Dented Diamonds, Carbon Cages and Exceptional Potential

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Image courtesy of Carnegie Institute of Washington

Simulated structures showing the starting material of carbon-60 "buckyballs" (magenta) and m-xylene solvent (blue) before being compressed.

How do you dent a diamond? It's tough since diamond is among the Earth's hardest stuff. But researchers supported by the Department of Energy's Office of Science recently created a new substance that can do so. Along the way, they developed a new process that could eventually lead to a variety of new materials with many different applications.

Diamonds gleam as if they've been shaped from glass, but in reality, they're formed from the element carbon. Carbon forms the backbone of plants, pencil lead (graphite) and even petroleum products. In fact, the oft-feared organic chemistry is simply the study of carbon and its chemical doings. And carbon is the material with which researchers at the Carnegie Institution of Washington's Center for Energy Frontier Research in Extreme Environments (EFree) started.

EFree is one of 46 Energy Frontier Research Centers, set up to bring the talents of leading scientists to accelerate research with the goal of meeting the nation's critical energy challenges. The team—which included researchers from SLAC National Accelerator Laboratory—actually conducted its work at Argonne National Lab through the High Pressure Collaborative Access Team that operates a beamline on the Advanced Photon Source, which provides the brightest storage ring-generated hard X-rays in the Western Hemisphere.

To make the new material, the researchers started with 'buckyballs,' soccer-ball shaped cages composed of sixty carbons. They then added in a liquid, a solvent called xylene (m-xylene for the organic chemists out there), which like the buckyballs, is also composed of carbon. The molecules in the liquid "link" the buckyballs together in a regular, crystalline pattern like beads on a string. Finally, they squeezed.

The cages refused to crack under the normal, or even the extraordinary pressures applied by the experiment's diamond anvil. But something extraordinary happened around 320,000 times atmospheric pressure. (That's roughly 4.7 million pounds per square inch. By comparison, the pressure at the bottom of the Marianas Trench, the deepest point in the Pacific Ocean is a 'mere' 16,000 pounds per square inch.) At that pressure the buckyballs collapsed and formed disordered, amorphous clusters that were held together by the xylene molecules. The resulting hybrid material had both extraordinary and interesting properties.

The material was extraordinarily hard, strong enough to dent a diamond anvil. It also had an unusual, never-before-seen structure of disordered, amorphous clusters (the collapsed buckyballs) were in an ordered, crystalline array (held together by xylene molecules). What's more, the material stayed in the same shape after the pressure was released, which makes it potentially useful for a variety of different devices, especially future electronics.

That's because carbon-based structures are becoming increasingly important to electronics. For instance, researchers at Argonne Lab recently devised a way to use diamond films to improve the performance of electronic devices (see Springtime and Sparkling Films). Other Office of Science-supported researchers are working with graphene, which consists of flat sheets of carbon but is stronger than steel and conducts electricity better than copper (see Graphene: Amazing Material Found Thanks to Scotch Tape and Persistent Science), and has potential use in a host of applications.

Moreover, xylene is only one of many carbon solvents that could potentially be used in future experiments. Tweaking the mixture might result in the making other new materials with novel or needed properties. That's the Office of Science at work: Elemental science in national service, diamond-denting materials with extraordinary possibilities.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about Argonne Lab, please go to http://www.anl.gov/.

Charles Rousseaux is a Senior Writer in the Office of Science.