Diamond point defects have been applied to various quantum devices, including quantum interfaces, quantum memory, and quantum sensing. Recently, group IV-V centers, which consist of group IV ions such as silicon (Si), germanium (Ge), and tin (Sn), along with atomic vacancies (V), are getting high hopes for potential application in quantum devices. This is because group IVV centers exhibit a longer spin relaxation time T2 on the order of milliseconds at cryogenic temperatures and have bright zero phonon line (ZPL) emission intensities1 . The formation process of group IV-V centers can be roughly classified into two steps: (1) generation of interstitial atoms and vacancies by ion implantation, and (2) diffusion of vacancies and substitutional atoms by hightemperature annealing. High-temperature annealing is thought to graphitize the diamond substrate and is typically performed under high pressure. In this presentation, we focus on optimizing the annealing processes in an argon atmosphere at 1800oC. While the optimization of the annealing processes has been actively studied for nitrogen-vacancy (NV) centers, it has not been thoroughly explored for group IV-V centers. Group IV-V centers are constructed with an atom between split vacancies, whereas an NV center is constructed with an interstitial atom and an atomic vacancy. These structural differences could lead to variations in the elementary processes of their formations. Therefore, the optimization processes of annealing conditions need to be re-examined. In this study, we investigated atmospheric annealing processes using HPHT (grown by NIMS) and CVD (Element 6 electric grade) diamonds. Each diamond sample was irradiated with 18 MeV Si, Ge, and Sn ion beams and implanted at about 3 μm from the sample surface. We report efficient formation processes of group IV-V centers at atmospheric pressure, and in a very short time for high-temperature processes compared to the conventional process. In addition, we will discuss the interpretation of the examination result that the number of group IV-V centers formed does not necessarily increase monotonically with annealing time, as shown in Figure 1.
Diamond point defects have been applied to various quantum devices, including quantum interfaces, quantum memory, and quantum sensing. Recently, group IV-V centers, which consist of group IV ions such as silicon (Si), germanium (Ge), and tin (Sn), along with atomic vacancies (V), are getting high hopes for potential application in quantum devices. This is because group IVV centers exhibit a longer spin relaxation time T2 on the order of milliseconds at cryogenic temperatures and have bright zero phonon line (ZPL) emission intensities1 . The formation process of group IV-V centers can be roughly classified into two steps: (1) generation of interstitial atoms and vacancies by ion implantation, and (2) diffusion of vacancies and substitutional atoms by hightemperature annealing. High-temperature annealing is thought to graphitize the diamond substrate and is typically performed under high pressure. In this presentation, we focus on optimizing the annealing processes in an argon atmosphere at 1800oC. While the optimization of the annealing processes has been actively studied for nitrogen-vacancy (NV) centers, it has not been thoroughly explored for group IV-V centers. Group IV-V centers are constructed with an atom between split vacancies, whereas an NV center is constructed with an interstitial atom and an atomic vacancy. These structural differences could lead to variations in the elementary processes of their formations. Therefore, the optimization processes of annealing conditions need to be re-examined. In this study, we investigated atmospheric annealing processes using HPHT (grown by NIMS) and CVD (Element 6 electric grade) diamonds. Each diamond sample was irradiated with 18 MeV Si, Ge, and Sn ion beams and implanted at about 3 μm from the sample surface. We report efficient formation processes of group IV-V centers at atmospheric pressure, and in a very short time for high-temperature processes compared to the conventional process. In addition, we will discuss the interpretation of the examination result that the number of group IV-V centers formed does not necessarily increase monotonically with annealing time, as shown in Figure 1.
Diamonds and nanodiamonds (NDs) containing quantum color centers, such as nitrogen-vacancy (NV) centers, have been widely studied in recent years for their promising applications across various fields, including cryptography and telecommunications, medical sciences, and sensing. In the context of sensing, recent studies on color centers such as silicon-vacancy (SiV) and germanium-vacancy (GeV) centers have shown great potential for measuring physical quantities like magnetic fields, temperature, and strain. This is due to their intense zero-phonon line (ZPL) optical signal, which accounts for about 80% of their total luminescence and is characteristic of group-IV color centers (G4V) [1]. In our recent papers, we demonstrated that as-grown CVD NDs containing SiV and GeV centers, featuring luminescent ZPLs and excellent photostability at room temperature, can function effectively as nanosensors under high stress and pressure conditions (up to 180 GPa) [2, 3]. To advance our research, in this work we investigate the optical properties of SiV centers in as-grown NDs at cryogenic temperatures. For SiV centers, which have spin 1/2, the fine structure should become accessible through the Jahn-Teller effect, which lifts the degeneracy at cryogenic temperatures (< 20 K). However, experiments on our as-grown NDs reveal significant spectral broadening even at around 9 K, caused by lattice strain, which prevents access to the optically addressable electronic spin states of the SiV center. To overcome this limitation, we propose an original post-treatment involving high-pressure and high-temperature (HPHT) annealing using the Paris–Edinburgh press. This approach allows the gradual increase of temperature and pressure allows for control over the undesired diamond-to-graphite phase transition. HPHT annealing experiments were conducted at the PSICHE beamline of Synchrotron SOLEIL [4], where X-ray diffraction and tomography analyses enabled precise monitoring of P-T parameters and made it possible for the first time to access single fine-structure transitions of SiV centers in such NDs.References[1] C. Bradac, et al., Nat. Commun. 10, 1 (2019). [2] B. Vindolet, et al., Phys. Rev. B 106, 214109 (2022).[3] M. De Feudis, et al., Adv. Mater. Interfaces 7, 1901408 (2019).[4] L. Henry et al., J. Synchrotron Rad. 29 (2022).
