Researchers Find New Phase of Carbon, Make Diamond at Room Temperature

Researchers from North Carolina State University have discovered a new phase of solid carbon, called Q-carbon, which is distinct from the known phases of graphite and diamond. They have also developed a technique for using Q-carbon to make diamond-related structures at room temperature and at ambient atmospheric pressure in air.

Phases are distinct forms of the same material. Graphite is one of the solid phases of carbon; diamond is another.

“We’ve now created a third solid phase of carbon,” says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and lead author of three papers describing the work. “The only place it may be found in the natural world would be possibly in the core of some planets.”

Q-carbon has some unusual characteristics. For one thing, it is ferromagnetic – which other solid forms of carbon are not.

“We didn’t even think that was possible,” Narayan says.

In addition, Q-carbon is harder than diamond, and glows when exposed to even low levels of energy.

“Q-carbon’s strength and low work-function – its willingness to release electrons – make it very promising for developing new electronic display technologies,” Narayan says.

But Q-carbon can also be used to create a variety of single-crystal diamond objects. To understand that, you have to understand the process for creating Q-carbon.

Researchers start with a substrate, such as such as sapphire, glass or a plastic polymer. The substrate is then coated with amorphous carbon – elemental carbon that, unlike graphite or diamond, does not have a regular, well-defined crystalline structure. The carbon is then hit with a single laser pulse lasting approximately 200 nanoseconds. During this pulse, the temperature of the carbon is raised to 4,000 Kelvin (or around 3,727 degrees Celsius) and then rapidly cooled.

This operation takes place at one atmosphere – the same pressure as the surrounding air.

The end result is a film of Q-carbon, and researchers can control the process to make films between 20 nanometers and 500 nanometers thick.

By using different substrates and changing the duration of the laser pulse, the researchers can also control how quickly the carbon cools. By changing the rate of cooling, they are able to create diamond structures within the Q-carbon.

“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,” Narayan says. “These diamond objects have a single-crystalline structure, making them stronger than polycrystalline materials. And it is all done at room temperature and at ambient atmosphere – we’re basically using a laser like the ones used for laser eye surgery. So, not only does this allow us to develop new applications, but the process itself is relatively inexpensive.”

And, if researchers want to convert more of the Q-carbon to diamond, they can simply repeat the laser-pulse/cooling process.

If Q-carbon is harder than diamond, why would someone want to make diamond nanodots instead of Q-carbon ones? Because we still have a lot to learn about this new material.

“We can make Q-carbon films, and we’re learning its properties, but we are still in the early stages of understanding how to manipulate it,” Narayan says. “We know a lot about diamond, so we can make diamond nanodots. We don’t yet know how to make Q-carbon nanodots or microneedles. That’s something we’re working on.”

NC State has filed two provisional patents on the Q-carbon and diamond creation techniques.

North Carolina State University

Not all diamonds are forever

Images taken by Rice University scientists show that some diamonds are not forever.

Rice University researchers see nanodiamonds created in coal fade away in seconds

The Rice researchers behind a new study that explains the creation of nanodiamonds in treated coal also show that some microscopic diamonds only last seconds before fading back into less-structured forms of carbon under the impact of an electron beam.

The research by Rice chemist Ed Billups and his colleagues appears in the American Chemical Society’s Journal of Physical Chemistry Letters.

A series of images shows a small nanodiamond (the dark spot in the lower right corner) reverting to anthracite. Rice University scientists saw nanodiamonds form in hydrogenated coal when hit by the electron beam used in high-resolution transmission electron microscopes. But smaller diamonds like this one degraded with subsequent images. The scale bar is 1 nanometer. Courtesy of the Billups Lab

Billups and Yanqiu Sun, a former postdoctoral researcher in his lab, witnessed the interesting effect while working on ways to chemically reduce carbon from anthracite coal and make it soluble. First they noticed nanodiamonds forming amid the amorphous, hydrogen-infused layers of graphite.

It happened, they discovered, when they took close-ups of the coal with an electron microscope, which fires an electron beam at the point of interest. Unexpectedly, the energy input congealed clusters of hydrogenated carbon atoms, some of which took on the lattice-like structure of nanodiamonds.

