HexSeed have announced their £600k raise just a few months after finishing Cohort 9 of the Carbon13 Venture Builder. HexSeed are ready to disrupt with a carbon to diamond thermal coating solution that will accelerate data centre cooling. The depth of expertise across the team is striking: Mark Tandy brings 20+ years in energy, the last five in carbon capture, utilisation, and storage; Dr. Leonardo Santoni holds a PhD in chemistry from UCL specialising in crystal growth and metal deposition; and Michael Glerum, PhD holds a PhD in engineering from Cambridge, after which he built and ran a pilot plant for advanced carbon nanotube manufacturing. With a $91 billion market opportunity, a low capex model, and a plan to eventually integrate directly into existing fabrication lines, hear all about HexSeed’s road to scale below.
Carbon13’s investment in HexSeed came from our Carbon13 SEIS Fund IX earlier this year. Our tenth SEIS Fund is open now for this tax year (2026-2027). If you would like to explore investing in high potential climatetech startups across energy, AI, super materials, food systems, and more, then view our upcoming events and fund info at investors.carbonthirteen.com.
Sara: Hi everybody, and today we have a very interesting Carbon13 startup joining us, which is HexSeed Technology. Can you tell us, in a nutshell, what does HexSeed do?
Mark: One of the things you can do with captured carbon dioxide is use it as a raw material to produce diamond, and one thing you can do with diamond is coat semiconductor power devices. We’ve also got an interesting team amongst us that’s got all the skills we hope will bring this to market.
The team
Sara: Tell us a little bit more about that. Why is your team so qualified to do this?
Mark: My background is in carbon capture, utilization, and storage, I’ve been working in that space for about five years. Leo has a PhD from UCL in chemistry, and Michael has a PhD from Cambridge University in engineering.
Leo: I’m the chemist of the group. I did my PhD in chemistry at UCL in London, working on precursor design for metal deposition and single crystal growth. Then I did a bit of postdoc and decided to pivot completely into the startup world. As soon as I heard about diamonds, I was super excited to grow them on semiconductors.
Michael: I have a PhD in engineering from the University of Cambridge. After my PhD I built a pilot plant in the northwest of England focusing on another advanced carbon material, carbon nanotubes. My role was very much in industry, building reactors, designing them, and a lot of the chemistry around them. We exited that startup, and then I met Mark and Leo during the Carbon13 venture. Mark came to me with this idea of doing something with CO2, and diamonds was a suggestion.
technological breakthrough
Sara: What’s the technological breakthrough with HexSeed that means you’re going to out-compete the alternatives?
Leo: As we said, we’re using diamonds to transfer heat away from the active parts of the semiconductors. Why diamond? Because it has the highest thermal conductivity of any bulk material. It’s been the right answer for years, but very few people have made a practical use of that in semiconductors. Our solution enables us to grow the diamonds at low temperatures and coat the device directly.
Sara: Is it fair to call this a high-capex startup? What’s the first milestone you’ve been able to tick off?
Mark: Not wishing to contradict you, but it’s not actually a capital-intensive process the way we intend to do it. We have three steps in our process:
- The first is proving the technology, that’s what we’re set up to do over the next 12 months, a proof of concept.
- Then we’re looking at a pilot project, which is relatively low capital, lower than you might expect.
- Once we’ve got the defensive moat around the technology, we’d look to license it to fabrication or semiconductor fabricators or OSATs.
£600k raise
Sara: Got it. And you’ve also raised your first round?
Mark: After Carbon13’s investment, the Net Zero Technology Centre also made a small investment in HexSeed, and we’ve recently closed with Vento Ventures as well. That cumulatively takes us to a sum which matches the Innovate UK grant we were awarded on a conditional basis earlier in the year. So, we’ve now got just over £600,000 in the bank, which gives us about 12-plus months of runway to take us through proof of concept and hopefully our first patent application.
Sara: If we zoom out to the next 10 to 20 years, what does success look like at scale for HexSeed?
Michael: Success at scale really means our diamond deposition method becomes an industry gold standard, a way of depositing diamond across all the power semiconductors being used right now. We’re specifically focusing on the gallium nitride market at the moment, because that’s set to grow to around $91 billion with the advancements required for AI data centers. Our real global goal would be to become an industry standard, partnering with tier-one manufacturers and OSATs, and enabling us to spread across multiple countries and devices without needing such high capital investment upfront.
the opportunity
Sara: You’ve mentioned this market’s going to $91 billion, can you tell us a bit more about why 2026 is the right time for your venture?
Michael: What’s happened recently is this rapid rise in compute, and it looks like it’s going to stick around for a number of years, in fact, it looks like we’re going to need even more of it. This is really where the timing comes in for diamond specifically, and specifically for cooling. As people try to extract more from their data centers, power density massively increases, which is why they’re moving away from traditional silicon-based chips to gallium nitride.
This creates a unique, critical thermal bottleneck when they’re operating, which is why cooling techniques, diamond being one of them, are such a vital component. It also means you can put in more power, giving the customer a higher yield for their end user, while also addressing some climate challenges.
Sara: That makes sense. When you were talking to investors for that raise, what was the one takeaway you wanted them to have after meeting with you about HexSeed?
Mark: The one thing we had to overcome with investors was that when they heard the word “diamond,” they assumed straight away this was an expensive solution, because you’re coating something in diamond, so that must be a lot of diamond. What they needed to understand was how little diamond we’re using. It’s a diamond-like structure that we coat using a layer that’s nanometre-thick, several times thinner than a human hair, which is hard to envisage.
But because it’s that thin over a full 300mm wafer, you’re still talking about less than a carat of diamond to coat the whole thing. So, the uplift in price on a single device is in pennies, and these are expensive devices we’re talking about. We wanted them to understand, one, it wasn’t capital intensive, and two, it wasn’t a big uplift in price on the actual device that would ultimately be incorporated into the power systems.