Stabilizing NV centers in diamond nanopillars under cryogenic conditions through alumina surface passivation

Nitrogen-Vacancy centers in diamond (NVs) have emerged as robust quantum sensor under ambient conditions, however near-surface NVs have been found to degrade under non-ambient environments, limiting the scope of their applications. Recently, we identified surface reconstruction under optical excitation as the origin of NV degradation due to irreversible charge state conversion (NV^-→ NV⁰) and went on to stabilize them using dielectric passivation (~ 2 nm Al₂O₃) of diamond surface.[1] These results present a promising approach to stabilize NV-AFM probes through optimized surface passivation for cryogenic applications, motivating our study on NV-diamond nanopillars. In this work, we explore the effect of functionalization (oxygen and Al₂O₃ passivation) on shallow NV centers in diamond nanopillars, at high vacuum (~ 5×10^-7 mbar) and low T (4K), under optical illumination. We also perform ex-situ Raman and surface spectroscopy to quantify changes to the nanopillar surface under different environments.

[1] R. Kumar, S. Mahajan and JJL Morton et al. ACS Photonics 11, 1244 (2024)