring that only a single layer of tin is deposited and keeping that single layer intact during high-temperature chip-making processes.

“Eventually, we can imagine stanene being used for many more circuit structures, including replacing silicon in the hearts of transistors,” Zhang said. “Someday we might even call this area Tin Valley rather than Silicon Valley.”

Large Graphene Crystals Grown for super fast electronics in relative near term and potential for superstrong materials later

November 14, 2013

Texas researchers used surface oxygen to grow centimeter-size single graphene crystals on copper. The crystals were about 10,000 times as large as the largest crystals from only four years ago. Very large single crystals have exceptional electrical properties.

One of the world’s strongest materials, graphene is flexible and has high electrical and thermal conductivity that makes it a promising material for flexible electronics, solar cells, batteries and high-speed transistors. The team’s understanding of how graphene growth is influenced by differing amounts of surface oxygen is a major step toward improved high-quality graphene films at industrial scale.

The team’s method “is a fundamental breakthrough, which will lead to growth of high-quality and large area graphene film,” said Sanjay Banerjee, who heads the Cockrell School’s South West Academy of Nanoelectronics (SWAN). “By increasing the single-crystal domain sizes, the electronic transport properties will be dramatically improved and lead to new applications in flexible electronics.”

Graphene has always been grown in a polycrystalline form, that is, it is composed of many crystals that are joined together with irregular chemical bonding at the boundaries between crystals (“grain boundaries”), something like a patch-work quilt. Large single-crystal graphene is of great interest because the grain boundaries in polycrystalline material have defects, and eliminating such defects makes for a better material.

“In the long run it might be possible to achieve meter-length single crystals,” Ruoff said. “This has been possible with other materials, such as silicon and quartz. Even a centimeter crystal size — if the grain boundaries are not too defective — is extremely significant."

“We can start to think of this material’s potential use in airplanes and in other structural applications — if it proves to be exceptionally strong at length scales like parts of an airplane wing, and so on,” he said.

Another major finding by the team was that the “carrier mobility” of electrons (how fast the electrons move) in graphene films grown in the presence of surface oxygen is exceptionally high. This is important because the speed at which the charge carriers move is important for many electronic devices — the higher the speed, the faster the device can perform.

Yufeng Hao says he thinks the knowledge gained in this study could prove useful to industry.

“The high quality of the graphene grown by our method will likely be developed further by industry, and that will eventually allow devices to be faster and more efficient,” Hao said.

Single-crystal films can also be used for the evaluation and development of new types of devices that call for a larger scale than could be achieved before, added Colombo.

“At this time, there are no other reported techniques that can provide high quality transferrable films,” Colombo said. “The material we were able to grow will be much more uniform in its properties than a polycrystalline film.”


The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper

The growth of high-quality single crystals of graphene by chemical vapor deposition on copper (Cu) has not always achieved control over domain size and morphology, and the results vary from lab to lab under presumably similar growth conditions. We discovered that oxygen (O) on the Cu surface substantially decreased the graphene nucleation density by passivating Cu surface active sites. Control of surface O enabled repeatable growth of centimeter-scale single-crystal graphene domains. Oxygen also accelerated graphene domain growth and shifted the growth kinetics from edge-attachment–limited to diffusion-limited. Correspondingly, the compact graphene domain shapes became dendritic. The electrical quality of the graphene films was equivalent to that of mechanically exfoliated graphene, in spite of being grown in the presence of O.

24 pages of supplemental material

Koreans say graphene supercapacitors are ready for electric cars

November 14, 2013

Conventional batteries take so long to charge that they cannot efficiently store braking energy. But now graphene supercapacitors that store almost as much but charge in just 16 seconds could do the job instead.

Now Santhakumar Kannappan at the Gwangju Institute of Science and Technology in Korea and a few pals say they have a solution based on the wonder material of the moment–graphene. These guys have built high-performance supercapacitors out of graphene that store almost as much energy as a lithium-ion battery, can charge and discharge in seconds and maintain all this over many tens of thousands of charging cycles.

The trick these guys have perfected is to make a highly porous form of graphene that has a huge internal surface area. They create this graphene by reducing graphene oxide particles with hydrazine in water agitated with ultrasound.

The graphene powder is then packed into a coin-shaped cell, and dried at 140 degrees C and at a pressure of 300/kg/cm for five hours.

Arxiv - Graphene based Supercapacitors with Improved Specific Capacitance and Fast Charging Time at High Current Density

Kannappan and co have measured the performance of their supercapacitor and are clearly impressed with the results. They say it has a specific capacitance of over 150 Farrads per gram can store energy at a density of more than 64 Watt hours per kilogram at a current density of 5 Amps per gram.

That’s almost comparable with lithium-ion batteries which have an energy density of between 100 and 200 Watt hours per kilogram.

Graphene is a promising material for energy storage, especially for high performance supercapacitors. For real time high power applications, it is critical to have high specific capacitance with fast charging time at high current density. Using a modified Hummer's method and tip sonication for graphene synthesis, here we show graphene-based supercapacitors with high stability and significantly-improved electrical double layer capacitance and energy density with fast charging and discharging time at a high current density, due to enhanced ionic electrolyte accessibility in deeper regions. The discharge capacitance and energy density values, 195 Fg-1 and 83.4 Whkg-1, are achieved at a current density of 2.5 Ag-1. The time required to discharge 64.18 Whkg-1 at 5 A/g is around 25 sec. At 7.5 Ag-1 current density, the cell can deliver a specific capacitance of about 137 Fg-1 and maintain 98 % of its initial value after 10,000 cycles, suggesting that the stable performance of supercapacitors at high current rates is suitable for fast charging-discharging applications. We attribute this superior performance to the highly porous nature of graphene prepared with minimum restacking due to crimple nature wrinkles and the improved current collecting method.

Stable three-dimensional metallic carbon with interlocking hexagons

November 06, 2013

Carbon is an amazing material: it not only forms the chemical basis for all known life but also, because of its rich physics and chemistry, displays an array of structures: from the age-old graphite and diamond to more recent C60 fullerene, 1D nanotube, and 2D graphene. One of the unsolved issues in carbon science has been to find a 3D form of carbon that is metallic under ambient conditions. This paper addresses this important challenge. Using state-of-the-art theoretical calculations, we predict the existence of such a phase that is formed from interlocking hexagons and is dynamically, mechanically, and thermally stable. It is suggested that this new form of carbon may be synthesized chemically by using benzene or polyacenes molecules.

“The new metallic carbon structures may have important applications in lightweight metals for space applications, catalysis and in devices showing negative differential resistance or superconductivity,” Wang said.

According to Jena, the team is still early in its discovery process, but hope that these findings may move the work from theory to the experimental phase.

Abstract

Design and synthesis of 3D metallic carbon that is stable under ambient conditions has been a long-standing dream. We predict the existence of such phases, T6- and T14-carbon, consisting of interlocking hexagons. Their dynamic, mechanical, and thermal stabilities are confirmed by carrying out a variety of state-of-the-art theoretical calculations. Unlike the previously studied K4 and the simple cubic high pressure metallic phases, the structures predicted in this work are stable under ambient conditions. Equally important, they may be synthesized chemically by using benzene or polyacenes molecules.

SOURCES - PNAS, Virginia Commonwealth University