Spin properties of very shallow nitrogen vacancy defects in diamond

We investigate spin and optical properties of individual nitrogen vacancy centers located within 1-10 nm from the diamond surface. We observe stable defects with a characteristic optically detected magnetic-resonance spectrum down to the lowest depth. We also find a small but systematic spectral broadening for defects shallower than about 2 nm. This broadening is consistent with the presence of a surface paramagnetic impurity layer [Tisler et al., ACS Nano 3, 1959 (2009)] largely decoupled by motional averaging. The observation of stable and well-behaved defects very close to the surface is critical for single-spin sensors and devices requiring nanometer proximity to the target.