Formation of group IV-vacancy color centers in diamond by FIB: role of graphitization

The wide bandgap of diamond enables the engineering of photoluminescent defects, allowing controlled photon emission in the visible range, even at the single-photon level. Fabricating color centers (CC) in diamond is crucial for quantum technologies, including sensing, metrology, and computing. Among the various techniques for introducing defects, Focused Ion Beam (FIB) implantation stands out due to its unique spatial resolution and the ability to deliver fluences of a few ions, allowing the controlled introduction of defects at the nanometer scale [1]. However, the ion implantation process damages the diamond lattice, potentially causing amorphization. Thermal annealing is required to activate CC and restore the lattice, but irreversible changes like graphitization and lattice swelling occur if the amorphization threshold is reached, reducing the formation yield of CC [2] and photoluminescence emission. In particular, the extremely focused ion beams (~15 nm spot diameters) allow to reach the amorphization threshold even for low fluences (<1000 ions). In this study, FIB was used to implant (70 keV kinetic energy) silicon and germanium ions into electronic-grade diamonds, rastering 10×10 μm² areas at different fluences. Graphitization and phase changes induced by implantation and annealing were analyzed for each ion species and correlated with the optical properties of silicon-vacancy (SiV) and germanium-vacancy (GeV) CC formed by introducing germanium or silicon ions by FIB. The CC optical properties were investigated through photoluminescence and Raman spectroscopy. The results were compared with those from the arrays produced via single-spot ion implantation. The amorphization of the implanted area, despite the small beam spot size, was investigated to assess its impact on CC formation and photoluminescence properties. Our results highlight the importance of optimizing implantation conditions to balance structural damage and efficient CC formation.