The designs of synthetic diamonds grown in a lab have been further improved and they could soon be used in biosensing applications like magnetic brain imaging.

To synthetically create large sheets of diamonds for industrial applications requires chemical processes. The diamonds can be grown on many surfaces. Where they are grown affects the hardness of the gem, the wear of tools and the ability to harness their high thermal conductivity as a heat sink for electronics. Scientists have been able to manipulate these properties by altering the chemical composition of diamond, called doping. ‘Doped’ diamonds are a cheap alternative material in many technologies that are normally expensive to create.

(a) Schematic illustration of the nin diamond junction in the xy-plane and in the (b) z-plane. (c) Optical microscopy image of the nin diamond. (d) Scanning confocal microscopy images of the mesa structures of d = 2 μm and (e) d = 10 μm. (Source: Applied Physics Letters)

Diamonds created with nitrogen-vacancy (NV) centers have the ability to detect a change in magnetic fields. They are a powerful tool for biosensing technologies and medical detection, and diagnosis of diseases, like magnetoencephalography (MEG) which is used to map brain activity and trace abnormalities in the brain.

"MEG is commercially available and used in some hospitals but is very expensive so not many MEGs are used," said Norikazu Mizuochi, an author on the paper. Diamonds with NV centers could reduce those equipment costs.

These biosensing technologies need light activation to induce charge switching in NV centers. Neutral NV centers can’t detect magnetic fields. Because of this, switching is a challenge in diamond utilization.

“Only the minus [negative] charge can be used for such sensing applications, therefore stabilizing [NV] centers is important for operation," Mizuochi said.

Previously doped diamonds have been successfully developed with the ability to stabilize NV centers with phosphorus. Phosphorus doping pushed more than 90 percent of NV centers to negative charge state which in turn enables magnetic field detection but phosphorus introduced noise to the readout.

The team further adapted the diamond to preserve the stabilization of the negative NV center while getting rid of the noise introduced with the phosphorus. To do this, they created a layered structure, similar to a sandwich. The phosphorus-doped diamonds were the bread and a 10μm thick NV-center diamond was the filling. This diamond sandwich stabilized 70-80 percent of NV centers in the negative charge state with a reduced noise.

"At the moment, we have just demonstrated stabilization, but we expect it to also improve sensitivity," Mizuochi said.

The new design is being tested for sensitivity and changes in magnetic fields. The goal is to use the diamond sandwich for biosensing applications.

A paper on the new diamond design was published in Applied Physics Letters.