Ultrahigh Vacuum Surface Chemistry and Stability in Single-Crystalline Diamond Surfaces

Shallow nitrogen-vacancy (NV) centers in diamond are a leading platform for nanoscale quantum sensing, offering high magnetic sensitivity and spatial resolution. However, their performance is limited by surface defects and adsorbates that introduce magnetic noise and cause charge-state instability. To study these effects under controlled conditions, we constructed an ultrahigh vacuum (UHV) system capable of surface preparation, spectroscopy, and cryogenic confocal imaging of single NV centers. This environment allows precise control over surface conditions while enabling high-numerical-aperture imaging and high-power microwave driving. Using in situ annealing under UHV, we create clean diamond surfaces to study how the removal of surface adsorbates affects shallow NV coherence and charge stability. In addition, we are able to study surface terminations that are unstable under ambient conditions, allowing us to design new surfaces that stabilize shallow NV centers and extend coherence for quantum sensing applications.