Materials and spin characteristics of amino-terminated nanodiamonds embedded with nitrogen-vacancy color centers

Abstract:Fluorescent nanodiamonds (FNDs) with optically read qubits hold great potential for detecting electric and magnetic fields, temperature, and other nanoscale physico-chemical quantities relevant to chemistry and biology. Proper surface functionalization is essential for their application as probes, but surface modifications can impact qubit sensor properties. We systematically study nitrogen-vacancy (NV) color centers in FNDs as a function of size and surface termination. FNDs were produced from high-pressure, high-temperature diamonds, with NV centers introduced via electron irradiation and annealing. The initial oxygen-covered FNDs were homogenized with hydroxyl (-OH) groups as reference samples, while the non-invasive Hofmann degradation introduced amino (-NH2) groups for potential direct biomolecule attachment. Amino groups may not cover the nanodiamonds homogeneously, but we label them as -NH2 terminated throughout. We monitored charge state stability and the zero-field splitting parameters of the embedded NV centers. First, we resolve the size dependence of the NV(-) zero-field splitting parameters across the 10-140 nm range and show that the symmetry-breaking E parameter decreases monotonically from about 8 to about 5 MHz with increasing size, while the axial D parameter is shifted only in the smallest (<= 30 nm) particles, thereby disentangling the static-strain and fluctuating-electric-field contributions to the spin levels. Second, while NV charge state stabilization was observed in both -OH- and -NH2-terminated FNDs above a certain size, we demonstrate that a remarkably high and laser-power-independent NV(-) content (f_NV(-) = 0.8) is achieved by wet-chemical Hofmann amino termination only at 140-nm particles, an effect we link through electron spin resonance to the degradation of surface paramagnetic defects rather than to the introduction of new ones.

Quantum Physics (quant-ph); Materials Science (cond-mat.mtrl-sci)

arXiv:2502.07706 [quant-ph]

(or arXiv:2502.07706v3 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2502.07706 Focus to learn more arXiv-issued DOI via DataCite

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