Overcoming fabrication challanges of color centers in diamond with a focused ion beam

Defects in diamonds such as nitrogen-vacancy (NV), silicon-vacancy (SiV), and germanium-vacancy (GeV) color centers have become extremely important in quantum sensing, quantum communication, and quantum computing technologies, for their remarkable optical and spin properties. This work is focused on the deterministic color center fabrication technique based on ion implantation using a FIB system with a Liquid Metal Alloy Ion Source (LMAIS). This method enables the accurate implantation of several ions (such as Si and Ge) down to the nanometer scale, thus facilitating the precise engineering of color centers without the necessity of elaborate lithographic techniques. Regardless of its benefits, this method offers several challenges in fabrication. One significant challenge is the local amorphization, which occurs when high local ion fluence, resulting from concentrating ions into small regions, damage the diamond lattice and induce amorphization and then graphitization after a thermal annealing process. The damaged areas compromise the quality of the crystal but also leads to additional undesired emitting sources of photons. Furthermore, the mass resolution of the Wien filter can lead to ion cross-contamination, especially when using large or degraded apertures. For instance, Ge and Si cross- contamination may occur, unintentionally forming mixed color center types. Another concern is the implantation of neutral atomic species, which, in systems without dedicated hardware to handle them, can travel undisturbed down the column to the substrate, introducing defects at the center of the writing field. To overcome these issues, we investigate approaches like layout modification, a few guidelines about beam, and a post-implantation protocol to treat the substrates. All these strategies seek to improve the control of defect formation, background noise reduction, and operational dependability of quantum devices that take advantage of diamond color centers.