Innovative Low-Pressure Diamond Production

For decades, diamond production has required transforming carbon under immense pressures and temperatures, where diamond is stable, or using chemical vapor deposition where it is not. However, Professor Eiichi Nakamura and his team from the Department of Chemistry at the University of Tokyo have chosen a completely different path. They have experimented with a low-pressure technique that relies on electron irradiation directed at a molecule known as adamantane (C10H16).

Starting with Adamantane

Adamantane possesses a carbon structure that mirrors the tetrahedral arrangement of diamond, making it an attractive starting material for creating nanodiamonds. However, to convert adamantane into diamond, scientists must precisely remove hydrogen atoms and replace them with carbon-carbon bonds, arranging the atoms into a three-dimensional diamond lattice. Although this method was theoretically known, Nakamura explained, “The real issue was that no one believed it was possible.”

Real-Time Diamond Formation Monitoring

Previous research using mass spectrometry showed that single-electron ionization could help break C-H bonds, but this method could only infer structures in the gas phase and could not isolate solid products. To overcome this limitation, Nakamura’s team turned to transmission electron microscopy (TEM), a tool capable of imaging materials with atomic precision. They exposed small crystals of adamantane to electron beams with energies of 80-200 kiloelectron volts at temperatures between 100-296 Kelvin in a vacuum for several seconds.

Nanodiamond Formation Under Radiation

This setup allowed the team to observe the nanodiamond formation process directly. In addition to illustrating how electron irradiation drives polymerization and restructuring, the experiment revealed the potential of electron microscopy to study directed reactions in other organic molecules as well.

Under prolonged exposure, the process produced nearly perfect nanodiamonds with a cubic crystal structure and diameters up to 10 nanometers, releasing hydrogen gas. Electron microscope images showed how chains of adamantane molecules gradually transformed into spherical nanodiamonds, with the reaction rate controlled by breaking C-H bonds. Other hydrocarbons failed to produce the same result, highlighting adamantane’s unique suitability for diamond growth.

Opening New Frontiers in Chemical Science

This discovery opens new possibilities for manipulating chemical reactions in fields such as electronic printing, surface science, and microscopy. The researchers also suggest that high-energy irradiation processes may explain how diamonds naturally form in meteorites or uranium-rich rocks. Additionally, the method could support the fabrication of doped quantum dots, essential components for quantum computing and advanced sensors.

Conclusion

This achievement fulfills a 20-year vision. As Nakamura described, “This example of diamond synthesis is the ultimate demonstration that electrons do not destroy organic molecules but allow them to undergo well-defined chemical reactions if we fix the appropriate properties in the molecules to be irradiated.” This accomplishment may reshape how scientists use electron beams, providing a clearer window into the chemical transformations occurring under irradiation.