Electron-beam activation of adamantane C–H bonds into nanodiamonds

Background

• Nanodiamonds are valuable in biomedical imaging, drug delivery, quantum computing, and sensors.

• Conventional synthesis requires extreme conditions:

• High pressure/high temperature (tens of GPa, thousands of K)

• CVD (chemical vapor deposition), but often unstable products.

• Adamantane (a crystalline hydrocarbon from petroleum) has a tetrahedral carbon skeleton very similar to diamond.

Discovery

• Researchers at the University of Tokyo (Eiichi Nakamura’s group) discovered a new bottom-up synthesis by chance.

• By irradiating adamantane crystals with high-energy electrons (80–200 keV) in a vacuum at 100 K, they observed conversion into defect-free nanodiamonds (2–4 nm).

• The process releases hydrogen gas.

• Intermediate stages: adamantane oligomers → spherical nanodiamonds.

Method Highlights

• No catalysts, additives, or support medium needed.

• Operates under ultra-low temperatures instead of extreme pressures/temperatures.

• Produces spherical single-crystalline nanodiamonds with narrow size distribution.

Significance

• First demonstration of direct diamond synthesis from adamantane.

• Potentially a safer, faster, and cheaper alternative to conventional methods.

• Opens new possibilities for electron lithography and nanoscale fabrication:

• Could enable construction of nanodiamond arrays.

• Useful for doped quantum dots in quantum computers and sensors.

Expert Commentary

• Nakamura: “Our synthesis is a true bottom-up assembly of molecules into 3D nanodiamonds.”

• Peter Schreiner (University of Giessen): Adamantane is accessible, and electron irradiation is scalable → strong promise for viable diamond particle synthesis.