Oct 29, 2020 |
Researchers find path to nanodiamond from graphene
(Nanowerk News) Marrying two layers of graphene is an easy route to the blissful formation of nanoscale diamond, but sometimes thicker is better.
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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.
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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 ("Nano-Thermodynamics of Chemically Induced Graphene–Diamond Transformation").
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Researchers have expanded their theory on converting graphene into 2D diamond, or diamane. They have determined that a pinpoint of pressure can trigger connections between layers of graphene, rearranging the lattice into cubic diamond. (Illustration: Pavel Sorokin)
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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.
Rice University researchers have expanded their theory on converting graphene into 2D diamond, or diamane. They have determined that a pinpoint of pressure can trigger connections between layers of graphene, rearranging the lattice into cubic diamond. (Credit: Illustration by Pavel Sorokin)
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Rice University researchers have expanded their theory on converting graphene into 2D diamond, or diamane. They have determined that a pinpoint of pressure can trigger connections between layers of graphene, rearranging the lattice into cubic diamond. Illustration by Pavel Sorokin
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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.
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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.
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“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.
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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.
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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.
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“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.”
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“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.”
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