02-Nov-2020 - Rice University

Scientists find path to nanodiamond from graphene

A spot of pressure enables chemical conversion to hardened 2D material

Marrying two layers of graphene is an easy route to the blissful formation of nanoscale diamond, but sometimes thicker is better.

While it may only take a bit of heat to turn a treated bilayer of the ultrathin material into a cubic lattice of diamane, a bit of pressure in just the right place can convert few-layer graphene as well.

The otherwise chemically driven process is theoretically possible according to scientists at Rice University, who published their most recent thoughts on making high-quality diamane -- the 2D form of diamond -- in the journal Small.

The research led by materials theorist Boris Yakobson and his colleagues at Rice's Brown School of Engineering suggests a pinpoint of pressure on few-layer graphene, the atom-thin form of carbon known for its astonishing strength, can nucleate a surface chemical reaction with hydrogen or fluorine.

From there, the diamondlike lattice should propagate throughout the material as atoms of hydrogen or fluorine alight on the top and bottom and covalently bind to the surfaces, prompting carbon-carbon connections between the layers.

The pressure applied to that one spot -- as small as a few nanometers - is entirely unnecessary for a bilayer but is needed and must be progressively stronger for thicker films, Yakobson said. Making synthetic diamond from bulk graphite at industrial scale requires about 10-15 gigapascals, or 725,000 pounds per square inch, of pressure.

"Only at the nanoscale -- in this case, at nanometer thickness -- does it becomes possible for the surface chemistry alone to change the thermodynamics of the crystal, shifting the phase-change point from very high pressure to practically no pressure," he said.

Single-crystal diamond film for electronics is highly desirable. The material could be used as a hardened insulator or as a heat transducer for cooling nanoelectronics. It could be doped to serve as a wide band gap semiconductor in transistors, or as an element in optical applications.

Yakobson and his colleagues developed a phase diagram in 2014 to show how diamane might be thermodynamically feasible. There's still no easy way to make it, but the new work adds a critical component the earlier research lacked: a way to overcome the energetic barrier to nucleation that keeps the reaction in check.

"So far only bilayer graphene has been reproducibly converted into diamane, but through sheer chemistry," Yakobson said. "Combining it with a pinch of local pressure and the mechanochemistry it triggers seems like a promising path to be tried."

"In thicker films, the barrier rises quickly with the number of layers," added co-author and former Rice postdoctoral associate Pavel Sorokin. "External pressure can reduce this barrier, but chemistry and pressure must play together to deliver a 2D diamond."

Facts, background information, dossiers
  • diamonds
More about Rice University
  • News

    Flash graphene rocks strategy for plastic waste

    Plastic waste comes back in black as pristine graphene, thanks to ACDC. That's what Rice University scientists call the process they employed to make efficient use of waste plastic that would otherwise add to the planet's environmental woes. In this instance, the lab of Rice chemist James T ... more

    Shape matters for light-activated nanocatalysts

    Points matter when designing nanoparticles that drive important chemical reactions using the power of light. Researchers at Rice University's Laboratory for Nanophotonics (LANP) have long known that a nanoparticle's shape affects how it interacts with light, and their latest study shows how ... more

    Boron nitride destroys PFAS 'forever' chemicals PFOA, GenX

    Rice University chemical engineers found an efficient catalyst for destroying PFAS "forever" chemicals where they least expected. "It was the control," said Rice Professor Michael Wong, referring to the part of a scientific experiment where researchers don't expect surprises. The control gr ... more