Not just a pretty face: lab-grown diamonds in engineering

Diamond’s abilities are all down to its structure. It is pure carbon, a lattice of carbon atoms in a neat tetrahedral arrangement, where one central atom is joined to four others by strong covalent bonds.

This super-strong structure puts diamond high on the medal table for many properties – it’s the hardest material, the stiffest, and has the highest thermal conductivity because of those closely packed atoms. It is such a good conductor of heat that you can easily cut through ice with a blunt, half-millimetre-thick wafer of diamond, as the heat from your fingers would go straight through the diamond and melt the ice.

We’ve long exploited its unbeatable hardness in engineering, to cut, grind, polish, and drill. But now we know how to build diamonds atom by atom, there’s no need to wait millions of years for the Earth to cook them up. Now it’s possible to deposit super thin layers of diamond onto other materials, and control their composition in minute detail. This means we can access all manner of tremendous capabilities we simply can’t get with regular diamonds.

As we get better at manipulating the material’s properties, we’re finding new applications for the material in areas as diverse as communication, navigation and public health. By making a profusion of energy-hungry electronic devices run more efficiently, it may also have a big role to play in a net zero world.

So, diamonds have the potential to make us healthier, our devices greener and our world cleaner. The fact that they can do all of these things comes down to how they’re made.

How to make a diamond

Natural diamonds form about 150 kilometres beneath the Earth’s surface, at temperatures way over 1,000°C and under extreme pressure. Later, the diamonds are delivered to the surface, to places where we can find them, by volcanic eruptions. For diamonds mined today, these volcanic eruptions would have happened in ancient times.

Once we’d worked out – in the late 18th century – that diamond is simply another form of carbon, making our own in the lab was just a case of simulating the pressure and temperature required, though this would be hugely challenging. “The pressure you need to grow a diamond is the equivalent of taking the Eiffel Tower and putting it upside down on a Coke can,” says Oliver Williams, chair of the condensed matter and photonics group at Cardiff University. “It’s difficult.”

Only in the 1950s did we crack it. Teams in Sweden and the US simulated the extreme conditions needed to force carbon atoms into the regular lattice of a diamond, with the appropriately named ‘high-pressure high‑temperature’ (HPHT) process. Back then, the HPHT process couldn’t produce diamonds that were big or pretty enough to be made into jewellery, and so instead, the resulting material was put to work for industrial uses such as cutting and grinding.

By the 1980s, researchers had developed another method called chemical vapour deposition (CVD), which works at lower pressures and produces a material whose properties we can more easily control.

In CVD, hydrogen and methane are heated in a chamber with microwaves up to 10 times more powerful than your microwave oven at home, until they form a plasma. The excess of atomic hydrogen, which “eats everything” but the diamond, Williams says, both prevents the formation of graphite and acts as a catalyst for the formation of diamond.

Under these conditions, the four hydrogen atoms are stripped from the methane, leaving a single carbon atom. The carbon atoms then bond to an existing bit of diamond, called a “seed”, layer by layer. Single diamonds can be made this way, which can go on to become jewellery, as can wafers, which can become electronic components. We can also coat electronic components in a thin layer of diamond using this process.

We said before that diamond is pure carbon, and in an ideal world, it would be. But because of how they’re formed, all natural diamonds contain some impurities. These impurities are responsible for a stone’s colour – for example, the Hope Diamond’s violet hue is due to the odd boron atom in its structure. Early HPHT diamonds often contained nitrogen, boron or transition metals from the catalysts used. 

Not so for CVD: because we can better control what’s in the CVD chamber, there are fewer impurities. “The advantage of this method is that you can grow diamond that is a million times purer than nature,” says Williams. “That’s where these new applications come from. We can start to exploit the really extreme properties of diamond.”

Tailoring diamond’s properties

With CVD, researchers can also add elements to diamond if they so wish. In its purest form, diamond can’t conduct electricity – there are no free electrons in that stiff lattice. But we can change that by adding certain atoms to its structure, a process physicists call ‘doping’. 

Doping diamond with boron atoms – which can be done by adding a boron-containing gas to the mix in the CVD reactor – makes the diamond a semiconductor. While an emerging area of research, diamond semiconductors won’t be replacing silicon ones any time soon, in no small part because the doping process is so difficult to control. However, we can also use these unique properties in electrochemical electrodes to treat waste water and clean swimming pool filters, though we’ve recently found another use for them – destroying PFAS (polyfluoroalkyl substances).

Element Six specialises in making pure synthetic diamond for industry and research. It recently partnered with a company called Lummus Technology to develop devices to eliminate PFAS from water supplies. 

The bonds between carbon and fluorine atoms in PFAS are what put the “forever” in these so-called “forever chemicals”. They’re extremely tough – it would take more than 1,000 years for them to break down – though with boron-doped electrodes, it’s possible to break these bonds more easily.

Channelling PFAS-contaminated water between electrodes made of boron-doped diamond splits the carbon-fluorine bonds in the material, explains Bruce Bolliger, head of business development, North America, at Element Six. “Boron-doped diamond electrodes are more effective than other electrodes,” he explains, as they can operate at very high current densities, are inert and thus less prone to fouling, and last “a very long time”.

