Surface engineering of diamond and diamond-like carbon for quantum technologies: interface chemistry, near-surface defects, and device-level performance

Diamond is an established solid-state platform for quantum sensing, integrated photonics, and spin-based quantum technologies. Still, the performance of shallow color centers is strongly affected by surface-induced band bending, charge-state instability, interface traps, spectral diffusion, and near-surface defects. This review critically examines how hydrogen-, oxygen-, fluorine-, nitrogen-, and mixed-surface terminations, molecular functionalization, dielectric passivation, plasma and electrochemical treatments, defect-engineering routes, and emerging diamond-like carbon interfaces modify the local electronic and spin environment. Particular attention is given to the relationships among interface chemistry, defect depth, charge-state stability, spin coherence, optically detected magnetic resonance response, optical linewidth, spectral diffusion, and device-level reliability. Evidence from wide-field sensing, scanning-probe, nanophotonic, and hybrid architectures is compared while accounting for differences in processing and measurement conditions. Persistent limitations include inter-study variability, incomplete chemical–quantum correlation, inconsistent performance reporting, and limited long-term stability data. Standardized surface characterization, matched-condition performance measurements, and device-specific interface design are therefore required to improve reproducibility and support integrating surface-engineered diamond into quantum sensors, photonic components, and integrated quantum devices.