Editor’s Note
This article explores the development of ‘Obelix,’ a plasma reactor at Germany’s Fraunhofer Institute, which is pioneering a method to grow synthetic diamonds layer by layer. The process could significantly impact the traditional diamond industry.
The machine that could one day shake the diamond world stands like a gigantic silver egg in a basement laboratory in northern Freiburg. “Obelix” is ready for the next layer. Almost two meters tall, the largest of eight plasma reactors at the Fraunhofer Institute for Applied Solid State Physics (IAF) towers upwards. At the push of a button, engineer Nicola Lang has ignited a plasma from hydrogen and methane gases inside Obelix’s belly. Through a viewing window in the aluminum casing of the microwave oven, she can observe the greenish-blue gas cloud glowing.
Exactly there, something magical is happening: layer by layer, within hours, a material that looks like colorless glass grows on a substrate. But it is a flawless, single-crystal diamond. Pure carbon in its super-compact lattice structure. When polished, it begins to sparkle in an inimitable way.
Moreover, Obelix is efficient; the silver colossus from Freiburg is designed for mass production. Recently, Lang and her team set a record with the machine:
The stones grown this way are just about the size of square confetti. But they are strikingly pure and have a quality that could be attractive to jewelers. That would be a lucrative market. More than 70 billion euros were spent worldwide on diamond jewelry last year.
Christoph Nebel waves it off. “Jewelry diamonds are a nice side aspect of our research,” says the head of the Semiconductor Sensors department at IAF. For the 59-year-old, diamond is a fascinating material.
If the carbon atom lattice is doped with additional elements, the diamond also gains excellent electronic properties. It is therefore considered a semiconductor material with a bright future. The Freiburg diamonds are intended for use particularly in power electronics, for example in components for satellite communication and in lenses for high-energy lasers.
It has only one flaw:
Nebel and his team want to change that. The Fraunhofer researchers have been working for years to turn diamond from a rare treasure into a mass-produced commodity. They want to apply the material onto thin slices. Such wafers, from which components are then manufactured, are the ultimate base format of the semiconductor industry.
Diamond as an alternative to silicon and iridium.
For about 60 years, researchers have succeeded in producing diamonds in the laboratory. In 1954, the American company General Electric presented its first synthetic diamonds to the world, created using the High-Pressure High-Temperature (HPHT) method. It mimics the conditions that prevail during the random formation of crystals deep in the Earth’s mantle. Graphite – that form of carbon found in pencil leads – is packed together with a catalyst like iron or nickel and a seed diamond into a metal vessel. The capsule is treated at 1500 degrees Celsius in a hydraulic press with pressures equivalent to 50,000 times the air pressure on the Earth’s surface. After about a week under high pressure, the layered carbon atoms in the graphite tetrahedrally bond together to form diamond. Tiny crystals form, often contaminated with inclusions and nitrogen, which is why they shimmer yellowish.
Such diamond powder is primarily used in tools for drilling, grinding, and cutting. The crumbs are not suitable for the jewelry industry. However, some companies have managed in the last 15 years to refine the elaborate process so that they can grow colorless or colored stones weighing several carats. Recently, the company “New Diamond Technologies” presented a cut synthetic diamond of ten carats. The record chunk grew in April in one of the 50 giant diamond presses the company operates in a factory hall in St. Petersburg. But the energy costs are so enormous that they call the profitability of such business models into question.
Diamond producers are therefore increasingly relying on a second manufacturing method, the coating technique also researched by the Fraunhofer team: Chemical Vapour Deposition (CVD). In this process, a diamond substrate is placed in a microwave oven, and a gas mixture of traces of methane and abundant hydrogen is pumped in. The microwaves create a hot plasma ball, causing the methane to lose a hydrogen atom. The residual molecule with one carbon atom essentially rains down from the plasma cloud onto the substrate and deposits in a diamond-like manner. Sometimes, graphite forms alongside diamond. It is etched away by the aggressive molecular hydrogen. Layer by layer, about one micrometer per hour, ultra-pure diamond grows almost autonomously.
