Diamonds with impurity color centers are a novel class of functional materials with potential for various photonics applications such as quantum optics, metrology, sensorics, and life sciences. When introducing defect centers, a broad range of questions arises about the nature of the photophysical processes in the new materials, in particular regarding the relationship between spectral and morphological properties. Here we present results of comprehensive spectroscopic studies on diamond films with germanium-vacancy (GeV – ) centers, synthesized by chemical vapor deposition from gaseous germane (GeH 4 ). The combination of different techniques (emission and fluorescence excitation spectroscopy, epi-microscopy, and nanoscopy up to the single-emitter level) at room and cryogenic temperatures has shed light onto the spatial distribution of the spectral properties of the GeV – centers in different microregions of the diamond crystal and its relation to local strain/stress. We demonstrate a clear correlation between inhomogeneous broadening and morphological heterogeneities of the sample. Ultranarrow (tens of MHz) stable zero-phonon lines have been observed, which are a prerequisite for various applications.
Group IV color centers in diamond (Si, Ge, Sn, and Pb) have recently emerged as promising candidates for realization of scalable quantum photonics. However, their synthesis in nanoscale diamond is still in its infancy. In this work we demonstrate controlled synthesis of selected group IV defects (Ge and Sn) into nanodiamonds and nanoscale single crystal diamond membranes by microwave plasma chemical vapor deposition. We take advantage of inorganic salts to prepare the chemical precursors that contain the required ions that are then incorporated into the growing diamond. Photoluminescence measurements confirm that the selected group IV emitters are present in the diamond without degrading its structural quality. Our results are important to expand the versatile synthesis of color centers in diamond.
Silicon has turned from a niche laboratory-scale material into the backbone of modern electronics. Diamond functionalized with color centers could follow a similar path and grow from proof-of-concepts experiments to application-oriented quantum technologies. Quantum sensing, communication, and information processing with color centers has been proven to work in scientific experiments and enhanced sensitivities as well as novel functionalities have been reported. While the first generation of diamond quantum devices relied on color centers formed uncontrolled in natural diamond with a high statistical variation in composition and crystallinity, the situation has changed nowadays. With the emergence of high purity monocrystals and the option for isotopic purification of the carbon matrix, technological progress in materials science on the atomic-scale enabled tailoring the spin properties in diamond. But, since many color centers typically require vacancies to combine with impurities in the carbon lattice via diffusion, the generation of color centers underlies a statistical process providing only little control on the center's final position in the crystal lattice. The negatively charged nitrogen-vacancy (NV
−) center is the most studied optically active defect in diamond and exhibits remarkable spin properties and sensing capabilities, even on the nanoscale and at room temperature. The spin properties of NV
− centers close to the surface (1\,nm - 30\,nm) have been thoroughly studied and the deeper the spins are located in diamond the less decoherence from surface defects is observed. Creating NV
− centers at the surface by nitrogen ion implantation and burying them beneath a thin diamond layer via chemical vapor deposition (CVD) of diamond is reported to enhance the coherence times significantly. By separating the color center generation from controlling the resulting depth by an additional diamond layer, narrow depth profiles can be achieved by reducing the ion energy during implantation. Although the coherence properties improve, many of the implanted NV
− center are reported to vanish in the hydrogen-rich plasma of growth CVD chambers. The mechanism responsible for the instability of NV
− centers towards the plasma remains unclear, though. One hypothesis is the formation of nitrogen-vacancy-hydrogen centers from diffusing hydrogen and implanted NV
− centers but is has not been proven, yet. Here, we demonstrate the fabrication of depth confined NV
− centers by combining low energy (1\,keV - 5\,keV) ion implantation and CVD overgrowth. By increasing the thickness of the overgrown layer (6\,nm - 100\,nm) the influence of surface noise is shown to decrease leading to bulk-like coherence properties of up to $450\,\upmu$s (Hahn-echo) and
T2∗ dephasing times around $20\,\upmu$s. Monitoring the NV
− density as a function of the overgrowth time, we analyze the kinetics of the passivation in case of implanting ion doses of 10
11 15N
+/cm
2 and 10
12 15N
+/cm
2. The passivation turns out to occur faster for lower doses offering insights into sub-surface hydrogen diffusion in diamond. Analyzing the spin bath before and after overgrowth reveals a drastic reduction in paramagnetic spins after the CVD process but no NVH
− is found around the surviving NV
− centers. Checking the chemical composition in overgrown implantation sites with secondary-ion-mass-specrometry (SIMS), however, confirms significant amounts of hydrogen in the
15N-implanted layers. Since the concentration found for hydrogen exceeds the one for nitrogen by far, we suggest that diffusing hydrogen interacts also with vacancies forming probably mostly diamagnetic defects. In the last part of this dissertation, NV
− centers are generated with sub-nanometer precision below a thin
13C-enriched layer for quantum simulation. For fabricating the spin architecture starting from a
12C base layer, we overgrow implanted nitrogen with a
13C layer and bury the spins beneath a 30\,nm-thick
12C capping layer. By measuring the coupling strength between the electron and nuclear spins, we deduce a NV
− placement accuracy reaching below one nanometer with respect to the
13C-layer. Regarding the spin properties of the electron spins, no reduction in
T2 is observed despite of the proximity to the dense
13C-bath. As a consequence, the overgrowth of NV
− centers is demonstrated as a bottom-up approach to produce buried spin architectures with sharp isotopic transitions and efficient
13C-NV
− coupling. Together with the potential for bulk-like coherence properties the synergy of implantation and overgrowth is a powerful tool to fabricate reproducible quantum systems with tailored properties and high depth confinement.
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.
The germanium vacancy in diamond (GeV) is a promising candidate for color center based quantum networking. Yet, like for other group-IV vacancy defects in diamond, achieving fast, high-fidelity qubit operations using traditional magnetic resonance techniques is experimentally challenging due to a weak magnetic dipole and susceptibility to thermally induced decoherence. Here, we perform all-optical control of the GeV and realize Rabi frequencies exceeding ∼ 20 MHz. We do so by driving the two Λ -systems of the GeV simultaneously and apply this to probe the spin coherence ( T 2 * = 224 ± 14 ns, T 2 H = 11.9 ± 0.3 µ s ). Our control scheme is applicable to other color centers and particularly, other group-IV defects for which the scheme may be optimized to improve all-optical control in these systems.
Group IV color centers in diamond have garnered great interest for their potential as optically active solid-state spin qubits. The future utilization of such emitters requires the development of precise site-controlled emitter generation techniques that are compatible with high-quality nanophotonic devices. This task is more challenging for color centers with large group IV impurity atoms, which are otherwise promising because of their predicted long spin coherence times without a dilution refrigerator. For example, when applied to the negatively charged tin-vacancy (SnV – ) center, conventional site-controlled color center generation methods either damage the diamond surface or yield bulk spectra with unexplained features. Here we demonstrate a novel method to generate site-controlled SnV – centers with clean bulk spectra. We shallowly implant Sn ions through a thin implantation mask and subsequently grow a layer of diamond via chemical vapor deposition. This method can be extended to other color centers and integrated with quantum nanophotonic device fabrication.