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Identification and Manipulation of NV Centers in Nanodiamond

The ability to unambiguously identify and directly position single-atom defects is important to the design and function of quantum technology devices. Color-centers in diamond are known single photon emitters (SPE) with applications in biomarking and quantum communication. Nanostructured diamonds, such as nanodiamonds and thin films, are the preferred morphologies for such applications. The properties of the nitrogen-vacancy (NV) center in nanodiamond, in which a N atom occupies a diamond lattice site with a neighboring lattice vacancy, is dependent on the defect charge state and nanodiamond surface, and directly probing a single defect is therefore important. Aberration-corrected scanning transmission electron microscopy (STEM) offers a sub-Angstrom diameter probe for single-atom sensitivity imaging and spectroscopy that can be used to investigate defects in nanostructured diamond. Using a Nion UltraSTEM-X operated at 60 kV with simultaneous electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS), we are able to identify single NV centers in 2-5 nm meteoritic nanodiamonds with EELS detection of the characteristic NV center peak at 282.4 eV [1] and the N signal in EDS [2,3]. Single-defect identification becomes more challenging when studying commercially-available, technologically-relevant synthetic nanodiamonds with diameters of 10-30 nm. As the sample thickness increases, the sensitivity to detect single-atom defects decreases, and it is likely that multiple NV centers need to be present within a single spectrum image pixel for the defects to be detected. Thus, while we do detect NV centers in the larger, synthetic nanodiamonds, isolated single NV centers may still be present and undetected. In addition to identifying single-atom defects, the directed positioning of