Diamond magnetometric sensor

High-sensitive magnetometer by NV centers in diamond

Nitrogen-Vacancy (NV) defect centers in diamond (Fig.1) have remarkable properties for some applications: magnetometer, electrometer, and quantum information, and so on. Particularly it is important that NV centers can work at room temperature. In contrast to SQUID, which has highest sensitivty in today but can operate only in the low-temperature environment, sensing systems by NV centers don’t require any cooling system, which results in downsizing of equipments. Moreover, the sensitivity of NV centers can be comparable to SQUID.

In our laboratory, we are trying to develop the application such as magnetic field imaging of cells, biomagnetism measurement and nano-NMR.

Detail of structure
Fig.1 Structure of NV center
Graphical explanation
Fig.2 Performance and applications of diamond sensor

Vector imaging of magnetic field by NV centers

The NV center consists of nitrogen - vacancy pair substituted for adjacent two carbon atoms in diamond, NV centers can be oriented along one of four possible directions and formed with high concentration, so we can measure the strength and the direction of magnetic field. Spatial resolutions of conventional magnetometer techniques (Hall devices, SQUIDs) are restricted by device size (typically ~ 100 um ), however NV centers can reach to diffraction-limited size (300 nm). By utilizing these merits, NV center can realize some of applications which conventional techniques cannot, such as magnetic imaging of cells. In our laboratory, we demonstrated magnetic field imaging of a micro-particle of neodymium magnet.

Measuremnt result
Fig.3 Vetor imaging of magnetic field by neodym micro particle

N-doped diamond growth for improvement of magnetic sensitivity of NV centers

For the improvement of magnetic sensitivity, selectively aligned high density NV centers are required. At low density (almost single), NV centers have been selectively aligned along one direction by microwave plasma chemical vaper deposition growth of diamonds on (111) substrates. In our laboratory, we fabricated the highest-density of selectively aligned NV centers by N-doped diamond growth on (111) substrate. We are trying to further improve the sensitivity of NV centers using this method.

Picture of light emission
Fig.4 (Left)Fluorescence from NV centers in N-dope diamond.
(Right)ODMR spectrum of selectively aligned NV centers

Ab initio calculation of the defects in group Ⅳ semiconductor

The nitrogen-vacancy (NV) center in diamond has been shown to possess extraordinary spintronic properties and it is a candidate for spin information devices. Based on these favorable properties, we are searching a spintronic properties of another color center in diamond using first-principle calculation. First-principle calculation solves Schrödinger equation numerically. So with this calculation, defect energy levels, wave function and ZPL can be evaluated. So far, because Boron is used as p-type dopant for diamond, we have focused on Boron-Vacancy (BV) center in diamond. (Fig. 5) We calculated defect energy level of BV center. (Fig. 6)

Structure of BV center
Fig5. Structure of BV center
Fig6. Energy level diaglam of BV- center