Researchers at the University of Tokyo have developed a method to form nanodiamonds from organic molecules using electron beams, bypassing traditional high-pressure and high-temperature processes. This breakthrough protects delicate materials from beam damage and could advance fields like materials science and quantum computing. The discovery challenges long-held assumptions about electron irradiation.
A team led by Professor Eiichi Nakamura at the University of Tokyo's Department of Chemistry has pioneered a low-pressure technique to produce artificial nanodiamonds. By exposing adamantane molecules (C10H16), which feature a carbon framework similar to diamond's tetrahedral structure, to controlled electron beams, the researchers transformed the material into flawless nanodiamonds.
The process involves transmission electron microscopy (TEM) imaging, where tiny adamantane crystals are irradiated with 80-200 kiloelectron volts at temperatures between 100-296 kelvins in a vacuum for several seconds. This setup allows real-time observation of the reaction, as electron beams break C-H bonds and form C-C links, polymerizing the molecules into a three-dimensional diamond lattice. The resulting nanodiamonds exhibit a cubic crystal structure and reach diameters up to 10 nanometers, with hydrogen gas released as a byproduct.
Nakamura, who has pursued this research since 2004, noted the skepticism surrounding the approach: "The real problem was that no one thought it feasible." Earlier studies using mass spectrometry suggested single-electron ionization could aid bond breaking, but they were limited to gas-phase inferences. The TEM method overcomes this by enabling atomic-resolution visualization and isolating solid products.
"Computational data gives you 'virtual' reaction paths, but I wanted to see it with my eyes," Nakamura said, fulfilling a 20-year vision. He emphasized, "This example of diamond synthesis is the ultimate demonstration that electrons do not destroy organic molecules but let them undergo well-defined chemical reactions, if we install suitable properties in molecules to be irradiated."
The discovery, detailed in the journal Science (2025; 389 (6764): 1024, DOI: 10.1126/science.adw2025) by authors Jiarui Fu, Takayuki Nakamuro, and Eiichi Nakamura, highlights adamantane's unique suitability, as other hydrocarbons did not yield similar results. Potential applications include electron lithography, surface science, microscopy improvements, and fabricating doped quantum dots for quantum computing and sensors. It may also shed light on natural diamond formation in meteorites or uranium-rich rocks through high-energy irradiation.