  Diamond is increasingly popular because of its unique material properties.
Diamond defects called nitrogen vacancy (NV) centers allow measurements with
unprecedented sensitivity. However, to achieve ideal sensing performance NV
centers need to be within nanometers from the surface and are thus strongly
dependent on the local surface chemistry. Several attempts have been made to
compare diamond surfaces. However, due to the high price of diamond crystals
with shallow NV centers, a limited number of chemical modifications have been
studied. Here, we developed a systematic method to investigate a continuity of
different local environments with a varying density and nature of surface
groups in a single experiment on a single diamond plate. To achieve this goal,
we used diamonds with a shallow ensemble of NV centers and introduced a
chemical gradient across the surface. More specifically we used air and
hydrogen plasma. The gradients were formed by low pressure plasma treatment
after masking with a right-angled triangular prism shield. As a result, the
surface contained gradually more oxygen/hydrogen towards the open end of the
shield. We then performed widefield relaxometry to determine the effect of
surface chemistry on the sensing performance. As expected, relaxation times and
thus sensing performance indeed varies along the gradient.
