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

Electrified Diamonds: Basel Physicists on the Trail of Quantum Information

With the help of tiny diamond crystals, physicists at the University of Basel have discovered new possibilities of quantum information: The scientists discovered at specific circumstances electric currents that made it possible to identify defects in the carbon lattice of single diamonds measuring only a few nanometers. 

The results have been published online in the magazine «Nano-Letters».

The team from the University of Basel and the French German Research Institute St. Louis (ISL) investigated diamond crystals of the size of only five nanometers (five millionths millimeter) using scanning tunneling microscopy and atomic force microscopy. 

The physicists then identified the atomic structure of the surface and observed crystalline, hexagonal carbon facets as well as graphitic reconstructions. In doing so, they discovered extra currents at specific voltages when the crystals were illuminated by green light.

These extra currents are related to the presence of defects in the carbon lattice of diamonds, so called Nitrogen-vacancy centers (NV-centers) that are optically active. These centers are promising candidates for future applications in quantum information processing systems, spin-magnetometry sensors or single photon sources. 

Their identification in the range of less than ten nanometers would have been very difficult with conventional methods, which is why the scientists applied a combination of different methods.

«With this study, we are able to show that it is possible to prove, with high resolution, the presence of optical centers in single nanodiamonds», says Prof. Ernst Meyer of the Department of Physics at the University of Basel. In the future, NV-centers could be used in quantum computers that work much more efficiently than conventional computers.

Source: http://www.unibas.ch/index.cfm?uuid=6AA790579D2002EF40FD481B016171E9&type=search&show_long=1

Flawed Diamonds: Gems for New Technology

Using ultra-fast laser pulses, a team of researchers led by UA assistant professor Vanessa Huxter has made the first detailed observation of how energy travels through diamonds containing nitrogen-vacancy centers – promising candidates for a variety of technological advances such as quantum computing.

A team of researchers led by University of Arizona assistant professor Vanessa Huxter has made the first detailed observation of how energy travels through diamonds that contain nitrogen-vacancy centers – defects in which two adjacent carbon atoms in the diamond's crystal structure are replaced by a single nitrogen atom and an empty gap.

 

These "flaws" result in unexpected and attractive properties that have put such diamonds in the spotlight as promising candidates for a variety of technological advances.

 

The findings, published online in Nature Physics, could help scientists better understand the properties of these diamonds, which have potential applications ranging from quantum computing to the imaging of individual atoms in molecules. 

 

Defect centers are locations in the otherwise repetitive lattice of carbon atoms where other elements have taken the spot of carbon atoms. Such defects create, for example, canary diamonds in which nitrogen atoms have replaced carbon atoms. In the case of a nitrogen vacancy, a nitrogen atom sits next to an empty slot where a carbon atom is missing. 

 

"Some of these defects have interesting optical and electronic properties," said Huxter, who recently joined the UA's Department of Chemistry and Biochemistry and led the research during a postdoctoral fellowship funded by the Natural Sciences and Engineering Research Council of Canada. Huxter did the research with co-authors Graham Fleming and Dmitry Budker at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and the University of California, Berkeley.

 

Huxter said because the nitrogen-vacancy defects can be manipulated with optical methods such as lasers, they could be used for computing, data storage, sensing and even advanced imaging techniques capable of revealing the structure of molecules. 

 

"In order to use this system for these applications, we have to understand its fundamental properties," said Huxter, whose team is the first to study the ultrafast dynamics in these crystals in real time. "To use these systems for quantum computing, you want to have to some idea of what we call vibrational modes, because they determine the local environment and may possibly be used for information processing." 

 

To understand what that means, one has to picture the crystal structure of a diamond: a three-dimensional lattice of carbon atoms forming a highly ordered and repetitive structure. But the atoms are not glued into place. Rather, they vibrate back and forth as if connected by tiny springs. Wherever a nitrogen-vacancy defect interrupts the uniform carbon lattice, the vibrational properties change in ways that can be manipulated, for example by laser pulses. 

 

"We use laser light to see what is happening in the system," Huxter said. "When we hit these things with ultrafast pulses, it's like hitting them with a hammer. We put a lot of energy into the system, and watch as that energy flows through it."

 

The laser pulse knocks the electrons in the nitrogen-vacancy centers into a higher level of energy, which physicists call the excited state. Over time, the electrons fall back into their ground state, in a process called relaxation, while dissipating the energy into their surroundings. 

 

To watch how vibrations influence the ultrafast relaxation of the system, Huxter's team used ultrafast laser pulses, because the relaxation occurs on a time scale of a few nanoseconds – billionths of a second.

 

Exactly how that energy moves through the crystal and how it influences the vibrations around the nitrogen-vacancy centers is crucial to figuring out how to take advantage of its properties, but nobody had ever been able to observe this process before. 

 

"This is the first time we have been able to directly observe the vibrational spectrum of the system in real time," Huxter said. 

 

With her team, she employed two-dimensional electronic spectroscopy, basically a way of creating two-dimensional correlation "maps" that allow the researchers to watch the system as it relaxes to the ground state. 

 

"Think of it as ultra-high-speed photography to freeze the action on a scale of atoms and molecules," Huxter said. "We can watch the energy flow through the system in real time, and take snapshots along the way. We can see where the energy is going in and where it is coming out."

 

In the world of ultrafast spectroscopy, which is reminiscent of the first high-speed photography developed by Edward Muybridge in the early 20th century to freeze the action of galloping horses, "nanoseconds are like a million years," Huxter said, thanks to laser pulses lasting only femtoseconds. A femtosecond is one millionth of one billionth of a second. "In our experiments we were able to observe vibrations local to the defect with femtosecond time resolution. Being able to directly follow these vibrations led to some surprising new results including that these vibrations are quantum mechanically coherent for thousands of femtoseconds."

 

"The question we ask is, what happens when you start replacing the atoms in the crystal?" Huxter explained. "Will you get a change in the elastic properties? Each nitrogen-vacancy center is like a softer region you can poke at. They absorb the laser energy where there was previously no absorption and we see all these extra vibrational modes we don't see in the rest of the crystal."

 

"In our scenario, the diamond is like a clear window. We look straight through it and only see the defects. We tailor our laser pulse to the absorption of the defects."

Source: http://uanews.org/story/flawed-diamonds-gems-for-new-technology

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/