Tin-vacancy ($\mathrm{Sn}\text{\ensuremath{-}}V$) color centers were created in diamond via ion implantation and subsequent high-temperature annealing up to $2100\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ at 7.7 GPa. The first-principles calculation suggested that a large atom of tin can be incorporated into a diamond lattice with a split-vacancy configuration, in which a tin atom sits on an interstitial site with two neighboring vacancies. The $\mathrm{Sn}\text{\ensuremath{-}}V$ center showed a sharp zero phonon line at 619 nm at room temperature. This line split into four peaks at cryogenic temperatures, with a larger ground state splitting ($\ensuremath{\sim}850\text{ }\text{ }\mathrm{GHz}$) than that of color centers based on other group-IV elements, i.e., silicon-vacancy ($\mathrm{Si}\text{\ensuremath{-}}V$) and germanium-vacancy ($\mathrm{Ge}\text{\ensuremath{-}}V$) centers. The excited state lifetime was estimated, via Hanbury Brown--Twiss interferometry measurements on single $\mathrm{Sn}\text{\ensuremath{-}}V$ quantum emitters, to be $\ensuremath{\sim}5\text{ }\text{ }\mathrm{ns}$. The order of the experimentally obtained optical transition energies, compared with those of $\mathrm{Si}\text{\ensuremath{-}}V$ and $\mathrm{Ge}\text{\ensuremath{-}}V$ centers, was in good agreement with the theoretical calculations.
Quantum information applications place stringent demands on the development of platforms that can host them. Color centers in diamond have been identified as important media for quantum information processing. Accordingly, the photoluminescence properties of nitrogen-vacancy (N-V) centers in diamond created by implantation and annealing are studied at cryogenic temperatures (below 10 K). We examine high pressure high temperature and chemical vapor deposition synthetic diamonds with varying nitrogen concentration and present an accurate method to estimate the concentration of the (N-V) centers created by ion implantation. The ion irradiation route produced up to 6 ppm of optically active (N-V) centers, while nitrogen implantation yielded up to 3 ppm of optically active (N-V) with 8% conversion efficiency. However, a broadening of the (N-V)− zero phonon line was observed in all samples.
ABSTRACT With unique optical and spin properties, the negatively charged nitrogen‐vacancy (NV − ) center in diamond has become a leading physical platform for quantum information processing. Fabrication of NV centers involves three steps: introducing nitrogen atoms, creating lattice vacancies, and combining these two types of defects. The final step is typically achieved by high‐temperature annealing, as vacancy migration in diamond is thermally activated above 600°C. Compared to low‐pressure high‐temperature (LPHT) annealing, high‐pressure and high‐temperature (HPHT) treatment allows for much higher annealing temperatures and longer durations, providing new opportunities to optimize key metrics of NV centers. This short review summarizes recent experimental progress in this direction. Dense NV centers with good spin coherence and single NV centers with excellent optical properties have been produced through HPHT growth and post‐treatment of single‐crystal diamonds. In addition, structural imaging, optical characterization, and DFT calculations provide further insights into the dynamics of defect migration under high‐temperature annealing. These results offer new perspectives on the fabrication of color centers in diamond and other wide‐gap semiconductor materials, including silicon carbide and hexagonal boron nitride, for advanced quantum applications.
The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.
Advances in material processing are rapidly improving the quality and scalability of nitrogen-vacancy (NV) and group-IV vacancy (G4V) color centers in diamond—key building blocks for quantum sensing and photonic networks. Central challenges remain: precise control of defect-formation pathways and the mitigation of nearby charge traps and parasitic states, which is especially problematic for near-surface emitters. Recent progress in sample preparation and in-situ thermal treatments (before, during and after growth, and during implantation) have reduced nonradiative dark defects and suppressed interface doping. Optimizing thermal strategies have illustrated an increased conversion yield for NV and G4V centers, while limiting unwanted photoluminescence. Similarly, surface treatments play an imperative role in stabilizing near-surface charge states for sensing applications. Complementary ex-situ protocols, such as high-temperature vacuum anneals, and hybrid incorporation methods that combine shallow implantation with epitaxial overgrowth continue to improve yields and coherence for shallow NV and G4V centers. Together, these integrated strategies are enabling deterministic, high-fidelity quantum emitters embedded in scalable diamond nanostructures.