Diamonds grown without extreme pressures
Tiny crystals grown within molten metals at atmospheric pressure
24 Apr 20245:35 PM ETByRobert F. Service
Synthetic diamonds are usually grown at crushing pressures. A new recipe works at ambient pressures.Jim Lambert/Alamy
"Diamonds, the hardest material, may have gotten easier to make. Researchers today report a new way to grow synthetic diamonds without the crushing pressures normally required. Although the approach yields crystals no bigger than 100 nanometers across—about the size of a typical virus—researchers suspect it may eventually yield larger crystals and the extended diamond films that are prized for advanced electronics and optics.
“The technique is quite interesting,” says John Ciraldo, who specializes in diamond growth at WD Advanced Materials. “If they could make larger single crystals that would be fantastic,” says Stephen Goodnick, an electrical engineer at Arizona State University who specializes in creating electronic devices on top of diamond films.
Diamond is a form of pure carbon, in which carbon atoms bond tightly to one another in a pyramidal arrangement. The result is extreme hardness and radiation resistance, as well as the ability to conduct heat and electricity at unmatched rates. Diamonds are used in quantum computers and magnetic sensors, high-power electric devices, radiation detectors, and lasers.
Natural diamonds form in Earth’s mantle, hundreds of kilometers below the surface, under intense pressures and temperatures. Engineers have long been able to make synthetic diamonds by reproducing these conditions. Today, the most common approach crushes carbon molecules at nearly 60,000 times atmospheric pressure at up to 1600°C, requiring expensive equipment.
Years ago, Rodney Ruoff, a materials scientist at the Institute for Basic Science in South Korea, started to notice clues that the extreme conditions might not be essential. In 2017, for example, researchers in Japan reported that when they exposed liquid gallium to methane gas, carbon atoms in the methane dissolved within the molten metal and bonded into solid, sheetlike layers of graphene, another form of pure carbon. “We thought that if we could find the right conditions, it might lead to diamond,” Ruoff says. “So, we said let’s have a go and give it a try.”
He and his colleagues initially placed flecks of diamond on shards of a silicon wafer and added droplets of molten gallium and other liquid metals, then exposed the mix to methane or other carbon-containing gases. Their hope, he says, was that carbon from the gases would diffuse into the gallium and bond to the diamond seeds, assembling into larger crystals. Initially, the silicon wafer, which was topped by a thick layer of silicon dioxide, seemed to prevent diamond growth. But in one experiment, a blob of liquid gallium flowed over the edge of the wafer, dissolving some of the exposed pure silicon. When they later looked within the hardened metal, they found a collection of tiny diamond crystals.
As Ruoff’s team reports today in Nature, the researchers refined the recipe using a small crucible containing a mix of liquid gallium, iron, nickel, and silicon heated to 1025°C and exposed to methane and hydrogen gases. No seed crystal or added pressure was required. The metals dissolve the carbon gas, and the silicon appears to somehow help the carbon atoms bond to one another in diamond’s pyramidal arrangement. “If we don’t add some silicon we don’t get diamond,” Ruoff says.
For future applications, the biggest question now is how far the technique can be pushed. Ruoff’s team has already used it to make diamond films composed of thousands of tiny crystals packed cheek by jowl. Ciraldo notes that such films can already be made at low pressure by a mature technique called chemical vapor deposition, but it requires more expensive semiconductor fabrication equipment. The multitude of crystals can also degrade the performance of electronics made from the films. Ruoff’s hopes the technique can eventually produce thin films consisting of a single layer of pure diamond.
In the meantime, Ruoff predicts, ... "
https://www.science.org/content/article ... -pressures
