Hitting the right spot
The ability to harness the NV centre properties hinges on making diamonds in which the nitrogen vacancy lies just beneath the surface of the crystal – essentially because efficient magnetic coupling depends on intimate contact between sensor and sample material. This is an area the team is working on at the moment.
“Our aim is to control all the properties of the nitrogen vacancy, including the position inside the diamond and the orientation,” says Debuisschert. “We need to control all of those properties in order to produce devices that can be used for different applications.”
One technique for getting the nitrogen atom in just the right spot is known as ion implantation. This involves shining a beam of ions containing nitrogen at the diamond crystal, which is typically 4mm square and just half a millimetre thick. “We can achieve nitrogen implantations a few nanometres below the surface by controlling the amount of energy of the incoming ions,” explains Debuisschert. Another way to trap nitrogen atoms is to add them while the diamond is still being grown. The stones being used by the DIADEMS team are synthetic and they’re grown using a process known as chemical vapour deposition, which uses a high-temperature gas containing carbon to create the diamond. “By adding nitrogen to this gas, we can create a layer of nitrogen at a controlled position below the surface,” says Debuisschert. “This technique is quite new and is something our research activity is focusing on.”