Nitrogen-Terminated Diamond Surface for Nanoscale NMR by Shallow Nitrogen-Vacancy Centers

The nitrogen-vacancy (NV) center in diamond is the most promising candidate for quantum sensing because of its beneficial properties. For quantum-sensing applications, a shallow NV center is critical for approximating the sensing target on a diamond surface. Such shallow NV centers are strongly affected by the diamond surface termination. The properties of shallow NV centers in hydrogen-, oxygen-, and fluorine-terminated diamond have been well studied. In recent years, silicon-terminated diamond has also been investigated; however, the effect of silicon-terminated diamond on the properties of shallow NV centers remains unclear. Recently, the suitability of nitrogen-terminated diamond for shallow NV centers has been theoretically and experimentally examined; however, quantum sensing has not yet been performed. In this work, we evaluated the effect of silicon and nitrogen termination on shallow NV centers. The negatively charged state of shallow NV centers was unstable below silicon termination. In contrast, the properties of shallow NV centers in nitrogen-terminated diamond were satisfactory for quantum sensing and enabled ¹ H NMR detection. Our results are in good agreement with previous reports on silicon and nitrogen terminations and provide the perspective that the stability of shallow NV centers highly depends on the polarity of electron affinity of the diamond surface.