“The beam is very powerful,” Billups said. “To knock hydrogen atoms off of something takes a tremendous amount of energy.”

Even without the kind of pressure needed to make macroscale diamonds, the energy knocked loose hydrogen atoms to prompt a chain reaction between layers of graphite in the coal that resulted in diamonds between 2 and 10 nanometers wide.

But the most “nano” of the nanodiamonds were seen to fade away under the power of the electron beam in a succession of images taken over 30 seconds.

“The small diamonds are not stable and they revert to the starting material, the anthracite,” Billups said.

Billups turned to Rice theoretical physicist Boris Yakobson and his colleagues at the Technological Institute for Superhard and Novel Carbon Materials in Moscow to explain what the chemists saw. Yakobson, Pavel Sorokin and Alexander Kvashnin had already come up with a chart – called a phase diagram — that demonstrated how thin diamond films might be made without massive pressure.

They used similar calculations to show how nanodiamonds could form in treated anthracite and subbituminous coal. In this case, the electron microscope’s beam knocks hydrogen atoms loose from carbon layers. Then the dangling bonds compensate by connecting to an adjacent carbon layer, which is prompted to connect to the next layer. The reaction zips the atoms into a matrix characteristic of diamond until pressure forces the process to halt.

Natural, macroscale diamonds require extreme pressures and temperatures to form, but the phase diagram should be reconsidered for nanodiamonds, the researchers said.

“There is a window of stability for diamonds within the range of 19-52 angstroms (tenths of a nanometer), beyond which graphite is more stable,” Billups said. Stable nanodiamonds up to 20 nanometers in size can be formed in hydrogenated anthracite, they found, though the smallest nanodiamonds were unstable under continued electron-beam radiation.

Billups noted subsequent electron-beam experiments with pristine anthracite formed no diamonds, while tests with less-robust infusions of hydrogen led to regions with “onion-like fringes” of graphitic carbon, but no fully formed diamonds. Both experiments lent support to the need for sufficient hydrogen to form nanodiamonds.

Kvashnin is a former visiting student at Rice and a graduate student at the Moscow Institute of Physics and Technology (MIPT). Sorokin holds appointments at MIPT and the National University of Science and Technology, Moscow. Yakobson is Rice’s Karl F. Hasselmann Professor of Mechanical Engineering and Materials Science, a professor of chemistry and a member of the Richard E. Smalley Institute for Nanoscale Science and Technology. Billups is a professor of chemistry at Rice.

The Robert A. Welch Foundation, the Ministry of Education and Science of the Russian Federation and the Russian Foundation for Basic Research supported the research.

http://news.rice.edu/2014/05/22/not-all-diamonds-are-forever-2/#sthash.42KRKrBn.dpuf

Researchers develop new method to control nanoscale diamond sensors

Technique allows tiny sensors to monitor small changes in magnetic fields, such as when neurons transmit electrical signals.

Diamonds may be a girl’s best friend, but they could also one day help us understand how the brain processes information, thanks to a new sensing technique developed at MIT.

A team in MIT’s Quantum Engineering Group has developed a new method to control nanoscale diamond sensors, which are capable of measuring even very weak magnetic fields. The researchers present their work this week in the journal Nature Communications. 

The new control technique allows the tiny sensors to monitor how these magnetic fields change over time, such as when neurons in the brain transmit electrical signals to each other. It could also enable researchers to more precisely measure the magnetic fields produced by novel materials such as the metamaterials used to make superlenses and “invisibility cloaks.”

In 2008 a team of researchers from MIT, Harvard University, and other institutions first revealed that nanoscale defects inside diamonds could be used as magnetic sensors. 

The naturally occurring defects, known as nitrogen-vacancy (N-V) centers, are sensitive to external magnetic fields, much like compasses, says Paola Cappellaro, the Esther and Harold Edgerton Associate Professor of Nuclear Science and Engineering (NSE) at MIT.

Defects inside diamonds are also known as color centers, Cappellaro says, as they give the gemstones a particular hue: “So if you ever see a nice diamond that is blue or pink, the color is due to the fact that there are defects in the diamond.”

