New model helps define optimaltemperature and pressure to forgenanoscale diamonds15 October 2018

To forge nanodiamonds, which have potentialapplications in medicine, optoelectronics and quantumcomputing, researchers expose organic explosivemolecules to powerful detonations in a controlledenvironment. These explosive forces, however, make itdifficult to study the nanodiamond formation process. Toovercome this hurdle, researchers recently developed aprocedure and a computer model that can simulate thehighly variable conditions of explosions on phenomenallyshort time scales. They report their work in The Journalof Chemical Physics. This image shows a carbonaceousnanoparticle (left) and its pure carbon core (right). Blue:carbon atoms. Red: oxygen atoms. White: diamondseed. Yellow: pure carbon network surrounding thediamond seed Credit: X. Bidault and N. Pineau

Nanodiamonds, bits of crystalline carbon hundredsof thousands of times smaller than a grain of sand,have intriguing surface and chemical propertieswith potential applications in medicine,optoelectronics and quantum computing. To forgethese nanoscopic gemstones, researchers exposeorganic explosive molecules to powerfuldetonations in a controlled environment. Theseexplosive forces, however, make it difficult to studythe nanodiamond formation process, even underlaboratory conditions.

To overcome this hurdle, a pair of Frenchresearchers recently developed a procedure and acomputer model that can simulate the highlyvariable conditions of explosions on phenomenallyshort time scales. The team reports their work in The Journal of Chemical Physics.

"Understanding the processes that formnanodiamonds is essential to control or even tunetheir properties, making them much better suited forspecific purposes," said Xavier Bidault, aresearcher at CEA DAM Ile-de-France, and a co-author on the paper.

Bidault and his co-author Nicolas Pineau used atype of simulation known as Reactive MolecularDynamics, which simulates the time evolution ofcomplex, chemically reactive systems down to theatomic level.

"The atomic-level interaction model is essential toreally understand what's happening," said Pineau."It gives us an intimate way to analyze, step-by-step, how carbon-rich compounds can formnanodiamonds in a high-pressure, high-temperature system."

Due to the extreme and fleetingly brief conditions ofa detonation, actual experimental investigation isimpractical, so researchers must rely on atomic-level simulations that show how and where thischemistry occurs.

The new results reveal that a delicate balance oftemperature and pressure evolution is necessaryfor nanodiamonds to form at all. If the initialdetonation pressure is too low, carbon solids areable to form, but not diamonds. If the pressure istoo high, the carbon "seeds" of nanodiamondsbecome polluted by other elements, such asoxygen or nitrogen, which prevent the transition to

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diamond.

Scientists have known for more than 50 years thatnanodiamonds form from detonations, but theatomic-level details of their formation have been anopen question for at least the last two decades. Themost common industrial route for their synthesis isthe detonation of carbon-rich organic highexplosives. Nanodiamonds can also form naturallyfrom explosive volcanic eruptions or asteroidimpacts on Earth.

"Our work shows that the right path seems to be ahigh initial pressure followed by a sharp pressuredecrease," said Bidault. If the precise conditionsare met, nanodiamonds form. These complexpressure paths are typical of detonation processes.

More information: X. Bidault et al, Dynamicformation of nanodiamond precursors from thedecomposition of carbon suboxide (C3O2) underextreme conditions—A ReaxFF study, The Journalof Chemical Physics (2018). DOI:10.1063/1.5028456

Provided by American Institute of PhysicsAPA citation: New model helps define optimal temperature and pressure to forge nanoscale diamonds(2018, October 15) retrieved 16 October 2018 from https://phys.org/news/2018-10-optimal-temperature-pressure-forge-nanoscale.html

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