  Near-surface nitrogen-vacancy ({NV}) centers in diamond have been
successfully employed as atomic-sized magnetic field sensors for external spins
over the last years. A key challenge is still to develop a method to bring NV
centers at nanometer proximity to the diamond surface while preserving their
optical and spin properties. To that aim we present a method of controlled
diamond etching with nanometric precision using an oxygen inductively coupled
plasma (ICP) process. Importantly, no traces of plasma-induced damages to the
etched surface could be detected by X-ray photoelectron spectroscopy (XPS) and
confocal photoluminescence microscopy techniques. In addition, by profiling the
depth of NV centers created by 5.0 keV of nitrogen implantation energy, no
plasma-induced quenching in their fluorescence could be observed. Moreover, the
developed etching process allowed even the channeling tail in their depth
distribution to be resolved. Furthermore, treating a 12C isotopically purified
diamond revealed a threefold increase in T2 times for NV centers with <4 nm of
depth (measured by NMR signal from protons at the diamond surface) in
comparison to the initial oxygen-terminated surface.