The N-V center defect consists of a nitrogen atom in place of a carbon atom and next to a vacancy — or hollow — within the diamond’s lattice structure. Many such defects within a diamond would give the gemstone a pink color, and when illuminated with light they emit a red light, Cappellaro says.

To develop the new method of controlling these sensors, Cappellaro’s team first probed the diamond with green laser light until they detected a red light being emitted, which told them exactly where the defect was located. 

They then applied a microwave field to the nanoscale sensor, to manipulate the electron spin of the N-V center. This alters the intensity of light emitted by the defect, to a degree that depends not only on the microwave field but also on any external magnetic fields present.

To measure external magnetic fields and how they change over time, the researchers targeted the nanoscale sensor with a microwave pulse, which switched the direction of the N-V center’s electron spin, says team member and NSE graduate student Alexandre Cooper. By applying different series of these pulses, acting as filters — each of which switched the direction of the electron spin a different number of times — the team was able to efficiently collect information about the external magnetic field. 

They then applied signal-processing techniques to interpret this information and used it to reconstruct the entire magnetic field. “So we can reconstruct the whole dynamics of this external magnetic field, which gives you more information about the underlying phenomena that is creating the magnetic field itself,” Cappellaro says.

The team used a square of diamond three millimeters in diameter as their sample, but it is possible to use sensors that are only tens of nanometers in size. The diamond sensors can be used at room temperature, and since they consist entirely of carbon, they could be injected into living cells without causing them any harm, Cappellaro says.

One possibility would be to grow neurons on top of the diamond sensor, to allow it to measure the magnetic fields created by the “action potential,” or signal, they produce and then transmit to other nerves.

Previously, researchers have used electrodes inside the brain to “poke” a neuron and measure the electric field produced. However, this is a very invasive technique, Cappellaro says. “You don’t know if the neuron is still behaving as it would have if you hadn’t done anything,” she says. 

Instead, the diamond sensor could measure the magnetic field noninvasively. “We could have an array of these defect centers to probe different locations on the neuron, and then you would know how the signal propagates from one position to another one in time,” Cappellaro says. 

In experiments to demonstrate their sensor, the team used a waveguide as an artificial neuron and applied an external magnetic field. When they placed the diamond sensor on the waveguide, they were able to accurately reconstruct the magnetic field. Mikhail Lukin, a professor of physics at Harvard, says the work demonstrates very nicely the ability to reconstruct time-dependent profiles of weak magnetic fields using a novel magnetic sensor based on quantum manipulation of defects in diamond.   

“Someday techniques demonstrated in this work may enable us to do real-time sensing of brain activity and to learn how they work,” says Lukin, who was not involved in this research. “Potential far-reaching implications may include detection and eventual treatment of brain diseases, although much work remains to be done to show if this actually can be done,” he adds.

Source: http://web.mit.edu/newsoffice/2014/researchers-develop-new-method-to-control-nanoscale-diamond-sensors-0124.html

CWRU makes nanodiamonds in ambient conditions

Microplasma dissociates ethanol vapor, carbon particles
are collected and dispersed in solution, and electron
microscope image reveals nanosized diamond particles.

Opens door for flexible electronics, implants and more

Instead of having to use tons of crushing force and volcanic heat to forge diamonds, researchers at Case Western Reserve University have developed a way to cheaply make nanodiamonds on a lab bench at atmospheric pressure and near room temperature.

The nanodiamonds are formed directly from a gas and require no surface to grow on.
The discovery holds promise for many uses in technology and industry, such as coating plastics with ultrafine diamond powder and making flexible electronics, implants, drug-delivery devices and more products that take advantage of diamond's exceptional properties.

Their investigation is published today in the scientific journal Nature Communications. The findings build on a tradition of diamond research at Case Western Reserve.

Beyond its applications, the discovery may offer some insight into our universe: an explanation of how nanodiamonds seen in space and found in meteorites may be formed.

