Production of High Yield, Ultra-Shallow Nitrogen-Vacancy Centre Ensembles Through High Purity Forming gas Annealing

Dense, ultra-shallow (<10 nm from the surface) ensembles of nitrogen-vacancy (NV) centers in diamond are sought-after for realising practical quantum sensing at the nanoscale. However, these ensembles typically suffer from reduced NV creation efficiency and spin coherence compared to their deeper and bulk counterparts. Consequently, most demonstrations in the literature to date have been restricted to using single NV centers with atypical coherence and charge stability properties not achievable across entire ensembles. In this work, we demonstrate that controlled annealing in a high purity forming gas atmosphere improves near-surface NV formation efficiency to over 20%. This environment preserves a high quality hydrogen termination throughout the anneal, avoiding material etching over many hours at temperatures up to 1100°C and possibly helping to suppress vacancy out-diffusion. We show that high temperature annealing is especially vital for improving spin properties in high density, ultra-shallow implanted samples due to the localised damage profiles produced. By allowing the formation of high yield NV ensembles with improved spin properties, the optimised forming gas anneal can facilitate the reliable production of more sensitive diamond sensors than have previously been accessible.