Ion implantation through a screening layer for shallow NV center formation in diamond for quantum sensing applications

Shallow nitrogen-vacancy (NV⁻) centers in diamond are of significant interest for high precision quantum sensing applications, like single biological imaging and environmental sensing [1]. When located within few nanometers (< 10 nm) from the diamond surface, the increased strength of their interaction makes their quantum properties, such as spin polarization, highly sensitive to local variation in external electromagnetic fields and temperature fluctuation at the surface. This proximity enhances therefore their potential for high-sensitive nanoscale sensing and mapping. In addition, the shallow position makes NV- centers advantageous for integration into compact nanoscale devices [2]. Various strategies have been explored to fabricate shallow NV- centers. This study presents the results of a methodology combining medium-energy broad-beam ion implantation at two different angles and a screening layer to control and reduce the penetration depth of ions into the diamond. Monte Carlo simulations (SRIM) predicted shallow nitrogen implantation depths, which were experimentally confirmed through angle-resolved X-ray photoelectron spectroscopy (ARXPS). Confocal photoluminescence (PL) mapping further highlighted how the implantation angle and the screening layer modulate the density of formed shallow NV⁻ centers, as measured by PL emission intensities. Single-point PL spectroscopy revealed distinct variations in the NV0 to NV- emission ratio, attributed to differing charge neutralization rates influenced by implantation conditions and the resulting proximity of NV- centers to the surface. Based on the experimental findings, strategies for improving the efficiency and uniformity of formation of shallow NV⁻ centers are discussed.