Surface Composition and Spin Properties of Near-Surface NV Center Ensembles in Diamond Across Various Oxidative Surface Treatments

Negatively charged nitrogen vacancy (NV) centers in diamond provide a versatile platform for quantum sensing, capable of measuring magnetic fields, electrical current, temperature, and strain with high spatial resolution. While NV centers are excellent quantum sensors due to their optical and spin properties being stable at room temperature, and multiple modalities available for sensing, near-surface NVs within 10 nm from the interface are subject to surface spin noise, which produce deleterious effects on the optical and spin properties, limiting the magnetic sensitivity of the NV. Terminating the diamond surface with electronegative elements, such as nitrogen, fluorine, and oxygen have been observed to provide a favorable charge state environment for the NV center, resulting in an increase in spin coherence times.

We analyzed oxygen-termination techniques on single crystalline diamond, particularly wet and dry chemistry oxidation methods, and found that dry oxidation methods hold promise towards producing diamond surfaces suitable for quantum applications, yielding surfaces that are low in molecular contamination, sp² amorphous carbon, and a relatively high oxygen content [1]. Furthermore, by using angle-resolved x-ray photoelectron spectroscopy (ARXPS) we showed that oxidized diamond samples harbor a disordered sp² carbon layer with an approximate depth of 0.4 nm, with the oxygen content being directly bonded to this layer [2]. With this updated understanding of the surface chemistry of diamond, we investigate the effects of three different surface terminations on the optical and spin properties of ion implanted shallow NV centers with an approximate depth of 10 nm and a nitrogen concentration of 1.1 ppm in single crystalline diamond. We correlate optical properties from Continuous Wave – Optically Detected Magnetic Resonance (CW-ODMR) and spin coherence data with the diamond surface composition, including oxygen functionalizations, amorphous carbon content, and degree of molecular contamination, of each surface as measured through x-ray photoelectron spectroscopy (XPS) as previously reported in [1]. The surfaces we explore include a contaminated surface, which shows evidence of substantial amounts of adventitious carbon and molecular contamination, a tri-acid cleaned surface, and a diamond surface subjected to water vapor pulses using an Atomic Layer Deposition (ALD) tool.

This work is supported by U.S. DOE, BES, under Award #DESC0020313.

[1] R. Vidrio, D. Vincent, B. Bachman, C. Saucedo, M. Zahedian, Z. Xu, J. Lai, T. A. Grotjohn, S. Kolkowitz, J.-H. Seo, R. J. Hamers, K. G. Ray, Z. Ma and J. T. Choy, "XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond," Materials for Quantum Technology, p. 025201, 2024.

[2] R. Vidrio, C. Saucedo, V. Lordi, S. Kolkowitz, K. G. Ray, R. J. Hamers and J. T. Choy, "Sub-nanometer thick native sp2 carbon on oxidized diamond surfaces," arXiv preprint, vol. arXiv:2409.06934, 2024.