  We investigated the effect of fluorine-terminated diamond surface on the
charged state of shallow nitrogen vacancy defect centers (NVs). Fluorination is
achieved with CF4 plasma and the surface chemistry is confirmed with x-ray
photoemission spectroscopy. Photoluminescence of these ensemble NVs reveal that
fluorine-treated surfaces lead to a higher negatively charged nitrogen vacancy
(NV-) population than oxygen-terminated surfaces. Using surface chemistry to
control NV charges, in particular increasing the density of NV- centers, is an
important step towards improving the optical and spin properties of NVs for
quantum information processing and magnetic sensing.
