Diamond: Hanging by a nanothread

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  • Published: Oct 1, 2014
  • Author: David Bradley
  • Channels: Raman
thumbnail image: Diamond: Hanging by a nanothread

A heart like diamond

Benzene-derived carbon nanothreads Credit: Badding et al/Nature Mater

For the first time, scientists have made ultra-thin 'diamond nanothreads' with a unique structure that could be stiffer and stronger than known polymers and nanotubes. The team used a range of techniques including Raman spectroscopy, X-ray and neutron diffraction, nuclear magnetic resonance spectroscopy, transmission electron microscopy and first-principle calculations to analyse and characterise the materials.

John Badding of Pennsylvania State University, and colleagues Thomas Fitzgibbons, Malcolm Guthrie, En-shi Xu, Vincent Crespi, Stephen Davidowski, George Cody and Nasim Alem, suggest that their finding is important. "From a fundamental science point of view, our discovery is intriguing because the threads we formed have a structure that has never been seen before," Badding says. The core of the nanothreads is a long, thin strand of carbon atoms in the zigzag cyclohexane structure, the unit of a diamond. Badding adds whimsically that, "It is as if an incredible jeweller has strung together the smallest possible diamonds into a long miniature necklace." He adds that, "Because this thread is diamond at heart, we expect that it will prove to be extraordinarily stiff, extraordinarily strong, and extraordinarily useful."

Chemists have spent almost a century hunting for a method that would allow them to spin out a liquid organic, such as benzene, into a compressed, ordered, diamond-like material. All it would take was sufficient pressure and a relatively large drop of liquid. "We used the large high-pressure Paris-Edinburgh device at Oak Ridge National Laboratory to compress a 6-millimetre-amount of benzene," explains co-author Malcolm Guthrie of the Carnegie Institution for Science. "We discovered that slowly releasing the pressure after sufficient compression at normal room temperature gave the carbon atoms the time they needed to react with each other and to link up in a highly ordered chain of single-file carbon tetrahedrons, forming these diamond-core nanothreads."

Under pressure

The work represents the first successful effort to coax organic molecules into such a structure. "Theory by our co-author Vin Crespi suggests that this is potentially the strongest, stiffest material possible, while also being light in weight," Guthrie adds.

"It really is surprising that this kind of organization happens," Badding suggests. "That the atoms of the benzene molecules link themselves together at room temperature to make a thread is shocking to chemists and physicists. Considering earlier experiments, we think that, when the benzene molecule breaks under very high pressure, its atoms want to grab onto something else but they can't move around because the pressure removes all the space between them. This benzene then becomes highly reactive so that, when we release the pressure very slowly, an orderly polymerization reaction happens that forms the diamond-core nanothread."

The team, which included colleagues from Penn State, Oak Ridge, Arizona State University, and the Carnegie Institution for Science, used various techniques to confirm the structures. However, parts of these first diamond nanothreads appear to be less than perfect, the researchers found. Improving the structure is an ongoing part of Badding's research program, as is finding ways to easily generate larger quantities. "The high pressures that we used limit our production capacity to only a couple of cubic millimetres at a time, so we are not yet making enough of it to be useful on an industrial scale," Badding concedes. "One of our goals is to remove that limitation by figuring out the chemistry necessary to make these diamond nanothreads under more practical conditions." An additional aim will be to create functionalised versions of the nanothreads with additional groups replacing the hydrogen atoms that essentially form a sheath around the carbon core.

Functional threads

"You can attach all kinds of other atoms around a core of carbon and hydrogen. The dream is to be able to add other atoms that would be incorporated into the resulting nanothread," says Badding. "By pressurizing whatever liquid we design, we may be able to make an enormous number of different materials."

"We'd like to understand the formation of the nanothreads in much greater detail," Badding added to SpectroscopyNOW. Exactly how do the molecules of benzene come together to form them? We'd also like to see if different nanothreads can be made from molecules that are related to benzene. And finally we'd like to understand the structure of the nanothreads, including their defects, at the level of individual atoms. In the longer term we'd like to see if these materials can be made into bundles that will have high strength and whether nanothreads with interesting electrical properties are possible. Over a long period of time, possibly decades, materials such as these nanothreads may be useful for applications where extreme strength combined with being lightweight is needed."

Related Links

Nature Mater, 2014, online: "Benzene-derived carbon nanothreads"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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