Open Access Conference Proceedings

Lattice defects in crystals serve as the base of quantum technologies. Among these, the nitrogen-vacancy (NV) center in diamond, particularly its negatively charged state (NV⁻) has attracted considerable attention due to its stability at room temperature and potential application as a solid-state qubit. Nanodiamonds (NDs) are commonly synthesized by the high-pressure, high-temperature (HPHT) method. During post-synthesis cleaning, strong oxidizing acids (e.g., HNO₃, H₂SO₄, HClO₄) are employed, introducing various surface functional groups such as carboxyls. These surface groups can influence lattice defect sites and offer possibilities for further chemical modification. One such modification is Hofmann degradation, a well-known organic reaction that enables the direct formation of amino groups from carboxyl functionalities via decarboxylation. This process yields primary amine termination, which can facilitate the formation of C−N−C bonds, thereby favorably affecting NV⁻ center stabilization. Carboxyl- and amino-functionalized NDs were annealed at 600 °C, 750 °C, and 850 °C during 10 minutes. The NV⁻ fraction was measured using a Raman microscope. Significant temperature-dependent variations in this fraction ratio were observed. These differences are attributed to surface chemical transformations, as confirmed by infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS).

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