How to produce lab-grown diamonds, the ultimate material for high-tech applications
At LakeDiamond, we grow diamonds with unparalleled degrees of purity. In this article we reveal some of our manufacturing secrets.
The advantages of lab-grown diamonds
Lab-grown diamonds used to be for industrial applications of little added value. However, with the recent considerable progress in techniques for growing diamonds, its exceptional properties have gradually gathered interest in a number of high-tech markets. The gems are grown using a meticulous process that only very few companies are capable of conducting.
Ultrapure lab-grown diamonds can leverage specific properties for high-tech applications such as thermal resistance, electrical conductivity, hardness, transparency, and stability.
The top-of-the-line purity it achieves creates opportunities in the technologies of the future, where diamonds could replace silicon in electronic devices, power new generations of lasers for aerospace, charge batteries remotely, or be used in biosensors for biomedical analysis. Here we describe how diamonds are formed for these different types of applications.
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Imitating the earth: the high pressure, high temperature (HPHT) technique
Once merely the object of a science fiction novel by Jules Vernes, man-made diamonds were first created in the 1950s. The approach was to copy what happens in the Earth’s mantle.
At depths of around 150 to 200 km, carbon is subjected to an extremely high pressure of up to 60,000 times the air pressure and temperatures that far exceed 1,000°C. In these extreme conditions, the bonds between carbon atoms change and are arranged into a cubic structure, which forms a diamond. Thus the diamonds formed then take millions of years to reach the Earth’s surface.
Back in those days, scientists were able to recreate the pressure and temperature conditions using a press that would squeeze a carbon source, graphite, inside a chamber; this would then be heated at a high temperature.
This technique — high pressure, high temperature, or HPHT — is still the most common method used today. HPHT diamonds are used for cutting tools — 95% of their application — or jewellery.
However, diamonds grown with this process lack the purity needed for use in high-tech industries, primarily due to the nitrogen or metal atoms that replace the carbon atoms and alter the diamond’s properties.
Capturing plasma energy: the Chemical Vapour Deposition (CVD) technique
A second technique developed in the 1980s offered more control over manufacturing conditions and therefore impurities: CVD, for Chemical Vapour Deposition. This method harnesses the fourth state of matter, plasma; This provides the energy needed to form a diamond.
Plasma is an environment that combines high-energy electrons and ions, found in lightning or the aurora borealis. An electromagnetic field, similar to the power generated by a microwave oven, is used to form plasma.
Then, in the presence of methane gas as a carbon source, the plasma grows the diamond.
However, a diamond seed is needed to initiate the reaction and allow the diamond to grow, layer by layer, atom by atom.
With a diamond substrate as fine as a hair, and at growth speeds of about 10 micrometres per hour, a cube 5 mm thick — i.e., about a carat — can be grown in three weeks.
The quest for purity
At LakeDiamond, founded on the campus of École Polytechnique Fédérale de Lausanne (EPFL), we are specialised in growing customised diamond using the CVD process in a laboratory.
Our secret for creating almost 100% pure diamonds is to tightly control growth conditions.
First, there is the rivalry between the two forms of carbon: graphite and diamond. They co-exist in certain pressure and temperature conditions.
“It’s by controlling these conditions that we can remove graphite properly,” says Mehdi Naamoun, Director of Diamond Development Operations at LakeDiamond. Plus, CVD also makes it possible to control the composition of plasma.
The purity of the gases used is, of course, crucial but that’s not all. A vacuum chamber is also needed to completely remove all impurities, such as nitrogen.
“At LakeDiamond, the minimisation of all traces of nitrogen was integrated into the basic design of our process. To do that, we produce our own reactors, and every machine is built to serve the end product. That is how we achieve growing some of the world’s purest diamonds,” Mr Naamoun says.
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