Improving NV centre density during diamond growth by CVD process using N2O gas

International audienceNitrogen-vacancy (NV) centres in diamond are point-like defects that have attracted a lot of attention as promising candidates for quantum technologies particularly for sensing and imaging nanoscale magnetic fields. For this application, the use of a high NV density within a high-quality diamond layer is of prime interest. In previous works, it has been demonstrated that in situ doping with N2O rather than N2 during chemical vapour deposition (CVD), limits the formation of macroscopic defects and improves NV's photostability. In this work, we focus on the optimization of the CVD growth conditions to obtain a high NV density keeping a constant N2O concentration in the gas phase (100 ppm). For this purpose, freestanding CVD layers are prepared varying two main growth parameters: methane content and substrate temperature. High energy electron irradiation followed by annealing is finally carried out in order to increase the NV yield through partial conversion of N impurities. Defect concentrations and spin properties are investigated. We find that growth under lower methane concentrations and lower temperatures enhances NV doping. NV ensembles with a density of the order of 2 ppm are finally obtained with narrow spin resonance linewidth. In addition, higher annealing temperatures of 1200 °C following irradiation are found to efficiently remove defects thus improving spin properties

Optimizing ion implantation to create shallow NV centre ensembles in high-quality CVD diamond

International audienceAbstract The negatively charged nitrogen-vacancy centre (so-called NV-centre) in diamond is one of the most promising systems for applications in quantum technologies because of the possibility to optically manipulate and read out the spin state of this defect, even at room temperature. Nevertheless, obtaining high NV densities (>500 ppb) close to the surface (5–20 nm) while maintaining good spin properties remain challenging. In this work we rely on a versatile ion implantation system allowing both implanting nitrogen using N 2 + and creating vacancies with He + ion bombardment at variable energies and fluence to create shallow NV ensembles. By optimizing the ion irradiation conditions as well as the surface preparation prior to treatment we successfully increase the amount of created colour centres while demonstrating narrow magnetic resonance linewidths

Optical properties of SiV and GeV color centers in nanodiamonds under hydrostatic pressures up to 180 GPa

We investigate the optical properties of silicon-vacancy (SiV) and germanium-vacancy (GeV) color centers in nanodiamonds under hydrostatic pressure up to 180 GPa. The nanodiamonds were synthesized by Si- or Ge- doped plasma-assisted chemical vapor deposition and, for our experiment, pressurized in a diamond anvil cell. Under hydrostatic pressure we observe blueshifts of the SiV and GeV zero-phonon lines by 17 THz (70 meV) and 78 THz (320 meV), respectively. These measured pressure-induced shifts are in good agreement with ab initio calculations that take into account the lattice compression based on the equation of state of diamond and that are extended to the case of the tin-vacancy (SnV) center. This work provides guidance on the use of group-IV-vacancy centers as quantum sensors under extreme pressures that will exploit their specific optical and spin properties induced by their intrinsic inversion-symmetric structure