Lasers turn plastic into intact nanodiamonds in a lab

Each laser shot in the German experiment produced about 10 trillion nanodiamonds. At a station of the Extreme Light Infrastructure (ELI) south of Prague, a laser fires three times per minute at a plastic film only 100 micrometers thick. Each pulse sends a shock wave through the film, compresses the plastic to pressures around 100 gigapascals, or roughly 14.5 million pounds per square inch, and forms diamonds that are flung toward a collection cylinder. The work comes from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Rostock, and it began with experiments that imitate conditions inside Neptune and Uranus, where temperatures reach several thousand degrees Celsius. The team could at first detect the crystals only briefly. Dominik Kraus of HZDR's HEDI Institute said the team expected nanodiamonds to form, but that the speed surprised them.

The real obstacle was the landing. When the compression wave leaves the sample and enters the vacuum, it accelerates the diamonds past 22,000 mph (10 kilometers per second), a speed comparable to a meteorite impact. The solution was a very soft medium: a water-soluble ionic gel that works in a vacuum. The gel caught the particles, and the team could then wash them out and examine them. At the University of Rostock, an ELMI-MV electron microscope, which can resolve individual atoms, confirmed their size and structure. Ben Heuser of HZDR, the study's primary author, called seeing the purified diamonds directly "a special moment we had been working towards for years." The output is still small: a few hundred micrograms took roughly 100 shots.

The interest lies in what the method changes. Smaller diamonds offer more surface area for a given amount of material, which the researchers believe could make them better catalysts, for example in splitting CO2 with sunlight. Starting from plastic also makes it easier to add other elements to the crystal, tailoring it for specific jobs such as improving contrast agents used in MRI scans. The researchers also point to the diamonds' use in quantum sensors. Those applications remain at the stage of proposals; the study itself reports a laboratory result.

The researchers aim to reach the milligram range, a quantity comparable to conventional production, and they say that more energy-efficient lasers from fusion research could fire powerful pulses more often and make the process scalable. No date for commercial output is given. The team also intends to use the same laser compression to make BC8, a form of carbon that so far exists only in theory and is expected to be denser than diamond, similarly hard and less brittle. Forming it requires conditions that do not occur naturally on Earth, so the first attempt, at higher pressures, is planned for November. The study was first published in Diamond and Related Materials.