How big can a diamond theoretically get?

Augsburg start-up grows the largest synthetic diamond in the world

Augsburg scientists have succeeded in producing the largest synthetic diamond in the world. It weighs 155 carats and is 92 mm in diameter. How did they do it?

Unprocessed diamonds from Botswana with inclusions: Natural diamonds can take billions of years to grow.

Photo: M. Gress / VU Amsterdam

Success didn't come overnight: 25 years of research have gone into the world's largest artificial diamond.

Superior to the Great Star of Africa in terms of area

The Augsburg diamond does not look like a real piece of jewelery: This is mainly due to the fact that the artificial diamond is a disc. The crystal structure, however, is identical to that of a natural diamond. Natural and artificial diamonds can only be distinguished from one another by the characteristic atomic defects that both have.

The Cullinan I from the scepter of the crown jewels of the British Queen in direct comparison with the Augsburg single crystal.

Source: University of Augsburg / IfP / EP IV

And so Dr. Matthias Schreck, head of the diamond working group at the Augsburg Chair for Experimental Physics IV, also fails to mention in one breath the Augsburg single crystals with the largest diamond ever found, Cullinan I, also known as the Great Star of Africa. “With its weight of 532 carats, the Cullinan I is still a long way ahead of us, and it will probably stay that way for longer. But we have already clearly beaten him in terms of area! "

Diamond is created layer by layer

Growing synthetic diamonds itself only took a few days. Compared to nature, which takes millions of years to transform graphite into diamond under massive pressure and high temperatures, that is impressively fast. For this purpose, the Augsburg laboratories work with chemical vapor deposition at a negative pressure of a few tenths of an atmosphere.

Under certain process conditions, hydrocarbon molecules from the gas phase are then deposited on the surface, allowing diamonds to grow layer by layer. "When we had set up our first system and the manufacturing company came into operation, the first process already delivered a comprehensive layer of perfectly acceptable diamond crystallites," reports Schreck, who has headed the diamond working group since its inception.

“Unfortunately,” says Schreck, “at that time the individual grains did not yet fit together at their borders, and so it was not possible to obtain a single crystal covering the entire area.” Now, two and a half decades later, the researchers are happy to present the world's largest artificial diamond to be able to.

Diamond grows on an iridium substrate

"It was fascinating to open the reactor after several days of growth under a plasma discharge of several thousand degrees and hold the first large-area samples in my hands," says Dr. Stefan Gsell, who together with Dr. Martin Fischer has been driving the work that has now led to the decisive breakthrough for over ten years.

Dr. Matthias Schreck, Dr. Martin Fischer and Dr. Stefan Gsell (from left) with her monocrystalline diamond disc. The shades of gray result predominantly from the nucleation layer that has not yet been removed.

Source: University of Augsburg / IfP / EP IV

After removing the growth base, which consists of the precious metal iridium, the quality of the cultured diamonds was also assessed in terms of their transparency and perfection: “When we had produced a transparent sample without cracks for the first time and the scales had a value of over 20 g , in other words over 100 carats, for the sample, the fascination was of course even greater, ”says Fischer.

AuDiaTec: application in various fields of technology

The Augsburg researchers are convinced of the economic benefits of their development. They jointly founded Augsburg Diamond Technology GmbH in November 2015. As managing directors of the startup, Fischer and Gsell continue to drive technological development and see many possible uses.

These range from cutting tools for the production of reflective surfaces of workpieces and optical components to detectors at large particle research facilities such as the European nuclear research center Cern in Geneva. Only recently, two Augsburg crystals were installed in the accelerator ring for measurements.

The Augsburg discs could also contribute to the success of the energy transition. "Ever since I started working at the University of Augsburg, I have been constantly hearing in the diamond community that diamond is the ultimate material for high-performance electronics, such as those required for setting up modern power grids," notes Schreck. He thinks that too.

Diamonds can do all of this

Diamonds can do more than just decorate: Researchers at Harvard University have built the smallest radio in the world out of pink diamonds. The radio receiver is only two atoms in size, but works like a normal, analog radio. In theory, you could even take the diamond radio with you into space.

The little pink dot in the picture is a diamond. It serves as a housing for the radio receiver, which is only two atoms in size.

Source: Eliza Grinnell / Harvard School of Engineering and Applied Sciences

And British researchers have developed an artificial diamond that, thanks to radioactive radiation, produces electricity for several thousand years. The researchers use British nuclear waste for their super battery. The battery diamonds would be ideal for devices such as pacemakers and satellites that require power for a long time.

Also worth mentioning is the success of the British geologist Dan Frost, who put a serving of peanut butter under so much pressure that it actually turned into diamonds.

 

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