"This is not a complex process: ethanol vapor at room temperature and pressure is converted to diamond," said Mohan Sankaran, associate professor of chemical engineering at Case Western Reserve and leader of the project. "We flow the gas through a plasma, add hydrogen and out come diamond nanoparticles. We can put this together and make them in almost any lab."

The process for making these small "forever stones" won't melt plastic so it is well suited for certain high-tech applications. Diamond, renowned for being hard, has excellent optical properties and the highest velocity of sound and thermal conductivity of any material.
Unlike the other form of carbon, graphite, diamond is a semiconductor, similar to silicon, which is the dominant material in the electronics industry, and gallium arsenide, which is used in lasers and other optical devices.

While the process is simple, finding the right concentrations and flows—what the researchers call the "sweet spot"—took time.

The other researchers involved were postdoctoral researcher Ajay Kumar, PhD student Pin Ann Lin, and undergraduate student Albert Xue, of Case Western Reserve; and physics professor Yoke Khin Yap and graduate student Boyi Hao, of Michigan Technical University.

Sankaran and John Angus, professor emeritus of chemical engineering, came up with the idea of growing nanodiamonds with no heat or pressure about eight years ago. Angus' research in the 1960s and 1970s led him and others to devise a way to grow diamond films at low pressure and high temperature, a process known as chemical vapor deposition that is now used to make coatings on computer disks and razor blades. Sankaran's specialty, meanwhile, is making nanoparticles using cool microplasmas.

It usually requires high pressures and high temperatures to convert graphite to diamond or a combination of hydrogen gas and a heated substrate to grow diamond rather than graphite.
"But at the nanoscale, surface energy makes diamond more stable than graphite," Sankaran explained. "We thought if we could nucleate carbon clusters in the gas phase that were less than 5 nanometers, they would be diamond instead of graphite even at normal pressure and temperature."

After several ups and downs with the effort, the process came together when Kumar joined Sankaran's lab. The engineers produced diamond much like they'd produce carbon soot.
They first create a plasma, which is a state of matter similar to a gas but a portion is becoming charged, or ionized. A spark is an example of a plasma, but it's hot and uncontrollable.

To get to cooler and safer temperatures, they ionized argon gas as it was pumped out of a tube a hair-width in diameter, creating a microplasma. They pumped ethanol—the source of carbon—through the microplasma, where, similar to burning a fuel, carbon breaks free from other molecules in the gas, and yields particles of 2 to 3 nanometers, small enough that they turn into diamond.

In less than a microsecond, they add hydrogen. The element removes carbon that hasn't turned to diamond while simultaneously stabilizing the diamond particle surface.
The diamond formed is not the large perfect crystals used to make jewelry, but is a powder of diamond particles. Sankaran and Kumar are now consistently making high-quality diamonds averaging 2 nanometers in diameter.

The researchers spent about a year of testing to verify they were producing diamonds and that the process could be replicated, Kumar said. The team did different tests themselves and brought in Yap's lab to analyze the nanoparticles by Raman spectroscopy.
Currently, nanodiamonds are made by detonating an explosive in a reactor vessel to provide heat and pressure. The diamond particles must then be removed and purified from contaminating elements massed around them. The process is quick and cheap but the nanodiamonds aggregate and are of varying size and purity.

The new research offers promising implications. Nanodiamonds, for instance, are being tested to carry drugs to tumors. Because diamond is not recognized as an invader by the immune system, it does not evoke resistance, the main reason why chemotherapy fails.

Sankaran said his nanodiamonds may offer an alternative to diamonds made by detonation methods because they are purer and smaller.

The group's process produces three kinds of diamonds: about half are cubic, the same structure as gem diamonds, a small percentage are a form suspected of having hydrogen trapped inside and about half are lonsdaleite, a hexagonal form found in interstellar dust but rarely found on Earth.

A recent paper in the journal Physical Review Letters suggests that when interstellar dust collides, such high pressure is involved that the graphitic carbon turns into londsdaleite nanodiamonds.

Sankaran and Kumar contend that an alternative with no high pressure requirement, such as their method, should be considered, too.

"Maybe we're making diamond in the way diamond is sometimes made in outer space," Sankaran proposed. "Ethanol and plasmas exist in outer space, and our nanodiamonds are similar in size and structure to those found in space."

