Stabilization of Shallow NV^- Centers under Hydrogen-terminated Diamond Surface Using Dielectric Encapsulation

The negatively charged nitrogen vacancy (NV) center in diamond that is nanometers away from the diamond surface is a promising platform for nanoscale quantum sensing. Its charge stability strongly depends on the diamond surface termination. Specifically, hydrogen (H)-terminated diamond features low surface defect density, potentially supporting shallow NVs with longer spin coherence. However, H-terminated diamond exposed to air suffers from near-surface band bending due to atmospheric adsorbates, which quenches shallow NV centers. In this work, we tackle this challenge by reducing the band bending with a thin layer of alumina. a H-terminated diamond hosting shallow NV centers was first baked in the ultrahigh vacuum chamber of an AJA sputterer to remove atmospheric adsorbates, followed by immediate alumina deposition in the same chamber. Confocal scan confirmed the successful recovery of NV centers after alumina deposition, with good ODMR contrast and spin coherence properties. Our results open new possibilities to use stable shallow NV centers under a H-terminated diamond surface for advanced quantum sensing.