Study of surface impurities on nanodiamonds by ELDOR-detected NMR

Diamond is a fascinating material, hosting nitrogen-vacancy (NV) defect centers with unique spin and optical properties. Spin coherence and optical stability of NV centers highly depends on paramagnetic impurity contents near the NV centers. Previous studies suggest the existence of several different types of paramagnetic impurities near the surface of diamond. For example, electron paramagnetic resonance (EPR) investigation of mechanically crushed nanodiamonds (NDs) as well as detonation NDs revealed g~2 like signals that are attributed to structural defects and dangling bonds near the diamond surface. In this presentation, we investigate the physical structures of the surface paramagnetic impurities of NDs by resolving the hyperfine coupling of the surface impurities. We employ high-frequency (HF) EPR and HF electron-electron double resonance (ELDOR)-detected NMR spectroscopy for the study. HF ELDOR-detected NMR method is a powerful method to detect the hyperfine coupling with high sensitivity and fine spectral resolution.