Diamond is also poised to play a role in making silicon-based semiconductors more efficient. Here, it’s diamond’s unbeatable thermal conductivity – five times greater than copper – that comes into play, particularly for compound semiconductors. Because they can handle more power than pure silicon ones, they’re ideal for applications such as solar panels, spacecraft and electric cars. The problem is, they get a lot hotter.

“There’s a big push to upgrade everything with compound semiconductors, but then you need to thermally manage them. And diamond is the greatest thermal conductor there is,” says Williams. Williams established the Cardiff Diamond Foundry, a part of Cardiff University’s physics department that tries to solve “real problems” with diamond, including making electronic components more efficient.

When we push high currents through electrical components, they heat up, making them less efficient. These inefficiencies add up, meaning a lot of wasted energy.

Coating electrical components with a thin layer of diamond just 50 to 200 micrometres thick means that the heat is rapidly channelled away. This process, known as thermal management, is important for devices that run on high voltages, such as those in cars and planes. Better thermal management of semiconductors can improve performance and reduce costs for applications such as longer distance satellite communication, explains Bolliger.

This ability to cool devices more rapidly will also be important for running the data centres we rely on for 5G and AI more efficiently – especially with US data centres projected to consume up to 12% of the country’s total electricity by 2028. Bolliger says thermal management could significantly reduce the power required by AI and high-performance computing devices at data centres.

Quantum sensing – detecting the tiniest signals

Sometimes a nitrogen atom and an empty space replace two carbon atoms in a diamond lattice, in what’s called a nitrogen vacancy. Thanks to the properties of the nearby electrons, certain types of nitrogen vacancies have their own quantum spin, and act like tiny bar magnets.

Magnetic fields change the spin state of these little “bar magnets”, which we can detect by shining a light on them. The strength of the light that comes back depends on the spin state, which means we can use it to measure things with devices known as quantum detectors.

The nitrogen vacancies in natural diamonds are distributed in such a way that makes them unviable as quantum detectors – as these little “bar magnets” interfere with each other, they can’t hold their spin state for long enough to make a measurement. However, researchers can deliberately introduce a smaller number of these vacancies to the structure with CVD, to unlock the material’s quantum properties.

Quantum detectors apply the same principle as MRI (which relies on the inherent spin of hydrogen atoms), but on a smaller scale. They can detect magnetic field changes with thousands of times more sensitivity, and on a cellular scale, opening up a new world of diagnostic science. Such sensors could detect tiny changes in the brain’s magnetic field, letting us spot early indicators of Alzheimer’s disease, for example, before symptoms develop.

Cardiovascular diseases, too, could be diagnosed earlier. “You could pick up very weak signals, magnetic signals from the heart that [classical detectors, such as ECGs] just can’t detect,” says Melissa Mather, professor of diamond quantum sensing and engineering at the University of Nottingham. Researchers in Mather’s lab are exploring quantum sensing for healthcare, food security, defence, green chemistry, and materials science. They’re designing devices that can be used and maintained by nonspecialists, with a view to finding more applications for the technology.

Launched in December 2024, Q-BIOMED is a research hub led by UCL, the University of Cambridge and the University of Oxford, seeking to improve diagnosis and treatment of disease with quantum technology. The hub is developing super-sensitive lateral flow tests (LFTs) that, by integrating nanodiamonds (diamond nanoparticles), can help diagnose cancer and infectious diseases, including COVID-19, In fact, according to a preprint paper by the research team published earlier this year, spin-enhanced LFTs could let us diagnose COVID-19 two days earlier than conventional ones, which could reduce transmissions and infections.

Shine on

What can we expect from diamond science in the near future? The quantum properties that make diamond an excellent detector of magnetic fields make it perfectly suited to mapping the Earth in fine detail by measuring variation in the planet’s magnetic field. This means we can navigate accurately without the need for satellites, which can fail or be inaccessible.

Mather is working with biologists to better understand the electron transport chain in cells using diamond quantum sensors. The electron transport chain is a process that happens within mitochondria, the part of the cell that produces energy. Dysfunctional mitochondria have been linked to diseases including Parkinson’s, heart disease and cancer. Quantum sensing can help us better understand the electron transport chain, and why things go wrong.

“With quantum sensing, we can start to sense the electrons as they move,” she says. “It opens the world to a window onto things that have been right in front of us, but previously unseen.” Her team is investigating the impact of too few or too many free radicals on this process, and how to treat problems when they occur. She says this may be able to help us understand the origin of some mitochondrial diseases, which affect about 1 in 5,000 people in the UK, and help us develop new types of treatments for them.

Mather suggests that with diamond quantum sensors, we can start to probe the quantum goings-on in our bodies and other biological systems. “While phenomena like entanglement, electron tunnelling, and coherence are thought to occur in biological building blocks, we need better tools to fully detect and measure them in a living system,” she says.

“We’re starting to open a new window on how the quantum world impacts biology, and we need more quantum sensors that can function directly within a biological system to really understand what’s happening.”

Wiliams describes the UK as “dominant” in diamond research, and with the UK government committing £2.5 billion to quantum technologies up to 2033, we should see even more exciting innovations coming to fruition in the years to come. It appears that solutions to some of the biggest problems we face as a society will come from the realm of the very small.