Ellen Phiddian
Cosmos science journalist
Scientists have fused a diamond to a sapphire. And to silicon, lithium, and a few other materials.
This chemically difficult feat isn’t for jewellery – instead, it could be part of next-generation quantum technology.
The researchers have published their achievement in Nature Communications.
Diamond is made from carbon atoms arranged in a highly regular crystalline structure. This makes it very hard, very inert, and perfect for a number of quantum and electronic applications.
But diamond is also homoepitaxial – it only grows on other diamonds. This makes it much less useful.
“Diamond stands alone in terms of its material properties,” says senior author Assistant Professor Alex High, a researcher at the University of Chicago, USA.
It’s coveted in electronics because it has very high electrical resistance, but it conducts heat very well. It’s popular among quantum scientists, meanwhile, because of tiny defects called nitrogen vacancy centres which are ideal for hosting quantum systems.
“But as a platform, it’s actually pretty terrible,” says High.
High and colleagues have found a way to bond synthetic diamonds to other materials.
“We make a surface treatment to the diamond and carrier substrates that makes them very attractive to each other. And by ensuring we have a pristine surface roughness, the two very flat surfaces will be bonded together,” explains first author Dr Xinghan Guo, a recent PhD graduate from the University of Chicago.
“An annealing process enhances the bond and makes it really strong.
“That’s why our diamond can survive various nanofabrication processes. It differentiates our process from simple placement of diamond on top of another material.”
The treatment involves rendering carbon atoms on the surface of the diamond slightly loose, attracted to other atoms it can bond with.
“You can almost think of it as like a sticky surface, because it wants to be attached to something else,” says co-author Avery Linder, an engineering student at the University of Chicago.
“And so basically, what we’ve done is create sticky surfaces and put them together.”
The result is a diamond membrane, as small as 10 nanometres thick, neatly bonded to another substance. The researchers have made it work with silicon, fused silica, sapphire, thermal oxide, and lithium niobate.
“This new technique has the potential to greatly influence the ways we do quantum and even phone or computer manufacturing,” says Linder. The team has patented the process and is now commercialising it.