The group is now investigating whether it can fine-tune the process to control which form of diamond is made, analyzing the structures and determining if each has different properties. Lonsdaleite, for instance, is harder than cubic diamond.

The researchers have made a kind of nanodiamond spray paint. "We can do this in a single step, by spraying the nanodiamonds as they are produced out of the plasma and purified with hydrogen, to coat a surface," Kumar said.

And they are working on scaling up the process for industrial use.

"Will they be able to scale up? That's always a crap shoot," Angus said. "But I think it can be done, and at very high rates and cheaply. Ultimately, it may take some years to get there, but there is no theoretical reason it can't be done."

If the scaled-up process is as simple and cheap as the lab process, industry will find many applications for the product, Sankaran said.

Source: http://www.eurekalert.org/pub_releases/2013-10/cwru-cmn101813.php

New Form of Carbon is Stronger Than Graphene and Diamond

Chemists have calculated that chains of double or triple-bonded carbon atoms, known as carbyne, should be stronger and stiffer than any known material.

The sixth element, carbon, has given us an amazing abundance of extraordinary materials. Once there was simply carbon, graphite and diamond. But in recent years chemists have added buckyballs, nanotubes and any number of exotic shapes created out of graphene, the molecular equivalent of chickenwire.

So it’s hard to believe that carbon has any more surprises up its sleeve. And yet today, Mingjie Liu and pals at Rice University in Houston calculate the properties of another form of carbon that is stronger, stiffer and more exotic than anything chemists have seen before.

The new material is called carbyne. It is a chain of carbon atoms that are linked either by alternate triple and single bonds or by consecutive double bonds.

Carbyne is something of a mystery. Astronomers believe they have detected its signature in interstellar space but chemists have been bickering for decades over whether they had ever created this stuff on Earth. A couple of years ago, however, they synthesised carbyne chains up to 44 atoms long in solution.

The thinking until now has been that carbyne must be extremely unstable. In fact some chemists have calculates that two strands of carbyne coming into contact would react explosively.

Nevertheless, nanotechnologists have been fascinated with potential of this material because it ought to be both strong and stiff and therefore useful. But exactly how strong and how stiff, no one has been quite sure.

This is where Liu and co step in. These guys have calculated from first principles the bulk properties of carbyne and the results make for interesting reading. 

  

For a start, they say that carbyne is about twice as stiff as the stiffest known materials today. Carbon nanotubes and grapheme, for example, have a stiffness of 4.5 x 10^8 N.m/kg but carbyne tops them with a stiffness of around 10^9 N.m/kg. 

Just as impressive is the new material’s strength. Liu and co calculate that it takes around 10 nanoNewtons to break a single strand of carbyne. “This force translates into a specific strength of 6.0–7.5×10^7 N∙m/kg, again significantly outperforming every known material including graphene (4.7–5.5×10^7 N∙m/ kg), carbon nanotubes (4.3–5.0×10^7 N∙m/ kg), and diamond (2.5–6.5×10”7 N∙m/kg4),” they say.

Carbyne has other interesting properties too. Its flexibility is somewhere between that of a typical polymer and double-stranded DNA. And when twisted, it can either rotate freely or become torsionally stiff depending on the chemical group attached to its end.

Perhaps most interesting is the Rice team’s calculation of carbyne’s stability. They agree that two chains in contact can react but there is an activation barrier that prevents this happening readily. “This barrier suggests the viability of carbyne in condensed phase at room temperature on the order of days,” they conclude.

All this should whet the appetite of nanotechnologists hoping to design ever more exotic nanomachines, such as nanoelectronic and spintronic devices. Given the advances being made in manufacturing this stuff, we may not have long to wait before somebody begins exploiting the extraordinary mechanical properties of carbyne chains for real.

Ref: arxiv.org/abs/1308.2258 : Carbyne From First Principles: Chain Of C Atoms, A Nanorod Or A Nanorope?

http://www.technologyreview.com/view/518301/new-form-of-carbon-is-stronger-than-graphene-and-diamond/