Inside a lab in South Korea, a rainbow-colored glint caught the eye of a graduate student. This gleam is the product of something extraordinary: diamonds, born not from the crushing pressures deep within Earth, but from a pool of liquid metal at atmospheric pressure. These new synthetic diamonds could change how we make one of the world’s hardest and most coveted materials.
Breaking the Diamond Mold
Natural diamonds are forged in the Earth’s upper mantle, where temperatures soar at 900–1400°C and pressures reach 5–6 gigapascals—thousands of times greater than the pressure at sea level. Since the 1950s, scientists have replicated these conditions in the lab using high-pressure, high-temperature (HPHT) methods to create synthetic diamonds.
But now, a team led by Rodney Ruoff at the Institute for Basic Science in Ulsan, South Korea, has shattered this paradigm, growing diamonds at just 1 atmosphere of pressure (sea level pressure) and 1,025 °C using a liquid metal alloy.
The journey to this breakthrough began with a 2017 study that showed liquid gallium could catalyze the production of graphene from methane at low temperatures inside a custom-built vacuum system. Intrigued, Ruoff’s team wondered if gallium could also facilitate diamond growth. Their experiments initially involved seeding diamonds on silicon-doped gallium, but the results were inconsistent.
Then, during one experiment, graduate student Yan Gong noticed tiny pyramids forming on the edge of a diamond crystal. “That led us to understand that silicon was somehow important,” Ruoff recalls. But adding more silicon only produced silicon carbide, not diamonds.
Undeterred, the scientists shifted their approach, experimenting with a liquid metal alloy composed of gallium, iron, nickel, and silicon. After hundreds of parameter adjustments, they struck gold — or rather, diamond. Gong recalls the moment vividly: “One day, I noticed a ‘rainbow pattern’ spread over a few millimeters on the bottom surface of the solidified liquid metal. We found out that the rainbow colors were due to diamonds!”
The Science Behind the Sparkle
The team’s liquid metal method involves exposing the alloy to a mixture of methane and hydrogen at 1,025°C. Carbon from the methane diffuses into the liquid metal, where it accumulates in a thin, amorphous subsurface layer. This layer, rich in carbon and silicon, serves as the birthplace for diamond nucleation.
“Approximately 27 percent of atoms at the top surface of this amorphous region were carbon atoms,” says co-author Myeonggi Choe. High-resolution imaging revealed that diamonds nucleate and grow in this layer, eventually merging to form a continuous film.
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The process began with small, isolated diamond crystals appearing after just 15 minutes of growth. Over time, these crystals grew larger and merged into continuous films. By 150 minutes, the researchers had produced a nearly complete diamond film, with only a few gaps remaining.
Theoretical calculations suggest that silicon stabilizes small carbon clusters, which act as “pre-nuclei” for diamond formation. Without silicon, no diamonds grew, suggesting that it helps catalyze the formation of diamond crystals.
Implications and Questions
The implications may be important. For one, it could make diamond synthesis more accessible and affordable. Traditional HPHT methods require expensive equipment and consume vast amounts of energy. The new method, by contrast, operates at room pressure and lower temperatures, potentially reducing costs and energy consumption. Diamonds have exceptional thermal conductivity, hardness, and electronic properties. These qualities make them ideal for use in high-power electronics, quantum computing, and even medical devices.
But many questions remain. Why does this specific combination of metals work? How stable are these diamonds? And can the process be refined to produce larger, purer diamonds? Ruoff is optimistic. “There are numerous intriguing avenues to explore,” he says.
The findings appeared in the journal Nature.
